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首页> 外文期刊>Neues Jahrbuch fur Geologie und Palaontologie. Abhandlungen >Petrographical and geochemical features of the granite-pegmatite transition in the Velasco Pegmatitic District, NW Argentina
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Petrographical and geochemical features of the granite-pegmatite transition in the Velasco Pegmatitic District, NW Argentina

机译：阿根廷西北部Velasco Pegmatitic区花岗岩-伟晶岩转变的岩石学和地球化学特征

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摘要

The Carboniferous post-orogenic Huaco and Sanagasta granites are located in the central sector of the Velasco Range, northwestern Argentina, and host rare-element (Be) pegmatites. They are highly fractionated peraluminous granites with porphyritic textures having variable sizes and abundances of K-feldspar megacrysts. Two different types of parental granites are recognized: a Regional Porphyritic Granite (RPG), distant from the Be-pegmatites, and an Adjacent Porphyritic Granite (APG) surrounding the Be-pegmatites. At the pegmatite margins, aplites (MA), or more rarely equigranular leucogranites, are in contact with the APG. The granite-to-pegmatite transition is characterized by a decreasing biotite/muscovite ratio and TiO_2-Fe_2O_3~t-MgO contents,which is consistent with fractional crystallization of biotite, and also by decreasing megacryst and grain size. A continuous magmatic crystallization trend from the RPG to the APG is observed,whereas the MA constitutes the earliest stage of pegmatite formation, characterized by depletion in ferro-magnesian elements, calcium and some trace elements (Ba, Sr, Y, Nb, Ce, Zr, Th). However, the granite-pegmatite evolution occurred by differentiation from a common magma source.
机译：石炭纪的造山后的Huaco和Sanagasta花岗岩位于阿根廷西北部的Velasco Range的中部，并拥有稀有（Be）伟晶岩。它们是高分馏的具有斑状质地的高铝质花岗岩，具有可变的大小和丰富的钾长石巨晶。可以识别两种不同类型的母体花岗岩：远离Be岩质岩的区域性斑岩质花岗岩（RPG）和围绕Be岩质岩的相邻斑岩质花岗岩（APG）。在伟晶岩边缘，APG接触到了斑状（MA）或更稀少的等粒白云母。花岗岩向成辉岩转变的特征是黑云母/白云母比例降低，TiO_2-Fe_2O_3〜t-MgO含量降低，这与黑云母的分级结晶相一致，同时巨晶和晶粒尺寸减小。从RPG到APG都有连续的岩浆结晶趋势，而MA则是伟晶岩形成的最早阶段，其特征是铁镁元素，钙和一些微量元素（Ba，Sr，Y，Nb，Ce， Zr，Th）。然而，花岗岩-斜辉岩的演化是通过与普通岩浆源的区分而发生的。

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