Neoarchean Magmatism in the Culaishan Area, Western Shandong:Evidence from SHRIMP Zircon U-Pb Dating
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摘要: 徂徕山是鲁西新太古代岩石的重要出露区。在野外地质基础上,本文对3个岩石样品进行了锆石SHRIMP U-Pb定年研究。英云闪长质片麻岩遭受一定重结晶影响的岩浆锆石年龄为(2711±11) Ma,变质作用时代可能为~2.6 Ga。变质石英闪长岩遭受强烈重结晶影响的岩浆锆石年龄为2.51 Ga,被解释为更接近构造热事件的时代,而岩浆锆石年龄可能在2.53~2.55 Ga之间。二长花岗岩锆石普遍存在强烈铅丢失,根据数据点在谐和线上的分布特征,二长花岗岩的形成时代应为~2.5 Ga。结合地球化学研究和前人工作,确定了徂徕山地区新太古代地质演化历史及新太古代早期古老岩石带(B带)和新太古代晚期新生岩石带(C带)之间的界线。
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关键词:
- 新太古代 /
- 岩浆作用 /
- 鲁西 /
- 徂徕山 /
- 锆石SHRIMP定年
Abstract: Culaishan is one of the most important areas with well-exposed Neoarchean rocks in western Shandong. In this paper, the authors carried out SHRIMP U-Pb zircon dating on three samples. Tonalitic gneiss has a weighted mean207Pb/206Pb age of (2711±11) Ma for magmatic zircon with some recrystallization. It is inferred that a metamorphic event occurred at ~2.6 Ga. Zircons from a meta-quartz diorite sample show banded zoning with strong recrystallization, the age of 2.51 Ga is considered to be closer to the metamorphic time, and the intrusive time of the quartz diorite should be between 2.53 Ga and 2.55 Ga. Magmatic zircons from monzogranite show lead loss to different degrees, but the crystallization age might be ~2.5 Ga, as shown by the distribution of age data on concordia. Combined with geochemical study and previous work, the authors determined the Neoarchean geological evolution in the Culaishan area and redefined the boundary between the early Neoarchean (2.60~2.75 Ga) rock belt and the late Neoarchean (2500~2550 Ma) belt of juvenile rocks in the northwestern portion of western Shandong.-
Key words:
- Neoarchean /
- magmatism /
- western Shandong /
- Culaishan /
- SHRIMP zircon dating
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