Early Cretaceous subduction-modified lithosphere beneath the eastern Qinling Orogen revealed from the Daying volcanic sequence in central China. (1st June 2019)

• Record Type: Journal Article
• Authors: Zhang, Feifei; Wang, Yuejun; Dong, Yunpeng; Cawood, Peter A.; Fan, Weiming
• Is Part Of: Journal of Asian earth sciences. Volume 176(2019)
• Page Start: 209
• Page End: 228
• Publication Date: 2019-06-01
• Subjects: Geochronology -- Sr–Nd–Hf isotopic compositions -- Early Cretaceous volcanics -- Subduction-modified mantle source -- Eastern Qinling Orogen; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2019.02.013
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: The Daying volcanic rocks from the eastern Qinling orogen were emplaced at 134–124 Ma. These volcanic rocks were derived from a hybridized source created by the North China Craton enriched mantle along with the input of the crustal materials from the Yangtze Block during the Triassic deep-subduction digestion. These rocks are related to an early Cretaceous extensional event in the Qinling-Dabie Orogenic belt in response to unrooting or delamination of the thickened lithosphere. Abstract: New geochronological, geochemical and Sr-Nd-Hf isotopic data for the early Cretaceous Daying volcanic sequence, eastern Qinling Orogen, provides a probe into the nature of, and tectonic process operating in, the underlying Mesozoic mantle. The volcanic rocks in the sequence are composed of basaltic trachyandesite, pyroxene-andesite, trachyandesite and trachyte. They yield zircon U-Pb and whole-rock 40 Ar/ 39 Ar plateau ages of 134–124 Ma, roughly synchronous with the Cretaceous igneous rocks throughout the eastern Qinling and Dabie orogens. Clinopyroxene and plagioclase phenocrysts of the volcanic rocks exhibit simple normal zonation with higher mg-number and An content in the core relative to the rim. The amphibole is characterized by tschermakite and tschermakitic hornblende with mg-number of 50–67. The Daying volcanic rocks have variable SiO2 (54.27–63.44 wt%), Al2 O3 (15.39–20.34 wt%), FeOt (5.23–9.94 wt%), and MgO (1.05–4.03 wt%) contents with low mg-number (26–49). They exhibit arc-like REE- and PM-normalized patterns with significant negative Nb-Ta anomalies, and highly- enriched Sr-Nd isotopic composition with ( 87 Sr/ 86 Sr)i ratios of 0.7066–0.7078 and εNd (t) values of −15.5 ∼ −11.0. Their zircons exhibit strongly negative εHf (t) values ranging from −27.3 to −17.2 and two-staged model ages from 2.90 Ga to 2.28 Ga. Such geochemical signatures suggest that the Daying volcanic rocks were derived from a hybridized source of the North China Craton enriched mantle with the input of some Yangtze crustal materials created by Triassic deep-subduction digestion. They also share similar eruption time, as well as elemental and Sr-Nd-Hf isotopic compositions, with those in the southern margin of the North China Craton, suggesting a northward subduction of the Yangtze block. It is proposed that the volcanic rocks are petrogenetically related to an early Cretaceous extensional event along the Qinling- Dabie Orogenic belt in response to unrooting of the thickened lithosphere.