The Preservation System of Epithermal Deposits in South Qiangtang Terrane of Central Tibetan Plateau and Its Significance: A Case Study of the Tiegelongnan Superlarge Deposit
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摘要: 由于青藏高原隆升不可避免的强烈剥蚀作用,中生代浅成低温热液矿床的形成、保存和发现就需要多种地质因素的耦合.西藏班公湖—怒江成矿带西段新发现的铁格隆南铜矿是一处隐伏、半隐伏的超大型斑岩-浅成低温热液叠加矿床.系统的地质编录发现,矿床的保存得益于成矿后美日切错组火山岩的覆盖.在矿体和火山岩之间发现了古风化壳,并识别出弱风化残积层、残积古土壤、半风化坡积物三种风化剥蚀界面,说明矿床形成以后经历了一定程度的隆升剥蚀.通过成矿系统的保存程度间接估算,118~111 Ma之间最小剥蚀厚度为600~1200 m,区间剥蚀速率为0.1~0.2,平均0.15 mm/a.矿床形成时的地表高程可能达到2000~2500 m.矿床形成于班公湖—怒江洋盆闭合末期,对其剥蚀作用的研究验证了南羌塘地体在早白垩世晚期经历过一次重要的剥蚀过程,同时指示了早白垩世晚期是青藏高原隆升历史的重要时期.Abstract: The formation and preservation of the Mesozoic epithermal deposits are attributed to many coupling geological factors during the erosion of the Tibetan Plateau. The newly discovered Tiegelongnan Cu deposit in the western part of Bangong Co–Nujiang metallogenic belt in Tibet is a superlarge superimposed porphyry-epithermal deposit. The preservation of the Tiegelongnan deposit resulted from the covered Meiriqiecuo andesite formed after the mineralization according to the systematic geological log. The paleocrust of weathering developed between the orebody and andesite and the weak weathered eluvial, ancient soil, half-regolith deluvial was identified, which indicates the uplift and erosion of the Tiegelongnan deposit. The minimum denudation depth was 600~1200 m in 118~111 Ma and the denudation rate was 0.1~0.2 mm/a with an average of 0.15 mm/a according to the indirect calculation of the metallogenic system protection. The ancient elevation of the Tiegelongnan deposit was about 2000~2500 m. The Tiegelongnan deposit formed at the last stage of the closure of the Bangong Co–Nujiang Ocean. The research in this paper has confirmed that southern Qiangtang terrane experienced an important denudation process in the late period of early Cretaceous and indicated the late period of early Cretaceous was an important period during the uplifting of Tibetan Plateau.
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Key words:
- epithermal deposit /
- porphyry deposit /
- preservation /
- uplift /
- Bangong Co–Nujiang /
- Tibet
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