东疆哈密小堡二重热变质岩及其矿物共生分析和pTt轨迹

THE TWO-FOLD-CONTACT METAMORPHIC ROCKS OCCURRING AT XIAOPU , HAMI , EASTERN XINJIANG, THEIR MINERAL PARAGENESIS ANALYSIS AND pTt PATH

哈密小堡变质地体是石碳系含碳砂泥质岩,先后在315Ma和259Ma经闪长岩和花岗岩体侵入导致的二重热变质作用产物,其中含红柱石铁铝榴石十字石黑云母绿泥石五种变斑晶角岩的变斑晶带状成分和结构记录了二重热变质作用特征。估算的两期热变质峰期温度压力分别为530.58℃,0.29GPa和566.06℃,0.40GPa,并获得一反时针pTt轨迹。这些特征暗示了该区岩浆作用和热变质作用与板底垫托(underplating)和碰撞造山带因陆 陆碰撞、地壳增厚诱发的深部地壳的深熔作用有关.

The Xiaopu metamorphic terrain lies within the Harerlike Collision-Orogeneny Zone between the Siberia Continent Plate and the Tarim Continent Plate. During the convergency-collision, both the diorite and granite bodies intruded into the Early Carboniferous in 315 Ma and 259 Ma, respectively, correspondingly inducing the two-fold contact metamorphism which turned some argillo-arenaceous rocks into hornfelses, among which, one carbon-rich hornfel contains five porphyroblasts: andalusite, almandine, staurolite, biotite and chlorite. They show zoning in both composition and texture which have recorded the history of two-fold contact metamorphism, with (530.58 ℃), (0.285 GPa,) and (566.06 ℃),(0.40 GPa) peaks, respectively, indicating an unticlockwise pTtpath. These characters imply that the magmatism and contact metamorphism occurring in the area are related to underplating and anatexis due to continent-continent collision which resulted in the increment of thickness of the continent crust.