In the Comechingones pegmatitic field, central Argentina, leucogranite and pegmatite bodies crop out in a relatively narrow (25 × 10 km) belt, and were emplaced synkinematically with the main deformational event of the crustal-scale Guacha Corral shear zone during the Early Ordovician (~ 475 Ma). These leucogranites and pegmatites are geochemically evolved rocks with high silica and alkalis, low Fe₂O₃, MgO, TiO₂ and CaO, and high ASI values. The leucogranites display quite variable Sr and Nd isotope compositions (initial ⁸⁷Sr/⁸⁶Sr ratios from 0.7048 to 0.7170, and ε_Nd values from + 2.0 to − 3.1), some of which do not overlap with almost any other pre-Famatinian rock from the Sierras de Córdoba. The major and trace element geochemistry and the particular Sr and Nd isotope compositions of the leucogranites are here explained by the following processes: (1) water-fluxed partial melting of amphibolites at relatively low P–T conditions generating currently unexposed granodioritic melts with unradiogenic ⁸⁷Sr/⁸⁶Sr ratios and radiogenic ε_Nd values; (2) fractionation of mostly plagioclase and monazite leading to compositions close to the leucogranite melts; and (3) assimilation of metasedimentary rocks with crustal isotopic signatures, modelled by assimilation and fractional crystallization processes. The major, trace and isotope compositions of the pegmatites suggest a derivation from partial melting of the same metasedimentary protoliths of the Sierras de Córdoba that were assimilated by leucogranite melts. We propose a feedback relationship among deformation, anatexis, magma evolution and mass transfer in the context of such a crustal-scale shear zone in the foreland of the Famatinian orogen.

在Comechingones的成岩田中，阿根廷中部的白云石和伟晶岩体在相对较窄的（25×10 km）带中生出，并与奥陶纪早期（Australia 〜475 Ma）。这些无色花岗岩和伟晶岩是具有高二氧化硅和碱含量，低Fe ₂ O ₃，MgO，TiO ₂和CaO以及高ASI值的地球化学演化岩石。所述淡色显示相当易变的Sr和Nd同位素组合物（初始⁸⁷ SR / ⁸⁶ Sr比值从0.7048到0.7170，以及ε_的Nd值介于+ 2.0到− 3.1之间），其中有些与塞拉德斯科尔多瓦山脉的法曼蒂纪以前几乎没有任何其他岩石重叠。白云石的主要和微量元素地球化学，以及特定的Sr和Nd同位素组成，可通过以下过程进行解释：（1）在相对较低的P–T条件下，水溶角闪石的部分熔融，生成当前未暴露的具有不放射源的花岗闪长熔体⁸⁷ SR / ⁸⁶ Sr比值和放射性ε_钕价值观 （2）主要是斜长石和独居石的分级分离，导致其组成接近白云石熔体。（3）同化和部分结晶过程模拟了具有地壳同位素特征的准沉积岩的同化。伟晶岩的主要组成，痕量组成和同位素组成表明，部分溶蚀的白云母熔岩吸收了相同的科尔多瓦山脉的沉积沉积原岩。我们提出了在法玛汀造山带前陆的这样一个地壳尺度剪切带的背景下，变形，食盐，岩浆演化和传质之间的反馈关系。