摘要
东南极普里兹构造带被认为受到格林维尔期及泛非期两期构造热事件的影响,分别与罗迪尼亚和冈瓦纳超大陆的演化密切相关,但对两期构造热事件的性质还存在争议。为了进一步完善该构造带的演化历史,从矿物学、岩石学、相平衡模拟、锆石年代学等角度对普里兹构造带米洛半岛尖晶石-堇青石麻粒岩进行了研究。结果表明其主期矿物组合为尖晶石+堇青石+黑云母+矽线石+少量石榴子石+钾长石+钛铁矿,温压条件为870~910℃、0.64~0.69 GPa,晚期退变至810~820℃、0.49~0.53 GPa,并暗示了更高的峰期变质条件(T>910℃,P>0.69 GPa)。CL图像显示锆石具有明显的核-幔-边结构,LA-ICP-MS锆石U–Pb年代学分析显示核部年龄主要集中在613±7 Ma到877±9 Ma,最大值916±11 Ma,比典型的格林维尔期年龄年轻。锆石边部加权平均年龄为526±8 Ma,其Th/U比值范围较大(0.06~1.23),多数Th/U比值较高(>0.1),应代表峰后冷却结晶阶段。尖晶石-堇青石麻粒岩记录了中低压/高温—超高温的变质条件,结合区域已有资料,可能具有顺时针轨迹,其变质演化历史可能反映了碰撞造山之后的伸展阶段,推测与冈瓦纳超大陆的聚合过程有关。
[Objective]The Prydz Bay belt in East Antarctica recorded two significant tectono-thermal events,the Grenvillian event and the Pan-African event,which are considered to be closely related to the evolution of the Rodinia and Gondwana supercontinents.However,the geological history and the tectonic nature of the two events remain controversial.[Methods]Mineralogical and petrological analyses,phase equilibria modelling and zircon geochronology are combined to investigate the spinel−cordierite granulite from the Mirror Peninsula in order to better understand the tectono-thermal history of the Prydz Bay belt.[Results]The spinel−cordierite granulite contains different stages of mineral assemblages.The major stage of mineral assemblage involves cordierite,spinel,biotite,sillimanite,K-feldspar and minor garnet and ilmenite.The later stage of mineral assemblage is indicated by the emergence of magnetite as the increasing volumes of biotite and cordierite.Minor garnet and corundum are locally preserved,implying the mineral reaction‘g+cor→sp+sill’and more garnet and corundum in the peak stage.The garnet grains consist of 70%−72%almandine,20%−22%pyrope,~4%grossularite and~4%spessartine.The X_(Fe)(Fe^(2+)/(Fe^(2+)+Mg^(2+)))of representative garnet grains ranges from 0.77 to 0.80.The spinel exhibits an X_(Fe)range from 0.80 to 0.86.Different cordierite grains have similar compositions with Al of 3.89−3.93 a.p.f.u(atoms per formula unit)and X_(Fe)of 0.32−0.36.Biotite has high TiO_(2)(4.13%−5.23%)and Ti(0.23−0.30 a.p.f.u).Kfeldspar grains consist of 78%−85%orthoclase,15%−23%albite and~1%anorthite.Based on the mineral compositions and phase equilibrium modelling,the pressure−temperature(P−T)conditions of the major stage of mineral assemblage are constrained to 870−910℃and 0.64−0.69 GPa,followed by later retrogression to 810−820℃and 0.49−0.53 GPa.A peak stage with higher P−T conditions(T>910℃,P>0.69 GPa)can be inferred based on the relict peak minerals and characteristic mineral composi
作者
刘昕淑
王伟
保红
龚庭楠
湛礼卿
刘晓春
赵越
LIU Xinshu;WANG Wei-(RZ);BAO Hong;GONG Tingnan;ZHAN Liqing;LIU Xiaochun;ZHAO Yue(Institute of Geomechanics,Chinese Academy of Geological Science,Beijing 100081,China;Key Laboratory of Paleomagnetism and Tectonic Reconstruction,Ministry of Natural Resources,Beijing 100081,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China)
出处
《地质力学学报》
CSCD
北大核心
2024年第3期487-505,共19页
Journal of Geomechanics
基金
国家自然科学基金项目(42172068,41941004,41530209,41672062)
中国地质科学院基本科研业务费项目(JYYWF201819)
中国地质调查局地质调查项目(DD20221810)。
