Neoarchean high-pressure margarite–phengitic muscovite–chlorite corona mantled corundum in quartz-free high-Mg, Al phlogopite–chlorite schists from the Bundelkhand craton, north central India
Neoarchean high-pressure margarite–phengitic muscovite–chlorite corona mantled corundum in quartz-free high-Mg, Al phlogopite–chlorite schists from the Bundelkhand craton, north central India
复制标题
印度中北部邦德尔坎德克拉通不含石英的高镁、铝金云母-绿泥石片岩中新太古代高压玛格丽特-白云母-绿泥石电晕刚玉
DOI：
--
复制
发表时间：
2011
期刊：
影响因子：
--
通讯作者：
M. Satynarayanan
中科院分区：
文献类型：
--
作者：
L. Saha;N. Pant;J. K. Pati;D. Upadhyay;J. Berndt;A. Bhattacharya;M. Satynarayanan
在印度中北部 Bundelkhand 克拉通的不含石英的铁、贫钠和高镁、铝片岩中，细交错的金云母-绿泥石聚集体中的刚玉成斑岩与稀有的斜帘石被白云母和绿泥石的细粒（<3μm）外环（>200μm宽）共生体覆盖。 （金云母 + 刚玉 + H2O → 多晶白云母 + 绿泥石），以及 <100 μm 宽的玛格丽特白云母内环（刚玉 + 斜帘石 + 多晶白云母 → 玛格丽石 + 白云母 + H2O）。宽束电子探针微量分析表明，双层电晕中的 Mg 从刚玉向外增加，Al 和 K 相应减少。Si 和 Ca 增加，然后减少到基体值。据推测，高度结构化的双层电晕上的尖锐化学梯度表明，电晕形成反应是由局部晶界控制的热力学不稳定性促进的，而不是通过平流扩散进行的元素传输。 KMASH 反应的 P-T 收敛和使用微域成分计算的 NCKMASH 伪截面相关系表明，绿泥石-白云母外环在 18-20 kbar 和约 18-20 kbar 下形成。 630°C。 NCKMASH 玛格丽特-白云母内环产生较低的变质 P-T 条件，约为 11 ± 3 kbar，约 11 ± 3 kbar。 630°C。变质独居石的 U-Th-Pb 化学测年和再平衡锆石的 LA-ICPMS U-Pb 同位素测年2.78 Ga年龄，被解释为邦德尔坎德克拉通中日冕形成和新太古代高磷变质作用的年代，这在印度前寒武纪中迄今为止是未知的。 (220)
In quartz-free Fe, Na-poor and high-Mg, Al schists from the Bundelkhand craton in north central India, corundum porphyroblasts in finely interleaved phlogopite–chlorite aggregates with rare clinozoisite are mantled by fine-grained (<3 μm) intergrowths of outer collars (>200 μm wide) of phengitic-muscovite and chlorite (phlogopite + corundum + H2O → phengitic-muscovite + chlorite), and <100 μm wide inner collars of margarite–muscovite (corundum + clinozoisite + phengitic muscovite → margarite + muscovite + H2O). Wide-beam electron probe microanalyses indicate Mg in the bi-layered corona increases from corundum outwards, with a complementary decrease in Al and K. Si and Ca increase and then decrease to matrix values. The sharp chemical gradients across the highly structured bi-layered corona are inferred to suggest that the corona-forming reactions were promoted by local grain-boundary-controlled thermodynamic instability as opposed to element transport by advective diffusion. The P–T convergence of KMASH reactions and NCKMASH pseudosection phase relations computed using micro-domain compositions indicate the chlorite–phengitic muscovite outer collar formed at 18–20 kbar and ca. 630°C. The NCKMASH margarite–muscovite inner collar yielded lower metamorphic P–T conditions of 11 ± 3 kbar, ca. 630°C. U–Th–Pb chemical dating of metamorphic monazite and LA-ICPMS U–Pb isotope dating of re-equilibrated zircon yield ca. 2.78 Ga ages, which are interpreted to date corona formation and Neoarchean high-P metamorphism in the Bundelkhand craton, hitherto unknown in the Indian Precambrian. (220)