Xuan-Ce Wang - Academia.edu (original) (raw)
Papers by Xuan-Ce Wang
Geochimica et Cosmochimica Acta, 2016
Precambrian Research, 2016
Chemical Geology, 2015
Disequilibrium-induced initial Os isotopic heterogeneity in gram aliquots of single basaltic rock... more Disequilibrium-induced initial Os isotopic heterogeneity in gram aliquots of single basaltic rock powders: implications for dating and source tracing,
Precambrian Research, 2012
The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Crat... more The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Craton, consists mainly of khondalite suite and S-type granites. It is thought to be a continental collision belt along which the Yinshan and Ordos Blocks amalgamated to form the Western Block of the North China Craton at ca. 1.95 Ga. While many resent studies revealed that the khondalite protoliths were sourced from juvenile crustal materials and the time interval between their deposition and subsequent metamorphism is less than 50 million years, the nature and depositional setting of the khondalite protoliths are still controversial. We carried out in this study an integrated analysis of U-Pb age and Hf-O isotopes for detrital zircons from the Helanshan Complex in the westernmost part of the Khondalite Belt. Precise SIMS U-Pb zircon results suggest that the timing of the deposition of the Helanshan khondalite protoliths can be constrained between ca. 2.00 and ca. 1.95 Ga by the minimum age of the detrital zircons from the khondalites and the maximum crystallization age of ca. 1.95 Ga for the intruded granites. The ca. 1.95 Ga granites, the oldest granites identified within the Khondalite Belt, were coeval with the regional highgrade metamorphism. The Helanshan khondalite protoliths were sourced mainly from a provenance with prolonged, episodic magmatism of ca. 2.18 Ga, 2.14 Ga, 2.09 Ga, 2.06 Ga, 2.03 Ga and 2.00 Ga, respectively. Detrital zircons of ca. 2.18-2.00 Ga from the khondalites have ε Hf (t) values ranging from +8.9 to −2.9 and Hf T DM C model ages between 2.8 and 2.1 Ga, with two major peaks at 2.6 Ga and 2.3 Ga. Their ı 18 O values show two major peaks at 6.6‰ and 8.2‰. Zircon Hf-O isotopic data indicate that both the juvenile and ancient crustal components were involved in their source rocks, and the Helanshan khondalite protoliths were most likely sourced from a ca. 2.18-2.00 Ga continental arc. The juvenile continental arc materials were uplifted, eroded, transported, deposited and metamorphosed within a short time interval of <50 million years. With the predominantly euhedral crystals of the detrital zircons and the immature clastic sediments for the Helanshan khondalite protoliths, we suggest that the khondalite protoliths were likely deposited in an active continental margin, rather than a passive margin as previously thought.
Precambrian Research, 2015
Middle Neoproterozoic sedimentary rocks are widespread in the South China Block, especially aroun... more Middle Neoproterozoic sedimentary rocks are widespread in the South China Block, especially around the periphery of the Yangtze Block. They are separated into the Sibao and Danzhou groups (and their equivalents) by a "mid-Neoproterozoic angular unconformity" in the south margin of the Yangtze Block. This unconformity, previously interpreted as the evidence of continental collision between the Yangtze and Cathaysia blocks, is crucial for understanding the early-middle Neoproterozoic tectonic regime in the South China Block. We report integrated in situ U-Pb, Hf and O isotopes analyses of detrital zircon grains from sandstones across this unconformity, and use these data to decipher their sedimentary provenances and shed new light on the basin evolution and the tectonic significance of this mid-Neoproterozoic unconformity.
Precambrian Research, 2013
Gondwana Research, 2015
a b s t r a c t Available online xxxx Handling Editor: W.J. Xiao Keywords: North China Craton Alx... more a b s t r a c t Available online xxxx Handling Editor: W.J. Xiao Keywords: North China Craton Alxa Block Cryptic suture zone High δ 18 O zircon Zircon Hf-O isotopes
Marnda Moorn LIP (large igneous province) Yilgarn Craton Mantle plume Plume-lithosphere interacti... more Marnda Moorn LIP (large igneous province) Yilgarn Craton Mantle plume Plume-lithosphere interaction Recycled oceanic crust Ultrahigh-temperature a b s t r a c t The 1.21 Ga Marnda Moorn large igneous province (LIP) of the Yilgarn Craton is important for understanding the final breakup of the Nuna (Columbia) supercontinent. However, its petrogenesis is poorly understood owing to the lack of geochemical data. We conducted geochemical analyses of the Gnowangerup-Fraser Dyke Suite, a major part of the Marnda Moorn LIP, and report the first geochemical and Nd isotope data for this LIP. Results of a complementary paleomagnetic study of these dykes will be published elsewhere. Most of the studied dykes consist of predominately tholeiitic and OIB-like dolerite (Group 1) and one arc-like and more felsic dyke (Group 2). Group 1 samples have incompatible trace element compositions similar to those of tholeiitic Hawaiian plume-induced OIB and typical asthenospheric mantle-derived Nd isotopes with Nd(t) varying from +3.7 to +7.5, produced mainly within the spinel stability field (<75 km depth). Their source region most likely contains recycled oceanic crust. Samples from the Group 2 dyke are characterized by extremely unradiogenic Nd isotopes with Nd(t) of about −12, strong depletion of Nb-Ta-Zr-Hf-Ti, chondritic Nb/Ta ratios (20-18), oversaturated silica, and strong deficiencies in CaO, FeOt, TiO 2 , and Ni. This implies that the dyke was produced by partial melting of enriched sub-continental lithospheric mantle. The coexistence of OIB-and arc-like end-members but mainly Hawaiian OIB-like tholeiitic mafic dykes, interpreted large-scale asthenosphere upwelling in a very short time, and the large volume of mafic magma, favour a plume origin for the Marnda Moorn LIP. The geochemical and emplacement characteristics are attributed to relief of the lithosphere-asthenosphere boundary across the Yilgarn craton and a complex interplay between the plume, heated lithosphere, normal asthenosphere, and recycled components. We propose a two-stage melting model to explain the geochemical composition and emplacement of the Marnda Moorn LIP. Our plume-lithosphere interaction model is consistent with the occurrence of synchronous ultrahightemperature events in the Musgrave Province of central Australia.
An emerging challenge for understanding the Earth system is to determine the relative roles of ea... more An emerging challenge for understanding the Earth system is to determine the relative roles of early planetary processes versus progressive differentiation in shaping the Earth's chemical architecture. An enduring tenet of modern chemical geodynamics is that the Earth started as a well-mixed and homogeneous body which evolved progressively over the geologic time to several chemically distinct domains. As a consequence, the observable chemical heterogeneity in mantle-derived rocks has generally been attributed to the Earth's dynamic evolution over the past 4.5 Ga. However, the identification of chemical heterogeneity formed during the period 4.53-4.45 Ga in the ca. 60 Ma Baffin Bay high-magnesium lavas provides strong evidence that chemical effects of early differentiation can persist in mantle reservoirs to the present day. Here, we demonstrate that such an ancient mantle reservoir is likely composed of enriched and depleted dense melts, and propose a model for early global differentiation of the bulk silicate Earth that would produce two types of dense melts with distinctive chemical compositions in the deep Earth. These dense melts ultimately became parts of the thermo-chemical piles near the coremantle boundary that have been protected from complete entrainment by subsequent mantle convection currents. We argue that although such dense melts likely exhibit some 'primordial' geochemical signatures, they are not representative of the bulk silicate Earth. Our work provides a strong case for the mantle chemical heterogeneity being formed by a major differentiation event shortly after planet accretion rather than through the subsequent geodynamic evolution.
A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-... more A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) in geological samples. The method is based on the separation of Mo by extraction chromatography using N-benzoyl-N-phenylhydroxylamine (BPHA) supported on a microporous acrylic ester polymeric resin (Amberlite CG-71). By optimising the procedure, Mo could be simply and effectively separated from virtually all matrix elements with a single pass through a small volume of BPHA resin (0.5 ml). This technique for separation and enrichment of Mo is characterised by high selectivity, column efficiency and recovery (~100%), and low total procedural blank (~0.18 ng). A 100 Mo-97 Mo double spike was mixed with samples before digestion and column separation, which enabled natural mass-dependent isotopic fractionation to be determined with a measurement reproducibility of < 0.09‰ (d 98/95 Mo, 2s) by MC-ICP-MS. The mean d 98/95 Mo SRM 3134 (NIST SRM 3134 Mo reference material; Lot No. 891307) composition of the IAPSO seawater reference material measured in this study was 2.00 ± 0.03‰ (2s, n = 3), which is consistent with previously published values. The described procedure facilitated efficient and rapid Mo isotopic determination in various types of geological samples. Une nouvelle m ethode de pr e-concentration est pr esent ee pour la d etermination des rapports isotopiques du Mo par spectrom etrie de masse a source plasma et multi-collection (MC -ICP-MS) dans des echantillons g eologiques. La m ethode est bas ee sur la s eparation du Mo par Chromatographie d'extraction en utilisant du Nbenzoyle-N-ph enylhydroxylamine (BPHA) support e par une r esine polym ere d'ester acrylique microporeuse (Amberlite CG-71). En optimisant la proc edure, le Mo peutêtre simplement et efficacement s epar e de la quasitotalit e des el ements de la matrice avec un seul passage a travers un petit volume de r esine BPHA (0,5 ml). Cette technique de s eparation et d'enrichissement du Mo est caract eris ee par une grande s electivit e, une grande efficacit e et une grande r ecup eration de la colonne (~100%), et un faible total de la proc edure de blanc (~0,18 ng). Un double spike Mo 100 -Mo 97 a et e m elang e avec les echantillons avant la digestion et la s eparation sur colonne, ce qui a permis la d etermination du fractionnement isotopique naturel d ependant de la masse avec une reproductibilit e de mesure de < 0,09 ‰ ( d98/95 Mo, 2s) par MC -ICP-MS. La composition moyenne d 98/95 Mo SRM3134 (mat eriau de r ef erence NIST SRM 3134 Mo; Lot n°891307) de l'eau de mer de r ef erence IAPSO mesur ee dans cette etude est de 2,00 ± 0,03 ‰ (2s, n = 3), ce qui est coh erent avec les valeurs pr ec edemment publi ees. La proc edure d ecrite facilite une d etermination efficace et rapide des rapports isotopiques du Mo dans divers types d' echantillons g eologiques.
The Alxa Block in northern China has been traditionally considered as the westernmost part of the... more The Alxa Block in northern China has been traditionally considered as the westernmost part of the Archean North China Craton (NCC). However, recent studies revealed that there are few Archean rocks exposed in the Alxa Block, and the Paleoproterozoic geology of this block is different from that of the western part of the NCC. Thus, the tectonic affinity of the Alxa Block to the NCC and/or other Precambrian blocks needs further investigations. In this study, we carry out integrated analyses of in situ zircon U-Pb age and Hf-O isotopes as well as whole-rock geochemistry and Nd isotopes for the Neoproterozoic Dabusushan and Naimumaodao granites from central Alxa Block. Secondary ion mass spectrometry SIMS) U-Pb zircon dating results indicate that the Naimumaodao and Dabusushan granite plutons were formed at ca. 930 Ma and ca. 910 Ma, respectively. These granites are peraluminous (A/CNK value >1.0), and contain peraluminous minerals such as muscovite and tourmaline, similar to those of S-type granites. They are characterized by high zircon ␦ 18 O values of ca. 8.2 to 12.1 permil, corresponding to a calculated magmatic ␦ 18 O value of ca. 10.5 to 14.3 permil, variable zircon Hf (t) values of ؊6.2 to ؉3.8 (corresponding to Hf model ages of 2.2 to 1.6 Ga) and whole-rock Nd (t) values of ؊10.1 to ؊4.5 (corresponding to Nd model ages of 2.4-1.
Precambrian Research, 2015
Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidenc... more Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent, Precambrian Research (2015), http://dx.
Lithos
In general, the mantle provides heat and/or material for the generation of the silicic igneous pr... more In general, the mantle provides heat and/or material for the generation of the silicic igneous provinces (SIPs). The rarity of mafic microgranular enclaves (MMEs), however, hampers understanding of the mantle’s role in generating SIPs and the process of crust-mantle interaction. The widespread distributed MMEs in the newly reported Alxa SIP provide an opportunity to study these processes. This study integrates in situ zircon U-Pb age and Hf–O isotope analyses, whole-rock geochemistry and Sr–Nd isotope results for the MMEs and host granitoids in the Alxa Block. SIMS zircon U-Pb dating reveals that there are two generations of MMEs and host granitoids. The MMEs in the Bayannuoergong batholith were formed at ca. 278 Ma, similar to the age (280 Ma) of host granitoids, and the MMEs and host granitoids in the Yamaitu pluton were formed at ca. 272-270 Ma. All MMEs have relatively low SiO2 (50.7–61.4 wt.%) and Th (0.8–2.8), but relatively high MgO (2.6–4.9 wt.%), Cr (23–146 ppm) and Ni (6–3...
The debate on the Mesozoic tectonics of the South China Block (SCB), featuring a broad orogenic b... more The debate on the Mesozoic tectonics of the South China Block (SCB), featuring a broad orogenic belt and a large continental magmatic province, has been rejuvenated in the past years. There are a number of competing tectonic models, each predicting different time, space, and compositional evolutional trends for the Mesozoic igneous rocks, including sporadic basalts. In this paper, we report high precision 40 Ar/ 39 Ar ages and geochemical and Sr-Nd isotopic data for basaltic rocks in central-eastern SCB. These results, together with a data compilation, indicate three evolutionary stages for the basalts. Stage 1 (195-160 Ma) basalts occur only in inland SCB. They exhibit low initial 87 Sr/ 86 Sr ratios (0.7038 to 0.7078), high ε Nd (t) values (− 1.5 to 6.0) and ocean island basalt (OIB)-like geochemical characteristics such as low La/Nb ratios (0.6 to 1.4), implying negligible to minor lithosphere contamination. Stage 2 (160-110 Ma) basalts, mostly from the same inland region with minor occurrence closer to the coast, are characterized by variable initial 87 Sr/ 86 Sr ratios (0.7053 to 0.7102), εNd(t) values (− 6.0 to 5.0) and low La/Nb ratios (0.9 to 1.8), indicating an enhanced asthenosphere-lithosphere interaction. Stage 3 (110 to ≤ 80 Ma) basalts can be further divided into two subgroups based on their geographic and geochemical variations. Basalts in the coastal regions are characterized by low εNd(t) values (− 8.1 to 3.7) and variably high La/Nb ratios (up to 4.8) indicating a strong arc signature. On the other hand, basalts in the inland regions have high ε Nd (t) values (− 1.9 to 6.8) and low La/Nb ratios (0.6 to 1.2) that are similar to the stage 1 basalts. We interpret these features as results of geodynamics processes related to the break-up, foundering and retreating of an early Mesozoic flat-subducted oceanic slab.
The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Crat... more The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Craton, consists mainly of khondalite suite and S-type granites. It is thought to be a continental collision belt along which the Yinshan and Ordos Blocks amalgamated to form the Western Block of the North China Craton at ca. 1.95 Ga. While many resent studies revealed that the khondalite protoliths were sourced from juvenile crustal materials and the time interval between their deposition and subsequent metamorphism is less than 50 million years, the nature and depositional setting of the khondalite protoliths are still controversial. We carried out in this study an integrated analysis of U-Pb age and Hf-O isotopes for detrital zircons from the Helanshan Complex in the westernmost part of the Khondalite Belt. Precise SIMS U-Pb zircon results suggest that the timing of the deposition of the Helanshan khondalite protoliths can be constrained between ca. 2.00 and ca. 1.95 Ga by the minimum age of the detrital zircons from the khondalites and the maximum crystallization age of ca. 1.95 Ga for the intruded granites. The ca. 1.95 Ga granites, the oldest granites identified within the Khondalite Belt, were coeval with the regional highgrade metamorphism. The Helanshan khondalite protoliths were sourced mainly from a provenance with prolonged, episodic magmatism of ca. 2.18 Ga, 2.14 Ga, 2.09 Ga, 2.06 Ga, 2.03 Ga and 2.00 Ga, respectively. Detrital zircons of ca. 2.18-2.00 Ga from the khondalites have ε Hf (t) values ranging from +8.9 to −2.9 and Hf T DM C model ages between 2.8 and 2.1 Ga, with two major peaks at 2.6 Ga and 2.3 Ga. Their ı 18 O values show two major peaks at 6.6‰ and 8.2‰. Zircon Hf-O isotopic data indicate that both the juvenile and ancient crustal components were involved in their source rocks, and the Helanshan khondalite protoliths were most likely sourced from a ca. 2.18-2.00 Ga continental arc. The juvenile continental arc materials were uplifted, eroded, transported, deposited and metamorphosed within a short time interval of <50 million years. With the predominantly euhedral crystals of the detrital zircons and the immature clastic sediments for the Helanshan khondalite protoliths, we suggest that the khondalite protoliths were likely deposited in an active continental margin, rather than a passive margin as previously thought.
Marine Geology
This study reported geochemical and Sr-Nd isotopic variation of fine-grained mineral components i... more This study reported geochemical and Sr-Nd isotopic variation of fine-grained mineral components in a deep-sea piston core G6-4, south of the Sumba Island, Eastern Indian Ocean. The new data enables us to characterise dust contributions from Australian continent and volcanic eruption history in the adjacent volcanic arc over approximately the last 300,000 years. The geochemical and isotopic features of the fine-grained components (﹤20 μm) in Core G6-4 are broadly consistent with mixing between aeolian dusts from the Australian continent and volcanic ashes of the Sunda arcs. Simple two-component modeling shows that the majority of the core samples probably are composed of 50-80% aeolian dusts derived from the Australian continent. Sr-Nd isotopic ratios are fairly uniform for samples older than 180 ka, in contrast with those of the samples younger than 180 ka, which are much more variable with three anomalies characterized by higher 143Nd/144Nd and lower 87Sr/86Sr values recognized. We...
Nature communications, 2015
It has previously been postulated that the Earth's hydrous mantle transition zone may play a ... more It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can poten...
Geochimica et Cosmochimica Acta, 2016
Precambrian Research, 2016
Chemical Geology, 2015
Disequilibrium-induced initial Os isotopic heterogeneity in gram aliquots of single basaltic rock... more Disequilibrium-induced initial Os isotopic heterogeneity in gram aliquots of single basaltic rock powders: implications for dating and source tracing,
Precambrian Research, 2012
The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Crat... more The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Craton, consists mainly of khondalite suite and S-type granites. It is thought to be a continental collision belt along which the Yinshan and Ordos Blocks amalgamated to form the Western Block of the North China Craton at ca. 1.95 Ga. While many resent studies revealed that the khondalite protoliths were sourced from juvenile crustal materials and the time interval between their deposition and subsequent metamorphism is less than 50 million years, the nature and depositional setting of the khondalite protoliths are still controversial. We carried out in this study an integrated analysis of U-Pb age and Hf-O isotopes for detrital zircons from the Helanshan Complex in the westernmost part of the Khondalite Belt. Precise SIMS U-Pb zircon results suggest that the timing of the deposition of the Helanshan khondalite protoliths can be constrained between ca. 2.00 and ca. 1.95 Ga by the minimum age of the detrital zircons from the khondalites and the maximum crystallization age of ca. 1.95 Ga for the intruded granites. The ca. 1.95 Ga granites, the oldest granites identified within the Khondalite Belt, were coeval with the regional highgrade metamorphism. The Helanshan khondalite protoliths were sourced mainly from a provenance with prolonged, episodic magmatism of ca. 2.18 Ga, 2.14 Ga, 2.09 Ga, 2.06 Ga, 2.03 Ga and 2.00 Ga, respectively. Detrital zircons of ca. 2.18-2.00 Ga from the khondalites have ε Hf (t) values ranging from +8.9 to −2.9 and Hf T DM C model ages between 2.8 and 2.1 Ga, with two major peaks at 2.6 Ga and 2.3 Ga. Their ı 18 O values show two major peaks at 6.6‰ and 8.2‰. Zircon Hf-O isotopic data indicate that both the juvenile and ancient crustal components were involved in their source rocks, and the Helanshan khondalite protoliths were most likely sourced from a ca. 2.18-2.00 Ga continental arc. The juvenile continental arc materials were uplifted, eroded, transported, deposited and metamorphosed within a short time interval of <50 million years. With the predominantly euhedral crystals of the detrital zircons and the immature clastic sediments for the Helanshan khondalite protoliths, we suggest that the khondalite protoliths were likely deposited in an active continental margin, rather than a passive margin as previously thought.
Precambrian Research, 2015
Middle Neoproterozoic sedimentary rocks are widespread in the South China Block, especially aroun... more Middle Neoproterozoic sedimentary rocks are widespread in the South China Block, especially around the periphery of the Yangtze Block. They are separated into the Sibao and Danzhou groups (and their equivalents) by a "mid-Neoproterozoic angular unconformity" in the south margin of the Yangtze Block. This unconformity, previously interpreted as the evidence of continental collision between the Yangtze and Cathaysia blocks, is crucial for understanding the early-middle Neoproterozoic tectonic regime in the South China Block. We report integrated in situ U-Pb, Hf and O isotopes analyses of detrital zircon grains from sandstones across this unconformity, and use these data to decipher their sedimentary provenances and shed new light on the basin evolution and the tectonic significance of this mid-Neoproterozoic unconformity.
Precambrian Research, 2013
Gondwana Research, 2015
a b s t r a c t Available online xxxx Handling Editor: W.J. Xiao Keywords: North China Craton Alx... more a b s t r a c t Available online xxxx Handling Editor: W.J. Xiao Keywords: North China Craton Alxa Block Cryptic suture zone High δ 18 O zircon Zircon Hf-O isotopes
Marnda Moorn LIP (large igneous province) Yilgarn Craton Mantle plume Plume-lithosphere interacti... more Marnda Moorn LIP (large igneous province) Yilgarn Craton Mantle plume Plume-lithosphere interaction Recycled oceanic crust Ultrahigh-temperature a b s t r a c t The 1.21 Ga Marnda Moorn large igneous province (LIP) of the Yilgarn Craton is important for understanding the final breakup of the Nuna (Columbia) supercontinent. However, its petrogenesis is poorly understood owing to the lack of geochemical data. We conducted geochemical analyses of the Gnowangerup-Fraser Dyke Suite, a major part of the Marnda Moorn LIP, and report the first geochemical and Nd isotope data for this LIP. Results of a complementary paleomagnetic study of these dykes will be published elsewhere. Most of the studied dykes consist of predominately tholeiitic and OIB-like dolerite (Group 1) and one arc-like and more felsic dyke (Group 2). Group 1 samples have incompatible trace element compositions similar to those of tholeiitic Hawaiian plume-induced OIB and typical asthenospheric mantle-derived Nd isotopes with Nd(t) varying from +3.7 to +7.5, produced mainly within the spinel stability field (<75 km depth). Their source region most likely contains recycled oceanic crust. Samples from the Group 2 dyke are characterized by extremely unradiogenic Nd isotopes with Nd(t) of about −12, strong depletion of Nb-Ta-Zr-Hf-Ti, chondritic Nb/Ta ratios (20-18), oversaturated silica, and strong deficiencies in CaO, FeOt, TiO 2 , and Ni. This implies that the dyke was produced by partial melting of enriched sub-continental lithospheric mantle. The coexistence of OIB-and arc-like end-members but mainly Hawaiian OIB-like tholeiitic mafic dykes, interpreted large-scale asthenosphere upwelling in a very short time, and the large volume of mafic magma, favour a plume origin for the Marnda Moorn LIP. The geochemical and emplacement characteristics are attributed to relief of the lithosphere-asthenosphere boundary across the Yilgarn craton and a complex interplay between the plume, heated lithosphere, normal asthenosphere, and recycled components. We propose a two-stage melting model to explain the geochemical composition and emplacement of the Marnda Moorn LIP. Our plume-lithosphere interaction model is consistent with the occurrence of synchronous ultrahightemperature events in the Musgrave Province of central Australia.
An emerging challenge for understanding the Earth system is to determine the relative roles of ea... more An emerging challenge for understanding the Earth system is to determine the relative roles of early planetary processes versus progressive differentiation in shaping the Earth's chemical architecture. An enduring tenet of modern chemical geodynamics is that the Earth started as a well-mixed and homogeneous body which evolved progressively over the geologic time to several chemically distinct domains. As a consequence, the observable chemical heterogeneity in mantle-derived rocks has generally been attributed to the Earth's dynamic evolution over the past 4.5 Ga. However, the identification of chemical heterogeneity formed during the period 4.53-4.45 Ga in the ca. 60 Ma Baffin Bay high-magnesium lavas provides strong evidence that chemical effects of early differentiation can persist in mantle reservoirs to the present day. Here, we demonstrate that such an ancient mantle reservoir is likely composed of enriched and depleted dense melts, and propose a model for early global differentiation of the bulk silicate Earth that would produce two types of dense melts with distinctive chemical compositions in the deep Earth. These dense melts ultimately became parts of the thermo-chemical piles near the coremantle boundary that have been protected from complete entrainment by subsequent mantle convection currents. We argue that although such dense melts likely exhibit some 'primordial' geochemical signatures, they are not representative of the bulk silicate Earth. Our work provides a strong case for the mantle chemical heterogeneity being formed by a major differentiation event shortly after planet accretion rather than through the subsequent geodynamic evolution.
A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-... more A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) in geological samples. The method is based on the separation of Mo by extraction chromatography using N-benzoyl-N-phenylhydroxylamine (BPHA) supported on a microporous acrylic ester polymeric resin (Amberlite CG-71). By optimising the procedure, Mo could be simply and effectively separated from virtually all matrix elements with a single pass through a small volume of BPHA resin (0.5 ml). This technique for separation and enrichment of Mo is characterised by high selectivity, column efficiency and recovery (~100%), and low total procedural blank (~0.18 ng). A 100 Mo-97 Mo double spike was mixed with samples before digestion and column separation, which enabled natural mass-dependent isotopic fractionation to be determined with a measurement reproducibility of < 0.09‰ (d 98/95 Mo, 2s) by MC-ICP-MS. The mean d 98/95 Mo SRM 3134 (NIST SRM 3134 Mo reference material; Lot No. 891307) composition of the IAPSO seawater reference material measured in this study was 2.00 ± 0.03‰ (2s, n = 3), which is consistent with previously published values. The described procedure facilitated efficient and rapid Mo isotopic determination in various types of geological samples. Une nouvelle m ethode de pr e-concentration est pr esent ee pour la d etermination des rapports isotopiques du Mo par spectrom etrie de masse a source plasma et multi-collection (MC -ICP-MS) dans des echantillons g eologiques. La m ethode est bas ee sur la s eparation du Mo par Chromatographie d'extraction en utilisant du Nbenzoyle-N-ph enylhydroxylamine (BPHA) support e par une r esine polym ere d'ester acrylique microporeuse (Amberlite CG-71). En optimisant la proc edure, le Mo peutêtre simplement et efficacement s epar e de la quasitotalit e des el ements de la matrice avec un seul passage a travers un petit volume de r esine BPHA (0,5 ml). Cette technique de s eparation et d'enrichissement du Mo est caract eris ee par une grande s electivit e, une grande efficacit e et une grande r ecup eration de la colonne (~100%), et un faible total de la proc edure de blanc (~0,18 ng). Un double spike Mo 100 -Mo 97 a et e m elang e avec les echantillons avant la digestion et la s eparation sur colonne, ce qui a permis la d etermination du fractionnement isotopique naturel d ependant de la masse avec une reproductibilit e de mesure de < 0,09 ‰ ( d98/95 Mo, 2s) par MC -ICP-MS. La composition moyenne d 98/95 Mo SRM3134 (mat eriau de r ef erence NIST SRM 3134 Mo; Lot n°891307) de l'eau de mer de r ef erence IAPSO mesur ee dans cette etude est de 2,00 ± 0,03 ‰ (2s, n = 3), ce qui est coh erent avec les valeurs pr ec edemment publi ees. La proc edure d ecrite facilite une d etermination efficace et rapide des rapports isotopiques du Mo dans divers types d' echantillons g eologiques.
The Alxa Block in northern China has been traditionally considered as the westernmost part of the... more The Alxa Block in northern China has been traditionally considered as the westernmost part of the Archean North China Craton (NCC). However, recent studies revealed that there are few Archean rocks exposed in the Alxa Block, and the Paleoproterozoic geology of this block is different from that of the western part of the NCC. Thus, the tectonic affinity of the Alxa Block to the NCC and/or other Precambrian blocks needs further investigations. In this study, we carry out integrated analyses of in situ zircon U-Pb age and Hf-O isotopes as well as whole-rock geochemistry and Nd isotopes for the Neoproterozoic Dabusushan and Naimumaodao granites from central Alxa Block. Secondary ion mass spectrometry SIMS) U-Pb zircon dating results indicate that the Naimumaodao and Dabusushan granite plutons were formed at ca. 930 Ma and ca. 910 Ma, respectively. These granites are peraluminous (A/CNK value >1.0), and contain peraluminous minerals such as muscovite and tourmaline, similar to those of S-type granites. They are characterized by high zircon ␦ 18 O values of ca. 8.2 to 12.1 permil, corresponding to a calculated magmatic ␦ 18 O value of ca. 10.5 to 14.3 permil, variable zircon Hf (t) values of ؊6.2 to ؉3.8 (corresponding to Hf model ages of 2.2 to 1.6 Ga) and whole-rock Nd (t) values of ؊10.1 to ؊4.5 (corresponding to Nd model ages of 2.4-1.
Precambrian Research, 2015
Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidenc... more Mid-Neoproterozoic diabase dykes from Xide in the western Yangtze Block, South China: New evidence for continental rifting related to the breakup of Rodinia supercontinent, Precambrian Research (2015), http://dx.
Lithos
In general, the mantle provides heat and/or material for the generation of the silicic igneous pr... more In general, the mantle provides heat and/or material for the generation of the silicic igneous provinces (SIPs). The rarity of mafic microgranular enclaves (MMEs), however, hampers understanding of the mantle’s role in generating SIPs and the process of crust-mantle interaction. The widespread distributed MMEs in the newly reported Alxa SIP provide an opportunity to study these processes. This study integrates in situ zircon U-Pb age and Hf–O isotope analyses, whole-rock geochemistry and Sr–Nd isotope results for the MMEs and host granitoids in the Alxa Block. SIMS zircon U-Pb dating reveals that there are two generations of MMEs and host granitoids. The MMEs in the Bayannuoergong batholith were formed at ca. 278 Ma, similar to the age (280 Ma) of host granitoids, and the MMEs and host granitoids in the Yamaitu pluton were formed at ca. 272-270 Ma. All MMEs have relatively low SiO2 (50.7–61.4 wt.%) and Th (0.8–2.8), but relatively high MgO (2.6–4.9 wt.%), Cr (23–146 ppm) and Ni (6–3...
The debate on the Mesozoic tectonics of the South China Block (SCB), featuring a broad orogenic b... more The debate on the Mesozoic tectonics of the South China Block (SCB), featuring a broad orogenic belt and a large continental magmatic province, has been rejuvenated in the past years. There are a number of competing tectonic models, each predicting different time, space, and compositional evolutional trends for the Mesozoic igneous rocks, including sporadic basalts. In this paper, we report high precision 40 Ar/ 39 Ar ages and geochemical and Sr-Nd isotopic data for basaltic rocks in central-eastern SCB. These results, together with a data compilation, indicate three evolutionary stages for the basalts. Stage 1 (195-160 Ma) basalts occur only in inland SCB. They exhibit low initial 87 Sr/ 86 Sr ratios (0.7038 to 0.7078), high ε Nd (t) values (− 1.5 to 6.0) and ocean island basalt (OIB)-like geochemical characteristics such as low La/Nb ratios (0.6 to 1.4), implying negligible to minor lithosphere contamination. Stage 2 (160-110 Ma) basalts, mostly from the same inland region with minor occurrence closer to the coast, are characterized by variable initial 87 Sr/ 86 Sr ratios (0.7053 to 0.7102), εNd(t) values (− 6.0 to 5.0) and low La/Nb ratios (0.9 to 1.8), indicating an enhanced asthenosphere-lithosphere interaction. Stage 3 (110 to ≤ 80 Ma) basalts can be further divided into two subgroups based on their geographic and geochemical variations. Basalts in the coastal regions are characterized by low εNd(t) values (− 8.1 to 3.7) and variably high La/Nb ratios (up to 4.8) indicating a strong arc signature. On the other hand, basalts in the inland regions have high ε Nd (t) values (− 1.9 to 6.8) and low La/Nb ratios (0.6 to 1.2) that are similar to the stage 1 basalts. We interpret these features as results of geodynamics processes related to the break-up, foundering and retreating of an early Mesozoic flat-subducted oceanic slab.
The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Crat... more The Khondalite Belt, one of the three major Paleoproterozoic mobile belts in the North China Craton, consists mainly of khondalite suite and S-type granites. It is thought to be a continental collision belt along which the Yinshan and Ordos Blocks amalgamated to form the Western Block of the North China Craton at ca. 1.95 Ga. While many resent studies revealed that the khondalite protoliths were sourced from juvenile crustal materials and the time interval between their deposition and subsequent metamorphism is less than 50 million years, the nature and depositional setting of the khondalite protoliths are still controversial. We carried out in this study an integrated analysis of U-Pb age and Hf-O isotopes for detrital zircons from the Helanshan Complex in the westernmost part of the Khondalite Belt. Precise SIMS U-Pb zircon results suggest that the timing of the deposition of the Helanshan khondalite protoliths can be constrained between ca. 2.00 and ca. 1.95 Ga by the minimum age of the detrital zircons from the khondalites and the maximum crystallization age of ca. 1.95 Ga for the intruded granites. The ca. 1.95 Ga granites, the oldest granites identified within the Khondalite Belt, were coeval with the regional highgrade metamorphism. The Helanshan khondalite protoliths were sourced mainly from a provenance with prolonged, episodic magmatism of ca. 2.18 Ga, 2.14 Ga, 2.09 Ga, 2.06 Ga, 2.03 Ga and 2.00 Ga, respectively. Detrital zircons of ca. 2.18-2.00 Ga from the khondalites have ε Hf (t) values ranging from +8.9 to −2.9 and Hf T DM C model ages between 2.8 and 2.1 Ga, with two major peaks at 2.6 Ga and 2.3 Ga. Their ı 18 O values show two major peaks at 6.6‰ and 8.2‰. Zircon Hf-O isotopic data indicate that both the juvenile and ancient crustal components were involved in their source rocks, and the Helanshan khondalite protoliths were most likely sourced from a ca. 2.18-2.00 Ga continental arc. The juvenile continental arc materials were uplifted, eroded, transported, deposited and metamorphosed within a short time interval of <50 million years. With the predominantly euhedral crystals of the detrital zircons and the immature clastic sediments for the Helanshan khondalite protoliths, we suggest that the khondalite protoliths were likely deposited in an active continental margin, rather than a passive margin as previously thought.
Marine Geology
This study reported geochemical and Sr-Nd isotopic variation of fine-grained mineral components i... more This study reported geochemical and Sr-Nd isotopic variation of fine-grained mineral components in a deep-sea piston core G6-4, south of the Sumba Island, Eastern Indian Ocean. The new data enables us to characterise dust contributions from Australian continent and volcanic eruption history in the adjacent volcanic arc over approximately the last 300,000 years. The geochemical and isotopic features of the fine-grained components (﹤20 μm) in Core G6-4 are broadly consistent with mixing between aeolian dusts from the Australian continent and volcanic ashes of the Sunda arcs. Simple two-component modeling shows that the majority of the core samples probably are composed of 50-80% aeolian dusts derived from the Australian continent. Sr-Nd isotopic ratios are fairly uniform for samples older than 180 ka, in contrast with those of the samples younger than 180 ka, which are much more variable with three anomalies characterized by higher 143Nd/144Nd and lower 87Sr/86Sr values recognized. We...
Nature communications, 2015
It has previously been postulated that the Earth's hydrous mantle transition zone may play a ... more It has previously been postulated that the Earth's hydrous mantle transition zone may play a key role in intraplate magmatism, but no confirmatory evidence has been reported. Here we demonstrate that hydrothermally altered subducted oceanic crust was involved in generating the late Cenozoic Chifeng continental flood basalts of East Asia. This study combines oxygen isotopes with conventional geochemistry to provide evidence for an origin in the hydrous mantle transition zone. These observations lead us to propose an alternative thermochemical model, whereby slab-triggered wet upwelling produces large volumes of melt that may rise from the hydrous mantle transition zone. This model explains the lack of pre-magmatic lithospheric extension or a hotspot track and also the arc-like signatures observed in some large-scale intracontinental magmas. Deep-Earth water cycling, linked to cold subduction, slab stagnation, wet mantle upwelling and assembly/breakup of supercontinents, can poten...