Petrogenesis and Geological Implications of the Oligocene Mingze monzodiorites, Southern Lhasa

Rong Liao,Feilin Zhu,Kailiang Zhang,Zeming Shi

doi:10.3390/min10040301

Abstract

The Mingze Cu-Mo deposit is located in the southern margin of the Lhasa block of the Himalayan Tibetan Plateau. Here, we report the geochronological and geochemical data from Mingze monzodiorites, which hosts the Mingze deposit. Zircon dating indicates that the Mingze monzodiorites were emplaced at ca. 31 Ma (i.e., the Oligocene). The monzodiorites have variable SiO2 and MgO contents, strongly negative high field-strength element (HFSE, such as Ta, Nb, Zr and Hf) anomalies on the normalized trace element diagram and show uniform (87Sr/86Sr)i (0.7066–0.7076), εNd(t) (−2.50 to −4.04) and εHf(t) (+1.50 to +7.50). Their geochemical compositions are different from coeval (40–30 Ma) adakite-like rocks but comparable to coeval mafic enclaves and gabbros. We propose that Mingze monzodiorites were derived from partial melting of the lithospheric mantle, which previously metasomatized by the subducted Indian continental plate that probably subducted into the overlying mantle. The concurrency of the genetically related mafic enclaves and associated intermediate to mafic rocks implies the heterogeneity of the Lhasa lower crust.

Highlights

The Himalayan Tibetan Plateau is interpreted as the result of the Cenozoic collision between the Indian and Asian continents and subsequent continental subduction
We suggest that the monzodiorites and mafic enclaves both originated from enriched lithospheric mantle beneath the
We propose that the parental magmas of the Mingze monzodiorites were derived from the enriched lithospheric mantle metasomatized by crustal materials in a subduction setting beneath the enriched mantlethere metasomatized by crustal materials in aofsubduction setting beneath the Lhasalithospheric terrane

Summary

Introduction

The Himalayan Tibetan Plateau is interpreted as the result of the Cenozoic collision between the Indian and Asian continents and subsequent continental subduction. These data indicate that Mingze monzodiorites were emplaced in the Early Oligocene (~31 Ma) Their geochemical and isotopic compositions are distinct from the contemporary adakite-like rocks, but comparable to the coeval mafic enclaves observed elsewhere in granitoids and the gabbros from south Tibet. These data provide us an opportunity to better understand the age and petrogenesis of the Mingze area and to address the processes responsible for Cu-Mo ore genesis

Geologic Background

Samples and Methods

Photographs and photomicrographs of of Mingze

U-Pb Zircon Ages and Hf Isotopes

Results

Representative

Whole-Rock

Whole-Rock Sr-Nd Isotopes

Discussion

Mechanism of Enriched Lithosphere Mantle

Origin of the Ancient Crustal Signature

Implications for Geodynamic Processes