【摘要】 桐柏-大别造山带中,面理化(含榴)花岗岩作为榴辉岩的重要围岩之一,仅分布在高压变质单元和超高压变质单元中。对高压变质单元中面理化(含榴)花岗岩进行了元素地球化学研究,结果显示,这类岩石SiO271.96%～77.99%,K2O+Na2O7.59%～8.66%,Al2O311.15%～14.50%,CaO0.10%～0.91%,MgO0.04%～0.73%,Sr27.3～269μg/g,A/CNK0.97～1.10。相对于S型和I型花岗岩,面理化(含榴)花岗岩具有某些A型花岗岩的地球化学特征,如岩石明显富硅、富碱质和富高场强元素(如Zr、Hf、Nb、Ta、Y等),贫Ca、Mg、Al、Sr等元素,高Ga/Al比值;在稀土元素特征方面,大部分样品具有明显的Eu负异常(Eu/Eu0.06～0.60),(La/Yb)N2.34～7.87。在岩石成因类型元素判别图解上,面理化(含榴)花岗岩主要落于A型花岗岩区;构造判别图解和构造学、岩石学特征表明该类花岗岩形成于碰撞后的构造环境。因此,高压变质单元面理化(含榴)花岗岩总体地球化学特征表明它们属于A型花岗岩类,形成于岩石圈伸展的碰撞后构造环境,与大别山超高压/高压变质岩的折返过程存在密切联系。更多还原

【Abstract】 Foliated garnet bearing granites, distributed in the high pressure (HP) unit and ultrahigh pressure (UHP) unit, are one of the major surrounding rocks of the eclogites in the Tongbai Dabie orogenic belt. The geochemicalcharacteristics of the foliated garnet bearing granites in the HP unit are reported in this paper. They have SiO2 71.96%～77.99%, K2O+Na2O 7.59%～8.66%, Al2O3 11.15%～14.50%, CaO 0.10%～0.91%, MgO 0.04%～0.73%,Sr 27.3～269 μg/g and A/CNK 0.97～1.10. They have the geochemical characteristics of A type granites relative to I and S type granites. They are rich in Si, alkali and HFSE (such as Zr, Hf, Nb, Ta, Y) and depleted in Ca, Mg, Aland Sr. They have high Ga/Al ratios. The REE patterns of most samples show obvious negative Eu anomaly with Eu/Eu 0.06～0.60, (La/Yb)N 2.34～7.87. In the discrimi nation diagrams for the petrogenesis interpretation they belong to A type granites. The studies of tectonic interpretation, tectonics and petrology show that they formed in the post COLG environment. The geochemical characteristics as a whole show that they are A type granites and the magma of foliated garnet bearing granites formed in the extensional tectonic setting postdating the HP and UHP metamorphism. The formation of foliated garnet bearing granites is related to the process of the UHP and HP metamorphic rocks exhumation frommantle to middle lower crust.更多还原