大别山太湖地区榴辉岩岩石学、矿物成分和P-T条件特征及其所揭示的构造含义  

The Characteristic of Petrology,minerals chemistry and P-T conditions of Eclogites from Talhu area in Dabie Mountains,and its Tectonic significance.

作　　者：石永红[1] 王清晨[2] 林伟[2] 

机构地区：[1]合肥工业大学资环学院,合肥230009 [2]中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2006年第2期414-432,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金(<辽东半岛中生代同造山期伸展穹隆的几何学和运动学>项目批号:40202021;<古元古代板块构造的痕迹-辽东半岛北部19亿年的碰撞造山带研究>项目批号:40202021)

摘　　要：根据对大别山太湖地区1：10000地质填图,以及对榴辉岩的精细的岩石学、矿物成分和P-T条件的研究分析表明,该地区的榴辉岩可分为：高压榴辉岩,高压-超高压榴辉岩和超高压榴辉岩。从高压榴辉岩至超高压榴辉岩,石榴石中钙铝榴石、镁铝榴石组分,多硅白云母中的Si^(4+)逐渐增加,峰期变质P-T条件则从T=535℃～652℃和P=1．50～2．26GPa,T=625℃～777℃和P=2．41～3．04GPa,逐渐增加到T=767℃～942℃和P=3．49～4．09GPa,显示了区域上的连续变化特征。结合构造几何学的分布特征和榴辉岩的共生围岩,应用石榴石-单斜辉石温度计和石榴石-单斜辉石-多硅白云母压力计,计算建立了一条近于“5℃/km”的地温梯度线和两条T=650℃,P=2．50GPa和T=750℃,P=3．00GPa温度和压力等值线,并将南大别变质块体从南自北分为三个变质单元：高压带,高压-超高压带和超高压带,从而表明该变质块体连续的特征。本次研究建立了三条P-T轨迹,并尝试性地探讨了这些榴辉岩的不同的抬升速率,推测不同类型的榴辉岩在地下40～50km的深度发生了强烈的缩短,“焊接”成一整体缓慢抬升到地表,从而导致现今榴辉岩的分布状态。Eclogites from Taihu area in Dabie Mountains can be identified into HP （high pressure） eclogites, HP-UHP （high/high- ultrahigh pressure） eclogites and UHP （ultrahigh pressure） elcogites, based on the result of geological mapping （1： 10000） , and the investigation on the petrology, minerals chemistry and P-T conditions of these eclogites. From HP eclogites to UHP eclogites, the component of grossular and pyrope in garnet and Si^4＋ content of phengites rise gradually. Peak P-T conditions of eclogites also transform from 535°C - 652°C, 1.50 - 2.26GPa of HP eclogite, 625°C - 777°C, 2.41 - 3.04GPa of HP/UHP eclogite to 767°C-942°C , 3.49-4.09GPa of UHP eclogites, and show a regional P-T gradient trend. Combine structure geometric characteristic in space and wall rocks of eclogites, application of Grt-Cpx thermometer and Grt-Cpx-Pbe barometer, we define a 5°C/km ＂geotherm＂ and two isopleth lines with T = 650°C, P = 2.50GPa; T = 750°C, P = 3.00GPa, and divided the South Dabie Terrain into three subzones： HP-Zone, HP-UHP-Zone and UHP-Zone, which imply the South Dabie Terrain is a consist terrain. According P-T paths of three types of eclogites in this study and previous chronology, we discuss different uplift rate of these eclogites tentatively, and guess that these eclogites can be shortened in the depth of 40 -50km and sealed as a ＂whole terrain＂. Subsequently, this ＂whole terrain＂ ascends to the crust gently and forms the present distribution.

关 键 词：大别山 太湖地区 榴辉岩 P—T条件 抬升速率 

分 类 号：P588.348[天文地球—岩石学]