桂北猫儿山印支期花岗岩成因:来自岩石学、岩石地球化学、锆石U-Pb年龄和Hf同位素的证据

Genesis of Indosinian granites in Maoershan,northern Guangxi:evidence from petrology,geochemistry,zircon U-Pb ages and Hf isotope

猫儿山印支期花岗岩与钨多金属及花岗岩型铀矿成矿关系密切,本文对其进行了岩石学、地球化学和年代学研究。印支期早阶段花岗岩形成于232～228 Ma,晚阶段形成于224～208 Ma。两阶段花岗岩均高SiO_2(70. 82%～76. 12%)、富Al_2O_3(12. 87%～14. 78%)。早阶段属强过铝花岗岩(A/CNK=1. 40～1. 67),晚阶段为弱铝—强过铝花岗岩(A/CNK=1. 01～1. 28);两阶段花岗岩均富集Rb、Th、U、Zr、Hf等,强烈亏损Ba、Sr、P、Ti等微量元素;稀土总量ΣREE=33. 95×10-6～323. 88×10-6,轻稀土富集(LREE/HREE=2. 60～11. 76),Eu强烈亏损(δEu=0. 11～0. 40),具弱的稀土四分组效应(TE1,3=1. 00～1. 16)。晚阶段花岗岩具有较高的εHf(t)值(-4. 88～-8. 91),且含有少量镁铁质微粒包体,暗示其形成过程中发生轻度的岩浆混合作用。综合判断:猫儿山印支期花岗岩形成与印支造山运动后的岩石圈伸展有关,源区为中元古代地壳物质的部分熔融,而晚阶段花岗岩中混入了少量地幔物质。

The tungsten polymetalic and granite type uranium deposit from Maoershan area are mainly related to the Indosinian granites.This thesis carried out a detailed petrology,gepchemistry characteristics and zircon U-Pb dating on the Indosinian granites.Early granite formed in 232-228 Ma and the late in 224-208 Ma.Tow stages granites show the feature of high of SiO 2(70.82%-76.12%)and Al 2O 3(12.87%-14.78%).The early stage granite belongs to strongly peraluminous,A/CNK range from 1.40-1.67.However,the late stage granite belongs to weakly peraluminous-strongly peraluminous,A/CNK range from 1.01to1.28.Tow stages granites are both characterized by enrichment of Rb,Th,U,Zr and Hf,severe depletion of Ba,Sr,P,Ti and Eu.TheΣREE has a range of 33.95×10-6-323.88×10-6,slight enrichment of LREE(LREE/HREE=2.60-11.76),strong depletion of Eu(δEu=0.11-0.40),and weak tetrad of rare earth elements pattern(TE 1,3=1.00-1.16).The late granite has a relatively high value ofεHf(t)(-4.88 to-8.91)and contains a small amount of mafic microgranular enclaves,indicating the occurrence of magma mixed in the formation of late granite.It is considered that the Indosinian granites from Maoershan were related to the lithospheric extension after the Indosinian Orogenesis,and formed from partial melting of the Mesoproter-ozoic crust material,and a small amount of mantle material was added to the late granites.