Petrogenesis of the Cretaceous Intraplate Mafic Intrusions in the Eastern Tianshan Orogen, NW China

Weifeng Zhang,Xinbiao Jin,Lianhong Peng,Bing Tu,Xin Deng

doi:10.3389/feart.2021.665610

Abstract

In this study, we conducted zircon U-Pb dating, and whole-rock geochemical and Sr-Nd isotope analyses on the Late Mesozoic dolerite dykes in the Bailingshan Fe deposit (Eastern Tianshan Orogen, NW China) to unravel their petrogenesis and regional tectonic significance. Zircon U-Pb dating on the dolerite yielded an Early Cretaceous age of 129.7 ± 1.4 Ma. The dolerite is calc-alkaline sodic (Na2O/K2O = 4.71 to 6.80), and enriched in LILEs (Rb, K, Sr, and Pb) but depleted in HFSEs (Nb, Ta, and Ti). The intermediate Nb/U (16.7 to 18.5) and Ce/Pb (6.33 to 6.90) values, and the presence of xenocrystic zircons in these dolerite dykes suggest crustal assimilation during the magma evolution. Petrological modeling suggests fractionation of olivine, pyroxene, garnet, and spinel. All the dolerite samples have low initial 87Sr/86Sr (0.7041 to 0.7043) and positive εNd(t) (+ 4.6 to + 5.1) values, indicative of a depleted asthenospheric mantle source. Partial melting modeling suggests that the melting has occurred in the spinel-garnet stability field. Integrating the data from ore deposit geology, geochronology, geochemistry and Sr-Nd isotopes, we proposed that the Late Cretaceous Eastern Tianshan mafic magmatism was developed in an intraplate extension setting.

Highlights

The Eastern Tianshan Orogen is located between the Tarim and Junggar blocks (Mao et al, 2005; Han et al, 2010; Wang et al, 2014; Hou et al, 2014)
Donggebi granite porphyry (233.8 ± 2.5 Ma) (Zhou et al, 2010; Deng et al, 2015; Zhang et al, 2015, 2016; Zhao et al, 2019). Since many of these intrusions are related to regional magmatichydrothermal mineralization, several studies were conducted to understand their geochronology, petrogenesis, and geodynamic setting (Zhang et al, 2015, 2016; Xiao et al, 2017; Zhao et al, 2019), which suggested that the Devonian-Carboniferous intrusions are arc-related, whereas the Permian-Triassic intrusions are syn- to post-collisional (Wu et al, 2006; Zhou et al, 2010; Wang et al, 2014; Zhao et al, 2019)
The Late Mesozoic tectonic setting is still poorly constrained due to the lack of robust indicator, which inhibits the reconstruction of the completed geological history for the Eastern Tianshan Orogen

Summary

INTRODUCTION

The Eastern Tianshan Orogen is located between the Tarim and Junggar blocks (Mao et al, 2005; Han et al, 2010; Wang et al, 2014; Hou et al, 2014). Recent review studies suggested that intraplate basalts can be distinguished from arc-related ones by ZrZr/Y and Th/Yb-Ta/Yb diagrams, whereas OIB and MORB are distinguishable from each other in the ternary 3Tb-Th-2Ta diagram (Xia and Li, 2019) In this contribution, we describe the newly-discovered Cretaceous dolerite dykes near the Bailingshan deposit in the Eastern Tianshan, and present their whole-rock geochemical and isotopic compositions. The Aqishan-Yamansu belt comprises mainly Carboniferous intermediate-felsic volcanic-volcaniclastic rocks with minor marine sediment interbeds (Zhang et al, 2012; Han et al, 2019) These sequences are widely intruded by Carboniferous-Permian granitoids, which include the Bailingshan intrusive complex, Hongyuntan granodiorite and Xifengshan granite (Zhou et al, 2010; Zhang et al, 2016).

RESULTS

DISCUSSION

DATA AVAILABILITY STATEMENT

CONCLUSION