The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform
James K. Mortensen - One of the best experts on this subject based on the ideXlab platform.
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Pre‐Mid‐Mesozoic tectonic evolution of the Yukon‐Tanana Terrane, Yukon and Alaska
Tectonics, 1992Co-Authors: James K. MortensenAbstract:Yukon-Tanana Terrane (YTT) underlies much of central and western Yukon and east central Alaska. Its history and tectonic evolution, particularly prior to mid-Mesozoic Time, has been largely obscured by younger magmatism and tectonism. The application of geochronological and isotopic techniques over the past decade, together with detailed field studies in certain critical areas of the terrane, has shed new light on the early history of YTT. Much of YTT is a product of episodic continental arc magmatism, with three main pulses in Late Devonian-Early Mississippian, mid-Permian, and Late Triassic-Early Jurassic Time. From Late Devonian to mid-Mississippian Time, subduction was north or northeast dipping, but arc polarity was apparently reversed by mid-Permian Time. The main, subhorizontal structural fabric characterizing much of YTT was produced between mid-Permian Time and the onset of renewed magmatism in Late Triassic Time and probably reflects a major continent-continent collision. Although the Triassic-Jurassic magmatism is also considered to be arc related, it occurred over a very broad area of not only YTT, but also Quesnellia, and the Stikine, Nisling, Cache Creek, and Slide Mountain terranes. This magmatism appears to have coincided with final amalgamation of the Intermontane Superterrane, and the arc polarity and the position and orientation of the associated subduction zone is still controversial. Available evidence suggests that Nisling Terrane is closely related to YTT and mainly consists of older strata that underlie the Devonian and younger units generally considered to be more typical of YTT. There are close similarities between YTT and a number of other “pericratonic” terranes in the central and eastern parts of the Cordillera, and it is likely that these terranes originally formed a single arc and arc basement assemblage which has now been fragmented and dispersed by transcurrent faulting.
Stefan Piasecki - One of the best experts on this subject based on the ideXlab platform.
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hot acidic late Permian seas stifle life in record Time
Earth and Planetary Science Letters, 2011Co-Authors: Svetoslav V Georgiev, Holly J Stein, Judith L Hannah, Bernard Bingen, Hermann M Weiss, Stefan PiaseckiAbstract:Abstract The end of Permian Time (252–251 Ma) hosts the largest mass extinction in Earth history, yet events heralding this global catastrophe remain intensely disputed. We present a chemostratigraphic marker, the 187Re/188Os ratio, which soars to unprecedented levels approaching the Permo-Triassic boundary. These ratios are tied to profound trace element changes and a precise Re–Os Time record at 252 Ma preserved in black shales from East Greenland and the mid-Norwegian shelf. Within a 36-meter shale section, an 80-fold increase in Re concentrations (two-fold for Os) signals seawater conditions that became increasingly inhospitable to life. Unwavering initial 187Os/188Os ratios of 0.6 preclude mafic volcanism and meteorite impact as the direct cause of Late Permian anoxia. We argue that extraordinarily high 187Re/188Os ratios are the hallmark of simultaneously rising ocean temperature and acidity, leading to loss of oxygen and the stifling of life in latest Permian Time.
Michel Laurin - One of the best experts on this subject based on the ideXlab platform.
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The reptile Macroleter: First vertebrate evidence for correlation of Upper Permian continental strata of North America and Russia
Geological Society of America Bulletin, 2001Co-Authors: Robert R. Reisz, Michel LaurinAbstract:The spectacular evolutionary history of terrestrial vertebrates is uncharacteristically poorly documented between the Paleozoic subequatorial exposures of the Permo–Carboniferous of North America and Europe, and the much higher latitude, Upper Permian deposits of central Russia and southern Africa. We report here that the discovery of the reptile Macroleter in Oklahoma provides the first direct vertebrate evidence of biochronological correlation between continental sediments from the Upper Permian of North America and Russia. The presence of the reptile Macroleter, a member of a major group of Upper Permian amniotes known previously only from central Russia, in North America improves dramatically our understanding of this early phase of amniote evolution, and also provides evidence of terrestrial tetrapod faunal interchange between North America and Russia in Late Permian Time.
Akira Ishiwatari - One of the best experts on this subject based on the ideXlab platform.
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Petrogenesis of greenstones from the Mino–Tamba belt, SW Japan: Evidence for an accreted Permian oceanic plateau
Lithos, 2020Co-Authors: Yuji Ichiyama, Akira Ishiwatari, Kazuto KoizumiAbstract:Abstract Permian greenstones in the Jurassic Mino–Tamba accretionary complex, southwest Japan, are divided into three distinct series on the basis of their geological occurrence, mineralogy, and geochemistry. A low-Ti series (LTS) is associated with Lower Permian chert and limestone, and is the most voluminous of the three series. The LTS shows slightly more enriched geochemical and isotopic characteristics than MORB. A transition series (TS) is mainly associated with Lower Permian chert, and has more enriched geochemical signatures than MORB. Its isotopic characteristics are divided into enriched and depleted types. A high-Ti series (HTS) occurs as sills and hyaloclastites within Middle Permian chert and as dikes intruding the TS. Some HTS rocks have high MgO contents. The HTS is characterized by enrichment in incompatible trace elements and an isotopic composition comparable to HIMU-type basalt. The geochemistry of the voluminous LTS is similar to that of the oceanic basalt series of the Kerguelen plateau, suggesting production by partial melting of a shallow mantle plume head below thick oceanic lithosphere in Early Permian Time. We infer that the TS formed simultaneously at the margins of the mantle plume head. In contrast, the HTS may have resulted from partial melting of a deep mantle plume tail in Middle Permian Time. Permian greenstones in the Mino–Tamba belt may have thus formed by superplume activity in an intra-oceanic setting. Given the presence of two known contemporary continental flood basalt provinces (Siberia and Emeishan) and some accreted oceanic plateau basalts, the vast magmatism of the Mino–Tamba oceanic plateau suggests a large-scale superplume pulse in Permian Time. Accretion of oceanic plateaux may have played an important role in the growth of continental margins and island arcs in Japan and elsewhere in the circum-Pacific region.
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HFSE-rich picritic rocks from the Mino accretionary complex, southwestern Japan
Contributions to Mineralogy and Petrology, 2005Co-Authors: Yuji Ichiyama, Akira IshiwatariAbstract:Sills, pillow lavas and hyaloclastites of the HFSE-rich picrite and related rocks (ankaramite and basanite) occur in the Middle Permian cherts in the Mino Jurassic accretionary complex, southwestern Japan. These rocks show systematic trace element patterns enriched in incompatible elements, which indicate that the associated ankaramite and basanite are formed by the crystal fractionation from the picrite. The presence of the hyaloclastite in the chert sequence covering a large tholeiitic greenstone body indicates that the picrite was produced in an intraoceanic setting in the Middle Permian Time subsequent to the extrusion of the voluminous oceanic island tholeiite. The Mino picrites resemble the Siberian meimechite and Polynesian picrites in its HFSE-rich chemical composition. The HFSE enrichment in these picrites cannot be explained by low degree of partial melting of primitive peridotite mantle only, and needs a source material involving recycled oceanic crust (eclogite). The differences in MgO content and in TiO_2/Al_2O_3 and Zr/Y ratios among the HFSE-rich picrites indicate that the melting pressure increases from the Polynesian picrite through Mino picrite to Siberian picrite. This may reflect the increasing thickness of the overlying lithosphere at the Time and place of magmatism. The HFSE-rich picrites may be a product of a superplume event. The presence of HFSE-rich picrite in Mino and Siberia indicate that the superplume activities occur in both continental and oceanic settings in the Permian Time.
Anna Vozarova - One of the best experts on this subject based on the ideXlab platform.
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late carboniferous to early Permian Time interval in the western carpathians northern tethys margin
Geodiversitas, 1998Co-Authors: Anna VozarovaAbstract:Carboniferous to Permian basins reflected compression regime of the Variscan orogeny during the continent-continent collision in final stages. The fragments of these microplates are preserved in the Alpine Western Carpathians basement (CWCZ, NGZ vers. IWCZ). On the basis of sedimentary sequence analysis two zones of continental collision differing in Time were established: (1) internal with termination of collision during Bretonian pre-Sudetian) events, resulting in the syn-collision Tournaisian-Visean flysch; (2) external with termination of collision during pre-Asturian events, comprising the Bashkirian, and in the innermost part of the Western Carpathians (Bukk Mountains in the northern part of Hungary) partly even the Early Moscovian flysch sequences.