Neoproterozoic Magmatism Research Articles

Early Neoproterozoic magmatism in the Central Qilian block, NW China: Geochronological and petrogenetic constraints for Rodinia assembly

Abstract The supercontinent Rodinia existed as a coherent large landmass from 900 to 750 Ma and is now dispersed over all current major continents. Controversy has long surrounded the reconstructions of the East Asian blocks in Rodinia, especially the South China craton and nearby microcontinents. The Central Qilian block is a Precambrian microcontinent in the early Paleozoic Qilian orogenic belt, which is located in the northeastern part of the Qinghai-Xizang (Tibet) Plateau and marks the junction of the North China, South China and Tarim cratons. The formation and tectonic affinity of the Precambrian basement in the Central Qilian block is unclear, which affects our understanding of the assembly of Rodinia. The Huangyuan Group and the Maxianshan Group crop out in the eastern part of the block and represent the lower part of the basement. In this paper, we present a systematic study of the petrology, whole-rock geochemistry, and geochronology of amphibolites and orthogneisses from the Huangyuan and Maxianshan Groups. The protolith of the amphibolites was tholeiitic and calc-alkaline gabbro or gabbroic diorite formed in a continental arc environment, with laser ablation–inductively coupled plasma mass spectrometry (LA-ICPMS) zircon U-Pb ages of 967–957 Ma, a wide range of εHf(t) values of –3.74 to +5.06 and TDM1 model ages peaking at 1470 Ma and 1607 Ma. Minor inherited zircon grains with older ages of 1207–1515 Ma were collected from the amphibolites. The primitive magma was derived from partial melting of a spinel-facies fertile (lherzolite) lithospheric mantle that was modified by fluids and melts from a subducted slab. Fractionation of olivine, Fe-Ti oxides and plagioclase played a dominant role in the magma differentiation for gabbroic rocks in the Huangyuan Group, while fractionation of olivine and clinopyroxene controlled differentiation to form Maxianshan Group gabbros. The protolith of orthogneisses includes weakly peraluminous I-type and A2-type granites with consistent LA-ICPMS zircon U-Pb ages of 963–936 Ma, a wide range of εHf(t) values of –3.86 to +6.15 and TDM2 model age peaks at 2001 Ma and 1772 Ma. A few inherited zircon grains yield ages of 1033–2558 Ma. The peraluminous I-type granites resulted from a low-pressure partial melting process and the peraluminous A-type granites were derived from a charnockite source heated by large-scale magmatic underplating. Fractionation of plagioclase, biotite, and K-feldspar from the magma played the main role during the generation of the granitoids. The intrusion of these granites is related to a back-arc extension. It is inferred that the lower part of Precambrian basement of the Central Qilian block is composed mainly of early Neoproterozoic rock assemblages formed in a trench-arc-basin system during the assembly of the Rodinia supercontinent, with probable existence of late Paleoproterozoic to Mesoproterozoic continental nuclei. Combining our results with existing data, we identify a sequence of initial intra-oceanic subduction (ca. 1121–967 Ma) in front of a continental nucleus, continuous subduction of oceanic crust beneath the continental mass with formation of a mature continental arc and a back-arc basin (ca. 967–896 Ma) and continental rifting (<ca. 882 Ma) during the formation of the Central Qilian block. As a mature continental arc after ca. 967 Ma, the Central Qilian block was located at the margin of Rodinia and faced the Neoproterozoic Mirovoi Ocean. The breakup of the supercontinent left the Central Qilian block as a late Neoproterozoic isolated arc terrane.

Age of the Early Paleozoic granitoid magmatismin the central part of the Bureya continental massif, Central Asian Fold Belt

The article presents new age data on the ‘key’ Early Paleozoic igneous complexes located in the central part of the Bureya continental massif of the Central Asian Fold Belt. Porphyroblastic quartz monzonites of the Kivili complex are dated to 453±2 Ma. The age of gneissic granites of the Sularin complex is ~481 Ma. The Sm-Nd isotope stu­dies show that Late Ordovician quartz monzonites were formed mainly from crustal sources with Paleoproterozoic Nd model isotopic ages. Both ancient (Paleoproterozoic?) and younger sources were involved in the formation of Cambrian granites. Our data, as well as previously published materials, suggest several stages of the Early Paleozoic magmatism in the evolution of the Bureya continental massif: ~541, ~504–500, ~487, ~474 and ~453 Ma. Early Paleozoic magmatism developed under a similar scenario in the Jiamusi continental massif. In addition to the synchronism of Neoproterozoic magmatism within these continental massifs, this feature testifies to their common geological history.

Record of Early Tonian mafic magmatism in the central Espinhaço (Brazil): New insights for break-up of the Neoproterozoic landmass ancestor of São Francisco-Congo paleocontinent

Petrological characterization, U–Pb geochronology, Lu–Hf analyses and major and trace element data from mafic intrusions in the Central Espinhaço (central portion of the Brazilian shield) are used here to investigate the geological significance of the Early Neoproterozoic magmatism in the context of the São Francisco-Congo paleocontinent. These mafic bodies are represented by medium to coarse-grained metagabbros with plagioclase, amphibole and clinopyroxene. Zircon U–Pb isotopic data from two samples yielded weighted mean 206Pb/238U ages of 895 ​± ​3.4 ​Ma (MSWD ​= ​1.7) and 896 ​± ​2.4 ​Ma (MSWD ​= ​0.64), regarded as the best estimates for the crystallization age of these mafic rocks. Major and trace element data (including REEs) show that the gabbros originated from a subalkaline tholeiitic magma, typical of intraplate magmatism. Such rocks are slightly enriched in LREEs and LILEs and depleted in HFSEs. Our new isotope and geochemical data, along with regional knowledge, indicate that these metagabbros mark the beginning of an important Tonian-age extensional tectonic event of the landmass of which the São Francisco-Congo paleocontinent was part (Rodinia supercontinent or Central African block?). We furthermore suggest that these rocks belong to a prominent suite of Tonian-age mafic rocks that mark a diachronic breakup attempt of this landmass which may have occurred from south to north along the Espinhaço mountain range.

Geochronology and geochemistry of Neoproterozoic magmatism in the Bureya Block, Russian Far East: Petrogenesis and implications for Rodinia reconstruction

The Bureya Block, located in the easternmost segment of the Central Asian Orogenic Belt (CAOB), is one of the least understood blocks in Russian Far East. Here we describe newly discovered Neoproterozoic magmatic rocks along the Bureya River in the northern Bureya Block. LA–ICP–MS zircon U–Pb dating demonstrates that these rocks were emplaced in two stages during the early Neoproterozoic: (1) 937–933 Ma, forming an intrusive rock association of gabbros, granodiorites, and monzogranites; and (2) 896–891 Ma, representing by a suite of syenogranites. The good correlation on the Neoproterozoic to Late Triassic geological events between the Jiamusi and Bureya blocks suggests the two blocks formed a contiguous crustal unit. Field observations, together with petrographic and geochemical features, and zircon Hf isotopic data, indicate a magma mixing/mingling origin for the 937–933 Ma gneissic granitoids and amphibolites, with the felsic melts generated by partial melting of a dominantly Mesoproterozoic lower crustal source with possible little addition of ancient crustal materials, whereas the mafic melts were derived from partial melting of a depleted lithospheric mantle wedge metasomatized by fluids dehydrated from the subducted oceanic slab. In addition, the 896–891 Ma syenogranites share a common crust source with the 937–933 Ma granitoids but experienced extensive assimilation and fractional crystallization during magma ascent and evolution. In the context of assembly, growth and breakup of the Rodinia supercontinent, together with the recognition of Neoproterozoic continental arc-type magmatic rocks in the Bureya–Jiamusi Block as well as the nearly coeval subduction-related magmatism recorded elsewhere on the globe, such as Seychelles, Madagascar, India, Lhasa, South China, and Australia, we conclude that the 937–891 Ma magmatism in the Bureya Block resulted from the Andean-type orogeny that formed along the northwestern margin of the Rodinia supercontinent.

The Neoproterozoic magmatism in the northern margin of the Yangtze Block: Insights from Neoproterozoic (950–706 Ma) gabbroic-granitoid rocks of the Hannan Complex

The Hannan Complex, located in the northwestern margin of the Yangtze Block, South China, consists of numerous mafic-ultramafic and felsic plutons formed at ca. 950–700 Ma. However, their geotectonic setting and petrogenesis keep in controversy. This study presents whole-rock geochemistry, zircon U-Pb geochronology and Lu-Hf composition and whole-rock Hf isotope of gabbroic-granitoid rocks of the Hannan Complex, aiming to clarify their spatial-temporal distribution and discuss their geological significance. The Dahanshan gabbro in the Hannan region yields zircon U-Pb age of 793–779 Ma. The positive zircon εHf(t) values (+8.0–+10.4) and positive whole-rock εHf(t) values (+7.0–+12.6) suggest a relatively depleted mantle source of the gabbro. However, Hf model ages and whole-rock geochemical data suggest addition of enriched components to magma source. Thus, the magmas derived from decompression melting of MORB-like mantle and flux-induced melting of metasomatized lithospheric mantle wedge both contributed to generation of Dahanshan gabbro in a back-arc setting. The Hongmiao granite pluton, having crystallization age of 802–791 Ma, is characterized by aluminous A-type granite signatures and showing A2-type granite affinities. Taking negative εHf(t) values (–24.5 to −3.3) of zircons into account, the Hongmiao granite was generated by partial melting of pre-existing crustal materials in an extensional enviroment. The Xishenba trondhjemitic biotite granite formed at ca. 890 Ma. It belongs to metaluminous to peraluminous calc-alkaline I-type granitoid rock series with negative zircon εHf (t) values (–19.4 to −6.2), implying a magma source of pre-existing crustal materials in an arc setting. Thus, combined with previously published data, it can be concluded that the gabbroic-granitoid rocks of the Hannan Complex were generated in subduction-related arc-back-arc setting during Neoproterozoic (950–706 Ma). The Neoproterozoic (ca. 950–706 Ma) magmatism represents a significant crustal growth event in the northern margin of the Yangtze Block, simultaneously, accompanied by certain degree of crustal reworking. According to temporal-spatial distribution of different rock types, the formation of the Neoproterozoic (ca. 950–706 Ma) Hannan Complex can be subdivided into four stages: ca.950–890 Ma and ca.890–840 Ma in a continental arc setting and a continuous continental arc setting, respectively; whereas, ca.840–765 Ma and ca.765–706 Ma in a back-arc setting and a compression-extension tectonic setting, respectively.

Slab breakoff beneath the northern Yangtze Block: Implications from the Neoproterozoic Dahongshan mafic intrusions

The Neoproterozoic magmatism in South China may have been related to assembly and breakup of the supercontinent Rodinia. The ca. 815-Ma mafic intrusions in the Dahongshan region at the northern Yangtze Block are composed of fine- to medium-grained gabbro and diabase, which show variable major and trace element compositions with (La/Yb)N ratios of 0.53–3.43. The mafic rocks also have large ranges of initial 87Sr/86Sr ratios (0.70318–0.70810), ƐNd values (−2.8 to +4.3) and Pb isotopes (206Pb/204Pb = 17.57–18.46, 207Pb/204Pb = 15.43–15.56, 208Pb/204Pb = 37.45–38.12). These lines of evidence suggest that the Dahongshan mafic rocks underwent significant crustal contamination during the magma emplacement. AFC calculations reveal that 10–20% crustal materials were involved in their petrogenesis. Two primary samples from the Dahongshan intrusions display low U/Th (0.36–0.37), Th/Zr (0.001–0.002), and Nb/Y (0.02–0.03) ratios, and show DMM-like ƐNd and Pb isotopes, indicating that their primary melts were derived from an asthenosphere mantle which had not been modified by slab-derived materials. In the northern margin of the Yangtze Block, the Neoproterozoic magmatism changed from arc-affinity to MORB- and OIB-like characters at around 815 Ma. Such transition is proposed to have resulted from slab tearing and detachment that induced upwelling of the asthenosphere mantle.

Neoproterozoic Magmatism in the Southern Arabian-Nubian Shield: Implications for Petrogenesis and Tectonic Setting

The metavolcano-sedimentary assemblages and the associated granitoid intrusions in Central Eritrea, part of the southern Arabian-Nubian Shield, were primarily formed by accretion of juvenile island arcs during the Neoproterozoic. The metavolcanic rocks comprise mafic to felsic rocks, which show tholeiitic affinities. They exhibit variable SiO2 (41.63–78.4 wt%), Al2O3 (8.51–23.41 wt%), MgO (0.05–13.98 wt%), Fe2O3 (3.11–15 wt%), Cr (2.83–834 ppm), Ni (1.63–244 ppm), and Zr (16.4–128 ppm) that form linear correlations. They have low ΣREE (20–144 ppm) and display flat chondrite-normalized REE patterns with negative and positive Eu anomalies (Eu/Eu* = 0.67–1.36). They are generally rich in LILE (Ba, Pb, and U) and depleted in HFSE (Ta, Nb, and Ti), and have low initial 87Sr/86Sr (0.70079–0.70525), positive eNd values (+ 4.0 to + 6.4) and moderate Pb isotope compositions (206Pb/204Pb = 17.598–19.446, 207Pb/204Pb = 15.518–15.639, and 208Pb/204Pb = 37.175–38.811). These lines of chemical evidence indicate that slab-derived fluids and melts significantly modified the mantle source. In contrast, the ca. 850 Ma Emba-Derho granites display restricted compositions which show high SiO2 (71.28–73.64 wt%), Al2O3 (14.93–15.89 wt%), Na2O (3.16–4.15 wt%), and low K2O (1.25–2.04 wt%). These samples exhibit highly fractionated REE patterns (e.g., La/Yb = 14–30), high Sr/Y (42–86), and low Y (3.75–6.03 ppm), as well as high eNd (+ 4.7 to + 7.8), suggesting that they were partial melts of the subducting oceanic crust. Both the metavolcanic rocks and the granitic intrusions are suggested to have been formed in a forearc setting.

Reviews of the Mesoproterozoic to Neoproterozoic sedimentary sequences and new constraints on the tectono-sedimentary evolution of the southern margin of the North China Craton

The North China Craton (NCC) is thought to experience multi-stage extensional events after the breakup of the Columbia (Nuna) Supercontinent, and even during the assembly of the Rodinia Supercontinent. In recent years, volcanic and detrital zircon U-Pb dating ages provided new insights into the Mesoproterozoic to Neoproterozoic tectonic framework in the NCC. As the Mesoproterozoic Xiong’er Group in the southern NCC is regarded as the oldest volcanic-sedimentary succession after the final amalgamation of the NCC, we reviewed the sedimentary environments and provenances of Mesoproterozoic to Neoproterozoic sedimentary sequences above the strata in order to understand tectono-sedimentary evolution of the southern NCC during this period. The early Mesoproterozoic sedimentary rocks were deposited in alluvial-fan to fluvial and (fan-) delta-coastal environments suggesting an initial stage of basin development. Fine-grained clastic sedimentary rocks interlayered with carbonate deposition formed on the southern NCC later, and implied a broad subsidence before ca. 1611 Ma. After that, depositional breaks caused by regional tectonic uplifts led to different sedimentary sequences and lateral migration of the depocenter from the north to the south (to the current co-ordinates). The unconformably overlying sedimentary rocks in the north of the southern NCC were deposited in restricted marine basins during late Mesoproterozoic to Neoproterozoic as a whole. However, the enlargement of shallow-marine shelf led to the thick accumulation of carbonates in the southernmost NCC characterized by a deepening-upward trend from the late Mesoproterozoic sequence. The Neoproterozoic sedimentary sequence is typified by sharp increasing terrigenous supplies and frequent changes in environment, and could be deposited in a tectonically active basin in consideration of its close association with volcanism. Detrital zircon grains from the oldest clastic sequence (i.e., the Bingmagou Formation) overlying the Xiong’er volcanic-sedimentary rocks and from the earliest Paleozoic sedimentary rocks (i.e., the Xinji Formation) are used to track changes of provenances. Detrital zircon grains from the Bingmagou Formation display two dominant age peaks at ca. 1850 and 2500 Ma and three secondary peaks at ca. 2100, 2350 and 2700 Ma. In contrast, detrital zircon grains from the Xinji Formation have three major age peaks at ca. 1850, 2200 and 2500 Ma and three subordinate populations of 950, 1100 and 1450 Ma. In combination with the uplifts during the Mesoproterozoic to Neoproterozoic, Neoproterozoic magmatism, and a large amount of detrital zircon derived from Rodinia-related orogenesis in the southern NCC, it is very likely that the major changes of basin configuration could be related to significant tectonic readjustment along with the evolution of the Rodinia Supercontinent.

Ca. 1.04 Ga hot Grenville granites in the western Yangtze Block, southwest China

The late Mesoproterozoic to early Neoproterozoic magmatism in the western Yangtze Block, though minor in volume, has offered a rare opportunity for understanding the role of the Yangtze Block in the Grenville orogeny. The Huidong K-feldspar granites have SIMS zircon U-Pb ages of 1048.5 ± 4.9 Ma and 1043.1 ± 5.1 Ma, whereas the Yuanmou biotite granites were dated at 1041 ± 12 Ma by LA-ICP-MS. Their ages are indistinguishable within error, suggesting that they were emplaced contemporaneously. Both Huidong and Yuanmou rocks show geochemical features typical of A-type granites, including high FeO*/MgO, Ga/Al ratios and elevated contents of high-field-strength elements (HFSE). The Huidong granites exhibit positive whole-rock εNd(t) (+0.58 to +4.4) and zircon εHf(t) (+6.0 to +8.3) values close to those of regional coeval mafic rocks. They have a narrow range of zircon δ18O from 6.2‰ to 7.2‰, which is only slightly higher than the ‘mantle zircon’ value of 5.3 ± 0.6‰. High Nb/La and Nb/Th ratios in these rocks overlap with those of regional coeval mantle-derived rocks. Along with high zircon saturation temperatures of >1000 °C, we suggest that the Huidong granites could have formed mainly by extreme fractionation from basaltic parental magmas, or alternatively by partial melting of newly emplaced tholeiite at high temperatures. By contrast, the Yuanmou granites have lower whole-rock εNd(t) (−2.0 to +0.59) and zircon εHf(t) (−1.5 to +5.1) values and a Hf isotope crustal model age of ∼1.56–1.97 Ga, suggesting that its parental magmas may be generated by partial melting of old crust during intrusion of mantle-derived magmas. Ca. 1.04 Ga granites in the region show geochemical features similar to A-type granites in orogenic belts, e.g., the aluminous A-type granites in the Lachlan Fold Belt, Southeast Australia. They are also characterized by high-extremely high (>1000 °C) temperature in their genesis, similar to coeval hot Grenville granites globally. Temporal correlation of metamorphic and magmatic records between South China and the Grenville Province leads us to conclude that the ∼1.04 Ga A-type granites in the western Yangtze Block form parts of the hot Grenville granites emplaced during post-orogenic crustal extension.

Early Neoproterozoic magmatism and the associated metamorphism in the Songnen Massif, NE China: Petrogenesis and tectonic implications

Zircon U–Pb dating and geochemistry data were collected for Neoproterozoic rocks in the Songnen Massif of NE China, with the aim of understanding the extent and nature of the Precambrian basement as well as the early stages of tectonic evolution history of the massif. The newly discovered Neoproterozoic magmatism can be subdivided into three stages: (1) 929–927 Ma quartz-syenitic and syenogranitic gneisses, (2) ∼895 Ma granitic gneisses, and (3) 871 Ma granitic pegmatites. Associated metamorphisms can also be subdivided into two stages, i.e., the 492 Ma and 546–530 Ma, suggesting that the study area underwent two stages of metamorphism during the late Pan-African. The petrographical and geochemical data indicate that the 929–927 Ma syenitic rocks most likely originated from enriched mantle sources, which were metasomatized by subducted sediments and underwent fractional crystallization during ascension, whereas the ca. 895 Ma granitic gneisses were generated by the partial melting of ancient mafic lower crustal material. Combined with our previous study, it is suggested that the ∼929–927 and 895 Ma magmatism were formed in a convergent margin related to compressive orogenesis, consistent with the evolution of the Rodinia supercontinent. Similar tectono-magmatic thermal events occurred within the Songnen and Jiamusi massifs, suggesting that they could be one coherent continental unit in Precambrian.

Coupled evolution of Neoproterozoic arc mafic magmatism and mantle wedge in the western margin of the South China Craton

Subduction of oceanic slabs can physically and chemically modify mantle wedges, but how mantle wedges are temporally evolved is difficult to be constrained. In this study, we use in situ zircon U–Pb ages and Hf–O isotopes of mafic intrusions to examine a coupled evolution of magmas and mantle sources above a subduction zone. Neoproterozoic mafic intrusions in the western margin of the Yangtze Block are mostly composed of gabbros that were formed in an arc system during 870–750 Ma followed by generation of voluminous slab-derived granitoids. The mantle wedge was progressively modified by slab fluids, sediment melts and altered oceanic crust (AOC) melts. Gabbros from the 870-Ma intrusion have normal δ18O (4.79‰ to 6.07‰), high eHf (+ 10.4 to + 15.0) and eNd (+ 4.0 and + 6.4) and were derived from a mantle source enriched by slab fluids. Gabbros from the 860–840-Ma intrusions have overall relatively high δ18O (5.61‰ to 7.42‰), but variable eHf values (− 3.5 to + 15.0) that are decoupled from eNd (+ 1.85 to + 3.87). These features are clearly suggestive of a mantle source modified by sediment melts. However, gabbros from the 820–780-Ma intrusions have relatively low δ18O (4.22‰ to 5.49‰), and constant eHf (+ 4.7 to + 9.6) that are decoupled from eNd (− 0.52 to + 1.92). Such features can be explained by a mantle source contaminated by 18O-depleted AOC melts. The widespread younger TTG-type granitoids were partial melts of the subducted oceanic slab and terminated the mafic magmatism in the region, indicating that slab break-off probably resulted in slab melting after a long period of subduction. Similar Neoproterozoic magmatism also occurred in Greater India and Madagascar, suggesting a giant Andean-type arc system along the western margin of Rodinia. In this arc system, mantle-derived magmas were dominated by an arc affinity in the earlier stage before 820 Ma and became rift-related after that, reflecting regional slab tearing and break-off. Our study also provides evidence for the linkage between the marginal subduction and the internal rifting in Rodinia, and suggest that slab break-off probably triggered its break-up.

Neoproterozoic magmatism in the northern margin of the Yangtze Block, China: Implications for slab rollback in a subduction-related setting

The South Qinling Belt was located in the northern part of the Yangtze Block during the Neoproterozoic. Here we investigate two major magmatic intrusions in the northern and southern part of the belt, the Douling plutons (DLP) and the Fenghuangshan plutons (FHSP), to gain insights into the Neoproterozoic tectonic processes along the northern segment of the Yangtze Block. Zircon grains in the DLP yield weighted mean 206Pb/238U ages of 750–709 Ma, whereas those from the FHSP show ages of 749–728 Ma. The new results, together with the published data, reveal that these plutons were emplaced at ca. 759–685 Ma and ca. 802–704 Ma, respectively. Geochemically, the intermediate-felsic rocks from the DLP and FHSP show enrichment of light rare earth elements (LREE) and large-ion lithophile elements (LILE) (Rb, Ba and K), depletion of high field strength elements (HFSE) (Nb, Ta, P and Ti), and low Sr/Y and (La/Yb)N values, which are typical features of arc magmatic rocks. The gabbros from the FHSP have high Mg#, and display LREE and LILE (Rb, Ba, K, and Sr) enrichment and depletion of HFSE (Th, U, Nb, Ta, and Ti), suggesting that they were probably formed in a mantle wedge setting. Both DLP and FHSP show arc-related geochemistry modified by slab-derived fluids, and were formed at relatively high-temperature and low-pressure conditions. However, they display distinct Sr-Nd-Hf isotopic compositions. Zircon grains of two samples from the DLP respectively show mean εHf(t) values of −2.6 ± 0.3 and 0.9 ± 0.3, whereas zircon grains of four samples from the FHSP show mean εHf(t) values ranging from 7.5 ± 0.5 to 8.7 ± 0.4. The DLP shows dominantly negative εNd(t) values and inconsistent initial 87Sr/86Sr ratios, whereas FHSP shows relatively constant and positive εNd(t) values (3.69–3.74) but variable initial 87Sr/86Sr ratios. The Sr-Nd-Hf isotopic and geochemical features suggest that the enriched mantle and crustal materials were involved in the magma evolution of the DLP, whereas the FHSP is characterized by significant juvenile components with a rising asthenospheric mantle source playing a key role. We propose a subduction-related setting for these intrusions, and envisage slab rollback during the Neoproterozoic.

From the Libyan border to the Nile – Neoproterozoic magmatism and basement evolution of southern Egypt

ABSTRACTIn southern Egypt, Neoproterozoic granitoids intrude the crust from Libya in the west to the Nile River in the east. Best exposed at Gebel Uweinat, Gebel Kamil, Bir Safsaf, Gebel El Asr and Gebel Umm Shaghir, these rocks represent the transition between the rejuvenated Archean to Paleoproterozoic crust of the east Saharan craton and the juvenile Neoproterozoic crust of the Arabian–Nubian Shield to the east. We present U-Pb zircon geochronology and whole rock geochemistry from 16 Neoproterozoic (c. 628–580 Ma) granitoids across southern Egypt which document the synchronous production of diverse compositions indicative of an intraplate or intracontinental tectonic setting. Our data better constrain the age relationships, petrogenesis, and Pan-African crustal growth associated with the amalgamation of Gondwana and contribute to understanding the crust-modifying processes that led to the development of the Saharan metacraton in the Ediacaran.

Geochronology, geochemistry and petrogenesis of the Laozhaishan dolerite sills in the southeastern margin of the North China Craton and their geological implication

The configuration of the North China craton (NCC) in the Rodinia supercontinent still remains controversial due to few reliable Neoproterozoic magmatism records. Here we report early Neoproterozoic dolerite sill swarms in the Laozhaishan region in the southeastern margin of the NCC. These sills intrude the Neoproterozoic sedimentary rocks (Wangshan, Gouhou and Shijia Formations), and are up to several hundred meters in thickness and >30 km in length. Baddeleyites separated from several representative dolerite samples show SIMS 207Pb-206Pb ages varying from 912 ± 4 Ma to 916 ± 4 Ma, which are consistent with concordant zircons U-Pb age of 913 ± 10 Ma. Geochemically, the Neoproterozoic dolerite samples have relatively low rare earth elements (REEs) contents and show weak positive Eu anomalies. Moreover, these dolerite rocks are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs; e.g., Rb and Ba) and some high field strength elements (HFSEs; e.g., Nb, U, Nd, Ti, Gd) and depleted in heavy rare earth elements (HREEs) and several HFSEs (e.g., Zr, Th), with geochemical affinities to within-plate tholeiitic basalts. The REE patterns, whole-rock εNd(t) (t = 913 Ma) values varying from −0.60 to +3.12, and in-situ εHf (t) (t = 913 Ma) values between +4.50 to +12.85 suggest that these dolerites were generated by mantle plumes, in which some enriched components were involved. In the context of assembly, growth and breakup of the Rodinia supercontinent, together with the recognition of ~913 Ma dolerite swarms in the NCC as well as nearly coeval rift-related magmatism recorded elsewhere on the globe such as the Congo craton and the São Francisco craton, we conclude that the NCC has involved in the evolution of Rodinia and the widespread dolerite swarms indicate the breakup of Rodinia.

Tracking the timing and nature of protolith, metamorphism, and partial melting of tourmaline‐bearing migmatites by zircon U–Pb and Hf isotopic compositions in the Yuka terrane, North Qaidam UHP metamorphic belt

An integrated study using cathodoluminescence (CL) images, U–Pb geochronology, and Hf isotopic characterization of zircons was performed on migmatites from the Yuka terrane to provide insights into the timing and nature of the protoliths, metamorphism, and partial melting of these rocks. Zircon grains separated from the migmatites have three distinct domains. Residual zircon cores in samples YKT01 and YKT02 exhibit oscillatory zoning, high Th/U ratios (0.10–0.79), steep heavy rare earth element (HREE) patterns, and mean ages of 936 ± 5 Ma and 927 ± 11 Ma, respectively, indicating that they are igneous in origin and record Neoproterozoic magmatism during the Grenvillian Orogeny. CL‐grey cores record an ultrahigh‐pressure (UHP) peak metamorphism age of 435 ± 5 Ma and have low Th/U and 176Lu/177Hf ratios, weak negative Eu anomalies, and relatively flat HREE patterns. The CL‐bright rims have steep HREE patterns with lower middle rare earth element (MREE) concentrations but higher HREE concentrations compared with the metamorphic cores and a weighted average age of 422 ± 4 Ma, which records the timing of melt crystallization. The migmatites incorporate garnet relicts coexisting with fluid inclusions and hydrous minerals like peritectic phengite and peritectic large anhedral poikilitic tourmaline in the leucosomes. Peak temperatures are less than 750°C, suggesting that the anatectic melts may be derived from melting of felsic gneiss in the presence of water. The timing of melt crystallization is ca. 13 Ma later than UHP metamorphism, indicating that the partial melting took place during the exhumation stage. The metamorphic zircon cores have higher 176Hf/177Hf(t) ratios than the residual magmatic cores, which provides powerful evidence for the generation of the metamorphic zircons through the incorporation of internal high Hf minerals other than zircon in a closed system. Anatectic rims with lower 176Hf/177Hf(t) ratios but higher 176Lu/177Hf ratios than metamorphic cores suggest that the main formation mechanism is dissolution‐reprecipitation of pre‐existing zircons. In conclusion, the elevated 176Hf/177Hf(t), TDM2 age and decreasing 176Lu/177Hf(t) ratios in the metamorphic and anatectic domains imply that the new zircons in some migmatites and granites may not reflect the Hf isotope compositions of their source rocks, accounting for the variable Hf isotope compositions in S‐type granites.

Neoproterozoic continental arc system along the NW margin of Rodinia supercontinent: Constraints from geochronological and geochemical studies of Neoproterozoic granitoids in the Diancangshan Massif

The Neoproterozoic period is a key geological time in earth history that witnessed the breakup of the Rodinia supercontinent. The Diancangshan and Ailaoshan Massifs are two major segments along the Ailaoshan tectonic zone, and the Neoproterozoic metamorphic igneous rocks in these massifs preserve key clues to elucidate the on-going dispute over the geodynamic drives for the break-up of Rodinia. Many studies have been performed on the Neoproterozoic igneous rocks along the Ailaoshan Massif, but the contemporaneous igneous rocks in the Diancangshan Massif have been poorly studied. In this study, zircon U-Pb-Hf isotopic, whole-rock elemental and SrNd isotopic data are presented for a granitoid suite from the Diancangshan Massif. Zircon UPb dating shows that all the monzodioritic and granitic samples from the inner part of the southern Diancangshan Massif yielded Neoproterozoic crystallization ages of 701–797 Ma without exception. One sample collected from the southern edge of the Diancangshan Massif gave intrusive ages of ~239 Ma. Therefore, the Neoproterozoic magmatic activities in the Diancangshan Massif have been underestimated, and the spatial distribution of the Neoproterozoic intrusions occupies at least 1/3 of the whole area of the Diancagnshan Massif. The monzodioritic samples originated from the mixing of magmas generated from a subduction-modified mantle wedge and mafic lower crust. The granitic samples can be subdivided into two groups. The Group 1 I-type granitic samples have moderate A/CNK values of 0.80–1.07, which were derived from the partial melting of mafic lower crust. The Group 2 strongly peraluminous granitic samples (A/CNK > 1.1) originated from a hybridized source of the graywacke and mafic-derived components. Geochronological, petrological and geochemical studies show that Neoproterozoic magmatism in the ATZ was generated in a prolonged (>80 Ma) continental arc system. An Andean-type orogeny formed along the NW margin of Rodinia (i.e., the Seychelles, Himalaya, Amdo and South China including the Ailaoshan tectonic zone) and induced the regional internal lithospheric extension.

Zircon U–Pb geochronology and Hf isotope of granitoids in East Kunlun: Implications for the Neoproterozoic magmatism of Qaidam Block, Northern Tibetan Plateau

The Neoproterozoic granitoids in East Kunlun Orogen (EKO) record critical information on the composition and evolution of the early crustal materials, as well as the Precambrian tectonic evolutionary history of the Qaidam Block, northern Tibetan Plateau. Zircon U–Pb geochronology and Hf isotopic compositions of three newly discriminated gneissic granitoids in the Hongshuihe, Dangennaomuru and south Bokalike areas are employed in this study to elucidate the Neoproterozoic tectonics of EKO. Petrological studies reveal that these granitoids are S–type granite with abundant Al–rich minerals like muscovite and garnet in their mineral assemblages. Zircon U–Pb geochronological results show that the Hongshuihe and Dangennaomuru plutons yield weighted mean 206Pb/238U ages of 914 ± 5 Ma (MSWD = 0.25) and 935 ± 6 Ma (MSWD = 0.56), respectively, indicating their magmatic crystallization ages. And the south Bokalike pluton yields upper and lower intercept ages of 1002 ± 31 Ma and 388 ± 39 Ma (MSWD = 0.63), disclosing its magmatic crystallization age and the time of subsequent Paleozoic metamorphic event, respectively. The εHf(t) values of zircons in this study are dominated by negative with minor positive values ranging from −7.18 to +2.76. The two–stage Hf model ages of the zircons having negative εHf(t) values are ca. 1.7–2.0 Ga, whereas those with positive εHf(t) values are ca. 1.5 Ga. Both the εHf(t) values and the two–stage Hf model ages indicate that these granitoids were probably derived from the reworking of ancient continental crustal materials with minor mantle contribution. Combined with available data of the granitoids in EKO, central and north Qaidam Block, we propose that the Neoproterozoic granitoids in Qaidam Block have similar crystallization ages of ca. 0.9–1.0 Ga, as well as same or similar geochemical and zircon Hf isotopic compositions revealing the Qaidam Block was involved into the amalgamation of the supercontinent Rodinia.

Neoproterozoic and Early Paleozoic magmatic records from the Chalukou ore district, northern Great Xing’an Range, NE China: Implications for tectonic evolution and Mesozoic Mo mineralization

To constrain the pre-mineralization tectonic evolutionary history and the nature of the magma source of the Chalukou Mo deposit, which is located on the western margin of the Xing’an block, we recognized and studied a period of Neoproterozoic magmatism and a suite of Early Paleozoic volcanic rocks in this ore district. The magmatic zircons of quartz chlorite schist collected from the Wolegen Group yielded a concordant 206Pb/238U age of 685.1 ± 4.5 Ma (MSWD = 0.21), and they show very high εHf(t) values (+15.5 to +17.3) and young Hf modal ages (573–664 Ma) close to the formation age, indicating that the protolith was generated during the Neoproterozoic, and was most likely derived from a depleted mantle region. This Neoproterozoic magmatism might represent an important crustal growth event within the Xing’an Block. The host wallrocks in the Chalukou deposit mainly consist of rhyolite, dacite, andesite and volcanic tuff which have undergone slight deformation and metamorphism. The results of zircon LA-ICP-MS U-Pb dating indicated that they were generated during 472–475 Ma. The results of whole-rock geochemical analysis indicate that they have arc-affinity features characterized by LREE enrichment with moderate to strong fractionation between LREE and HREE (LaN/YbN = 7.7–13.6), intense negative Eu anomalies (δEu = 0.36–0.71), pronounced positive Ba, Th, U, Pb and La anomalies and negative Nb-Ta, P and Ti anomalies. Hf isotopes show various εHf (t) values ranging from −2.0 to +5.9 and slightly old two-stage model ages ranging from 1070 Ma to 1573 Ma. Combined with discrimination diagrams, these data indicate that they were derived from the partial melting of a slightly older lower crust with the addition of a juvenile crust component in an active continental margin setting related to the subduction of the Paleo-Asian Ocean between the Xing’an and Songliao blocks. The existence of Neoproterozoic magmatic activity and Mesoproterozoic lower crustal materials obtained from the Hf model ages of the Paleozoic volcanic rocks in the Chalukou ore district demonstrated that Precambrian basement exists in the Xing’an Block, but its distribution area may be limited. As the largest porphyry Mo deposit in China, the ore-forming materials might have multiple sources, considering the long-term and multiple magmatic events that occurred under different tectonic settings in the ore district. The previous modification and refertilization of the lower crust and/or lithospheric mantle by the subduction of the Paleo-Asian Ocean might be important in the generation of the fertile lower crust, which is the direct source of the ore-related porphyries.

Crustal evolution in the South Tianshan Terrane: Constraints from detrital zircon geochronology and implications for continental growth in the Central Asian Orogenic Belt

The South Tianshan Terrane (STT) is located in the boundary between the south‐western Central Asian Orogenic Belt (CAOB) and the Tarim Craton and is a key area for understanding the geologic and tectonic history of the craton and the orogenic belt. In this paper, we report detrital zircon ages from the Late Palaeozoic and Mesozoic clastic sedimentary rocks from the southern part of STT. In combination with the U–Pb ages for felsic igneous and meta‐igneous rocks exposed in the STT and adjacent tectonic units, we identify several distinct age populations. Provenance analysis suggests that the detrital zircon grains were predominately derived from the felsic magmatic rocks in the Tarim Craton and South Tianshan Terrane. The pre‐Neoproterozoic age populations may be associated with the early history of the Tarim Craton. Several pulses of Neoproterozoic magmatism are revealed by our dataset, presumably related to the assembly and break‐up of the supercontinent Rodinia. The 995 to 901 Ma detrital zircon grains were likely sourced from magmatic rocks associated with the assembly of Neoproterozoic Tarim to Australia. Among the age population of 886 to 752 Ma, the older group might be related to the subduction‐related magmatism after the assembly of Rodinia, and the younger one records a protracted magmatic event in a continental rift‐related setting associated with the break‐up of Rodinia. Two younger Neoproterozoic age populations (736 to 694 Ma and 665 to 610 Ma), showing narrow spreads with weak peaks, represent the waning stages of igneous activities related to the break‐up of Rodinia. Regarding the Palaeozoic evolution, together with other evidence, our data indicate a two‐stage subduction model for the SW Palaeo‐Asian Ocean. The 490 to 384 Ma age population corroborates the existence of Early Palaeozoic continental arc magmatism at the northern margin of Palaeozoic Tarim generated by the bidirectional subduction of the South Tianshan Ocean. After a ~30 My period of tectonomagmatic quiescence, the second stage is marked by the northward subduction of the South Tianshan Terrane during Late Devonian to Early Carboniferous. The final collision of Tarim and the south‐western CAOB likely occurred during the Late Carboniferous, followed by syn‐ and post‐collisional magmatism, as represented by the 320 to 265 Ma age population. Based on the detrital zircon ages in conjunction with the Hf isotopic features of zircons from Palaeozoic igneous rocks, our study does not support the model of large‐scale Phanerozoic net continental growth in the South Tianshan Terrane.

Detrital apatite U-Pb and trace element analysis as a provenance tool: Insights from the Yenisey Ridge (Siberia)

The use of zircon U-Pb geochronology to study the provenance of sediment is well-established, yet there are fundamental biases that are hard to avoid. These biases are due, in part, to the limited range of magmatic compositions from which zircon will crystallise. This can manifest as the over/under representation of particular age populations (i.e. sediment sources) in the data. The analysis of apatite, a mineral found in a wide variety of igneous rocks, can help to address this bias in detrital geochronology. In this study, we combine geochemical and U-Pb LA-ICP-MS analysis of individual apatite grains to characterise the potential source rocks. This information is integrated with zircon U-Pb data from the same samples in order to demonstrate the complementary provenance information that can be derived from apatite and zircon archives. The analysis of detrital apatite from sedimentary rocks in the Yenisey Ridge (Siberia) found two main U-Pb age populations. An apatite U-Pb population at 880–720 Ma corresponds to Neoproterozoic magmatism in the Yenisey Ridge, and a second at ~1800 Ma to magmatism related to the assembly of the Siberian Craton. Abundant Neoproterozoic apatites, many of which have chemistries indicative of crystallising from a mafic magma, are considerably more common than the relatively rare zircons of the same age. The ability of apatite analysis to detect mafic magmatic sources is one of the strengths of this approach that makes it particularly useful when used in combination with zircon U-Pb geochronology. This study shows that multi-method analysis of detrital apatite has the potential to be an important tool in conjunction with detrital zircon analysis in future efforts to understand the provenance of sedimentary rocks.