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The Mesozoic South China is characterized by extensive magmatism, transition from Jurassic intraplate magmatism to Cretaceous active continental margin magmatism. However, the time and deep geodynamic processes accounting for the Mesozoic magmatism remains controversial. In this study, we presented new SIMS zircon U Pb ages, in-situ Sr isotope of plagioclase, whole-rock geochemical and Sr–Nd–Pb isotopic data on three suites of mafic dikes in eastern Guangdong, namely Anliu (AL) and Sanjiaowo (SJW) and Jishuimen (JSM) mafic dikes. The AL (154.3 ± 3.4 Ma) and SJW (141.3 ± 4.0 Ma and 143.2 ± 2.3 Ma) dikes show arc-like geochemistry and "crust-like" isotopic signatures, likely derived from partial melting of a subduction metasomatized lithospheric mantle. Meanwhile, the JSM dikes (141.7 ± 3.2 Ma) exhibit OIB-type geochemical and isotopic features, and were likely derived from partial melting of an enriched asthenospheric mantle. The development of late Jurassic AL lamprophyre may represent the oldest Paleo-Pacific subduction-related arc-type mafic rocks so far recorded in South China. Development of dikes (SJW vs JSM) with different geochemical signatures (Arc vs OIB) at the same time within a limited space indicates that asthenosphere-related process overprint and co-operate with subduction-related magmatism and imply the initiation of Paleo-Pacific subduction roll-back was potentially at least ca.141 Ma. • Late Jurassic–early Cretaceous mafic dikes were identified in Eastern Guangdong. • The ~154 Ma AL mafic dikes show typical arc-like features. • It was derived from the lithospheric mantle metasomatized by subducted slab fluids. • The simultaneous (~141) SJW and JSM dikes show arc-like and OIB-like features. • They imply the initiation of Paleo-Pacific subduction roll-back was before 141 Ma. [ABSTRACT FROM AUTHOR]

• Two pulses of magmatic-hydrothermal fluid are documented in Taoxihu deposit. • The first pulse of fluid is H 2 O-CO 2 -NaCl system and the second one is H 2 O–NaCl. • Fluid immiscibility is responsible for the precipitation of Sn during the first pulse. • The oxidizing process due to the influx of meteoric water accounts for the precipitation of Sn during the second pulse. The Taoxihu deposit is a newly discovered Sn-polymetallic deposit in eastern Guangdong, SE China. The mineralization is related to an Early Cretaceous, highly fractionated I-type granite porphyry. The ore-forming process is divided into six stages, i.e., garnet (stage I), quartz–fluorite–biotite (stage II), quartz–biotite–cassiterite–sulfides (stage III, main mineralization), quartz vein with minor sulfides and cassiterite (stage IV), quartz–K-feldspar–biotite–cassiterite–sulfides (stage V), and quartz–K-feldspar–chlorite–sulfides (stage VI). Fluid inclusion study shows that the hydrothermal fluids from stage II (salinity = 5.9 to 13.2 wt%, and T h = 302 to 382 °C) to stage IV (salinity = 0.2 to 5.9 wt%, and T h = 275 to 315 °C) are of H 2 O–CO 2 –(CH 4)–salt composition and show a trend of systematically decreasing temperature and salinity from early to late stages. In contrast, the fluids in stage V (salinity = 6.5 to 13.9 wt% and T h = 223 to 343 °C) and stage VI (salinity = 6.0 to 11.8 wt%, and T h = 140 to 300 °C) are of the H 2 O–salt compositional system, and demonstrate also a trend of decreasing temperature and salinity with time, representing a distinct hydrothermal event. H–O isotope data indicate that these two different fluid systems are all initially of magmatic origin. In view of the almost identical cassiterite U–Pb ages of stage III (139.7 ± 1.1 Ma) and stage V (139.8 ± 1.6), the two hydrothermal events are interpreted to represent two pulses of magmatic fluid releasing from the same magma chamber. The first pulse is characterized by an initially single-phase CO 2 -bearing magmatic fluid that was subsequently subject to unmixing or phase separation in relation to hydraulic fracturing and decompression, which lead to the main phase mineralization, whereas the second pulse is the release of residual, CO 2 -free magmatic fluid, which mixed with meteoric water and resulted in the second phase of mineralization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ore-forming fluid is a mixture of magmatic fluid and meteoric water. • The ore-forming fluid was derived mainly from crustal source, with minor proportions of mantle source input (<4.28%). • Fluid boiling and mixing with meteoric water were considered likely to be the possible mechanism for the ore precipitation in Tashan deposit. The Tashan deposit is hosted and genetically associated with the highly fractionated A-type granite porphyry formed at ca. 138 Ma. Its Sn metallogenic processes can be subdivided into three stages: biotite–K-feldspar–cassiterite (stage I, main Sn mineralization), quartz–cassiterite (stage II), and chlorite–sulphides (stage III). Fluid inclusion study indicates that the hydrothermal fluids from stage I (salinity = 5.2–12.8 wt%, and T h = 303–376 °C) through stage II (salinity = 2.7–10.9 wt%, and T h = 236–313 °C) to stage III (salinity = 1.7–8.5 wt%, and T h = 192–262 °C) are of H 2 O–CO 2 –salt composition and its temperature and salinity from early to late stages tend to decrease. The H and O isotopes of quartz from stage II and stage III show δD water values in the range of –66.7 to –60.5‰ and –52.8 to –39.6‰, and δ18O (‰) values in the range of 6.7 to 7.3‰ and 5.8 to 6.9‰, respectively, suggesting contributions of both magmatic fluids and meteoric water. Inclusion-trapped fluids in stage II pyrite show 3He/4He, He mantle (%), and 40Ar/36Ar values of 0.07–0.35 Ra, 0.76%–4.28%, and 302.6–309.0, respectively, indicating that the metallogenic fluids were derived mainly from crustal sources, with minor proportions of mantle source input (<4.28%), consistent with the magma sources of the granite porphyry. Lead isotopes indicate that there is no difference for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios between the sulfide minerals from the orebodies and the fertile granites parental to Sn mineralization in Eastern Guangdong, indicating a magmatic Pb origin. Sulfur isotopic values obtained from sulfides are in the range of –4.5‰ to 0.4‰ (average, –1.7‰), implying an initially of magmatic origin with some contamination of sedimentary sulfur through the interaction with sedimentary rocks of Jinji Formation (–6.67 to –2.41‰). Fluid boiling and mixing with meteoric water were considered likely to be the possible mechanism for the ore precipitation in Tashan deposit. [ABSTRACT FROM AUTHOR]

The recently discovered Jinkeng deposit, located in eastern Guangdong Province, SE China, is a granite-related cassiterite–sulfide-type Sn–Cu–Pb–Zn deposit in the Cathaysia Block. Zircon U–Pb dating of the biotite granite and fine-grained granite associated with the deposit yielded concordant ages of 144.7 ± 0.8 Ma and 141.1 ± 1.3 Ma, respectively. These ages are consistent, within error, with the molybdenite Re–Os isochron age of 139.3 ± 2.5 Ma for the deposit, indicating a temporal link between the emplacement of granitic plutons and polymetallic Sn mineralization. Combined with the regional mineralization ages, we propose that the 145–135 Ma interval represents another significant period of Sn–W mineralization in southern China, in addition to those already recognized. The biotite granite and fine-grained granite have similar geochemical characteristics; both are weakly peraluminous, high-K and calc-alkaline, containing abundant Si, Na, and K, and low concentrations of Fe, Mg, Ca, and P. Compared to primitive mantle and unfractionated granitoids, they are enriched in Rb, Th, U, K, and Pb, have relatively high Rb/Sr and low K/Rb values, are depleted in Ba, Sr, and Ti, and have prominent negative Eu anomalies (δEu = 0.05–0.19), characteristic of highly fractionated I-type granites. Zircons from these granites have ε Hf (t) values ranging from − 9.2 to − 3.3, and Hf model ages (T DM2 ) of 1776–1406 Ma, suggesting that the granites formed by the partial melting of Proterozoic basement material, and contain a minor mantle-derived component. Highly fractionated and reduced ( f O 2 below NNO) magma facilitated the enrichment of Sn. Existing knowledge on the tectonic evolution of this region and new data from this study, indicate that the granites and associated Sn mineralization in the Jinkeng deposit formed in an extensional environment at ~ 140 Ma, likely related to the rollback of the paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The newly discovered Dadaoshan Sn deposit is located in the eastern Guangdong Sn–W province, coastal SE China. The Sn mineralization, hosted in Jurassic porphyritic granite and the Lower Jurassic Jinji Formation sedimentary wall rocks, is considered to be granite-related. In this study, the porphyritic granite was LA–ICP–MS zircon U–Pb dated to be 153.2 ± 1.2 Ma, consistent with the syn -mineralization molybdenite Re–Os age of 152.6 ± 1.8 Ma. The porphyritic granite samples are weakly peraluminous (A/CNK = 1.0–1.1) and high-K calc-alkaline. The rocks contain high SiO 2 (72.9–75.6 wt%), moderate Rb/Sr (5–9) and low ΣREE (136–223 ppm). They are enriched in F, Li, Rb and Sn, depleted in Ba, Sr, P, Zr, Th, Nb and Y, and have distinct negative Eu anomalies (δEu = 0.09–0.18), suggesting that the porphyritic granite is highly fractionated I-type granite. The calculated initial 87 Sr/ 86 Sr (0.711582–0.715173), relatively low ɛ Nd (t) (−9.48 to −8.54; T DM2 = 1638–1814 Ma), and the zircon ε Hf (t) (−14.2 to −5.1; two-stage model ages = 1528–2103 Ma) all suggest that the granite was mainly crustal-derived with little mantle input. Sulfur isotopic compositions for the sulfides (arsenopyrite and chalcopyrite: δ 34 S = −1.1 to 1.4‰, average = −0.1) imply a dominantly magmatic sulfur source. The calculated zircon Ce 4+ /Ce 3+ and Eu N /Eu N ∗ ratios of the Dadaoshan granite range from 1.0 to 112 (mean = 31.7) and from 0.04 to 0.37 (mean = 0.14), respectively, indicating a low oxygen fugacity for the magma. The reducing and highly fractionated nature of the Dadaoshan granitic magma may have played a key role in the Sn mineralization. It was previously argued that the Jurassic Sn–W mineralization and its causative magmatism were largely confined in the South China interior, e.g., the Nanling Range. Our new data suggest that the Late Jurassic Sn–W mineralization and its causative magmatism actually extended to the SE China coastal area. The Dadaoshan granite may have been generated from partial crustal melting led by underplating of mantle-derived magmas in an extensional environment. Regional extension may have been related to the west-directed, flat-slab subduction and delamination of the Paleo-Pacific (Izanagi) plate beneath the South China block. Another suite of Early Cretaceous Sn–W-bearing granitic rocks in eastern Guangdong may have mainly been crustal-derived with minor mantle input, and likely occurred under back-arc extensional setting led by the Paleo-Pacific subduction rollback. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mineralization at Tashan is related to the granite porphyry, and both of them formed at ca. 138 Ma. • The granite porphyry is an A-type granite mainly produced from partial melting of crust with minor contribution of mantle materials. • Both the granite porphyry and the mineralization formed in an extensional setting induced by slab roll-back. The medium-sized Tashan Sn deposit, mainly hosted in the Tashan granite porphyry, is located in eastern Guangdong, Southeast China. Zircon U–Pb dating of the granite porphyry yielded a concordant age of 138.0 ± 1.1 Ma, which is consistent with the cassiterite U–Pb age of 138.0 ± 2.3 Ma from the Sn ores, indicating a temporal link between the emplacement of granitic pluton and Sn mineralization. The contents of Fe3+, Fe2+, and Mg2+ in biotite, low calculated zircon Ce4+/Ce3+ of 4.4–71.6, low Eu/Eu* ratios of 0.06–0.35, and low whole-rock Fe 2 O 3 /FeO of 0.04–0.13 of the granite porphyry reveals its low oxygen fugacity, which may have facilitated the Sn enrichment during magma evolution and played a key role in the Sn mineralization. Low K/Rb (150–175, aver. = 160), Nb/Ta (7.3–8.2, aver. = 7.8), and Zr/Hf (23.2–25.1, aver. = 23.9) values were observed for the granite porphyry, indicating its high fractionation and probable interaction with an aqueous fluid phase to some extent. The reduced and highly fractionated features and high F and Sn contents of the granite porphyry thus indicate it is a typical Sn-fertile granite. The granite porphyry is weakly peraluminous and belongs to high-K calc-alkaline type. The rocks are characterized by high SiO 2 , K 2 O + Na 2 O, F, and Zr + Nb + Ce + Y (360–410 ppm) contents; and 10000 Ga/Al (2.31–3.06) ratios and low CaO, MgO, TiO 2 , and P 2 O 5 contents; Rb, Cs, Th, and U enrichment; and Ba, Sr, Zr, Ti, and P depletion, exhibiting an A-type affinity. Moreover, the rocks display whole rock initial 87Sr/86Sr values of 0.70927–0.71218, εNd(t) of − 6.5 to − 6.3, and zircon εHf(t) values from − 5.7 to − 1.5 with Mesoproterozoic T DM2 ages for both Nd and Hf isotopes, indicating their formation by partial melting of a crustal source of Mesoproterozoic overall residence ages with minor input of mantle materials. By integrating new and published data on tectonic evolution, we suggest that the granite porphyry and associated Sn mineralization in the Tashan deposit that was formed in a back-arc extensional environment started before ∼ 141 Ma, related to the rollback of the paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]