Closure Of Paleo-Tethys Ocean Research Articles

Triassic I-type granitoids from the Torbat e Jam area, northeastern Iran: Petrogenesis and implications for Paleotethys tectonics

The closure of the Paleotethys ocean in the Tethyan orogenic belt in northeastern (NE) Iran, related to the collision between Gondwana-derived terranes in the south and Laurasia in the north, remains controversial due to the sparsity of Paleozoic ophiolitic outcrops but can be constrained by contemporaneous granitoids. The Late Triassic Torbat e Jam stock in NE Iran is composed of three intrusive suites: (1) the oldest gabbro to quartz diorite intruded at 215.5 ± 0.9 Ma; (2) granodiorite to monzonite; and (3) the youngest granite to alkali granite. All three suites are metaluminous to moderately peraluminous with enrichment in LILE, low LREE/HREE fractionation with (La/Yb)N = 8.4–13.6, and small negative Eu anomalies. The Torbat e Jam stock without primary magnetite is characterized by very low magnetic susceptibility (5 × 10−5 to 6 × 10−4 SI unit), indicative of the I-type granitoids. Zircon Hf isotopic compositions show positive εHf(t) values of +2.6 to +5.7, indicative of a predominantly mantle source with minor crustal contamination. Hf model ages are consistent with the presence of Neoproterozoic juvenile sources (TDMC = 0.88 to 1.09 Ga). These geochemical data and field relationships suggest that the Torbat e Jam stock formed in a late orogenic to post-collisional tectonic setting after the closure of a secondary Paleotethys ocean (Paleotethys II), which opened as an oceanic trough during the Late Palaeozoic in the Iranian block, and closed in the Late Permian-Early Triassic Indosinian orogeny.

Provenance change from the Middle to Late Triassic of the southwestern Sichuan basin, Southwest China: Constraints from the sedimentary record and its tectonic significance

The formation of the Sanjiang and Qinling orogens caused by closure of Paleo-Tethys Ocean along the western and northern margins of the Yangtze block during the early Mesozoic created a unique basin-mountain system. Petrology, geochemistry, geochronology, sedimentary facies and paleocurrent data are integrated in order to investigate the changing provenance of Middle-Late Triassic successions from the southwestern Sichuan region, SW China. The detrital compositions from the Middle Triassic successions indicate low mature sediments of mafic and intermediate rocks origin, which derivation mainly from recycled orogenic and secondarily from the Emeishan Large Igneous Province (ELIP). The detrital zircon U-Pb age distribution pattern of the Middle Triassic sandstone samples exhibits four major age Groups at ~257Ma, 650–500Ma, 880–710Ma, and 1000–900Ma. Combined with the geochemical characteristics, an interior Yangtze block source including the Khamdian uplift and ELIP is suggested. The Late Triassic sedimentary rocks yield seven U-Pb age Groups at 245–210Ma, 290–260Ma, 460–410Ma, 650Ma, 880–710Ma, 1900–1600Ma, and 2600–2400Ma, which are consistent with the data reported from the Sichuan basin, Songpan Ganzi basin and the southern Yidun terrane, and are partly similar to those of the south Qinling orogen, Jiangnan Xuefeng thrust belt. In contrast to the Middle Triassic successions, the sandstone composition modals and whole-rock geochemistry of the Late Triassic samples denote mature deposits and of intermediate and acid rocks origin. Therefore, during the Late Triassic, the southwestern Sichuan basin received materials from the Songpan Ganzi folded belt and Yidun arc complex dominantly, and from the Qinling orogen and Jiangnan Xuefeng thrust belt subsidiarily. The Sanjiang orogen and the Songpan Ganzi folded belt should have controlled the formation of the southwestern Sichuan basin, while the development of the Qinling orogen and the western Jiangnan-Xuefeng orogen may also influenced the formation of the southwestern Sichuan basin. The southwestern Sichuan region evolved from the passive continental margin basin in the Middle Triassic into a foreland basin in the Norian age of the Late Triassic.