Low eNd Values Research Articles

Origin of post-collisional A-type granites in the Mahakoshal Supracrustal Belt, Central Indian Tectonic Zone, India: Zircon U-Pb ages and geochemical evidences

There are several A-type granitic plutons in the central and western parts of the Mahakoshal Supracrustal Belt (MSB), India. We report new whole-rock elemental and Nd isotope data along with zircon U-Pb ages on these granites. The ID-TIMS zircon U-Pb ages of these granites are 1645 ± 25 Ma, 1695 ± 9 Ma, and 1796 ± 17 Ma. These granites are metaluminous to weakly peraluminous, alkali-calcic to calc-alkalic and ferroan in composition. They are characterized by enrichment in REEs (except Eu) and HFSEs (Zr, Y), and depletion in LILEs (Ba, Sr). They have high Ga/Al (2.6–5.4) ratios and elevated magmatic temperatures (≥900 °C). Elemental ratios such as Y/Nb, Nb/Ta, Th/Nb, La/Nb and Ce/Pb coupled with negative Nb, Sr, Eu, and Ti anomalies suggest their derivation from crustal sources. They have very low εNd(t) values (−11.4 to −5.6) and older Nd model ages (TDM: 2481–3225 Ma) confirming their crustal derivation. We propose that partial melting of the Archean tonalitic-granodioritic crust of basement Bundelkhand Craton in low-pressure high-temperature conditions generated the parental magma of these granites. Their A2-type affinity (Y/Nb ˃ 1.2) further suggests their emplacement in an extensional environment related to post-collisional tectonic setting.

Petrogenesis and oxidation state of granodiorite porphyry in the Jurassic Chuankeng skarn Cu deposit, South China: Implications for the Cu fertility and mineralization potential

Large-scale Jurassic porphyry–skarn Cu mineralization in the Qin-Hang metallogenic belt of South China has attracted much attention, but comparative studies of porphyries in large- and small-scale deposits are lacking. In this paper, we present new zircon U–Pb ages, trace element composition and Hf isotopic composition as well as whole-rock geochemical and Sr–Nd isotopic compositions for the porphyries associated with mineralization in the small-scale Chuankeng Cu deposit. Drawing on our data for the Chuankeng deposit and existing data for the nearby giant Dexing Cu deposit, we aim to identify factors controlling the mineralization potential of both deposits. Granodiorite porphyries of Chuankeng deposit were emplaced at ca. 161–158 Ma. They have moderate SiO2 contents of 61.9–66.1 wt% and high Sr/Y (59–135) and (La/Yb)N (4–14) ratios. Their high MgO contents (0.2–2.9 wt%), lack of negative Eu anomaly, depletion in Y and Yb, relatively high initial 86Sr/87Sr ratios (0.7076–0.7078), and low εNd(t) values (−4.5 to −4.9), indicating that the Chuankeng porphyries were derived from partial melting of delaminated lower crust. The Middle–Late Jurassic Chuankeng porphyries are considered to have been formed in a localized intra-continental extension environment along the Jiangshao Fault in response to far-field stress from Paleo-Pacific Plate subduction. Although no Middle–Late Jurassic magmatic arc rocks have been found in the study area, the Chuankeng porphyries display similar characteristics to arc rocks. On the basis of their zircon εHf(t) values (−2.6 to +0.9), two-stage Hf model ages (1.4–1.1 Ga), and regional geological history, we infer that magma source of Chuankeng porphyries were mainly Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. Thus their arc-like features were inherited from the Neoproterozoic juvenile crust that formed by subduction of oceanic crust during the Jiangnan orogeny. Chuankeng porphyries have lower zircon Ce4+/Ce3+ and higher Ti-in-zircon temperatures and lower whole rock εNd and zircon εHf values than the Dexing porphyries, indicating they are less oxidized and less hydrous and with more involvement of the ancient crustal material in the magma source, which could explain the relatively small-scale Cu mineralization in Chuankeng. This study highlights the values of integrated studies of whole rock Nd and zircon trace element and Hf isotopic compositions in assessing the potential for Cu mineralization.

Cretaceous granitic intrusions in Fujian Province, Cathaysia Block: Implications for slab rollback and break-off of the Paleo-Pacific plate

The geodynamic transformation of the Cathaysia Block and its relationship with the Cretaceous granitic intrusions have been controversial in recent decades. In this study, petrology, zircon U–Pb ages, Lu–Hf isotopic composition, whole-rock geochemistry and Sr–Nd isotopes were carried on Cretaceous granites that were collected from the Fujian province, SE China. Combining previously published ages with the new ages obtained in this study indicates that the magmatism in the study area occurred in three distinct stages at 145–137 Ma, 136–118 Ma and 107–86 Ma. The first stage I-type granites were intruded at 137 ± 1 Ma and 145 ± 1 Ma, which are characterized by low εNd(t) values of −7.3 to −6.8 and εHf(t) values of −12.5 to −2.5. It was formed by partial melting of Mesoproterozoic medium-to-high K basaltic rocks in the thickened crust of ~40 km without significant hybridization of mantle-derived magmas and fractional crystallization. The second stage highly differentiated I-type granites yield zircon U-Pb ages of 125 ± 1 Ma and 128 ± 1 Ma, which contain slightly negative εNd(t) values of −5.4 to −5.3 and εHf(t) values of −8.4 to −3.2. It was generated by partial melting of the Mesoproterozoic basement at the depth of 30–40 km triggered by underplating of a small amount of mantle-derived magma, with primary crustal melts undergoing plagioclase-dominated fractionation crystallization. The third stage I-type granites yield zircon U-Pb ages of 104 ± 1 Ma and 105 ± 1 Ma, which contain εNd(t) values of −1.7 to −7.3 and εHf(t) values of −6.0 to −0.5. It was derived from partial melting of Mesoproterozoic basaltic source at a depth of ~30 km. Besides, a mass of mantle-derived magma was mixed into the crustal melts, accompanied with plagioclase-dominated fractionation crystallization. Combining previously published data and those obtained in this study provides significant information for the tectonic evolution of Paleo-Pacific. In stage 1 (145–137 Ma), the existence of I-type granites and adakitic rocks suggests that the dip-angle subduction of the Paleo-Pacific Plate led to the partial melting of the thickened lower crust under the compressional environment. In stage 2 (136–118 Ma), the generation of I-type and A-type granitic magmas imply the thinning of the lithospheric crust under the extensional environment and the upwelling of the asthenospheric mantle, which are caused by slab rollback of Paleo-Pacific. In stage 3 (107–86 Ma), the appearance of much more I-type and A-type granites indicates that the break-off of the Paleo-Pacific plate led to much stronger crust–mantle interactions under the extensional environment.

Oceanic environment changes caused the Late Ordovician extinction: evidence from geochemical and Nd isotopic composition in the Yangtze area, South China

AbstractThe Ordovician–Silurian (O–S) transition was a critical interval in geological history. Multiple geochemical methods are used to explore the changes in oceanic environment. The Nd isotopic compositions in the Yangtze Sea are controlled by two sources: the continental erosion and the Panthalassa Ocean. HighεNd(t) values during the Katian, late Hirnantian and Rhuddanian intervals are associated with the high sea level, which resulted in less terrestrial input based on the low Ti/Al and Zr/Al ratios. In contrast, lowεNd(t) values during the early Hirnantian interval are related to the sea-level fall; in this case, the exposure of submarine highs and the growth of Yangtze Oldlands could lead to more continental materials being transported into the Yangtze Sea based on high Ti/Al and Zr/Al ratios. In addition, the negativeεNd(t) excursion can also be attributed to the weak circulation between the Yangtze Sea and Panthalassa Ocean when sea level was low. Furthermore, the sea-level eustacy plays a significant role in the changes in redox water conditions. The redox indices, mainly UEF, Ce/Ce* and Corg/PT, across the O–S transition show a predominance of anoxic ocean over the Yangtze Sea during the Katian, late Hirnantian and Rhuddanian intervals, and an oxygenated episode was briefly introduced during the early Hirnantian period because of the fall in sea level. The Late Ordovician biotic crisis was marked by two-phase extinction events, and the change in sea level and redox chemistry may be the important kill mechanisms.

The Role of Siliceous High-Magnesium Basalts during the Formation of a Neoproterozoic Mafic-Ultramafic Intrusion in the Tarim Craton (China)

The Xingdi No.2 intrusion in the Kuluktag Block of northeastern Tarim Craton, which intrudes into the Palaeoproterozoic basement with an exposed area of ca. 12 km2, is an orthopyroxene-rich mafic-ultramafic intrusion in a continental rift setting. It consists of gabbros, pyroxenites, and peridotites, and exhibits a crystallization sequence of the principal rock-forming minerals from olivine, orthopyroxene, clinopyroxene, to plagioclase. The gabbros show a concordant SHRIMP U-Pb zircon age of 752 ± 5.4 Ma. In addition, the olivine grains have forsterite content values of 78–85 mole% and mostly contain low NiO, MnO, CaO, and Cr2O3. The rocks are relatively enriched in large ion lithophile elements and LREE, and depleted in HSFE, have non-radiogenic Pb, low εNd (t) values (−2.8 to −23), initial 87Sr/86Sr ratios (0.7059–0.7130). It could be concluded that the rocks represent an analogue of siliceous high magnesium basaltic magma originated by the partial melting of a hydrous and enriched subcontinental lithospheric mantle and contaminated by the continental crust.

Infant intra-oceanic arc magmatism due to initial subduction induced by oceanic plateau accretion: A case study of the Bangong Meso-Tethys, central Tibet, western China

The Meso-Tethyan oceanic plateaus are becoming conspicuous as giant units on the oceanic floor and have played important roles in both continental marginal orogenesis and Tethys oceanic evolution. In this study, we present mineralogical, geochronological, geochemical and Sm–Nd isotopic data for basaltic lavas from the Namco ophiolite and a high-Mg pillow lava–dyke–gabbro association from the Pengco ophiolite in central Tibet. Zircon U–Pb and Ar–Ar dating reveals that the Namco lavas erupted at ∼181 Ma while the Pengco boninitic association formed at ∼164 Ma. The Namco lavas display nearly flat rare-earth element (REE) patterns with no Nb–Ta depletions as well as high εNd values, characteristic of oceanic plateau lava. In contrast, the Pengco high-Mg rocks exhibit low REE concentrations below the normal mid-ocean ridge basalt (N-MORB), ubiquitous Nb–Ta depletions and low εNd values, and the dykes and gabbros are characterized by U-shape REE patterns, indicating that they could have derived from a depleted mantle source that was contaminated by sedimentary flux and marking a mid-Jurassic initial intra-oceanic arc magmatism erupted on the Early Jurassic Meso-Tethyan oceanic plateau represented by the Namco ophiolite. Our Pengco boninitic rocks, along with the literature data, indicate a 167–160 Ma boninitic-like initial intra-oceanic arc within the Bangong Meso-Tethys, running from the Shiquanhe area to the Naqu area with a length of ∼1000 km, which was uniformly built on the Early Jurassic Meso-Tethyan oceanic plateau. Our literature investigation also indicates a ∼175 Ma accretionary orogeny with distinct signature of the oceanic plateau involvements along the southern Qiangtang continental margin, which is manifested by regional metamorphic, magmatic and depositional records. We thus suggest that the accretion of the Early Jurassic Meso-Tethyan oceanic plateau onto the southern Qiangtang continental margin resulted in the extensive orogeny along the continental margin, jammed the subduction zone at ∼175 Ma and induced intra-oceanic subduction initiation as well as the intra-oceanic infant arc magmatism in the Meso-Tethys at ∼164 Ma.

The application of Neodymium isotope as a chronostratigraphic tool in North Pacific sediments

AbstractIt has been suggested that dust generation was closely linked to the development of global ice sheets and/or cooling. This feature has allowed Asian dust to be a potential chronostratigraphic tool in North Pacific Ocean (NPO) sediments. The orbital-scale age control in NPO sediments is usually established by adjusting the benthic-foraminiferal δ18O to the global δ18O stack (LR04). However, it would become difficult if the sediments did not contain enough foraminifera. This study investigates Sr and Nd isotopes, trace elements, mineralogy and grain size of the ‘operationally defined aeolian dust’ (ODED) extracted from the sediments recovered at Ocean Drilling Program (ODP) site 1209B on the Shatsky Rise in the NPO covering the past five glacial–interglacial cycles. The geochemical results show that the ODED at site 1209B is actually a mixture of Asian dust and volcanic ash. The variation of Nd isotope mimics the cycles of glacial–interglacial ice sheets as revealed by the global benthic foraminifera’s oxygen isotope stack (LR04) over the past 500 ka. The low (high)ϵNdvalues corresponded with the cool (warm) periods. We propose thatϵNdvariation reflects the evolving aeolian dust in site 1209 sediments. The excellent agreement betweenϵNdvalues at site 1209B and LR04 stack over the past 500 ka allows establishing the orbital-timescale age control by tuningϵNdto the LR04 curve. We thus propose that Nd isotope provides a chronostratigraphic technique in NPO sediments, especially for sediments with a limited amount of foraminifera.

Early cretaceous igneous activities in the north flank of the North China Craton: the Shouwangfen complex example

ABSTRACT The Early Cretaceous igneous complexes in the north flank of the North China Craton (NCC) provide a window to investigate the Mesozoic magmatism in the NCC. Here we report the precise timing of Early Cretaceous magmatism and magma petrogenesis of the different rock types in the north flank of the NCC based on petrology, mineral chemistry, geochemistry, zircon geochronology and Sr-Nd isotopes. Zircon U-Pb dating reveals that the Shouwangfen complex was crystallized at 130–128 Ma. The rocks display enrichment in large ion lithophile elements (LILE) and LREE, and depletion in high field strength elements (HFSE) and HREE, with relatively high Sr/Y and La/Yb values, typical of subduction-related magmatic rocks. The mafic microgranular enclaves show typical igneous textures, acicular apatites, sieve-texture of plagioclase phenocrysts and overgrowth of amphibole around the pyroxene, corresponding to magma mixing and mingling and thermal exchange. The quartz monzonites display normal zoning of the plagioclase, low and homogeneous εNd(t) values and linear co-variations in two-component diagrams. The quartz monzodiorites are characterized by high and homogeneous εNd(t) values. Petrologic feature and geochemical data suggest that the quartz monzonites represent lower crustal magma with minor contribution of enriched melt of the sub-continental lithospheric mantle (SCLM), followed by fractional crystallization. The mafic microgranular enclaves were sourced from enriched SCLM, followed by mixing and mingling with the host quartz monzonitic magma. The quartz monzodiorites are mainly SCLM-derived and subsequently mixed with lower crust melts. The high water contents (≥3%) of these Early Cretaceous igneous complexes suggests a hydrous SCLM beneath the NCC. The Early Cretaceous igneous complexes formed within an extensional tectonic setting which were related to the retreat and dehydration of the paleo-Pacific slab. The hydration of the lithosphere induced extensive crust-mantle interaction and large-scale water-rich magmatism, leading to lithospheric thinning in the NCC during the Mesozoic.

Late early Cretaceous peraluminous biotite granites along the Bangong–Nujiang suture zone, Central Tibet: Products derived by partial melting of metasedimentary rocks?

The petrogenesis of biotite granites, which may be metaluminous or peraluminous in composition, is a subject of debate. In this study, we present new zircon U-Pb geochronology and O-Hf isotopic, and whole-rock major and trace element, and Sr-Nd isotopic data for biotite granites in the Langla–Laqinpu area of northern Lhasa Terrane, central Tibet. The rocks are distributed along the eastern segment of the Bangong–Nujiang Tethys Ocean suture, and were emplaced during the late Early Cretaceous (ca.119 Ma). The biotite granites are peraluminous, and have high SiO2 (67.5–72.4 wt%) and low MgO (0.57–1.20 wt%) and CaO (2.36–4.38 wt%) contents with variable K2O/Na2O ratios (0.77–1.32), and show geochemical affinity with the upper-continental crust, e.g., enrichment of Rb, Th, U, K and Pb, depletion of Nb, Ta, Ti, P, Eu, and Sr. They are characterized by relatively high initial 87Sr/86Sr ratios ((87Sr/86Sr)i = 0.7098–0.7137) and low εNd(t) values (−8.4 to −10.3), and high zircon δ18O values (8.29–13.47‰) and variable εHf(t) values (−0.02 to −21.36), indicating they were derived through partial melting of a crustal source consisting of metagreywackes with or without minor metaigneous rocks. Taking into account all available regional geological data, we suggest that the Bangong–Nujiang Tethys Ocean may undergo diachronous closure–although the eastern segment may have been closed by the late Early Cretaceous, its western and western–middle segments may still have been at least partially open and active at that time. The Langla–Laqinpu biotite granites were probably generated in post-collisional setting, following slab break-off after closure of the Bangong–Nujiang Tethys Ocean.

Nd Isotopic and Model Age Study of the Shandong Province, North China Craton: Implications for Correlation with South Korea

The geological units in Shandong Province, North China are important parts of the North China Craton and offer important insights into their crustal evolutionary history. This work compiled 611 sets of Nd isotopic data of Archean-Mesozoic rocks from Shandong including the Luxi, Jiaobei, and Sulu terranes, which provided important constraints for crustal growth and reactivation. Nd-depleted mantle model ages (TDM) of Archean rocks with positive eNd(t) values showed that ca. 2.9 and 2.8-2.7 Ga were the most important periods of crustal growth in the Jiaobei and Luxi terranes, respectively, while the period of ca. 2.6-2.5 Ga in the Jiaobei terrane likely indicated a coherent event of crustal growth and reworking. During the Proterozoic, multi-stage rifting and collisional orogenic events possibly led to the reworking of Archean crust in the source region. The Nd isotopic data of the Paleoproterozoic and Neoproterozoic rocks from Sulu indicated significant reworking of older crust with juvenile magmatic input. Crustal reactivation occurred during the Mesozoic. The younger TDM ages of the Mesozoic rocks with low negative eNd(t) values indicated that a juvenile crustal/mantle component was added to the ancient basement. The reactivation reflected significant crust-mantle interaction via the mechanism of crustal subduction and mantle-derived magma un-derplating, or possibly asthenospheric upwelling. Our work also attempted to establish the crustal correlation between Shandong and Korea (including the Gyeonggi massif, Ogcheon belt, and Yeongnam massif). The TDM age distribution provided evidence favoring the affinity relationship between the Gyeonggi massif and Ogcheon belt of South Korea and the Jiaobei and Sulu terranes of Shandong, while the Yeongnam massif was more correlated with the South China Block.

Accessory mineral chemistry as a monitor of petrogenetic and metallogenetic processes: A comparative study of zircon and apatite from Wushan Cu- and Zhuxiling W(Mo)-mineralization-related granitoids

In this study, we explore the chemistry of accessory apatite and zircon as tools to monitor the petrogenetic and metallogenetic processes involved in the formation of the Wushan Cu- and Zhuxiling W (Mo)-mineralization related granodiorite porphyry. The Wushan granitoids are metaluminous with A/CNK of 0.88–1.01, and the Zhuxiling intrusions are weakly peraluminous with higher A/CNK values (1.02–1.12). The Wushan granitoids have εNd(t) values of −4.6 to −4.7, which, combined with the relatively elevated Mg# values (57–62) and adakitic features (high Sr/Y ratios of 51–60), indicate that they were derived from melting of a thickened lower crust of the Yangtze block with addition of small amounts of mantle components. Compared to the Wushan granitoids, the Zhuxiling granitoids have relatively high (87Sr/86Sr)i (0.70945–0.70951) and low εNd(t) values (−5.9 to −6.3) and zircon εHf(t) values (−3.8 to −9.0), suggesting their derivation dominantly from partial melting of the Neoproterozoic crust.The apatites from the Zhuxiling samples are characterized by relatively high MnO and FeO, variable Y and low Ce, which is consistent with the weakly peraluminous feature of whole rock chemistry. These apatites show notable depletion of Th and LREE, with a lower (La/Sm)N ratio (0.74–1.44) and (La/Yb)N ratio (6.2–17.9) relative to those of the host rock (3.04–3.61 and 19.1–23.4, respectively), suggesting early crystallization of some LREE- and Th-enriched minerals such as allanite/monazite before apatite crystallization. The steep trend of Ce/Sm versus Yb/Gd ratios shown by zircons from the Zhuxiling granitoids suggests that the crystallization of zircon is affected by the crystallization of titanite and apatite. Thus, the crystallization sequence of accessory minerals in the Zhuxiling intrusion is allanite, apatite, titanite and zircon. The apatites from the Wushan granitoids, however, show strongly LREE-enriched REE patterns with weak negative Eu anomalies, which indicate minor feldspar fractionation and mildly magmatic differentiation. The flat trend of Ce/Sm versus Yb/Gd ratios shown by zircon from the Wushan pluton indicates that its REE composition is affected by hornblende saturation.Zircon grains from the metaluminous Wushan granitoids exhibit remarkably higher Ce4+/Ce3+ ratios and weaker Eu/Eu* anomalies than those of the peraluminous Zhuxiling samples. And the apatites from the Wushan samples show higher Eu/Eu* (0.55–0.62) and lower Ce/Ce* (0.91–1.04) and MnO (0.05–0.09%) compared to those of the Zhuxiling pluton (with Eu/Eu* = 0.41–0.50, Ce/Ce* = 1.06–1.11, and MnO = 0.15–0.18%, respectively). The apatite and zircon chemistry suggest that the Cu-bearing granitoid formed at an oxygen fugacity higher than the W-bearing granitoid, which agrees with the fact that the Wushan granitoids show whole-rock Fe3+/Fe2+ ratios higher than the Zhuxiling granitoids. In addition, apatites from the Wushan intrusion show enrichment of Cl and higher F/Cl ratios compared to those of the Zhuxiling samples, suggesting that a water-rich parental magma with relatively high Cl content is favourable for copper mineralization.This case study shows that apatite and zircon chemistry could reflect the geochemical characteristics of their host rock and magma evolution. Moreover, they provide insights into the oxidation state, halogen fugacity, and magma differentiation of the magmatic system, which are key factors for mineralization. Our data suggest that magma associated with Cu mineralization is relatively oxidizing, chlorine enriched and less fractionated compared to W-bearing magma.

Continental subduction during arc-microcontinent collision in the southern Siberian craton: Constraints on protoliths and metamorphic evolution of the North Muya complex eclogites (Eastern Siberia)

The eclogites of the North Muya complex (Eastern Siberia) are located within the Early Neoproterozoic metasedimentary and felsic rocks of the Baikal-Muya Fold Belt (BMFB). The eclogites show subduction-related affinity, with large-ion lithophile (LILE) and light rare-earth element (LREE) enrichment and high field-strength element (HFSE) depletion signatures, similar to the exposed plutonic and volcanic rocks of the Early Neoproterozoic (Early Baikalian) subduction setting in the BMFB. Coupled Nd (εNd(T) of +6 to −1.4) and Sr (87Sr/86Sr ratio of 0.705–0.708), along with key trace-element indicators, imply progressive crustal recycling (up to 5–10%) from the Early Precambrian continental rocks to a depleted mantle source or equivalent crustal contribution via intracrustal contamination. Mineral δ18O data (+3.9 − +11.5) indicate that the contaminant or recycled crustal substrate might be represented by rocks altered at both low and high-temperature, or result from variable fluid-rock interaction in the subduction channel. Pseudosection modelling of eclogites, coupled with zircon UPb geochronology (~630 Ma) suggest that the Ediacarian high-pressure metamorphic event for different rocks shared a maximum depth corresponding to 2.5–2.7 GPa with variable temperature range (560–760 °C), reflecting their potential relation to distinct slices of the subducted crust. The estimated metamorphic conditions for both the burial and exhumation of rocks indicate a continental subduction setting, but with a relatively cold geotherm (~20–25 °C/kbar). These conditions resulted from the continental subduction of the Baikal-Muya composite structure beneath the relatively thin and immature overlying arc lithosphere of southern Siberia. Some carbonate-bearing eclogites and garnet-pyroxene rocks, metamorphosed under T below 700 °C and a minimum P up to 1.4 GPa, exhibit LREE-enriched patterns and low εNd(T) values of −7 to −16. These rocks have Paleoproterozoic to Archean model ages and may support the existence of a Paleoproterozoic or older lithosphere in the Baikal-Muya Fold Belt, but their subduction history and origin remain uncertain due to geochemical and isotopic signatures probably overprinted by carbonate metasomatism.

Rare-metal mineralization potential and petrogenesis of Early Cretaceous I-type granitic rocks in the Lizikeng volcanic basin of Jiangxi Province, South China: evidence from mineralogy, geochemistry, and geochronology

The North Wuyi area is an important metallogenic belt in South China and hosts many Pb–Zn–Ag deposits within the Jurassic–Cretaceous volcanic basins. These deposits are mostly genetically associated with Late Jurassic magmatism. The Cretaceous granitic rocks in the Lizikeng basin, at the eastern part of the North Wuyi area, were investigated for their mineralogical and geochemical characteristics in this study. Three types of granitic rocks, quartz monzonite, granite porphyry, and monzogranite, occur, and zircon U–Pb dating reveals that they all formed during the short period of 133–129 Ma, corresponding to the early Cretaceous volcanic-intrusive activities in South China. The whole-rock geochemistry indicates that all three granitic rocks have I-type affinity. The quartz monzonite and granite porphyry have consistently low whole-rock eNd(t) values of − 10.4 to − 9.6 and zircon eHf(t) values of − 14.2 to − 8.2, and they were likely derived from Proterozoic crustal sources without any significant contribution of mantle-derived material. The monzogranite, which shows also negative but slightly higher eNd(t) and eHf(t) values of − 7.6 to − 7.1 and − 9.3 to − 7.0, respectively, might also be derived from a major Proterozoic crustal source but with some input of mantle magma. The geochemical data show that the monzogranite belongs to tungsten-bearing granite with highly evolved characteristics, and with high Nb and W contents similar to the typical rare-metal and W-bearing granites in South China. A large number of typical hydrothermal rare-metal minerals are identified in the monzogranite, such as W-bearing rutile, niobian rutile, and columbite-group minerals as well as ferberite. The discovery of the early Cretaceous granitic rocks with tungsten mineralization potential indicates that the North Wuyi area is prospective for rare-metal mineralization, which opens a new window for rare-metal prospecting in the volcanic basins, as this type of ore deposit was previously thought to occur in granites from mountain range areas in South China, such as the Nanling Range.

Water Contents of Early Cretaceous Mafic Dikes in the Jiaodong Peninsula, Eastern North China Craton: Insights into an Enriched Lithospheric Mantle Source Metasomatized by Paleo–Pacific Plate Subduction–Related Fluids

The Early Cretaceous lithospheric mantle beneath the Jiaodong Peninsula has been recognized as ancient and enriched mantle with widespread mafic dike swarms. However, the enriching agent and the process of the lithospheric mantle remain under debate. In this study, we recovered the H2O contents of the primitive magmas of Early Cretaceous mafic dikes in the Jiaodong Peninsula by using the H2O contents of clinopyroxene (Cpx) phenocrysts and H2O partition coefficients DH2Ocpx/melt. We also present whole-rock geochemical data and in situ major- and trace-element contents for Cpx phenocrysts from these mafic dikes. These dikes are characterized by low SiO2 contents, high MgO contents, enrichment of large-ion lithophile elements and light rare earth elements, depletion of high-field-strength elements, high (87Sr/86Sr)i ratios, and low εNd(t) values. These geochemical features imply an origin of enriched subcontinental lithospheric mantle. The calculated H2O contents of the primitive magmas range from 1.38 to 4.45 wt%, with associated H2O/Ce ratios varying from 237 to 322, suggesting that their mantle source was metasomatized by oceanic slab subduction–related fluids. In addition, covariations between H2O/Ce and incompatible elements indicate the addition of a dehydrated marine sediment component in the mantle source of the Jiaodong mafic dikes. In combination with the H2O contents of Early Cretaceous basaltic rocks in the southeastern North China Craton, the lithospheric mantle was metasomatized through fluids related to paleo–Pacific plate subduction.

Staged fine-grained sediment supply from the Himalayas to the Bengal Fan in response to climate change over the past 50,000 years

The Bengal Fan, as the largest submarine fan in the world, receives a large amount of sediments discharged from the Himalayas through the Ganges-Brahmaputra (G-B) river system. However, previous studies of this system seldom focused on the role of channels, which are widely developed in the Bengal Fan, in sediment transportation over the last glacial cycle. Here, we discuss the coupled sedimentary archive in two gravity cores along the Active Channel in the Bengal Fan. Our findings are based on grain size, clay minerals, and Sr and Nd isotope compositions of these two sediment cores. End-member modeling of grain-size data reveals that the intermediate end-member represents the flux of distal fluvial particles from the G-B river system, the fine end-member denotes regional sediment supply of weathered volcanic materials, especially from the eastern Indian Peninsula, and the coarse end-member probably reflects nearby terrigenous input, aeolian input and/or volcanic glass. Sediment provenance analysis based on clay minerals, and Sr and Nd isotopes confirmed sediment supply from the G-B river system which was characterized by high illite percentage, high 87Sr/86Sr ratios and low εNd values, especially during five stages (50–45 ka, 42–37 ka, 31–28.5 ka, 24–20 ka and 14–9 ka). During these stages, heavy fine-grained sediment supply from the G-B river system was discharged into the study area under the influence of climate change rather than sea-level fluctuation, additionally emphasizing the importance of channels in the sediment transport process. Moreover, we find a significant alteration of sediment sources at ∼26 ka, which may be related to conversion of the deep-water currents in the Bay of Bengal.

Sr–Nd–Hf isotopic compositions of lamprophyres in western Shandong, China: Implications for the nature of the early cretaceous lithospheric mantle beneath the eastern North China Craton

This paper presents new zircon UPb ages and Hf isotope data, and whole-rock geochemical and SrNd isotopic data, for lamprophyres in the western Shandong area of China. These data provide new insights into the nature of the lithospheric mantle beneath the eastern North China Craton (NCC) during the Early Cretaceous. The lamprophyres are divided into low-Ti (TiO2 < 1.1 wt%; Ti/Y < 270) and high-Ti (TiO2 > 2 wt%; Ti/Y > 370) suites, where the Xiaya and Jingziyu minettes are defined as low-Ti lamprophyres and the Jingziyu pyroxene lamprophyres are defined as high-Ti lamprophyres. The igneous zircons yield weighted-mean ages of 126, 132, and 130 Ma for the low- and high-Ti lamprophyres, respectively, indicating these units formed during the Early Cretaceous. The inherited zircons within the Xiaya and Jingziyu minettes define six (2517, 1852, 725, 375, 276, and 236 Ma) and two (2523 and 462 Ma) main age populations, respectively. In comparison, the inherited zircons from the Jingziyu pyroxene lamprophyres yield two main age populations (2523 and 1848 Ma). The low-Ti lamprophyres are enriched in the light rare earth elements (LREE) and large-ion lithophile elements (LILE), depleted in the heavy REE (HREE) and high-field-strength elements (HFSE), and have small negative Eu anomalies. In comparison, the high-Ti lamprophyres are enriched in the LREE but are slightly depleted in the HFSE. The low-Ti lamprophyres also have high 87Sr/86Sr(t) ratios (0.7121–0.7123), low εNd(t) values (−18.81 to −18.62), and contain igneous zircons with relatively high εHf(t) values (generally between −9.94 and −3.36). In comparison, the high-Ti lamprophyres have 87Sr/86Sr(t) ratios of 0.7066–0.7068, εNd(t) values from −5.01 to −4.64, and contain igneous zircons with εHf(t) values from −11.77 to −8.50. These data indicate the low-Ti lamprophyres formed from primary magmas generated by the partial melting of an enriched region of the lithospheric mantle that was previously strongly modified jointly by subduction breakoff of the downgoing Yangtze Craton basement material and delamination of the lower continental crust within the NCC. In comparison, the magmas that formed the high-Ti lamprophyres were generated by the partial melting of an enriched region of the lithospheric mantle that was weakly modified by interaction with the lower continental crust of the NCC. Both the low- and high-Ti lamprophyres formed in an extensional tectonic environment during lithospheric thinning, and the presence of these two suites of lamprophyres indicates that lithospheric thinning of the eastern NCC peaked during the Early Cretaceous.

Early Cretaceous potassic volcanic rocks from the northern margin of the Sulu orogenic belt, Shandong Province, eastern China: Constraints on petrogenesis and crust–mantle interaction

A major and trace element, Sr–Nd–Hf isotope, and zircon U–Pb geochronology study was conducted on Early Cretaceous volcanic rocks from the northern margin of the Sulu orogenic belt in Shandong Province, eastern China. These results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of crust–mantle interaction. The rocks comprise high‐K basaltic andesite, shoshonites, latites, high‐K dacites, and high‐K rhyolites. U–Pb zircon dating of four representative samples of latite, two high‐K dacites, and high‐K rhyolite indicates that these rocks formed from 126 to 122 Ma. The volcanic rocks are characterized by high K2O (2.04–6.70 wt.%) and total alkalis (Na2O + K2O; 5.3–10.9 wt.%) that plot within the field for shoshonitic rocks. All the rocks are enriched in light rare earth and large‐ion lithophile elements (e.g., Rb, Th, U, and K) and are depleted in high‐field‐strength elements (e.g., Nb, Ta, and Ti). The rocks have high initial 87Sr/86Sr ratios (0.706760–0.708898), low εNd(t) values (−19.5 to −12.5), and negative εHf(t) values (−31.3 to −19.7), similar to the Early Cretaceous Jiaodong mafic dikes and intermediate–mafic volcanic rocks. These geochemical and isotopic characteristics indicate that the volcanic rocks formed through simultaneous fractional crystallization and crustal assimilation of a basaltic magma derived from metasomatized mantle. The metasomatized mantle source might have been produced by the recycling of subducted Yangtze Craton crust into the ancient lithospheric mantle of the North China Craton.

Ore genesis of the Zhuxi supergiant W-Cu skarn polymetallic deposit, South China: Evidence from scheelite geochemistry

Scheelite is the main ore mineral in skarn-type tungsten deposits, which can be used to track the ore-forming processes and sources. The Zhuxi W-Cu deposit (3.44 Mt WO3 at 0.54% and 0.10 Mt Cu at 0.57%), located in the northern part of the Jiangnan orogen, is one of the largest tungsten deposits in the world. Skarn and orebodies occur mainly within the contact zone between the Mesozoic highly fractionated intrusions and Carboniferous carbonate sediments (Huanglong and Chuanshan formations). Our data reveal that the REEs of scheelite are mainly controlled by the substitution mechanism 3Ca2+ = 2REE3+ + □Ca. Scheelites from the Zhuxi deposit show negative Eu anomalies in the prograde skarn stage, but positive Eu anomalies in the retrograde skarn stage in the chondrite-normalized REE patterns. Variation of Eu anomalies recorded the ore-forming processes. The negative Eu anomalies were inherited from the Mesozoic granites and the positive ones formed under more reduced redox conditions. The decrease of Mo concentrations, along with increase of δEu and δCe of scheelite from prograde to retrograde skarn stage, support a temporal decrease in oxygen fugacity of the mineralization fluids. The scheelites from the Zhuxi deposit are characterized by low εNd(t) values (−10.1 to −7.0) and high initial 87Sr/86Sr ratios (0.71231–0.72371), which are different from the scheelites hosted in vein-type Au-W deposits contributed mainly by mantle. The Nd-Sr isotopes of scheelites are consistent with the results of the three Mesozoic granites, indicating their genetic relationship. However, the scheelites show variable Nb/Ta compositions, which straddle between the values of Mesozoic granites and the country rock of Shuangqiaoshan Group meta-sedimentary rocks, indicating the Shuangqiaoshan Group also has contributed to mineralization. This is different from a commonly accepted model that the ore-forming fluids and metals were exsolved exclusively from the granite plutons.

Coexistence of MORB- and OIB-like dolerite intrusions in the Purang ultramafic massif, SW Tibet: A paradigm of plume-influenced MOR-type magmatism prior to subduction initiation in the Neo-Tethyan lithospheric mantle

The Yarlung Zangbo Suture Zone (YZSZ) of South Tibet is divided by the ZhongbaZhada terrane into two subparallel ophiolitic belts in its western end. The peridotite massifs of the southern belt tectonically overlie the Tethyan Himalaya sequence. The Purang peridotite body in this belt is intruded by two groups of dolerite dikes, providing significant compositional, geochronological, and isotopic information about the melting history of the Neo-Tethyan mantle. U-Pb ages of zircons separated from dolerites show that peridotites of West Purang were intruded by an early generation of dikes at 138.5 +/- 2.0 Ma (Valanginian). These dolerites show ocean island basalt (OIB)-type normalized multi-elemental profiles and Sr-Nd isotopic signatures [(La/Yb)(N )= 13-16], high initial Sr-87/Sr-86 ratios (0.70598-0.70765), and low epsilon(Nd)(t) values (-2.6 to -2.3). Zircons separated from this group of dolerites have slightly radiogenic epsilon(Hf)(t) values (+2.6 to +4.6). The next generation of dolerite dikes intruded the East Purang peridotites between 124.5 +/- 2.5 Ma and 124.4 +/- 3.2 Ma (Aptian). These East Purang dolerites show normal mid-ocean ridge basalt (N-MORB)-type normalized multi-element patterns [(La/Yb)(N) = 0.6-0.9] with noticeable negative Nb and Th (+/- Ti) anomalies, and have high Sr-87/Sr-86((i)) (0.70295-0.70618) and high epsilon(Nd)(t) values (+7.7 to +9.2). Zircons separated from the East Purang dolerites show strongly radiogenic epsilon(Hf)(t) values (+3.5 to +17.0).Semiquantitative geochemical modeling demonstrates that the parental magmas of West Purang dolerites were generated from 5 %-10 % polybaric partial melting of a deep-seated juvenile asthenospheric source enriched by plume-type components. In contrast, the parental melts of East Purang dolerites were derived from more than 20% melting of a juvenile spinel-bearing MORB-type mantle source that was modified by subduction-related melts/fluids to a minor extent. A possible tectono-magmatic model for the petrogenesis of the Purang ophiolitic massif could be linked to incipient continental rifting and subsequent oceanic seafloor spreading associated with decompression upwelling of an asthenospheric source contaminated by plume-type components. This plume-proximal seafloor spreading-system was succeeded by the initiation of Neo-Tethyan intra-oceanic subduction close to the active continental margin of Eurasia during the Early Cretaceous.

Early Cretaceous arc granitoids from the central Lhasa subterrane: Production of the northward subduction of Yarlung Zangbo Neo‐Tethyan Ocean?

There is ongoing debate as to the genesis of the Lhasa Terrane during the Mesozoic (northward subduction of Yanglu‐Zangbo Tethyan Ocean [YZTO] or southward subduction of Bangong–Nujiang Tethyan Ocean [BNTO]). In this paper, we report a dataset of geochronology, geochemistry, and Sr–Nd–Hf isotopes for the Azhale granitoids in order to elucidate the dominant geodynamic processes of the central subterrane. These rocks are dated at 142.2 ± 1.0 and 136.6 ± 0.6 Ma by zircon LA–ICP–MS method, indicating that these rocks were contemporaneous. In situ zircon Hf isotopic analyses yielded εHf(t) values of −4.2 to −0.1. Geochemically, these samples mostly belong to calc‐alkaline series and show strong enrichments in large‐ion lithophile elements (LILE;e.g., Rb, Ba, and Th) and depletions in high‐field‐strength elements (HFSE;e.g., Nb and Ta), indicating the Azhale granitoids are typically I‐type granite. In terms of isotopic composition, these rocks also have low εNd(t) values (−6.51 to −6.80) and high initial 87Sr/86Sr ratios (0.7078 to 0.7084) relative to melts derived from partial melting of ancient mafic lower crust. We considered that these rocks should be interpreted to have resulted from melting, assimilation, storage, and homogenization (MASH process) above subduction zones. In conclusion, combined with the published and our new data, we argued for the petrogenesis of Early Cretaceous arc‐related granitoids were due to the YZTO lithosphere subducted northward beneath the Lhasa Terrane.