SHRIMP Zircon U-Pb Ages and Its Geological Significance of CrystalIgnimbrite in the Duocaima Pb-Zn Deposit, Tuotuohe Area
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摘要: 多才玛铅锌矿是近年来沱沱河地区发现的一处超大型铅锌矿床,位于青藏高原东北部的东羌塘地块。恶劣的气候条件以及矿床发现时间晚,造成该地区地质研究程度极低。笔者重点对容矿围岩之一的晶屑熔结凝灰岩进行了SHRIMP锆石U-Pb测年和岩石化学成分分析。研究表明,晶屑熔结凝灰岩中锆石呈自形-半自形,发育典型的岩浆锆石振荡生长环带,Th/U值较高(0.39~0.69),为典型的岩浆锆石。测得晶屑熔结凝灰岩U-Pb加权平均年龄为(254.0±2.9) Ma, MSWD=1.9;谐和年龄值为(254.0±3) Ma,MSWD=1.9,属海西末期。岩石化学成分表现为高硅过铝、贫钙和镁,明显富集Rb、Th、U等大离子亲石元素,强烈亏损P、Ti、Nb、Ta等高场强元素,富集LREE,Nb/Ta值(7.78~8.29)等特征表现为壳源岩浆和弧火山岩特征。综合分析认为,254 Ma±时期本区处于深俯冲消减阶段。
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关键词:
- 晶屑熔结凝灰岩 /
- 锆石SHRIMP年龄 /
- 地球化学特征 /
- 多才玛
Abstract: The DuocaimaPb-Zn deposit, is a super-large scale Pb-Zn deposit found in Tuotuohe area recently, which is located in the East Qiangtang Block of Northeast Qinghai-Tibet Plateau.Because the adverse weather conditions in this exploration area, the researches on this depositare very low, especially magmatic evolution and tectonic setting. In this paper, the zircon SHRIMP U-Pb age and geochemical compositions of crystal ignimbrites from this deposit have beentested.The zircons of crystal ignimbrite mainly show euhedral and hypidiomorphic texture, with clear ring and high Th/U ratios (0.39~0.69), which belong to the typical magmatic zircons.The dating results show that the 206Pb/238U average weighted age of these crystal ignimbrites is(254.0±2.9) Ma (MSWD=1.9), and their concordant agesare (254.0±2.9) Ma (MSWD=1.9). The geochemical data suggest that these crystal ignimbrites are enriched in large ion lithophile elements (LILE)and LREE, strongly depleted in high field-strength element (HFSE). The trace elements ratios, such as Nb/Ta ratio (7.78-8.29), showthat these crystal ignimbrites belong to arc volcanic rocks, which are derived from the crustalmaterials.Combined with regional geological information, the new geochemical and geochronology datareveal that this research area was experienced the consistent subduction stage in 254Ma±.-
Keywords:
- crystal ignimbrite /
- zircon SHRIMP dating /
- geochemical characteristics /
- Duocaima
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