Petrogenesis of two stages of Cretaceous granites in south‐west Fujian Province: Implications for the tectonic transition of South‐east China

Abstract

Zircon U-Pb data indicate that Cretaceous magmatism in Fujian Province occurred in two pulses, with the Xiyang, Yangshan, Wuci, Dehua, Juzhou, and Xiandu plutons emplaced between 147 ± 1 and 126 ± 1 Ma and the Hutou and Guangqiao plutons emplaced at 109 ± 1 Ma. Combining these previously published ages with the new data obtained during this study indicates that the magmatism in the study area occurred in two distinct stages at 145-125 and 110-100 Ma, both have I-type characteristics. The earlier I-type granites are characterized by relatively high concentrations of SiO 2 (mean = 75.73 wt.%) and low concentrations of MgO (mean of 0.21 wt.%) and are metaluminous to weakly peraluminous (mean A/CNK = 1.03). They contain relatively high total rare-earth element (ΣREE) concentrations (mean of 139.3 ppm) with well-developed Eu anomalies and are relatively enriched in the large-ion lithophile elements (LILE) and the light REE (LREE) but depleted in Ba, Sr, P, Ti, Nb, and Ta. In contrast, the younger I-type granites contain lower concentrations of SiO 2 (mean of 67.63 wt.%), higher concentrations of MgO (mean of 1.47 wt.%), and are metaluminous to weakly peraluminous (mean A/CNK = 0.96). They also have moderate REE values (mean of 150.26 ppm) without significant Eu anomalies and are relatively enriched in LREE, Rb, Th, U, K, Sr, and Pb and depleted in Nb, Ta, P, Ti, Y, and Yb. The two-stage Nd model ages (T 2DM ) of Cretaceous granites are 1.46 to 1.88 Ga (mean of 1.57 Ga) and 1.16-1.60 Ga (mean of 1.36 Ga), respectively. The two-stage Hf model ages (T 2DM ) of Cretaceous gran-ites are 1.19-1.82 Ga (mean of 1.54 Ga) and 0.46-1.20 Ga (mean of 0.91 Ga), respectively. It is likely that the earlier I-type granites were derived from magmas generated by the partial melting of Mesoproterozoic metabasaltic material, whereas the later I-type granites were derived from magmas generated by partial melting of a mixed lithology containing Mesoproterozoic to Neoproterozoic metabasaltic to metatonalitic rocks that were underplated by medium-to high-K basaltic magmas. A geological comparison between south-western Fujian Province and adjacent areas indicates that the earlier I-type granites were emplaced in a compressional environment associated with the subduction of the paleo-Pacific Plate at 145-125 Ma. In contrast, the later I-type plutons are associated with intraplate extension accompanied by the post-subduction slab roll-back of the paleo-Pacific Plate. The two magmatic stages represent a transition from compressional to intraplate extensional tectonics between 125 and 110 Ma, with mantle-derived material playing a crucial role in the formation of the I-type granites.

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

“…12), suggesting an increasing mantle-derived material contribution in their petrogenesis. The combined geochemical features of the Phase 3 volcanic rocks in the study area and A-type granites in SE China (Zhao et al 2018c(Zhao et al , 2019b, together with the previous studies of Early Cretaceous volcanic rocks, granites, extensional structures and metamorphic core complexes (Guo et al 2012;Yan, X. et al 2016;Chu et al 2019;Dong et al 2020), indicate that the Early Cretaceous volcanic rocks in the study area were dominated by an extensional tectonic regime, such as post-orogenic extension triggered by subduction retreat of the palaeo-Pacific slab (Suo et al 2019).…”

Magmatic record of the Mesozoic geology of Hainan Island and its implications for the Mesozoic tectonomagmatic evolution of SE China: effects of slab geometry and dynamics in continental tectonics

“…The post-orogenic collapse models are problematic because: (a) granitic plutons and their volcanic counterparts in E-SE China are much more extensive in their areal coverage beyond the collision zones (i.e. Qinling-Dabie, Sulu, Ailaoshan and Jiang Saho sutures and fault zones), and these plutonic-volcanic rocks are spatially and temporally associated with extensional tectonic features (see, for example, Shu et al (2009) and Wei et al (2018) for Jurassic, and Yang et al (2011), Zhao et al (2019) and for Cretaceous magmatic suites and related extensional tectonics); (b) their emplacement times are at least~60-80 Ma after the collisional events, which represents a very large time window in comparison to an average timespan for the initiation of post-collisional magmatism in other Mesozoic and Cenozoic orogenic belts (for some examples, see Dilek & Moores, 1999;Dilek & Whitney, 2000;Dilek, 2006;Dilek et al 2010;Jamali et al 2010); and (c) there is no viable explanation for the heat source to drive the lithospheric-scale magmatism. Significant variations in the geochemistry and melt origin of the plutonic and volcanic rocks do not support the second and third models above.…”

Origin of Qinxi Silver Polymetallic Deposit in Southeast Coast, China: Evidences from H–O–S–Pb Isotopes and Mineral Rb–Sr Geochronology

“…The Qinxi deposit is located in the east part of the South China plate and belongs to the southeastern margin of the Eurasian continental plate. It lies in the Meso-Cenozoic giant tectonic-magmatic belt of the Pacific Rim [53,54], which features large volumes of volcanic rocks. The southeast coastal area of China experienced a transformation from the Tethys tectonic domain to the Pacific tectonic domain.…”