Geochemistry and Nd-Sr-Pb Isotopic Compositions of Granitoids from Qaidam and Oulongbuluke Micro-Blocks, NW China: Constraints on Basement Nature and Tectonic Affinity
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摘要: 本次工作研究了柴达木地块和欧龙布鲁克地块中的古元古代莫河岩体、新元古代沙柳河岩体、早三叠世香日德岩体和察汉诺岩体以及晚三叠世可日岩体的主量元素、微量元素和Nd-Sr-Pb同位素组成.沙柳河岩体和可日岩体具S型过铝质花岗岩成因特征, 其他岩体具Ⅰ型花岗岩类成因特征.TDM和εNd(t) 值的对比揭示, 沙柳河岩体的源岩区为欧龙布鲁克地块的Ⅱ型基底变质表壳岩系, 其余岩体的岩浆都不可能源自暴露地表的基底变质表壳岩系.花岗岩类和基底变质表壳岩系的亏损地幔最大模式年龄集中在1.52.3Ga和0.91.3Ga, 在欧龙布鲁克地块中亦有2.5Ga及2.8Ga显示, 一般Pb同位素比值(206Pb/204Pb)t>18, (207Pb/204Pb)t>15.5, (208Pb/204Pb)t>38, 具高放射成因铅特征.这表明, 柴达木地块和欧龙布鲁克地块基底与扬子陆块具有密切的亲缘性, 现今的扬子陆块范围可扩大到中国西部阿尔金断裂东、西两侧的微陆块群, 昆中断裂带和柴北缘高压-超高压变质岩带代表扬子陆块内部裂解小地块的再汇聚带.
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关键词:
- Nd-Sr-Pb同位素地球化学 /
- 花岗岩类 /
- 基底属性 /
- 柴达木和欧龙布鲁克地块 /
- 中国西部
Abstract: The formation of major-and trace-elemental and Sr-Nd-Pb isotopic geochemistries in Early Paleoproterozoic Mohe pluton and Early Triassic Cahanno pluton of the Oulongbuluke micro-block and Neoproterozoic Shaliuhe pluton, Late-Permian to Early-Triaasic Xiangride pluton and Late-Triassic Keri pluton of the Qaidam Block of northwestern China, were investigated. The Shaliuhe pluton and Keri muscovite pluton are characterized by S-type and paraaluminium granite, the others are by Ⅰ-type granodiorite or granite. It is concluded from the comparsion of TDM and εNd(t) that the magma source area of the Shaliuhe granite belongs to the Ⅱ-type metabasement of the Oulongbuluke micro-block, and the magma of the rest of the plutons could not originate from the exposed supracurstal sequences. The TDM are clustered at ~1.5-2.3 Ga and 0.9-1.3 Ga, with peak value of ~ 1.2 Ga, ~1.6 Ga and ~2.05 Ga for both granitoids and meta-supracurstal rocks, ~2.5 Ga and 2.8 Ga are solely distributed in the Oulongbuluke micro-block. The two micro-blocks have ratios of (206Pb/204Pb)t, (207Pb/204Pb)t and (206Pb/204Pb)t generally higher than 18, 15.5 and 38, respectively. These data suggest that the basements of the Oulongbuluke micro-blocks and the Qaidam micro-blocks are geochemically akin to that of the Yangtze Block, and that the Yangtze Block Domain can be extended northwestwards to the micro blocks on both sides of the Altyn-Tagh fault, and that the UHP-HP tectonic belt along the northern margin of the Qaidam micro-block is only a convergent boundary among the earlier broken-up micro-blocks within the Yangtze Block. -
图 1 中国西北部微陆块群分布和柴达木及邻区地质简图(据陆松年等, 2002a, 2002b修改)
Fig. 1. Distribution of micro-continental blocks in NW China and geological sketch maps of Qaidam and adjacent areas
图 2 (a) 花岗岩TAS分类图; (b) A/NK-A/CNK图解
(据Shand, 1927; Maniar and Piccoli, 1989)
Fig. 2. (a) TAS diagram for classification of the granitoids; (b) Plot of A/NK vs A/CNK
图 4 球粒陨石标准化稀土元素和洋中脊花岗岩标准化微量元素图谱
(标准化数据据Pearce et al., 1984)
Fig. 4. Chrondrite normalized REE patterns and ORG normalized trace elemental patterns of the granitoids
图 5 花岗岩和基底表壳岩εNd(t) -T2DM图解
基底表壳岩资料源于张建新等(2003)和万渝生等(2003)
Fig. 5. εNd(t) -T2DM diagram for the granitoids and basemental suparacrusts
图 6 花岗岩类和基底表壳岩二阶段Nd模式年龄统计直方图
数据来源: 本文、张建新等(2003)和万喻生等(2003)
Fig. 6. Histogram for T2DM of the granitoids and basemental supracrusts
图 7 花岗岩类长石和有关岩石的207Pb/204Pb-206Pb/204Pb和208Pb/204Pb-206Pb/204Pb图解
图中分区据张本仁等(2002) : SNC.华北陆块南缘花岗岩和斑岩长石; NYCE.扬子陆块北缘东段中生代花岗岩长石; NQ1.北秦岭新元古代和早古生代花岗岩类长石; NQ2.北秦岭印支期和燕山期花岗岩类长石; SQE1.南秦岭东段新元古代和早古生代花岗岩类长石; SQE2.南秦岭东段印支期花岗岩类长石; SQW.南秦岭西段中生代花岗岩类长石
Fig. 7. 206Pb/204Pb-207Pb/204Pb and208Pb/204Pb-206Pb/204Pb diagrams for the granitoids and the potassium feldspars
表 2 Sr-Nd同位素成分
Table 2. Sr-Nd isotopic compositions
表 1 花岗岩类岩体主量(%) 和微量元素(μg/g) 成分
Table 1. Major and trace element compositions of granitoids
表 3 花岗岩全岩和钾长石铅同位素成分
Table 3. Pb isotopic compositions from the whole rock of granitoids and potassiam feldspar
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