【作者】 杨岩；

【导师】 郑常青；

【作者基本信息】 吉林大学 ， 矿物学、岩石学、矿床学， 2022， 博士

【摘要】 佳木斯地块东南缘的麻山杂岩被认为是中国东北地区东部最古老的变质基底。麻山杂岩性质和时代的研究是确定佳木斯地块麻粒岩相变质作用演化及形成机制,探讨佳木斯地块前寒武纪地壳形成和演化过程的关键。本文对佳木斯地块柳毛、西麻山和上三阳地区麻山杂岩进行了系统详细的岩石学、矿物微区化学以及岩石地球化学研究,利用相平衡模拟和传统地质温压计估算温压的方法,结合锆石U–Pb年代学,估算了麻粒岩相变质作用不同变质阶段的变质温压条件,反演了麻山杂岩麻粒岩相变质作用P–T–t轨迹,限定了变质作用从峰期阶段至退变质阶段的变质作用时间及麻山杂岩中表壳岩的沉积时限,分析了晚泛非期高级变质作用与早古生代岩浆作用的关系,探讨了麻山杂岩的形成机制及佳木斯地块的构造亲缘性,对佳木斯地块可能的时空演化进行了尝试性恢复。1.柳毛地区麻粒岩相变质作用柳毛地区麻山杂岩的岩石类型主要分为两类:麻粒岩相的堇青矽线石榴二长片麻岩和石榴斜方黑云角闪斜长片麻岩,以及角闪岩相的矽线石榴黑云斜长片麻岩、矽线石榴斜长片麻岩和石榴黑云斜长片麻岩。堇青矽线石榴二长片麻岩的变质过程可划分为三个变质阶段:峰期麻粒岩相变质阶段（M₂:～9.2 kbar/845–865°C）,峰后近等温降压变质阶段（M₃:4.7–5.1 kbar/820–865°C）和晚期近等压冷却变质阶段（M₄:4.0–4.8 kbar/660–720°C）。石榴斜方黑云角闪斜长片麻岩的峰期变质阶段（M₂）的温压条件为9.0–9.2 kbar/845–870°C。2.西麻山地区麻粒岩相变质作用西麻山地区麻山杂岩泥质系列变质岩主要有四种岩石类型,分别为:含尖晶石矽线堇青石榴二长片麻岩、含尖晶石石榴矽线二长片麻岩、含尖晶石堇青石榴矽线二长片麻岩和含石榴石二长片麻岩。其麻粒岩相变质过程可划分为三个变质阶段:峰期麻粒岩相变质阶段（M₂:～8 kbar/835–850°C）,峰后近等温降压变质阶段（M₃:～4 kbar/775–835°C）和晚期近等压冷却变质阶段（M₄:<4 kbar/～510–710°C）。3.上三阳地区麻粒岩相变质作用上三阳地区麻山杂岩的主要岩石类型有:石榴矽线堇青黑云二长片麻岩、石榴矽线二长片麻岩和石榴矽线黑云二长片麻岩。石榴矽线堇青黑云二长片麻岩的变质过程可划分为四个变质阶段:进变质阶段,峰期麻粒岩相变质阶段（M₂:6.5–8.5 kbar/815–825°C）,峰后近等温降压变质阶段（M₃:5.3–5.7 kbar/780–795°C）和晚期近等压冷却变质阶段（M₄:4.5–5.3 kbar/730–775°C）。4.麻山杂岩的变质演化过程研究发现,佳木斯地块柳毛、西麻山和上三阳地区麻山杂岩峰期变质级别都达到了麻粒岩相。变质作用演化P–T轨迹为顺时针型,与造山带型类似,特别是从峰期到退变质阶段,总体经历了峰后近等温降压（ITD）及晚期冷却的演化过程。根据变质条件的估算结果,可以初步推断佳木斯地块由东北至西南方向（柳毛→西麻山→上三阳地区）麻山杂岩的变质作用强度逐渐减弱。5.麻山杂岩地球化学及年代学特征柳毛、西麻山和上三阳地区麻山杂岩泥质系列变质岩的原岩为粘土岩或砂岩,物源以长英质岩石为主,构造环境为大陆岛弧。锆石U–Pb年代学测试结果表明,佳木斯地块麻山杂岩原岩的沉积时间不早于古元古代（～1927 Ma）且不晚于新元古代（～898 Ma）。麻粒岩相变质作用的峰期变质时间可能为530～500 Ma,峰后减压过程大致发生在500～490 Ma,晚期降温过程认为发生在476～453 Ma。这些岩石被同构造花岗质岩石（530～500 Ma）和后构造花岗质岩石（490～476 Ma）侵入。6.佳木斯地块的构造亲缘性综合上述研究成果,结合已发表的区域地质资料,与全球范围内晚泛非期变质地体进行系统对比,认为佳木斯地块和兴凯地块具有相同的构造属性,在新元古代晚期之后属于统一陆块整体。佳木斯-兴凯地块并非中亚造山带的原地微陆块,也不是直接起源于华北克拉通、华南克拉通和塔里木克拉通,而与西伯利亚克拉通具有亲缘性,是晚泛非期形成在西伯利亚克拉通南缘Altai-Sayan–Baikal造山带的一部分。更多还原

【Abstract】 The Mashan Complex in the southeastern margin of the Jiamusi Massif has traditionally been interpreted to be the oldest stratigraphic sequence in eastern NE China.The nature and age of the Mashan Complex（or Mashan Group）in northeast China is key for determining the Precambrian geological evolution and origins of the Jiamusi Massif.Here we present petrological,mineralogical chemistry,geochemical analysis,geothermobarometry,phase equilibria modelling,in addition with zircon U–Pb dating of the Mashan Complex from the Liumao,Ximashan,and Shangsanyang area,Heilongjiang Province,China.Four aspects of achievements are obtained,i.e.,（1）estimate the granulite-facies metamorphic P–T conditions of different stage and plot the P–T–t path;（2）limit the metamorphism timing from peak to retrogradeof the granulite-facies metamorphism,as well as the depositional age of the supracrustal rocks within the Mashan Complex;（3）determine the relationship between the early Paleozoic magmatism and the Late Pan-African high-grade metamorphism;and（4）discuss the formation mechanism of the Mashan Complex and the tectonic attribute of the Jiamusi–Khanka Massif,and accordingly propose a tentative spatio-temporal evolution model for the Jiamusi/Khanka/Bureya massifs.1.Metamorphism of granulite facies in the Liumao areaThe metamorphic rocks of the Mashan Complex in the Liumao area consist mainly of two groups:granulite-facies Crd–Sil–Grt–Kfs–Pl and Grt–Opx–Bi–Amp–Pl gneisses;amphibolite-facies Sil–Grt–Bi,Sil–Grt,and Grt–Bi gneisses.Three metamorphic assemblages（M₂–M₄）were identified in the Crd–Sil–Grt–Kfs–Pl gneisses.The metamorphic P–T conditions of the peak granulite-facies stage（M₂）,the post-peak decompression stage（M₃）,and the final cooling stage（M₄）assemblages in the pelitic granulite were estimated as 9.2 kbar/845–865°C,4.7–5.1 kbar/820–865°C,and 4.0–4.8kbar/660–720°C,respectively.Similar results were obtained for the felsic granulite,with the metamorphic P–T conditions of the peak assemblage（M₂）evaluated as 9.0–9.2kbar/845–870°C.2.Metamorphism of granulite facies in the Ximashan areaThe metamorphic rocks of the Mashan Complex in the Ximashan area are mainly composed of four types:Spl-bearing Sil–Cord–Grt–Kfs–Pl gneiss,Spl-bearing Grt–Sil–Kfs–Pl gneiss,Spl-bearing Cord–Grt–Sil–Kfs–Pl gneiss and Grt-bearing Kfs–Pl gneiss.Three metamorphic assemblages（M₂–M₄）were recognized in the granulite-facies metamorphic rocks:a peak granulite-facies stage（M₂:～8 kbar/835–850°C）,a post-peak near-isothermal decompression stage（M₃:～4 kbar/775–835°C）,and a late near-isobaric cooling stage（M₄:4.5–5.3 kbar/730–775°C）.3.Metamorphism of granulite facies in the Shangsanyang areaThe metamorphic rocks of the Mashan Complex in the Shangsanyang area are mainly three types:Grt–Sil–Cord–Bi–Kfs–Pl,Grt–Sil–Kfs–Pl,and Grt–Sil–Bi–Kfs–Pl gneisses.Four metamorphic assemblages（M₂–M₄）were recognized in the Grt–Sil–Cord–Bi–Kfs–Pl gneisses:a prograde metamorphism（M₁）,a peak granulite facies metamorphism（M₂:6.5–8.5 kbar/815–825°C）,a post-peak decompression stage（M₃:5.3–5.7 kbar/780–795°C）,and retrograde stage（M₄:4.5–5.3 kbar/730–775°C）.4.Metamorphic evolution of the Mashan ComplexIt is found that the peak metamorphic grade of the Mashan Complex in Liumao,Ximashan and Shangsanyang areas of the Jiamusi Massif all reached granulite facies.These metamorphic stages imply a collisional orogenic process with typical clockwise P–T paths with post-peak near-isothermal decompression（ITD）and late near-isobaric cooling segments.According to the results of the P–T condition estimation,it can be preliminarily inferred that the metamorphism intensity of the Mashan Complex in the Jiamusi Massif gradually weakened from northeast to southwest（Liumao→Ximashan→Shangsanyang）.5.Geochemical and chronological characteristics of the Mashan ComplexThe protoliths of the metapelites from the Mashan Complex were clay rocks and sandstones,whose provenance is dominantly felsic rocks which formed from a continental island arc.Zircon U–Pb geochronology shows that the protolith of the Mashan Complex deposited during the Early Neoproterozoic（～898 Ma）,and the earliest time might be Paleoproterozoic（～1927 Ma）.The peak,post-peak near-isothermal decompression,and final cooling stages of the granulite-facies metamorphism in the Jiamusi Massif might have occurred at 530～500 Ma,530～490 Ma,and 476～453 Ma,respectively.These rocks have been intruded by syn-（530～500 Ma）and post-tectonic（490～476 Ma）granitic rocks.6.Tectonic affinity of the Jiamusi MassifTaking into account of the above research results,published regional geological data,and global late Pan-African metamorphic terranes correlations,it is inferred that the Jiamusi and Khanka massifs should be regarded as forming part of a contiguous massif from the late Neoproterozoic time.In summary,the Jiamusi–Khanka Massif cannot be directly derived from the North China Craton,South China Craton,and Tarim Craton.Instead,it might be a rifted portion of the Altai-Sayan–Baikal orogen and derived from the southern margin of the Siberia Craton during the late Pan-African period.更多还原