ABSTRACT

Erinpura Granites form the basement for the Neoproterozoic Malani Igneous Suite in NW India. Based on this study, the Erinpura granites can be divided into Erinpura-East (gneissic fabric), a belt parallel to the southern sector of the South Delhi Fold Belt, and Erinpura-West (magmatic fabrics). EPMA dating on monazites gives a time frame of 890 to 860 Ma for crystallization of both types. The geochemically homogeneous peraluminous S-type granites with ε_Nd values of −2.1 to −10.8 are interpreted as melting products of Archaean crust. REE pattern follows the pattern of the average continental crust, but Erinpura-East samples are more fractionated with steeper HREE depletion indicating melting in a deeper crustal level. A thermal pulse between 835 and 820 Ma constrains the timing of deformation in granite-gneisses during uplift along thrust planes, coeval with shear-bound exhumation of high-grade metamorphic rocks and initiated by delamination of the lower crust in this southern sector of the South Delhi Fold Belt. This is in contrast to the northern sector of the SDFB with arrested orogenic development and without considerable delamination or erosion of the lower crust. Latest movement related to the 200 Ma tectono-magmatic history overlaps with initiation of rifting during the Malani igneous event. A change from S-type to A-type granites and shift of isotopic signatures to ε_Nd values of −2.8 to −1.7 indicate substantial contribution of asthenospheric material in the Malani melting process.

摘要

Erinpura 花岗岩形成了印度西北部新元古代马拉尼火成岩组的地下室。根据这项研究，Erinpura 花岗岩可分为 Erinpura-East（片麻岩组构）、与南德里褶皱带南段平行的带和 Erinpura-West（岩浆组构）。对独居石进行 EPMA 测年为这两种类型的结晶提供了 890 至 860 Ma 的时间范围。_{具有 ε Nd}的地球化学均质过铝质 S 型花岗岩-2.1 到 -10.8 的值被解释为太古代地壳的熔融产物。REE 模式遵循平均大陆地壳的模式，但 Erinpura-East 样品更加分馏，HREE 消耗更陡峭，表明在更深的地壳水平熔化。835 至 820 Ma 之间的热脉冲限制了花岗片麻岩在沿逆冲平面抬升过程中的变形时间，与高级变质岩的剪切剥落同时发生，并由南部该南部地区下地壳的分层引发德里折叠腰带。这与 SDFB 的北部区域形成对比，该区域的造山带发育受阻，下地壳没有明显的分层或侵蚀。与 200 Ma 构造岩浆历史相关的最新运动与 Malani 火成事件期间裂谷的开始重叠。_{-2.8 到 -1.7 的Nd}值表明软流圈材料在 Malani 熔融过程中的重要贡献。