The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet
The origin of shoshonites: new insights from the Tertiary high-potassium intrusions of eastern Tibet
复制标题
钾辉石的起源：藏东第三纪高钾侵入的新见解
DOI：
10.1007/s00410-014-0983-9
复制
发表时间：
2014-02
影响因子：
3.5
通讯作者：
Xie Ying-Wen
中科院分区：
文献类型：
--
作者：
Allen CharlotteM;Norman MarcD;Zhang Yu-Qiang;Xie Ying-Wen
该套岩基性和超基性成员以云母、橄榄石和斜辉石斑晶为特征，SiO2低，MgO高，Mg/Fe比值高，橄榄石forsterite含量为fo87 ~ Fo93，与地幔橄榄石和正辉石平衡。另一方面，地幔的直接融化不可能产生长英质成员。它们具有斜长石、角闪洞和石英的斑晶组合，高sio2和低MgO， Mg/Fe比率远低于与地幔平衡熔体的预期值。此外，从超镁铁质到长英质岩石中，Cr含量并没有随着sio2的增加和MgO的减少而减少，这排除了长英质成员是由基性成员分离结晶而来的可能性。同样，可以排除岩浆混合、地壳污染和晶体聚集等重要过程。然而，该套的所有成员都具有相似的不相容元素和放射性成因同位素比率，这表明它们有共同的起源和来源。我们认为，舒顺岩套的所有成员的熔融都是在大陆地壳中开始的，大陆地壳沿着跨洋的红河-牢山-八塘-丽江断裂系统在不同的点上被推入上地幔。在高t和高p条件下，以牺牲黑云母和云母为代价，由高熔点、无流体熔炼反应形成的熔体。熔体中含有高浓度的不相容元素，这是先前存在的辅助矿物完全溶解的结果。所产生的熔体是石英饱和的，并在上升过程中与上覆的地幔反应产生石榴石和辉石。长英质岩浆与邻近地幔反应较少，保留了高SiO2、低Ni、Cr和MgO含量、低Mg/Fe比值等原始化学性质的基本特征，而基性和超基性岩浆则是与地幔广泛反应的结果。基性岩浆虽然保留了其地壳源的不相容元素和放射性成因同位素比值，但橄榄石和正辉石的缓冲作用使其MgO、Ni、Cr、sio2含量和Mg/Fe比值广泛地改变为与地幔平衡的值。
The shoshonitic intrusions of eastern Tibet, which range in age from 33 to 41 Ma and in composition from ultramafic (SiO2= 42 %) to felsic (SiO2= 74 %), were produced during the collision of India with Eurasia. The mafic and ultramafic members of the suite are characterized by phenocrysts of phlogopite, olivine and clinopyroxene, low SiO2, high MgO and Mg/Fe ratios, and olivine forsterite contents of Fo87to Fo93, indicative of equilibrium with mantle olivine and orthopyroxene. Direct melting of the mantle, on the other hand, could not have produced the felsic members. They have a phenocryst assemblage of plagioclase, amphibole and quartz, high SiO2and low MgO, with Mg/Fe ratios well below the values expected for a melt in equilibrium with the mantle. Furthermore, the lack of decrease in Cr with increasing SiO2and decreasing MgO from ultramafic to felsic rocks precludes the possibility that the felsic members were derived by fractional crystallization from the mafic members. Similarly, magma mixing, crustal contamination and crystal accumulation can be excluded as important processes. Yet all members of the suite share similar incompatible element and radiogenic isotope ratios, which suggests a common origin and source. We propose that melting for all members of the shoshonite suite was initiated in continental crust that was thrust into the upper mantle at various points along the transpressional Red River-Ailao Shan-Batang-Lijiang fault system. The melt formed by high-degree, fluid-absent melting reactions at high-T and high-P and at the expense of biotite and phengite. The melts acquired their high concentrations of incompatible elements as a consequence of the complete dissolution of pre-existing accessory minerals. The melts produced were quartz-saturated and reacted with the overlying mantle to produce garnet and pyroxene during their ascent. The felsic magmas reacted little with the adjacent mantle and preserved the essential features of their original chemistry, including their high SiO2, low Ni, Cr and MgO contents, and low Mg/Fe ratio, whereas the mafic and ultramafic magmas are the result of extensive reaction with the mantle. Although the mafic magmas preserved the incompatible element and radiogenic isotope ratios of their crustal source, buffering by olivine and orthopyroxene extensively modified their MgO, Ni, Cr, SiO2contents and Mg/Fe ratio to values dictated by equilibrium with the mantle.
登录
查看更多内容
DOI：
10.1086/627871
发表时间：
1973-05
期刊：
The Journal of Geology
影响因子：
--
作者：
I. Nicholls;A. .. Ringwood
通讯作者：
I. Nicholls;A. .. Ringwood
影响因子：
3.5
作者：
J. Meen
通讯作者：
J. Meen
影响因子：
0.9
作者：
V. Chupin;D. V. Kuz’min;I. A. Madyukov
通讯作者：
V. Chupin;D. V. Kuz’min;I. A. Madyukov
影响因子：
1.1
作者：
I. A. Madyukov;V. Chupin;D. Kuzmin
通讯作者：
I. A. Madyukov;V. Chupin;D. Kuzmin
影响因子：
3.5
作者：
D. Küster;U. Harms
通讯作者：
D. Küster;U. Harms