Petrogenesis and mantle source characteristics of Cenozoic alkaline diabase, Jiangxi Province, southeastern China

Abstract

Major element, trace element, and Sr-Nd-Pb isotopic compositions of Cenozoic diabase in southeastern China provide insights into the nature of their mantle sources and processes. The diabases are alkaline in lithochemistry (Na 2 O + K 2 O = 4.37-5.19 wt.%) and have overall oceanic island basalt-like trace element patterns, without negative Nb-Ta anomalies. In addition, they are characterized by lower La/Nb (<1.5) and La/Ta (<22), and higher Ce/Pb (>15) and Nb/U (>30) ratios, indicating an origin in the asthenospheric mantle. The relatively lower 143 Nd/ 144 Nd (0.512632-0.512648) and 206 ), but intermediate 87 Sr/ 86 Sr (0.7061-0.7063) ratios of the diabases are similar to enriched mantle type 1, suggesting crustal contamination or mixing with metasomatized lithsopheric mantle. However, the low Th and U contents and lack of correlations of Nd isotope compositions and MgO preclude significant crustal contamination. Alternatively, the moderate TiO 2 contents (2.01-2.09 wt.%) and high Cr concentrations (>240 ppm) suggest interaction between asthenosphere-derived melts and metasomatized lithospheric mantle. Petrological modelling suggests that the diabases were generated from a low degree (~3-5%) of partial melting of lherzolite with~2-3% garnet. Jiangxi diabase was generated in a within-plate extensional regime, probably related to the far effect of the Himalaya-Tibetan orogen.

Geochemistry and Sr–Nd isotopes of the Late Mesozoic lamprophyres in the Chaohu area, eastern China: Petrogenesis and tectonic implications

“…The Lower Yangtze region is located in the northeastern margin of the Yangtze Block (Figure 1). The Late Mesozoic magmatism was widespread in the Lower Yangtze region, mainly including Late Jurassic to Cretaceous calc‐alkaline intrusions, Early Cretaceous sub‐alkaline to alkaline volcanic rocks, and a small amount of Cretaceous A‐type granitoids (Chen et al, 2001; Jiang, 2017; Li, Lin, et al, 2014; Xie et al, 2006; Xie, Mao, et al, 2008; Yang & Jiang, 2018; Yue et al, 2020; Zhang et al, 2018). The Chaohu area is located in the northern margin of the Lower Yangtze region and adjacent to the Tancheng‐Lujiang Fault Zone (Figure 1).…”

“…A large‐scale magmatic province dominated by Yanshannian granitic and volcanic rocks had been formed in South China (Figure 1) (Li & Li, 2007; Zhou et al, 2006; Zhou & Li, 2000). In previous studies, different models have been proposed for their generation, including (1) the continental extension‐rifting (Gilder et al, 1991; He et al, 2010; Li et al, 2003, 2004); (2) mid‐ocean ridge subduction and slab window (Ling et al, 2009, 2013; Liu et al, 2012; Sun et al, 2007); (3) subduction of the Paleo‐Pacific plate (Chen et al, 2008; Jiang et al, 2015; Lapierre et al, 1997; Li, 2000; Li & Li, 2007; Li et al, 2009; Li, Lin, et al, 2014; Li, Qiu, & Yang, 2014; Zhou & Li, 2000). Although the model of the Paleo‐Pacific plate subduction has been widely accepted, the mechanism of the subduction remains controversial, including a normal subduction model (Lapierre et al, 1997), subduction with changing subduction angles (Zhou & Li, 2000), a flat‐slab subduction model (Li & Li, 2007), shallow subduction and slab roll‐back model (Jiang et al, 2009) and repeated slab advance‐retreat subduction (Jiang et al, 2015).…”