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首页> 外文期刊>Contributions to Mineralogy and Petrology >Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area(Antarctica)
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Geochemical and O-isotope constraints on the evolution of lithospheric mantle in the Ross Sea rift area(Antarctica)

机译：罗斯海裂谷地区（南极洲）岩石圈地幔演化的地球化学和O同位素约束

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Peridotite xenoliths found in Cenozoic alkali basalts of northern Victoria Land, Antarctica, vary from fertile spinel-lherzolite to harzburgite. They often contain glass-bearing pockets formed after primary pyroxenes and spinel. Few samples are composite and consist of depleted spinel lherzolite crosscut by amphibole veins and/or lherzolite in contact with poikilitic wehrlite. Peridotite xenoliths are characterized by negative Al_9O_3-Mg# and TiO_2-Mg# covariations of clino- and ortho-pyroxenes, low to intermediate HREE concentrations in clinopyroxene, negative Cr-Al trend in spinel, suggesting variable degrees of partial melting. Metasomatic overprint is evidenced by trace element enrichment in clinopyroxene and sporadic increase of Ti-Fe_(tot). Preferential Nb, Zr, Sr enrichments in clinopyroxene associated with high Ti-Fe_(tot) contents constrain the metasomatic agent to be an alkaline basic melt. In composite xenoliths, clinopyroxene REE contents increase next to the veins suggesting metasomatic diffusion of incompatible element. Oxygen isotope data indicate disequilibrium conditions among clinopyroxene, olivine and orthopy-roxene. The highest delta~18O values are observed in minerals of the amphibole-bearing xenolith. The delta~18O_(cpx) correlations with clinopyroxene modal abundance and geochemical parameters (e.g. Mg# and Cr#) suggest a possible influence of partial melting on oxygen isotope composition. Thermobarometric estimates define a geotherm of 80 deg C/GPa for the refractory lithosphere of NVL, in a pressure range between 1 and 2.5 GPa. Clinopyroxene microlites of melt pockets provide P-T data close to the anhydrous peridotite solidus and confirm that they originated from heating and decompression during transport in the host magma. All these geothermometric data constrain the mantle potential temperature to values of 1250-1350 deg C, consistent with the occurrence of mantle decompressional melting in a transtensive tectonic regime for the Ross Sea region.
机译：在南极维多利亚地区北部新生代碱性玄武岩中发现的橄榄石异岩，从肥沃的尖晶石-绿铁矿到哈兹石。它们通常包含在伯辉石和尖晶石之后形成的带有玻璃的袋。很少有样品是复合的，且由角闪石脉横切的尖晶石斜纹锂铁矿和/或与斜辉绿白云母接触的斜铁石组成。橄榄岩异种岩的特征是斜和正斜py和邻斜py的Al_9O_3-Mg＃和TiO_2-Mg＃负变，斜cl中的HREE浓度从低到中等，尖晶石的Cr-Al负的趋势，表明部分熔融程度不同。交联叠印是通过微量元素富集在次氯环己烯和零星增加的Ti-Fe_（tot）来证明的。与高Ti-Fe_（tot）含量相关的次氯苯酚中Nb，Zr，Sr的优先富集会限制交代剂为碱性碱性熔体。在复合异种岩中，斜辉石的稀土元素含量在静脉附近增加，表明不相容元素的交代扩散。氧同位素数据表明，斜吡咯烯，橄榄石和邻苯二酚之间存在不平衡条件。在含闪石的异种岩的矿物中观察到最高的δ〜18O值。 δ〜18O_（cpx）与斜向茂铁模态丰度和地球化学参数（例如Mg＃和Cr＃）的相关性表明部分熔融可能对氧同位素组成产生影响。热压法估计为NVL的难熔岩石圈定义了80摄氏度/ GPa的地热，压力范围为1至2.5 GPa。熔体囊的斜辉石微晶提供了接近无水橄榄岩固相线的P-T数据，并证实它们源自宿主岩浆中运输过程中的加热和减压。所有这些地热数据将地幔潜在温度限制在1250-1350摄氏度，这与罗斯海地区在大地构造构造中地幔减压融化的发生是一致的。

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