Petrogenesis of late carboniferous adakitic dikes and granodiorites in the Chinese Altai, NW China: Implications for lower crustal melting and slab roll-back

Guo, Shuaiyu, Yin, Jiyuan, Fowler, Mike, Kerr, Andrew C. ORCID: https://orcid.org/0000-0001-5569-4730, Zeng, Yunchuan, Tao, Zaili, Yang, Fan, Zhang, Jianjun, Wang, Tao and Xiao, Wenjiao 2026. Petrogenesis of late carboniferous adakitic dikes and granodiorites in the Chinese Altai, NW China: Implications for lower crustal melting and slab roll-back. Lithos: Journal of Petrology, Mineralogy and Geochemistry 538-53 , 108597. 10.1016/j.lithos.2026.108597

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Abstract

Late Carboniferous to Early Permian magmatism in the Altai Orogenic Belt provides crucial insights into its tectonic evolution and crustal growth. Here, we present new zircon Usingle bondPb ages, in situ Hfsingle bondO isotopic compositions and whole-rock geochemical data for granodioritic dikes and granodiorites from Habahe region, Chinese Altai. Zircon Usingle bondPb dating yields emplacement ages of 303 Ma for the granodioritic dikes and of 307–305 Ma for the granodiorites. The granodioritic dikes exhibit high SiO2 (65.1–67.4 wt%), Sr (368–491 ppm) and Sr/Y (80.0–118), along with low Y (3.86–4.98 ppm), Yb (0.33–0.46 ppm), Cr (13.9–25.1 ppm) and Ni (5.00–6.78 ppm). They show adakitic geochemical features and no evidence of significant mantle interaction. Compared with adakites derived from thickened lower crust, these dikes have lower Nb/Ta and moderate Al2O3/(MgO + FeOT) and CaO/(MgO + FeOT) ratios. This indicates that they formed by partial melting of normal-thickness basaltic lower crust with minor addition of metasedimentary rocks, under garnet-amphibolite-facies conditions. The granodiorites are calc-alkaline and display I-type affinities. They are depleted in Nb, Ta and Ti, and exhibit moderate negative Eu anomalies (average Eu* = 0.77). Their zircon εHf(t) varies from +3.01 to +13.9, with TDM of 388–826 Ma and elevated δ18O (7.10–8.18‰). These isotopic features suggest derivation from a heterogeneous lower crustal source that incorporated sedimentary components. Hfsingle bondO isotope mixing models, together with trace element systematics, indicate partial melting of such crustal sources under low-pressure conditions, followed by fractional crystallization of Ti-rich minerals, apatite, and plagioclase. The coexistence of the granodioritic dikes and I-type granitoids with coeval A-type granites and mafic intrusions indicates a high-temperature, low-pressure extensional setting. This setting was likely triggered by slab roll-back of the northward-subducting Irtysh-Zaysan Ocean, which promoted crust-mantle interaction and contributed to late Paleozoic crustal growth in the Altai Orogenic Belt.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Publisher:	Elsevier
ISSN:	0024-4937
Date of First Compliant Deposit:	9 June 2026
Date of Acceptance:	7 May 2026
Last Modified:	09 Jun 2026 08:45
URI:	https://orca.cardiff.ac.uk/id/eprint/187067

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