藏南错那洞中新世早期淡色花岗岩岩石成因:全岩地球化学、矿物学特征约束  

Early Miocene leucogranitic magmatism in Cuonadong, southern Tibet: Constraints from whole-rock geochemical and mineralogical characteristics

作　　者：黄春梅 李光明 付建刚 梁维 张志 王艺云 HUANG Chunmei;LI Guangming;FU Jiangang;LIANG Wei;ZHANG Zhi;WANG Yiyun(Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,China)

机构地区：[1]中国地质调查局成都地质调查中心(西南地质科技创新中心),四川成都610218

出　　处：《地学前缘》2023年第5期74-92,共19页Earth Science Frontiers

基　　金：国家重点研发计划项目(2021YFC2901903);国家自然科学基金项目(42202061,91955208);第二次青藏高原综合科学考察项目(2019QZKK0806);中国地质调查局成都地质调查中心“刘宝珺院士基金”。

摘　　要：为进一步揭示喜马拉雅淡色花岗岩的成因以及对稀有金属成矿的作用,本文选取了喜马拉雅东段错那洞Be-W-Sn多金属矿床内的弱定向二云母花岗岩和含石榴子石白云母花岗岩进行全岩主、微量和独居石年代学、微量元素分析,以及主要矿物原位成分分析。分析结果显示弱定向二云母花岗岩和含石榴子石白云母花岗岩为同一期次岩浆作用,形成年龄分别为(20.1±0.3) Ma和(20.7±0.2) Ma;全岩地球化学表现出富Si、富Al的特征,含石榴子石白云母花岗岩的全岩地球化学以及独居石均出现稀土四分组效应;矿物分析显示,含石榴子石白云母花岗岩斜长石An牌号更低,均为钠长石,白云母较弱定向二云母花岗岩更富FeO、MnO、F,石榴子石中锰铝榴石组分明显增高。综合以上特征分析,含石榴子石白云母花岗岩比弱定向二云母花岗岩具有更高的演化程度,其来源很可能是晶粥体分离结晶形成的粒间高演化熔体/流体,而二云母花岗岩则是高演化熔体/流体不完全抽取后的剩余晶粥体。错那洞约20 Ma的高分异淡色花岗岩促使Be、Sn等成矿元素初始富集,是后期成矿的关键。In order to better understand the petrogensis of Himalayan leucogranites and its role in the mineralization of rare metals,we performed whole-rock major and trace element,monazite age and trace element,and main mineral composition analyses of weakly oriented two-mica granite and garnet-bearing muscovite granite in the Cuonadong Be-W-Sn polymetallic deposit in eastern Himalayas.Results show the Cuonadong two-mica and muscovite granites are formed during the same magmatic event and dated respectively to(20.1±0.3)Ma and(20.7±0.2)Ma.Whole-rock geochemical analysis shows the granites are rich in Si/Al,and monazite and the muscovite granite both exhibit REE tetrad effect.According to mineral analysis,plagioclase in the muscovite granite is more sodic,and the muscovite granite has higher FeO,MnO and F contents and higher spessartine content compared to the two-mica granite.These characteristics suggest the muscovite granite is more evolved and likely formed from highly evolved interstitial melt/fluid within the magmatic crystal mush,while the two-mica granite likely formed from the residual melt.Early(~20 Ma)differentiation of leucogranites in the Cuonadong dome promoted the initial enrichment of ore-forming elements such as Be and Sn,which is the key to late mineralization.

关 键 词：错那洞淡色花岗岩 岩石成因 岩浆演化 四分组效应 稀有金属成矿 

分 类 号：P581[天文地球—岩石学] P595[天文地球—地质学] P574