绵阳—长宁拉张槽位于四川盆地西缘,是下寒武统筇竹寺组黑色页岩的重要沉积—保存单元,也是克拉通伸展研究的关键窗口。然而,其形成机制与起始时限仍存争议。早寒武时期海洋氧化—还原状态的非均一性与长期海侵过程叠加,进一步加剧了地...绵阳—长宁拉张槽位于四川盆地西缘,是下寒武统筇竹寺组黑色页岩的重要沉积—保存单元,也是克拉通伸展研究的关键窗口。然而,其形成机制与起始时限仍存争议。早寒武时期海洋氧化—还原状态的非均一性与长期海侵过程叠加,进一步加剧了地层连续性与缺失判别的难度。区域年代学与综合地层学研究将筇竹寺组的时代界限限定为526~514 Ma(Compston et al,2008),天文旋回记录为检验沉积分层节律与实现等时对比提供了高分辨率时标,但关于西南段是否存在显著缺环仍存分歧(Liu et al,2022;周杨等,2024)。展开更多
In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present pet...In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present petrological,geochemical and whole-rock Sr-Nd and zircon Hf isotopic data for basalts and gabbros sampled from the Qianmai mélange.Zircon grains from six basaltic and gabbroic samples yielded U-Pb ages of 495-482 Ma.These rocks are characterized by tholeiitic and Nbenriched compositions,with Nb/La ratios in the range of 0.38-1.38,similar to the typical Nb-enriched basalts.All the mafic rocks show slightly negative to positiveε_(Nd)(t)(-1.67 to+4.32)and zirconε_(Hf)(t)values(-7.3 to+3.8).Elemental and isotopic data suggest that the Qianmai Nb-enriched mafic rocks were mainly derived from the mixing of an OIB-like source with a subduction-modified mantle wedge source.Together with magmatic and sedimentary records of similar ages in the Lancang terrane and the Baoshan Block,our results reveal Early Paleozoic magmatic and sedimentary sequences along an active margin of the Proto-Tethys.Taking into account the recently identified Early Paleozoic ophiolitic mélange in the Yunxian-Menghai belt,we consider the Qianmai magmatic rocks to represent the products of early-stage subduction-related magmatism within a primitive island arc or fore-arc setting associated with the southward subduction of the Proto-Tethys.We infer that prolonged south-dipping subduction on the northern margin of Gondwana persisted from the Cambrian to the Late Ordovician.展开更多
文摘绵阳—长宁拉张槽位于四川盆地西缘,是下寒武统筇竹寺组黑色页岩的重要沉积—保存单元,也是克拉通伸展研究的关键窗口。然而,其形成机制与起始时限仍存争议。早寒武时期海洋氧化—还原状态的非均一性与长期海侵过程叠加,进一步加剧了地层连续性与缺失判别的难度。区域年代学与综合地层学研究将筇竹寺组的时代界限限定为526~514 Ma(Compston et al,2008),天文旋回记录为检验沉积分层节律与实现等时对比提供了高分辨率时标,但关于西南段是否存在显著缺环仍存分歧(Liu et al,2022;周杨等,2024)。
基金supported by projects from the“Xingdian Talent”Youth Talent Program in Yunnan Province(No.XDYCQNRC-2022-0041)the National Natural Science Foundation of China(Nos.42162020,41873062,92055314)。
文摘In this study,we investigated Early Paleozoic magmatic rocks of the Manlai Formation exposed along the eastern margin of the Lancang terrane to better understand the tectonic history of the Proto-Tethys.We present petrological,geochemical and whole-rock Sr-Nd and zircon Hf isotopic data for basalts and gabbros sampled from the Qianmai mélange.Zircon grains from six basaltic and gabbroic samples yielded U-Pb ages of 495-482 Ma.These rocks are characterized by tholeiitic and Nbenriched compositions,with Nb/La ratios in the range of 0.38-1.38,similar to the typical Nb-enriched basalts.All the mafic rocks show slightly negative to positiveε_(Nd)(t)(-1.67 to+4.32)and zirconε_(Hf)(t)values(-7.3 to+3.8).Elemental and isotopic data suggest that the Qianmai Nb-enriched mafic rocks were mainly derived from the mixing of an OIB-like source with a subduction-modified mantle wedge source.Together with magmatic and sedimentary records of similar ages in the Lancang terrane and the Baoshan Block,our results reveal Early Paleozoic magmatic and sedimentary sequences along an active margin of the Proto-Tethys.Taking into account the recently identified Early Paleozoic ophiolitic mélange in the Yunxian-Menghai belt,we consider the Qianmai magmatic rocks to represent the products of early-stage subduction-related magmatism within a primitive island arc or fore-arc setting associated with the southward subduction of the Proto-Tethys.We infer that prolonged south-dipping subduction on the northern margin of Gondwana persisted from the Cambrian to the Late Ordovician.
