卢氏八宝山花岗斑岩地球化学特征及成因研究  

Geochemistry and petrogenesis of the Babaoshan granite porphyry in Lushi county,Henan Province

作　　者：曾令君[1,2] 周栋[1,2] 星玉才[3] 赵太平[1] 姚军明[1] 包志伟[1] 

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]河南省地矿局第一地质调查院,河南洛阳471023

出　　处：《地球化学》2013年第3期242-261,共20页Geochimica

基　　金：国家重点基础研究发展计划项目(2012CB416602)

摘　　要：河南省卢氏县八宝山岩体位于华北克拉通南缘、东秦岭造山带西段。岩体呈筒状,可能为古火山机构岩颈相的超浅成侵入体。岩体的形成时代为（146±2）Ma（LA-ICPMS锆石U-Pb年龄）。岩体边缘相为钾长花岗斑岩、中心相为黑云母二长花岗斑岩。岩体出现以铁为主的多金属矿化,与区内同时代成矿花岗岩有着显著的差别。岩石SiO2含量较高（64.8%～73.5%）,ACNK值为0.98~1.56,属于准铝质-过铝质钾玄岩系列花岗岩类。轻稀土相对富集（La/Yb）N=2.29～23.8,Eu异常不显著（δEu=0.61~1.39）,Rb、Ba、U和K等元素强烈富集,Sr、Nb、Ti和P等元素显著亏损,属于高分异的I型花岗岩,并且钾长花岗斑岩具有相对较高的演化分异程度。岩体具有较低的Nd（t）初始值（-19.46～-16.4）和较古老的二阶段模式年龄（2.49～2.27 Ga）,与锆石Hf同位素模式年龄一致,表明该岩体的源区物质以壳源物质为主。斑岩体为碰撞后的拉伸环境下地壳物质部分熔融的产物。根据黑云母地质压力计估算,八宝山岩体的的侵位深度为1.89～2.55 km,与该岩体浅成相的地质产状一致,推测其深部可能存在有利于斑岩Cu-Au-Mo-Pb-Zn的多金属成矿区段。The Babaoshan granite porphyries in Lushi county, Henan province, is tectonically located at the southern margin of North China Craton, in the western part of the East Qinling orogen. The granite porphyries occur as circular column which might have been the neck of volcanic edifice. Formed at （146±2） Ma （LA-ICPMS zircon U-Pb）, the intrusion is unique for the associated iron predominated ore deposit with accompanying Cu-Mo-Pb-Zn mineralization, which makes it a meaningful target for metallogenetic investigation in the East Qinling area. The Babaoshan granite intrusion is a zoned granitic stock consisting of syenogranite porphyry in the outer zone and biotite monzogranite porphyry in the inner part. The granite porphyries have high SiO2 （64.8% - 73.5%） contents, with ACNK values varying between 0.98- 1.56. It can be classified as mctaluminous- peraluminous granite. The rocks arc relatively enriched in LILE such as Rb, Ba, U, K and LREE （（La/Yb）N= 2.29 - 23.8）, depleted in Sr, Nb, Ti, and P, with insigni[lcant Eu anomalies. The geochemical characteristics of the Babaoshan granite porphyries suggest a highly fractionated I-type origin, while the syenogranite porphyry is more fractionated. The low εNd（t） （-19.46--16.4） and rather old model ages （Nd TDM2= 2.46 Ga to 2.27 Ga） are consistent with Hf isotopic compositions. It demonstrates that the rocks might have been derived from partial melting of crustal material. It possibly derived from partial melting of the lower crust under extensional tectonic regime following the collision condition. Biotite geobarometer calculations show that the Babaoshan granite porphyries may form at depth of 1.89 km to 2.55 km, which is consistent with the sub-volcanic occurrence. We deduce that there might be an underlying porphyry Cu-Mo-Pb-Zn polymetallic mineralization section at depths.

关 键 词：高分异I型花岗岩 ND同位素 斑岩 八宝山岩体 华北克拉通南缘 

分 类 号：P581[天文地球—岩石学] P597[天文地球—地质学]