How was the Triassic Songpan‐Ganzi basin filled? A provenance study

Abstract

The Triassic Songpan‐Ganzi complex comprises >200,000 km2 of 5–15 km thick turbiditic sediments. Although surrounded by several magmatic and orogenic belts, the Triassic high‐ and ultrahigh‐pressure Qinling‐Tongbai‐Hong'an‐Dabie (QTHD) orogen, located several hundred kilometers to the east, was proposed as its major source. Middle to Late Triassic samples from the northern and southern Songpan‐Ganzi complex, studied using detrital white mica 40Ar/39Ar ages, Si‐in‐white mica content, and detrital zircon U/Pb ages, suggest that the northern Songpan‐Ganzi deposystem obtained detritus from the north: the north China block, east Kunlun, northern Qaidam, Qilian, and western Qinling; the southern Songpan‐Ganzi deposystem was supplied from the northeasterly located Paleozoic QTHD area throughout the Ladinian and received detritus from the Triassic Hong'an‐Dabie orogen during the Carnian, indicative of exhumation of the orogen at that time. The QTHD orogen fed the Norian samples in the southeastern southern Songpan‐Ganzi deposystem, signifying long drainage channels along the western margin of the south China block. An additional supply from the Emeishan magmatic province and/or the Yidun arc is suggested by the paucity of white mica in the southern Songpan‐Ganzi deposystem. Mica ages of Rhaetian sediments from the northwestern Sichuan basin best correlate with those of the Triassic QTHD orogen. Our Si‐in‐white mica data demonstrate that the high‐ and ultrahigh‐pressure rocks of the Hong'an–Dabie Shan were not exposed in the Middle to Late Triassic.

Provenance and tectonic-paleogeographic evolution: Constraints from detrital zircon U–Pb ages of Late Triassic-Early Jurassic deposits in the northern Sichuan basin, central China

“…8b), which is similar to those of the detrital zircons from the Middle-Upper Triassic sandstones in the eastern SGT ( Fig. 8e; Deng et al, 2008;Enkelmann et al, 2007;Weislogel et al, 2006). The distribution is also well consistent with data published previously for the same region ( Fig.…”

“…West of the Longmen Shan, the triangular-shaped SongpanGanzi turbidite complex, which represents a Paleo-Tethyan accretionary complex , is dominated by a thick succession (10-15 km) of Triassic flysch turbidites that settled mainly during Ladinian through Norain ( 230-203 Ma) (Bruguier et al, 1997;Enkelmann et al, 2007;Huang and Chen, 1987;Weislogel et al, 2006;Zhang et al, 2008Zhang et al, , 2012. The nature of the basement is unknown as it is covered by the thick turbidites.…”

“…8b and c, Table S2; Chen, 2011;Li et al, 2010a;Luo et al, 2014;Zhang et al, 2015). The detrital zircons with the oldest population, 2.6-2.4 Ga, are considered to likely derive from the NCB (e.g., Deng et al, 2008;Enkelmann et al, 2007;Weislogel et al, 2006;Luo et al, 2014;Zhang et al, 2015) and the northern Yangtze block margin (Zeng and Yan, 2014;Zhang et al, 2015), since rocks with ages of 2.5 Ga are exposed widely in the former (Geng et al, 2012;Kröener et al, 1993;Kusky and Li, 2003;Zhao and Cawood, 2012) and locally in the latter (e.g., Chen et al, 2013). The available Hf isotope data show that most of the 2.50 Ga zircons from both the NCB (Geng et al, 2012, and references therein) and northern Yangtze block display mainly positive and subordinately negative e Hf(t) values, which are in accordance with those of the detrital zircons with similar ages from the Sichuan basin .…”

Sedimentary provenance of the Hengyang and Mayang basins, SE China, and implications for the Mesozoic topographic change in South China Craton: Evidence from detrital zircon geochronology

“…The absence of the 1.8-2.0 Ga zircon population in the Paleozoic sandstones and recent sands from the Min River imply the principal provenance of the igneous/metamorphic Luliang zircons (1.8-2.0 Ga) in the Hengyang and Mayang basins derived from the North China Craton. The recent study on Late Triassic provenance of SongpanGanzi also suggests that the sediments were sourced by the erosion of the Qinling-Dabie orogen and the North China Craton throughout their depositional history, with only a minor input from the South China Craton (Bruguier and Lancelet, 1997;Weislogel et al, 2006;Enkelmann et al, 2007).…”

“…Large volume of detrital material is also assumed to have been transported westward and deposited in the Songpan-Ganzi oceanic basin (Nie et al, 1994). However, there is only scattered Jurassic deposition in the Songpan-Ganzi Basin (Enkelmann et al, 2007). The majority of the detritus denuded from the North China Craton and Dabie Belt had to be carried southward to the inland basins of the South China Craton (Fig.…”