Geochemistry of early Mesozoic potassium-rich diorites-granodiorites in southeastern Hunan Province, South China: Petrogenesis and tectonic implications

Abstract

The diorites-granodiorites emplaced at ca. 175 Ma in southeastern Hunan tectonic-magmatic belt (SHB), South China Block (SCB), are high-K calc-alkaline. They are characterized by LREE-LILE enrichment and HFSE depletion with slight or no Eu anomalies. Age-corrected initial 87 Sr/ 86 Sr ratio spans a narrow range of 0.707962~0.710396 and ε Nd (t) of -6.98~-2.30. These features are significantly different from those of the neighboring other Mesozoic granitic plutons (Eu/Eu* = 0.30-0.70; 87 Sr/ 86 Sr > 0.710; ε Nd = -12 to -16) in South China, which have been interpreted as the remelting products of Precambrian basement. The crust anatexis cannot account for the geochemical characteristics of these diorites-granodiorites in the SHB. The partial melting of an enriched lithosphere mantle directly produced mafic-intermediate rather than acid magma, and can also not explain the geochemical and isotopic variations exhibited by these diorites-granodiorites. These diorites-granodiorites likely represent partial melting products of mantle-derived basaltic rocks, which were underplated and hybridized with old crust material at lower/middle crust level. Theoretical modeling further suggests that this hybridized source consisted of 15-30% of the lower/middle crust and 70-85% of depleted mantle-derived basaltic rocks. The occurrence of these dioritegranodiorites in southeastern Hunan province therefore marked a major intra-lithospheric extension episode during early Mesozoic.

Zircon U–Pb, molybdenite Re–Os and muscovite Ar–Ar isotopic dating of the Xitian W–Sn polymetallic deposit, eastern Hunan Province, South China and its geological significance

“…1) (Li, 2000;Wang et al, 2003aWang et al, , 2003bWang et al, , 2007Zhou et al, 2006;Li and Li, 2007;Niu et al, 2015). Nearly all of the polymetallic tungsten and tin deposits in South China are associated with Late Mesozoic granites, and are located at the endo-and exo-contacts of granitic intrusions (Mao and Li, 1995;Mao et al, , 1996aMao et al, , 1996bZaw et al, 2007;Yin et al, 2002;Wang et al, 2008;Guo et al, 2011Guo et al, , 2014.…”

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

“…It is difficult to assess the assimilation between intermediate-basic magma and crustal materials, due to the lack of knowledge of the basement and sedimentary rocks in the area. However, the data from the other areas of the SCB provide some constraints (Chen and Jahn 1998;Shen et al 1998;Li 2000;Wang et al 2003b). The gneisses and their derivation in the SCB, which can be regarded as the equivalent of average crustal materials (Wang et al 2003b;Shen et al 1998), have Nd contents of 26-62 ppm (average of 37 ppm) that are close to those of the group 1 and 2 rocks (21.0-49.9 ppm).…”

“…However, the data from the other areas of the SCB provide some constraints (Chen and Jahn 1998;Shen et al 1998;Li 2000;Wang et al 2003b). The gneisses and their derivation in the SCB, which can be regarded as the equivalent of average crustal materials (Wang et al 2003b;Shen et al 1998), have Nd contents of 26-62 ppm (average of 37 ppm) that are close to those of the group 1 and 2 rocks (21.0-49.9 ppm). The crustal materials in the SCB have an average Nd (t) value of À11 (Wang et al 2003a;Shen et al 1998;Chen and Jahn 1998), suggesting that an unrealistic proportion of crustal assimilation (>60%) would be required to produce the group 2 rocks ( Nd (t) = À9.44 to À7.78).…”

“…Normalized values for chondrite and primitive mantle are from Taylor and McLennan (1985) and Sun and McDonough (1989), respectively. The data for the average gneisses and granulites in the SCB are from Wang et al (2003b). The fields for the Antang alkaline basalts (168 Ma) in central and the Zhaibei and Pitou A-type granites in southern Jiangxi Province are from Wang et al (2004) and Li et al (2003), respectively Chen and Jahn (1998) and Chen et al (1999).…”

Mesozoic large scale magmatism and mineralization in South China: Preface

“…These models include the following: (1) an Andean-type active continental margin related to the northwestward (Jahn et al, 1990;Li et al, 2012c;Zhou and Li, 2000;Zhou et al, 2006) or southwestward followed by northwestward (changed at~125 Ma, Sun et al, 2007) subduction of the Pacific plate in the Mesozoic (Wang et al, 2011b); (2) intraplate lithospheric subduction as a result of the closure of an oceanic basin in the interior of South China (Hsü et al, 1990); (3) post-collisional extension (Chen et al, 2008); (4) continental rifting and extension (Gilder et al, 1991;Liu et al, 2012a;Wang et al, 2003Wang et al, , 2005; and (5) Mesozoic mantle plume activities (Deng et al, 2004). The subduction models are becoming more and more popular.…”