Document Type

Article

Publication Date

Spring 4-2016

Publication Title

Precambrian Research

Volume

275

Issue

4

First Page

310

Last Page

331

DOI

http://dx.doi.org/10.1016/j.precamres.2016.01.021

Keywords

Zircon geochronology, Zircon Hf isotope, Arc-related intrusion, Neoproterozoic tectonics, Northern margin of the Yangtze Block

Abstract

There are voluminous Neoproterozoic arc-related volcano-sedimentary sequences and small intrusionson the northern margin of the Yangtze Block, South China. The understanding the origin of the Sanli-gang granitoid intrusion and the spatially associated mafic dikes in the region is crucial for unravelingthe tectonic evolution and continental crust growth processes in the Yangtze Block. Zircon U–Pb dat-ing suggests that the mafic dikes (ca. 871 Ma) and granitoids (ca. 860 Ma) are contemporaneous. Themafic dikes have low SiO2(45.37–46.55 wt.%), K2O (0.32–0.82 wt.%) and Na2O (2.01–2.85 wt.%), and arecharacterized by enrichment in large ion lithophile elements (LILEs) and depletion in high-field strengthelements (HFSEs), suggesting that their mantle source was modified by subducted materials. The San-ligang granitoids have intermediate to high SiO2(60.35–71.38 wt.%), intermediate K2O (1.38–3.67 wt.%)and Na2O (3.97–5.33 wt.%), and high MgO (1.03–3.16 wt.%). They show LREE-enriched REE patterns(La/YbN= 7.2–12.3) with no or minor negative Eu anomalies. Their primitive mantle-normalized trace ele-ment patterns are characterized by enrichment of LILEs and depletion of HFSEs. Both the mafic dikes andgranitoids share similar zircon εHf(t) values (+10.5 to +12.9, +7.9 to +11.7, respectively), whole-rock initial87Sr/86Sr ratios (0.7051–0.7057, 0.7033–0.7041, respectively) and εNd(t) values (+4.0 to +7.1, +3.4 to +4.9,respectively), suggesting that the granitoids were generated by partial melting of juvenile basaltic crust.High Mg# values (49–58) in the granitoids may have resulted from assimilation of residual mafic miner-als in their source region. Based on its arc-related geochemical affinity and contemporaneous arc-relatedmagmatism, the Sanligang pluton is proposed to be generated in a Neoproterozoic arc setting duringcrustal growth and reworking. The early Neoproterozoic assemblage from the Sangligang–Sanyang faultbelt provides an important record of oceanic slab subduction in the northern margin of the Yangtze Block.

Funding Reference Number

NSERC, 250926

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