The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid-Ordovician continental arc on the Gondwana margin
The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid-Ordovician continental arc on the Gondwana margin
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潘皮纳斯山脉中部的法马提尼岩浆弧：冈瓦纳大陆边缘的早奥陶世至中奥陶世大陆弧
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发表时间：
1998
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通讯作者：
C. Fanning
中科院分区：
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作者：
R. Pankhurst;C. Rapela;J. Saavedra;E. Baldo;J. Dahlquist;I. Pascua;C. Fanning
摘要对中Sierras Pampeanas进行了一项新的多学科研究，包括野外工作、岩相学、变质和显微构造分析、地球化学和地质年代学。残留的低至中等品位变质沉积序列，也出现在Sierras de科尔多瓦东部，被认为是区域等同于Puncoviscana组; a？中寒武世Rb-Sr全岩等时线（513 ± 31 Ma）可能确定了其主要变质作用的年代。Los Llanos-Ulapes岩基的主要花岗岩类构成了一个代表Famatinian俯冲相关岩浆弧的钙碱性套件。岩基的主要花岗闪长岩阶段与S2组构和剪切带形成有关，并在变质沉积物的变形历史中晚些时候侵位。常规和SHRIMP锆石U-Pb定年结果为490 ± 5 Ma。较年轻的二长花岗岩给出了470-450 Ma的Rb-Sr全岩年龄，这是法马蒂纳山脉花岗岩的典型年龄，但与主要花岗闪长岩套的地球化学连续性提高了这些年龄部分重置的可能性。一个小的堇青石花岗岩相是由于当地的热所造成的花岗闪长岩深熔。Los Llanos-Ulapes岩基的所有钙碱性岩石都具有高的初始87 Sr/86 Sr（0.7075-0.7105）和低的δ Ndt（-4.6至-6.3），继承自下地壳。Sm-Nd模式年龄为1600-1700 Ma，表明下伏地壳与东部前陆下地壳一致。因此，这部分的法马提安弧是一个大陆岩浆弧，并在奥陶纪中期的异地前Cordillera Aparthae到达之前建立。
Abstract A new multi-disciplinary study of the central Sierras Pampeanas encompasses fieldwork, petrography, metamorphic and micro-structural analysis, geochemistry and geochronology. Remnants of a low-to-medium grade metasedimentary sequence, which also occurs in the Sierras de Córdoba to the east, are considered regionally equivalent to the Puncoviscana Formation; a ?mid-Cambrian Rb-Sr whole-rock isochron of 513 ± 31 Ma probably dates their main metamorphism. The predominant granitoids of the Los Llanos-Ulapes batholith constitute a calc-alkaline suite representative of the Famatinian subduction-related magmatic arc. The main granodiorite phase of the batholith is associated with an S2 fabric and shear zone formation, and was emplaced late during the deformational history of the metasediments. Conventional and SHRIMP U-Pb zircon dating yielded a combined age of 490 ± 5 Ma. Younger monzogranites gave Rb-Sr whole-rock ages of 470–450 Ma, typical of granites in the Sierra de Famatina, but geochemical continuity with the main granodiorite suite raises the possibility that these are partially reset ages. A minor cordierite granite phase is ascribed to local anatexis caused by heat from the granodiorites. All the calc-alkaline rocks of the Los Llanos-Ulapes batholith have high initial 87Sr/86Sr (0.7075–0.7105) and low ɛNdt (−4.6 to −6.3), inherited from lower crust. Sm-Nd model ages of 1600–1700 Ma indicate that the underlying crust is identical to that beneath the foreland to the east. This part of the Famatinian arc was thus a continental magmatic arc and was established significantly before the arrival of the allochthonous Precordillera terrane in mid-Ordovician times.