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1
Peter, Jan M., and Wayne D. Goodfellow. "Mineralogy, bulk and rare earth element geochemistry of massive sulphide-associated hydrothermal sediments of the Brunswick Horizon, Bathurst Mining Camp, New Brunswick." Canadian Journal of Earth Sciences 33, no. 2 (February 1, 1996): 252–83. http://dx.doi.org/10.1139/e96-021.
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Massive sulphides are spatially and temporally associated with iron formation (IF) and other hydrothermal sedimentary rocks in the vicinity of the Brunswick No. 12, Brunswick No. 6, and Austin Brook deposits, Bathurst Mining Camp. Sulphide-, carbonate-, oxide-, and silicate-predominant IF is present. Carbonate-predominant IF is best developed in and around the Brunswick No. 12 deposit, whereas hematite-bearing IF is absent here but prominent in the Austin Brook–Brunswick No. 6 area. The IF is composed dominantly of Si, CO2, Fe, Mn, and Ca. Minor constituents include Mg, P, Ti, Al, and S. Statistically significant interelement correlations between Eu, Fe, Mn, Pb, Zn, Cd, Au, Ca, Sr, Ba, P, CO2, and S indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor. Positive interelement correlations between Si, Ti, Al, Mg, K, Zr, rare earth elements (REE's) except Eu, Se, V, Y, Yb, Co, Ni, and Cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and hydrogenous sedimentary components. Felsic volcanic and pyroclastic rocks are considered to be the source for the detritus. REE patterns of IF at Brunswick No. 12 display similarities with those of modern high-temperature hydrothermal vent solutions, sea water, and host rhyolitic tuff and sedimentary rocks. These patterns are largely controlled by the relative proportions of hydrothermal and detrital components. The IF formed from reduced hydrothermal fluids vented into a stratified marine basin. The mineral precipitates were widely dispersed from the sites of venting and massive sulphide accumulation.
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Dub, S. A., N. V. Cherednichenko, D. V. Kiseleva, N. P. Gorbunova, T. Ya Gulyaeva, and L. K. Deryugina. "Trace element behaviour in acidic leachates (acetic, nitric and hydrochloric) from siliciclastic-carbonate rocks of the Upper Riphean Uk formation in the Southern Urals." LITHOSPHERE (Russia) 19, no. 6 (January 3, 2020): 919–44. http://dx.doi.org/10.24930/1681-9004-2019-19-6-919-944.
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Research subject. 14 samples of limestone and one sample of carbonate-siliciclastic rock from siliciclastic-carbonate deposits of the Upper Riphean Uk Formation (the Southern Urals) were studied.Methods. Mineral and chemical composition of the samples were determined; the main tool for detecting the concentrations of trace elements was the ICPMS method. X-ray diffraction analysis was carried out using a Shimadzu XRD-7000 diffractometer, the content of major (rock-forming) oxides in bulk samples was established by X-ray fluorescence spectrometry on the SRM-35 and Shimadzu XRF 1800 spectrometers. Microelement composition of bulk samples and acidic leachates obtained with using acetic (10%), nitric (36%) and hydrochloric (17%) acids was determined on a Perkin Elmer ELAN 9000 spectrometer.Results. The distribution of lithophile, rare-earth and a number of other elements (Sr, Ni, U) both in bulk samples and in acidic leachates was analyzed. The main carrier phases of these elements were revealed.Conclusions. 1. The use of any listed acids leads to the non-carbonate component entering the solution, including contamination of the “carbonate” leachates by lithophile elements. In particular, a transition Rb, Zr, Li, Th, Ti, Sc to leachates was noted. This process is most active in nitric and hydrochloric acids, less intensive in acetic acid. 2. Among the carriers of rare earth elements (REE) in the studied rocks are clays (1), accessory minerals (2), including phosphate-bearing grains, secondary carbonate phases represented by dolomite and, possibly (3), finely disseminated iron and manganese (oxy)hydroxides (4). It is assumed that the REE pattern in limestones is determined by the content of the epigenetic dolomite. The contribution of lanthanides bound in the sedimentary calcite crystal lattice in the total REE pattern is rather large only in relatively “pure” limestones. However, the use of acids with such concentrations did not allow to obtain a leachate, which the REE pattern with high probability corresponds to the distribution of REE in the Uk time seawater. But acetic acid is more effective for achieving this goal than the others. 3. In addition to Sr, sedimentary calcite also contains Ni and U.
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Giuliani, Gaston, Lee Groat, Anthony Fallick, Isabella Pignatelli, and Vincent Pardieu. "Ruby Deposits: A Review and Geological Classification." Minerals 10, no. 7 (June 30, 2020): 597. http://dx.doi.org/10.3390/min10070597.
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Corundum is not uncommon on Earth but the gem varieties of ruby and sapphire are relatively rare. Gem corundum deposits are classified as primary and secondary deposits. Primary deposits contain corundum either in the rocks where it crystallized or as xenocrysts and xenoliths carried by magmas to the Earth’s surface. Classification systems for corundum deposits are based on different mineralogical and geological features. An up-to-date classification scheme for ruby deposits is described in the present paper. Ruby forms in mafic or felsic geological environments, or in metamorphosed carbonate platforms but it is always associated with rocks depleted in silica and enriched in alumina. Two major geological environments are favorable for the presence of ruby: (1) amphibolite to medium pressure granulite facies metamorphic belts and (2) alkaline basaltic volcanism in continental rifting environments. Primary ruby deposits formed from the Archean (2.71 Ga) in Greenland to the Pliocene (5 Ma) in Nepal. Secondary ruby deposits have formed at various times from the erosion of metamorphic belts (since the Precambrian) and alkali basalts (from the Cenozoic to the Quaternary). Primary ruby deposits are subdivided into two types based on their geological environment of formation: (Type I) magmatic-related and (Type II) metamorphic-related. Type I is characterized by two sub-types, specifically Type IA where xenocrysts or xenoliths of gem ruby of metamorphic (sometimes magmatic) origin are hosted by alkali basalts (Madagascar and others), and Type IB corresponding to xenocrysts of ruby in kimberlite (Democratic Republic of Congo). Type II also has two sub-types; metamorphic deposits sensu stricto (Type IIA) that formed in amphibolite to granulite facies environments, and metamorphic-metasomatic deposits (Type IIB) formed via high fluid–rock interaction and metasomatism. Secondary ruby deposits, i.e., placers are termed sedimentary-related (Type III). These placers are hosted in sedimentary rocks (soil, rudite, arenite, and silt) that formed via erosion, gravity effect, mechanical transport, and sedimentation along slopes or basins related to neotectonic motions and deformation.
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Li, Ying Shu, Yan Cai, Jiao Jiao Chen, Nan Chen, Lun Wang, Yi Ke Zhang, and Da Qing He. "Isotopic Dating and Geological Significance of Stratiform Orebody in Gejiu Tin Deposit, Yunnan, China." Advanced Materials Research 616-618 (December 2012): 43–47. http://dx.doi.org/10.4028/www.scientific.net/amr.616-618.43.
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Gejiu tin ore deposit is a famous tin-polymetallic deposit in the world because of its enormous metal reserves. Besides tin, there are copper, lead, zinc, silver, iron, sulphur, tungsten, bismuth, indium and rare earth elements. It was believed that there mainly are skarn-type tin deposit, stratiform tin deposit and basalt-type copper deposit in Gejiu tin orefield. The stratiform tin deposit are distributed in Lutangba, Malage and Huangmaoshan, which are hosted by carbonate rocks of Gejiu formation in Middle Triassic Series. 40Ar-39Ar dating of cassiterite from the sratiform tin deposit in Lutangba yields plateau age of 202.18±2.35Ma and isochron age of 206.81±3.23 Ma respectively. The ages are obviously older than those of the ore of the skarn type deposit of the Yanshanian epoch．The mineralization is the seabed exhalative hydrothermal sedimentary mineralization of the Indosinia epoch.
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James, Noel P., Guy M. Narbonne, and T. Kurtis Kyser. "Late Neoproterozoic cap carbonates: Mackenzie Mountains, northwestern Canada: precipitation and global glacial meltdown." Canadian Journal of Earth Sciences 38, no. 8 (August 1, 2001): 1229–62. http://dx.doi.org/10.1139/e01-046.
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The 3-27 m-thick cap carbonate overlying "Marinoan" Ice Brook Formation glacigene sediments and Keele Formation carbonate and terrigenous clastic rocks consists of two distinctive stratigraphic units. A lower, splintery, buff-weathering, microcrystalline dolostone of extensive lateral uniformity comprises mm-laminated peloidal sediment with local, low-angle, hummocky-like cross-stratification, micro-ridges, and synsedimentary tepees, all elongated perpendicular to depositional strike. This dolostone is unconformably overlain by an upper limestone that exhibits pronounced facies variation from inboard peloidal lime grainstone and mudstone to shelf-edge cementstone to outboard lime wackestone and mudstone. Calcite cementstones range from isolated crystal fans in laminated limestone to huge, decimetre-scale crystal arrays, to hemispherical and elongate crystal stromatolites wholly composed of acicular crystals that form decametre-scale reeflike structures. Crystal stromatolites are precipitates and replaced microbiolites that constructed biostromes and bioherms, like those on many flat-topped, reef-rimmed platforms. The calcite crystals have all the physical and chemical attributes of neomorphosed aragonite. This aragonite extensively replaced sediment and microbiolite just below the sea floor and grew upward into the overlying water column. Such interpreted massive synsedimentary replacement is rare in geological history and attests to the highly saturated state of the immediate postglacial ocean. All sediment is interpreted to have been CaCO3 originally. Low and constant δ18O values reflect diagenetic modification of these carbonates, although chemical attributes, such as Sr and C isotopes in some lithologies, are near pristine. Lower dolostones, virtually identical to most other coeval Marinoan caps worldwide, were part of a global precipitation event of remarkable similarity. Upper limestones are a more local phenomenon, deposited during sea-level rise in an aragonitic sea returning to equilibrium after global glaciation. Low 87Sr/86Sr ratios and varying δ13C values with carbonate sedimentary facies indicate that both units must have formed relatively rapidly, prior to significant fluvioglacial runoff, or that the influence of this runoff on the chemistry of seawater along continental shelves was minimal. The cap carbonate is thus interpreted to have formed in two steps: (1) during initial marine ice melting accompanied by oceanic overturn and upwelling, preceding continental margin rebound, and (2) during initial stages of sea-level rise accompanying continental deglaciation. While confirming brief, but extensive, carbonate precipitation from an ocean highly perturbed by global glaciation, the rocks also suggest that this event did not permanently affect either late Neoproterozoic ocean chemistry or the contained marine biosphere.
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Corriveau, Louise, and Anne-Laure Bonnet. "Pinwarian (1.50 Ga) volcanism and hydrothermal activity at the eastern margin of the Wakeham Group, Grenville Province, Quebec." Canadian Journal of Earth Sciences 42, no. 10 (October 1, 2005): 1749–82. http://dx.doi.org/10.1139/e05-086.
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Volcanic belts developed along the southeastern continental margin of Laurentia between 1.70 and 1.30 Ga and subsequently metamorphosed at high grade are today largely concealed among gneiss complexes of the Grenville Province. At the eastern end of the Wakeham Group and in the La Romaine Supracrustal Belt to the east, four 1.50 Ga volcanic centres were found among gneissic synvolcanic intrusions typical of the 1.521.46 Ga Pinwarian continental magmatic arc. Upper amphibolite- to granulite-facies rhyolitic to dacitic lavas and coarse lapillistone overlie or are intimately associated with arenites typical of the Wakeham Group. Garnetite, ironstone, carbonate rock, calc-silicate rock, and sillimanite-bearing nodules, veins, and gneiss, locally preserving lapilli, are also present. The distribution, paragenesis, and modes of most of these latter units differ from those of normal metasediments but are diagnostic of metamorphosed exhalites and hydrothermal alteration zones. In the La Romaine Supracrustal Belt, they are associated with pyroclastic horizons and a mineralized composite amphibolite unit. Volcanic textures include flow banding, wispy lapilli moulding fragmented lapilli and rounded lapilli with quartz-feldspar mosaics (filled vesicles), and in situ shattering of lapilli. These textures and the presence of advanced argillic alteration point to vesicular volcanism and hydrothermal activity in a subaerial to shallow submarine environment. Rare mafic lapilli attest to coeval mafic magmatism. The pervasive calc-alkaline signature of the eruptive and intrusive felsic to mafic rocks and their distribution are compatible with the development of 1.50 Ga intra-arc volcano-sedimentary belts stemming from the Wakeham Group basin and extending eastward within the Pinwarian continental magmatic arc.
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Brugger, J., J. Ogierman, A. Pring, H. Waldron, and U. Kolitsch. "Origin of the secondary REE-minerals at the Paratoo copper deposit near Yunta, South Australia." Mineralogical Magazine 70, no. 6 (December 2006): 609–27. http://dx.doi.org/10.1180/0026461067060361.
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AbstractThe Paratoo copper deposit, located in the Neoproterozoic to Cambrian Adelaide Geosyncline, South Australia, produced around 360 tons of Cu between 1888 and 1967 from oxidized ores. The deposit is located in the core of a breached, doubly plunging anticline, near a zone of disruption containing brecciated Adelaidean sedimentary rocks and dolerite (‘Paratoo Diapir’), and hosted in dolomitic shales of the Neoproterozoic Burra Formation. Near the surface, the mineralization resides mainly in deeply weathered quartz-magnetite-sulphide (pyrite, chalcopyrite) veins (⩽10 cm wide). At depth, drill cores reveal disseminated magnetite, pyrite, chalcopyrite, copper sulphide and native copper associated with extensive potassic alteration. K-Na-rich fluids also affected the dolerite in the ‘Paratoo diapir’, resulting in the precipitation of K-feldspar, dravite and K-bearing chabazite-Na. The most likely scenario for the genesis of the Paratoo deposit involves circulation of basinal fluids, focusing into the ‘Paratoo Diapir’, and ore precipitation through neutralization by fluid-rock interaction with the dolomitic shales hosting the mineralization.The Paratoo deposit is deeply weathered, with malachite and chrysocolla (± tenorite and cuprite) containing the bulk of the copper recovered from the shallow workings. A diverse assemblage of secondary REE-bearing carbonate minerals, including the new species decrespignyite-(Y) and paratooite-(La), is associated with the weathered base metal and magnetite ores. Whole-rock geochemical analyses of fresh and mineralized host rock and of vein material reveals that the mineralization is associated with a strong, albeit highly variable, enrichment in light rare earth elements (LREE). This association indicates that REE and base metals were introduced by the same hydrothermal fluid. The strong negative Ce anomaly found in secondary REE minerals and mineralized rock samples suggests an upgrade of the REE contents in the weathering zone, insoluble Ce4+ being left behind.The Fe-oxide-REE-base metal association at Paratoo is also characteristic of the giant Mesoproterozoic Fe oxide copper gold deposit of Olympic Dam, located 350 km to the NW. A similar association is found in the Palaeozoic deposits of the Mt Painter Inlier, 300 km to the NNE. The widespread occurrence of this elemental association in the Province probably reflects the geochemistry of the basement, which contains numerous Mesoproterozoic granites enriched in REE and U.
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Lodes, Emma, Nancy R. Riggs, Michael E. Smith, and Paul Stone. "Cordilleran Subduction Initiation: Retroarc Timing and Basinal Response in the Inyo Mountains, Eastern California." Lithosphere 2020, no. 1 (December 24, 2020): 1–20. http://dx.doi.org/10.2113/2020/9406113.
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Abstract Subduction zones drive plate tectonics on Earth, yet subduction initiation and the related upper plate depositional and structural kinematics remain poorly understood because upper plate records are rare and often strongly overprinted by magmatism and deformation. During the late Paleozoic time, Laurentia’s western margin was truncated by a sinistral strike-slip fault that transformed into a subduction zone. Thick Permian strata in the Inyo Mountains of central-eastern California record this transition. Two basins that were separated by a transpressional antiform contain sedimentary lithofacies that record distinct patterns of shoaling and deepening conditions before and during tectonism associated with subduction initiation. Sandstone petrography and lithofacies analysis show that rocks in a southeastern basin are dominated by carbonate grains derived from adjacent carbonate shelves, whereas sandstones in a northwestern basin are predominantly quartzose with likely derivation from distant ergs or underlying strata. Detrital zircon spectra from all but the youngest strata in both basins are typical of Laurentian continent spectra with prominent peaks that indicate ultimate sources in Appalachia, Grenville, Yavapai/Mazatzal, and the Wyoming or Superior cratons. The first Cordilleran arc-derived detrital zircon grains appear in the uppermost strata of the northwestern basin and record Late Permian (ca. 260 Ma) Cordilleran arc magmatism at this approximate latitude, and a possible source area is suggested by geochemical similarities between these detrital zircons and broadly coeval magmatic zircons in the El Paso Mountains to the southwest. Deformation responsible for basin partitioning is consistent with sinistrally oblique contraction in the earliest Permian time. The data presented from the Inyo Mountains shed more light on the nature of Cordilleran subduction initiation and the upper-crustal response to this transition.
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Landing, Ed, Georgia Pe-Piper, William SF Kidd, and Karem Azmy. "Tectonic setting of outer trench slope volcanism: pillow basalt and limestone in the Taconian orogen of eastern New York." Canadian Journal of Earth Sciences 40, no. 12 (December 1, 2003): 1773–87. http://dx.doi.org/10.1139/e03-076.
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The only pillow basalt in synorogenic sedimentary rocks at the exterior margin of the Taconic orogen in eastern North America is at Stark's Knob in eastern New York. Earlier reported as extrusive into allochthonous Ordovician slope and rise facies, this small lens (ca. 125+ m long, 39 m thick) is a fault-bounded block in Upper Ordovician melange under the Taconian frontal thrust. Its N-MORB (normal mid-ocean ridge basalt) basalt geochemistry and spinel composition are characteristic of oceanic ridge settings at a water depth of 2 km or more. Abundant limestone lenses on pillows and lava shelves within pillows yielded a middle Late Ordovician gastropod. The limestones are reconciled with this extrusion depth and with limited early Paleozoic pelagic carbonate production by lime mud transport from the Laurentian platform or abiotic carbonate precipitation with sea-water heating during basalt extrusion. A genetic relationship between the parautochthonous Stark's Knob basalts and the allochthonous Jonestown volcanics in slope and rise facies of the Hamburg klippe, eastern Pennsylvania, is likely. Both are Ordovician MORB basalts that reflect volcanism on the subducting outer trench slope prior to the Taconic arc Laurentia collision. Taconic orogenesis may have led to basalt production on the subducting plate by (1) the setting up of orogen-parallel, predominantly strike-slip motion on the subducting slab with MORB basalt generated at offsets in a setting analogous to the Gulf of California or (2) development of faults in a flexure-induced extensional regime. By either process, mafic volcanism appears to be a rare but tectonically significant process on outer trench slopes as continental margins or oceanic plates enter subduction zones.
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Tolstov, Alexander, Vladimir Cherenkov, and Leonid Baranov. "GENESIS AND AGE OF THE TOMTOR Nb AND RARE-EARTH DEPOSIT ORE SEQUENCE, NORTHEASTERN SIBERIAN PLATFORM." Ores and metals, no. 4 (February 2, 2021): 32–44. http://dx.doi.org/10.47765/0869-5997-2020-10026.
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The northeastern Siberian platform (Republic of Sakha, Yakutia) hosts the Udzhinskaya province of alkaline ultrabasic massifs with carbonatites as final phases of magmatic system evolution; they form i ts central carbonatite core and are characterized by elevated Fe, Al and P concentrations. They also contain a complex of rare and rare-earth elements. Crust of laterite weathering of up to 400 m thick is present within the massifs. Phosphate, Nb, Y, Sc and TR content in crust of carbonatite weathering is much higher compared to unaltered rock differences. Their maximum values are in the sequence of specific sedimentary deposits f ormed a s denudation products of ore-bearing carbonatite crust precipitated in minor lake depressions and due to their intensive chemogenic transformation in hot humid climate. They are unique high-grade ores, with no world analogs in terms of mineral potential. Sometimes, these rocks are their natural concentrates averaging (in weight %) 7,21 Nb2O5, 0,578 Y2O3, 0,045 Sc2O3 and 10,16 TR2O3. The rocks composing the ore-bearing sequence show distinct evidence of sedimentary genesis: well-pronounced layered texture and facial zoning, presence of carbonized vegetable detrite and bacteriomorphic aggregates. Therefore, it is reasonable to regard a set of these formations as an independent stratigraphic unit, Tomtor sequence. Geological data suggest that it formed 340-280 Ma. Tomtor sequence can be an important prospecting criteria in prospecting for rare and rare-earth elements.
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Milton, Jack E., Kenneth A. Hickey, Sarah A. Gleeson, Hendrik Falck, and Julien Allaz. "In Situ Monazite Dating of Sediment-Hosted Stratiform Copper Mineralization in the Redstone Copper Belt, Northwest Territories, Canada: Cupriferous Fluid Flow Late in the Evolution of a Neoproterozoic Sedimentary Basin." Economic Geology 112, no. 7 (November 1, 2017): 1773–806. http://dx.doi.org/10.5382/econgeo.2017.4529.
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Abstract The 300-km-long Redstone copper belt in the Mackenzie Mountains, Northwest Territories, Canada, is composed of a series of sediment-hosted stratiform copper (SSC) deposits hosted in Neoproterozoic fault-bounded intracontinental rift basins. Mineralization at Coates Lake, the largest of these deposits, is concentrated within microbial laminite layers in the transition zone between underlying continental red beds of the Redstone River Formation and overlying marine carbonates of the Coppercap Formation. Disseminated cupriferous sulfides (chalcopyrite, bornite, and chalcocite) form part of a late diagenetic mineral association with dolomite, K-feldspar, albite, quartz, monazite, apatite, and pyrite that partially replaced detrital and early diagenetic minerals, including calcite cements, sulfate, and earlier generations of pyrite. Bornite (± minor chalcopyrite), calcite, dolomite, quartz, K-feldspar, and albite were also deposited in rare bedding-parallel veins adjacent to the lowermost mineralized microbial laminite layer in the transition zone. The absolute timing of mineralization was constrained by in situ U-Th-Pb chemical dating of monazite from four samples hosting disseminated SSC-type mineralization. The monazite have rounded, Th-U-heavy rare earth element-rich, detrital cores surrounded by Th-U-poor, light rare earth element-S-Sr-rich rims. The rim stage of monazite growth is intergrown with and enveloped by cupriferous sulfide and is paragenetically constrained as being part of the disseminated SSC-type mineralizing event. Eleven detrital cores yielded dates between 1843 and 1025 Ma, older than the depositional age of transition zone strata previously constrained to be between 775 and 732 Ma. Ten monazite rims yielded dates between 661 and 607 Ma. A weighted average date of 635 ± 13 Ma provides a maximum estimate, and is our preferred interpretation, for the absolute age of all copper mineralization at the Coates Lake deposit. Mineralization formed approximately 100 m.y. after deposition of the host rocks, during the thermal sag phase of continental rifting. Stratigraphic reconstructions, coupled with estimates of sediment compaction, indicate that at 635 Ma the transition zone was buried by ~4 km of sediments and overlaid another ~1.7 km of sediments that formed the Redstone River and Thundercloud Formations. Mudstone and carbonate-rich units above the transition zone acted as low permeability caps that led to suprahydrostatic fluid pressures in the underlying sediments. The bedding-parallel veins indicate transient supralithostatic fluid pressures. Free convection of pore fluids began within the transition zone and underlying units once they became hydrologically isolated from overlying strata. Mineralization formed as oxidized saline pore fluids circulated through the red beds (± underlying basaltic flows and basal sedimentary detritus), stripping copper and carrying it up into the transition zone. The salinity of the pore fluids may have, at least in part, originated from cryogenic brines generated by the Sturtian (717–662 Ma) global glaciation event.
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Koski, Randolph A. "Ferromanganese deposits from the Gulf of Alaska Seamount Province: mineralogy, chemistry, and origin." Canadian Journal of Earth Sciences 25, no. 1 (January 1, 1988): 116–33. http://dx.doi.org/10.1139/e88-012.
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Ferromanganese-oxide deposits dredged from four seamounts (Welker, Miller, Murray, and Patton) in the Gulf of Alaska Seamount Province include poorly crystallized microlaminated crusts on basalt substrate, well-crystallized Mn-oxide veins in epiclastic sedimentary rocks, and crystalline Mn-oxide layers and micronodules in phosphorite. The principal rock types dredged are alkali-basalt pillow fragments and tuffaceous conglomerate and sandstone. The glassy rims of pillow fragments, the glassy goundmass of large volcanic clasts, and the tuffaceous component of the sediment are altered to palagonite. Other low-temperature alteration products include phillipsite, smectite, and carbonate-apatite.Thick (10–50 mm) Fe–Mn crusts consist mainly of δ-MnO2; straight and cuspate growth laminae indicate variable growth rates and periods of nondeposition. A larger number of detrital particles toward the top of thick crusts record the increasing influence of active volcanoes of the Aleutian arc during northwestward movement of the Pacific plate. Thick crusts on basalt substrate have higher Mn/Fe ratios and lower Co content than Fe–Mn crusts from low-latitude seamounts of the central Pacific region. Thin (< 10 mm) crusts on volcaniclastic substrate contain todorokite and birnessite and have higher Mn/Fe ratios, Ni, and Cu and lower Fe and Co than thick Gulf of Alaska crusts.Veins of todorokite and cryptomelane with complex internal structure occur in altered tuffaceous sandstone and conglomerate from Miller Seamount. Fibrous todorokite has a composition similar to those of other marine examples but may contain up to 7% Mn2+ in M2 sites. Microprobe analysis of the marine cryptomelane indicates a composition that is approximately (K,Ba)1–2(Mn4+,Co)7–8O16∙x(H2O).A third type of Fe–Mn deposit in phosphorite is an intimate mixture of todorokite (and minor δ-MnO2)-bearing layers and micronodules, carbonate-apatite, and phillipsite that encloses grains of altered volcanic glass and lithic fragments.The microlaminated structure, mineralogy (predominantly δ-MnO2), and composition (Mn/Fe ratio and transition metal, rare earth element, U, and Th contents) of the thick crusts are characteristic of hydrogenetic Fe–Mn crusts elsewhere in the Pacific. Conversely, the crystallinity and chemical composition of the Mn-oxide veins and thin crusts indicate formation during diagenesis of the volcanogenic sediment substrate. Mn and other transition metals are mobilized during low-temperature oxidative alteration (palagonitization) of basaltic volcanic glass; the oxidation of Fe2+ to Fe3+ during palagonitization and the dissolution of the dilute biogenic fraction of the sediment combine to lower the Eh of ambient pore fluid and enhance the mobility of Mn2+. Diagenesis in the phosphatic sandstone from Patton Seamount involves organic-rich sediment and pore waters elevated in phosphorus owing to upwelling above a large volcanic edifice.
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Drenth, Benjamin J. "Geophysical expression of a buried niobium and rare earth element deposit: The Elk Creek carbonatite, Nebraska, USA." Interpretation 2, no. 4 (November 1, 2014): SJ23—SJ33. http://dx.doi.org/10.1190/int-2014-0002.1.
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The lower Paleozoic Elk Creek carbonatite is a 6–8-km-diameter intrusive complex buried under 200 m of sedimentary rocks in southeastern Nebraska. It hosts the largest known niobium deposit in the U.S. and a rare earth element (REE) deposit. The carbonatite is composed of several lithologies, the relations of which are poorly understood. Niobium mineralization is most enriched within a magnetite beforsite (MB) unit, and REE oxides are most concentrated in a barite beforsite unit. The carbonatite intrudes Proterozoic country rocks. Efforts to explore the carbonatite have used geophysical data and drilling. A high-resolution airborne gravity gradient and magnetic survey was flown over the carbonatite in 2012. The carbonatite is associated with a roughly annular vertical gravity gradient high and a subdued central low and a central magnetic high surrounded by magnetic field values lower than those over the country rocks. Geophysical, borehole, and physical property data are combined for an interpretation of these signatures. The carbonatite is denser than the country rocks, explaining the gravity gradient high. Most carbonatite lithologies have weaker magnetic susceptibilities than those of the country rocks, explaining why the carbonatite does not produce a magnetic high at its margin. The primary source of the central magnetic high is interpreted to be mafic rocks that are strongly magnetized and are present in large volumes. MB is very dense (mean density [Formula: see text]) and strongly magnetized (median 0.073 magnetic susceptibility), producing a gravity gradient high and contributing to the aeromagnetic high. Barite beforsite has physical properties similar to most of the carbonatite volume, making it a poor geophysical target. Geophysical anomalies indicate the presence of dense and strongly magnetized rocks at depths below existing boreholes, either a large volume of MB or another unknown lithology.
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Daryono, Lutfian Rusdi, Kazunori Nakashima, Satoru Kawasaki, Anastasia Dewi Titisari, and Didit Hadi Barianto. "Sediment Characteristics of Beachrock: A Baseline Investigation Based on Microbial Induced Carbonate Precipitation at Krakal-Sadranan Beach, Yogyakarta, Indonesia." Applied Sciences 10, no. 2 (January 10, 2020): 520. http://dx.doi.org/10.3390/app10020520.
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Isolation of ureolytic bacteria and geochemical analysis of beachrock from Krakal-Sadranan Beach (Yogyakarta, Indonesia) were conducted to determine natural sedimentary characteristics of the beachrock. The beachrock was also examined to determine the depositional conditions and distribution of rare earth elements. An increased concentration of total rare earth elements, both heavy rare earth elements (terbium, dysprosium, yttrium, holmium, erbium, thulium, ytterbium, and lutetium) and light rare earth elements (lanthanum, cesium, praseodymium, neodymium, samarium, europium, and gadolinium) signals that the beachrock deposition process happened under oxidative environmental conditions. This study proposes the novel use of ureolytic bacteria in a depositional environment for carbonate control of a sedimentary process for the development of artificial rock to mitigate coastal erosion. The resulting bacterial strains are highly homologous to the 16S rDNA nucleotide sequence of the species Oceanobacillus profundus, Vibrio maritimus, and Pseudoalteromonas tetradonis.
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Lapierre, H., M. Tardy, C. Coulon, E. Ortiz Hernandez, J. L. Bourdier, J. Martínez Reyes, and C. Freydier. "Caractérisation, genèse et évolution géodynamique du terrain de Guerrero (Mexique occidental)." Canadian Journal of Earth Sciences 29, no. 11 (November 1, 1992): 2478–89. http://dx.doi.org/10.1139/e92-194.
Full textAbstract:
The Guerrero terrane (western Mexico) is composed of Late Jurassic – Early Cretaceous plutono-volcanic and volcano-sedimentary sequences of the Alisitos–Teloloapan arc that accreted to the North American craton at the end of the Early Cretaceous. The geodynamic evolution of the Guerrero terrane is that of the Alisitos–Teloloapan intraoceanic arc, partly built on continental crust and partly on oceanic crust. The growth of the arc was likely linked to the subduction of the Arperos and Olvidada basins fringing the North American borderland. The subduction was dipping west-south-west.The continent-based segment of the arc, which is presently exposed mainly in northwestern Mexico, is composed of aerial and submarine K-rich calc-alkaline basalts, andesites, and rhyolites and of siliceous pyroclastic rocks interbedded with Aptian–Albian bioclastic carbonates or red beds bearing dinosaurus foot prints. The calc-alkaline basalts and andesites show light rare earth elements enriched patterns and high concentrations in large ion lithophile elements. The siliceous andesites and rhyodacites display low contents in Y and heavy rare earth elements, uncommon for such calc-alkaline SiO2-saturated rocks. This depletion is likely linked to amphibole fractionation and to the presence of sphene and zircon, minerals known to concentrate the heavy rare earth elements.In contrast, the magmatic arc sequences built on oceanic crust, that crops out in central-southern areas of the Guerrero terrane, show an evolution with time. The activity of the arc began with depleted tholeiitic igneous rocks, followed first by mature tholeiitic basalts, then by calc-alkaline olivine basalts interbedded with micritic limestones and radiolarian oozes of Early Cretaceous age (Neocomian). At the end of the arc development, in Late Aptian–Albian, calc-alkaline pillow basalts and andesites erupted at the volcanic front whereas shoshonitic basalts emitted backwards. In the late Early Cretaceous, the arc drifted towards the north and collided with the craton. Arc tholeiites are characterized by flat rare earth element patterns or slightly depleted in light rare earth elements and by high εNd ratios. The calc-alkaline plutonic and volcanic rocks show light rare earth elements enriched patterns and their εNd ratios decrease with time. This decrease of the εNd ratios suggests that either the mantle source of the calc-alkaline rocks was contaminated by subducted terrigenous sediments derived from an old continental crust (North American craton) or that these calc-alkaline rocks derive from the partial melt of an oceanic island basalt source present in the mantle wedge. The shoshonitic features of the basalts are marked by the presence of sanidine in the groundmass and the high levels of K2O, Ba, and Sr of the unaltered rocks.
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Premovic, Pavle, Maja Stankovic, Mirjana Pavlovic, and Milos Djordjevic. "Cretaceous-Paleogene boundary Fish Clay at Højerup (Stevns Klint, Denmark): Zn, Pb and REE in kerogen." Journal of the Serbian Chemical Society 73, no. 4 (2008): 453–61. http://dx.doi.org/10.2298/jsc0804453p.
Full textAbstract:
Geochemical analyses of Zn, Pb and rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in the kerogen of the black marl at the Cretaceous - Paleogene boundary Fish Clay at H?jerup were performed. Substantial proportions of the Zn, Pb and rare earths were probably contained in terrestrial humic substances (the kerogen precursor) arriving at the marine sedimentary site. This is in accord with a previous hypothesis that kerogen is mainly derived from humic acids of an oxic soil in of the adjacent coastal areas of eastern Denmark. It is also suggested that humics enriched in Zn, Pb and rare earth elements were transported mainly through fluvial transport into the deposition site of the Fish Clay. Local weathering/leaching of the impact-eject fallout on the land surface and local terrestrial rocks by impact-induced? acid surface waters perhaps played an important role in providing Zn, Pb and rare earths to these humic substances. Apparently, chondritic and non-chondritic Zn originated from the impact fallout; Pb and rare earth elements were most likely sourced by exposed rocks in the coastal areas of eastern Denmark.
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Premović, Pavle I., Bratislav Ž Todorović, and Mirjana S. Pavlović. "Cretaceous – Paleogene boundary Fish Clay at Højerup (Stevns Klint, Denmark): trace metals in kerogen." Bulletin de la Société Géologique de France 178, no. 5 (September 1, 2007): 411–21. http://dx.doi.org/10.2113/gssgfbull.178.5.411.
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Abstract Geochemical analyses of trace metals (Ir, Ni, Co, Cr, Zn, Au and Pb) and rare earth elements (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in kerogen of the black marl at the Cretaceous–Paleogene boundary Fish Clay at Højerup have been undertaken. Substantial proportions of the trace metals and rare earths were probably contained in terrestrial humic substances (the kerogen precursor) arriving at the marine sedimentary site. This is in accord with a previous hypothesis that kerogen is mainly derived from humic acids of an oxic soil in of the adjacent coastal areas of eastern Denmark. It is also suggested that humics were transported mainly through fluvial transport into the site of the deposition of the Fish Clay. The local weathering/leaching of the impact-ejecta fallout on the land surface or local terrestrial rocks by impact-induced? acid surface waters perhaps played an important role in providing trace metals and rare earths for these humic substances. Apparently, chondritic Ir, Au, Ni, Co, Cr and chondritic and non-chondritic Zn originated from the impact fallout; Pb and rare earth elements were most likely sourced by the rocks exposed in the coastal areas of eastern Denmark.
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ARRAGONI, S., L. P. FERNÁNDEZ, A. CUESTA, M. MAGGI, P. CIANFARRA, and F. SALVINI. "Origin of exotic clasts in the Central-Southern Apennines: clues to the Cenozoic fold-and-thrust collisional belt in the Central Mediterranean area." Geological Magazine 155, no. 2 (October 30, 2017): 479–505. http://dx.doi.org/10.1017/s0016756817000930.
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AbstractThe Central-Southern Apennines are the result of the collision between Europe and Africa. Despite the volume of existing literature, many problems remain unsolved such as the presence of Tertiary conglomerates containing exotic basement clasts. The lack of basement rocks in the Central-Southern Apennines implies that the origin of these clasts has to be sought in areas where the basement is extensively exposed. These include the Calabro–Peloritani arc and the Sardinia–Corsica block, which in Cenozoic time were connected to the Central-Southern Apennines. In this work we present the results of sedimentary, geochemical and petrographic analyses performed on the exotic basement-derived clasts. These analyses include lithological, major- and minor-element and rare Earth element compositions which are compared to analogous rocks from Calabria and Sardinia basements. Results indicate Eastern Sardinia as the primary source area for the studied conglomeratic units, linking the Central-Southern Apennines sedimentary cover to the Mesozoic carbonates of Eastern Sardinia prior to the opening of Tyrrhenian Sea. The Cilento unit (Campania) was directly fed by an uplifting Cenozoic orogen, and the Filettino, Gavignano (Latium) and Ariano Irpino (Campania) units were produced by the successive reworking of ‘Cilento-like’ sedimentary units. These results may imply that part of the Central-Southern Apennines represented a portion of the European margin of the Tethys.
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Perevoznikova, E. V., and V. T. Kazachenko. "Mineralogy of spessartine-quartz rocks of the Sikhote-Alin." LITHOSPHERE (Russia) 21, no. 1 (March 4, 2021): 70–89. http://dx.doi.org/10.24930/1681-9004-2021-21-1-70-89.
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Research subject. The article is devoted to the study of spessartine-quartz rocks of the Triassic chert formation of the Sikhote-Alin. The research objects involved the outcrops of spessartine-quartz rocks of the Gornaya and Shirokaya Pad areas from Malinovka and Olga ore districts (in the Samarka and Taukha terranes respectively). Materials and methods. The selection of stone materials was performed manually. The diagnostic of minerals was performed using the microscope in transmitted and reflected light and carried out by the determination of their composion. The polished sections of the minerals were investigated at the FEGI FEB RAS using JXA8100 microanalysers. Results. Spessartine-quartz and manganese silicate rocks occupy the same position in the section of the Triassic deposits of the Taukha and Samarka terrains. This indicates a synchronous accumulation of sediments (protoliths of these rocks) in a single sedimentary basin. The rocks formed by contact metamorphism in the Late and Early Cretaceous large granitoid massifs. This process is manifested in the presence of a variety of such minerals, as spessartine, members of the ilmenite-pyrophanite series, titanite, monazite, bastnesite, allanite, apatite, zircon, baddeleyite, torianite and others. The rocks under study also include such rare minerals, as cheralite, greyite and a rare variety of fluorine-aluminous titanite. Conclusion. The occurrence (during contact metamorphism of siliceous-rhodochrosite rocks) of spessartine-quartz or manganesesilicate rocks composed mainly of pyroxenoids, was determined by both the relative amounts of carbonate and clay matter, as well as the concentrations of Ba and alkalis in the initial sediments.
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Vladimir Sergeevich, PONOMAREV, IVANOV Kirill Svyatoslavich, EROKHIN Yuriy Viktorovich, and FARRAKHOVA Nadezhda Nikolaevna. "Features of the composition of metapelites from the basement of the Arctic part of the West Siberian megabasin (Verkhnerechenskaya exploration area, Yamal Peninsula)." NEWS of the Ural State Mining University, no. 2 (June 15, 2021): 29–38. http://dx.doi.org/10.21440/2307-2091-2021-2-29-38.
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Relevance of the work. Comprehensive studies of the geology of the Arctic part of Western Siberia are very important for the search for oil and gas in this vast but understudied territory. At present, unfortunately, we know little about the geological structure of the Arctic in the region of Western Siberia, where the sedimentary cover is mainly investigated (the thickness of which is about 3–4 km) and only a few wells are drilled to the foundation. Therefore, a comprehensive study of core samples from this little-studied territory seems extremely relevant. The purpose of the work is a detailed description of the mineralogy and petro-geochemical features of garnetquartz-chlorite-muscovite schists from the well Verkhnerechenskaya no. 2 from the foundation Arctic part of the West Siberian megasbasin. Scope of application of work. This work can be useful in constructing geological maps of the pre-Jurassic foundation of the Yamal Peninsula. Results of work and conclusions. Mineralogy has been studied in detail and the trace element composition of garnetquartz-chlorite-muscovite schists is obtained. The mineral composition of the rocks is as follows: almandine, muscovite, quartz, chamosite, calcite, albite, rutile, titanite, fluorapatite, zircon, xenotime-(Y) and pyrite. The progressive zonality in the almandine is determined, which is confirmed by the calculated data of metapelite formation temperature, progressive metamorphism. Distribution of rare, scattered and REE in the studied rocks is characteristic of metamorphic schists from the foundation of the Urals part of the West Siberian megasbasin, which compel the framing of monzodiorite-granite massifs of Shaimsko-Kuznetsov meganticlinorium of Western Siberia. Probably, the metapelites studied are the result of warming up the thickness of sedimentary rocks with granite intrusion located in the vicinity of Verkhnerechenskaya area. Later, the rocks underwent propylitization with the formation of secondary carbonate and pyrite.
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Hagni, Richard D., and Musa Karakus. "Cathodoluminescence Microscopy: A Valuable Technique for Studying Ceramic Materials." MRS Bulletin 14, no. 11 (November 1989): 54–59. http://dx.doi.org/10.1557/s0883769400061212.
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Over the past 10 to 20 years, cathodo-luminescence microscopy (CLM) has become an important, standard technique for studying many geological materials, but its application to ceramic material has not been fully realized. CLM has been found to be especially valuable in determining original porosity in carbonate rocks, a feature that was extremely important in determining the ability of petroleum and related fluids to migrate through the rocks and concentrate in the favorable structures where petroleum is found today. CLM constitutes one of the most significant techniques employed in the exploration for petroleum, but the results of those investigations remain largely unpublished in company files. A number of investigations have discussed the application of cathodoluminescence (CL) to studies of porosity in carbonates.Other applications of CLM to geology involve metals exploration. Halos of red CL feldspar in the rocks around carbon-atite deposits, which may contain rare earths, copper, and other metals, contrast with feldspar crystals with blue or blue-green CL that are distal from the ore deposits. Dolomite associated with lead-zinc ores may exhibit growth zoning by CL that can be used to trace the path of the ore fluids for distances of 100 miles or more. The detection of host rock limestone alteration in the Tri-State zinc-lead district, potassic and argillic alteration at the Henderson molybdenite mine, and ore guides in other metallic deposits by CL was discussed by Hagni.
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Popuiac, Aurelia. "Rare Earths in Geological Formations of Central Region of the Dniester River Basin, Republic of Moldova." Advances in Geology 2015 (January 5, 2015): 1–13. http://dx.doi.org/10.1155/2015/713282.
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In the different varieties of crystalline basement of Archean and Proterozoic age and in Vendian (Ediacaran) basal layers of platform coverture in the Central Basin of the Dniester River were found relatively high concentrations of Lanthanum, Cerium, Yttrium, Ytterbium, and Scandium. Because the petrographic formations, which are genetic associated with RE elements in Dniester region are absent, the origin of these elements is unclear. At the same time, in the geological mapping, it was detect that geochemical aureoles of REE, found in the northern region of Republic of Moldova, are generated by accessory minerals monazite and zircon present in the rock of basement platform and fragments of crystalline rock in the composition of terrigenous formations from basal levels of sedimentary coverture. Probably mentioned minerals are brought from Ukrainian Crystalline Shield regions, in which are spread varieties of granitic rocks and alkaline pegmatite. It is not excluded that in these basal layers in the sedimentogenes processes and differentiation of detrital material to be formed the mechanic aureoles rich in monazite and zircon, which in turn can form significant concentrations of rare earths. To solve the perspective problem of detection of industrial mineral accumulations of RE in the central region of the Dniester River basin, it is necessary to conduct within this area detailed geological and geochemical research.
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Möller, Peter, Peter Dulski, and Marco De Lucia. "REY Patterns and Their Natural Anomalies in Waters and Brines: The Correlation of Gd and Y Anomalies." Hydrology 8, no. 3 (August 6, 2021): 116. http://dx.doi.org/10.3390/hydrology8030116.
Full textAbstract:
Rare earths and yttrium (REY) distribution patterns of the hydrosphere reveal systematic correlations of Gd and Y anomalies besides the non-correlated redox-dependent Ce and Eu anomalies. Eu anomalies are inherited by dissolution of feldspars in igneous rocks, whereas Ce, Gd and Y anomalies develop in aqueous systems in contact with minerals and amorphous matter. Natural, positive Gd and Y anomalies in REY patterns characterize high-salinity fluids from the Dead Sea, Israel/Jordan, the Great Salt Lake, USA, the Aral Sea, Kazakhstan/Uzbekistan, ground- and surface water worldwide. Extreme Gd anomalies mostly originate from anthropogenic sources. The correlation of Gd and Y anomalies at low temperature in water bodies differ from geothermal ones. In nature, dynamic systems prevail in which either solids settle in water columns or water moves through permeable sediments or sedimentary rocks. In both cases, the anomalies in water develop due to repeated equilibration with solid matter. Thus, these anomalies provide information about the hydrological history of seawater, fresh groundwater and continental brines. When migrating, the interaction of aqueous phases with mineral surfaces leads to increasing anomalies because the more hydrophillic Gd and Y preferentially remain in the aqueous phase compared to their nearest neighbors. The correlation coefficients between Gd and Y anomalies in groundwater is 0.5–0.9. In lakes and oceans, it is about 0.1–0.8, under anomalous conditions it can increase to 1.
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Marinkovic, Goran, Petar Papic, Jana Stojkovic, and Veselin Dragisic. "Factors contributing to the formation of carbonated mineral water systems in Serbia." Annales g?ologiques de la Peninsule balkanique, no. 73 (2012): 117–24. http://dx.doi.org/10.2298/gabp1273117m.
Full textAbstract:
There are more than 65 occurrences of carbonated mineral water (CMW) within the territory of Serbia. More than 93 % of these systems are found in the geotectonic unit referred to as the Vardar Zone and on the fringes of nearby units. To the east, west and north of the Vardar Zone, CMWs are either rare or nonexistent. The area featuring CMWs is characterized by Tertiary magmatism, a complex geology and deep neotectonic structures. Based on ?13C values of CO2 and HCO3 - in several CMWs in Serbia, and also in carbonates and CO2 from liquid inclusions in several hydrothermal deposits around the world, it was concluded that CO2 in the lithosphere of Serbia could originate from hydrothermal carbonates, and carbonates from sedimentary, metamorphic and magmatic rocks. The findings clearly showed that the main generators of CO2 are located in the Vardar Zone and that CO2 degasification is accomplished through temperature metamorphosis of carbonates (dolomite, calcite). Based on the carbonate transformation temperatures and the temperature conditions in the lithosphere of Serbia, the CO2 might be the result of temperature-induced carbonate transformation below a depth of 3 km. Therefore, the conclusion of the study of CMWs in Serbia is that the formation of CMW systems in the lithosphere depends on the geochemical, temperature, and the magmatic and structural-neotectonic conditions.
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AZIZ, NABAZ R. H., KHALID J. A. ASWAD, and HEMIN A. KOYI. "Contrasting settings of serpentinite bodies in the northwestern Zagros Suture Zone, Kurdistan Region, Iraq." Geological Magazine 148, no. 5-6 (July 11, 2011): 819–37. http://dx.doi.org/10.1017/s0016756811000409.
Full textAbstract:
AbstractProtrusions and lenses of serpentinite–matrix mélanges occur at several places along the thrust faults of the Zagros Suture Zone. They separate the lower allochthonous thrust sheet, the ‘Lower Allochthon’ (i.e. Walash–Naopurdan nappe), of Paleocene–Eocene age from sediments of the Arabian platform and the upper thrust sheet of Mesozoic, ophiolite-bearing terranes termed the ‘Upper Allochthon’ (i.e. Gemo–Qandil nappe). The serpentinite–matrix mélanges occur mostly as stretched bodies (slices) on both sides of the Lower Allochthon (Hero, Halsho and Pushtashan (HHP) and Galalah, Qalander and Rayat (GQR)). Their overall chondrite-normalized rare earth element (REE) patterns form two main groups. Group One exhibits enrichment in the total REEs (> 1 × chondrite) whereas the Group Two pattern shows depletion (i.e. < 1 × chondrite). Bulk-rock MORB-normalized profiles of Group Two are almost flat in the MREE–HREE region with flattening profiles in the Gd–Lu range (> 3 times the MORB composition). In comparison with Group One, Group Two has extremely high REE content and displays variable depletions in the moderately incompatible high-field-strength elements (HFSEs) (Zr, Hf, Y) relative to their adjacent REEs. The REEs in the GQR serpentinite–matrix mélanges have a noticeably high LREE content, and a positive Eu anomaly, and their HREE content never reaches more than 1 × chondrite (i.e. < 0.01 to 1 × chondrite). The latter indicates that the hemipelagic sedimentary, melt-like components (i.e. high LREE, U/La, La/Sm and low Ba/Th) control the geochemical peculiarities of this type of serpentinite. The HHP serpentinite–matrix mélanges, however, are either equally divided between the two REE pattern groups (e.g. Hero, Halsho) or inclined towards Group One (e.g. Pushtashan). Contrary to GQR serpentinites, the variation in HHP serpentinite–matrix mélanges spans a compositional spectrum from U/La-rich to more Ba/Th-rich. Such ratio variations reflect the large variation in these two subducted sedimentary components (i.e. carbonate and hemipelagic sediment mix). The obvious differences in the trace element signatures of the GQR and HHP serpentinite–matrix mélanges might be related to plate tectonic parameters such as convergence rate, subduction age and thickness and type of subducted slab. It is more likely that the influx of subducted components to the mantle wedge relied heavily on the composition of the sedimentary inputs. These vary considerably with time from the relatively deepwater hemipelagic sediments (Qulqula Radiolarite Formation) to platform carbonate sediments (Balambo limestone). The trace element signatures of the GQR and HHP serpentinite–matrix mélanges might suggest multi-staging of the allochthonous sheet emplacement on the Arabian platform sediments.
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RICE, SAMUEL P., ALASTAIR H. F. ROBERTSON, TIMUR USTAÖMER, NURDAN İNAN, and KEMAL TASLI. "Late Cretaceous–Early Eocene tectonic development of the Tethyan suture zone in the Erzincan area, Eastern Pontides, Turkey." Geological Magazine 146, no. 4 (May 18, 2009): 567–90. http://dx.doi.org/10.1017/s0016756809006360.
Full textAbstract:
AbstractSix individual tectonostratigraphic units are identified within the İzmir–Ankara–Erzincan Suture Zone in the critical Erzincan area of the Eastern Pontides. The Ayıkayası Formation of Campanian–Maastrichtian age is composed of bedded pelagic limestones intercalated with polymict, massive conglomerates. The Ayıkayası Formation conformably overlies the Tauride passive margin sequence in the Munzur Mountains to the south and is interpreted as an underfilled foredeep basin. The Refahiye Complex, of possible Late Cretaceous age, is a partial ophiolite composed of ~75% (by volume) serpentinized peridotite (mainly harzburgite), ~20% diabase and minor amounts of gabbro and plagiogranite. The complex is interpreted as oceanic lithosphere that formed by spreading above a subduction zone. Unusual screens of metamorphic rocks (e.g. marble and schist) locally occur between sheeted diabase dykes. The Upper Cretaceous Karayaprak Mélange exhibits two lithological associations: (1) the basalt + radiolarite + serpentinite association, including depleted arc-type basalts; (2) the massive neritic limestone + lava + volcaniclastic association that includes fractionated, intermediate-composition lavas, and is interpreted as accreted Neotethyan seamount(s). The several-kilometre-thick Karadağ Formation, of Campanian–Maastrichtian age, is composed of greenschist-facies volcanogenic rocks of mainly basaltic to andesitic composition, and is interpreted as an emplaced Upper Cretaceous volcanic arc. The Campanian–Early Eocene Sütpınar Formation (~1500 m thick) is a coarsening-upward succession of turbiditic calcarenite, sandstone, laminated mudrock, volcaniclastic sedimentary rocks that includes rare andesitic lava, and is interpreted as a regressive forearc basin. The Late Paleocene–Eocene Sipikör Formation is a laterally varied succession of shallow-marine carbonate and siliciclastic lithofacies that overlies deformed Upper Cretaceous units with an angular unconformity. Structural study indicates that the assembled accretionary prism, supra-subduction zone-type oceanic lithosphere and volcanic arc units were emplaced northwards onto the Eurasian margin and also southwards onto the Tauride (Gondwana-related) margin during Campanian–Maastrichtian time. Further, mainly southward thrusting took place during the Eocene in this area, related to final closure of Tethys. Our preferred tectonic model involves northward subduction, supra-subduction zone ophiolite genesis and arc magmatism near the northerly, Eurasian margin of the Mesozoic Tethys.
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Strzeboński, Piotr, Justyna Kowal-Kasprzyk, and Barbara Olszewska. "Exotic clasts, debris flow deposits and their significance for reconstruction of the Istebna Formation (Late Cretaceous – Paleocene, Silesian Basin, Outer Carpathians)." Geologica Carpathica 68, no. 6 (August 1, 2017): 562–82. http://dx.doi.org/10.1515/geoca-2017-0037.
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AbstractThe different types of calcareous exotic clasts (fragments of pre-existing rocks), embedded in the Paleocene siliciclastic deposits of the Istebna Formation from the Beskid Mały Mountains (Silesian Unit, Western Outer Carpathians), were studied and differentiated through microfacies-biostratigraphical analysis. Calcareous exotics of the Oxfordian- Kimmeridgian age prevail, representing a type of sedimentation comparable to that one documented for the northern Tethyan margin. The Tithonian exotic clasts (Štramberk-type limestones), which are much less common, were formed on a carbonate platform and related slope. The sedimentary paleotransport directions indicate the Silesian Ridge as a main source area for all exotics, which were emplaced in the depositional setting of the flysch deposits. The exotics constitute a relatively rare local component of some debrites. Proceedings of the sedimentological facies analysis indicate that these mass transport deposits were accumulated en-masse by debris flows in a deep-water depositional system in the form of a slope apron. Exotics prove that clasts of the crystalline basement and, less common, fragments of the sedimentary cover, originated from long-lasting tectonic activity and intense uplift of the source area. Mass transport processes and mass accumulation of significant amounts of the coarse-grained detrital material in the south facial zone of the Silesian Basin during the Early Paleogene was due to reactivation of the Silesian Ridge and its increased denudation. Relative regression and erosion of the emerged older flysch deposits were also forced by this uplift. These processes were connected with the renewed diastrophic activity in the Alpine Tethys.
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PONOMAREV, Vladimir Sergeevich, Yuriy Viktorovich EROKHIN, Kirill Svyatoslavich IVANOV, and Nadezhda Nikolaevna FARRAKHOVA. "Mineralogical and geochemical features of volcanics from the pre-Jurassic basement of the western part of Yamal." NEWS of the Ural State Mining University, no. 4 (December 20, 2020): 103–14. http://dx.doi.org/10.21440/2307-2091-2020-4-103-114.
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Relevance of the work. The Arctic part of the West Siberian megabasin is the main source of oil and gas in Russia, therefore, the study of the geological structure of this region is extremely important. Recently, Russia has lodged an application to extend its territory in the Arctic Ocean along the ridges that stretch from the continental shelf. Unfortunately, at the same time, we know little about the geological structure of the Arctic in the region of Western Siberia, where the thickness of the sedimentary cover is very high (about 3–4 km), therefore, the study of the basement of the Yamal Peninsula seems to be extremely urgent. The purpose of this work is mineralogical, petrological and geochemical study of dolerites from the pre-Jurassic basement of the Bovanenkovskaya area (well No. 114) within the territory of the gas condensate field of the same name, located in the western part of the Yamal Peninsula. Scope of the work. This work can be useful in constructing geological maps of the pre-Jurassic basement of the Yamal Peninsula. Results and conclusions. We have studied the mineralogical and geochemical features of dolerites from the pre-Jurassic basement of the Bovanenkovskaya area (well No. 114, sampling depth – 3210 m) of the West Siberian megabasin. The mineralogy of the rocks is represented by augite, diopside, albite, magnesian chamosite, ferrous hornblende, calcite, siderite, dolomite, anorthoclase, grossular, zeolite (gmelenite-K), pyrite, chalcopyrite, and rare lead chloride – cotunnite. The rocks underwent minor transformations in the conditions of the lower greenschist metamorphism, as well as secondary alterations in the form of superimposed propylitization. As a result of this low-temperature metasomatic process, zeolite, carbonate (calcite, dolomite, and siderite) and sulfide mineralization composed of pyrite and chalcopyrite, as well as cotunnite, which apparently replaced the dissemination of galena, were formed in the rock. Judging by geological position of the region, these dolerites are most likely formed at shallow depths during continental rifting. Remelting of the Paleozoic island arc substrate during the Early Triassic rifting and volcanism provided some closeness to the island arc trend in the geochemical features of these rift volcanics.
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Galyamov, A. L., A. V. Volkov, K. Yu Murashov, N. V. Sidorova, and T. P. Kuznetsova. "Prospects for identifying the Mississippi Valley type deposits in the North-East of Russia." LITHOSPHERE (Russia) 20, no. 2 (April 25, 2020): 254–70. http://dx.doi.org/10.24930/1681-9004-2020-20-2-254-270.
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Research subject. The Mississippi Valley type deposits make up about a third of the global balance of lead and zinc reserves, resources and production. Additionally, silver, antimony, arsenic, barium, bismuth, cadmium, cobalt, gallium, indium, mercury, molybdenum, nickel and thallium can be present in the ores of these deposits. In the North-East of Russia, the Mississippi Valley type of deposits is poorly represented. In this work, we investigate the deposits of the Sardana ore cluster of the Republic of Sakha (Yakutia) and individual deposits of the Magadan region. Materials and methods. The article discusses the results of previous scientific research and new data on the geochemical features, isotopic composition of ores and geological and structural conditions for the formation of the Sardana cluster deposit. In addition, the potential for identifying stratiform lead-zinc deposits is associated with favourable geodynamic conditions in the region, as well as with the refinement and adaptation of the forecast-search model of MVT deposits for the North-East of Russia. Results. The mineralogical and geochemical features of the rocks and ores of the Sardana cluster deposits, the morphology of ore bodies, their zoning elements, as well as isotopic ratios indicate that the ores are likely to be of the Mississippi Valley type with the onset of ore deposition at early diagenetic and catagenetic stages. The distribution of rare elements indicates a significant role of superimposed metamorphism of the host carbonate-terrigenous strata in the deposition of the ores of producing stages. Conclusion. The potential possibility of increasing the mineral and raw material base of lead and zinc is associated with the identification of sedimentary basins with a stagnant anoxic regime of carbonate accumulation in the immediate vicinity of the development areas of rift complexes, as well as with the presence of other critically important forecast-search signs. In addition to the well-known Killakh metallogenic zone, Tuora-Sis and Orulgan metallogenic taxa located in the north of the Republic of Sakha (Yakutia) with known stratiform manifestations of lead and zinc belong to such areas.
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Picard, Christian, and Michel Piboule. "Pétrologie des roches volcaniques du sillon de roches vertes archéennes de Matagami – Chibougamau à l'ouest de Chapais (Abitibi est, Québec).1. Le groupe basal de Roy." Canadian Journal of Earth Sciences 23, no. 4 (April 1, 1986): 561–78. http://dx.doi.org/10.1139/e86-056.
Full textAbstract:
In the northeastern part of the Abitibi orogenic belt, the Archean Matagami–Chibougamou greenstone belt (2700 Ma) includes a basal volcanic sequence named the Roy Group, unconformably overlain by a volcano-sedimentary series called the Opemisca Group.The Roy Group, to the west of the town of Chapais, consists of a thick, stratified, and polycyclic volcanic series (thickness = 11 000 m) resembling the large, western Abitibi submarine stratovolcanoes constructed by three mafic to felsic magmatic cycles. The first cycle (Chrissie Formation) shows lateral spreading and is composed only of a meta-andesite and felsic pyroclastite sequence of calc-alkaline affinity. The other two cycles (Obatogamau and Waconichi formations; then Gilman, Blondeau, and Scorpio formations) are characterized by a sequence of repeated MORB type basaltic lava flows of tholeiitic affinity and by intermediate to acid lava and pyroclastic sequences calc-alkaline affinity.The stratigraphic and petrographic data suggest emplacement of mafic lavas on an abyssal plain (Obatogamau Formation) or at a later time on the flanks of a large submarine volcanic shield (Gilman and Blondeau formations). The lava and felsic pyroclastite flows were formed by very explosive eruptions from central spreading type volcanoes above a pre-existing continental crust. In particular, the Scorpio volcanic rocks were emplaced on volcanic islands later dismantled by erosion.The contents and distribution of trace elements and rare earths show that basaltic lavas resulted from an equilibrium partial melting (F = 15–35%) of spinel lherzolite type mantle sources depleted to weakly enriched in Th, Ta, Nb, and light rare-earth elements (LREE), and from fractional crystallization at low pressure of feldspar, clinopyroxene, and olivine. The lavas and the felsic pyroclastites of the Waconichi and Scorpio formations appear to result from partial melting of a mantle source of lherzolite type enriched in LREE and involving some garnet. At a late stage, the melts were probably contaminated by some continental crust materials and then differentiated by fractional crystallization of plagioclase, amphibole, biotite, and magnetite. The lavas in the Chrissie Formation and the middle member of the Gilman Formation seem to result from partial melting of a mantle source enriched in LREE with a composition between the two described above. They were subsequently modified by fractional crystallization of the plagioclase, clinopyroxene, olivine, and titanomagnetite.In general, the mafic to felsic magmatic cycles observed are characterized by a thick sequence of repeated tholeiitic basalt flows similar to those of modern mid-oceanic ridges and by a lava and felsic pyroclastite sequence of calc-alkaline affinity comparable to those occurring in orogenic belts. The transition from one lava sequence to another is marked by a significant chemical discontinuity, and the mantle sources exhibit an increasing enrichment in LREE during a given magmatic cycle. A model is proposed to satisfactorily explain all the stratigraphic, petrographic, and geochemical data implying a hot spot type mechanism, which could be responsible for the cyclic, rising diapirs inside the stratified Archean mantle and for initiating the repeated mantle source meltings, depleted and enriched in LREE, respectively. [Journal Translation]
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Scopelliti, Giovanna, and Valeria Russo. "Petrographic and geochemical characterization of the Middle‒Upper Jurassic Fe–Mn crusts and mineralizations from Monte Inici (north-western Sicily): genetic implications." International Journal of Earth Sciences 110, no. 2 (January 18, 2021): 559–82. http://dx.doi.org/10.1007/s00531-020-01971-0.
Full textAbstract:
AbstractFe–Mn concretions and mineralizations, associated with condensed horizons and hardground, are significant archives in ancient carbonate rocks. Their petro-chemical study allows an assessment of the palaeoenvironmental context in which they were formed also connected to their biotic or abiotic origin. At the western side of the Monte Inici (Fornazzo section, north-western Sicily) a well exposed outcrop of condensed pelagic limestones (Rosso Ammonitico facies: Middle‒Upper Jurassic) is well-known and thoroughly studied. In this section, the base of the Rosso Ammonitico facies consists of a very condensed level rich in fossils with a variable thickness deposited from the early Bathonian to the early/middle Callovian. It is characterized, at the top, by the noticeable presence of Fe–Mn concretions, typical of the Tethyan Jurassic and related to very low sedimentation rates. For this study, Fe–Mn crusts and mineralizations from the Fornazzo section were investigated using X-ray diffraction, scanning electron microscopy, X-ray fluorescence, ICP and stable-isotope mass spectrometry. The collected samples, deposited in submarine conditions (as testified by stable oxygen and carbon isotopes), have been subdivided in two typologies with different macroscopic and mineralogical features. The Fe–Mn crusts consist of hematite, todorokite and birnessite and are characterized by a relatively low Mn/Fe ratio. Their content in trace elements, rare earths and yttrium (REY) is compatible with a hydrogenetic origin involving the oxy-hydroxides colloids precipitation directly from seawater. Microbially mediated processes are here testified by the recognition of filamentous and coccoid-shaped microstructures referable to coexistence of chemosynthetic fungi and photosynthetic cyanobacteria and accounting for a deposition in the deep euphotic zone. An average growth rate of ~ 8.5 mm/Myr for the Fe–Mn crusts, estimated by cobalt concentrations, suggests a time elapsed for deposition of ~ 3.5 ± 1 Myr. This value is compatible with the stratigraphic gap embracing the time span from the early/middle Callovian to the middle Oxfordian. In the neighbouring pelagic limestones, Fe–Mn deposits are present in the form of micro-dendrites mainly consisting of pyrolusite, sometimes associated with carbonato-fluorapatite. The geochemical composition gives evidence of a prevalent early diagenetic origin with precipitation, at the sediment/water interface or in the first centimeters of sediments, of metals diffused from the crusts as consequence of fluctuating redox conditions. Although the well-preserved Frutexites texture is commonly related to a microbial activity, other bacterial microstructures have not been recognized, having probably been obliterated during the growth of the dendrites. Nevertheless, it is possible to suppose a deepening in the bathymetry consistent with the involvement of chemosynthetic microorganisms in the formation of Frutexites structures.
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Bédard, Jean H., Valentin R. Troll, Frances M. Deegan, Christian Tegner, Benoit M. Saumur, Carol A. Evenchick, Stephen E. Grasby, and Keith Dewing. "High Arctic Large Igneous Province Alkaline Rocks in Canada: Evidence for Multiple Mantle Components." Journal of Petrology, June 9, 2021. http://dx.doi.org/10.1093/petrology/egab042.
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Abstract The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135-90 Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (∼96 Ma) scatter around major fault and basement structures. They are represented by the newly-defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanics. The younger alkaline group is represented by the Wootton Intrusive Complex (92.2-92.7 Ma), and the Audhild Bay Suite (83-73 Ma); both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba-K-Zr-Ti that are nearly orthogonal to predicted fractionation- or melting-related variations; which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5-Ba-Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba-Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally-derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare-earth (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar-Hassel rocks, whereas other samples trend towards possible High-P2O5+Zr (PZr) and High-P2O5+K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases like apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1), could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K-Rb-U-Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provide little support for an ubiquitous fossil sedimentary subduction zone component in the HALIP mantle source.
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Li, Hongxia, Fengming Jin, Dunqing Xiao, Xiugang Pu, and Wenya Jiang. "Provenance and sedimentary environment of the Ek2 shale in the Cangdong Sag, the central Bohai Bay Basin, China." Interpretation, September 3, 2021, 1–59. http://dx.doi.org/10.1190/int-2020-0173.1.
Full textAbstract:
The second member of the Kongdian Formation (usually abbreviated as the E k2 shale) is one of the most significant exploring targets for shale oil at the Cangdong Sag of the central Bohai Bay Basin. It consists of siliceous shale, mixed shale, and calcareous shale. To better understand why organic matter accumulated in the E k2 shale, we have analyzed major and trace elemental compositions to reconstruct the provenance and sedimentary environment. Tectonic discriminatory diagrams suggest that the tectonic setting of the parental rocks for the E k2 shale belonged to the Continental Island Arc. The distribution patterns of trace elements and rare earth elements + yttrium (REEs + Y) are close to the intermediate igneous rock. The ratios of Al2O3/TiO2 ranging from 21.41 to 27.59 with a mean value of 23.93 also demonstrate a parental rock of the intermediate igneous rock. Siliceous and mixed shales indicate K2O/Al2O3 of 0.17–0.29, chemical index of weathering of 28.79–97.79, plagioclase index of alteration of 38.24–95.57, and chemical index of alteration of 40.29–80.23. These weathering proxies denote that the E k2 shale underwent a low weathering degree in an arid climate and a high weathering degree in a semiarid climate. The V/(V + Ni) ratios and pyrite framboids indicate an anoxic sedimentary condition. The δ18O values of carbonate minerals in the E k2 shale range from −9.8‰ to 0.7‰, and they are positively correlated to the δ13C values. The Sr/Ba ratios, δ18O, and chemical mineral associations indicate that siliceous and mixed shales were deposited in a fresh to brackish anoxic water column under a semiarid climate. Whereas calcareous shale was deposited in a saline to hypersaline anoxic water column under an arid climate.
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Xu, Lingang, Anja B. Frank, Bernd Lehmann, Jianming Zhu, Jingwen Mao, Yongze Ju, and Robert Frei. "Subtle Cr isotope signals track the variably anoxic Cryogenian interglacial period with voluminous manganese accumulation and decrease in biodiversity." Scientific Reports 9, no. 1 (October 21, 2019). http://dx.doi.org/10.1038/s41598-019-51495-0.
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Abstract Earth’s atmosphere experienced a step of profound oxygenation during the Neoproterozoic era, accompanied by diversification of animals. However, during the Cryogenian period (720–635 million years ago) Earth experienced its most severe glaciations which likely impacted marine ecosystems and multicellular life in the oceans. In particular, large volumes of Mn and Fe accumulated during the interglacial intervals of the Cryogenian glaciations, indicating large anoxic marine metal reservoirs. Here we present chromium isotope-, rare earth element-, and redox-sensitive trace element data of sedimentary rocks from the interglacial Datangpo Formation deposited between the Sturtian and Marinoan glaciations in South China, in an attempt to investigate the oxidation state of the oceans and atmosphere. Both the Cr isotope and trace element data indicate mainly anoxic water conditions with cryptic oxic surface water incursions after the Sturtian glaciation. Glacial-fed manganese precipitated as manganese carbonate in anoxic basins, and the non-fractionated δ53Cr record of −0.10 ± 0.06‰ identifies anoxic conditions with a cryptic component of slightly fractionated Cr isotope composition in manganese ore, in line with distinctly fractionated Mo isotope composition. Both the manganese carbonate ore and the black shales exhibit very low redox-sensitive element concentrations. Our study demonstrates that the oxygenation of the seawater, and inferably of the atmosphere, at the beginning of the Cryogenian interglacial interval was much subdued. The post-glacial rebound then allowed the Ediacaran biological diversity.
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"PROCESSES OF DEEP OUTGASSING OF THE EARTH AS THE CAUSE OF BOTTOM CARBONATE BUILDUP FORMATION IN THE OCEAN SHELF ZONES." Visnyk of Taras Shevchenko National University of Kyiv. Geology, no. 2 (89) (2020): 102–9. http://dx.doi.org/10.17721/1728-2713.89.14.
Full textAbstract:
Bottom carbonate buildups of northwest of the Black Sea and western shelf of the South China Sea are considered in the article. The actual material for these researches was received when carrying out submarine works with application of underwater laboratory "Bentos-300" in the Black Sea and submersible vehicle "Sever-2" in the South China Sea. As a result of researches gas emissions from bottom depositions and carbonate builups were discovered at depths of 160-300 m. Investigation of landscape and geological setting on seabed was carried out by direct observation of gas emission fields. It was established within their limits that gas component is only one portion of fluid flow which formation is caused by deep outgassing processes of the Earth. The main portion is represented by fluid mineralized phase saturated with soluble compounds. In the marine water which is characterized by different hydrochemical parameters superimposed biochemogenic sedimentation, predominantly calcium carbonate occurs from fluid flow. Relation between buildup types, sea depth and bottom relief is defined. The most carbonate builups are confined to vertex sites of ridges. On slopes the buildups are rare and their number decreases. Cover formations of solid very strong rocks in the form of massive blocks that is 40-60 cm thick prevail at depths of 160-190 m. Distribution pattern of calcium carbonate over the section of crusts and tabular shapes points to the relation between a source of carbonates with lateral distribution of mineralized waters in near-bottom layer on the surface of sedimentary substrate. Comparative data on composition of carbonate buildups of Black and Southern Chinese Seas testify for their common features of deep hydrocarbon outgassing and tectono-geodynamic similarity between areas of their distribution. Considering the fact that within the shelf area of Vietnam, giant oil and gas fields have already been discovered and are under exploralion, prospects for discovery of similar deposits in northwest part of the Black Sea are rather reasonable. Results of studying of carbonate formations in the Black Sea can be used for forecasting and prospectings of hydrocarbonic raw material.
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CONTE, Mohamed Samuel Moriah, Abdellah BOUSHABA, and Ali MOUKADIRI. "Petro-Geochemical and Statistic Studies of the Nimba Region in the Republic of Guinea." International Journal of Multidisciplinary and Current Research 6, no. 02 (March 6, 2018). http://dx.doi.org/10.14741/ijmcr/v.6.2.2.
Full textAbstract:
Summary: Guinea is described as a geological scandal, due to the richness of its soil, its subsoil, and its complexity. But this geology is poorly studied and under exploited and the region of Nimba hardly escapes to this fact. Located in the south-east of the country, Nimba is about 60 km long and 25 km wide, it belongs to the Precambrian domain (Archean basement (Craton) and Proterozoic) and is characterized by volcano-sedimentary rocks. In addition to mineral diversity, shear, brecciation and fault structures are observed in the rocks (Nion District), while they are not observable in rocks of other parts of the region. Large deposits of iron (magnetite, hematite, goethite) occupy the summits of the region. Granites exhibit magmatic differentiation whereas amphibolites occupy the MORB domain set upby rifting. The major elements exhibit perfect positive and negative linear relationships, while the rare earths exhibit perfect positive linear relationships. The PCA of the major elements confirms the differentiation of granitic rocks while the amphibolites do not show differentiation due to weathering. Objective: Geological cross sections of the Nimba range, petrographic studies of the different rocks and mineralogical description of these rocks were realized. And this to know the context of setting up of the region using the results of chemical analysis, the knowing of the different correlations which allow to visualize a space with p dimensions using spaces of smaller dimensions of the Geochemical data. Materials and Methods: This study in the Nimba region was done in two stages. The first stage performed in the field (period from November 25 to December 20, 2015 and from January 23 to February 15, 2017); it permits to collect the samples, the realization of two geological cross sections (one in the South near the border between the Republic of Guinea and Liberia, and one in the North in the fan zone of the region). The second step, carried out in the laboratories, with the digitalization of the two (2) geological cross sections (using Canvas version: 11Build 1252), then a microscopic description of the samples and the analysis of the different spectroscopies and diffractograms of the rocks of the Nimba region (using the Bruker Raman SENTERRA type spectroscope and the Pert Pro Panalytical X-type diffractometer). The rocks were analyzed geochemically by ICP-AES and ICP-MS. Finally, the geochemical data is processed by statistical methods (using Statgraphic Centurion software version _16.1.11). Results: The Nimba region contains two (2) groups of rocks, the first group clear and SiO2 rich (Gneiss, Granites, and Quartzites) and the second group is dark and SiO2 poor (Muscovitites, Amphibolites). But il also contains Itabirite-type iron deposits (Banded Irons Formations: BIFs) which occupy the main peaks of the Nimba region chain. These rocks contain minerals that are abundant in some and rare in others or even absent (Table 1). Next, they reveal that the quartzite facies are characterized by open muscovite crystals in the form of "S" slits and crystals of quartz, K feldspar and "C" plagioclases that give the "C / S" structures and hence the formation of "Shears Zones" (District of Nion, photo 2r). Amphibolitic rocks (Nion District) reveal both a breccia zone and a fault zone (Figure 2w and 2x). The breccia zone constitutes the phase S1 which is filled by the grunerite and the fault zone constitutes the phase S2 filled with microcrystals of quartz, magnetite, feldspars and grunerite. This phase S2 is characterized by the displacement of the blocks due to the fault activity. On the other hand, in the district of Gbié, the amphibolites do not contain zones of breccias or of faults, but they reveal the arrangement of the minerals (figure 2z and 2aa). The spectroscopies and diffractograms of the different rocks of the Nimba region confirm the results obtained from the petrographic description but also the appearance of new minerals (Table 2). The chemical rocks analyses of the Nimba region reveal that they are sub-alkaline. The amphibolites are tholeiitics, occupying the area of MORBs, with REE spectra (normalized to chondrites of N-MORBs derived from depleted upper mantle) showing depletion in LREE and almost flat in HREE. The granitics rocks are calco-alkaline, peraluminous, marked by the decrease of minerals ferromagnesian, ferro-titanic oxides and plagioclase with an increase of the alkali feldspar content. The spectra of REE of granitic rocks chondrite normalized at the chondrite show both negative in Eu anomalies suggesting on one hand that the plagioclase was fractioned and positive anomalies in EU that indicates on the other hand that the plagioclase has not been fractioned. All these spectra present the enrichment in LREE and a poverty in HREE. The Bravais-Pearson correlation of the major elements of amphibolitic and granitic rocks shows that Al2O3 does not correlate with other major elements and P2O5 correlates only with TiO2. The rest of the major elements have both positive linear relations and perfect negatives with P-Values less than 0.05. The Pearson-Pearson correlation of REE of amphibolitic and granitic rocks shows perfect positive linear relationships with P-Values less than 0.05. The Principal Components Analysis (PCA) of the major elements of amphiboles and granites has three groups of major elements, the first formed of SiO2, Na2O and K2O which correlate with each other to the component 1. The second formed of MgO , TiO2, MnO, Fe2O3t and CaO correlate with each other at component 1; these groups are anti-correlated with respect to component 2. The third group of major elements consists of Al2O3 and P2O5 which correlate neither with component 2 nor with the first two groups of major elements. Only TiO2 correlates with P2O5. Finally, the amphibolites have an affinity with the second group and do not exhibit magmatic differentiation due to weathering and weather conditions. The granitic rocks have an affinity with the first group, they are distributed according to the magmatic differentiation. The Principal Component Analysis (PCA) of REE of amphibolitic and granitic rocks has two groups: the first formed of Ce, La, Pr, Nd, Sm, Gd, and Eu which correlate with each other at component 1. The second, Tb, Dy, Er, Ho, Tm, Yb and Lu that correlate with each other at component 1. These two groups of chemical elements are not anti-correlated to component 2, which is confirmed by the hypothesis of the linear correlation method. Conclusions: The region of Nimba belongs to the precambrian domain, it is largely correlated with those of Brazil and Venezuella. It is formed by metavolcanic and metasedimentary rocks: quartzitic rocks characterized by 'C / S' shear and zoned zircon; grunerite amphibolites (cummingtonite family) rich in iron and associated with large iron deposits in fault and breccia zones. These amphibolites are located in the MORB field, which was emplaced by rifting, while the granitic rocks were emplaced by magmatic differentiation. This region is rich in iron deposits that occupy the main peaks and whose establishment was made by precipitation of a silico-ferruginous gel in a closed basin, virtually protected from other terrigenous inputs. This precipitation of dissolved iron results from an enrichment in atmospheric O2 characteristic of the Archean and Paleoproterozoic.