Late Jurassic–Early Cretaceous magmatic activity in the Central Lhasa Terrane: Petrogenesis and implications for the initial subduction of the Slainajap oceanic lithosphere

doi:10.1016/j.palaeo.2021.110438

Palaeogeography, Palaeoclimatology, Palaeoecology

Volume 573, 1 July 2021, 110438

https://doi.org/10.1016/j.palaeo.2021.110438 Get rights and content

Highlights

•
A J₃–K₁ magmatic belt (165–135 Ma) is present within the northern Tibet.
•
Southward arc migration occurred over time within these arc rocks.
•
Initial subduction of the Slainajap oceanic lithosphere was proposed.

Abstract

Models for the magmatic and tectonic evolution of the late Mesozoic Lhasa Terrane remain controversial. This study presents new zircon U-Pb age and Hf isotopic, whole-rock major and trace element, and Sr-Nd isotopic data for silicic igneous rocks within the Shiquanhe and Guchang areas. The Shiquanhe rhyolites yield zircon U-Pb ages of ca. 148 Ma, which are consistent with the 144 Ma age of the Guchang granites. All of these silicic igneous rocks are peraluminous, high-K calc-alkaline, and have negative ε_Hf(t) and ε_Nd(t) values and low (⁸⁷Sr/⁸⁶Sr)t values. These characteristics are indicative of derivation from magmas formed by the partial melting of ancient crustal metagraywackes. Combining our new data with the results of previous research suggests that a Late Jurassic–Early Cretaceous (165–135 Ma) magmatic belt is present along the Shiquan River–Nam Tso mélange zone within northern Tibet. These rocks collectively record the magmatic evolution from forearc to continental arc settings during the initial southward subduction of the Slainajap Ocean. Our results provide critical constraints on the tectonic evolution of the Slainajap Ocean and the tectono-magmatic evolution of the Lhasa Terrane.

Introduction

The Tibetan Plateau formed during the largest active collisional orogen on Earth, as a result of the ultimate subduction of Neo-Tethyan oceanic crust and the India–Asia collisional event (Fig. 1a; Sengör, 1987; Yin and Harrison, 2000; Chung et al., 2005; Pan et al., 2012). Collisional orogens generally experience three major stages of evolution, namely oceanic subduction, continental collision, and continental subduction (e.g., Chung et al., 2005). The oceanic subduction stage may be associated with changes in subducting slab geometry that can occur at different stages (e.g., flat subduction, slab rollback, and/or slab breakoff), changing the thermal structure of the subduction zone and resulting in changes in the distribution of igneous rocks within the crust and at the surface (e.g., Kay et al., 1991; Haschke et al., 2002; Li and Li, 2007; Wu et al., 2016a, Wu et al., 2016b, Wu et al., 2019a, Wu et al., 2019b). This means that understanding the spatiotemporal variations in arc magmatism in a collisional belt can provide critical information about the geodynamic evolution of subduction systems.

The Lhasa Terrane in northern Tibet represents the forefront of the India–Asian and Lhasa–Qiangtang collisional events (Yin and Harrison, 2000; Chung et al., 2005; Zhu et al., 2011). The Mesozoic geology of the Lhasa Terrane is characterized by widespread igneous rocks that are dominated by intermediate–silicic units with subordinate amounts of mafic igneous rocks (e.g., Mo et al., 2007, Mo et al., 2008; Zhang et al., 2010; Zhu et al., 2011). Previous research has generated significant amounts of geochronological and geochemical data for these igneous rocks, providing important constraints on the formation and evolution of the Lhasa Terrane (Chung et al., 2005; Zhu et al., 2011, Zhu et al., 2018; Meng et al., 2019a, Meng et al., 2019b; Xu et al., 2019). However, the spatiotemporal variations in this magmatism remain controversial, meaning that the geodynamic setting of this magmatism remains unclear. The Mesozoic magmatism of the Lhasa Terrane may be related to either the northward subduction of the Neo-Tethyan oceanic lithosphere along the Indus–Yarlung–Zangbo suture zones (IYZSZ) and/or the southward-directed subduction of the Bangong–Nujiang Tethyan oceanic lithosphere along the Bangong–Nujiang suture zone (BNSZ; Zhu et al., 2011, Zhu et al., 2016; Cao et al., 2016; Zheng et al., 2018; Liu et al., 2019; Tang et al., 2020).

Recent field and geochronological research have identified widespread late Mesozoic magmatic rocks within the Central Lhasa Terrane (Fig. 1b; e.g., Zhu et al., 2011, Zhu et al., 2016). These igneous rocks provide an ideal opportunity to understand the petrogenesis and geodynamic setting of the late Mesozoic magmatism in this region. This study presents new geochronological and geochemical data for silicic igneous rocks within the Shiquanhe and Guchang areas. Combining these new data with the results of previous research allows the determination of spatial and temporal variations within the late Mesozoic magmatism in this area, furthering our understanding of the geological evolution of northern Tibet.

Section snippets

Geological framework and petrographic characteristics

The Tibetan Plateau is located in SW China and represents an amalgamation of several terranes. The Lhasa Terrane is separated from the Himalaya terrane to the south by the IYZSZ and from the Qiangtang terrane to the north by the BNSZ (Yin and Harrison, 2000; Zhu et al., 2011). The IYZSZ and BNSZ represent remnants of the Neo-Tethyan and the Bangong–Nujiang Tethyan oceanic lithosphere, respectively. Previous research determined that the Neo-Tethyan oceanic lithosphere initially subducted during

LA–ICP–MS zircon U-Pb dating

Zircon U-Pb dating undertaken during this study used laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) employing an Agilent 7900 ICP–MS instrument at the Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources, Jilin University, Changchun, China. The analytical procedures used are outlined by Yuan et al. (2004).

Whole-rock geochemical analysis

Major element concentrations were determined by X-ray fluorescence spectrometry using a Rigaku Primus II instrument with

Zircon U-Pb dating

Three samples from the Shiquanhe (T11 and T13) and Guchang (T19) areas were dated using the zircon U-Pb approach during this study. The results of this dating are given in Supplementary Table 1 and are shown in Fig. 3.

Zircons separated from these samples are typically euhedral–subhedral, 100–200 μm long, and have aspect ratios of 1:1–2:1. Cathodoluminescence (CL) imaging indicates they contain clear oscillatory zoning that is consistent with a magmatic origin. These zircons yielded ²⁰⁶Pb/²³⁸U

Late Jurassic–early cretaceous arc magmatism along the SNMZ

Late Mesozoic igneous rocks that yield diverse geochronological data and have a wide range of geochemical compositions are widespread throughout the Central Lhasa Terrane (Fig. 1b). Although recent research has presented new geochronological data for igneous rocks within the Central Lhasa Terrane, the spatial and temporal variations in the magmatism recorded in this area remain unclear, meaning the geodynamic processes that caused this magmatism remain controversial (e.g., Zhu et al., 2011;

Conclusions

1.
Combining new zircon U-Pb ages for silicic igneous rocks within the Guchang and Shiquanhe areas with the results of previously published research indicates that Late Jurassic–Early Cretaceous (165–135 Ma) arc-type magmatism occurred along the SNMZ within the northern Tibet.
2.
The silicic igneous rocks in these areas are peraluminous and high-K calc-alkaline and formed from magmas generated by the partial melting of ancient crustal metagraywackes. These magmas also underwent varying degrees of

Declaration of Competing Interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

Acknowledgements

We appreciate the assistance of Hang Li and Xiaowen Zeng for their assistance during field work. This study was jointly supported by National Key R&D Program of China (2016YFC0600407), the National Natural Science Foundation of China (92055208, 4177205), Shandong Provincial Natural Science Foundation (ZR2020QD045), China Geological Survey (DD20190236), and Talent-Introduction Program of Guilin University of Technology (GUTQDJJ2020126, 2021KY0249).

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Late Jurassic–Early Cretaceous magmatic activity in the Central Lhasa Terrane: Petrogenesis and implications for the initial subduction of the Slainajap oceanic lithosphere

Highlights

Abstract

Introduction

Section snippets

Geological framework and petrographic characteristics

LA–ICP–MS zircon U-Pb dating

Whole-rock geochemical analysis

Zircon U-Pb dating

Late Jurassic–early cretaceous arc magmatism along the SNMZ

Conclusions

Declaration of Competing Interest

Acknowledgements

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