Cretaceous high-potassium intrusive rocks in the Yueshan-Hongzhen area of east China: Adakites in an extensional tectonic regime within a continent

Abstract

Adakites are generally associated with subduction zones (i.e., at convergent plate margins). This paper reports geochemical and isotopic data for early Cretaceous high-potassium adakitic intrusive rocks in the Yueshan-Hongzhen area of east China, which occur in an extensional tectonic regime within a continent. Based on petrology and geochemistry, these adakitic intrusive rocks are classified into two groups. One group (the Hongzhen adakitic granites) is characterized by high SiO 2 (69-75%) contents and K 2 O/Na 2 O (>1.0), low MgO (or Mg # ) values, Ni and V concentrations, low ε Nd (t) (-17.01~-18.13), and high ( 87 Sr/ 86 Sr) i (0.7071~0.7072). The other group (the Yueshan and Zongpu adakitic rocks) is characterized by relatively low SiO 2 (58-67%) contents and K 2 O/Na 2 O (<1.0), high MgO (Mg # ) values, Ni and V concentrations, as well as relatively high ε Nd (t) (-6.63~-9.62) and low ( 87 Sr/ 86 Sr) i (0.7064~0.7069). Both groups are associated with the contemporary Dongling metamorphic core complex, A-type granites, and some per-alkaline igneous rocks that are formed only in an extensional setting. The tectonic setting and chemical compositions suggest that: (1) the adakitic intrusive rocks in the Yueshan-Hongzhen area were formed in an extensional tectonic regime within a continental plate; (2) the Hongzhen adakitic granites were most likely derived directly from partial melting of mafic material with high potassium contents at the base of the continental crust at pressures of ~1.2 GPa, leaving residual garnet ± hornblende ± plagioclase in the source; (3) the Yueshan and Zongpu adakitic rocks were most probably derived from dehydration melting of basaltic materials delaminated into underlying mantle at pressures >1.2 GPa, leaving residual garnet + pyroxene in their sources. Both groups of adakitic rocks have high La/Yb and Sr/Y, indicating that the crustal thickness in the YueshanHongzhen area exceeded 40 km when the adakitic magmas were generated in the early Cretaceous. The present thickness of the crust in the Yueshan-Hongzhen area is only ~31 km, and therefore the crust appears to have been thinned by at least 10 km since the early Cretaceous. The relatively high MgO, Ni, and V values of the Yueshan and Zongpu adakitic rocks suggest that adakitic magmas interacted with mantle rocks, possibly concurrently with delamination of the lower crust.Keywords: adakite, delamination, lower crust, high potassium, east China geochemical similarity Drummond and Defant, 1990;Martin, 1999). However, some rocks with adakitic compositional features have been argued to be alternative origins, e.g., partial melting of mafic lower crust (Atherton and Petford, 1993;Muir et al., 1995;Petford and Atherton, 1996;Johnson et al., 1997), assimilation and fractional crystallization (AFC) processes involving basaltic magmas (Feeley and Hacker, 1995;Wareham et al., 1997;Castillo et al., 1999). Experimental studies (e.g., Rapp et al., 1991Rapp et al., , 1999Sen and Dunn, 1994;Rapp, 1995; Rapp and Waston, 1995;Springer and Seck, 19...

Adakitic rocks and destruction of the North China Craton: Evidence from experimental petrology and geochemistry

“…According to Mg # (MgO/(MgO+FeO) mole ratio), the northern China adakites can be divided into two groups: high Mg # (>40-45) type and low Mg # (<40-45) type. The high Mg # adakites, which were added with significant mantle compositions, can be formed in many ways, including reaction between mantle and melt derived from the delaminated lower crust [11,18,19,[54][55][56][57], mixing of magmas derived from mantle and crust [63,64,88,92], and reaction between mantle and melt derived from subducted oceanic crust [93]. Experimental methods have difficulty in identifying the specific formation mechanism, whereas studies on tectonic settings and detailed petrology and geochemistry analyses may be helpful [11].…”

Petrogenesis of Early Cretaceous Magmatism in Eastern China and the Gyeongsang Basin, Korean Peninsula

“…Data sources from Charoy and Raimbault (1994), Lapierre et al (1997), Swell and Campbell (1997), Li and McCulloch (1998), Jahn et al (1999), Chen et al ( , 2004Chen et al ( , 2008, Fan et al (2001Fan et al ( , 2004, Guo et al (2001Guo et al ( , 2004Guo et al ( , 2005Guo et al ( , 2013Guo et al ( , 2014, Xu et al (2002Xu et al ( , 2006, Zhang et al ( , 2012, , Wang et al (2003Wang et al ( , 2004Wang et al ( , 2005 Sr (a) and εNd(t) (b) for Early Cretaceous igneous rocks from eastern China. Data sources and symbols as in Fig.…”

“…The boundary line dividing the alkaline and subalkaline series is from Irvine and Baragar (1971). Data sources for eastern China from Charoy and Raimbault (1994), Martin et al (1994), Lapierre et al (1997), Swell and Campbell (1997), Li and McCulloch (1998), Jahn et al (1999), Chen et al (2001Chen et al ( , 2004Chen et al ( , 2008, Fan et al (2001Fan et al ( , 2004, Guo et al (2001Guo et al ( , 2004Guo et al ( , 2005Guo et al ( , 2006Guo et al ( , 2013Guo et al ( , 2014, Xu et al (2002Xu et al ( , 2006, Zhang et al ( , 2004Zhang et al ( , 2005Zhang et al ( , 2010Zhang et al ( , 2012, , Wang et al (2003Wang et al ( , 2004Wang et al ( , 2005Wang et al ( , 2007Wang et al ( , 2008, Shu et al (2004), Yang et al (2004Yang et al ( , 2005aYang et al ( , 2006Yang et al ( , 2012aYang et al ( , b, 2013, Zhao et al (2005Zhao et al ( , 2007a, Huang et al (2006Huang et al ( , 2007, Liu et al (2006Liu et al ( , 2008aLiu et al ( , b, 2009…”

“…이는 위 암석들이 고-칼륨 칼크-알 칼리 내지는 쇼쇼나이트 계열에 속한다 (Fig. 2) Sr isotopic ratios for Early Cretaceous basaltic rocks from eastern China (Lapierre et al, 1997;Li and McCulloch, 1998;Jahn et al, 1999;Chen et al, 2001Chen et al, , 2004Chen et al, , 2008Fan et al, 2001Fan et al, , 2004Guo et al, 2001Guo et al, , 2004Guo et al, , 2005Guo et al, , 2013Guo et al, , 2014Xu et al, 2002;Zhang et al, , 2004Zhang et al, , 2012Wang et al, 2003Wang et al, , 2004Wang et al, , 2005Wang et al, , 2008Yang et al, 2004Yang et al, , 2005aYang et al, , 2006Yang et al, , 2012aLiu et al, 2006Liu et al, , 2008aLiu et al, , b, 2009Yu et al, 2006;Huang et al, 2007;Zhao et al, 2007b;Gao et al, 2008;Xie et al, 2008;Tang et al, 2009;Ma et al, 2014a, b). Data source for basaltic rocks from the Hayang Group in the Gyeongsang basin from Kwon et al (2013).…”

Late Early Cretaceous adakitic granitoids and associated magnesian and potassium‐rich mafic enclaves and dikes in the Tunchang–Fengmu area, Hainan Province (South China): Partial melting of lower crust and mantle, and magma hybridization

“…1a). In recent years, many Jurassic-Cretaceous adakitic intrusive rocks (intermediate-acidic rocks characterized by a depletion of Y and heavy rare earth elements (HREEs), and high Sr/Y and La/Yb ratios) have been documented in the eastern Yangtze Block (e.g., Xu et al, 2002a;Wang et al, 2004aWang et al, , b, 2006aHuang et al, 2008;Xie et al, 2008;Li et al, 2009;Ling et al, 2009;Liu et al, 2010a;Sun et al, 2011). Only very minor occurrences of adakitic rocks have been reported in the central part of the Cathaysia Block, (e.g., Xiong et al, 2003), however, despite the widespread occurrence of Mesozoic intrusive rocks in the region.…”