山阳色河花岗岩地球化学特征和锆石SHRIMP U Pb年代学

山阳色河二长花岗岩出露于泥盆纪地层中,并与泥盆纪地层呈断层接触关系.花岗岩主要由钾长石、斜长石和石英组成,其SiO_2含量介于71%～77%之间、高碱(K_2O+Na_2O＝7.43%～8.50%),低CaO(0.25%～2.81%),为高钾钙碱性花岗岩,A/CNK的平均值为<1.05,属弱过铝质岩石;较强的轻、重稀土元素分馏程度(La/Yb)_N=4.23],明显的Eu负异常(δEu＝0.511),富集Rb、Th、K、La和Cs等大离子亲石元素,亏损Ba、Nb、Sr、P和Ti元素为特征,属后碰撞花岗岩类.在泥盆纪地层中的花岗岩砾石的岩石地球化学与色河二长花岗岩具有形似性质,高精度的锆石SHRIMPⅡU-Pb定年获得花岗岩与花岗岩砾石形成时代相一致,分别为709±5Ma和700±11Ma.山阳后碰撞花岗岩的发现,标志着新元古代在东秦岭地区表现为造山后伸展拉张阶段,从而为东秦岭造山带从元古代到古生代的构造体制转换提供证据.

Geochemical Charactericstic and Zircon SHRIMP U-Pb Dating of Sehe Granite in Shanyang County,Shanxi Province and Its Geological Significance

The Sehe monzonitic granite crops out in the Devonian, and is of fault contact to the late Devonian. The granite is composed mainly of potassium feldspars, plagioclases and quartzs. Its high SiO_2(71%～77%) and alkali content (K_2O+Na_2O＝7.43%～8.50%) and low CaO content (0.25%～2.81%) suggests that it belongs to weakly peraluminous (A/CNK<1.05). A high LREE and HREE fractionation (La/Yb)_N=4.23], distinct Eu negative anomaly (δEu＝0.511), enrichment in large ion lithophile elements Rb, Th, K, La and Cs, and depletion in Ba, Nb, Sr, P and Ti, all indicate the feature of post-collisional granite. The geochemical signature of granite gravel in Late Devonian is similar to that of the Sehe granite. The SHRIMP dating results of granite and granite gravels are similar (709±5Ma and 700±11Ma). The discovery of Neoproterozoic post-collision granite in East Qinling indicates a post-orogenic extensional setting in the East Qinling area, thus providing evidence for the tectonic system transition from protozoic to paleozoic in the East Qinling orogenic belt.