{"title":"中国东天山造山带早二叠世红柳井花岗岩群的岩石成因:中天山微大陆地壳增长的证据","authors":"Zhen‐Yu He, R. Klemd, T. Lu, Lili Yan, Hua Xiang","doi":"10.1130/b36970.1","DOIUrl":null,"url":null,"abstract":"The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geochronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hongliujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of εHf(t) and lower εNd(t) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. Thus, our study reveals that microcontinents with Precambrian crustal basement were major sites of juvenile continental growth during the accretionary evolution of the Central Asian Orogenic Belt.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":null,"pages":null},"PeriodicalIF":3.9000,"publicationDate":"2023-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Petrogenesis of the early Permian Hongliujing granite complex in the Chinese Eastern Tianshan orogen: Evidence for crustal growth in the Central Tianshan microcontinent\",\"authors\":\"Zhen‐Yu He, R. Klemd, T. Lu, Lili Yan, Hua Xiang\",\"doi\":\"10.1130/b36970.1\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geochronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hongliujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of εHf(t) and lower εNd(t) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. 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引用次数: 0
摘要
硅质岩浆体系的生成和变质是解决大陆地壳分异的重要过程。这一认识推动了中亚造山带南缘天山中微大陆早二叠世红流井花岗岩杂岩的年代学和地球化学研究,该杂岩由石英二长岩、花岗岩和浅花岗岩组成。激光烧蚀-电感耦合等离子体-质谱(LA-ICP-MS)锆石U-Pb测年结果显示,红柳井杂岩单元的年龄(279±2 Ma ~ 270±2 Ma)几乎一致。高硅白花岗岩体和花岗岩具有Rb正、Eu负异常和Ba、Sr、P、Ti亏缺的特征。锆石微量元素具有较低的Ti、Th/U和较高的Yb/Gd的特征。石英二长岩及其基性微颗粒包体呈现少量负Ba、Sr、P、Ti、Eu异常,锆石微量元素表现为较高的Ti、Th/U和较低的Yb/Gd。该杂岩具有相似的锆石Hf和全岩Nd同位素组成,Hf和Nd模型年龄小于1.4 Ga,表明它们的岩浆来自于同位素衰竭的地幔,并有地壳熔体的贡献。浅花岗岩的εHf(t)变化较大,而εNd(t)变化较小,表明其岩浆受较大的地壳污染影响。本文认为,结晶-熔体分离是岩浆系统演化的主要机制,早二叠世岩浆活动是由俯冲的南天山洋板块在中天山微大陆东部下方的板块回滚引发的地壳形成事件。因此,具有前寒武纪地壳基底的微大陆是中亚造山带增生演化中幼年大陆发育的主要场所。
Petrogenesis of the early Permian Hongliujing granite complex in the Chinese Eastern Tianshan orogen: Evidence for crustal growth in the Central Tianshan microcontinent
The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geochronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hongliujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of εHf(t) and lower εNd(t) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. Thus, our study reveals that microcontinents with Precambrian crustal basement were major sites of juvenile continental growth during the accretionary evolution of the Central Asian Orogenic Belt.
期刊介绍:
The GSA Bulletin is the Society''s premier scholarly journal, published continuously since 1890. Its first editor was William John (WJ) McGee, who was responsible for establishing much of its original style and format. Fully refereed, each bimonthly issue includes 16-20 papers focusing on the most definitive, timely, and classic-style research in all earth-science disciplines. The Bulletin welcomes most contributions that are data-rich, mature studies of broad interest (i.e., of interest to more than one sub-discipline of earth science) and of lasting, archival quality. These include (but are not limited to) studies related to tectonics, structural geology, geochemistry, geophysics, hydrogeology, marine geology, paleoclimatology, planetary geology, quaternary geology/geomorphology, sedimentary geology, stratigraphy, and volcanology. The journal is committed to further developing both the scope of its content and its international profile so that it publishes the most current earth science research that will be of wide interest to geoscientists.