Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block
Crustal contamination versus an enriched mantle source for intracontinental mafic rocks: Insights from early Paleozoic mafic rocks of the South China Block
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陆内镁铁质岩石的地壳污染与富集地幔来源：来自华南地块早古生代镁铁质岩石的见解
DOI：
10.1016/j.lithos.2017.06.023
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发表时间：
2017-08
期刊：
影响因子：
3.5
通讯作者：
Zeng Gang
中科院分区：
文献类型：
--
作者：
Xu Wenjing;Xu Xisheng;Zeng Gang
最近的几项研究表明，硅质岩石（SiO2> 65重量%）包括硅质大火成岩省是由部分熔融的地壳促进的底侵/内侵的“隐藏的”大火成岩省规模的玄武岩浆。华南陆块早古生代陆内岩浆岩以花岗岩类为主，面积约22, 000 km ~ 2。相比之下，镁铁质岩石的暴露总量仅为~ 45平方公里。这些镁铁质岩石具有从贫化到富集的极其不均匀的同位素特征全岩初始87 Sr/86 Sr = 0.7041-0.7102，εNd（t）=-8.4 ~+1.8;加权平均锆石εHf（t）= − 7.4至+5.2），显示出较低的Ce/Pb和Nb/U比值（分别为0.59-13.1和3.5-20.9），Th/La比值可变（0.11-0.51）。高镁基性岩（MgO > 10 wt.%）倾向于具有较低的εNd（t）值（<− 4）和Sm/Nd比值（< 0.255），而大多数低MgO基性岩石（MgO < 10 wt.%）具有较高的εNd（t）值（>− 4）和Sm/Nd比（> 0.255）。高镁和低镁基性岩石地球化学的差异表明地壳物质对高镁基性岩浆的成分有较大的改造作用。此外，εNd（t）与初始87 Sr/86 Sr比值、MgO和K2 O之间普遍存在良好的负相关关系，沿着某些岩体中存在继承性锆石，表明镁铁质岩的地球化学和同位素组成反映了显著的地壳混染，而不是富集的地幔源区。结果表明，高MgO镁铁质岩石与肥沃的同位素组成可能是指示地壳污染，除了富集的地幔来源，它更有可能是在早古生代的SCB下的岩石圈地幔是中度亏损比富集的古代俯冲过程。
Several recent studies have documented that the silicic rocks (SiO2> 65 wt.%) comprising Silicic Large Igneous Provinces are derived from partial melting of the crust facilitated by underplating/intraplating of “hidden” large igneous province-scale basaltic magmas. The early Paleozoic intracontinental magmatic rocks in the South China Block (SCB) are dominantly granitoids, which cover a combined area of ~ 22,000 km2. In contrast, exposures of mafic rocks total only ~ 45 km2. These mafic rocks have extremely heterogeneous isotopic signatures that range from depleted to enriched (whole rock initial87Sr/86Sr = 0.7041–0.7102; εNd(t) = − 8.4 to + 1.8; weighted mean zircon εHf(t) = − 7.4 to + 5.2), show low Ce/Pb and Nb/U ratios (0.59–13.1 and 3.5–20.9, respectively), and variable Th/La ratios (0.11–0.51). The high-MgO mafic rocks (MgO > 10 wt.%) tend to have lower εNd(t) values (<− 4) and Sm/Nd ratios (< 0.255), while the majority of the low-MgO mafic rocks (MgO < 10 wt.%) have higher εNd(t) values (>− 4) and Sm/Nd ratios (> 0.255). The differences in geochemistry between the high-MgO and low-MgO mafic rocks indicate greater modification of the compositions of high-MgO mafic magmas by crustal material. In addition, generally good negative correlations between εNd(t) and initial87Sr/86Sr ratios, MgO, and K2O, along with the presence of inherited zircons in some plutons, indicate that the geochemical and isotopic compositions of the mafic rocks reflect significant crustal contamination, rather than an enriched mantle source. The results show that high-MgO mafic rocks with fertile isotopic compositions may be indicative of crustal contamination in addition to an enriched mantle source, and it is more likely that the lithospheric mantle beneath the SCB during the early Paleozoic was moderately depleted than enriched by ancient subduction processes.
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DOI：
10.1016/b978-0-08-095975-7.00303-x
发表时间：
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