Provenance studies of very low- to low-grade metasedimentary rocks of the Puncoviscana complex, northwest Argentina
Udo Zimmermann, 2005. "Provenance studies of very low- to low-grade metasedimentary rocks of the Puncoviscana complex, northwest Argentina", Terrane Processes at the Margins of Gondwana, A. P. M. Vaughan, P. T. Leat, R. J. Pankhurst
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A provenance study of Neoproterozoic to Lower Cambrian rocks for the entire Puncoviscana Basin was conducted, using 119 samples from 15 different outcrops. Pétrographie data (Qt60–80, F15–35, L5–20, P/F 0.2–0.4, Lv/L = 0) show a composition comparable to foreland-basin successions. Lithoclasts are of metamorphic and metasedimentary origin. Volcanic debris is detected only in the form of sanidine, and volcanic lithoclasts were probably decomposed to form pseudo-matrix. Framework clasts are sub-angular to sub-rounded, and the rocks are poorly sorted. Major element geochemistry shows a moderate to high Chemical Index of Alteration (56–77) and failed to provide coherent provenance and rock classification. Trace element geochemistry suggests a rhyo-dacitic composition overall. Rare earth element patterns are comparable to those of model upper continental crust (UCC), as are concentrations of Nb, Ta, Ti, Th-Sc and Eu/Eu* (0.45–0.87; 95% between 0.4 and 0.7); reworking signatures are not detected. The uniform mineralogical and geochemical composition reflects supra-crustal source(s) for the entire basin, including significant metamorphic rock debris. The Puncoviscana complex is interpreted as a peripheral Pampean foreland basin, fed mainly from an eastern fold-thrust belt, but includes relicts of pre- and syn-collisional magmatic activity as well. A source area of UCC composition to the west is represented by the Arequipa block.
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Terrane Processes at the Margins of Gondwana
The Australide orogen, the southern hemisphere Neoproterozoic to Mesozoic terrane accretionary orogen that forms the palaeo-Pacific margin of Gondwana, is one of the largest and longest-lived orogens on Earth. This book brings together a series of reviews and multidisciplinary research papers that comprehensively cover the Australides from the Tasman orogen of eastern Australia to the Neoproterozoic and Palaeozoic orogens of South America, taking in New Zealand and Antarctica along the way. It deals with the evolution of the southern Gondwana margin, as it grew during a series of terrane accretion episodes from the late Proterozoic through to final fragmentation in mid-Cretaceous times. Global perspectives are given by comparison with the Palaeozoic northern Gondwana margin and documentation of world-wide terrane accretion episodes in the Late Triassic-Early Jurassic and mid-Cretaceous. The Tasmanides of eastern Australia, and the terrane histories of New Zealand and souther South America are given comprehensive up-to-date reviews.