Xigaze forearc basin revisited (South Tibet): Provenance changes and origin of the Xigaze Ophiolite

Abstract

Our new stratigraphic, sedimentological, and micropaleontological analysis, integrated with basalt geochemistry, sandstone petrography, and detrital-zircon U-Pb and Hf isotope data, suggests the revision of current models for the geological evolution of the Asian active margin during the Cretaceous. The Xigaze forearc basin began to form in the late Early Cretaceous, south of the Gangdese arc, during the initial subduction of the Neotethyan oceanic lithosphere under the Lhasa terrane. Well-preserved stratigraphic successions document the classical upwardshallowing pattern of the forearc-basin strata and elucidate the origin of the associated oceanic magmatic rocks. The normal midocean-ridge basalt (N-MORB) geochemical signature and stratigraphic contact with the overlying abyssal cherts (Chongdui Formation) indicate that the Xigaze Ophiolite formed by forearc spreading and represents the basement of the forearc sedimentary sequence. Volcaniclastic sedimentation began with thick turbiditic sandstones and interbedded shales in the late Albian-Santonian (Ngamring Formation) followed by shelfal, deltaic, and fl uvial strata (Padana Formation), with fi nal fi lling of the basin by the Campanian age. Forearc sandstones do not show the classical trend from feldspatholithic volcaniclastic to quartzo-feldspathic plutoniclastic compositions, indicating limited unroofi ng of the Gangdese arc prior to collision. U-Pb age spectra of detrital zircons are unimodal with a 107 Ma peak in the lower Ngamring Formation (104-99 Ma), bimodal with a subordinate additional peak at 157 Ma in the middle Ngamring Formation (99-88 Ma), and multimodal with more abundant pre-Mesozoic ages in the upper Ngamring and Padana Formations (88-76 Ma). These three petrofacies with distinct provenances document the progressive erosional evolution of the Gangdese arc, with uplift of the central Lhasa terrane and expanding river catchments to include the central Lhasa terrane during the Late Cretaceous.

New insights into the timing of the India – Asia collision from the Paleogene Quxia and Jialazi formations of the Xigaze forearc basin, South Tibet

“…Extensive detrital-zircon U-Pb-Hf data confirmed provenance from the Gangdese arc (Wu et al, 2010;Aitchison et al, 2011;Orme et al, 2015). Most recently, An et al (2014) documented in detail how sedimentation in the forearc basin began with abyssal cherts of late Barremian-Aptian age in the south (Chongdui Fm.) and reefal limestones of late Aptian-earliest Albian age in the north (Sangzugang Fm.…”

“…(2) The Xigaze forearc basin was filled by turbiditic sandstones and interbedded mudrocks during the Albian to Santonian (Einsele et al, 1994;Dürr, 1996;Wan et al, 1998;Wang et al, 1999Wang et al, , 2012, and by shelfal to deltaic deposits during the CampanianMaastrichtian Wang et al, 2012;An et al, 2014), as described in more detail below. (3) The Yarlung Zangbo suture zone marks the contact between India and Asia, and includes ophiolites and tectonic mélange with serpentinite or shale matrix (Cai et al, 2012;Chan et al, 2015;Xu et al, 2015).…”

“…9) and Enba and Zhaguo formations in Tingri (Najman et al, 2010) (b). Detrital modes of Cretaceous Xigaze forearc-basin strata are from Dürr (1996) and An et al (2014). Q = monocrystalline quartz; F = feldspar; L = lithic fragment (Lp = shale/siltstone; Lch = chert; Lv = volcanic; Lm = metamorphic; Lu = ultramafic).…”

“…A belt of forearc basins formed along the southern margin of Asia during northward subduction of the NeoTethys Ocean. Forearc-basin successions displaying the classic shallowing-upward trend from turbidites to shelfal and fluvio-deltaic sediments during the late Early to Late Cretaceous are well developed along the Himalayas An et al, 2014;Orme et al, 2015), including the Indus forearc basin in Ladakh (Garzanti and Van Haver, 1988) and the Xigaze forearc basin in South Tibet Einsele et al, 1994;Dürr, 1996;Wang et al, 2012;An et al, 2014;Orme et al, 2015) (Fig. 1).…”

Zircon U-Pb geochronological constraints on rapid exhumation of the mantle peridotite of the Xigaze ophiolite, southern Tibet

“…In the north, the ophiolite is directly overlain by the deep-sea radiolarian cherts (An et al, 2014;Wang et al, 2012;Wu et al, 2010). The Xigaze ophiolite is characterized by large amounts of mantle peridotites relative to minor mafic rocks and by the absence of sheeted dike complex replaced by sheeted sills (Fig.…”