Mesoproterozoic juvenile crust in microcontinents of the Central Asian Orogenic Belt: evidence from oxygen and hafnium isotopes in zircon

Zhen-Yu He,Li-Li Yan,Reiner Klemd,Tian-Yu Lu,Ze-Ming Zhang

doi:10.1038/s41598-018-23393-4

Abstract

We report in situ O and Hf isotope data of zircon grains from coeval Mesoproterozoic (ca. 1.4 Ga) igneous metamafic (amphibolite) and granitic rocks of the Chinese Central Tianshan microcontinent (CTM) in the southern Central Asian Orogenic Belt (CAOB). Zircon grains from amphibolite have mantle-like δ18OVSMOW values of 4.7–5.6‰ and juvenile Hf isotopic compositions (εHf(t) = 8.4–15.3; TDMC = 1.57–1.22 Ga), whereas those from granitic rocks have δ18OVSMOW values of 5.6–7.0‰ and evolved Hf isotopic compositions (εHf(t) = −1.0–8.2; TDMC = 2.09–1.62 Ga). Zircon O–Hf isotopic compositions of the metamafic and granitic rocks provide evidence for Mesoproterozoic (ca. 1.4 Ga) crustal growth and a substantial Palaeoproterozoic supracrustal component in the CTM. These findings and previous studies, reporting ca. 1.4 Ga magmatic rocks from other microcontinents of the CAOB, suggest that a large belt of Mesoproterozoic (ca. 1.4 Ga) juvenile continental crust formed in a continental terrane, fragments of which now occur over a distance of more than a thousand kilometres in the southern CAOB.

Highlights

The Central Asian Orogenic Belt (CAOB), one of the largest Neoproterozoic to Palaeozoic accretionary orogens on Earth, has been extensively studied in order to constrain juvenile continental crustal growth during the Phanerozoic[1,2,3,4]
We present in situ O and Hf isotope compositions of zircon grains from Mesoproterozoic magmatic metamafic and granitic rocks from the Alatage area in the Chinese Central Tianshan microcontinent (CTM) of the southern CAOB to gain insight into crustal evolution of the CTM (Fig. 1)
The Mesoproterozoic granitic rocks in the Alatage area intruded into marble and schist of the Xingxingxia Group and were in turn intruded by Palaeozoic granitoids, occurring as sporadic outcrops (Fig. 1b)

Summary

Introduction

The Central Asian Orogenic Belt (CAOB), one of the largest Neoproterozoic to Palaeozoic accretionary orogens on Earth, has been extensively studied in order to constrain juvenile continental crustal growth during the Phanerozoic[1,2,3,4]. Microcontinents with Precambrian crystalline basement are essential components of the CAOB by constituting approximately 50% of its crust[5] Their geological evolution is only poorly constrained due to restricted exposure of the Precambrian rocks, which were extensively overprinted by Palaeozoic tectonic, metamorphic and magmatic events and were largely incorporated into Palaeozoic magmatic arcs[6,7,8,9]. We present in situ O and Hf isotope compositions of zircon grains from Mesoproterozoic magmatic metamafic and granitic rocks from the Alatage area in the Chinese Central Tianshan microcontinent (CTM) of the southern CAOB to gain insight into crustal evolution of the CTM (Fig. 1). The new data allow us to propose Mesoproterozoic (ca. 1.4 Ga) juvenile magmatism in the microcontinents of the southern CAOB

Methods

Results

Conclusion