Provenance of the Middle-Upper Triassic Songpan-Ganzi Flysch of Western China Revealed by Anisotropy of Magnetic Susceptibility Measurements: Implications for the Tectonic-Paleogeographic Evolution of the Paleo-Tethys Ocean

IF 3.3 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Geochemistry Geophysics Geosystems Pub Date : 2026-10-05 DOI:10.1029/2026GC012964

Yuhan Yang, Yong Cao, Xiaozhou Ye, Zhenyu Yang, Zhiming Sun, Haibing Li

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Abstract

The Triassic Songpan-Ganzi turbidite complex (SGC) on the eastern Tibetan plateau is one of the largest flysch turbiditic complexes on Earth. However, the provenance of its extremely thick turbidites is hotly debated. We conducted the measurement of anisotropy of magnetic susceptibility (AMS) of Triassic turbidites from nine profiles in Ruo'ergai, Aba, Ganzi, Seda, and Xiaojin counties in the Songpan-Ganzi Basin. The AMS of 937 samples from 130 sampling sites shows a very low anisotropy degree (P < 1.07), and an oblate shape with the minimum axis (k₃) of the magnetic susceptibility ellipsoid being nearly perpendicular to the bedding plane. These findings reveal the primary sedimentary magnetic fabric in these rocks. The paleocurrent system during the Middle to Late Triassic was constructed based on the direction of the maximum axis (k₁) of the magnetic susceptibility ellipsoid. The results indicate that the SGC has a multi-source provenance, including the Qinling-Dabie orogenic belt, the Yidun arc and the North Qiangtang orogenic belt, and the East Kunlun-Qaidam block. The deposition of the great thick Upper Triassic flysch is genetically linked to the syn-collisional uplift of the surrounding orogenic belts. Therefore, we conclude that the Upper Triassic turbidites in the SGC were derived from surrounding collisional orogen sources, rather than only distant Dabie-Qinling sources eroded after the North China-South China collision. This challenges the traditional model that interprets the Triassic Songpan-Ganzi Basin as a simple, large-scale submarine fan system similar to the Cenozoic Bengal-Indus fans.

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磁化率各向异性揭示中国西部中上三叠统松潘-甘孜复理石物源：古特提斯洋构造-古地理演化的意义

青藏高原东部三叠系松潘-甘孜浊积岩杂岩是地球上最大的复理质浊积岩杂岩之一。然而，其极厚浊积物的来源却备受争议。对松潘—甘孜盆地若尔盖、阿坝、甘孜、色达、小金等9个地区三叠系浊积岩的磁化率各向异性进行了测量。130个采样点937个样品的磁化率各向异性度极低（P < 1.07），磁化率椭球呈扁圆形，磁化率椭球的最小轴线（k3）几乎垂直于顺层平面。这些发现揭示了这些岩石中的原始沉积磁性结构。根据磁化率椭球的最大轴线（k1）方向，构建了中晚三叠世古海流体系。结果表明，该盆地具有多源物源特征，包括秦岭—大别造山带、益墩弧和北羌塘造山带以及东昆仑—柴达木地块。上三叠统大厚复理石的沉积与周围造山带的同碰撞隆升有遗传关系。因此，我们认为上三叠统的浊积岩主要来自于周围的碰撞造山带源，而不仅仅是遥远的大别-秦岭源在南北碰撞后的侵蚀作用。这挑战了将三叠纪松潘-甘孜盆地解释为类似于新生代孟加拉-印度河扇的简单、大规模海底扇系统的传统模型。

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来源期刊

Geochemistry Geophysics Geosystems 地学-地球化学与地球物理

CiteScore

5.90

自引率

11.40%

发文量

252

审稿时长

1 months

期刊介绍： Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.