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<p>Numerous Indosinian igneous rocks in the North Qaidam (NQ) provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean. This paper presents a comprehensive study of the petrography, mineralogy, geochemistry, zircon U–Pb geochronology, and Hf isotope composition of dioritic rocks from the eastern NQ. Zircon U–Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic (244–240&#xa0;Ma). The rocks exhibit high-K calc-alkaline characteristics with variable SiO<sub>2</sub> (55.25–65.39 wt%) and elevated K<sub>2</sub>O + Na<sub>2</sub>O (4.81–6.94 wt%) contents. They show enrichment in LILEs (Rb, Ba, K) and depletion in HFSEs (Nb, Ta, Ti), with slight negative Eu anomalies (Eu/Eu* = 0.89–0.97). Zircon ε<sub>Hf</sub>(t) values (−20.93 to + 5.60) and T<sub>DM2</sub> ages (0.85–1.72&#xa0;Ga) suggest mixed sources. Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures (including reverse zoning), primarily composed of andesine and labradorite, with a small amount of oligoclase. The clinopyroxenes are all augites and have high crystallization temperatures (1111–1151&#xa0;°C). These features, particularly the reverse zoning of plagioclase, support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust, followed by mixing of underplated basaltic magma with crust-derived felsic magma. Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.</p>

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Petrogenesis of the dioritic rocks in the eastern North Qaidam: Implications for the tectonic evolution of the Paleo-Tethys Ocean

  • 期刊论文

  • 发表日期：

    2025年6月18日

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  • Panlong Wang,
  • Yongjun Li,
  • Yujun Zhuang,
  • Pingyang Gu,
  • Chao Shi,
  • Jiaxin Yan,
  • Gaoxue Yang,
  • Wei Li,
  • Hai Li,
  • Jianye Zhang,
  • Hao Fu

摘要

Numerous Indosinian igneous rocks in the North Qaidam (NQ) provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean. This paper presents a comprehensive study of the petrography, mineralogy, geochemistry, zircon U–Pb geochronology, and Hf isotope composition of dioritic rocks from the eastern NQ. Zircon U–Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic (244–240 Ma). The rocks exhibit high-K calc-alkaline characteristics with variable SiO2 (55.25–65.39 wt%) and elevated K2O + Na2O (4.81–6.94 wt%) contents. They show enrichment in LILEs (Rb, Ba, K) and depletion in HFSEs (Nb, Ta, Ti), with slight negative Eu anomalies (Eu/Eu* = 0.89–0.97). Zircon εHf(t) values (−20.93 to + 5.60) and TDM2 ages (0.85–1.72 Ga) suggest mixed sources. Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures (including reverse zoning), primarily composed of andesine and labradorite, with a small amount of oligoclase. The clinopyroxenes are all augites and have high crystallization temperatures (1111–1151 °C). These features, particularly the reverse zoning of plagioclase, support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust, followed by mixing of underplated basaltic magma with crust-derived felsic magma. Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.