摘要
马关老君山花岗岩体位于滇东南-桂西锡钨多金属成矿带上。为了限定马关地区晚中生代岩浆事件的准确时间,本文对老君山花岗岩体进行了LA-ICP-MS锆石U-Pb定年和地球化学研究。对第一期花岗岩的定年结果为96±2Ma,表明老君山花岗岩应为晚白垩世,与华南西部晚白垩世成岩-成矿事件耦合。老君山花岗岩具有中等SiO2(69.6%～73.6%),高碱(K2O+Na2O=6.56%～8.66%),高钾(K2O>Na2O),强过铝质(A/CNK>1.1)的特征。较低的Sr(<50×10-6),较高的Rb(>270×10-6),低Na2O、CaO,以及P2O5、Y与Rb的演化趋势表明其应为分异的S型花岗岩。低CaO/Na2O值(<0.3),高Rb/Sr、Rb/Ba值的特征表明其源岩为富粘土泥质岩石。结合区域构造背景,老君山花岗岩应与滇东南-桂西晚白垩世成岩-成矿事件形成于同一动力学背景下,即华南西部晚白垩世岩石圈伸展作用。通过对区域地球化学资料和成矿地质背景的分析,围绕岩体(和隐伏岩体)的内外接触带及盖层内受伸展构造控制的断层系统是区域上的重点找矿方向。
The Maguan Laojunshan granites are located in the Sn-W metallogenic belt trending from southeastern Yunnan Province to western Guangxi Province.To limit the precise age of the Late Mesozoic magmatic mineralization in the Maguan area,the Laojunshan granites have been analyzed using LA-ICP-MS zircon U-Pb techniques and geochemical methods,producing an age of 96 2Ma for the early stage.This suggests a late Cretaceous age for the Laojunshan granite,coupled with Late Cretaceous diagenesis-mineralization in western South China.The Laojunshan granites are geochemcially characterized by medium content of SiO2（69.6% ~ 73.6%）,high alkali（K2O＋Na2O=6.56%~8.66%）,high-K（K2ONa2O）,and peraluminous ratio（A/CNK1.1）.Low contents of Na2O,CaO and Sr（50×10-6）,high abundances of Rb（270×10-6）,and P2O5-Rb and Y-Rb change trends indicate that the Laojunshan granites are fractioned S-type granites.Low CaO/Na2O ratios（0.3）,high Rb/Sr and Rb/Ba ratios suggest a plagioclase-poor,clay-rich pelites source.Combined with regional tectonic setting,the Laojunshan granites formed at the same geodynamic setting as the Late Cretaceous diagenesis-mineralization belt from southeastern Yunnan Province to western Guangxi Province,i.e.Late Cretaceous lithospheric extension in western South China.Basing on the analysis of regional geochemical anomalies and geological setting,we outline that the contact zones of the granites（and concealed granites） and the faulting system in sedimentary covers are the significant ore prospecting direction in this area.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2012年第4期587-601,共15页
Acta Geologica Sinica
基金
中国地质调查局"越北古陆北缘地质构造演化及其成矿效应研究"项目(编号1212010911065)
"云南麻栗坡地区矿产远景调查"项目(编号1212010880402)的资助成果
关键词
晚白垩世
强过铝质
花岗岩
锆石U-PB定年
云南马关
Late Cretaceous
peraluminous
granite
zircon LA-ICP-MS dating
Maguan
Yunnan Province
作者简介
张斌辉，男，1981年生。工程师，主要从事区域地质、岩石学、地球化学研究工作。Email：zbinhui@cgs．cn。
