Petrogenesis of Early-Middle Jurassic gabbros in southern Tibet with implications for crustal growth in the southern Lhasa subterrane

ABSTRACT

As a natural laboratory for the study of crustal growth and accretionary tectonics, the Lhasa terrane was once a microcontinent with a Precambrian basement, which was transformed into a juvenile terrane by remarkable Phanerozoic crustal reworking and growth. Here, we report the geochronological, mineralogical, and geochemical data of the Numa hornblende gabbros and Dongga cumulate hornblende gabbros in the southern Lhasa subterrane (SLS). Zircon U-Pb dating yields ages of 163.7 ± 2.2 Ma and 182.8 ± 2.2 Ma for the Numa hornblende gabbros and Dongga cumulate hornblende gabbros, respectively, which suggests generation in the Early-Middle Jurassic. Both the Numa hornblende gabbros and Dongga cumulate hornblende gabbros are enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs), and they have positive ε_Hf(t) (+11.1 to +17.3) and ε_Nd(t) (+3.6 to +6.0) values. Whole-rock geochemical and isotopic data indicate that their primary magma was derived by the partial melting of a depleted mantle wedge metasomatized by hydrous fluids. Our data, combined with previous research results, indicate that the Numa-Dongga gabbros formed in a continental margin arc setting related to the northward subduction of the Neo-Tethys oceanic slab. In addition, comprehensive studies reveal that the Early Jurassic to Late Cretaceous were the most important periods for crustal growth in the SLS and crustal thickening in the Mesozoic was concentrated mainly in the Early Jurassic (ca. 190–170 Ma) and early Late Cretaceous (ca. 100–80 Ma), which is related to the magmatic flare-up induced by slab roll-back. The recycling of subducted oceanic crust and the underplating of mantle-derived magmas play important roles in the growth and evolution of the continental crust in the SLS.

Graphical abstract

KEYWORDS:

• Lhasa terrane
• Early-Middle Jurassic
• gabbros
• crustal growth
• Neo-Tethys

Highlights

1. The hornblende gabbros originated from depleted mantle wedge metasomatized by hydrous fluids.

2. The Numa-Dongga gabbros formed in a continental margin arc setting related to the northward subduction of the Neo-Tethys.

3. The Mesozoic is one of the important periods of crustal growth in the SLS.

Acknowledgments

This research was jointly supported by the Everest Scientific Research Program of Chengdu University of Technology (2021ZF11407); the National Natural Science Foundation of China (41502079 and 41972084), the Sichuan Science and Technology Program (2020JDJQ0042), the National Key Research and Development Project of China (2018YFC0604105); the Start-up Funding Project for Scientific Research of the High-level Talent by Luzhou Vocational and Technical College (No.ZLYGCC202103).

Disclosure statement

The author(s) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Funding

This work was supported by the the Everest Scientific Research Program of Chengdu University of Technology (2020ZF11407); National Natural Science Foundation of China [41502079,41972084]; Sichuan Science and Technology Program [2020JDJQ0042]; National Key Research and Development Project of China [2018YFC0604105]; Start-up Funding Project for Scientific Research of the High-level Talent by Luzhou Vocational and Technical College (No.ZLYGCC202103).