Early Jurassic Mafic Intrusions in the Southern Youjiang Basin, SW China: Petrogenesis, Tectonic and Metallogenic Implications

Wen Jiang,Zhongjin Xiang,Bin Zhou,Wenjing Xia,Quanren Yan,Li Deng

doi:10.3390/min9120771

Abstract

A suite of mafic intrusions, composed of diabase and micro-gabbro outcrops in the Jingxi area of southern Youjiang Basin, SW China. This study conducts geochronological, geochemical, and Sr–Nd isotopic analyses on the mafic intrusions in Jingxi with the aim of determining their petrogenesis, tectonic setting, and metallogenic implications. Zircon U–Pb dating for the mafic intrusions yielded an age of 183 ± 3 Ma (MSWD = 2.3), which is coeval with the Carlin-like gold mineralization in the Youjiang Basin. The mafic intrusions are alkaline in composition and characterized by low TiO2 (1.25–1.87 wt %) contents and low Ti/Y ratios (410–550). They exhibit OIB-like patterns of trace element distribution and they have low (87Sr/86Sr)i ratios of 0.704341 to 0.705677, slightly negative εNd(t) values of −0.30 to −2.16, low La/Ta (11.57–15.66) and La/Nb (0.77–1.06) ratios, with [La/Yb]N = 6.52–10.63. The geochemical characteristics, combined with regional considerations, suggest that the mafic intrusions originated from partial melting of upwelling asthenosphere within the garnet-spinel transition zone, as a result of intracontinental back-arc extension triggered by the steep subduction of the Paleo-Pacific plate beneath the South China Block. Moreover, the new data not only suggest Early Jurassic magma was a possible heat source, but also support a magmatism-related model for the Carlin-like gold mineralization in the Youjiang Basin.

Highlights

Mafic magmas originate from the partial melting of the upper mantle, recording the nature of the mantle source
The samples of mafic intrusions in Jingxi have a relatively high LOI (2.43–4.67 wt %, Table 2), and it is necessary to evaluate the potential effects of alteration processes on the use of trace elements
The high field strength elements (HFSE, e.g., Nb, Ta, Hf, and Ti), REE, Y, Th, and U are significantly correlated with Zr, which suggests that these elements were basically immobile during the alteration [42]

Summary

Introduction

Mafic magmas originate from the partial melting of the upper mantle, recording the nature of the mantle source. The geochemical composition and crystallization age of mafic rocks, in this regard, can be used to analyze deep geodynamic processes and regional tectonic setting. Mafic magmas may carry ore-forming elements and drive ore-forming hydrothermal fluid circulation. Can provide important information to understand regional metallogenesis. South China Block (SCB), and the sporadically exposed magmatic rocks in the basin are dominated by mafic rocks (Figure 1). Previous studies have focused on the Late Paleozoic-Triassic mafic rocks [1,2,3,4,5,6,7], while the Late Mesozoic magmatic rocks, especially the Jurassic mafic rocks, were rarely reported

Methods

Results

Conclusion