Re–Os evidence for the age and origin of peridotites from the Dabie–Sulu ultrahigh pressure metamorphic belt, China
Re–Os evidence for the age and origin of peridotites from the Dabie–Sulu ultrahigh pressure metamorphic belt, China
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中国大别—苏鲁超高压变质带橄榄岩年龄和起源的真实证据
DOI：
10.1016/j.chemgeo.2006.10.009
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发表时间：
2007-01
期刊：
影响因子：
3.9
通讯作者：
刘勇胜
中科院分区：
文献类型：
--
作者：
高山;于日东;Igor S. Puchtel;Richard J. Walker;金振民;袁洪林;Roberta L. Rudnick;刘勇胜
中国中东部苏鲁超高压变质地体徐沟橄榄岩体内的蛇纹岩石榴石橄榄岩为难熔橄榄岩(橄榄岩的FO91.7-93.1)，表明其成因为残留地幔。全岩氧化镁与二氧化钛、三氧化二铝、总铁、氧化钙呈负相关(r=−0.90~−0.95)，全岩三氧化二铝与氧化钙与不相容元素[Li、V、Cu、Ga、SR、Y、Zr、重稀土元素、Hf、Pb、U]呈正相关(r=0.69~0.98)，可能反映熔体亏损趋势。选择了4个高耐火样品进行Re-Os同位素分析。尽管187Re/188Os或187Os/188Os与La或Re不存在相关性(r=0.00~0.17)，但它们显示出蛇纹岩/交代过程中不相容元素不同程度的富集。这些结果表明，任何Re添加都是较新的，对Os的同位素组成没有明显的影响。因此，187Os/188Os和187Re/188Os之间的相关性很可能反映了一次古老的熔体提取事件。徐沟橄榄岩的TRD、TMA和ERRORICRON年龄都很相似，表明这些橄榄岩形成于2.0 Ma左右。该年龄与大别地体中地幔橄榄岩的Os模式年龄相似，但与北中国克拉通东部地块之下大陆岩石圈地幔的太古宙年龄形成鲜明对比。如果我们假设大别-苏鲁带是扬子克拉通与华北克拉通东部地块三叠纪碰撞形成的，并且后者的太古宙CLM持续到三叠纪，那么古元古代年龄表明这些大别-苏鲁地幔橄榄岩来自扬子克拉通。扬子克拉通成因与大别-苏鲁超高压带已有的构造模式一致。我们的研究结果支持扬子克拉通地壳和下伏岩石圈地幔俯冲至180-200千米以下形成世界上最大的超高压带的假说。
Serpentinized garnet peridotites from the Xugou peridotite body of the Sulu ultrahigh-pressure (UHP) metamorphic terrane, central eastern China, are refractory (olivines have Fo91.7–93.1), indicating their origin as residual mantle. Negative correlations between whole-rock MgO and TiO2, Al2O3, total Fe2O3and CaO (r=−0.90 to −0.95) and positive correlations between whole-rock Al2O3and CaO and incompatible elements [Li, V, Cu, Ga, Sr, Y, Zr, heavy rare earth elements (HREEs), Hf, Pb and U] (r=0.69 to 0.98) likely reflect melt depletion trends. Four highly refractory samples were selected for Re–Os isotopic analysis. Although they show evidence of variable enrichment of incompatible elements during serpentinization/metasomatism, no correlations exist between187Re/188Os or187Os/188Os with either La or Re (r=0.00 to 0.17). These results indicate that any Re addition was fairly recent and did not affect the Os isotopic composition significantly. The correlation between187Os/188Os and187Re/188Os ratios thus, most likely reflects an ancient melt extraction event. The TRD, TMAand errorchron ages of the Xugou peridotites are all similar, suggesting that these peridotites formed around 2.0 Ga ago. This age is similar to Os model ages of mantle peridotites from the Dabie terrane, but contrasts markedly with the Archean ages of the continental lithospheric mantle (CLM) beneath the eastern block of the North China craton (NCC). If we assume that the Dabie–Sulu belt formed by the Triassic collision of the Yangtze craton with the eastern block of NCC and that the Archean aged CLM of the latter persisted until the Triassic, the Paleoproterozoic ages suggest derivation of these Dabie–Sulu mantle peridotites from the Yangtze craton. A Yangtze craton origin is consistent with the existing tectonic model of the Dabie–Sulu UHP belt. Our results support the hypothesis that the crust and underlying lithospheric mantle of the Yangtze craton were subducted to depths of >180–200 km to form the world's largest UHP belt.
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