Статті в журналах: "Back arc extension"

1

Sibuet, Jean-Claude, Jean Letouzey, Florence Barbier, Jacques Charvet, Jean-Paul Foucher, Thomas W. C. Hilde, Masaaki Kimura, et al. "Back Arc Extension in the Okinawa Trough." Journal of Geophysical Research: Solid Earth 92, B13 (December 10, 1987): 14041–63. http://dx.doi.org/10.1029/jb092ib13p14041.

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2

Avigad, Dov, Zvi Garfunkel, Laurent Jolivet, and José M. Azañón. "Back arc extension and denudation of Mediterranean eclogites." Tectonics 16, no. 6 (December 1997): 924–41. http://dx.doi.org/10.1029/97tc02003.

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3

Faccenna, Claudio, Massimo Mattei, Renato Funiciello, and Laurent Jolivet. "Styles of back-arc extension in the Central Mediterranean." Terra Nova 9, no. 3 (May 1997): 126–30. http://dx.doi.org/10.1046/j.1365-3121.1997.d01-12.x.

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4

Patriat, M., J. Collot, L. Danyushevsky, M. Fabre, S. Meffre, T. Falloon, P. Rouillard, B. Pelletier, M. Roach, and M. Fournier. "Propagation of back-arc extension into the arc lithosphere in the southern New Hebrides volcanic arc." Geochemistry, Geophysics, Geosystems 16, no. 9 (September 2015): 3142–59. http://dx.doi.org/10.1002/2015gc005717.

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5

ΚΙΛΙΑΣ, Α. "Late orogenic extension in Hellenides." Bulletin of the Geological Society of Greece 34, no. 1 (January 1, 2001): 149. http://dx.doi.org/10.12681/bgsg.16955.

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In the Hellenic orogen both typs of late orogenic extension, associated with deep crustal parts exhumation, are recognized during the Tertiare: In the areas of Olympos-Ossa and Pelion Mts in Northern Greece, as well as in the island of Crete in Southern Greece a bivergent late orogenic extension is recognized. Nappes collapse took place immediately above the cold accretionary wedge while compression was active at depth. Heer high pressure assemplages were good preserved. On the contrary, in the Rhodope and Cyclades areas an asymmetric extension dominates. Heer extensional exhumation of deep crustal rocks took place in the high thermal flow back-arc region and high pressure metamorphic rocks were highly overprinted by greenschist to amphibolite facies metamorphism. Partial melting and granitoids intrusions followed the high grade metamorphic reworking of the rocks. Tertiary late orogenic extension in the Hellenides tooke place simultaneously with successive subductions processes and crustal thickening at the front of the extended plate, forming with the associated compression a SW-ward migrated system. Extension started in the Rhodope massif during the Eocene/Oligocene to be reached in the Olympos, Ossa, Pilion and Cyclades areas in the Oligocene/Miocene and final in the Crete island at the more external Hellenides, during the Mid-Miocene. Changes in the rate of convergence between Africa and Eurasia associated with retreating plate boundaries conditions allowed the successive, extensional exhumation of the deep crustal rocks in the Hellenides. Assymetric collapse in the back-arc area was possibly favoured, because the high potential energy of the thickened crust in the active orogenic arc was counteracted by the continuing subduction along the boundaries of the converging segments of Africa and Eurasia. Symmetric collapse of the overthickened crust above the cold accretionary prism was favoured probably, due to an increasing of the upward pressure produced by the unterplating of the lithospheric slap beneath the accretionary wedge.

6

SOWERBUTTS, ALISON. "Sedimentation and volcanism linked to multiphase rifting in an Oligo-Miocene intra-arc basin, Anglona, Sardinia." Geological Magazine 137, no. 4 (July 2000): 395–418. http://dx.doi.org/10.1017/s0016756800004246.

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Three extensional phases can be recognized in the northern, Anglona area of the Oligo-Miocene Sardinian Rift during a fifteen million year period which spanned Corsica–Sardinia continental microplate separation and Western Mediterranean back-arc basin opening. In response to this multiphase rifting, a complex facies architecture involving clastic, carbonate and volcanic rocks developed. Integrated onshore facies and structural analysis, dating and offshore seismic data are here used to reconstruct the tectono-stratigraphic history of the Anglona area. Initial late Oligocene extension created a half-graben geometry with syn-rift clastic deposits shed locally from fault-bounded highs, passing laterally to lacustrine marlstones. Calc-alkaline volcanic activity subsequently predominated as volcanic centres developed along one half-graben bounding fault. Voluminous pyroclastic and epiclastic material was supplied to the adjacent half-graben accommodation space and was deposited in marginal to marine conditions. Second-phase mid-Aquitanian–early Burdigalian extensional faulting, recognized from localized clastic syn-rift stratal wedges, truncated and subdivided the half-graben. The syn-rift sediments were sealed by a regionally correlated ignimbrite that in turn was offset by late second-phase faulting. Third-phase extensional fault movement which reactivated the original fault trend then occurred. A perched lake developed in the resultant topography coeval with the progressive marine transgression of lower areas. As sea-level rose during mid-Burdigalian times, reefal carbonates and grainstones developed on fault-block highs whilst calcarenites and marlstones were deposited in hangingwall locations. Initial extension was coeval with the formation of the Sardinian proto-rift and the initiation of the Western Mediterranean basin. Second-phase faulting occurred as the Corsica–Sardinia microplate rotated to its present position during Western Mediterranean back-arc basin spreading. Final extension can be correlated to a second major extension phase along the Oligo-Miocene Sardinian Rift following back-arc basin opening, as extension was transferred towards the fore-arc. In Anglona, the main influence of multiphase tectonism was on rift topography, providing accommodation space and localized uplifted source areas. Varying relative sea-level mainly controlled the broad types of facies belts that developed. Contemporaneous calc-alkaline volcanism played a major role in the supply of basin filling material and in changing the topography locally.

7

Caress, David W. "Structural trends and back-arc extension in the Havre Trough." Geophysical Research Letters 18, no. 5 (May 1991): 853–56. http://dx.doi.org/10.1029/91gl01060.

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8

Bevis, Michael, F. W. Taylor, B. E. Schutz, Jacques Recy, B. L. Isacks, Saimone Helu, Rajendra Singh, et al. "Geodetic observations of very rapid convergence and back-arc extension at the Tonga arc." Nature 374, no. 6519 (March 1995): 249–51. http://dx.doi.org/10.1038/374249a0.

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9

Werner, Reinhard, Boris Baranov, Kaj Hoernle, Paul van den Bogaard, Folkmar Hauff, and Igor Tararin. "Discovery of Ancient Volcanoes in the Okhotsk Sea (Russia): New Constraints on the Opening History of the Kurile Back Arc Basin." Geosciences 10, no. 11 (November 6, 2020): 442. http://dx.doi.org/10.3390/geosciences10110442.

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Here we present the first radiometric age and geochemical (major and trace element and isotope) data for samples from the Hydrographer Ridge, a back arc volcano of the Kurile Island Arc, and a newly discovered chain of volcanoes (“Sonne Volcanoes”) on the northwestern continental slope of the Kurile Basin on the opposite side of the arc. The 40Ar/39Ar age and geochemical data show that Hydrographer Ridge (3.2–3.3 Ma) and the “Sonne Volcanoes” (25.3–25.9 Ma) have very similar trace element and isotope characteristics to those of the Kurile Island Arc, indicating derivation from a common magma source. We conclude that the age of the “Sonne Volcanoes” marks the time of opening of the Kurile Basin, implying slow back arc spreading rates of 1.3–1.8 cm/y. Combined with published data from the Kurile fore arc, our data suggest that the processes of subduction, Kurile Basin opening and frontal arc extension occurred synchronously and that extension in the rear part and in the frontal part of the Kurile Island Arc must have been triggered by the same mechanism.

10

Romagny, Adrien, Laurent Jolivet, Armel Menant, Eloïse Bessière, Agnès Maillard, Albane Canva, Christian Gorini, and Romain Augier. "Detailed tectonic reconstructions of the Western Mediterranean region for the last 35 Ma, insights on driving mechanisms." BSGF - Earth Sciences Bulletin 191 (2020): 37. http://dx.doi.org/10.1051/bsgf/2020040.

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Slab retreat, slab tearing and interactions of slabs are first-order drivers of the deformation of the overriding lithosphere. An independent description of the tectonic evolution of the back-arc and peripheral regions is a pre-requisite to test the proposed conceptual, analogue and numerical models of these complex dynamics in 3-D. We propose here a new series of detailed kinematics and tectonic reconstructions from 35 Ma to the Present shedding light on the driving mechanisms of back-arc rifting in the Mediterranean where several back-arc basins all started to form in the Oligocene. The step-by-step backward reconstructions lead to an initial situation 35 Ma ago with two subduction zones with opposite direction, below the AlKaPeCa block (i.e. belonging to the Alboran, Kabylies, Peloritani, Calabrian internal zones). Extension directions are quite variable and extension rates in these basins are high compared to the Africa-Eurasia convergence velocity. The highest rates are found in the Western Mediterranean, the Liguro-Provençal, Alboran and Tyrrhenian basins. These reconstructions are based on shortening rates in the peripheral mountain belts, extension rates in the basins, paleomagnetic rotations, pressure-temperature-time paths of metamorphic complexes within the internal zones of orogens, and kinematics of the large bounding plates. Results allow visualizing the interactions between the Alps, Apennines, Pyrenean-Cantabrian belt, Betic Cordillera and Rif, as well as back-arc basins. These back-arc basins formed at the emplacement of mountain belts with superimposed volcanic arcs, thus with thick, hot and weak crusts explaining the formation of metamorphic core complexes and the exhumation of large portions of lower crustal domains during rifting. They emphasize the role of transfer faults zones accommodating differential rates of retreat above slab tears and their relations with magmatism. Several transfer zones are identified, separating four different kinematic domains, the largest one being the Catalan-Balearic-Sicily Transfer Zone. Their integration in the wider Mediterranean realm and a comparison of motion paths calculated in several kinematic frameworks with mantle fabric shows that fast slab retreat was the main driver of back-arc extension in this region and that large-scale convection was a subsidiary driver for the pre-8 Ma period, though it became dominant afterward. Slab retreat and back-arc extension was mostly NW-SE until ∼ 20 Ma and the docking of the AlKaPeCa continental blocks along the northern margin of Africa induced a slab detachment that propagated eastward and westward, thus inducing a change in the direction of extension from NW-SE to E-W. Fast slab retreat between 32 and 8 Ma and induced asthenospheric flow have prevented the transmission of the horizontal compression due to Africa-Eurasia convergence from Africa to Eurasia and favored instead upper-plate extension driven by slab retreat. Once slab retreat had slowed down in the Late Miocene, this N-S compression was felt and recorded again from the High Atlas to the Paris Basin.

11

Fabbri, Olivier, and Marc Fournier. "Extension in the southern Ryukyu arc (Japan): Link with oblique subduction and back arc rifting." Tectonics 18, no. 3 (June 1999): 486–97. http://dx.doi.org/10.1029/1999tc900001.

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12

Jolivet, L., J. M. Daniel, C. Truffert, and B. Goffé. "Exhumation of deep crustal metamorphic rocks and crustal extension in arc and back-arc regions." Lithos 33, no. 1-3 (October 1994): 3–30. http://dx.doi.org/10.1016/0024-4937(94)90051-5.

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13

Faccenna, Claudio, Thorsten W. Becker, Francesco Pio Lucente, Laurent Jolivet, and Federico Rossetti. "History of subduction and back-arc extension in the Central Mediterranean." Geophysical Journal International 145, no. 3 (June 2001): 809–20. http://dx.doi.org/10.1046/j.0956-540x.2001.01435.x.

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14

Maity, Barun, and Aphrodite Indares. "The Geon 14 arc-related mafic rocks from the central Grenville Province." Canadian Journal of Earth Sciences 55, no. 6 (June 2018): 545–70. http://dx.doi.org/10.1139/cjes-2017-0197.

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The late Paleoproterozoic to Mesoproterozoic (ca. 1.7–1.2 Ga) evolution of the active southeastern margin of Laurentia terminated with the Grenvillian continental collision and the development of a large, hot, long-duration orogen at ca. 1.09–0.98 Ga. As a result, much of the hinterland of the Grenville Province consists of Paleoproterozoic and Mesoproterozoic rocks, mostly preserved as an imbricate stack of high-grade gneisses, that represent a potential repository of active-margin processes. This study presents geochronologic, geochemical, and isotopic analyses of two granulite-facies suites of ca. 1.45–1.40 Ga mafic tholeiites from the Canyon domain (Manicouagan area, central Grenville Province). One suite consists of 1439 +76/–68 Ma high-FeTi mafic sills with εNd values of –0.4 (TDM 2.57–2.72 Ga), indicate derivation from variably depleted to enriched MORB-type mantle sources, probably in an extensional back-arc setting, before intrusion in a ca. 1.5 Ga supracrustal metasedimentary sequence. The other, previously dated, 1410 ± 16 Ma Mafic to intermediate unit exhibits εNd values of 0.0 to +0.9 (TDM 2.02–2.25 Ga), and variably enriched MORB to arc geochemical signatures, for which formation in a transitional back-arc to arc setting is suggested. Integrated with published information, the new data support a model of a long-lived continental-margin arc and intermittent back-arc development on southeast Laurentia during the mid-Mesoproterozoic (ca. 1.5–1.4 Ga), in which repeated short periods of extension and crustal thinning in the back-arc or intra-arc regions were followed by compression and crustal thickening.

15

Haase, Karsten M., and Christoph Beier. "Chapter 3.2b Bransfield Strait and James Ross Island: petrology." Geological Society, London, Memoirs 55, no. 1 (2021): 285–301. http://dx.doi.org/10.1144/m55-2018-37.

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AbstractYoung volcanic centres of the Bransfield Strait and James Ross Island occur along back-arc extensional structures parallel to the South Shetland island arc. Back-arc extension was caused by slab rollback at the South Shetland Trench during the past 4 myr. The variability of lava compositions along the Bransfield Strait results from varying degrees of mantle depletion and input of a slab component. The mantle underneath the Bransfield Strait is heterogeneous on a scale of approximately tens of kilometres with portions in the mantle wedge not affected by slab fluids. Lavas from James Ross Island east of the Antarctic Peninsula differ in composition from those of the Bransfield Strait in that they are alkaline without evidence for a component from a subducted slab. Alkaline lavas from the volcanic centres east of the Antarctic Peninsula imply variably low degrees of partial melting in the presence of residual garnet, suggesting variable thinning of the lithosphere by extension. Magmas in the Bransfield Strait form by relatively high degrees of melting in the shallow mantle, whereas the magmas some 150 km further east form by low degrees of melting deeper in the mantle, reflecting the diversity of mantle geodynamic processes related to subduction along the South Shetland Trench.

16

Faccenna, Claudio, Francesca Funiciello, Domenico Giardini, and Pio Lucente. "Episodic back-arc extension during restricted mantle convection in the Central Mediterranean." Earth and Planetary Science Letters 187, no. 1-2 (April 2001): 105–16. http://dx.doi.org/10.1016/s0012-821x(01)00280-1.

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17

Avigad, D., Z. Garfunkel, L. Jolivet, and J. M. Azañón. "Reply [to “Comment on ‘Back arc extension and denudation of Mediterranean eclogites’’]." Tectonics 19, no. 2 (April 2000): 410–14. http://dx.doi.org/10.1029/1999tc900069.

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18

Rivers, Toby, and David Corrigan. "Convergent margin on southeastern Laurentia during the Mesoproterozoic: tectonic implications." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 359–83. http://dx.doi.org/10.1139/e99-067.

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A continental-margin magmatic arc is inferred to have existed on the southeastern (present coordinates) margin of Laurentia from Labrador to Texas from ~1500-1230 Ma, with part of the arc subsequently being incorporated into the 1190-990 Ma collisional Grenville Orogen. Outside the Grenville Province, where the arc is known as the Granite-Rhyolite Belt, it is undeformed, whereas within the Grenville Province it is deformed and metamorphosed. The arc comprises two igneous suites, an inboard, principally quartz monzonitic to granodioritic suite, and an outboard tonalitic to granodioritic suite. The quartz monzonite-granodiorite suite was largely derived from continental crust, whereas the tonalitic-granodiorite suite is calc-alkaline and has a juvenile isotopic signature. Available evidence from the Grenville Province suggests that the arc oscillated between extensional and compressional settings several times during the Mesoproterozoic. Back-arc deposits of several ages, that formed during relatively brief periods of extension, include (1) mafic dyke swarms subparallel to the arc; (2) continental sediments, bimodal volcanics and plateau basalts; (3) marine sediments and volcanics formed on stretched continental crust; and (4) ocean crust in a marginal basin. Closure of the back-arc basins occurred during the accretionary Pinwarian (~1495-1445 Ma) and Elzevirian (~1250-1190 Ma) orogenies, as well as during three pulses of crustal shortening associated with the 1190-990 Ma collisional Grenvillian Orogeny. During the Elzevirian Orogeny, closure of the Central Metasedimentary Belt marginal basin in the southeastern Grenville Province was marked by subduction-related magmatism as well as by imbrication of back-arc deposits. The presence of a continental-margin magmatic arc on southeastern Laurentia during the Mesoproterozoic implies that other coeval magmatism inboard from the arc took place in a back-arc setting. Such magmatism was widespread and chemically diverse and included large volume "anorogenic" anorthosite-mangerite-charnockite-granite (AMCG) complexes as well as small volume alkaline, quartz-saturated and -undersaturated "within-plate" granitoids. Recognition of the ~300 million year duration of the Mesoproterozoic convergent margin of southeastern Laurentia suggests that there may be useful parallels with the evolution of the Andes, which has been a convergent margin since the early Paleozoic.

19

Kandemir, Özgür, Kenan Akbayram, Mehmet Çobankaya, Fatih Kanar, Şükrü Pehlivan, Turgut Tok, Aynur Hakyemez, Erkan Ekmekçi, Füsun Danacı, and Uğur Temiz. "From arc evolution to arc-continent collision: Late Cretaceous–middle Eocene geology of the Eastern Pontides, northeastern Turkey." GSA Bulletin 131, no. 11-12 (May 9, 2019): 1889–906. http://dx.doi.org/10.1130/b31913.1.

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Abstract The Eastern Pontide Arc, a major fossil submarine arc of the world, was formed by northward subduction of the northern Neo-Tethys lithosphere under the Eurasian margin. The arc’s volcano-sedimentary sequence and its cover contain abundant fossils. Our new systematical paleontological and structural data suggest the Late Cretaceous arc volcanism was initiated at early-middle Turonian and continued uninterruptedly until the end of the early Maastrichtian, in the northern part of the Eastern Pontides. We measured ∼5500-m-thick arc deposits, suggesting a deposition rate of ∼220 m Ma–1 in ∼25 m.y. We have also defined four different chemical volcanic episodes: (1) an early-middle Turonian–Santonian mafic-intermediate episode, (2) a Santonian acidic episode; when the main volcanic centers were formed as huge acidic domes-calderas comprising the volcanogenic massive sulfide ores, (3) a late Santonian–late Campanian mafic-intermediate episode, and (4) a late Campanian–early Maastrichtian acidic episode. The volcaniclastic rocks were deposited in a deepwater extensional basin until the late Campanian. Between late Campanian and early Maastrichtian, intra-arc extension resulted in opening of back-arc in the north, while the southern part of the arc remained active and uplifted. The back-arc basin was most probably connected to the Eastern Black Sea Basin. In the back-arc basin, early Maastrichtian volcano-sedimentary arc sequence was transitionally overlain by pelagic sediments until late Danian suggesting continuous deep-marine conditions. However, the subsidence of the uplifted-arc-region did not occur until late Maastrichtian. We have documented a Selandian–early Thanetian (57–60 Ma) regional hiatus defining the closure age of the İzmir-Ankara-Erzincan Ocean along the Eastern Pontides. Between late Thanetian and late Lutetian synorogenic turbidites and postcollisional volcanics were deposited. The Eastern Pontide fold-and-thrust belt started to form at early Eocene (ca. 55 Ma) and thrusting continued in the post-Lutetian times.

20

Philippon, Mélody, Jean-Pierre Brun, Frédéric Gueydan, and Dimitrios Sokoutis. "The interaction between Aegean back-arc extension and Anatolia escape since Middle Miocene." Tectonophysics 631 (September 2014): 176–88. http://dx.doi.org/10.1016/j.tecto.2014.04.039.

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21

Okada, Shinsuke, and Yasutaka Ikeda. "Quantifying crustal extension and shortening in the back-arc region of Northeast Japan." Journal of Geophysical Research: Solid Earth 117, B1 (January 2012): n/a. http://dx.doi.org/10.1029/2011jb008355.

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22

Rollet, Nadège, Jacques Déverchère, Marie-Odile Beslier, Pol Guennoc, Jean-Pierre Réhault, Marc Sosson, and Catherine Truffert. "Back arc extension, tectonic inheritance, and volcanism in the Ligurian Sea, Western Mediterranean." Tectonics 21, no. 3 (June 2002): 6–1. http://dx.doi.org/10.1029/2001tc900027.

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23

Moghadam, Hadi Shafaii, R. J. Stern, W. L. Griffin, M. Z. Khedr, M. Kirchenbaur, C. J. Ottley, S. A. Whattam, et al. "Subduction initiation and back-arc opening north of Neo-Tethys: Evidence from the Late Cretaceous Torbat-e-Heydarieh ophiolite of NE Iran." GSA Bulletin 132, no. 5-6 (October 15, 2019): 1083–105. http://dx.doi.org/10.1130/b35065.1.

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Abstract How new subduction zones form is an ongoing scientific question with key implications for our understanding of how this process influences the behavior of the overriding plate. Here we focus on the effects of a Late Cretaceous subduction-initiation (SI) event in Iran and show how SI caused enough extension to open a back-arc basin in NE Iran. The Late Cretaceous Torbat-e-Heydarieh ophiolite (THO) is well exposed as part of the Sabzevar-Torbat-e-Heydarieh ophiolite belt. It is dominated by mantle peridotite, with a thin crustal sequence. The THO mantle sequence consists of harzburgite, clinopyroxene-harzburgite, plagioclase lherzolite, impregnated lherzolite, and dunite. Spinel in THO mantle peridotites show variable Cr# (10–63), similar to both abyssal and fore-arc peridotites. The igneous rocks (gabbros and dikes intruding mantle peridotite, pillowed and massive lavas, amphibole gabbros, plagiogranites and associated diorites, and diabase dikes) display rare earth element patterns similar to MORB, arc tholeiite and back-arc basin basalt. Zircons from six samples, including plagiogranites and dikes within mantle peridotite, yield U-Pb ages of ca. 99–92 Ma, indicating that the THO formed during the Late Cretaceous and was magmatically active for ∼7 m.y. THO igneous rocks have variable εNd(t) of +5.7 to +8.2 and εHf(t) ranging from +14.9 to +21.5; zircons have εHf(t) of +8.1 to +18.5. These isotopic compositions indicate that the THO rocks were derived from an isotopically depleted mantle source similar to that of the Indian Ocean, which was slightly affected by the recycling of subducted sediments. We conclude that the THO and other Sabzevar-Torbat-e-Heydarieh ophiolites formed in a back-arc basin well to the north of the Late Cretaceous fore-arc, now represented by the Zagros ophiolites, testifying that a broad region of Iran was affected by upper-plate extension accompanying Late Cretaceous subduction initiation.

24

Papazachos, Costas B. "Deep Structure and Active Tectonics of the South Aegean Volcanic Arc." Elements 15, no. 3 (June 1, 2019): 153–58. http://dx.doi.org/10.2138/gselements.15.3.153.

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The seismotectonic setting of the Aegean Sea, based on information from seismicity, neotectonics and global positioning system studies, is characterized by a sharp transition from a compressional outer arc to a complex back-arc, with an approximate north–south extension along the volcanic arc. Seismicity and 3-D tomography studies reveal the geometry of the subducting slab and image the low-velocity/high-attenuation mantle wedge at depths of 50–80 km beneath the volcanic arc where magma is generated. The 1956 Amorgos M7.5 earthquake and the impact from its seismic shaking and landslide-triggered tsunamis are discussed in the context of the regional seismotectonic setting.

25

Jutras, Pierre, J. Brendan Murphy, Dennis Quick, and Jaroslav Dostal. "Evolution of Subduction Dynamics beneath West Avalonia in Middle to Late Ordovician Times." Lithosphere 2020, no. 1 (September 23, 2020): 1–22. http://dx.doi.org/10.2113/2020/8837633.

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Abstract Middle to Upper Ordovician volcanic rocks in the Arisaig area of Nova Scotia, Canada, constitute the only known record of volcanism in West Avalonia during that interval. Hence, they have been extensively studied to test paleocontinental reconstructions that consistently show Avalonia as a drifting microcontinent during that period. Identification of volcanic rocks with an intermediate composition (the new Seaspray Cove Formation) between upper Darriwilian bimodal volcanic rocks of the Dunn Point Formation and Sandbian felsic pyroclastic rocks of the McGillivray Brook Formation has led to a reevaluation of magmatic relationships in the Ordovician volcanic suite at Arisaig. Although part of the same volcanic construction, the three formations are separated by significant time-gaps and are shown to belong to three distinct magmatic subsystems. The tectonostratigraphic context and trace element contents of the Dunn Point Formation basalts suggest that they were produced by the high-degree partial melting of an E-MORB type source in a back-arc extensional setting, whereas trace element contents in intermediate rocks of the Seaspray Cove Formation suggest that they were produced by the low-degree partial melting of a subduction-enriched source in an arc setting. The two formations are separated by a long interval of volcanic quiescence and deep weathering, during which time the back-arc region evolved from extension to shortening and was eventually onlapped by arc volcanic rocks. Based on limited field constraints, paleomagnetic and paleontological data, this progradation of arc onto back-arc volcanic rocks occurred from the north, where an increasingly young Iapetan oceanic plate was being subducted at an increasingly shallow angle. Partial subduction of the Iapetan oceanic ridge is thought to have subsequently generated slab window magmatism, thus marking the last pulse of subduction-related volcanism in both East and West Avalonia.

26

Mitchell, A. H. G., and J. C. Carlile. "Mineralization, antiforms and crustal extension in andesitic arcs." Geological Magazine 131, no. 2 (March 1994): 231–42. http://dx.doi.org/10.1017/s001675680001075x.

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AbstractThe distribution and stratigraphic position of porphyry copper and epithermal gold deposits in andesitic arcs of the western Pacific and eastern Europe suggest that porphyry copper and epithermal vein deposits of adularia–sericite type develop successively under different stress regimes in an evolving arc, rather than being genetically related as commonly supposed. Absence of coeval high-level stocks in the root zones of many adularia-sericite deposits suggests that circulation of the dominantly meteoric hydrothermal fluids is not driven by shallow intrusions. The location of several world-class deposits on basement geanticlines, and on more localized antiforms of which at least one has been interpreted as a metamorphic core complex, implies that elevation of the arc, emplacement of magmatic sills at depth and adularia–sericite type gold mineralization are genetically related to subduction-induced crustal extension. Ascent of deep hydrothermal fluids, predominantly meteoric but with a metamorphic or magmatic component, may be controlled by regional low-angle structures at depth, analogous to those inferred for some mesothermal gold deposits. Mineralization at shallow (epithermal) depths in high-angle structures largely reflects the high geothermal gradient and mixing of deep fluid with cool meteoric water in or at the base of the permeable volcanic cover. Andesitic magmatism may resume following porphyry copper mineralization, adularia–sericite epithermal gold mineralization, or continued extension to form a ‘back arc’ spreading system, depending on the relative plate motion.

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Hadlari, T., and R. H. Rainbird. "Retro-arc extension and continental rifting: a model for the Paleoproterozoic Baker Lake Basin, Nunavut1Geological Survey of Canada Contribution 20100436." Canadian Journal of Earth Sciences 48, no. 8 (August 2011): 1232–58. http://dx.doi.org/10.1139/e11-002.

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Within Baker Lake sub-basin, the ca. 1.84–1.78 Ga Baker Sequence formed in two stages. At the start of the first stage, during rift initiation, half-graben were host to siliciclastic alluvial, eolian, and lacustrine deposits and to localized felsic minette volcanics. Back-stepping of facies indicate high accommodation rates and areal expansion, which, combined with extrusion of voluminous minette volcanic rocks, are interpreted to record increased extension and rift climax. Low accommodation post-rift deposits from the second stage of basin development are relatively thin and coeval felsite domes spatially restricted. Volcanic rocks and some siliciclastic units correlate between sub-basins, and hence the interpreted history of Baker Lake sub-basin is extended across greater Baker Lake Basin. This implies that the basin formed in response to regional extension and crustal thinning. The Baker Lake Basin marks the northern extent of a series of basins that trend northeastward along the Snowbird Tectonic Zone, including an inlier of the correlative Martin Group in northern Saskatchewan. The high accommodation first stage of basin development is proposed to have been the result of intra-continental retro-arc extension during ca. 1.85–1.84 Ga formation of the Kisseynew back-arc basin of the Trans-Hudson Orogen. Upon closure of the Kisseynew back-arc basin and collision of the Superior Province with the western Churchill Province, Baker Lake Basin was subject to strike-slip faulting. The second, low accommodation stage of basin development and strike-slip faulting is proposed to record lateral tectonic escape between the Saskatchewan–Manitoba and Baffin Island – Committee Bay foci of the western Churchill – Superior Province collision.

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Morishita, Tomoaki, Naoto Hirano, Hirochika Sumino, Hiroshi Sato, Tomoyuki Shibata, Masako Yoshikawa, Shoji Arai, Rie Nauchi, and Akihiro Tamura. "Alkali basalt from the Seifu Seamount in the Sea of Japan: post-spreading magmatism in a back-arc setting." Solid Earth 11, no. 1 (January 7, 2020): 23–36. http://dx.doi.org/10.5194/se-11-23-2020.

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Abstract. We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM basalt is a high-K to shoshonitic alkali basalt that is characterized by light rare earth element enrichment. The trace element features of the basalt are similar to those of ocean island basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM basalt differ from those of back-arc basin basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.

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Putiš, Marián, Peter Ivan, Milan Kohút, Ján Spišiak, Pavol Siman, Martin Radvanec, Pavel Uher, et al. "Meta-igneous rocks of the West-Carpathian basement, Slovakia: indicators of Early Paleozoic extension and shortening events." Bulletin de la Société Géologique de France 180, no. 6 (October 1, 2009): 461–71. http://dx.doi.org/10.2113/gssgfbull.180.6.461.

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Abstract The paper reviews the main West-Carpathian Early Paleozoic metamorphosed originally sedimentary-magmatic complexes, dated by SHRIMP on zircons, as indicators of crustal extension and shortening events. Igneous precursors of a Layered Amphibolite Complex (LAC) – fractionated upper mantle gabbros to diorites, dated at 503 ± 4 and 492 ± 4 Ma from the North-Veporic, or 480 ± 5 and 450 ± 6 Ma from the Tatric basement are contemporaneous with subaluminous to metaluminous I-type (507 ± 4 Ma, the South-Veporic basement), peraluminous S-type (497 ± 4 Ma, the South-Veporic basement; 516 ± 7, 485 ± 6 and 462 ± 6 Ma, the North-Veporic basement; 497 ± 6, 472 ± 6 and 450 ± 6 Ma, the Tatric basement), alkaline A-type (511 ± 6 Ma, South-Veporic basement) granitic orthogneisses and calcalkaline rhyolitic (482 ± 6 Ma) and dacitic (476 ± 7 Ma) metavolcanics (Gemeric basement), indicating a magmatic immature back arc setting. The ages point to Middle/Late Cambrian, Early and Late Ordovician magmatic phases, coeval with the extension in the northern Gondwana margin. Separation of an inferred Avalonian and/or Galatian terranes distal continental ribbon corresponds with the opening of a Medio-European Basin. A 430-390 Ma dated MP/HP metamorphic event, recorded in the LAC and associated orthogneisses, occurred in the area of thinned immature back arc basin crust due to closure of the Medio-European Basin. Thus a distal Gondwana continental ribbon north of this basin could be an eastward lateral pendant of Armorica, derived from Galatian terrane. Metaophiolites of the Pernek Group (a metagabbrodolerite dated at 371 ± 4 Ma) in the Tatric basement, analogous to island-arc tholeiites and back-arc basin basalts, indicate a back-arc basin setting north of a 430-390 Ma old northward dipping subduction/collision zone, dividing the northward drifting western Galatian terrane microplate from the Gondwana margin. Some metabasites of the Gemeric basement might indicate Late Devonian to Mississippian opening of a peri-Gondwanan Paleotethyan oceanic basin: a 383 ± 3 Ma old remelted metagabbro (482 ± 9 Ma) from the Klátov gneiss-amphibolite complex, ca. 385 Ma old porphyritic metabasite of the Zlatník ophiolite complex, as well as a 350 ± 5 Ma old HP metabasite as tectonic fragment within the Rakovec Group. The closure of Devonian-Mississippian basins, accompanied by medium-pressure (the Pernek Group) to high-pressure (blueschist to eclogitic tectonic fragments in greenschist facies rocks of the Rakovec Group) metamorphism, occurred in late Carboniferous to early Permian, when Paleotethyan realm complexes accreted to a Galatian terrane microplate, the latter represented by the older and the higher-grade Tatric and Veporic basement complexes.

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McKibbin, Seann J., Bill Landenberger, and C. Mark Fanning. "First magmatism in the New England Batholith, Australia: forearc and arc–back-arc components in the Bakers Creek Suite gabbros." Solid Earth 8, no. 2 (April 5, 2017): 421–34. http://dx.doi.org/10.5194/se-8-421-2017.

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Abstract. The New England Orogen, eastern Australia, was established as an outboard extension of the Lachlan Orogen through the migration of magmatism into forearc basin and accretionary prism sediments. Widespread S-type granitic rocks of the Hillgrove and Bundarra supersuites represent the first pulse of magmatism, followed by I- and A-types typical of circum-Pacific extensional accretionary orogens. Associated with the former are a number of small tholeiite–gabbroic to intermediate bodies of the Bakers Creek Suite, which sample the heat source for production of granitic magmas and are potential tectonic markers indicating why magmatism moved into the forearc and accretionary complexes rather than rifting the old Lachlan Orogen arc. The Bakers Creek Suite gabbros capture an early ( ∼ 305 Ma) forearc basalt-like component with low Th ∕ Nb and with high Y ∕ Zr and Ba ∕ La, recording melting in the mantle wedge with little involvement of a slab flux and indicating forearc rifting. Subsequently, arc–back-arc like gabbroic magmas (305–304 Ma) were emplaced, followed by compositionally diverse magmatism leading up to the main S-type granitic intrusion ( ∼ 290 Ma). This trend in magmatic evolution implicates forearc and other mantle wedge melts in the heating and melting of fertile accretion complex sediments and relatively long ( ∼ 10 Myr) timescales for such melting.

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Piercey, Stephen J., James K. Mortensen, Donald C. Murphy, Suzanne Paradis, and Robert A. Creaser. "Geochemistry and tectonic significance of alkalic mafic magmatism in the Yukon-Tanana terrane, Finlayson Lake region, Yukon." Canadian Journal of Earth Sciences 39, no. 12 (December 1, 2002): 1729–44. http://dx.doi.org/10.1139/e02-090.

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This paper provides an integrated field and geochemical study of weakly alkalic, ~360 Ma mafic rocks from the YukonTanana terrane in the Finlayson Lake region, southeastern Yukon. These mafic rocks occur as dykes and sills that crosscut older felsic metavolcanic rocks and metasedimentary rocks (Kudz Ze Kayah unit) or as flows interlayered with carbonaceous metasedimentary rocks. The mafic rocks have signatures similar to those of ocean-island basalts, moderate TiO2 and P2O5 contents, elevated high field strength element and light rare earth element contents, and εNd350 = +1.1. A subset of the dykes (group 4b) has similar geochemical characteristics but with higher Th/Nb and lower Nb/U ratios, higher Zr and light rare earth element contents, and εNd350 = 2.8. The geochemical and isotopic attributes of these rocks are consistent with formation from either lithospheric or asthenospheric sources during decompression melting of the mantle, with some rocks exhibiting evidence for crustal contamination (group 4b). The alkalic basalts are interpreted to represent ~360 Ma ensialic back-arc rifting and basin generation. It is envisioned that east-dipping subduction, represented by slightly older magmatic suites (Fire Lake unit), was disrupted by subduction hinge roll-back, westward migration of arc magmatism, and the onset of back-arc extension. Decompression melting of the mantle associated with back-arc generation resulted in mantle melting and the formation of the alkalic basalts. The spatial association of this mafic magmatism with crustally derived felsic volcanic rocks and contained volcanogenic massive sulphide mineralization suggests that the associated deposits (Kudz Ze Kayah, GP4F) formed within an ensialic back-arc environment.

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Pe-Piper, G., D. J. W. Piper, C. N. Kotopouli, and A. G. Panagos. "Neogene volcanoes of Chios, Greece: the relative importance of subduction and back-arc extension." Geological Society, London, Special Publications 81, no. 1 (1994): 213–31. http://dx.doi.org/10.1144/gsl.sp.1994.081.01.12.

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Dec, Tomasz, H. Scott Swinden, and R. Greg Dunning. "Lithostratigraphy and geochemistry of the Cottrells Cove Group, Buchans – Roberts Arm volcanic belt: new constraints for the paleotectonic setting of the Notre Dame Subzone, Newfoundland Appalachians." Canadian Journal of Earth Sciences 34, no. 1 (January 1, 1997): 86–103. http://dx.doi.org/10.1139/e17-008.

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New sedimentological, geochemical, and geochronological data from the Cottrells Cove Group in central Newfoundland provide important constraints on the nature of the Notre Dame Subzone, its tectonic setting, and the history of the Laurentian margin during the Early Ordovician. The Cottrells Cove Group forms the eastern extension of the Roberts Arm Group and correlates with the Chanceport Group on New World Island. It is represented by two volcano-sedimentary formations that occur in a complex thrust stack. The Fortune Harbour Formation consists of calc-alkalic, island-arc lavas, followed by a 1250 m thick succession of volcaniclastic deposits, radiolarian cherts, and calc-alkalic, mafic flows, which were deposited in a back-arc, basin-plain setting. The volcaniclastic deposits include felsic tuff, which has a U–Pb zircon age of 484 ± 2 Ma and an inheritance component of 2517 ± 26 Ma. These new U–Pb and Nd-isotope data suggest that the island-arc–back-arc volcanism and sedimentation in the Notre Dame Subzone developed in the vicinity of continental margin and approximately 10 Ma earlier than has previously been established. The Moores Cove Formation is undated but contains boulders of calc-alkalic basalt and is presumed to be at least in part younger than the Fortune Harbour Formation. Tholeiitic lavas, together with associated radiolarian cherts and volcaniclastic deposits, constitute the basal part of the Moores Cove Formation and may have been deposited in a back-arc environment synchronously with some parts of the Fortune Harbour Formation. They are conformably followed by an over 1200 m thick, coarsening-upward succession of lower-slope and submarine-fan deposits. The polymictic flysch, containing clasts of island-arc basalt, accompanied by other volcanic, plutonic, ultramafic, and sedimentary detritus, may record Middle or Upper Ordovician uplift and erosion of obducted arc–back-arc, volcano-sedimentary sequences and their ophiolitic substrate.

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Huot, François, Réjean Hébert, and Bruno Turcotte. "A multistage magmatic history for the genesis of the Orford ophiolite (Quebec, Canada): a study of the Mont Chagnon massif." Canadian Journal of Earth Sciences 39, no. 8 (August 1, 2002): 1201–17. http://dx.doi.org/10.1139/e02-030.

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This paper concerns the petrogenesis of the 504 ± 3 Ma Mont Chagnon massif, the southern extension of the Orford ophiolite in the Quebec Appalachians. The evolution of this massif is summarized in three stages marked by different magmatic series. In the Late Cambrian, the onset of southeastern subduction of the Iapetus basin generated an immature oceanic island arc made up of light rare-earth-element-depleted tholeiites, now preserved in the massif as a portion of the intrusive crustal unit, the dyke complex, and part of the lower volcanic unit. A phase of arc splitting, and concomitant partial erosion of the crustal section, was shortly followed by the eruption of rhyolite genetically related to felsic and low-Ti dykes, and trondhjemite. The geochemistry of these magmas bear some similarities with boninitic series. We believe these liquids derived from the partial melting of the Iapetus amphibolitized oceanic crust, with that of its Laurentian-derived sediments and nearby peridotite, either found as a trapped sliver above the subducting slab or as the slab itself. The final stage, preserved in the massif as a part of the intrusive section, the upper volcanic rocks, and the late-stage dykes, represents the back-arc opening. An ocean-island component is involved in the back-arc related petrogenetic processes, producing magmas with compositions intermediate between arc tholeiites and enriched back-arc basin basalts. This is the first report that the Iapetus basin was locally closing as early as Late Cambrian in the southern Quebec area.

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SUNAL, GÜRSEL, and OKAN TÜYSÜZ. "Palaeostress analysis of Tertiary post-collisional structures in the Western Pontides, northern Turkey." Geological Magazine 139, no. 3 (May 2002): 343–59. http://dx.doi.org/10.1017/s0016756802006489.

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Fingerprints of the opening of the Western Black Sea Basin and collision of Pontides and Sakarya Continent along the Intra-Pontide suture can be traced in the area between Cide (Kastamonu) and Kurucaşile (Bartin) in northern Turkey, along the southern coast of the Black Sea. The Western Black Sea Basin is an oceanic basin opened as a back-arc basin of the northward-subducting Intra-Pontide Ocean. Basement units related to this opening are represented by Lower Cretaceous and older units. The first arc magmatism related to this subduction began during Turonian times. Coeval with this magmatism, back-arc extension affected the region and caused development of horst-graben topography. This extensional period resulted in the break-up of continental crust and the oceanic spreading in the Western Black Sea Basin during Late Santonian times. During the Late Campanian–Early Maastrichtian period, the Sakarya Continent and Pontides collided and arc magmatism on the Pontides ended. After this collision, the Western Pontides thickened, imbricated and developed a mainly N-vergent foreland fold and thrust belt character since Late Eocene–Oligocene times. The palaeostress directions calculated from thrust faults of this foreland fold and thrust belt are 4.6°/156.6° for σ1, 6.4°/66.1° for σ2, and 83.2°/261.9° for σ3. The nature of the imbrication indicates that it was a northward prograding foreland system connected to a floor thrust (detachment) fault at the bottom. Field observations on curved slickenfibres support the theory that the thrust faults of this imbricated structure have transformed to oblique thrusts and strike-slip faults over time.

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Alonso-Chaves, F., J. I. Soto, M. Orozco, A. A. Kilias, and M. D. Tranos. "TECTONIC EVOLUTION OF THE BETIC CORDILLERA: AN OVERVIEW." Bulletin of the Geological Society of Greece 36, no. 4 (January 1, 2004): 1598. http://dx.doi.org/10.12681/bgsg.16563.

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The Betic (Southern Spain) and the Rif (Morocco) mountain chains, connected through the Gibraltar Strait, shapes a W-E elongated and arcuate Alpine orogenic belt. The Alborân Sea, in continuity to the east with the South Balearic Basin, is located in the inner part of this alpine belt. The Iberian and African continental forelands bound the region as a whole to the north and south, respectively, and to the east it is connected to the oceanic Sardine-Balearic Basin. The peculiarities of these westernmost Mediterranean chains result from: (1) its position between two large convergent plates -Africa and Europe- that have had variable directions of relative motion since the late Cretaceous; and (2) the Neogene westward migration of the orogenic hinterland and its simultaneous "back-arc"-like extension, generating the Alborén Sea basin. The complexes and large paleogeographic terrains traditionally recognized in the Betic and Rif chains belong to four pre-Neogene crustal domains: the South-Iberian and Maghrebian passive continental paleomargins (External Zones of the orogen), the Flysch Units, and the Alborân Crustal Domain composed mainly of a pre- Miocene metamorphosed thrust-stack (Nevado-Filabride, Alpujârride, and Malaguide complexes, from bottom to top). The boundaries between the main metamorphic complexes of the Alborân Domain are extensional detachments, which finally developed under brittle conditions and are commonly sealed by middle-to-late Miocene marine-to-continental sediments. They, nonetheless, are not the most recent structures in the Alborân Domain, because upright, E-W open folds warp the extensional detachments, and finally, high-angle normal faults and strike-slip faults, many of which are still active, offset folds and extensional detachments. The tectonic evolution of the Betic Alborân orogenic system shows close similarities with the one depicted in other arcuate-shaped, Alpine mountain ranges in the Mediterranean, such as the Hellenic Arc and the Aegean Sea. Like in the westernmost Mediterranean, a thickened (pre Miocene) crust is bounding there a thinned, continental (?) basin. Extension is also formed here in a "back-arc" setting, being developed simultaneously with the N-S convergence between the African and European plates.

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El Bakili, Asmae, Michel Corsini, Ahmed Chalouan, Philippe Münch, Adrien Romagny, Jean Marc Lardeaux, and Ali Azdimousa. "Neogene polyphase deformation related to the Alboran Basin evolution: new insights for the Beni Bousera massif (Internal Rif, Morocco)." BSGF - Earth Sciences Bulletin 191 (2020): 10. http://dx.doi.org/10.1051/bsgf/2020008.

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Located in the Internal domain of the Rif belt, the Beni Bousera massif is characterized by a stack of peridotites and crustal metamorphic units. The massif is intruded by granitic dykes and affected by several normal ductile shear zones. Structural, petrological and 40Ar–39Ar dating analyses performed on these two elements highlight that (1) the granitic dykes are emplaced within major N70° to N140° trending normal faults and shear zones, resulted from an NNE-SSW extension (2) the Aaraben fault in its NE part is characterized by N70° to N150° trending ductile normal shear zones, resulted from a nearly N-S extension and (3) the age of this extensional event is comprised between 22 and 20 Ma. Available paleomagnetic data allow a restoration of the initial orientation of extension, which was nearly E-W contemporary with the Alboran Basin opening in back-arc context, during the Early Miocene. At the onset of the extension, the peridotites were somehow lying upon a partially melted continental crust, and exhumed during this event by the Aaraben Normal Shear Zone. Afterward, the Alboran Domain suffered several compressional events.

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Irianto, Komang Agung, Raymond Parung, and William Putera Sukmajaya. "Open reduction in neglected elbow dislocation in children: a case series." Universa Medicina 38, no. 1 (January 30, 2019): 63. http://dx.doi.org/10.18051/univmed.2019.v38.63-68.

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Background Elbow deformity in children due to neglected proper fracture management is a devastating condition. The stiffness and pain complicated the function in daily activity. Successful management of neglected elbow dislocation is a challenging problem for orthopedic surgeons. In this study, we aimed to evaluate results of open reduction for neglected elbow dislocation in children. Case Description This is a case series of 13-14 years old neglected elbow dislocations, for up to 15 months. Open reduction after external distractor and followed by intensive rehabilitation was implemented. Clinical and functional outcome were evaluated within 4-7 years. Initial average elbow flexion was 53,3°, extension was 0°, arc of flexion was 53,3°, arc of pronation-supination was 150° and Mayo Elbow Performance Index (MEPI) was 80. Clinical and functional outcome were evaluated within 4-7 years. At follow-up after open reduction, the improvement in whole range of movement was significant. Average elbow flexion was 118,3°, extension was 36,67°, arc of flexion was 81,67°, arc of pronation-supination was 133°. The average improvement of flexion was 65°, arc of flexion was 31,67°, and arc of pronation-supination was 8,3°. The average loss of flexion was 15,5%, arc of flexion was 44,2%, and arc of pronation-supination was 10,7% compared with uninjured side. The average Mayo Elbow Performance Index (MEPI) was 96,67; all with excellent results. Conclusion Planned and well execution open reduction in pediatric neglected elbow dislocation may bring back the painless movement within normal daily function.

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Colman-Sadd, S. P., P. Stone, H. S. Swinden, and R. P. Barnes. "Parallel geological development in the Dunnage Zone of Newfoundland and the Lower Palaeozoic terranes of southern Scotland: an assessment." Transactions of the Royal Society of Edinburgh: Earth Sciences 83, no. 3 (1992): 571–94. http://dx.doi.org/10.1017/s0263593300005885.

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AbstractThe Notre Dame and Exploits subzones of Newfoundland's Dunnage Zone are correlated with the Midland Valley and Southern Uplands of Scotland, using detailed comparisons of two key Lower Palaeozoic successions which record similar histories of extension and compression. It follows that the Baie Verte Line, Red Indian Line and Dover Fault are equivalent to the Highland Boundary Fault, Southern Upland Fault and Solway Line, respectively.The Betts Cove Complex and overlying Snooks Arm Group of the Notre Dame Subzone are analogous to the Ballantrae Complex of the Midland Valley, both recording the Arenig evolution and subsequent obduction of an arc and back-arc system. The Early Ordovician to Silurian sequence unconformably overlying the Ballantrae Complex is poorly represented in the Notre Dame Subzone but important similarities can still be detected suggesting corresponding histories of continental margin subsidence and marine transgression.In the Exploits Subzone, Early Ordovician back-arc volcanic rocks are overlain by Llandeilo mudstones and Late Ordovician to Early Silurian turbidites. A similar stratigraphy occurs in the Northern and Central Belts of the Southern Uplands and both areas have matching transpressive structural histories. Deeper erosion in the Exploits Subzone reveals Cambrian and Early Ordovician volcano-sedimentary sequences structurally emplaced on the Gander Zone, and such rocks are probably present beneath the Southern Uplands. Combined data from the Notre Dame Subzone and Midland Valley suggest an Arenig southeast-dipping subduction zone. Early Ordovician volcanic rocks in the Exploits Subzone and Southern Uplands have back-arc basin geochemistry and support the model of the Southern Uplands as a transition from back-arc to foreland basin. Preferential emergence of the Dunnage Zone and contrasts between Exploits Subzone and Southern Uplands turbidite basins are attributed to collision of Newfoundland with a Laurentian promontory and Scotland with a re-entrant. This hypothesis also explains the transpressive structural regime common to both areas.

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Hamling, Ian J., Sigrun Hreinsdóttir, Stephen Bannister, and Neville Palmer. "Off-axis magmatism along a subaerial back-arc rift: Observations from the Taupo Volcanic Zone, New Zealand." Science Advances 2, no. 6 (June 2016): e1600288. http://dx.doi.org/10.1126/sciadv.1600288.

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Continental rifting and seafloor spreading play a fundamental role in the generation of new crust. However, the distribution of magma and its relationship with tectonics and volcanism remain poorly understood, particularly in back-arc settings. We show evidence for a large, long-lived, off-axis magmatic intrusion located on the margin of the Taupo Volcanic Zone, New Zealand. Geodetic data acquired since the 1950s show evidence for uplift outside of the region of active extension, consistent with the inflation of a magmatic body at a depth of ~9.5 km. Satellite radar interferometry and Global Positioning System data suggest that there was an increase in the inflation rate from 2003 to 2011, which correlates with intense earthquake activity in the region. Our results suggest that the continued growth of a large magmatic body may represent the birth of a new magma chamber on the margins of a back-arc rift system.

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Jolivet, Laurent, Laurent Arbaret, Laetitia Le Pourhiet, Florent Cheval-Garabédian, Vincent Roche, Aurélien Rabillard, and Loïc Labrousse. "Interactions of plutons and detachments: a comparison of Aegean and Tyrrhenian granitoids." Solid Earth 12, no. 6 (June 16, 2021): 1357–88. http://dx.doi.org/10.5194/se-12-1357-2021.

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Abstract. Back-arc extension superimposed on mountain belts leads to distributed normal faults and shear zones interacting with magma emplacement within the crust. The composition of granitic magmas emplaced at this stage often involves a large component of crustal melting. The Miocene Aegean granitoids were emplaced in metamorphic core complexes (MCCs) below crustal-scale low-angle normal faults and ductile shear zones. Intrusion processes interact with extension and shear along detachments, from the hot magmatic flow within the pluton root zone to the colder ductile and brittle deformation below and along the detachment. A comparison of the Aegean plutons with the island of Elba MCC in the back-arc region of the Apennine subduction shows that these processes are characteristic of pluton–detachment interactions in general. We discuss a conceptual emplacement model, tested by numerical models. Mafic injections within the partially molten lower crust above the hot asthenosphere trigger the ascent within the core of the MCC of felsic magmas, controlled by the strain localization on persistent crustal-scale shear zones at the top that guide the ascent until the brittle ductile transition. Once the system definitely enters the brittle regime, the detachment and the upper crust are intruded, while new detachments migrate upward and in the direction of shearing.

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Sheng, Jian, Cunzhu Li, Jie Liao, Ze Yang, and Shiyi Jiang. "Dynamics of back‐arc extension controlled by subducting slab retreat: Insights from 2D thermo‐mechanical modelling." Geological Journal 54, no. 6 (October 5, 2018): 3376–88. http://dx.doi.org/10.1002/gj.3336.

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43

Faccenna, Claudio, Philippe Davy, Jean-Pierre Brun, Renato Funiciello, Domenico Giardini, Massimo Mattei, and Thierry Nalpas. "The dynamics of back-arc extension: an experimental approach to the opening of the Tyrrhenian Sea." Geophysical Journal International 126, no. 3 (September 1996): 781–95. http://dx.doi.org/10.1111/j.1365-246x.1996.tb04702.x.

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44

Shi, Yao-lin, and Jian Zhang. "Deep geodynamics of far field intercontinental back-arc extension: Formation of Cenozoic volcanoes in northeastern China." Acta Seismologica Sinica 17, S1 (November 2004): 1–8. http://dx.doi.org/10.1007/s11589-004-0061-x.

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45

Syme, E. C., S. B. Lucas, A. H. Bailes, and R. A. Stern. "Contrasting arc and MORB-like assemblages in the Paleoproterozoic Flin Flon Belt, Manitoba, and the role of intra-arc extension in localizing volcanic-hosted massive sulphide deposits." Canadian Journal of Earth Sciences 36, no. 11 (November 10, 1999): 1767–88. http://dx.doi.org/10.1139/e98-084.

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The Flin Flon Belt (Trans-Hudson Orogen, Manitoba and Saskatchewan) is the largest Paleoproterozoic volcanic-hosted massive sulphide (VMS) district in the world, with 118.7 million tonnes (Mt) of Zn-Cu-(Au-Ag) sulphide ore in 25 past or presently producing mines and 64.3 Mt in subeconomic deposits. The orebodies are restricted to isotopically juvenile volcanic-arc sequences, dated at 1.903-1.881 Ga at Flin Flon. Sequences of ca. 1.904-1.901 Ga back-arc and ocean-plateau basalts and related plutonic rocks, structurally juxtaposed with the arc assemblages at 1.880-1.870 Ga, are not known to contain economic base metal deposits. The juvenile arc tectono-stratigraphic assemblages are generally marked by older and stratigraphically lower tholeiitic submarine volcanic packages (ca. 1.903-1.886 Ga) that are observed or interpreted to be overlain by extensive and lithologically varied sequences of calc-alkaline and alkaline (shoshonitic) arc rocks and arc rift deposits (ca. 1.888-1.881 Ga). VMS deposits occur in both the tholeiitic and calc-alkaline arc sequences, but the 62 Mt Flin Flon deposit occurs in a 1.903 Ga tholeiitic primitive arc package. It can be demonstrated that for the Flin Flon - Callinan - Triple 7, Cuprus, and White Lake VMS deposits, whose stratigraphic context is preserved, deposition of the massive sulphides was temporally associated with inferred arc rifting processes. Critical observations for arc rifting include evidence for extensional faulting, erosion, and development of unconformities; extrusion of MORB-like basalts and associated rhyolites; and development of depositional basins with thick sequences of shoshonitic turbidites. As has been proposed for other major VMS camps (e.g., Kuroko, Kidd Creek, Bathurst), arc rifting can generate the loci of sustained high heat flow and fluid pathways required for the development of long-lived hydrothermal convection systems.

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JIANG, YAO-HUI, SHAO-YONG JIANG, KUI-DONG ZHAO, and HONG-FEI LING. "Petrogenesis of Late Jurassic Qianlishan granites and mafic dykes, Southeast China: implications for a back-arc extension setting." Geological Magazine 143, no. 4 (April 26, 2006): 457–74. http://dx.doi.org/10.1017/s0016756805001652.

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A late Mesozoic belt of volcanic-intrusive complexes occurs in Southeast China. The Qianlishan granites are distributed in the northwest of the belt. The pluton is composed of porphyritic biotite granite (153 Ma) and equigranular biotite granite (151 Ma) and was intruded by granite-porphyry dykes (144 Ma) and mafic dykes such as lamprophyre and diabase (142 Ma). The granitic rocks, consisting mainly of K-feldspar, plagioclase, quartz and Fe-rich biotite, have SiO2 contents of 72.9–76.9%, and are enriched in alkalis, rare earth elements (REE), high field strength elements (HFSE) and Ga with high Ga/Al ratios, but depleted in Ba, Sr and transition metals. Trace-element geochemistry and Sr–Nd isotope systematics further imply that the Qianlishan granitic magmas were most probably derived by partial melting of Palaeo- to Mesoproterozoic metamorphic lower-crustal rocks that had been granulitized during an earlier thermal event. These features suggest an A-type affinity. The Qianlishan lamprophyre and neighbouring coeval mafic dykes (SiO2 = 47.9–53.8 wt%) have high MgO and compatible element contents. These rocks also have high K2O contents and are enriched in alkalis, light REE, large ion lithophile elements, and depleted in HFSE. They have low initial εNd values and relatively high initial 87Sr/86Sr ratios. We suggest a subduction-modified refractory lithospheric mantle (phlogopite-bearing harzburgite or lherzolite) for these high-Mg potassic magmas. The Qianlishan diabases (SiO2 = 48.4–48.7 wt%) are alkaline and have high TiO2 and total Fe2O3 contents, together with the positive initial εNd value, suggesting derivation from fertile asthenopheric mantle (phlogopite-bearing lherzolite). A back-arc extensional setting, related to subduction of the Palaeo-Pacific plate, is favoured to explain the petrogenesis of the Qianlishan granites and associated mafic dykes. Between 180 and 160 Ma, Southeast China was a continental arc, forming the 180–160 Ma plutons of the late Mesozoic volcanic-intrusive complex belt, and the lower-crust was granulitized. Since 160 Ma the northwestern belt has been in a back-arc extensional setting as a consequence of slab roll-back, resulting in the lithosphere thinning and an influx of asthenophere. The upwelling asthenosphere, on the one hand, induced the local lithospheric mantle to melt partially, forming high-Mg potassic magmas, and on the other hand it underwent decompression melting itself to form alkaline diabase magma. Pulsatory injection of such high-temperature magmas into the granulitized crustal source region induced them to partially melt and generate the A-type magmas of the Qianlishan granitic rocks.

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Nicholson, K. N., P. M. Black, P. W. O. Hoskin, and I. E. M. Smith. "Silicic volcanism and back-arc extension related to migration of the Late Cainozoic Australian–Pacific plate boundary." Journal of Volcanology and Geothermal Research 131, no. 3-4 (March 2004): 295–306. http://dx.doi.org/10.1016/s0377-0273(03)00382-2.

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48

Flerit, Frédéric, Rolando Armijo, Geoffrey King, and Bertrand Meyer. "The mechanical interaction between the propagating North Anatolian Fault and the back-arc extension in the Aegean." Earth and Planetary Science Letters 224, no. 3-4 (August 2004): 347–62. http://dx.doi.org/10.1016/j.epsl.2004.05.028.

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49

Zhu, Bei, Zhaojie Guo, Shaonan Zhang, Ingrid Ukstins, Wei Du, and Runchao Liu. "What triggered the early-stage eruption of the Emeishan large igneous province?" GSA Bulletin 131, no. 11-12 (February 28, 2019): 1837–56. http://dx.doi.org/10.1130/b35030.1.

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Abstract The formation of the Emeishan large igneous province is widely regarded as being related to a mantle plume, but plate tectonics may also have played an important role. We analyzed the regional facies architecture of the early-stage subaqueous volcanic rocks of the central Emeishan large igneous province. The results suggest that these rocks were emplaced in a N-S–striking subaqueous rift, which existed immediately before the onset of volcanism and was persistently maintained during the early eruption stage. By linking this conclusion with the background information indicating that (1) the basaltic geochemistry in this section is indicative of a subcontinental lithospheric mantle source rather than a mantle plume source, and (2) the western Yangtze plate, where the Emeishan large igneous province was developed, was located in the back-arc region of the Permian Paleo-Tethys subduction system, we propose a new view that the early-stage eruptions of the Emeishan large igneous province were triggered by back-arc extension. The dominant functioning of the mantle plume occurred shortly after this process and inherited it, as evidenced by the following: (1) The subaqueous volcanic architecture showing back-arc geochemical affinity is laterally restricted in the presumed rift, but the overlying subaerial lavas showing plume-related geochemical features overwhelmingly flooded the whole province; (2) vertically, the source of the basaltic component in these intrarift sequences underwent a gradual transition from lithospheric origin to mantle plume origin along the stratigraphic order, as evidenced by an intercalated basaltic succession showing mixed geochemical features from the two contextual origins.

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Richards, S. W., and W. J. Collins. "Growth of wedge-shaped plutons at the base of active half-grabens." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 95, no. 1-2 (March 2004): 309–17. http://dx.doi.org/10.1017/s0263593300001097.

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ABSTRACTCombined field and geophysical data show that plutons from the Bega Batholith are elongate, meridional, wedge-shaped bodies which intruded during a period of regional east–west extension in the Palaeozoic eastern Lachlan orogen, eastern Australia. Plutons within the core of the batholith have intruded coeval, syn-rift sediments and co-magmatic volcanics. The batholith is bound by high-temperature, dip-slip faults, and contains several major NE-trending transtensional faults which were active during batholith construction. In the central part of the batholith, the Kameruka pluton is an asymmetric, eastward-thickening, wedge-shaped body with the base exposed as the western contact, which is characterised by abundant, shallow-dipping schlieren migmatites which contain recumbent folds and extensional shear bands. A shallow (<30°), east-dipping, primary magmatic layering in the Kameruka pluton steepens progressively westward, where it becomes conformable to the east-dipping basal migmatites. The systematic steepening of the layering is comparable to sedimentary units formed during floor depression in syn-rift settings. The present authors suggest that the wedge-shaped plutons of the Bega Batholith are the deeper, plutonic expression of a hot, active rift. The batholith was fed and sustained by injection of magma through sub-vertical dykes. Displacement along syn-magmatic, NE-trending faults suggests up to 25 km of arc-perpendicular extension during batholith construction. The inferred tectonic setting for batholith emplacement is a continental back-arc, where modern half-extension rates of 20–40 mm yr−1 are not unusual, and are sufficient to emplace the entire batholith in ∼1 Ma. This structural model provides a mechanism for the emplacement of some wedge-shaped plutons and is one solution to the ‘room problem’ of batholith emplace

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