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

Liu

Acta Geologica Sinica (Eng)

et al. 2021

In view of the importance of mafic dyke swarms and their contribution to current scientific problems relating to South China, herein, we present the findings of studies on twenty-five representative mafic dykes cropping out in Hunan Province and Guangxi Zhuang Autonomous Region, within the southern Wuling Mountain gravity lineament, China. These results include new zircon LA-ICP-MS U-Pb age, whole rock geochemical, Sr-Nd-Pb isotopic, and zircon Hf isotopic data for these dykes. The dykes formed between 131.5 ± 1.2 and 121.6 ± 1.1 Ma, and have typical doleritic textures. They fall into the alkaline and shoshonitic series, are enriched in light rare earth elements (LREE), some large ion lithophile elements (LILE; e.g., Rb, Ba, and Sr), Th, U, and Pb, and are depleted in Nb, Ta, Hf, and Ti. Moreover, the dolerites have high initial 87 Sr/ 86 Sr ratios (0.7055-0.7057), negative ε Nd (t) and zircon ε Hf (t) values (

Section: Origin Of the Studied Wmgl Mafic Dykesmentioning

confidence: 99%

Zircon U‐Pb Age, Geochemical, and Sr‐Nd‐Pb‐Hf Isotopic Constraints on the Time Frame and Origin of Early Cretaceous Mafic Dykes in the Wuling Mountain Gravity Lineament, South China

Liu

Acta Geologica Sinica (Eng)

et al. 2021

“…Tectonic transition from subduction to retreat of the palaeo-Pacific plate outcrops in the Nanling region are mainly Early Jurassic small-scale tholeiitic bimodal volcanic assemblages occurring as E-W linear arrays and are spatially associated with bimodal intrusive rocks and layered ultrabasic-basic rocks, proposed as a product of intracontinental lithospheric extension (e.g. Jiang et al 2009;Zhu et al 2010;Ye et al 2013;Bai et al 2015;Cen et al 2016;Gan et al 2018). In contrast, the sporadic Middle-Late Jurassic (173-146 Ma) volcanic rocks in the coastal regions of SE China are mainly high-K calc-alkaline medium-acid volcanic rocks, with minor mafic rocks in some areas (e.g.…”

Section: Geological Backgroundmentioning

confidence: 99%

Tectonic transition from subduction to retreat of the palaeo-Pacific plate: new geochemical constraints from the late Mesozoic volcanic sequence in eastern Fujian Province, SE China

et al. 2020

The widespread occurrence of late Mesozoic volcanic rocks in SE China is associated with widespread mineralization. Most geologists have accepted the model of Pacific plate subduction beneath the eastern Asian continent, but there are still controversies, especially the initial timing of the tectonic transition. In order to understand the tectonic evolution of the palaeo-Pacific plate subduction, an integrated study of zircon U–Pb, Lu–Hf isotope compositions and whole-rock geochemistry was carried out for Mesozoic volcanic rocks in eastern Fujian Province. According to the field observations and zircon U–Pb ages, these volcanic rocks can be divided into three phases: an early stage of Late Jurassic volcanic rocks (Phase 1, 159–153 Ma), a late stage of Late Jurassic volcanic rocks (Phase 2, 152–146 Ma) and an early stage of Early Cretaceous volcanic rocks (Phase 3, 143–139 Ma). Overall, these volcanic rocks are composed of intermediate–acid pyroclastic rocks and lava, with high SiO2, Na2O, K2O and Al2O3 contents, belonging to the high-K calc-alkaline and peraluminous series, with enrichment in large ion lithophile and light rare earth elements but depletion in high-field-strength elements and heavy rare earth elements. However, the Phase 1 and 2 volcanic rocks contain different zircon Hf isotopic compositions and whole-rock geochemistry to the Phase 3 volcanic rocks, implying that they have a different petrogenesis. Our study combined with previous research shows that the decreasing zircon ϵHf(t) values of the Middle–Late Jurassic volcanic rocks indicate a decreasing mantle-derived material contribution. On the contrary, the majority of the Early Cretaceous volcanic rocks have variable ϵHf(t) values, requiring varied degrees of involvement of juvenile components in their origin. Thus, we consider that the Late Jurassic volcanic rocks were generated in a compressional tectonic environment during the early stage (> 146 Ma) of palaeo-Pacific subduction. In contrast, the Cretaceous volcanic rocks were formed in an extensional tectonic setting during a later stage (< 143 Ma) of subduction.

“…Though they assigned the slip to be the Proterozoic, we argue that they could have been active during the early Mesozoic because they intensely involved the Palaeozoic-Upper Triassic cover sediments (Xiang, 1992) The coarse-grained, basin-margin facies forms narrow bands along the faults at the edges of the basins (e.g., FJBGM, 1990;GDBGM, 1988;GXBGM, 1990;HNBGM, 1990;JXBGM, 1984). These basins also are locally characterized by metamorphic core exhumation (Figure 8; e.g., GXBGM) and intracontinental rift-related, mantle-derived, Early Jurassic magmatism (e.g., Cen et al, 2016;Chen, Lee, & Shinjo, 2008;Zhou et al, 2018). Xia et al (1996).…”

Section: Sinistral Transtension Of Central South Chinamentioning

confidence: 99%

“…The coarse‐grained, basin‐margin facies forms narrow bands along the faults at the edges of the basins (e.g., FJBGM, 1990; GDBGM, 1988; GXBGM, 1990; HNBGM, 1990; JXBGM, 1984). These basins also are locally characterized by metamorphic core exhumation (Figure 8; e.g., GXBGM) and intracontinental rift‐related, mantle‐derived, Early Jurassic magmatism (e.g., Cen et al, 2016; Chen, Lee, & Shinjo, 2008; Zhou et al, 2018).…”

Section: Early Mesozoic Lateral Extrusion In the South China Block: Rmentioning

confidence: 99%

Extrusion model for the Early Mesozoic intracontinental deformation of South China related to the North and South China collision

Tang

et al. 2020

Geological Journal

The Early Mesozoic tectonic regime of the South China Block was characterized by strike-slip movement. The northeastern South China Block dominated by recumbent folding, thrusting, and foreland imbrication. Between the North and South China blocks in southern Qinling, there was dextral transpression, but in the western South China Block, sinistral transpression took place. In central South China, sinistral transtension prevails. In contrast, both the eastern and western South China margins, composed of Precambrian basement, appears to be little deformed. These differences are due to lateral extrusion of the South China Block. Extrusion resulted from (a) an overall southerly compression (the North China Block against the South China Block) and indentation of the rigid North China Block into the weaker South China Block, (b) unconstrained South China southern margin, containing a subduction zone between the Indochina Block and the South China Block, allowing the escaped materials to be consumed, (c) an association of strongly constrained margins of the central Sichuan Craton in the western South China margin and the Southeast China Massif in the eastern South China margin, (d) structural obstacle of the Jiangnan Uplift mainly composed of the Proterozoic metamorphic basement, and (e) a previously thickened, gravitationally unstable, thermally weakened crust of the eastern Yangtze valley. The extrusion deformation began about at the beginning of the Jurassic/the end of the Triassic, and terminated at the end of the Cretaceous.