Post-orogenic magmatic-hydrothermal system in the southern Songpan-Ganze Orogen, eastern Tibetan Plateau

ABSTRACT

Post-orogenic magmatism is uncommon in the Songpan-Ganze Orogen (SGO), and could provide deep insights into geodynamic evolution and related metallogenesis. Here we present zircon U-Pb-Hf isotopes and whole-rock geochemical data, for post-orogenic granitoids newly identified in the southern SGO. The Longxigou and Yangfanggou granites yield crystallization age of ca. 165 Ma and ε_Hf(t) values of +3.8 to −9.1. This age post-dates regional ca. 220–200 Ma orogenic magmatism and ca. 205–190 Ma peak metamorphism, and corresponds to ca. 200–150 Ma post-orogenic magmatism which is exemplified by neighbouring and coeval Wenjiaping and Wulaxi felsic plutons. They are crosscut by ca. 133 Ma granitic pegmatites, with ε_Hf(t) values of −4.3 to −14.2. These post-orogenic granites show high SiO₂ contents, as well as low Mg# values, (Zr + Nb + Ce + Y) concentrations and zircon saturation temperatures. They have continental crust-like REE patterns and trace element profiles, and exhibit negative Eu anomalies, enrichment in large ion lithophile elements and depletion in high field strength elements. Their mineral assemblages lack typical high-temperature (e.g. pyroxene and fayalite) and peraluminous (e.g. garnet and cordierite) varieties. All these features indicate an I-type granite affinity, and a dominant derivation from thickened lower crust. In comparison, these post-orogenic granites are compositionally distinct from regional late-orogenic (>200 Ma) categories, which have more positive ε_Hf(t) values and higher Mg# values, with subduction-related signatures involving significant mantle components. Further, several high-grade stratiform Cu deposits and a tungsten deposit occur to the south of these granitic plutons, and have mineralization ages of 164–151 Ma together with biotite alteration age of ca. 134 Ma. Hence, ca. 165–133 Ma magmatic-hydrothermal system was most likely responsible for Cu-W mineralization and effective upgrading of metal deposits in the southern SGO.

GRAPHICAL ABSTRACT

KEYWORDS:

• Zircon U-Pb-Hf isotopes
• post-orogenic I-type granites
• magmatic-hydrothermal fluids
• thickened lower crust
• Songpan-Ganze Orogen

Acknowledgment

We thank Changnan Wang, Gaolin Tang and Xianze Zhang for their help during the fieldwork. Qiuyun Yuan and Hongfang Chen are thanked for their analytical assistances. We are grateful to Dr Robert J. Stern and two anonymous reviewers for their constructive comments and many important corrections in English.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2024.2376323.

Additional information

Funding

This work was funded by the National Natural Science Foundation of China [41902068, 42272106], Young Scholars Development Fund of Southwest Petroleum University [201499010083] and China Geological Survey Project [DD20230338, DD20242494].