کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
9524454 1635186 2005 18 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Potassic and low- and high-Ti mildly alkaline volcanism in the Neoproterozoic Ramada Plateau, southernmost Brazil
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
پیش نمایش صفحه اول مقاله
Potassic and low- and high-Ti mildly alkaline volcanism in the Neoproterozoic Ramada Plateau, southernmost Brazil
چکیده انگلیسی
Ramada Plateau Neoproterozoic volcanism represents a portion of the shoshonitic and mildly alkaline magmatism related to postcollisional events of the Brasiliano/Pan African cycle of southernmost Brazil. It is constituted by shoshonitic basic-intermediate lavas, followed by a bimodal sequence characterized by pyroclastic deposits, lava flows, and hypabyssal rocks with ages of 549±5 Ma. The shoshonitic magmatism presents greater K2O than Na2O2, K2O/Na2O ratios close to 1, and moderate large ion lithophile and high-field strength element contents. The bimodal basic-acid volcanism presents a transitional chemical affinity with features of sodic, silica-saturated alkaline to continental tholeiitic series. Observed basic and acid rocks with contrasting Ti contents are referred to as high- and low-Ti basalt-rhyolites. Another group of acid rocks with higher Nb, Ta, and Rb values was identified as high-Nb rhyolites. The Ramada Plateau magmatism is comparable to associations related to the final stages of orogenic cycles, in which shoshonitic and high- and low-Ti alkaline magmatism reflects the melting of subduction-modified sources, whereas the high-Nb magmas show less influence of subduction-related metasomatism and are closer to magmas produced from anorogenic sources. A model of magma generation in collisional settings involving slab break-off and asthenospheric upwelling is applied to the evolution of magmatism from subduction-related to anorogenic in the Ramada Plateau.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of South American Earth Sciences - Volume 18, Issues 3–4, March 2005, Pages 237-254
نویسندگان
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