北山野马井地区泥盆纪富钾酸性岩浆岩地球化学特征及其地质意义

为了理清北山南部晚古生代构造演化过程，对野马井地区的二长花岗岩与流纹岩进行了岩石学、全岩主微量元素地球化学、锆石U-Pb年代学及Hf同位素等研究.LA-ICP-MS锆石U-Pb定年结果表明二长花岗岩与流纹岩的就位年龄分别为402.7±2.4 Ma与392.9±2.5 Ma.二者均为富钾钾质岩浆岩，呈现过铝质-强过铝质，轻重稀土弱到中等分馏且相对富集轻稀土，二长花岗岩呈现无或弱的负Eu异常，流纹岩呈现较明显的负Eu异常，二者均富集Rb、Th、U、Pb等，亏损Nb、Ta、Ba、Sr、Ti等，为I型酸性岩浆岩.二长花岗岩与流纹岩的锆石ε_Hf（t）值介于-2.2~+6.8，对应Hf模式年龄（t_DM2）为962~1 533 Ma；指示二者主要由中元古代陆壳物质熔融所形成.依据野马井地区泥盆纪富钾酸性岩浆岩的地球化学特征，结合该区域其他地质资料，可推测其为后碰撞构造环境的产物. 

Geochronology,Petrogenesis and Tectonic Implications of Devonian High-K Acid Magmatic Rocks from Yemajing Area in Beishan Orogen

In order to further clarify the tectonic evolution of the southern Beishan orogen during the Late Paleozoic, a comprehensive study including whole rock geochemistry and zircon U-Pb-Hf isotopes has been carried out on the monzonitic granites and rhyolites collected from the Yemajing area. The results of zircon LA-ICP-MS U-Pb dating for the monzonitic granites and rhyolites are 402.7±2.4 Ma and 392.9±2.5 Ma (206Pb/238U ages) respectively, showing these rocks formed during the Devonian. The monzonitic granites and rhyolites in the research area were characterized by potassic, peraluminous to strongly peraluminous, relatively enriched in LREE and depleted in HREE with weak to moderate fractionation between LREE and HREE. The monzonitic granites display no or small negative Eu anomalies, whereas the rhyolites show more obviously negative Eu anomalies. They exhibit similar geochemical compositions including positive Rb, Th, U and Pb, but negative Nb, Ta, Ba, Sr and Ti anomalies, and belong to I-type granites. The zircon ε_Hf(t) values of the monzonitic granites and rhyalites vary from -2.2 to +6, and the Hf model ages (t_DM2) vary from 962 Ma to 1533 Ma. Consequently, it can be concluded that the potassic igneous rocks from this area were mainly derived from partial melting of the Middle Proterozoic continental crust. Combining with regional geological evidence, we suggest that the monzonitic granites and rhyolites were probably emplaced or erupted in a post-collision extensional setting. This study provides new crucial evidence for understanding the tectonic evolution of the southern CAOB during the Late Paleozoic.