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首页> 外文期刊>Contributions to Mineralogy and Petrology >Composition and evolution of the lithospheric mantle beneath the interior of the South China Block: insights from trace elements and water contents of peridotite xenoliths
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Composition and evolution of the lithospheric mantle beneath the interior of the South China Block: insights from trace elements and water contents of peridotite xenoliths

机译：南中国内部岩石架的构图和演变：缺乏元素和水含量的岩石Xenoliths的洞察力

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摘要

Major and trace elements and water contents were analyzed in 16 peridotite xenoliths embedded by the Cenozoic basalts in Pingnan (southeastern Guangxi Province), to constrain the chemical composition and evolution of the lithospheric mantle located in the central part of the South China Block (SCB). The peridotites are mainly moderately refractory harzburgites and lherzolites (Mg#-Ol = 90.3-91.7) and minor fertile lherzolites (Mg#-Ol = 88.9-89.9). Clinopyroxenes in the peridotites show LREE-depleted pattern, and commonly exhibit negative anomalies in Nb and Ti, suggesting the peridotites probably represent residues after 1-10% of partial melting without significant mantle metasomatism. Water contents range from 146 to 237 ppm wt. H2O in clinopyroxene, and from 65 to 112 ppm wt. H2O, in orthopyroxene but are below detection limit (2 ppm wt. H2O) in olivine. Calculated bulk water contents, based on the mineral modes and partition coefficient, range from 14 to 83 ppm wt. H2O (average 59 ppm wt. H2O). There is a correlation between melting indices (such as Mg#-Ol, Yb-n in clinopyroxene) and water contents in clinopyroxene and orthopyroxene, but no correlation is observed between the whole-rock water contents and the redox state (Fe3+/aFe ratios in spinel), suggesting that water contents in the peridotites are mainly controlled by the degree of partial melting rather than by oxygen fugacity. The lithospheric mantle beneath the interior of the SCB may not be compositionally stratified; fertile and moderately refractory mantle coexist at the similar depths. Geochemical data and water contents of the studied peridotites are similar to the proposed MORB source and indicate that the ancient refractory lithospheric mantle was irregularly eroded or reacted by the upwelling asthenosphere, and eventually replaced by juvenile fertile accreted mantle through the cooling of the asthenosphere.
机译：分析了主要和微量元素和水含量，在广西（广西东南部）的新生岩玄武岩嵌入了嵌入式底栖岩石，以限制位于南部中国中部部分（SCB）的岩石树木地幔的化学成分和演变。恒星主要是中度难治性麦芽螟和萝尔硼（Mg＃-Ol = 90.3-91.7）和轻微的肥沃的洛溪泽（Mg＃-Ol = 88.9-89.9）。在恒星中的临床表现出嗜嘴耗尽的图案，并且通常在Nb和Ti中表现出阴性异常，表明恒星可能代表1-10％的部分熔化后的残留物，而没有显着的裂缝弥扑术。水含量为146至237ppm wt。临床中的H2O，65-112 ppm wt。 H2O，在橄榄石中低于检测极限（2ppm wt.h2O）。基于矿物模式和分区系数的计算散装水含量，范围为14至83ppm wt。 H2O（平均59ppm wt。H2O）。熔融索引（如Mg＃-OL，Clinopocogoxene中的YB-N）和冠状藻烯和垂直烯的水含量之间存在相关性，但在整个岩石水质和氧化还原状态之间没有观察到相关性（Fe3 + / AFE比率在尖晶石）中，表明恒星的水含量主要由部分熔化的程度而不是通过氧不足来控制。在SCB的内部下方的岩石罩可能不会被合成分层;肥沃和中度难治性地幔在类似深度时共存。研究的恒星的地球化学数据和水含量类似于提出的Morb来源，并表明古代难治性岩性地幔不规则地侵蚀或由升高的哮喘圈而反应，最终通过冷却哮喘圈的冷却冷却少年肥沃的型菌状物。

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