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谢志鹏,王建,HATTORI Keiko,薛传东,钟军伟,王泽利. 2018. 苏鲁超高压变质带胡家林超镁铁质岩成因及构造意义. 岩石学报, 34(6): 1539-1556
苏鲁超高压变质带胡家林超镁铁质岩成因及构造意义
作者单位
谢志鹏 昆明理工大学国土资源工程学院, 昆明 650093
吉林大学地球科学学院, 长春 130061 
王建 吉林大学地球科学学院, 长春 130061 
HATTORI Keiko 渥太华大学地球科学系, 渥太华 K1N 6N5 
薛传东 昆明理工大学国土资源工程学院, 昆明 650093 
钟军伟 昆明理工大学国土资源工程学院, 昆明 650093 
王泽利 山东科技大学地球科学与工程学院, 青岛 266590 
基金项目:本文受国家自然科学基金项目(41603032、41472051)和中国博士后科学基金项目(2016M602721)联合资助.
摘要:
      胡家林超镁铁质杂岩体产于苏鲁超高压变质带中部,纯橄岩和(石榴)单斜辉石岩呈不连续透镜体产于蛇纹石化橄榄岩中。纯橄岩遭受了部分蛇纹石化(烧失量=6.6%~13.2%),全岩富集强相容元素(Ni、Cr、Co)和Ir族PGE(IPGE;Ir、Os、Ru)及高IPGE/PPGE值,亏损Al、Ti、V,具高Mg#橄榄石(Fo=91.7~92.4)和高Cr#(0.68~0.76)尖晶石。纯橄岩高耐熔地球化学及矿物化学特征和古老的大陆岩石圈地幔相一致,表明其原岩来源于弧前地幔,代表了华北克拉通古老的大陆岩石圈地幔残留。(石榴)单斜辉石岩全岩呈相对低含量的强相容元素(Cr、Ni、Co)和IPGE,高含量的Al、Ti、V和流体迁移元素(Sr、Pb和Ba),球粒陨石标准化REE配分图呈明显"上凸"型,具低Mg#橄榄石(Fo=76.6~76.8)和低Al2O3(<2.76%)和高SiO2(54.56%~56.87%)的单斜辉石。全岩组成和矿物化学表明其原岩为俯冲带内超镁铁质火成堆晶岩,最初岩浆由地幔岩高程度部分熔融的熔体和俯冲带中富H2O流体和/或熔体构成。(石榴)单斜辉石岩原岩曾被地幔流带入扬子大陆俯冲板片和上覆地幔楔之间的俯冲通道,经历了超高压变质作用和生成大量石榴石。(石榴)单斜辉石岩在折返过程中,与大陆岩石圈地幔楔剥离的蛇纹石化橄榄岩及纯橄岩相结合,形成超镁铁质杂岩体,整体被低密度的俯冲板片(主要由花岗质片麻岩和变质沉积岩组成)裹挟,折返至地壳浅部。
英文摘要:
      The Hujialin ultramafic complex in the central region of Sulu ultrahigh-pressure (UHP) metamorphic belt mainly consists of discontinuous lenses of garnet-bearing clinopyroxenite and dunite surrounded by marginal serpentinized peridotites. Dunite samples, which are partially hydrated (LOI=6.6%~13.2%), contain high concentrations of compatible elements (Ni, Cr, Co) and IPGE with high ratios (up to 8.8) of IPGE/PPGE, low concentrations of Al, Ti, V in bulk rocks, olivine in dunite shows high Fo (91.7~92.4) and Cr-spinel displays high Cr# (0.68~0.76). The high refractory geochemical characteristics and mineral chemistries of dunite samples are similar to that of the ancient subcontinental lithospheric mantle, suggesting that dunites originated from forearc mantle, and represented the relic of the ancient subcontinental lithospheric mantle. Garnet-bearing clinopyroxenites show relatively low concentrations of compatible elements (Ni, Cr, Co) and IPGE, high concentrations of Al, Ti, V, and fluid-mobile elements (Sr, Pb and Ba) in buck rocks. They show convex chondrite-normalized REE patterns, low Fo (76.6~76.8) in olivine, low Al2O3 (<2.76%) and high SiO2 (54.56%~56.87%) in clinopyroxene. The bulk rock compositions and mineral chemistry suggest garnet-bearing clinopyroxenite is initially cumulate of subduction-related ultramafic melt, and the parental magma was formed by the melt from high degree of partial melting of mantle rocks and H2O-rich fluids/melt from subduction zone. The protoliths of garnet-bearing clinopyroxenite was individually incorporated into the subduction channel between the Yangtze subducted plate and overlying North China Craton by a mantle flow and then underwent UHP metamorphism. Garnet-bearing clinopyroxenite probably physically mixed with serpentinized peridotite lenses off-scraped from the overlying subcontinental lithospheric mantle (SCLM) wedge in the exhumation process, and both of them were coerced by low-density subducted slab (granitic gneiss and metamorphosed sedimentary rocks) and exhumed to the surface together.
关键词:苏鲁超高压变质带  铂族元素(PGE)  纯橄岩  (石榴)单斜辉石岩  岩石成因
投稿时间:2017-10-16  修订日期:2018-05-23
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