Elemental and Sr?Nd isotopic systematics of the early Mesozoic volcanic sequence in southern Jiangxi Province, South China: petrogenesis and tectonic implications

Abstract

Elemental and Sr-Nd isotopic results are presented for the early Mesozoic volcanic sequence ($172 Ma) in southern Jiangxi Province, South China. The sequence is voluminously composed of $45% subalkaline basaltic rocks (group 1), <5% high-mg andesite-dacites (group 2) and $50% rhyolites (group 3). The group 1 rocks are characterized by (La/Yb) cn = 3.8-7.2, Eu/Eu* = 0.65-1.15, Nb/La = 0.64-0.99, 87 Sr/ 86 Sr(t) = 0.70602 $ 0.70822 and Nd (t) = À1.63 to +0.11, similar to those of an EMII-like source. The group 2 rocks have mg=0.42 $ 0.60, SiO 2 =60.24 $ 66.71%, MgO =2.65 $ 5.54%, Ni=24 $ 102 ppm and Cr=84 $266 ppm, classified as high-mg andesitic rocks. These rocks are more enriched in LILEs and LREE with more significant negative Eu anomaly (0.63$0.79), are more depleted in HFSEs with Nb/La ratios of 0.40-0.56 and have lower Nd (t) (À9.44 to À7.78) and higher 87 Sr/ 86 Sr(t) (0.70985 $ 0.71016), in comparison with the group 1 rocks. They most likely originated from metasomatised veins in the lithospheric mantle. The origination of the group 1 and group 2 magma suggests the development of a peridotite-plus-vein lithospheric mantle during early Mesozoic era beneath the interior of the Cathaysian block. The group 3 rhyolites are characterized by high SiO 2 (72.75 $ 77.97%), Zr (99 $ 290 ppm), Hf (3.9 $ 9.7 ppm) and Ga/Al (2.76 $ 3.87) and significant Nb-Ta, Ba-Sr and P-Ti depletions. These rhyolites exhibit Sr-Nd isotopic compositions ( 87 Sr/ 86 Sr(t) = 0.70962$0.71104, Nd (t) = À4.63 to À5.80) similar to the contemporaneous Zhaibei and Pitou A-type granites in the area. Such characteristics suggest that they might be derived from the underplating basaltic magma contaminated by crustal materials. Therefore, an early Mesozoic rifting model in response to intracontinental lithospheric extension is proposed to account for the early Mesozoic volcanism in southern Jiangxi Province, South China.

Kwangsian and Indosinian reworking of the eastern South China Block: Constraints on zircon U–Pb geochronology and metamorphism of amphibolites and granulites

“…Therefore, the Cathaysia and Yangtze Blocks should remain contiguous during the Phanerozoic period (e.g., Charvet et al, 2010;Chen et al, 2010;Gupta, 1989; Z.X. Rowley et al, 1989;Shu et al, 2008aShu et al, , 2008bWang et al, 2005aWang et al, , 2005bY.J. Wang et al, 2007aY.J.…”

“…However, there are still controversies about whether the Kwangsian and Indosinian events are related to either oceaniccontinental subduction and collision processes or an intracontinental reworking regime (e.g., Charvet et al, 1996Charvet et al, , 1999Charvet et al, , 2010Chen and Jahn, 1998;Huang, 1945;Li and Li, 2007; C. ; Z.X. Shu et al, 1999Shu et al, , 2006Shu et al, , 2008aShu et al, , 2008bWang et al, 2005aWang et al, , 2005b; Y.J. Wang et al, 2007aWang et al, , 2007bWang et al, , 2007cWang et al, 2010Wang et al, , 2011Zhou et al, 2006Zhou et al, , 2007.…”

“…Wang et al, 2007aWang et al, , 2007bWang et al, , 2007cWang et al, 2010Wang et al, , 2011Zhou et al, 2006Zhou et al, , 2007. Previous studies mainly focused on (1) the geochronology and petrogenesis of widespread peraluminous granites, and (2) the spatial patterns of angular unconformities between the lower and upper Paleozoic strata and upper Triassiclower Jurassic sequences (e.g., Deng et al, 2004;Fujian BGMR, 1985;Guangdong BGMR, 1988;Guangxi BGMR, 1985;Hunan BGMR, 1988;Jiangxi BGMR, 1984;Wang et al, 2005aWang et al, , 2005b; Y.J. Wang et al, 2007aWang et al, , 2007bWang et al, 2010Wang et al, , 2011Wu and Zhang, 2003;Xu et al, 2003).…”

Mesozoic large magmatic events and mineralization in SE China: oblique subduction of the Pacific plate

“…Most models can be classified into one of two types: an active continental margin related to the northwestward subduction of the Pacific plate in the Mesozoic (Jahn et al 1990;Zhou and Li 2000;Zhou et al 2006;Chen et al 2008); or an intraplate lithospheric event, for example, a result of the closure of an oceanic basin in the SE China interior (Hsü et al 1990;Li 1998). Other models, such as wrench faulting and/or continental rifting and extension (Gilder et al 1991;Li 2000;Wang et al 2003Wang et al , 2005c, have also been proposed based on the intracontinental lithospheric extension and thinning since the early Mesozoic (Wang et al 2006). A few papers have even proposed Mesozoic mantle plume activities in South China (Xie and Tao 1996;Xie et al 2001;Deng et al 2004a).…”

Petrogenesis of early Jurassic basalts in southern Jiangxi Province, South China: Implications for the thermal state of the Mesozoic mantle beneath South China

“…Furthermore, a mantle plume should have produced a large volume of flood basalts and continental-scale doming, neither of which has been observed in the Mesozoic of South China. Although a rifting and lithospheric extension model was widely accepted for explaining the petrogenesis of the within-plate magmatism (Chen et al, 1999a(Chen et al, , 1999bLi et al, 2003Li et al, , 2004Li and Li, 2007;Y.J. Wang et al, 2005Y.J.…”