摘要:
黄陵岩基A型花岗岩为钾长-二长花岗岩,为准铝质、富SiO2、高碱、低CaO和MgO、高FeO*/MgO;明显亏损Ba、Sr、P、Ti、Eu,富Nb、Th、Zr、Y等高场强元素,Ga/Al比值高。这些特征与该区I型花岗岩有明显的区别,是一种典型的A2型花岗岩。黄陵岩基A型花岗岩形成时代为800~770M a,表明扬子地块北缘在新元古代处于拉张阶段,可能与Rodinia超大陆的裂解背景有关。
Abstract:
The A-type granites were discovered for the first time from the Huangling granite batholith in western Hubei. This kind of granites consisting of K-feldspar and monzonitic granites is characterized by metaluminous rocks (A/CNK=0.95 -1.09), high SiO2(72.64%-75.64%), high alkali (K2O + Na2O ranging between 8.23% and 8.46%), low CaO and MgO contents, and high FeO*/MgO ratios (12.49 -23.07), depletion of the elements Ba, Sr, P, Ti and Eu, enrichment of the high field strength elements Nb, Th, Zr and Y, and higher Ga/Al ratios, implying that the granites in the study area are typical of A2 granites differing greatly from the I-type granites. The ages of 800 -770 Ma for the A-type granites from the Huangling granite batholith indicate that the northern margin of the Yangtze landmass was in the extension phases during the Neoproterozoic, and may be related with the breakup of the suppercontinent Rodinia.
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