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Eppawala-AP is investigated as the first chlorine and strontium rich apatite reference material for Sr isotope microanalysis, and can also be used as a working reference for in situ Nd isotope and trace element analysis.

article i nfo The relationship between high Sr/Y (adakitic) rocks and Cu mineralization has been long recognized but the mechanism remains unclear. The Cretaceous high Sr/Y porphyries in the Ningzhen area host major Cu polymetallic deposits in the Lower Yangtze River Belt (LYRB) of eastern China. These rocks exhibit some geochemical characteristics (e.g., non-radiogenic Pb isotope ratios) that differ from adakitic rocks from adjacent locations in the LYRB. In this study, we present a study of the zircon U-Pb-Hf-O isotope and trace element compositions for five porphyries from Ningzhen to reveal their petrogenesis and how that correlates with Cu- Fe-Mo mineralization. Zircon U-Pb ages of Anjishan (Cu deposit), Tongshan (Cu-Mo deposit) and Xiangshan (Fe deposit) plutons in the Ningzhen area are 108.8 ± 1.5 Ma, 105-107 Ma and 100-105 Ma, respectively, which are significantly younger than the ore-bearing adakites (140 ± 5 Ma) in the western part of the LYRB. Zircon eHf(t) and δ 18 O values range from −23.4 to −10.6 and from 5.7 to 7.0‰, respectively, falling between subduction-related adakites from the other regions in the LYRB and delamination-related adakitic rocks from the adjacent South Tan-Lu Fault Zone. The similarities of Ce

The Dexing porphyry Cu deposit is the largest Cu deposit in eastern China, with total reserves of 8.4 Mt Cu. The Dexing porphyries have geochemical characteristics typical of adakites: they are similar to examples in the Circum-Pacific Belt and in the Lower Yangtze River Belt but different from adakites from the Dabie Mountains and the Tibetan Plateau. Ce4+/Ce3+ and values calculated from zircon trace-element compositions vary from 495 to 1922 and from 0.51 to 0.82, respectively, and reflect high oxygen fugacity similar to that measured in or inferred for porphyry Cu-Au deposits in the South America. The high oxygen fugacity is consistent with abundant anhydrite and magnetite-hematite intergrowths in the porphyry, which indicate that the highest oxygen fugacity of Dexing porphyry reached the hematite-magnetite buffer. Based on the geochemical characteristics and the drifting history of the Pacific Plate, we propose that the Dexing adakitic porphyries formed through slab melting, most likely during...

The petrogenesis of Early Cretaceous adakitic intrusions in the Lower Yangtze River belt (LYRB), central-eastern China, and their genetic association with Cu–Au mineralization have recently been debated. This study presented integrated in-situ zircon U–Pb–Hf–O isotopic and trace elemental data for the LYRB adakites, and a comparison with ore-barren adakites from the south Tan-Lu fault (STLF) adjacent to the LYRB. Magmatic zircons from these two series of intrusions have U–Pb ages of 145–132 Ma and 136–132 Ma respectively. The STLF zircons have δ18O ranging from 5.6 to 6.7‰ and eHf(t) from − 28.8 to − 16.4, plotted within the range of global lower crustal metabasaltic xenoliths, consistent with low-radiogenic Pb of the host adakitic rocks. In contrast, both Hf and O isotopic compositions of zircons from the LYRB are greatly variable with heavier δ18O (4.7 to 9.6‰) and higher eHf(t) values (− 25.5 to + 2.0) compared with the STLF series. The co-variations of Hf–O isotopes in the LYRB series reflect source heterogeneity as a result of mixing of basaltic oceanic crust with sediments (10–20%), consistent with high-radiogenic Pb and enriched Sr–Nd isotopic compositions of the host adakites. The high La, U and low Ti concentrations in the LYRB zircons also imply a volatile (perhaps, CO32 −-rich, carbonatite-like) source. Combined with whole-rock geochemical data, the new results further suggest contrasting origins of the LYRB and STLF adakites from subducted oceanic crust and foundering lower continental crust, respectively. The LYRB zircons have much higher ratios of Ce4 +/Ce3 + (avg.417) and Eu/Eu* (avg. 0.67) than the STLF zircons (avg. 84 and 0.44). This difference confirms that the ore-bearing adakitic magmas are more oxidized relative to the ore-barren ones. There is roughly a positive correlation between zircon Ce4 +/Ce3 + and δ18O in the LYRB series, probably indicating that the elevated fO2 was related to components enriched in heavy oxygen isotopes. A possible candidate is sediments, carried by subducting slabs. The involvement of sediments may significantly promote oxidation of the resulting adakitic melts, a key factor for generation of Cu–Au mineralization, e.g., in the LYRB. This study also indicates that combined in-situ analysis of zircon REEs and δ18O could be a powerful tool to decipher the intrinsic links of fO2 with sediment components in subduction zones.

article i nfo Petrology, geochemistry and Re-Os isotopes of peridotite xenoliths from Yantai (Shandong Province) are reportedinthispaperwith aimsof constrainingthe ageandevolutionofthelithosphericmantlebeneath eastern North China Craton. The Yantai xenoliths contain predominant harzburgites and subordinate lherzolites. Al- though their highly incompatible element compositions have been modified by metasomatism, the heavy rare earth element (REE) and Y contents in the Yantai peridotites are primarily governed by partial melting, which startedingarnetstability fieldthencontinuedinspinelstability fieldafterbreakdownofgarnettotwopyroxenes and spinel. Such a polybaric melting produced a residual mantle in which degree of depletion decreases with depth. Os isotopic ratios of the most refractory peridotites (Al2O3b1.2 wt.%) range from 0.117 to 0.126, yielding TRD model ages between 0.5 and 1.7 Ga. This suggests co-existence of Phanerozoic and Proterozoic mantle be- neath Shandong Province. Alternatively, the whole lithospheric mantle beneath Yantai was likely formed during the Phanerozoic, given the resemblance of their Os isotopic ratios with those of abyssal peridotites. The latter in- terpretation is consistent with the fact that all the studied samples plot along the oceanic trend in a plot of forsterite content in olivine versus olivine mode. It also gains further support from the contrasting eNd between the late Mesozoic lithospheric mantle and Cenozoic mantle beneath the region. The data presented in this study therefore argue for a complete replacement of the cratonic mantle by upwelling asthenosphere.

Nanling is the largest W–Sn mineralization belt in the world, the formation of which remains obscure. In contrast to most other deposits in the Nanling region, Dabaoshan is a polymetallic deposit, located in north Guangdong province, southeastern China. Porphyry Mo deposit was found in 2008 in the north part of Dabaoshan ore district. Here we report zircon and molybdenite ages and geochemistry results of zircon and apatite. Zircon U–Pb LA–ICP-MS dating shows that the porphyry Mo deposit formed at 167.0 ± 2.5 Ma (2σ), which is identical to the molybdenite Re–Os age for the ore deposit (166 ± 1 Ma) within error. These ages are marginally older than the major W–Sn mineralization event in the Nanling region (160 ± 5 Ma). Zircon grains associated with the Dabaoshan porphyry Mo deposit have high Ce(IV)/Ce(III) values (356–1300), which indicate high oxygen fugacity, likely associated with plate subduction. Apatite from the Dabaoshan porphyry has high and varied F with low Cl concentrations, suggesting that it formed in a F-enriched environment with high F/Cl components in the magma source. This is consistent with abundant high-F granites in the Nanling region. Chlorine is highly mobile at the early stage of plate subduction. In contrast, F is mainly hosted by minerals that are fairly stable at shallow depths, e.g., apatite, phengite, such that is much less mobile than Cl before phengite decomposition. Therefore, the F/Cl ratio increases with increasing distance from the subduction zone. Compared to the Dexing porphyry deposit to the northeast, the Dabaoshan porphyry has lower Ce(IV)/Ce(III) and high F/Cl. It is also about 5 Ma younger than the Dexing porphyry Cu deposits. All these phenomena can be plausibly interpreted by slab rollback of the obliquely subducted Pacific plate in the Jurassic. We propose that the subducting slab reached the Dabaoshan region before ~ 167 Ma, through a “flat” subduction regime, resulted in high oxygen fugacity in the magmas, which is followed by abrupt slab rollback. The onset of slab rollback is the most favorable event that leads to decomposition of phengite in the subducting slab because of abruptly elevated temperatures, releases F and consequently increases F/Cl in magmas. The Ti-in-zircon temperatures of the mineralized porphyry range from 608 to 641 °C, with an average of about 630±15 °C, whereas average temperature of the barren granodiorite nearby is 700 ± 9 °C. Considering that the Mo porphyry deposit appears as an egg shell surrounding the granodiorite and the geochemical behavior of Mo, we propose that the mineralization was related to the assimilation of metamorphosed sedimentary rocks by the granodiorite.

Qinling ore belt is the largest known molybdenum belt in the world with a total reserve of >5 Mt of Mo metal. Based on the geochemical behaviour of Mo, the structural settings of the Qinling orogenic belt, and geological events in eastern China, we propose that tectonic settings are of critical importance to the formation of these ore deposits. Molybdenum is very rare in the earth with an abundance of ∼0.8 ppm in the continental crust. Both surface- and magmatic-hydrothermal enrichment processes are required for Mo mineralization. It can be easily oxidized to form water-soluble MoO4 – in the surface environment, especially in the Phanaerozoic, and then precipitated under anoxic conditions. Therefore, closed or semi-closed water bodies with large catchment areas and high chemical erosion rates are the most favourable locations for Mo-enriched sediments. The Qinling orogenic belt was located in the tropics during crustal collisions, such that the chemical erosion was presumably intense, whereas the Erlangpi...

Xihuashan tungsten deposit is one of the earliest explored tungsten deposits in southeastern China. It is a vein type deposit genetically associated with the Xihuashan granite pluton. Here we report new dating and zircon geochemistry results. Re–Os isotopic dating for molybdenite intergrowth with wolframite in the oldest generation of the Xihuashan pluton yielded an isochron age of 157.0 2.5 Ma (2s). Zircon U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating shows that the pluton crystallized at 155.7 2.2 Ma (2s). This age is similar to the molybdenite Re–Os age for the ore deposit within error. This, together with published data, suggests that the major W(Mo)-Sn mineralization occurred between 160–150 Ma in southeastern China. These deposits constitute a major part of the magmatic-metallogenic belt of eastern Nanlin. The lower Re content in molybdenite of the Xihuashan tungsten deposit shows crustal origin for the ore-forming material. The limited direct contributions from the subducting slab for the tungsten mineralization in the Nanling region suggest a change of the style of the paleo-Pacific plate beneath southeastern China.

The Early Cretaceous Huangmeijian Pluton is an A-type granite located on the northern bank of the Lower Yangtze River in Anhui Province, east-central China. It intruded the SE edge of the Early Cretaceous Luzong volcanic basin. The moderate- to coarse-grained granite is mainly composed of alkali feldspar, plagioclase, and quartz and has a typical A-type geochemical signature. LA-ICP-MS zircon dating yielded a weighted mean 206Pb/238U age of 127.1 ± 1.4 Ma, similar to other A-type granites in the Lower Yangtze River belt, indicating an Early Cretaceous extensional environment. Temperatures calculated using the Ti-in-zircon thermometer suggest that the magma formed under high-temperature conditions (720–880°C). The low calculated Ce(IV)/Ce(III) ratio based on zircon rare earth element patterns indicates low oxygen fugacity for this A-type magma. Previous studies suggested that eastern China was an active plate margin related to the Early Cretaceous subduction of the Pacific and Izanagi plates. The ridge bet...

SE China is well known for its Mesozoic large-scale granitoid plutons and ore deposits. In SE China, igneous rocks with intrusion ages between 180 and 125 Ma generally become progressively younger towards the NE. More specifically, 180–160 Ma igneous rocks are distributed throughout a broad area, with mineralization ranging from Cu–Au and Pb–Zn–Ag to W–Sn; 160–150 Ma plutons are present mainly in the Nanling region and are associated with the large-scale W–Sn mineralization; younger igneous rocks occur in the NE area that has many fewer deposits. These can be plausibly interpreted as reflecting a southwestward subduction followed by a northeastward rollback of a subducted oceanic slab, in rough agreement with contemporaneous drift of the Pacific plate. Consistent with this scenario, SE China contains three Jurassic metallogenic belts distributed systematically from NE to SW: (1) a Cu–(Au) metallogenic belt in the NE corner of the South China Block, represented by the Dexing porphyry Cu deposits; (2) a Pb–...

Cretaceous adakites are widely distributed in the Lower Yangtze River Belt (LYRB) and the Dabie Mountains, east-central China. Adakites from the LYRB in general are closely associated with Cu–Au deposits, whereas Dabie adakites lack any mineralization. Based on geochemical characteristics, we show that these adakites have different origins; for example, adakites from the Dabie Mountains have more variable Sr/Y (6.47–1303) and systematically higher La/Yb (20.8–402), Th/U (2.28–50.6), and Nb/Ta (5.07–65.2) compared to adakites from the LYRB, Sr/Y (28.8–185), La/Yb (14.1–49), Th/U (0.33–8), and Nb/Ta (7.5–23). The systematically higher La/Yb of Dabie adakites supports their continental origin, because the La/Yb of the lower continental crust is more than 10 times higher than that of mid-ocean ridge basalt (MORB). Moreover, the lower continental crust is also highly enriched in Sr, with Sr/Y > 10 times that of MORB. Interestingly, with the exception of those from Fuziling, most Dabie adakites have Sr/Y compar...

Fluid inclusions hosted by quartz veins in high-pressure to ultrahigh-pressure (HP-UHP) metamorphic rocks from the Chinese Continental Scientific Drilling (CCSD) Project main drillhole have low, varied hydrogen isotopic compositions (δD = −97‰ to −69‰). Quartz δ18O values range from −2.5‰ to 9.6‰; fluid inclusions hosted in quartz have correspondingly low δ18O values of −11.66‰ to 0.93‰ (T h = 171.2∼318.8°C). The low δD and δ18O isotopic data indicate that protoliths of some CCSD HP-UHP metamorphic rocks reacted with meteoric water at high latitude near the surface before being subducted to great depth. In addition, the δ18O of the quartz veins and fluid inclusions vary greatly with the drillhole depth. Lower δ18O values occur at depths of ∼900–1000 m and ∼2700 m, whereas higher values characterize rocks at depths of about 1770 m and 4000 m, correlating roughly with those of wall-rock minerals. Given that the peak metamorphic temperature of the Dabie-Sulu UHP metamorphic rocks was about 800°C or higher, m...

The Lower Yangtze river belt is one of the most important metallogenic belts in China. The mechanisms responsible for ore genesis and the formation of related Cretaceous igneous rocks, such as adakite, A-type granitoid, and Nb-enriched basalt, remain controversial. Mesozoic granitoids in the Lower Yangtze river belt were mostly formed in the Early Cretaceous (140–125 Ma), and three granitoid belts—the inner, the south, and the north—have been defined according to petrological and geochemical characteristics. Previously, based mainly on negative eNd and high initial Sr isotope values, the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust, both of which require crustal thickening. Mesozoic crustal thickening, however, is not supported by the development of extensional basins in the region. From the Late Jurassic to Cretaceous, eastern China was closely associated with subduction of the Pacific plate in the south and the Izanagi plate in the north. The midocean ridge (MOR) between these two plates was drifting toward and likely subducting under the Lower Yangtze river belt. A ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt. Partial melting of subducting young, hot oceanic slabs close to the ridge formed adakitic rocks. The negative eNd values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle, and/or crustal materials through AFC process. A slab window opened during ridge subduction as indicated by A-type granitoids in the center of the inner belt. Nb-enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths.

We have identified abundant exsolutions in apatite aggregates from eclogitic drillhole samples of the Chinese Continental Scientific Drilling (CCSD) project. Electron microscope and laser Raman spectroscopy analyses show that the apatite is fluorapatite, whereas exsolutions that can be classified into four types: (A) platy to rhombic monazite exsolutions; (B) needle-like hematite exsolutions; (C) irregular magnetite and hematite intergrowths; and (D) needle-like strontian barite exsolutions. The widths and lengths of type A monazite exsolutions range from about 6–10 lm (mostly 6 lm) and about 50–75 lm, respectively. Type B exsolutions are parallel with the C axis of apatite, with widths ranging from 0.5 to 2 lm, with most around 1.5 lm, and lengths that vary dramatically from 6 to 50 lm. Type C exsolutions are also parallel with the C axis of apatite, with lengths of � 30–150 lm and widths of � 10 to 50 lm. Type D strontian barite exsolutions coexist mostly with type B hematite exsolutions, with widths of about 9 lm and lengths of about 60–70 lm. Exsolutions of types B, C and D have never been reported in apatites before. Most of the exsolutions are parallel with the C axis of apatite, implying that they were probably exsolved at roughly the same time. Dating by the chemical Th–U-total Pb isochron method (CHIME) yields an U–Pb isochron age of 202 ± 28 Ma for monazite exsolutions, suggesting that these exsolutions were formed during recrystallization and retrograde metamorphism of the exhumed ultrahigh pressure (UHP) rocks. Quartz veins hosting apatite aggregates were probably formed slightly earlier than 202 Ma. Abundant hematite exsolutions, as well as coexistence of magnetite/hematite and barite/hematite in the apatite, suggest that the oxygen fugacity of apatite aggregates is well above the sulfide-sulfur oxide buffer (SSO). Given that quartz veins host these apatite aggregates, they were probably deposited from SiO2-rich hydrous fluids formed during retrogression of the subducted slab. Such SiO2-rich hydrous fluids may act as an oxidizing agent, a feasible explanation for the high oxygen fugacity in convergent margin systems. � 2007 Elsevier Ltd. All rights reserved.