相平衡模拟对吉南地区集安群-老岭群变沉积岩系变质-深熔演化过程的制约

The metasedimentary rocks of Ji'an and Laoling groups preserved mineral assemblages and various metamorphic reactions during multiple metamorphic stages which record complex metamorphic-anatectic evolution history and are suitable to investigate the evolution and dynamic setting of the Jiao-Liao-Ji Mobile Belt. The metasedimentary rocks of Ji'an and Laoling groups are therefore treated as the main study object, phase equilibria modeling combined with calibrated thermobarometer is firstly applied to precisely constrain the P-T conditions of metamorphic mineral assemblages with multi-stages, as well as link observed microstructures with possible metamorphic reaction, illustrating the mechanism of partial melting, melt behavior and the genetic relationship between melt and metamorphic evolution. On the basis of Laser Raman spectroscopy, cathodoluminescence and backscattered image analyses, U-Th-Pb dating is used to monazite, xenotime, and zircon, together with Ar-Ar dating of mica and amphibolite, in order to restrict the timing of protolith and multi-stage metamorphism, and subsequently construct the P-T-t path. The study shows scientific significance of depicting the metamorphic evolution of the metasedimentary rocks of Ji'an and Laoling groups and reconstructing the regional orogenic evolution and relative geodynamic process.

吉南地区集安群-老岭群变沉积岩系保存多期/多阶段矿物组合和变质反应结构信息，记录了复杂的变质-深熔热演化历史，是探究胶-辽-吉古元古代活动带形成演化及动力学背景的理想靶区。本申请拟以集安群-老岭群变沉积岩系为重点研究对象，率先采用相平衡模拟并配合修正矿物对温压计等综合研究手段，精确限定各变质阶段矿物组合特征及形成的P-T条件，模拟矿物相转变结构与变质反应间的关系，揭示变沉积岩系部分熔融成因机制、熔体行为及其与变质演化之间的成因链接。在矿物包体激光拉曼、阴极发光和背散射图像分析的基础上，对独居石、磷钇矿和锆石进行U-Th-Pb定年，并配合云母、角闪石等矿物的Ar-Ar定年，精确构筑变沉积岩系原岩形成时代-进变质时代-峰期变质时代-晚期退变质时代的年代格架及完整的变质演化P-T-t轨迹。该项研究对于精细刻画集安群和老岭群变沉积岩系变质演化历史、重塑复杂的造山演化动力学过程具有重要的科学意义。

胶-辽-吉带吉林南部的清河镇大东岔和文字沟一带、头道镇、上活龙村等地区均识别出集安群麻粒岩相变质岩石，包括夕线堇青石榴泥质麻粒岩、紫苏堇青石榴泥质麻粒岩，并见少量基性麻粒岩等。紫苏堇青石榴泥质麻粒岩与堇青石榴泥质麻粒岩呈互层状产出，其内可见条带状长英质浅色体，反映岩石部分熔融过程形成的部分熔体残留在岩石内。详细的岩相学、矿物化学、传统地质温压计和相平衡模拟综合研究结果显示，集安群紫苏堇青石榴泥质麻粒岩保留了多阶段麻粒岩相变质矿物组合，其主要组成矿物为石榴石、斜方辉石、堇青石、黑云母、斜长石和石英，含少量石墨、钛铁矿和磁铁矿等。该岩石保留了峰期麻粒岩相变质（M2）和峰后近等温减压变质（M3）阶段的矿物组合，并显示顺时针P–T演化轨迹，其中M2阶段的矿物组合为石榴石 + 黑云母 + 斜长石 + 石英 + 钛铁矿 + 磁铁矿 + 熔体，峰期P–T条件分别为860 ~ 870 °C和~10 kbar。峰后减压过程，随着压力的降低，岩石进入斜方辉石的稳定域。M3阶段矿物组合为黑云母 + 堇青石 + 石榴石 + 斜方辉石 + 钾长石 + 斜长石 + 石英 + 磁铁矿 + 熔体，P–T 条件为850 ~ 890 °C和~7.5 kbar。集安群泥质麻粒岩变质锆石和独居石的U-Pb年龄分别为1870 ~ 1890 Ma和1840 ~ 1880 Ma，与前人报道的变质时代近一致。本研究对集安群泥质麻粒岩限定的峰期温度高于前人报道的结果，表明集安群变质岩石应普遍经历了麻粒岩相变质作用而非高角闪岩相变质。此外，集安群泥质麻粒岩近等温减压型顺时针P-T轨迹样式与前人报道的辽南地区南辽河群、胶北地区荆山群高压泥质麻粒岩顺时针P-T轨迹类似，均反映了俯冲碰撞过程。