四川丹巴地区中低压变质作用及P-T轨迹

四川丹巴地区地处华北板块、扬子板块和羌塘板块的汇合处,这里集中了中压型的巴罗变质带和低压型的巴肯变质带,该区中低压变质作用的研究对于探讨松潘-甘孜造山带的形成过程与地壳演化过程具有重要的理论意义和大陆动力学意义。本文通过地质温压力计估算了研究区的峰期变质温度和压力,从微区的角度分析了各变质带的P-T轨迹和地热梯度, 结果表明,丹巴地区巴罗型变质带和巴肯型变质带都具有顺时针的P-T轨迹,但是巴肯型变质带的地热梯度高于巴罗带。结合研究区的变质带的分布,变质矿物共生组合及变质反应,本文认为丹巴地区的确并存巴罗带和巴肯带,两种地热梯度反映了构造条件上的差异。

Medium-low pressure metamorphism and P-T paths in Danba domain, Sichuan province of the western China

Danba Domain is in the convergent junction of North China block, Yangtze block and Qiangtang block. There are Medium pressure barrovian type metamorphic zones and low pressure Buchan metamorohic sequences. The study is of great theoretic and dynamic significance in understanding the formation of Songpan - Ganzi orogen and the crust evolution. On the basis of geothermbarometry, we set up P-T paths and calculated the geothermal gradient for each of the metamorphic zones. The results show that both the barrovian and the Buchan metamorphic rocks have clockwise P-T paths but there are difference in geothermal gradient. Combined with the field, mineral assemblages and metamorphic reactions, we think that there do exist barrovian and Buchan zones in Danba domain and that different geothermal gradient may indicate various tectonic settings.