Characterization of the accreted Ophiolite slices of Rutland island, Andaman sea: Evolution in a Suprasubduction zone setting

IF 1.2 4区 地球科学 Q2 GEOLOGY
A. Bhattacharya, T. Pal, B. Ghosh
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引用次数: 10

Abstract

Detailed mapping of a  rocks110 km 2 area of the Rutland Island has demarcated four dismembered thrust slices of Cretaceous ophiolite which are interleaved with Eocene sediments. The ophiolite sequence is represented by tectonite, chromitite pods, transitional peridotite, layered ultramafic-mafic, intrusives of plagiogranite-diorite suite and extrusives of basalt and boninite, capped by pelagic sediments. The layered ultramafics and the massive chromitites are characterized by high Mg-olivine (Fo 92-93 ), high Mg-orthopyroxene (En 88–90 ), low CaO (X Ca M2 = 0.01 to 0.03), low alumina (Al 2 O 3 = 0.66 to 1.20 wt %) and high Cr-chromites, which is typical of boninitic melts in suprasubduction zone (SSZ) environments. The estimated Al 2 O 3 contents of the parental melt (10.80 wt%) correspond to a boninitic parental melt. The Type-2 low-Ca boninite extrusives with SiO 2 < 58 wt%, MgO = 8.4 to 9.5 wt% is the extrusive equivalent of boninitic parental lava. As boninitic rocks show higher depletion of Zr and Y than the basaltic rocks, the source rock for boninite was more depleted than that of  basalts. Tectonites showing embayed clinopyroxene grains and irregular shaped Cr-spinel as residual phases preserve records of partial melting. The degree of partial melting of the mantle tectonite has been estimated as ~ 20%, based on Cr content of the spinel. Petrographic features of the transitional peridotites show dissolution of orthopyroxene and clinopyroxene grains and development of small fresh olivine grains along the embayed margins and fractures, displaying melt-rock interaction effects in the mantle rocks. The melt-rock interaction features as well as the bivariant relation of TiO 2 wt% vs. Al 2 O 3 wt% of the chromites reflect the evolution of the Rutland ophiolite in a SSZ setting.
安达曼海拉特兰岛增生蛇绿岩片的特征:在超俯冲带背景下的演化
在Rutland岛一个110 km2的岩石区域的详细测绘中,划分出了白垩纪蛇绿岩的4个断裂逆冲切片,它们与始新世沉积物交织在一起。蛇绿岩序列以构造岩、铬铁矿豆角岩、过渡橄榄岩、层状超基性岩、斜花岗闪长岩套侵入物、玄武岩和博宁岩挤压物为代表,并以远洋沉积物为盖层。层状超镁铁质和块状铬铁矿具有高镁橄榄石(Fo 92 ~ 93)、高镁正辉石(En 88 ~ 90)、低CaO (X Ca M2 = 0.01 ~ 0.03)、低氧化铝(Al 2o3 = 0.66 ~ 1.20 wt %)和高铬铬铁矿的特征,是上俯冲带(SSZ)环境下典型的硼质熔体。母熔体中Al 2o3的含量(10.80 wt%)与硼质母熔体相对应。sio2 < 58 wt%, MgO = 8.4 ~ 9.5 wt%的2型低钙博云母岩挤出物相当于博云母岩熔岩。由于博宁质岩石的Zr和Y的衰竭程度高于玄武岩,因此博宁质烃源岩的衰竭程度高于玄武岩烃源岩。以镶嵌斜辉石颗粒和不规则cr尖晶石为残余相的构造岩保存了部分熔融的记录。根据尖晶石的Cr含量,估计地幔构造岩的部分熔融程度为~ 20%。过渡性橄榄岩的岩石学特征表现为正辉石和斜辉石颗粒的溶蚀,以及小的新鲜橄榄石颗粒沿凸起边缘和裂缝发育,显示出熔融-岩石在地幔岩石中的相互作用作用。熔体-岩石相互作用特征以及铬铁矿tio2wt %与al2o3 wt%的变化关系反映了拉特兰蛇绿岩在SSZ环境下的演化。
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来源期刊
Ofioliti
Ofioliti 地学-地质学
CiteScore
2.40
自引率
7.70%
发文量
1
期刊介绍: Since 1976, Ofioliti provides an international forum for original contributions and reviews in the field of the geodynamics, petrology, geochemistry, biostratigraphy, stratigraphy, tectonics and paleogeography applied to ophiolitic terrains and modern oceanic lithosphere, including their sedimentary cover. Studies of topics such as geodynamics of the mantle, the evolution of orogens including ophiolites and paleoceanography are also welcome
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