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1
Hill, R. I., B. W. Chappell, and I. H. Campbell. "Late Archaean granites of the southeastern Yilgarn Block, Western Australia: age, geochemistry, and origin." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 211–26. http://dx.doi.org/10.1017/s0263593300007902.
Повний текст джерелаАнотація:
ABSTRACTLate Archaean granitic rocks from the southern Yilgarn Craton of Western Australia have a close temporal relationship to the basaltic and komatiitic volcanism which occurs within spatially associated greenstone belts. Greenstone volcanism apparently began ∼2715 Ma ago, whereas voluminous felsic magmatism (both extrusive and intrusive) began about 2690 Ma ago. A brief but voluminous episode of crust-derived magmatism ∼2690-2685 Ma ago resulted in the emplacement of a diverse assemblage of plutons having granodioritic, monzogranitic and tonalitic compositions. This early felsic episode was followed immediately by the emplacement of mafic sills, and, after a further time delay, by a second episode of voluminous crust-derived magmatism dominated by monzogranite but containing plutons covering a wide compositional range, including diorite, granodiorite and tonalite. The products of this 2665–2660 Ma magmatic episode now form a significant fraction of the exposed southern Yilgarn Craton. Later magmatism, which continued to at least 2600 Ma ago, appears largely restricted to rocks having unusually fractionated compositions.The magmatic sequence basalt-voluminous crust-derived magmatism-later diverse magmatism, is interpreted in terms of a dynamically-based model for the ascent of the head of a new mantle plume. In this model basalts and komatiites are derived by decompression melting of rising plume material, and the crust-derived magmas result after conductive transport of heat from the top of the plume head into overlying continental crust. This type of magmatic evolution, the fundamentally bimodal nature of the magmatism, the presence of high-Mg volcanics (komatiites), and the areal extent of the late Archaean magmatic event, are all suggested to be characteristic of crustal reworking above mantle plumes rather than resulting from other processes, such as those related to subduction.
2
Hollis, Steven P., Sabri Foury, Stefano Caruso, Sean Johnson, Vitor Barrote, and Andrew Pumphrey. "Lithogeochemical and Hyperspectral Halos to Ag-Zn-Au Mineralization at Nimbus in the Eastern Goldfields Superterrane, Western Australia." Minerals 11, no. 3 (February 28, 2021): 254. http://dx.doi.org/10.3390/min11030254.
Повний текст джерелаАнотація:
With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle halos surrounding orebodies at minimal expense. The Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity, and tectonic setting, it is interpreted to represent a shallow water (~650 mbsl) and low-temperature (<250 °C) volcanogenic massive sulfide (VMS) deposit with epithermal characteristics (i.e., a hybrid bimodal felsic deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization to aid exploration. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic sulfides that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb ± Pb ± As ± (Cu)-bearing sulfosalts, minor pyrrhotite, arsenopyrite, and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite, and bournonite. Zones of sulfide mineralization in quartz-sericite(±carbonate)-altered dacite are marked by significant mass gains in Fe, S, Zn, Pb, Sb, Ag, As, Cd, Ni, Cu, Ba, Co, Cr, Tl, Bi, and Au. Basaltic rocks show reduced mass gains in most elements, with zones of intense quartz-chlorite-carbonate±fuchsite alteration restricted to thick sequences of hyaloclastite, and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, and are marked by high Alteration Index and Chlorite-Carbonate-Pyrite Index (CCPI) values, strong Na-Ca depletion, and an absence of feldspar (albite) in thermal infrared (TIR) data. White mica compositions are predominantly muscovitic in weakly altered sections of the dacitic footwall sequence. More paragonitic compositions are associated with zones of increased sericitization and high-grade polymetallic sulfide mineralization. Chlorite in dacitic rocks often occurs adjacent to zones of sulfide mineralization and is restricted to narrow intervals. Carbonate abundance is sporadic in dacite, but is most abundant outside the main zones of Na-Ca depletion. Basaltic rocks are characterized by strongly paragonitic white mica compositions, and abundant chlorite and carbonate. Shifts from Ca carbonates and Fe-rich chlorites to more Mg-rich compositions of both minerals occur in more intensely hydrothermally altered basaltic hyaloclastite, and near contacts with dacitic rocks. Hanging-wall polymict conglomerates are characterized by minor amounts of muscovitic to phengitic white mica (2205–2220 nm), and an absence of chlorite and carbonate alteration.
3
Arndt, Nicholas, and Catherine Chauvel. "Crust of the Hadean Earth." Bulletin of the Geological Society of Denmark 39 (December 20, 1991): 145–51. http://dx.doi.org/10.37570/bgsd-1991-39-05.
Повний текст джерелаАнотація:
High temperatures in the interior of the young Earth led to the initiation of melting at great depths in the mantle (> 150 km) and the production of large volumes of magma that erupted to form a >40 km thick basaltic crust. The ubiquitous presence of this crust dominated Archaean tectonics. Granitoid rocks, the source for >4 Ga Western Australian zircons, formed by partial melting at the base of the crust during the first 600 Ma of Earth history, but were always subordinate to basalt. The lunar record provides evidence that both the Moon and Earth experienced major impacting during this period. The impacts mixed granitoid with mantle-derived basalt to produce a composite granitoid-basalt layer with isotopic compositions close to bulk-Earth values. No record of its existence was retained in the oldest extant continents which formed - 3.9 Ga ago, after major impacting had ceased.
4
Alavi, Norman, Leon Bagas, Peter Purcell, Irena Kivior, and John Brett. "Lower Paleozoic stratigraphy and petroleum potential of the Wallal Rift System, southwest Canning Basin, Western Australia." APPEA Journal 54, no. 2 (2014): 521. http://dx.doi.org/10.1071/aj13094.
Повний текст джерелаАнотація:
The Wallal Rift System (new name) extends north-northwest for more than 300 km along the southwestern margin of the Canning Basin. The rift contains the Wallal and the Waukarlycarly embayments and the Samphire Graben. The rift segments vary in depth to 4.5 km and are all under-explored. Seismic coverage is better in the north than in the south. Six shallow wildcat and stratigraphic wells in the north provide some control on the age of the pre-Permian section. Another well on the northeastern flank of the Samphire Graben terminated in Neoproterozoic granitic rocks beneath the Lower Ordovician Nambeet Formation. The well is tied to a seismic line that indicates a synrift Ordovician section in the graben. An equivalent section is inferred in the Wallal and the Waukarlycarly embayments, and Permian syn-rift sediments are recognised in all rifts. Transtension along a regional geosuture—the Camel-Tabletop Fault Zone—may have caused initial rifting during the waning of the Paterson Orogeny (c. 550 Ma), co-incident with extrusion in the Kalkarindji Large Igneous Province. Thus, Cambrian volcano-clastics deposits may be present at the base of the (2–3 km thick) pre-Permian section, which is considered to be primarily Early Paleozoic sediments and expected to contain potential source rocks. A relatively hot Proterozoic crust and eruption of continental flood basalts during the Cambrian may have facilitated source rock maturation. Reservoirs may be more common along rift-margins and intra-rift ridges, where fault-controlled traps are also present.
5
Priyono, J., and R. J. Gilkes. "Dissolution of milled-silicate rock fertilisers in the soil." Soil Research 42, no. 4 (2004): 441. http://dx.doi.org/10.1071/sr03138.
Повний текст джерелаАнотація:
Dissolution of dry-milled basalt, dolerite, gneiss, and K-feldspar added to 23 soils has been related to milling time and soil properties. The rocks milled for 10, 60, and 120 min were mixed with 23 type of soils from south-western Australia at a rock/soil ratio of 1/100 (≈10 t/ha), wetted to 110% field capacity, then incubated at 20°C for 2 and 10 months. Measurements of cations extractable by 1 M CH3COONH4 at pH 7 indicate that substantial dissolution occurred in the soil and that milling increased dissolution. After 10 months of incubation, about 18% of Ca and Mg had dissolved from basalt and dolerite milled for 120 min and 40% of Na and K from gneiss and K-feldspar milled for 120 min. Some dissolution occurred with 1 h extraction of non-incubated rock–soil mixtures and these released elements are considered to be readily available plant nutrients. The silicate rocks had minor effects on soil pH and EC of soil-rock mixtures (i.e. increased pH by ≤0.5 unit and EC by ≤127 μS/cm in 1 : 5 water extracts). The large increases in silicate rock dissolution in soils due to milling indicate that milled basalt and dolerite may be used as Ca and Mg fertilisers, and K-feldspar as a K fertiliser. Further research is needed to identify soils and plants for which the application of the silicate rock fertilisers will be most beneficial.
6
Whiteway, Tanya, Andrew Heap, Tara Anderson, and Rachel Przeslawski. "Marine mapping survey reveals broad-scale seabed environments of remote offshore basins in Western Australia." APPEA Journal 50, no. 2 (2010): 730. http://dx.doi.org/10.1071/aj09094.
Повний текст джерелаАнотація:
Between October 2008 and January 2009, Geoscience Australia conducted a marine mapping survey to document the seabed environments and subsurface geology of the Zeewyck, Houtman, Exmouth sub-basins and the deep-water Wallaby (Cuvier) Plateau, Western Australia. The seabed mapping survey, the second and largest mapping survey of the Federal Government’s Offshore Energy Security Program, documented seabed environments and biota from multibeam sonar and sub-bottom profiler data, towed video footage and physical samples. Preliminary analysis of the data indicates that for all of the sub-basins the seabed is comprised of carbonate mud that supports relatively sparse infaunal populations. Rocky substrates, principally in the numerous submarine canyons, supported sparse communities of sessile organisms. Interestingly, some of these hard-grounds were associated with volcanic (basaltic) peaks on the upper slope that attain 200 metres above the surrounding seabed. Data collected from the survey are being analysed in conjunction with existing environmental data to establish a series of environmental summaries that describe the key seabed habitats and biota for the offshore basins. The environmental summaries are being made available to support future acreage release in the sub-basins. The marine mapping survey was run in combination with a regional 2D seismic survey of the same offshore basins, also completed as part of the Offshore Energy Security Program.
7
Witt, W. K. "Porphyry intrusions and albitites in the Bardoc–Kalgoorlie area, Western Australia, and their role in Archean epigenetic gold mineralization." Canadian Journal of Earth Sciences 29, no. 8 (August 1, 1992): 1609–22. http://dx.doi.org/10.1139/e92-127.
Повний текст джерелаАнотація:
Minor intrusions in the Menzies – Kambalda greenstone belt of the Archean Eastern Goldfields Province, Western Australia, range from quartz–feldspar porphyry to plagioclase–hornblende porphyry. The porphyries display enrichment of mobile and incompatible elements (K to Zr) and depletion of relatively compatible elements, with negative Nb, P, and Ti anomalies, on mid-ocean-ridge basalt-normalized spidergrams. The composition and timing of emplacement of the porphyries are consistent with a genetic relationship with spatially related granitoids. Porphyries occur in 30% of gold mines in the Menzies–Kambalda belt. The association appears to be largely structural, since both the intrusions and the mineralizing fluids exploit zones of weaknesses, such as lithological contacts and shear zones. Porphyries have been modified to varying degrees by hydrothermal alteration, especially pervasive albitization. Textural evidence indicates that secondary albite and associated sodic amphibole formed late in the deformation history of the greenstones and were broadly contemporaneous with secondary phyllosilicate, carbonate and sulphide minerals related to gold mineralization. Recent studies in the Alleghany district of California suggest the initial rock composition may critically influence the nature of alteration associated with gold mineralization. Therefore, albitization of porphyries may be caused by the same hydrothermal fluids that deposit gold and produce potassic alteration in mafic rocks.
8
Prytchin, M. E., E. I. Soroka, and V. N. Puchkov. "Novel U-Pb isotopic zircon data on the rhyolite of the Saf’yanovskoe Cu-Zn deposit (Middle Urals)." LITHOSPHERE (Russia) 21, no. 6 (December 29, 2021): 884–93. http://dx.doi.org/10.24930/1681-9004-2021-21-6-884-893.
Повний текст джерелаАнотація:
Research subject. Zircons from the Saf’yanovskoe Cu-Zn deposit rhyolite (Middle Urals). For the first time, zircon U-Pb dating for the rhyolite of the ore-bearing volcanic-sedimentary rocks of the Saf’yanovskoe deposit was performed. The volcanites are characterized by an andesite-rhyodacite composition and are localized at the southern edge of the Rezhevskaya structural-formation zone (SFZ) of the Eastern Ural megazone. A number of publications assign these rocks either to the basalt-rhyolite formation of the Middle Devonian, or to the basalt-andesite-dacite-rhyolite formation of the Lower-Middle Devonian.Aim. To estimate the age of the ore-bearing volcanic rocks under study using the U-Pb SHRIMP-II isotop ic system of zircon from the rhyolite of the eastern side of the Saf’yanovskoe deposit. By its chemical composition, the rhyolite belongs to the silicic varieties of subvolcanic rocks. Methods and results. The U-Pb isotopic system of zircon was studied by 5-collector mass-spectrometer of high precision and emission of the secondary ions SHRIMP-II (ASI, Australia) in the VSЕGEI Institute. U-Pb relations were investigated by a procedure developed by I.S. Williams. The U-Pb data obtained based on 13 zircon grains showed the age of 422.8 ± 3.7 Ma. Conclusions. The U-Pb dating of zircon obtained previously from the lens-shaped andesite bodies of the western side of the Safyanovskoe deposit gave the age of 422.8 Ma, which corresponds to the Przydoli series epoch of the Upper Silurian. We established that, among the volcanic rocks of the Saf’yanovskoe deposit, the effusive formations of the Upper Silurian are present.
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Beslier, Marie-Odile, Jean-Yves Royer, Jacques Girardeau, Peter J. Hill, Eric Boeuf, Cameron Buchanan, Fabienne Chatin, et al. "A wide ocean-continent transition along the south-west Australian margin: first results of the MARGAU/MD110 cruise." Bulletin de la Société Géologique de France 175, no. 6 (November 1, 2004): 629–41. http://dx.doi.org/10.2113/175.6.629.
Повний текст джерелаАнотація:
Abstract Introduction and geodynamic setting. – Syn-rift exhumation of mantle rocks in a continental breakup zone was highlighted along the present-day west Iberian passive margin [e.g. Boillot et al., 1988, 1995; Whitmarsh et al., 1995, 2001; Beslier et al., 1996; Brun and Beslier, 1996; Boillot and Coulon, 1998; Krawczyk et al., 1996; Girardeau et al., 1998] and along the fossil Tethyan margins [e.g. Froitzheim and Manatschal, 1996; Manatschal and Bernoulli, 1996; Marroni et al., 1998; Müntener et al., 2000; Desmurs et al., 2001]. Along the west Iberian margin, serpentinized peridotite and scarce gabbro and basalt lay directly under the sediments, over a 30 to 130 km-wide transition between the thinned continental crust and the first oceanic crust [Girardeau et al., 1988, 1998; Kornprobst and Tabit, 1988; Boillot et al., 1989; Beslier et al., 1990, 1996; Cornen et al., 1999]. The formation of a wide ocean-continent transition (OCT), mostly controlled by tectonics and associated with an exhumation of deep lithospheric levels, would be an essential stage of continental breakup and a characteristic of magma-poor passive margins. The southwest Australian margin provides an opportunity to test and to generalize the models proposed for the west Iberian margin, as both margins present many analogies. The south Australian margin formed during the Gondwana breakup in the Mesozoic, along a NW-SE oblique extension direction [Willcox and Stagg, 1990]. From north to south, the continental slope is bounded by (1) a magnetic quiet zone (MQZ) where the nature of the basement is ambiguous [Talwani et al., 1979; Tikku and Cande, 1999; Sayers et al., 2001], (2) a zone where the basement shows a rough topography associated with poorly expressed magnetic anomalies [Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999; Sayers et al., 2001], and which is the eastward prolongation of the Diamantina Zone, and (3) an Eocene oceanic domain. The continental breakup zone is believed to be located near or at the southern edge of the MQZ [Cande and Mutter, 1982; Veevers et al., 1990; Sayers et al., 2001]. Breakup is dated at 125 Ma [Stagg and Willcox, 1992], 95 ± 5 Ma [Veevers, 1986] or at 83 Ma [Sayers et al., 2001], and followed by ultra-slow seafloor spreading until the Eocene (43 Ma), and fast spreading afterwards [Weissel and Hayes, 1972; Cande and Mutter, 1982; Veevers et al., 1990; Tikku and Cande, 1999]. The western end of the margin (fig. 1) is starved and bounded in the OCT by basement ridges where peridotite, gabbro and basalt were previously dredged [Nicholls et al., 1981]. Altimetry data [Sandwell and Smith, 1997] show that some of these ridges are continuous over 1500 km along the OCT of the south Australian margin and of the conjugate Antarctic margin. The objectives of the MARGAU/MD110 cruise (May-June 1998; [Royer et al., 1998]; fig. 2) were to define the morpho-structure and the nature and evolution of the basement in the SW Australian OCT. An area of 180 000 km2 was explored with swath bathymetry. Gravimetric data (11382 km) were simultaneously recorded whereas few single channel seismic (1353 km) and magnetic (5387 km) data were obtained due to technical difficulties. Crystalline basement rocks, made of varied and locally well-preserved lithologies, were dredged at 11 sites located on structural highs. Main results. – The bathymetric map unveils three E-W domains (fig. 2). From north to south, they are the continental slope of Australia, prolonged westward by that of the Naturaliste Plateau, a 160 km-wide intermediate flat sedimented area corresponding to the MQZ, and a 100 km-wide zone of rough E-W oriented topography which continues the Diamantina Zone (fig. 3). The first two domains are cut through in three segments by two major fracture zones (FZ), the Leeuwin FZ along the eastern side of the Naturaliste Plateau, and the Naturaliste FZ along its western flank. These NW-SE trending FZ terminate north of the E-W trending fabric of the Diamantina Zone. Accordingly, extension occurred along the NW-SE direction during the formation of the slope and of the MQZ, and then turned to N-S during the formation of the Diamantina Zone. In the Diamantina Zone, the mantle rocks dredged at Site MG-DR02 are mainly lherzolites, rich in pyroxenitic micro-layers, and pyroxenites. They contain spinel rimmed by plagioclase and locally coronas of olivine + plagioclase between opx and spinel, which suggest that they underwent some subsolidus reequilibration in the plagioclase field (fig. 4C). Westward (Site DR09), the mantle rocks are harzburgitic, with lesser pyroxenitic bandings and no plagioclase. The rocks have coarse-grained porphyroclastic textures that are locally overprinted by narrow mylonitic shear bands, and then by a cataclastic deformation, which indicate decreasing temperatures and increasing stresses during their evolution. Basalts were sampled at Sites MG-DR01, −04, −05, and together with gabbros at Sites MG-DR02, -03, -09. They have a transitional composition as shown by their REE patterns, except one sample from site MG-DR-05 which is an alkaline basalt (fig. 5). The gabbros are clearly intrusive in the peridotite at Sites DR02 and -09. They contain olivine and clinopyroxene (cpx) at Site DR02, cpx, plagioclase and hornblende at Site DR03, and cpx and amphibole or orthopyroxene or olivine at Site DR09 (fig. 4D). At that site, a tonalite containing K-feldspar and biotite and alkaline in composition (fig. 5), has also been sampled. All these plutonic rocks display either their primary magmatic textures or secondary porphyroclastic ones that are locally overprinted by mylonitic shear zones (fig. 4E). Retrograde minerals of amphibolite to greenschist facies developed during the deformation. The basalts are clearly intrusive in the gabbros at Site DR03. They are altered and exhibit porphyric textures with abundant plagioclase and plagioclase + olivine phenocrysts at Sites DR03, -04, -08, -10, and have a transitional composition (fig. 5). The nature and evolution of the peridotites and associated gabbros are compatible with an exhumation under a rift zone, on both sides of the Leeuwin FZ. It includes a mylonitic deformation which attests that these rocks underwent a shearing deformation under lithospheric conditions, in probable relation with their exhumation during the early stages of the oceanic opening. The crustal rocks are represented only by intrusive gabbros and by transitional basalts. In the MQZ, the peridotites recovered at Site MG-DR06 are mainly spinel and plagioclase lherzolites (fig. 4B) and a few pyroxenites (fig. 4A) with high temperature porphyroclastic textures. Their discovery indicates that the basement in the MQZ is not exclusively formed of thinned continental crust. Lavas sampled westward of the Leeuwin FZ at Site DR10 have also transitional compositions (fig. 5). On the Australian slope, samples dredged at Site MG-DR07 are continental quartz-bearing rocks (mostly gneisses and rare granites), some showing a high grade paragenesis (upper amphibolite to granulite facies) marked by the presence of K-feldspar, biotite, sillimanite and/or kyanite and garnet, and without primary muscovite (fig. 4G). Some of these rocks underwent an intense mylonitic shear deformation followed by post-tectonic recrystallisation or migmatization. Depending on the age of the high grade evolution (metamorphism and shearing), these rocks document either the syn-rift exhumation of lower continental crust, or the formation of the older Australian craton. On the slope of the Naturaliste Plateau, at Site DR11, rocks of oceanic origin (gabbro-diorites/dolerite/basalt; fig. 4F) were dredged together with acid rocks (gneiss and granites) of probable continental origin, some having a quartz, K-feldspar, biotite and garnet metamorphic paragenesis (fig. 4H). At that site, the transitional basalts intrude the gabbros and associated dolerites. The presence of metamorphic acid rocks indicate that the Naturaliste Plateau is likely a continental fragment that was later intruded by mafic rocks, whose origin and ages of intrusion have to be determined. Discussion and conclusions. – The retrograde tectono-metamorphic evolution of the peridotites recovered in the MQZ, which includes a reequilibration in the plagioclase field (marked by the development of olivine and plagioclase after spinel and pyroxene), is compatible with an exhumation under a rift zone [Girardeau et al., 1988; Kornprobst and Tabit, 1988; Cornen et al., 1999]. By analogy with the Iberia Abyssal Plain, the MQZ could represent a wide OCT where the mantle was exhumed and stretched mostly by amagmatic extension before the initiation of oceanic accretion [Beslier et al., 1996; Boillot and Coulon, 1998] (fig. 6). This hypothesis is supported by the tectonic structures (horsts and grabens) imaged in the seismic data over the MQZ [Boeuf and Doust, 1975]. Accordingly, the limit of the continental crust would be located at the foot of the slope, i.e. 160 km (or 250 km in the NW-SE extension direction) northward of the assumed location of the OCT at the southern edge of the MQZ. The age of the Australia-Antarctic breakup would thus be (1) older than that inferred from the magnetic anomalies (circa 95 Ma [Cande and Mutter, 1982; Veevers, 1986]), which would rather date the onset of oceanic accretion, and (2) older than the age of the breakup unconformity estimated as Santonian (83 Ma), further east, in the Great Australian Bight [Sayers et al., 2001]. The origin of the Naturaliste Plateau, continental or oceanic, is still disputed. The discovery of metamorphic rocks of probable continental origin on the southern flank of the Plateau (Site DR11) shows that it consists at least partially of rocks of the Gondwana continent. All the samples from the Diamantina Zone confirm that its basement is made of a peridotite-gabbro-basalt assemblage. The nature and age of the peridotites and of the associated magmas will help understanding the origin of this domain, which can result either from Neocomian seafloor spreading with further remobilization during the Australia-Antarctic separation, or from post-Neocomian ultra-slow seafloor spreading. Because of the omnipresence of extensive tectonic structures (fig. 3) and of the relatively small proportion of crustal rocks relative to the mantle rocks, we argue that the formation of the Diamantina Zone was mainly controlled by tectonics rather than by magmatic processes. In conclusion, the data collected along the southwest Australian margin during the MARGAU/MD110 survey evidence two major tectonic phases with formation of a wide OCT where abundant mantle rocks, in association with few mafic rocks, outcrop or lay directly beneath the sediments. The evolution of the crystalline rocks is compatible with an exhumation under a rift zone during a phase of magma-poor extension primarily controlled by tectonic processes. The domains where basement highs were sampled seem to be continuous over more than 1500 km eastward along the south Australian margin. Additional evidence on such large-scale structural continuity and on the nature of the associated basement highs may help generalizing the models for continental breakup and formation of non-volcanic passive margins, where oceanic accretion does not immediately follow continental breakup.
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Townson, W. G. "THE SUBSURFACE GEOLOGY OF THE WESTERN OFFICER BASIN — RESULTS OF SHELL'S 1980-1984 PETROLEUM EXPLORATION CAMPAIGN." APPEA Journal 25, no. 1 (1985): 34. http://dx.doi.org/10.1071/aj84003.
Повний текст джерелаАнотація:
The Officer Basin described in this paper includes four Proterozoic to Lower Palaeozoic sub-basins (Gibson, Yowalga, Lennis, Waigen) which extend in a northwest to southeast belt across 200 000 sq. km of central Western Australia. These sub-basins are bounded by Archaean to Proterozoic basement blocks and are almost entirely concealed by a veneer of Permian and Cretaceous sediments. Depth to magnetic basement locally exceeds eight kilometres.Until recently, information on the sub-surface geology was limited to shallow levels, based on the results of a petroleum exploration campaign in the 1960s and the work of State and Federal Geological Surveys. In 1980, the Shell Company of Australia was awarded three permits (46 200 sq. km) covering the Yowalga and Lennis Sub-basins. The results of 4700 km of seismic data and three deep wildcat wells, combined with gravity, aeromagnetic, Landsat, outcrop and corehole information, has led to a better understanding of the regional subsurface geology.The Lennis Sub-basin appears to contain Lower to Middle Proterozoic sediments, whereas the Yowalga Sub- basin is primarily an Upper Proterozoic to Lower Cambrian sequence which comprises a basal clastic section, a middle carbonate and evaporite sequence and an upper clastic section. Widespread Middle Cambrian basalts cap the Upper Proterozoic to Lower Cambrian prospective sequence. Late Proterozoic uplift resulted in salt- assisted gravity tectonics leading to complex structural styles, especially in the basin axis.Despite oil shows, organic matter in the oil and gas generation windows and reservoir-quality sandstones with interbedded shales, no convincing source rocks or hydrocarbon accumulations have yet been located. The area remains, however, one of the least explored basins in Australia.
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Carpenter, Chris. "Reservoir Characterization, Scenario-Based Models Optimize Development Planning." Journal of Petroleum Technology 73, no. 07 (July 1, 2021): 48–49. http://dx.doi.org/10.2118/0721-0048-jpt.
Повний текст джерелаАнотація:
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202273, “Reservoir Characterization and Scenario-Based Modeling To Optimize Development Planning of the Jurassic Plover Formation in the Ichthys Field, North West Shelf of Australia,” by Kazuyuki Yamamoto, SPE, Shuji Yamamoto, and Toby Jones, INPEX, et al., prepared for the 2020 SPE Asia Pacific Oil and Gas Conference and Exhibition, originally scheduled to be held in Perth, Australia, 20–22 October. The paper has not been peer reviewed. The Plover Formation is one of two reservoirs in the Ichthys field of the Australian North West Shelf. The objective of this study is to build multiple scenario-based models to optimize development planning in preparation for the upcoming production phase. The authors have integrated data and interpretations of thin sections, cores, well logs, and seismic data to create multiple geological concepts for the field and to identify key geological uncertainties. Introduction The Ichthys liquefied natural gas project is one of the world’s largest and involves the development of a gas-condensate field in the Browse Basin. The field is approximately 220 km offshore Western Australia and covers an area of approximately 800 km2 with an average water depth of approximately 250 m. The field is currently under preparation for the development of the Plover Formation. The authors conducted an integrated subsurface evaluation and built reservoir models with newly reprocessed 3D seismic data to optimize Plover development planning. Considering the geological uncertainty given the limited production data gathered before the production phase, the multiple deterministic approach was selected as the best option to optimize development planning. In this approach, it is important to capture all geological scenarios that may occur in the field and to build reservoir models in which the scenario concepts are explicitly integrated. A multidisciplinary team was organized to conduct this study. Geology of the Plover Formation The Plover Formation consists of sandstones, shales, igneous rocks, and a minor amount of coal. The depositional environment is fluvial to shallow marine. The average thickness of the formation is approximately 360 m. Based on the stratigraphic correlation anchored by mainly palynological biostratigraphic data, the formation has been subdivided into five stratigraphic members. The formation is overlain by the Ichthys Formation, which is composed mainly of argillaceous sandstone and shale deposited in a tidally influenced, lower-delta-to-shelf environment. Although the nine existing exploration wells broadly cover the entire field, the spacing between the wells is still large (8–10 km). Further-more, core coverage is low, especially in the reservoir sandstone intervals. Igneous rock, predominantly basaltic in composition and likely extrusive in origin, occurs more in the eastern part of the field. Igneous activity has complicated the distribution and connectivity of the reservoir sandstones in the Ichthys field. Key Geological Uncertainties Rock Type (RT). The results of petrographic analysis of rock samples from the Ichthys field and other surrounding fields indicate that the sandstones of the Plover Formation can be separated into multiple RTs: RT1 and RT2, with RT1 subdivided into RT1a and RT1b. Very little data exist from RT2 in the fluvial/distributary channel sandstones in the Ichthys field in comparison with other fields; this is considered to be the result of limited core. The assumption that RT2 exists in the field is critical to prepare for the possibility that a future well may be drilled that might have some nontrivial quantity of RT2.
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SINTON, C. W., K. HITCHEN, and R. A. DUNCAN. "40Ar–39Ar geochronology of silicic and basic volcanic rocks on the margins of the North Atlantic." Geological Magazine 135, no. 2 (March 1998): 161–70. http://dx.doi.org/10.1017/s0016756898008401.
Повний текст джерелаАнотація:
At the submerged margins of the North Atlantic, andesitic to dacitic and basaltic volcanic rocks occur together. The silicic rocks were derived by processes requiring the presence of continental crust (crustal anatexis and/or contamination of mafic magmas) while the majority of the basaltic lavas had little or no contact with continental crust. We report 40Ar–39Ar incremental heating ages for several dacitic and basaltic rocks recovered from three offshore localities of the North Atlantic Igneous Province. Dacitic lavas and tuffs at the southeast Greenland margin and trachytic lavas in the Scottish Hebrides erupted contemporaneously with basaltic lavas at 62–61 Ma. In contrast, the silicic lavas from the northern Rockall Trough (offshore western Scotland) and the Vøring Plateau (offshore Norway) erupted at ∼55 Ma followed shortly by basaltic volcanism. At this time, silicic magmatism at the southeast Greenland margin had ceased and only oceanic basalts were erupted. Similarly, ∼55 Ma lavas on the southwest Rockall Plateau are wholly basaltic. The compositions of all of the dated silicic volcanic rocks are consistent with derivation from partial melting of either continental crust or sediments. The heat necessary for partial melting appears to have been provided by basaltic magmas. Therefore, the existence of the silicic rocks indicates the presence of continental crust as well as a stable tectonic environment that allowed the stagnation and pooling of basaltic melts within the crust. With this in mind, it is apparent that at 62–60 Ma, both western and eastern sides of the present North Atlantic margins were characterized by extensional environments within continental crust that were restrictive to the passage of mafic magmas. By 55 Ma, at the time of continental breakup, the proximal margins at southeast Greenland and the Rockall Plateau were devoid of continental crust. But the presence of 55 Ma silicic magmatism on the eastern North Atlantic margin can be attributed to a broader zone of magmatism and sediment-filled Mesozoic rift basins.
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Ghori, K. Ameed R. "Petroleum source rocks of Western Australia." APPEA Journal 58, no. 1 (2018): 282. http://dx.doi.org/10.1071/aj17051.
Повний текст джерелаАнотація:
Petroleum geochemical analysis of samples from the Canning, Carnarvon, Officer and Perth basins identified several formations with source potential, the: • Triassic Locker Shale and Jurassic Dingo Claystone of the Northern Carnarvon Basin; • Permian Irwin River Coal Measures and Carynginia Formation, Triassic Kockatea Shale and Jurassic Cattamarra Coal Measures of the Perth Basin; • Ordovician Goldwyer and Bongabinni formations, Devonian Gogo Formation and Lower Carboniferous Laurel Formation of the Canning Basin; • Devonian Gneudna Formation of the Gascoyne Platform and the Lower Permian Wooramel and Byro groups of the Merlinleigh Sub-basin of the Southern Carnarvon Basin; and • Neoproterozoic Brown, Hussar, Kanpa and Steptoe formations of the Officer Basin. Burial history and geothermal basin modelling was undertaken using input parameters from geochemical analyses of rock samples, produced oil, organic petrology, apatite fission track analysis (AFTA), heat flows, subsurface temperatures and other exploration data compiled by the Geological Survey of Western Australia (GSWA). Of these basins, the Canning, Carnarvon, and Perth basins are currently producing oil and gas, whereas the Southern Carnarvon and Officer basins have no commercial petroleum discovery yet, but they do have source, reservoir, seal and petroleum shows indicating the presence of petroleum systems. The Carnarvon Basin contains the richest identified petroleum source rocks, followed by the Perth and Canning basins. Production in the Carnarvon Basin is predominantly gas and oil, the Perth Basin is gas-condensate and the Canning Basin is oil dominated, demonstrating the variations in source rock type and maturity across the state. GSWA is continuously adding new data to assess petroleum systems and prospectivity of these and other basins in Western Australia.
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Oljira, Temesgen, Olugbenga Akindeji Okunlola, Akinade Shadrach Olatunji, Dereje Ayalew, and Bekele Ayele Bedada. "Petrogenesis of the Neoproterozoic rocks of Megele area, Asosa, Western Ethiopia." Earth Sciences Research Journal 26, no. 2 (September 8, 2022): 157–72. http://dx.doi.org/10.15446/esrj.v26n2.98451.
Повний текст джерелаАнотація:
The Western Ethiopian Shield is underlain by volcano-sedimentary terranes, gneissic terranes, and ophiolitic rocks intruded by different granitoid bodies. The Megele area is part of Western Ethiopian Shield and consist of a low-grade volcano-sedimentary zone that has been intruded by mafic (dolerite dyke) and granitoid intrusions (granodiorite, diorite, granite gneiss). To establish the origin of the distinctive lithologies of the locality and evaluate its mineral potential, petrological, petrographical, and geochemical characterization of these rocks were carried out. Hence, the lithological, geochemical, and petrogenetic features of the Neoproterozoic granitoid intrusives and associated metavolcanic, were illustrated through a combination of field mapping, petrological, and geochemical analysis. The petrological result obtained from the thin section analysis of the granitoids and metabasalt from Megele area indicates that, these rocks has been metamorphosed from lower green-schist facies to lower amphibolite facies as denoted by mineral assemblages such as albite + muscovite + prehnite+ quartz and actinolite + hornblende + epidote + garnet. The major and trace element geochemical analysis of granodiorite, diorite, and granite gneiss revealed that the rocks in the studied area were mainly calc-alkaline and peraluminous in nature in the SiO2 versus Na2O+K2O and A/NK versus A/CNK, the details of the results on the major and rare elements are stated in the result section respectively. The granitoids are S-type granites revealed silica saturated rock formed at the volcanic arc subduction (VAG) to syn-collisional (syn-COLD) tectonic setting by fractionation of LREE-enriched, HREE-depleted basaltic magma with considerable crustal input. This basaltic magma seems to be generated from the LREE-enriched, HREE-depleted mantle. In conclusion, the metabasalt is sub-alkaline (tholeiitic), metaluminous bodies generated at mid-oceanic ridge tectonic setting by partially melting of HREE-depleted and LREE-enriched basaltic magma. The magma sources are associated with the reworked sediment-laden crustal slabs from the subduction zone and resulted in S-type granitoid.
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Samkari, Abdulaziz, David W. Farris, and Haitham M. Baggazi. "Activation of Ad Damm shear zone, western Saudi Arabian margin, and its relation to the Red Sea rift system." Open Geosciences 14, no. 1 (January 1, 2022): 165–77. http://dx.doi.org/10.1515/geo-2022-0343.
Повний текст джерелаАнотація:
Abstract The Ad Damm shear zone (ADSZ) is a major mylonitic right-lateral structure that bounds the Jeddah terrane to the north from the Asir terrane to the south. High-resolution field mapping coupled with petrological and geochemical analyses indicate that Jeddah terrane is characterized by heterogeneous magmatism with extensive meta-basalt intruded by silicic plutons of varying size. South of the ADSZ, Asir terrane is characterized by larger scale granitic batholiths. A younger generation of Eocene–Miocene basaltic dikes cut the mylonitic shear zone at a high angle. Petrographic analyses of the ADSZ mylonitic rocks indicate dynamic recrystallization and grain-size reduction, suggesting high-temperature recrystallization. Field observations also found a lack of low-temperature fault zone rocks (e.g. gouge) except for isolated brittle slickensides. Spider diagrams of Jeddah, Asir terranes, and ADSZ rocks are characterized by an arc-related signature, which related to the amalgamation of Jeddah and Asir terranes and defined ADSZ as Neoproterozoic structure. In contrast, Eocene–Miocene basaltic dikes and southern basaltic flow are represented by a rift-related signature, which associated with the development of the Red Sea rift system. Offshore, south of the ADSZ, the Red Sea rift exhibits well-developed linear magnetic anomalies and large topographic escarpment perpendicular to the rift margin, but they are not present north of it. In addition, recent seismicity recorded along the ADSZ and differences in the crustal thickness and characteristics of Asir and Jeddah terranes, collectively, make ADSZ acted as an active crustal boundary and still influence the ongoing tectonic evolution of the Red Sea rift.
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Rogers, John J. W., and Elaine J. Callahan. "Diapiric trondhjemites of the western Dharwar craton, southern India." Canadian Journal of Earth Sciences 26, no. 2 (February 1, 1989): 244–56. http://dx.doi.org/10.1139/e89-020.
Повний текст джерелаАнотація:
Diapiric, comparatively massive trondhjemites were emplaced in the western part of the Dharwar craton of southern India about 3000 Ma ago. This age coincides with the age of (i) closure of Rb–Sr systems that now form the youngest isochrons in the predominantly gneissic terrane, and (ii) metasomatic enrichment of the gneisses in U. Younger events, principally about 2500 Ma ago, are recorded by sparse granites and by deformation of supracrustal sequences without major metamorphism. Thus, the trondhjemites appear to have formed during the last extensive thermochemical event in the craton. The trondhjemites are not associated with any mafic rocks and show very little fractionation within and among the various bodies.Presumably they formed as a single product of partial melting. Likely source materials for the magmas are rocks of basaltic composition (probably amphibolites) in the lower crust or along the crust–mantle boundary. Very low Zr and high Cr contents in the trondhjemites may indicate a slightly ultramafic (possibly basaltic komatiite) source. A lack of fractionation of Zr and Y and low light/heavy rare-earth element ratios in the trondhjemites may indicate an absence of equilibration of the magmas with major amounts of garnet. Lack of significant garnet equilibration could have resulted from production of hydrous magmas, either by partial melting of amphibolite or by introduction of water from an external source during the melting process.
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ROBERTSON, ALASTAIR H. F., KEMAL TASLI, and NURDAN İNAN. "Evidence from the Kyrenia Range, Cyprus, of the northerly active margin of the Southern Neotethys during Late Cretaceous–Early Cenozoic time." Geological Magazine 149, no. 2 (August 31, 2011): 264–90. http://dx.doi.org/10.1017/s0016756811000677.
Повний текст джерелаАнотація:
AbstractSedimentary geology and planktonic foraminiferal biostratigraphy have shed light on the geological development of the northern, active continental margin of the Southern Neotethys in the Kyrenia Range. Following regional Triassic rifting, a carbonate platform developed during Jurassic–Cretaceous time, followed by its regional burial, deformation and greenschist-facies metamorphism. The platform was exhumed by Late Maastrichtian time and unconformably overlain by locally derived carbonate breccias, passing upwards into Upper Maastrichtian pelagic carbonates. In places, the pelagic carbonates are interbedded with sandstone turbidites derived from mixed continental, basic volcanic, neritic carbonate and pelagic lithologies. In addition, two contrasting volcanogenic sequences are exposed in the western-central Kyrenia Range, separated by a low-angle tectonic contact. The first is a thickening-upward sequence of Campanian–Lower Maastrichtian(?) pelagic carbonates, silicic tuffs, silicic lava debris flows and thick-bedded to massive rhyolitic lava flows. The second sequence comprises two intervals of basaltic extrusive rocks interbedded with pelagic carbonates. The basaltic rocks unconformably overlie the metamorphosed carbonate platform whereas no base to the silicic volcanic rocks is exposed. Additional basaltic lavas are exposed throughout the Kyrenia Range where they are dated as Late Maastrichtian and Late Paleocene–Middle Eocene in age. In our proposed tectonic model, related to northward subduction of the Southern Neotethys, the Kyrenia platform was thrust beneath a larger Tauride microcontinental unit to the north and then was rapidly exhumed prior to Late Maastrichtian time. Pelagic carbonates and sandstone turbidites of mixed, largely continental provenance then accumulated along a deeply submerged continental borderland during Late Maastrichtian time. The silicic and basaltic volcanogenic rocks erupted in adjacent areas and were later tectonically juxtaposed. The Campanian–Early Maastrichtian(?) silicic volcanism reflects continental margin-type arc magmatism. In contrast, the Upper Maastrichtian and Paleocene–Middle Eocene basaltic volcanic rocks erupted in an extensional (or transtensional) setting likely to relate to the anticlockwise rotation of the Troodos microplate.
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Rodríguez García, Gabriel, and Gloria Obando. "Volcanism of the La Quinta Formation in the Perijá mountain range." Boletín Geológico, no. 46 (June 30, 2020): 51–94. http://dx.doi.org/10.32685/0120-1425/boletingeo.46.2020.535.
Повний текст джерелаАнотація:
This study reports new data on the petrography, total rock chemistry and U-Pb zircon geochronology of volcanic rocks of the La Quinta Formation that outcrop the western flank of the Perijá mountain range and the Cesar and La Guajira departments. The volcanic rocks consist of basaltic, andesitic, dacitic and rhyolitic lavas, and the volcaniclastic rocks consist of crystal-vitric and crystal-lithic tuffs and agglomerates of calc-alkaline affinity, formed in a continental margin arc setting. Geochronological data suggest that the La Quinta Formation was volcanically active for approximately 25 Ma, during which its composition varied from basaltic trachyandesites to rhyolites. U-Pb dating suggests that the volcanism began in approximately 191 Ma (Sinemurian age) and continued until approximately 164 Ma, with at least three periods of increased volcanic activity. The inherited zircons contain Triassic, Permian, Neoproterozoic and Mesoproterozoic populations, indicating that this arc was emplaced on rocks of the Chibcha Terrane along the South American paleomargin and that it is part of the same arc that formed the Jurassic volcanic rocks of the Sierra Nevada de Santa Marta, Cocinas and San Lucas mountain ranges and the Upper Magdalena Valley.
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Mulyaningsih, Sri, Muchlis Muchlis, Nur W. A. A. T. Heriyadi, and Desi Kiswiranti. "Volcanism in The Pre-Semilir Formation at Giriloyo Region; Allegedly as Source of Kebo-Butak Formation in the Western Southern Mountains." Journal of Geoscience, Engineering, Environment, and Technology 4, no. 3 (September 30, 2019): 217. http://dx.doi.org/10.25299/jgeet.2019.4.3.2262.
Повний текст джерелаАнотація:
Kebo-Butak Formation was known to be the oldest volcanic rocks limited in regional terms in the lower Baturagung Hills, Gedangsari area, Gunungkidul Regency. The main constituents of the Kebo-Butak Formation consist of intersection of volcanic-clastic rocks and calcareous sediments, locally also found basalt lava with pillow structures; which distinguished it from other volcanic rock formations in the Southern Mountains. This study aims to determine the relationship of volcanic rocks exposed in Giriloyo with the Kebo-Butak Formation in the Baturagung Hills; the chronostratigraphy and the history of volcanic activities that produced the volcanic rocks of Giriloyo. This research was approached by volcanic geological mapping using surface mapping suported by gravity anayses. From the bottom to the top of the frontier areas result volcaniclastic rocks consisting of black tuffs with several fragments of volcanic bombs with basalt composition intersecting with thin basaltic lava inserted by calcareous claystone having an age of N5-7 (Early Miocene); pyroxene-rich basalt volcanic sequence consists of thick layers of tuff with creamy-brown color intersecting with lava and breccia inserted by calcareous sandstone aged N7-8; dikes, lava and agglomerates with basaltic composition and lava and agglomerates with andesitic composition. Stratigraphically, the volcanic rocks exposed at Giriloyo correlated with the volcanic rocks exposed at Karangtalun (Wukirsari) were under the Semilir Formation, bordered with normal fault N210oE/77o, the hanging wall composed by light grey tuff of Semilir Formation. Gravity analyses found high anomalies below the Semilir Formation exposed at Karangtalun-Munthuk (east of study area) continued to below the Giriloyo area. The high anomalies were identified as the igneous/ignimbrite volcanic sequence. Descriptively and stratigraphically, the Giriloyo volcanic sequence are a part of Kebo-Butak Formation. The petrogenesis of the volcanic rocks will be discussed in further research to interpret magmatological properties, the evolving paleo-volcano, and the absolute age of the rocks.
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BONEV, NIKOLAY, YILDIRIM DILEK, JOHN M. HANCHAR, KAMEN BOGDANOV, and LASLO KLAIN. "Nd–Sr–Pb isotopic composition and mantle sources of Triassic rift units in the Serbo-Macedonian and the western Rhodope massifs (Bulgaria–Greece)." Geological Magazine 149, no. 1 (September 26, 2011): 146–52. http://dx.doi.org/10.1017/s0016756811000938.
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AbstractWe report on the field occurrence and isotopic compositions of metamafic rocks exposed in the Serbo-Macedonian (Volvi and Therma bodies) and western Rhodope (Rila Mountains) massifs of Bulgaria and Greece. These metamafic units consist of high- and low-Ti gabbroic and basaltic rocks, whose Nd–Sr–Pb isotopes are compatible with mantle-derived MORB and OIB components with a small amount of crustal material involved in their melt source. These isotopic features combined with the field observations are consistent with an intra-continental rift origin of the metamafic rocks protolith, and are comparable to those of the Triassic rift-related mafic rocks in the northern Aegean region.
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Shellnutt, J. Gregory. "Igneous Rock Associations 21. The Early Permian Panjal Traps of the Western Himalaya." Geoscience Canada 43, no. 4 (December 15, 2016): 251. http://dx.doi.org/10.12789/geocanj.2016.43.104.
Повний текст джерелаАнотація:
The Early Permian (290 Ma) Panjal Traps are the largest contiguous outcropping of volcanic rocks associated with the Himalayan Magmatic Province (HMP). The eruptions of HMP-related lava were contemporaneous with the initial break-up of Pangea. The Panjal Traps are primarily basalt but volumetrically minor intermediate and felsic volcanic rocks also occur. The basaltic rocks range in composition from continental tholeiite to ocean-floor basalt and nearly all have experienced, to varying extent, crustal contamination. Uncontaminated basaltic rocks have Sr–Nd isotopes similar to a chondritic source (ISr = 0.7043 to 0.7073; eNd(t) = 0 ± 1), whereas the remaining basaltic rocks have a wide range of Nd (eNd(t) = –6.1 to +4.3) and Sr (ISr = 0.7051 to 0.7185) isotopic values. The calculated primary melt compositions of basalt are picritic and their mantle potential temperatures (TP ≤ 1450°C) are similar to ambient mantle rather than anomalously hot mantle. The silicic volcanic rocks were likely derived by partial melting of the crust whereas the andesitic rocks were derived by mixing between crustal and mantle melts. The Traps erupted within a continental rift setting that developed into a shallow sea. Sustained rifting created a nascent ocean basin that led to sea-floor spreading and the rifting of microcontinents from Gondwana to form the ribbon-like continent Cimmeria and the Neotethys Ocean.RÉSUMÉLes Panjal Traps du début Permien (290 Ma) constituent le plus grand affleurement contigu de roches volcaniques associées à la province magmatique de himalayienne (HMP). Les éruptions de lave de type HMP étaient contemporaines de la rupture initiale de la Pangée. Les Panjal Traps sont essentiellement des basaltes, mais on y trouve aussi des roches volcaniques intermédiaires et felsiques en quantités mineures. La composition de ces roches basaltiques varie de tholéiite continentale à basalte de plancher océanique, et presque toutes ont subi, à des degrés divers, une contamination de matériaux crustaux. Les roches basaltiques non contaminées ont des contenus isotopiques Sr–Nd similaires à une source chondritique (Isr = 0,7043 à 0,7073; eNd (t) = 0 ± 1), alors que les roches basaltiques autres montrent une large gamme de valeurs isotopiques en Nd (eNd (t) = –6,1 à +4,3) et Sr (Isr = de 0,7051 à 0,7185). Les compositions de fusion primaire calculées des basaltes sont picritiques et leurs températures potentielles mantelliques (TP de ≤ 1450°C) sont similaires à la température ambiante du manteau plutôt que celle d’un manteau anormalement chaud. Les roches volcaniques siliciques dérivent probablement de la fusion partielle de la croûte alors que les roches andésitiques proviennent du mélange entre des matériaux de fusion crustaux et mantelliques. Les Traps ont fait irruption dans un contexte de rift continental qui s’est développé dans une mer peu profonde. Un rifting soutenu a créé un début de bassin océanique lequel conduit à une expansion du fond océanique et au rifting de microcontinents tirés du Gondwana pour former le continent rubané de Cimméria et l'océan Néotéthys.
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R. Ghori, K. Ameed. "Emerging unconventional shale plays in Western Australia." APPEA Journal 53, no. 1 (2013): 313. http://dx.doi.org/10.1071/aj12027.
Повний текст джерелаАнотація:
Production of shale gas in the US has changed its position from a gas importer to a potential gas exporter. This has stimulated exploration for shale-gas resources in WA. The search started with Woodada Deep–1 (2010) and Arrowsmith–2 (2011) in the Perth Basin to evaluate the shale-gas potential of the Permian Carynginia Formation and the Triassic Kockatea Shale, and Nicolay–1 (2011) in the Canning Basin to evaluate the shale-gas potential of the Ordovician Goldwyer Formation. Estimated total shale-gas potential for these formations is about 288 trillion cubic feet (Tcf). Other petroleum source rocks include the Devonian Gogo and Lower Carboniferous Laurel formations of the Canning Basin, the Lower Permian Wooramel and Byro groups of the onshore Carnarvon Basin, and the Neoproterozoic shales of the Officer Basin. The Canning and Perth basins are producing petroleum, whereas the onshore Carnarvon and Officer basins are not producing, but they have indications for petroleum source rocks, generation, and migration from geochemistry data. Exploration is at a very early stage, and more work is needed to estimate the shale-gas potential of all source rocks and to verify estimated resources. Exploration for shale gas in WA will benefit from new drilling and production techniques and technologies developed during the past 15 years in the US, where more than 102,000 successful gas production wells have been drilled. WA shale-gas plays are stratigraphically and geochemically comparable to producing plays in the Upper Ordovician Utica Shale, Middle Devonian Marcellus Shale and Upper Devonian Bakken Formation, Upper Mississippian Barnett Shale, Upper Jurassic Haynesville-Bossier formations, and Upper Cretaceous Eagle Ford Shale of the US. WA is vastly under-explored and emerging self-sourcing shale plays have revived onshore exploration in the Canning, Carnarvon, and Perth basins.
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Cousens, Brian L., and Mary Lou Bevier. "Discerning asthenospheric, lithospheric, and crustal influences on the geochemistry of Quaternary basalts from the Iskut–Unuk rivers area, northwestern British Columbia." Canadian Journal of Earth Sciences 32, no. 9 (September 1, 1995): 1451–61. http://dx.doi.org/10.1139/e95-117.
Повний текст джерелаАнотація:
Pleistocene- to Holocene-age basaltic rocks of the Iskut–Unuk rivers volcanic field, at the southern terminus of the Stikine Volcanic Belt in the northern Canadian Cordillera, provide information on the geochemical composition of the underlying mantle and processes that have modified parental magmas. Basaltic rocks from four of the six eruptive centres are moderately evolved (MgO = 5.7–6.8%) alkaline basalts with chondrite-normalized La/Sm = 1.6–1.8, 87Sr/86Sr = 0.70336–0.70361, εNd = +4.4 to +5.9, and 206Pb/204Pb = 19.07–19.22. The small range of isotopic compositions and incompatible element ratios imply a common "depleted" mantle source for the basalts, similar to the sources of enriched mid-ocean ridge basalts from northwest Pacific spreading centres or alkali olivine basalts from the western Yukon. Positive Ba and negative Nb anomalies that increase in size with increasing SiO2 and 87Sr/86Sr indicate that the basalts are contaminated by Mesozoic-age, arc-related, Stikine Terrane crust or lithospheric mantle through which the magmas passed. Lavas from a fifth volcanic centre, Cinder Mountain, have undergone greater amounts of fractional crystallization and are relatively enriched in incompatible elements, but are isotopically identical to least-contaminated Iskut–Unuk rivers basalts. Iskut–Unuk rivers lavas share many of the geochemical characteristics of volcanic rocks from other Stikine Belt and Anahim Belt centres, as well as alkali olivine basalts from the Fort Selkirk volcanic centres of the western Yukon.
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Vozár, Jozef, Ján Spišiak, Anna Vozárová, Jakub Bazarnik, and Ján Krái. "Geochemistry and Sr, Nd isotopic composition of the Hronic Upper Paleozoic basic rocks (Western Carpathians, Slovakia)." Geologica Carpathica 66, no. 1 (February 1, 2015): 3–17. http://dx.doi.org/10.1515/geoca-2015-0007.
Повний текст джерелаАнотація:
Abstract The paper presents new major and trace element and first Sr-Nd isotope data from selected lavas among the Permian basaltic andesite and basalts of the Hronicum Unit and the dolerite dykes cutting mainly the Pennsylvanian strata. The basic rocks are characterized by small to moderate mg# numbers (30 to 54) and high SiO2 contents (51-57 wt. %). Low values of TiO2 (1.07-1.76 wt. %) span the low-Ti basalts. Ti/Y ratios in the dolerite dykes as well as the basaltic andesite and basalt of the 1st eruption phase are close to the recommended boundary 500 between high-Ti and low-Ti basalts. Ti/Y value from the 2nd eruption phase basalt is higher and inclined to the high-Ti basalts. In spite of this fact, in all studied Hronicum basic rocks Fe2O3* is lower than 12 wt. % and Nb/La ratios (0.3-0.6) are low, which is more characteristic of low-Ti basalts. The basic rocks are characterized by Nb/La ratios (0.56 to 0.33), and negative correlations between Nb/La and SiO2, which point to crustal assimilation and fraction crystallization. The intercept for Sr evolution lines of the 1st intrusive phase basalt is closest to the expected extrusions age (about 290 Ma) with an initial 87Sr/86Sr ratio of about 0.7054. Small differences in calculated values ISr document a partial Sr isotopic heterogeneity source (0.70435-0.70566), or possible contamination of the original magma by crustal material. For Nd analyses of the three samples, the calculated values εCHUR (285 Ma) are positive (from 1.75 to 3.97) for all samples with only subtle variation. Chemical and isotopic data permit us to assume that the parental magma for the Hronicum basic rocks was generated from an enriched heterogeneous source in the subcontinental lithospheric mantle.
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Tamirat, Tilahun, Takele Chekol, and Daniel Meshesha. "Petrology and geochemistry of basaltic rocks from north western Ethiopian plateau continental flood Basalt." Journal of African Earth Sciences 182 (October 2021): 104282. http://dx.doi.org/10.1016/j.jafrearsci.2021.104282.
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ÖZPINAR, YAHYA. "Petrographical, petrochemical investigation of Sandikli volcanic and usability of these rocks as trass, in Afyon region (Western Anatolia), Turkey." Bulletin of the Geological Society of Greece 34, no. 3 (January 1, 2001): 959. http://dx.doi.org/10.12681/bgsg.17128.
Повний текст джерелаАнотація:
Investigated area and its surrounding district consist of volcanic rocks. The Sanduklu volcanic are mainly composed of lavas, tuffs and tuffits. Using to K-Ar age method, the age of Sanduklu Lavas have been dated and ranged from 14 ± 0.3-8.0 to ± 0.6 Ma (Ercan, 1986).On the basis of diagrams Si02-(K20+Na20), Log (Zr/ TiO2*0.0001)-SiO2, Nb/Y-Log (Zr/TiO2*0.0001) and Ti02-Zr lavas are thrachyandesite, phonolitic tefrite, basaltic andésite, basaltic thrachy-nephelinite, andésite and dacite. Tuffs have been widely zeolitizated and dominant zeolite minerals are chabazite and phillipsite. Three phillipsite form were determined. These are potassiumsodium-aluminum-silicate hydrate, sodium-aluminum-silicate hydrate and potassium-calcium-silicate-silicate hydrate. The chemical and technological tests of zeolitic tuffs, altered lavas and tuffits were carried out and they are suitable to trass standards in cement industry.
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Gater, Will. "Drones used to recover meteorite rocks." Physics World 35, no. 4 (August 1, 2022): 5i. http://dx.doi.org/10.1088/2058-7058/35/04/07.
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Borissova, Irina, Barry Bradshaw, Chris Nicholson, Heike Struckmeyer, and Danielle Payne. "New exploration opportunities on the southwest Australian margin—deep-water frontier Mentelle Basin." APPEA Journal 50, no. 1 (2010): 47. http://dx.doi.org/10.1071/aj09004.
Повний текст джерелаАнотація:
Acreage release by the Australian Government in 2010 offers exploration opportunities in the frontier Mentelle Basin for the first time. The Mentelle Basin is a large deep-water basin on the southwest Australian margin. It consists of a large, very deep water (2,000—4,000 m) depocentre in the west and several depocentres in the east, in water depths of 500–2,000 m. The major depocentres are estimated to contain 7–11 km of sediments. Initial rifting in the Mentelle Basin occurred in the Early Permian, followed by thermal subsidence during the Triassic to Early Jurassic. In the Middle Jurassic renewed extension led to the accumulation of very thick sedimentary successions in half-graben depocentres. Early Cretaceous continental breakup was accompanied by extensive volcanism resulting in a thick syn-breakup volcanic succession in the western Mentelle Basin. Assessment of the petroleum prospectivity of the Mentelle Basin is based on correlations with the adjacent Vlaming Sub-basin. These correlations suggest that the Mentelle Basin depocentres are likely to contain multiple source rock intervals associated with coals and carbonaceous shales, as well as regionally extensive reservoirs and seals within fluvial, lacustrine and marine strata. Petroleum systems modelling suggests that potential source rocks are thermally mature and commenced generation in the Early Cretaceous. The Mentelle Basin offers a wide range of play types, including faulted anticlines and fault blocks, sub-basalt anticlines and fault blocks, drape and forced fold plays, and a large range of stratigraphic and unconformity plays.
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Teitler, Yoram, Pascal Philippot, Martine Gérard, Guillaume Le Hir, Frédéric Fluteau, and Magali Ader. "Ubiquitous occurrence of basaltic-derived paleosols in the Late Archean Fortescue Group, Western Australia." Precambrian Research 267 (September 2015): 1–27. http://dx.doi.org/10.1016/j.precamres.2015.05.014.
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Liu, Zairong, Joshua J. Shea, Stephen F. Foley, Yannick Bussweiler, Arno Rohrbach, Stephan Klemme, and Jasper Berndt. "Clarifying source assemblages and metasomatic agents for basaltic rocks in eastern Australia using olivine phenocryst compositions." Lithos 390-391 (June 2021): 106122. http://dx.doi.org/10.1016/j.lithos.2021.106122.
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Zhang, Ming, and Suzanne Y. O'Reilly. "Multiple sources for basaltic rocks from Dubbo, eastern Australia: geochemical evidence for plume—lithospheric mantle interaction." Chemical Geology 136, no. 1-2 (March 1997): 33–54. http://dx.doi.org/10.1016/s0009-2541(96)00130-1.
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Mugnier, Jean-Louis, Sebastien Cannic, and Henriette Lapierre. "The tholeiites of the Valaisan domain (Versoyen, western Alps): a Carboniferous magma emplaced in a small oceanic basin." Bulletin de la Société Géologique de France 179, no. 4 (July 1, 2008): 357–68. http://dx.doi.org/10.2113/gssgfbull.179.4.357.
Повний текст джерелаАнотація:
Abstract The mafic-ultramafic assemblages of the Versoyen complex exposed in the Valaisan domain is close to the boundary between the Internal and the External domains of the western Alps. Zircons extracted from the Versoyen complex suggest an emplacement during Paleozoic times, and probably during the Visean (~337 Ma). The base of the Versoyen complex is formed of laccoliths and sills associated with black shales, while pillow basalts and tuffs predominate at the uppermost levels. Locally, basaltic dikelets intruded leucocratic gneiss. Ultramafic-mafic cumulates form the bottom of the thickest intrusions while diabases are present along the chilled margins. All these rocks have been affected by a polyphased metamorphism under eclogitic to blueschist and greenschist facies conditions. Magmatic textures have been destroyed and the igneous mineralogy is seldom preserved. The mafic rocks of the Versoyen complex show tholeiitic to alkali-transitional affinities. The pillow basalts and the sill cores have flat REE patterns characteristic of N-MORB and T-MORB. Their εNd (assuming an age of 337 Ma) ratios range from + 5.7 to + 9 which suggest a mixing of N-MORB and OIB sources. The sill margins show Th, U and LREE-enrichments and negative εNd ratios. These features are likely related to contamination when hot mafic magmas intruded unconsolidated sediments rich in water. The high Th, U, LREE abundances and low εNd ratio of the basaltic dikelet are probably related to crustal contamination occurring during magma ascent. The geochemical characteristics of the Versoyen rocks are compatible with a tholeiitic magma emplaced into a small oceanic basin in the vicinity of a continent. The importance of pre-Mesozoic crustal thinning evidenced in one segment of the boundary between the Internal and External zones of the Alps suggests that the Pennine Front is an Alpine mega-thrust inherited from a Variscan suture.
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Cornelius, M., E. F. Stumpfl, D. Gee, and W. Prochaska. "Platinum group elements in mafic-ultramafic rocks of the Western Gneiss Terrain, Western Australia." Mineralogy and Petrology 36, no. 3-4 (July 1987): 247–65. http://dx.doi.org/10.1007/bf01163263.
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Wang, Jialin, Chaodong Wu, Zhuang Li, Tianqi Zhou, Yanxi Zhou, Geng Feng, and Yue Jiao. "The Pennsylvanian Composite Volcanism in the Bogda Mountains, NW China: Evidence for Postcollisional Rift Basins." Lithosphere 2020, no. 1 (October 6, 2020): 1–22. http://dx.doi.org/10.2113/2020/8852440.
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Abstract In this paper, we present new petrological, zircon U–Pb–Hf isotopic, bulk-rock geochemical, and Sr–Nd isotopic data for the rocks from the Pennsylvanian Liushugou and Qijiagou Formations, Bogda Mountains (BMs), northwest China. The new data help in understanding the petrogenesis and geodynamic background of the two formations, further constraining the evolution of BMs during the Pennsylvanian. The eastern Liushugou Formation is composed mainly of bimodal volcanic rocks, while the western Liushugou Formation is dominated by pillow basalts with interstitial limestones, peperites, and pyroclastic rocks. The Qijiagou Formation consists principally of bioclastic limestones, peperites, and volcanic and volcaniclastic rocks with turbidites. Depositional environment analyses of the Liushugou and Qijiagou Formations reveal subaqueous volcanism and a progressively deepening shallow marine environment with times. Zircon LA-ICP-MS U–Pb dating of felsic volcanic rocks from the Liushugou Formation indicates that the subaqueous volcanism occurred at ca. 310–302 Ma, viz., the Pennsylvanian era. The basaltic rocks from the Liushugou and Qijiagou Formations are high-K calc-alkaline, enriched in light rare earth elements and large-ion lithophile elements, and depleted in high-field-strength elements (Nb, Ta, and Ti). The above characteristics, together with their depleted isotopic signature (εNdt=3.0-8.1, εHft=8.0-15.6, and ISr=0.703-0.707), suggest the derivation from a depleted mantle source metasomatized by slab-derived fluids and sediment-derived melts. Most felsic volcanic rocks of the high-K calc-alkaline to shoshonite series from the Liushugou and Qijiagou Formations show features of the A2-type granites and have similar trace and isotopic composition to the basaltic rocks, which were probably generated from the partial melting of juvenile continental crust. Combining the newly acquired data with the regional geology, we propose that the Pennsylvanian volcanic and sedimentary rocks in the BMs were formed in a series of postcollisional rift basins which were related to local strike-slip faulting. Moreover, the volcanic rocks in the east were derived from a relatively deeper mantle source (thick lithosphere) due to their smaller rifting.
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GRENNE, T., R. B. PEDERSEN, T. BJERKGÅRD, A. BRAATHEN, M. G. SELASSIE, and T. WORKU. "Neoproterozoic evolution of Western Ethiopia: igneous geochemistry, isotope systematics and U–Pb ages." Geological Magazine 140, no. 4 (July 2003): 373–95. http://dx.doi.org/10.1017/s001675680300801x.
Повний текст джерелаАнотація:
New geochemical, isotopic and age data from igneous rocks complement earlier models of a long-lived and complex accretionary history for East African Orogen lithologies north of the Blue Nile in western Ethiopia, but throw doubt on the paradigm that ultramafic complexes of the region represent ophiolites and suture zones. Early magmatism is represented by a metavolcanic sequence dominated by pyroclastic deposits of predominantly basaltic andesite composition, which give a Rb–Sr whole-rock errorchron of 873±82 Ma. Steep REE patterns and strong enrichments of highly incompatible trace elements are similar to Andean-type, high-K to medium-K calc-alkaline rocks; εNd values between 4.0 and 6.8 reflect a young, thin continental edge. Interlayered basaltic flows are transitional to MORB and compare with mafic rocks formed in extensional, back-arc or inter-arc regimes. The data point to the significance of continental margin magmatism already at the earliest stages of plate convergence, in contrast with previous models for the East African Orogen. The metavolcanites overlap compositionally with the Kilaj intrusive complex dated at 866±20 Ma (U–Pb zircon) and a related suite of dykes that intrude thick carbonate-psammite sequences of supposedly pre-arc, continental shelf origin. Ultramafic complexes are akin to the Kilaj intrusion and the sediment-hosted dykes, and probably represent solitary intrusions formed in response to arc extension. Synkinematic composite plutons give crystallization ages of 699±2 Ma (Duksi, U–Pb zircon) and 651±5 Ma (Dogi, U–Pb titanite) and testify to a prolonged period of major (D1) contractional deformation during continental collision and closure of the ‘Mozambique Ocean’. The plutons are characterized by moderately peraluminous granodiorites and granites with εNd values of 1.0–2.0. They were coeval with shoshonitic, latitic, trachytic and rare trachybasaltic intrusions with very strong enrichments of highly incompatible trace elements and εNd of 0.4–8.0. The mafic end-member is ascribed to partial melting of enriched sub-continental mantle that carried a subduction component inherited from pre-collision subduction. Contemporaneous granodiorite and granite formation was related to crustal underplating of the mafic magmas and consequent melting of lower crustal material derived from the previously accreted, juvenile arc terranes of the East African Orogen.
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Ponomarenko, Aleksandr N., Stepan G. Kryvdik, and Aleksandr V. Grinchenko. "Alkaline rocks of the Ukrainian Shield: Some mineralogical, petrological and geochemical features." Mineralogia 44, no. 3-4 (July 1, 2013): 115–24. http://dx.doi.org/10.2478/mipo-2013-0008.
Повний текст джерелаАнотація:
AbstractThe Ukrainian Shield (USh) is a typical province of Proterozoic alkaline magmatism where about 50 massifs and occurrences of alkaline rocks and carbonatites have been found. In spite of the wide distribution of Devonian basaltic- and alkaline magmatic rocks in the Dnieper-Donetsk depression adjacent to the USh, and in a marginal zone of the USh adjacent to folded Donbass, only alkaline rocks of Proterozoic age (1.8-2.1 Ga) that have been identified in the central interior of the USh. Some discrete bodies of 2.8 Ga subalkaline rocks also occur in Bogdanivka massif (Azov area). Occurrences of both Proterozoic (prevailing) and Phanerozoic (Devonian) alkaline rocks and kimberlites are only found in the eastern part of the USh (Azov area). Kimberlites in the central part of the Ukrainian Shield (Kirovograd region) are also of Proterozoic age (ca 1.8 Ga). It is this predominance of Precambrian rocks that makes the USh so different from other alkaline provinces where Phanerozoic alkaline rocks and kimberlites commonly prevail over Precambrian rocks. The lack of Phanerozoic alkaline magmatism on USh is poorly understood. Two main complexes of alkaline rocks - alkaline-ultrabasic (carbonatitic) and gabbro- syenitic - are distinguished in the USh. There are also rare occurrences of rock types such as alkaline- and alkaline-feldspar granites that may represent one separate alkaline-granite complex. Alkaline rocks present in the Eastern (Azov) province and in the Western province display essentially different geochemical character. Those of the Eastern province show characteristics typical of alkaline-ultrabasic rocks (e.g. high contents of incompatible rare elementssuch as Nb, REE, Zr, Y, Sr, whereas those in the Western province are characterized by low contents of Nb and Zr, and REE in some cases. This fact is interpreted as reflecting different geodynamic conditions of their origin. The Eastern rocks were formed in rift settings, the Western rocks in crustal compressional settings (collision, subduction). Various mineral deposits of phosphorus (apatite), niobium, REE, yttrium and zirconium, including unusually rich ores of REE, Y and Zr (Azov and Yastrybetsky) are associated with the alkaline rocks and carbonatites of the USh.
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Nemec, Ondrej, and Monika Huraiová. "Provenance study of detrital garnets and rutiles from basaltic pyroclastic rocks of Southern Slovakia (Western Carpathians)." Geologica Carpathica 69, no. 1 (February 1, 2018): 17–29. http://dx.doi.org/10.1515/geoca-2018-0002.
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AbstractDetrital garnets and rutiles have been recovered from basaltic pyroclastic rocks in the northern part of the Pannonian Basin and characterized using electron probe microanalysis and imaging. All garnets are dominated by the almandine component, except for one sample dominated by spessartine. A total of three garnet groups have been distinguished according to the increased contents of grossular (Group I), pyrope (Group II) and spessartine components (Group III). Compositions of the group I and II garnets with fluctuating Ca- and relatively low Mg contents are consistent with low- to medium-grade metasediments and/or metabasites. Locally increased Mg contents could indicate higherP–Tmetamorphic overprint. The dominantly metamorphic origin of the Group I and II garnets (composed of >99 % of samples) is also corroborated by chlorite, tourmaline, staurolite, ilmenite and andalusite inclusions. Spessartine-rich garnets (Group III composed of <1 % of samples) could be genetically linked with granitoids. Detrital rutiles invariably plot within the field of metasediments metamorphosed under amphibolite-facies conditions. Possible proximal (subjacent basement sampled by ascending lava) or distal sources (catchment sediments from uplifted Central Carpathian basement) of heavy mineral assemblages are discussed.
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Coyle, Marylou, and D. F. Strong. "Geology of the Springdale Group: a newly recognized Silurian epicontinental-type caldera in Newfoundland." Canadian Journal of Earth Sciences 24, no. 6 (June 1, 1987): 1135–48. http://dx.doi.org/10.1139/e87-110.
Повний текст джерелаАнотація:
Volcanic–sedimentary facies and structural relationships of the Silurian Springdale Group in west-central Newfoundland are indicative of a large collapse caldera with an area of more than 2000 km2. Basaltic flows, andesite flows and pyroclastic rocks, silicic ash-flow tuffs, high-silica rhyolite domes, and volcanically derived debris flows and breccias, fluviatile red sandstones, and conglomerates make up the group. It is bounded on the east and west by up-faulted basement rocks, which include gneisses, amphibolites, and pillow lavas, and in the northwest it unconformably overlies Lower Orodovician submarine volcanics. These margins are intruded by cogenetic and younger granitoid rocks. The volcanic rocks form a calc-alkaline series, although gaps in silica content at 52–56, 67–68, and 73–74% separate them into four groups: basalts, andesites–dacites, rhyolites, and high-silica rhyolites.The high-silica rhyolites are chemically comparable to melts thought to form the upper parts of large, layered silicic magma chambers of epicontinental regions. Such an environment is also suggested by the large area of the Springdale caldera and the fact that it is one of a number of calderas that make up a large Silurian volcanic field in western Newfoundland. An epicontinental tectonothermal environment for central Newfoundland in Silurian–Devonian times is readily explained by the fact that this magmatic activity followed a period of destruction and closure of the early Paleozoic Iapetus Ocean, with trapped heat and basaltic magma causing large-scale melting of thickened and subducted continental crust in an overall transpressional tectonic regime.
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Barr, S. M., and C. E. White. "Tectonic setting of Avalonian volcanic and Plutonic rocks in the Caledonian Highlands, southern New Brunswick, Canada." Canadian Journal of Earth Sciences 33, no. 2 (February 1, 1996): 156–68. http://dx.doi.org/10.1139/e96-015.
Повний текст джерелаАнотація:
The Caledonian Highlands of southern New Brunswick consist of Late Proterozoic to Cambrian rocks generally considered typical of the Avalon terrane of the northern Appalachian Orogen. Mainly tuffaceous volcanic and sedimentary rocks of the Broad River Group and cogenetic dioritic to granitic plutons with ages ca. 620 Ma form most of the eastern Caledonian Highlands. They have petrological features indicative of origin in a continental margin subduction zone. Significantly younger ca. 560–550 Ma dacitic to rhyolitic lapilli tuffs and flows, laminated tuffaceous siltstone, basaltic and rhyolitic flows, and clastic sedimentary rocks of the Coldbrook Group form most of the western highlands, and occur locally throughout the highlands. The mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group. This voluminous subaerial magmatism may have formed during postorogenic extension in the earlier ca. 620 Ma subduction zone complex represented by the Broad River Group and associated plutons. This tectono-magmatic model differs from other interpretations that related most of the igneous units to ca. 630–600 Ma subduction, and did not recognize the importance of ca. 560–550 Ma magmatism. The ca 620 Ma subduction-related volcanic and plutonic rocks of the Caledonian Highlands are comparable to units in other parts of the Avalon terrane, but voluminous ca. 560–550 Ma igneous activity like that represented by the Coldbrook Group and related plutons has not been documented yet in other Avalonian areas.
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Baziotis, I., P. D. Asimow, A. Koroneos, G. Poli, and T. Ntaflos. "Multi-stage history of compound mantle xenoliths from Western USA: Implications for metasomatic processes in the deep mantle." Bulletin of the Geological Society of Greece 47, no. 1 (December 21, 2016): 357. http://dx.doi.org/10.12681/bgsg.11010.
Повний текст джерелаАнотація:
The compound mantle xenoliths from Cima Volcanic Field and Chino Valley (Western U.S.A.) represent outstanding candidates to illustrate the processes that occur prior to their delivery to the surface by alkali-basaltic volcanism. The xenoliths share characteristics like pyroxene zonation, amphibole breakdown and formation of glass and armalcolite. Their petrogenetic evolution involved partial melting of the silicate minerals, infiltration of reactive melts and dissociation of minerals en route to the surface, suggesting that these rocks followed multi-stage histories that initiated deep in the mantle (>1.0 GPa) and proceeded during a very short period of time.
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Baillie, P. W., and E. P. Jacobson. "PROSPECTIVITY AND EXPLORATION HISTORY OF THE BARROW SUB-BASIN, WESTERN AUSTRALIA." APPEA Journal 37, no. 1 (1997): 117. http://dx.doi.org/10.1071/aj96007.
Повний текст джерелаАнотація:
The Carnarvon Basin is Australia's leading producer of both liquid hydrocarbons and gas. Most oil production to date has come from the Barrow Sub-basin. The success of the Sub-basin is due to a fortuitous combination of good Mesozoic source rocks which have been generating over a long period of time, Lower Cretaceous reservoir rocks with excellent porosity and permeability, and a thick and effective regional seal.A feature of Barrow Sub-basin fields is that they generally produce far more petroleum than is initially estimated and booked, a result of the excellent reservoir quality of the principal producing reservoirs.Structural traps immediately below the regional seal (the 'top Barrow play') have been the most successful play to date. Analysis of 'new' and 'old' play concepts show that the Sub-basin has potential for significant additional hydrocarbon reserves.
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Zhu, Bei, Zhaojie Guo, Shaonan Zhang, Ingrid Ukstins, Wei Du, and Runchao Liu. "What triggered the early-stage eruption of the Emeishan large igneous province?" GSA Bulletin 131, no. 11-12 (February 28, 2019): 1837–56. http://dx.doi.org/10.1130/b35030.1.
Повний текст джерелаАнотація:
Abstract The formation of the Emeishan large igneous province is widely regarded as being related to a mantle plume, but plate tectonics may also have played an important role. We analyzed the regional facies architecture of the early-stage subaqueous volcanic rocks of the central Emeishan large igneous province. The results suggest that these rocks were emplaced in a N-S–striking subaqueous rift, which existed immediately before the onset of volcanism and was persistently maintained during the early eruption stage. By linking this conclusion with the background information indicating that (1) the basaltic geochemistry in this section is indicative of a subcontinental lithospheric mantle source rather than a mantle plume source, and (2) the western Yangtze plate, where the Emeishan large igneous province was developed, was located in the back-arc region of the Permian Paleo-Tethys subduction system, we propose a new view that the early-stage eruptions of the Emeishan large igneous province were triggered by back-arc extension. The dominant functioning of the mantle plume occurred shortly after this process and inherited it, as evidenced by the following: (1) The subaqueous volcanic architecture showing back-arc geochemical affinity is laterally restricted in the presumed rift, but the overlying subaerial lavas showing plume-related geochemical features overwhelmingly flooded the whole province; (2) vertically, the source of the basaltic component in these intrarift sequences underwent a gradual transition from lithospheric origin to mantle plume origin along the stratigraphic order, as evidenced by an intercalated basaltic succession showing mixed geochemical features from the two contextual origins.
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Hassanipak, A. A., A. Mohamad Ghazi, and J. M. Wampler. "Rare earth element characteristics and K–Ar ages of the Band Ziarat ophiolite complex, southeastern Iran." Canadian Journal of Earth Sciences 33, no. 11 (November 1, 1996): 1534–42. http://dx.doi.org/10.1139/e96-116.
Повний текст джерелаАнотація:
The Band Ziarat complex of southeastern Iran is located on the western boundary of the Jaz Murian depression and is bounded by two major fault systems. The principal rock units of this complex are a gabbro sequence that includes low-and high-level cumulate gabbros, a late intrusive sequence that consists of diorite and plagiogranite, and a volcanic sequence that includes diabase dikes and a lesser amount of basaltic lava. Mantle rocks are virtually absent because of the presence of the two bounding fault systems, but we consider the complex to be an ophiolite in nature. Rare earth element (REE) whole-rock data clearly differentiate the classic ophiolitic lithologies for the crustal rocks in this complex. Based on the REE data, there are two distinct types of basalt present at Band Ziarat: (i) those that formed from an initial basaltic melt with a light rare earth element (LREE) enriched signature (similar to intraplate basalts), and (ii) those that have LREE-depleted patterns (similar to normal mid-ocean-ridge basalts). The data also suggest (i) that the gabbros are accumulates and were derived from a source slightly enriched in LREE, with fractionation controlled by removal of clinopyroxene or hornblende and plagioclase, and (ii) that the late intrusive rocks as well as a majority of the diabase dikes are cogenetic and were derived from the same LREE-enriched source. K–Ar ages ranging from 134 ± 4 to 146 ± 5 Ma for low-level gabbros and from 121 ± 4 to 130 ± 4 Ma for high-level gabbros were measured on five hornblende and two whole-rock samples, which suggests that these rocks may have formed early in the Cretaceous period.
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DENTITH, M. C., A. W. R. BEVAN, J. BACKHOUSE, W. E. FEATHERSTONE, and C. KOEBERL. "Yallalie: a buried structure of possible impact origin in the Perth Basin, Western Australia." Geological Magazine 136, no. 6 (November 1999): 619–32. http://dx.doi.org/10.1017/s0016756899003386.
Повний текст джерелаАнотація:
An enigmatic buried structure, located in Mesozoic sedimentary rocks in the Perth Basin, Western Australia, was discovered in 1990 by Ampol Exploration. The basin-like Yallalie structure (centred on 30° 26′ 40.3″ S, 115° 46′ 16.4″ E) is circular in plan view and about 12 km in diameter. High-resolution, seismic-reflection profiles across the structure show a basin-shaped area of chaotic reflections that extend to a depth of approximately 2 km below the surface. The structure has sharp boundaries with surrounding faulted, but otherwise relatively undisturbed, rocks. In the centre of the structure there is an uplifted area approximately 3–4 km across, similar to those described from complex meteorite impact structures. The seismically defined structure coincides with a circular topographic depression, and image processing of digital elevation data has allowed recognition of concentric and radial structures extending as far as 40 km from the centre of the depression. Gravity surveys show the structure to be associated with a positive gravity anomaly of about 30 gu. Aeromagnetic surveys have defined annular anomalies associated with the central uplifted section, and possibly margins, of the structure. A search for siderophile element enrichments (by neutron activation analysis) in the rocks of the structure, which would indicate the presence of a meteorite component, proved negative. Quartz grains in cores that penetrate the structure show the development of prismatic cleavage fractures and irregular, slightly curved planes formed by brittle fracture. An allochthonous breccia of Late Cretaceous rocks occurs a few kilometres west of the western margin of the structure. Quartz grains from a thin veneer of Tertiary sediments that drape the structure are essentially undeformed. However, multiple sets of closely spaced planar deformation features in quartz, characteristic of highly shocked rocks, have yet to be observed in the rocks of the Yallalie structure and the allochthonous breccia. The morphology of the Yallalie structure determined from topographic and geophysical data suggests strongly that it is of impact origin. Geological and geochemical evidence is equivocal, but is not inconsistent with this interpretation.
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Shea, Joshua J., and Stephen F. Foley. "Evidence for a Carbonatite-Influenced Source Assemblage for Intraplate Basalts from the Buckland Volcanic Province, Queensland, Australia." Minerals 9, no. 9 (September 10, 2019): 546. http://dx.doi.org/10.3390/min9090546.
Повний текст джерелаАнотація:
Eastern Australia contains a widespread suite of primitive (MgO ≥ 7.5 wt.%) intraplate basaltic provinces, including those sited along the longest continental hotspot track on Earth (≈2000 km), the Cosgrove track. The Buckland volcanic province is the most southerly basaltic province on the Cosgrove track before a >1600 km stretch that contains only sparse leucitite volcanism. Buckland is also situated just northeast of the edge of thick cratonic lithosphere where it transitions to a thinner continental lithosphere (<110 km) to the east, which may influence the production of plume-derived melts. Here, analysis of minor and trace elements in olivines in alkali basalts and basanites from the Buckland Province are combined with whole-rock compositions to elucidate the mantle source assemblages, and to calibrate minor and trace element indicators in olivine for application to source mineralogy. Olivine xenocrysts show element concentration ranges typical for peridotites; Mn and Al concentrations indicate that the ambient mantle is spinel, rather than garnet, peridotite. High modal pyroxene content is indicated by high Ni, Zn/Fe, and Fe/Mn in olivines, while high Ti/Sc is consistent with amphibole in the source. Residual phlogopite in the source of the basanites is indicated by low K/Nb in whole rocks, while apatite contains high P2O5 and low Rb/Sr (≥0.015) and Sr/La (≥13). The basanite source assemblage probably contains apatite, phlogopite, olivine, clinopyroxene and orthopyroxene, whereas the alkali basalt source assemblage is probably amphibole, olivine, orthopyroxene and clinopyroxene ± phlogopite ± apatite. Both source assemblages correspond broadly to olivine websterite, with the basanite source lying deeper than that for alkali basalt, explaining the occurrence of phlogopite in the source. This mineralogy, along with whole-rock Ti/Eu, Zr/Hf and P2O5/TiO2 values approaching those of natural carbonatites, provide evidence showing that the Buckland source consists of a peridotite that has interacted with a carbonate-rich melt whose origin may be in the deep lithosphere or asthenosphere beneath the craton. Similar enrichment processes are probably common throughout eastern Australia, controlling trace element characteristics in basaltic provinces. The topography of the underside of the lithosphere may play a significant role in determining mantle source assemblages by diverting and concentrating melt flow, and thus influence the location of basaltic provinces.
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Choi, Eunjoo, Marco L. Fiorentini, Andrea Giuliani, Stephen F. Foley, Roland Maas, and Stuart Graham. "Petrogenesis of Proterozoic alkaline ultramafic rocks in the Yilgarn Craton, Western Australia." Gondwana Research 93 (May 2021): 197–217. http://dx.doi.org/10.1016/j.gr.2021.01.011.
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Delle Piane, C., L. Esteban, N. E. Timms, and S. Ramesh Israni. "Physical properties of Mesozoic sedimentary rocks from the Perth Basin, Western Australia." Australian Journal of Earth Sciences 60, no. 6-7 (October 2013): 735–45. http://dx.doi.org/10.1080/08120099.2013.831948.
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Gaynor, Andrea. "State, Scientists and Citizens: Conserving Lake Magenta and Dragon Rocks, Western Australia." Historical Records of Australian Science 25, no. 2 (2014): 202. http://dx.doi.org/10.1071/hr14015.
Повний текст джерелаАнотація:
The story of efforts to establish two major nature reserves in the south-eastern wheatbelt of Western Australia illuminates some of the many factors shaping the interaction of citizens, scientists, land management bureaucracies, and other stakeholders around the creation of conservation reserves in a semi-arid region in the mid-20th century. This article highlights the significance of citizen scientists as well as professionals in the reservation process, and traces the increasingly strained relationship between Lands and conservation bureaucracies in the context of the rise of the new environment movement. It also points to the importance of international ideas about conservation aims and methods, and suggests that although shifting appraisals of the productive potential of the land were critical to the outcome of negotiations over the proposed reserves, in this period these semi-arid lands were increasingly valued for their scientific and intrinsic qualities.
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Ostwald, J., and B. R. Bolton. "Diagenetic braunite in sedimentary rocks of the proterozoic Manganese Group, Western Australia." Ore Geology Reviews 5, no. 4 (May 1990): 315–23. http://dx.doi.org/10.1016/0169-1368(90)90036-m.
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Messenger, P. R. "Geochemistry of the Yandal belt metavolcanic rocks, Eastern Goldfields Province, Western Australia." Australian Journal of Earth Sciences 47, no. 6 (December 2000): 1015–28. http://dx.doi.org/10.1046/j.1440-0952.2000.00828.x.
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