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Joaquin Bastias Mauricio Calderón Lea Israel Francisco Hervé Richard Spikings Robert Pankhurst 《International Geology Review》2020,62(11):1467-1484
ABSTRACT This paper addresses the Jurassic–Cretaceous stratigraphic evolution of fore-arc deposits exposed along the west coast of the northern Antarctic Peninsula. In the South Shetland Islands, Upper Jurassic deep-marine sediments are uncomformably overlain by a Lower Cretaceous volcaniclastic sequence that crops out on Livingston, Snow and Low islands. U-Pb zircon ages are presented for the upper Anchorage Formation (153.1 ± 1.7 Ma) and the Cape Wallace granodiorite of Low Island (137.1 ± 1.7 Ma) as well as 40Ar/39Ar ages of 136–139 Ma for Low Island andesites. Data are also presented for a U-Pb age of 109.0 ± 1.4 Ma for the upper volcanic succession of Snow Island. In combination with published stratigraphy, these data provide a refined chrono- and litho-stratigraphic framework for the deposits herein referred to as the Byers Basin. Tentative correlation is explored with previously described deposits on Adelaide and Alexander islands, which could suggest further continuation of the Byers Basin towards the south. We also discuss possible correlation of the Byers Basin with the Larsen Basin, a sequence that shows the evolution of foreland to back-arc deposits more or less contemporaneously with the fore-arc to intra-arc evolution of the Byers Basin. 相似文献
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Reiser Martin Kaspar Schuster Ralf Spikings Richard Tropper Peter Fügenschuh Bernhard 《International Journal of Earth Sciences》2017,106(2):659-685
International Journal of Earth Sciences - New Ar–Ar muscovite and Rb–Sr biotite age data in combination with structural analyses from the Apuseni Mountains provide new constraints on... 相似文献
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R. A. Spikings D. A. Foster B. P. Kohn P. B. O'Sullivan 《Australian Journal of Earth Sciences》2013,60(1):9-24
Carboniferous‐Permian volcanic complexes and isolated patches of Upper Jurassic — Lower Cretaceous sedimentary units provide a means to qualitatively assess the exhumation history of the Georgetown Inlier since ca 350 Ma. However, it is difficult to quantify its exhumation and tectonic history for earlier times. Thermochronological methods provide a means for assessing this problem. Biotite and alkali feldspar 40Ar/39Ar and apatite fission track data from the inlier record a protracted and non‐linear cooling history since ca 750 Ma. 40Ar/39Ar ages vary from 380 to 735 Ma, apatite fission track ages vary between 132 and 258 Ma and mean track lengths vary between 10.89 and 13.11 μm. These results record up to four periods of localised accelerated cooling within the temperature range of ～320–60°C and up to ～14 km of crustal exhumation in parts of the inlier since the Neoproterozoic, depending on how the geotherm varied with time. Accelerated cooling and exhumation rates (0.19–0.05 km/106 years) are observed to have occurred during the Devonian, late Carboniferous‐Permian and mid‐Cretaceous — Holocene periods. A more poorly defined Neoproterozoic cooling event was possibly a response to the separation of Laurentia and Gondwana. The inlier may also have been reactivated in response to Delamerian‐age orogenesis. The Late Palaeozoic events were associated with tectonic accretion of terranes east of the Proterozoic basement. Post mid‐Cretaceous exhumation may be a far‐field response to extensional tectonism at the southern and eastern margins of the Australian plate. The spatial variation in data from the present‐day erosion surface suggests small‐scale fault‐bounded blocks experienced variable cooling histories. This is attributed to vertical displacement of up to ～2 km on faults, including sections of the Delaney Fault, during Late Palaeozoic and mid‐Cretaceous times. 相似文献
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Cristian Vallejo Richard A. Spikings Leonard Luzieux Wilfried Winkler David Chew Laurence Page 《地学学报》2006,18(4):264-269
The determination of accurate and precise ages for the timing of collision between oceanic plateaus and continental crust requires an understanding of how the indenting and buttressing plates respond to the collision. We present geochronological, thermochronological, geochemical and isotopic analyses of magmatic rocks from the Ecuadorian Andes, which relate to the collision of the Late Cretaceous Caribbean Plateau and Great Arc sequence with NW South America. The cessation of subduction magmatism during 65–64 Ma beneath the eastern edge of Caribbean Plateau was synchronous with accelerated surface uplift and exhumation within the buttressing continental margin during 75–65 Ma. We interpret this as the collision of the leading edge of the Caribbean Plateau and arc sequence with the South American Plate at 75–65 Ma. A U/Pb (zircon) SHRIMP age of 87.10 ± 1.66 (2σ) Ma, yielded by an accreted fragment of the plateau, precludes previous estimates of collision at 85–80 Ma if the plateau erupted above the Galápagos hotspot. Terra Nova, 18, 264–269, 2006 相似文献
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The western cordilleras of the Northern Andes (north of 5°S) are constructed from allochthonous terranes floored by oceanic crust. We present 40Ar/39Ar and fission-track data from the Cordillera Occidental and Amotape Complex of Ecuador that probably constrain the time of terrane collision and post-accretionary tectonism in the western Andes. The data record cooling rates of 80–2 °C/my from temperatures of 540 °C, during 85 to 60 Ma, in a highly tectonised mélange (Pujilí unit) at the continent–ocean suture and in the northern Amotape Complex. The rates were highest during 85–80 Ma and decelerated towards 60 Ma. Cooling was a consequence of exhumation of the continental margin, which probably occurred in response to the accretion of the presently juxtaposing Pallatanga Terrane. The northern Amotape Complex and the Pujilí unit may have formed part of a single, regional scale, tectonic mélange that started to develop at ~85 Ma, part of which currently comprises the basement of the Interandean Depression. Cooling and rotation in the allochthonous, continental, Amotape Complex and along parts of the continent–ocean suture during 43–29 Ma, record the second accretionary phase, during which the Macuchi Island Arc system collided with the Pallatanga Terrane. Distinct periods of regional scale cooling in the Cordillera Occidental at 13 and 9 Ma were synchronous with exhumation in the Cordillera Real and were probably driven by the collision of the Carnegie Ridge with the Ecuador Trench. Finally, late Miocene–Pliocene reactivation of the Chimbo–Toachi Shear Zone was coincident with the formation of the oldest basins in the Interandean Depression and probably formed part of a transcurrent or thrust system that was responsible for the inception and subsequent growth of the valley since 6 Ma. 相似文献
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Ronner Bendezú Laurence Page Richard Spikings Zoltan Pecskay Lluís Fontboté 《Mineralium Deposita》2008,43(7):777-789
We present 40Ar/39Ar data acquired by infra-red (CO2) laser step-heating of alunite crystals from the large Miocene Colquijirca district in central Peru. Combined with previously
published data, our results show that a long (at least 1.3 My) and complex period of magmatic-hydrothermal activity associated
with epithermal Au–(Ag) mineralization and base metal, Cordilleran ores took place at Colquijirca. The new data indicate that
incursion of magmatic SO2-bearing vapor into the Colquijirca epithermal system began at least as early as ∼11.9 Ma and lasted until ∼10.6 Ma. Four
alunite samples associated with high-sulfidation epithermal Au–(Ag) ore gave 40Ar/39Ar plateau ages between ∼11.9 and ∼11.1 Ma (compared to the previously documented ∼11.6 to ∼11.3 Ma). By combining individually
these new ages with crosscutting relationships, the duration of the Au–(Ag) deposition period can be estimated to at least
0.4 My. Three new 40Ar/39Ar plateau ages on alunite associated with the base-metal Cordilleran ores are consistent with previously obtained ages, all
of them between 10.83 ± 0.06 and 10.56 ± 0.06 Ma, suggesting that most of the sulfide-rich polymetallic deposits of Smelter
and Colquijirca formed during this short period. The recognition of consecutive alunite-bearing and alunite-free mineral assemblages
within both the Au–(Ag) and the base-metal Cordilleran ores may suggest that SO2-bearing magmatic vapor entered the epithermal environment as multiple discontinuous pulses, a number of which was not necessarily
associated in time with ore fluids. It is likely that a period of SO2-bearing vapor degassing longer than 11.9 to 10.6 Ma may be recognized with further more detailed work.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Hydrothermal iron ores at Divri?i, east Central Anatolia, are contained in two orebodies, the magnetite-rich A-kafa and the limonitic B-kafa (resources of 133.8 Mt with 56% Fe and 0.5% Cu). The magnetite ores are hosted in serpentinites of the Divri?i ophiolite at the contact with plutons of the Murmano complex. Hydrothermal biotite from the Divri?i A-kafa yield identical weighted mean plateau ages of 73.75?±?0.62 and 74.34?±?0.83 Ma (2σ). This biotite represents a late alteration phase, and its age is a minimum age for the magnetite ore. Similar magnetite ores occur at Hasançelebi and Karakuz, south of Divri?i. There, the iron ores are hosted in volcanic or subvolcanic rocks, respectively, and are associated with a voluminous scapolite ± amphibole ± biotite alteration. At Hasançelebi, biotite is intergrown with parts of the magnetite, and both minerals formed coevally. The weighted mean plateau ages of hydrothermal biotite of 73.43?±?0.41 and 74.92?±?0.39 Ma (2σ), therefore, represent mineralization ages. Hydrothermal biotite from a vein cutting the scapolitized host rocks south of the Hasançelebi prospect has a weighted mean plateau age of 73.12?±?0.75 Ma (2σ). This age, together with the two biotite ages from the Hasançelebi ores, constrains the minimum age of the volcanic host rocks, syenitic porphyry dikes therein, and the scapolite alteration affecting both rock types. Pyrite and calcite also represent late hydrothermal stages in all of these magnetite deposits. The sulfur isotope composition of pyrite between 11.5 and 17.4‰ δ34S(VCDT) points towards a non-magmatic sulfur source of probably evaporitic origin. Calcite from the Divri?i deposit has δ18O(VSMOV) values between +15.1 and +26.5‰ and δ13C(VPDB) values between ?2.5 and +2.0‰, which are compatible with an involvement of modified marine evaporitic fluids during the late hydrothermal stages, assuming calcite formation temperatures of about 300°C. The presence of evaporite-derived brines also during the early stages is corroborated by the pre-magnetite scapolite alteration at Divri?i, and Hasançelebi-Karakuz, and with paleogeographic and paleoclimatic reconstructions. The data are compatible with a previously proposed genetic model for the Divri?i deposit in which hydrothermal fluids leach and redistribute iron from ophiolitic rocks concomitant with the cooling of the nearby plutons. 相似文献
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D. Koehn K. Link T. Sachau C. W. Passchier K. Aanyu A. Spikings R. Harbinson 《International Journal of Earth Sciences》2016,105(6):1693-1705
This contribution discusses the development of the Palaeoproterozoic Buganda-Toro belt in the Rwenzori Mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori Mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south, the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal-scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori Mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal-scale nappe, whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle reverse faulting. The Palaeoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori Mountains are situated and where the Lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development within the Rwenzori Mountains and that this stiff belt may form part of the reason why the Rwenzori Mountains are relatively high within the rift. 相似文献