Abstract
The upper Oligocene–lower Miocene Gangdese conglomerate is deposited along the Yarlung-Zangbo suture zone, which extends 1,500 km from west to east and is located in the core area of the India–Eurasia plate collision zone. The Gangdese conglomerate records richly uplift and denudation histories of the Lhasa terrane and Tethyan Himalaya on both sides of the suture zone, thus revealing the growth process of the southern Tibetan Plateau during the Late Oligocene–Early Miocene. In this study, we documented the detailed sedimentology and chronology of the Gangdese conglomerate. The Gangdese conglomerate is dominated by conglomerate and sandstone, with minor volumes of siltstone and tuff deposited in an alluvial fan and fluvial system. Based on sedimentology and structural relationships, we suggest that the Gangdese conglomerate was deposited in an extensional tectonic environment in the early period and an extrusion tectonic environment in the late period, which was controlled by Indian slab shearing and breakoff during the Late Oligocene–Miocene. According to the new magnetostratigraphy and detrital zircon U-Pb dating, the main depositional age of the Gangdese conglomerate was likely the Late Oligocene–Early Miocene (26–18 Ma), and it trended younger from west to east. Moreover, paleocurrent data from the Gangdese conglomerate showed westward axial sediment transport; thus, we inferred that a westward axial palaeo-Yarlung-Zangbo River occurred along the whole Yarlung-Zangbo suture zone during the Late Oligocene–Early Miocene, and its flow was opposite to that of the current Yarlung-Zangbo River.
Highlights
A narrow Cenozoic conglomerate unit is deposited in unconformity above in the north part of the Yarlung-Zangbo suture zone, which extends 1,500 km from west to east and is located in the core area of the India–Eurasia plate collision zone (Wang J.-G. et al, 2013; Zhang et al, 2013a) (Figure 1)
U-Pb zircon dating of volcanic interlayers and detrital zircon dating of sandstone in the Gangdese conglomerate have suggested that the sedimentary age of the Gangdese conglomerate is Late Oligocene to Early Miocene (Aitchison et al, 2002; DeCelles et al, 2011; Wang J.-G. et al, 2013; Carrapa et al, 2014; DeCelles et al, 2016; Leary et al, 2016)
Previous chronology and structural relationship studies indicate that the main depositional age of the Gangdese conglomerate was likely the Late Oligocene–Early Miocene (26–18 Ma), and it trended younger from west to east
Summary
A narrow Cenozoic conglomerate unit is deposited in unconformity above in the north part of the Yarlung-Zangbo suture zone, which extends 1,500 km from west to east and is located in the core area of the India–Eurasia plate collision zone (Wang J.-G. et al, 2013; Zhang et al, 2013a) (Figure 1). DeCelles et al (2011), DeCelles et al (2016) and Wang et al (2013a) studied the Gangdese conglomerate in the Kailas Basin and Qiabulin area of Xigaze and pointed out that the lower strata of the Gangdese conglomerate were formed under an extensional tectonic setting, whereas the upper strata were formed under a compression background, representing the reversal and detachment of the subducted Indian plate during the Oligocene to Early Miocene. After being exposed at the surface, the Gangdese batholith experienced reheating during burial beneath the Kailas Formation between ~28–26 and 21–20 Ma, followed by rapid cooling between 20 and 17 Ma. Previous chronology and structural relationship studies indicate that the main depositional age of the Gangdese conglomerate was likely the Late Oligocene–Early Miocene (26–18 Ma), and it trended younger from west to east. Based on the new age control, we studied the sedimentology and provenance of the seven Gangdese conglomerate sections, produced a sedimentarytectonic model of the Gangdese conglomerate, and further discussed the implications of these findings for the evolution of the Yarlung-Zangbo River
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