A Study on the Provenance of Early to Late Triassic Clastic Rocks From the Northwestern Sichuan Basin, Southwestern China: Constraints on the Early Mesozoic Tectonic Evolution of the Western Yangtze Block

Abstract

U–Pb ages of 637 new detrital zircons of Triassic sandstones from the Northwestern Sichuan Basin (NWSB), together with the petrology and paleocurrent data, are used to constrain the sediment provenance and tectonic–paleogeographic evolution of the western Yangtze Block. The U–Pb age data for the Lower Triassic detrital zircons generally show populations at ∼1,850 Ma, 980–705 Ma, 680–510 Ma, and 290–230 Ma with a minor cluster at ∼2.4 Ga. Such age spectrum features together with the eastward to northeastward paleocurrent direction implied that the Northwestern Sichuan Basin was dominantly fed by the uplifted Khamdian Paleoland. The Upper Triassic detrital zircons yield age populations at 855–730 Ma, 455–415 Ma, and 290–215 Ma and a prominent age group of 1.9–1.7 Ga. These age spectrum features together with paleocurrent data showed a provenance change with a major source of the Longmenshan thrust belt and Songpan-Ganzi terrane for the south area of NWSB and the Qinling orogenic belt for the north part of NWSB. Such transition of the provenance probably indicated the subsidence of the Khamdian Paleoland and uplift of the Songpan-Ganzi terrane and Qinling orogenic belt from the Early Triassic to the Late Triassic. This tectonic inversion most likely resulted from the gradually thermal subsidence of the Emeishan large igneous province (ELIP) and the gravitational loading triggered by the eastward shortening of the Songpan-Ganzi terrane as well as the ongoing convergence between Yangtze Block and North China Block.

The timing of the initial collision between the South and North China blocks constraining from the sediments in the eastern Sichuan Basin

“…The detrital zircon age spectrum of the Early Triassic Feixianguan Formation is samilar to those of the cotemporary clastic sediments in the northwestern Sichuan Basin and Zigui Basin 12 , 41 , and all shows the major peaks at ~ 2500 Ma, ~ 1850 Ma and ~ 850 Ma. This age peaks are consistent with the episodes of magmatic activities in the South China Block 42 , 43 .…”

Meso–Cenozoic Exhumation in the South Qinling Shan (Central China) Recorded by Detrital Apatite Fission-Track Dating of Modern River Sediments

“…The gravel and sandstone found in the northern Jianghan Basin document the unroofing history of the South Qinling Shan during the Early Jurassic [40,69] (Figure 4b; Figure 7(5)). At the same time, previous studies have demonstrated the U-Pb provenance tracing results of detrital zircon, which indicate that the South Qinling Shan served as a stable provenance area in the northern Sichuan Basin during the Early Jurassic [39,70,71] (Figure 7(6)). The unannealed zircon fission-track and zircon (U-Th)/He ages obtained from these formations in the northern Sichuan Basin indicate that the exhumation of the South Qinling Shan occurred between 196 and 180 Ma [66,72] (Figure 7(7,8)).…”

“…This exhumation led to the formation of large rivers that flowed into the Jianghan Basin and Sichuan Basin on the east and west sides of the Huangling anticline, respectively [110,111]. The western (4) [39]; (5) [40,67]; (6) [39,70,71]; (7) [65]; (8) [72]; (9) [41,73]; (10) [74]; (11) [75]; (12) This study; (13) [28]; (14) [7,8,[76][77][78]; (15) [67]; (16) [79]; (17) [80]; (18) [81]; (19) [74]; (20) [82]; (21) [70]; (22) [83]; (23) [84]; (24)…”

“…Therefore, the outward expansion of the Tibetan Plateau during the Cenozoic era played a crucial part in the exhumation process of the Qinling orogenic belt. [40,67]; (6) [39,70,71]; (7) [65]; (8) [72]; (9) [41,73]; (10) [74]; (11) [75]; (12) This study; (13) [28]; (14) [7,8,[76][77][78]; (15) [67]; (16) [79]; (17) [80]; (18) [81]; (19) [74]; (20) [82]; (21) [70]; (22) [83]; (23) [84]; (24) [40,41]; (25) This study; (26) …”

“…Figure 7. A summary map of Mesozoic and Cenozoic thermal events, sedimentary records, tectonic settings, and geological significance in the Qinling Orogenic Belt: (1) this study; (2) [30]; (3) [68];(4)[39];(5) [40,67];(6) [39,70,71];(7) [65];(8) [72];(9) [41,73];(10) [74];(11) [75];(12) This study;(13) [28];(14) [7,8,[76][77][78];(15) [67];(16) [79];(17) [80];(18) [81];(19) [74];(20) [82];(21) [70];(22) [83];(23) [84];(24) [40,41];…”