Neoproterozoic Magmatic Events Research Articles

Petrogenesis and tectonic setting of mafic magmatism within the Laguna Amarga Metamorphic Complex, Andes of Catamarca, Argentina: Insights into the opening of the Cuyania/Precordillera terrane from the Ouachita rift

Neoproterozoic crystalline basement rocks are exposed as fault-bounded blocks over the high Andes of Catamarca. The crystalline basement is stratigraphically grouped into the unique Laguna Amarga Metamorphic Complex and represents the northern extension of the Cuyania/Precordillera terrane. Tabular bodies of meta-mafic rocks are widespread in the basement interspersed within a thick sequence of meta-sedimentary rocks derived from siliciclastic, calc-silicate, and limestone protoliths. Overall, the geochemical characteristics of meta-mafic rocks are in the compositional range of Normal-Mid Ocean Ridge Basalt (Normal-MORB), reflecting a common depleted-mantle source with varying degrees of partial melting. While preserving the typical bulk chemistry of MORB magmatism, some mafic magma underwent differentiation at emplacement, leading to the development of high-Ti mafic rocks. New U-Pb zircon geochronology reveals three distinct age peaks, with two coinciding with ages identified in the metasedimentary host rocks. The dominant Mesoproterozoic age cluster is linked to inherited zircon crystals assimilated within a single meta-mafic rock. In contrast, zircon ages from the late Ordovician to early Devonian are attributed to metamorphic overgrowths. Notably, the third age cluster, delineates a Late Neoproterozoic magmatic event, indicating the temporal span of mafic magmatism. The finding agrees with the best available age (576 ± 17 Ma) for mafic magmatism on the Precordillera Mafic-Ultramafic Belt. Stratigraphic relationships and geochemical fingerprints enable correlation among the meta-mafic rocks from Laguna Amarga, tracing a belt of mafic magmatism with an oceanic affinity that extends southward. Building upon previous works, this study reaffirms that the rift-drift transition of the Cuyania/Precordillera terrane, linked to the Ouachita rift opening from southeastern Grenville, evolved during the latest Neoproterozoic.

Neoproterozoic and early Paleozoic metamorphism recorded in gneisses from the East Kunlun Orogenic belt

The East Kunlun Orogen (EKO) is a long-lived accretionary orogenic belt that records the Paleozoic–Mesozoic amalgamation processes of the East Asia continent. The belt consists mainly of various kinds of gneisses with minor amounts of eclogite and garnet amphibolite occurring as lenses. We report zircon U–Pb ages and Hf–O isotopic compositions for the granitic gneisses and paragneisses in the Xiarihamu area near Golmud in Qinghai Province, to investigate the metamorphic history and evolution of the orogenic belt. For the granitic gneisses, zircon U–Pb chronology reveals a Neoproterozoic magmatic event and an early Paleozoic metamorphic event. The magmatic crystallization ages of the two granitic gneisses are 920 ± 6 and 929 ± 2 Ma, and yield εHf(t) values of −8.4 to 1.7 and δ18O values of 7.94–11.19‰, suggesting their derivation mainly from continental crustal materials. The detrital zircons from the paragneisses record a Neoproterozoic metamorphic event and a Paleozoic metamorphic event. Most of the detrital zircons from the two paragneiss samples yielded ages of 2.1–0.9 Ga, indicating that the sources of the sediment were formed mainly during the Neoproterozoic to Paleoproterozoic. These Neoproterozoic magmatic and metamorphic events suggest that the EKO underwent a Neoproterozoic tectonothermal event that was related to the assembly of the Rodinia supercontinent. The similar tectonic histories of the EKO and North Qaidam belt (NQB) indicate they were probably part of a single tectonic unit during the Neoproterozoic. Some of the zircons have metamorphic overgrowth rims yielding two stages of Paleozoic metamorphic ages of ca. 440 Ma (438 ± 2 Ma) and ca. 420 Ma (419 ± 6 Ma, 416 ± 6 Ma, and 423 ± 6 Ma). Combined the discover of high-pressure mineral inclusions (jadeite + quartz) in these rims with the results in previous studies, the ages of these rims (ca. 440 Ma and ca. 420 Ma) are suggested to represent of HP-UHP metamorphism of the EKO. These age data imply that the gneisses in this study might share common early Paleozoic metamorphic event with the HP–UHP eclogites in the EKO.

Neoproterozoic and middle Paleozoic geological events in the eastern Wolhyeonri complex of the southwestern Gyeonggi Massif, South Korea, and their tectonic correlations in northeastern Asia

The eastern Wolhyeonri complex in the southwestern Gyeonggi Massif, South Korea, which has a close affinity with the northern margin of the South China Craton, primarily consists of Neoproterozoic igneous and sedimentary rocks that were metamorphosed by the middle Paleozoic thermal event. In this study, we present the results from thermobarometry, whole-rock chemistry, and zircon geochronology of rocks in the eastern Wolhyeonri complex near Gwangcheon. The main rock type, such as the migmatitic biotite gneisses, was deposited after ca. 722–680 Ma, and the associated foliated amphibolites exhibit a rift-related Neoproterozoic origin. The ca. 845–820 Ma arc-related metadolerite and mafic layer in the metavolcanic-sedimentary unit are also exposed. Two Neoproterozoic magmatic events support the idea that the southwestern Gyeonggi Massif developed along the northern margin of the South China Craton. These Neoproterozoic rocks experienced upper amphibolite-facies (7–10.5 kbar and 710–735 °C) to low-pressure granulite-facies metamorphism (10.5–12.0 kbar and 810–830 °C) during 424–412 Ma, were associated with ca. 418 Ma leucogranite formation, and then underwent retrograde amphibolite-facies metamorphism. Combined with the results from previous studies, the early-middle Paleozoic orogeny in the southern Gyeonggi Massif is characterized by 470–456 Ma subduction associated with a high P/T metamorphism, and the initiation of intermediate P/T metamorphism from ca. 445 Ma followed by low-pressure granulite-facies metamorphism at 432–403 Ma, and high-pressure granulite-facies metamorphism at 392–381 Ma, indicating that the tectonic setting transitioned from a continental collision to a post-collisional setting between 432 Ma and 392 Ma. These events and the absence of Paleozoic ultrahigh-pressure metamorphism strongly correlated with the Wuyi-Yunkai orogen in the South China Craton, rather than the Qinling belt in the North China Craton. Therefore, the early-middle Paleozoic orogeny in the southern Gyeonggi Massif was caused by the subduction and subsequent collision within the South China Craton.

Petrogenesis and Tectonic Significance of the Neoproterozoic Magmatism of the Tusham Ring Complex (NW Indian Shield): Insight into Tectonic Evolution of the Malani Igneous Suite and Rodinia Supercontinent

The present study is carried out to probe geodynamic evolution and tectonic history of A-type granitoids from the Riwasa and Nigana areas in the Tusham Ring Complex (TRC), western Peninsular India on the basis of petrological and geochemical aspects. The investigated rocks have the characteristics of hypersolvus, calc-alkaline, peraluminous and A-type granitoids. They are enriched in SiO2, Na2O+K2O, Fe/Mg, Th, U, REE (except Eu), LILE+HFSE, elevated in Fe/Mg, Ga/Al, Th/U, A/CNK ratios, and depleted in CaO, MgO, Sr, Cr, Ni, P, and Ti, and having Eu abundances. They also show high heat production (HHP) affinity and high mineralization potential. Elemental geochemistry in conjunction with mineralogical variants attested that they were formed by limited fractional crystallization of a parental magma derived from partial melting of crustal protolith accreted during the Neoproterozoic magmatic event. Physicochemical features i.e. F and Cl-rich biotite, pegmatite rim, substantial model content of albite, high mineralized veins and altered mineralogy indicate rock-fluid interactions which are caused by magmatic origin or secondary metasomatic alteration superimposed on the host rock. The magmatism occurred in the TRC is interpreted to represent the Malani Igneous Suite (MIS) and their linkage with Rodinia Supercontinent and Pan-African thermal event.

3D inversion of the Sichuan Basin magnetic anomaly in South China and its geological significance

The Sichuan Basin magnetic anomaly is the most striking regional aeromagnetic anomaly in South China. It is characterized by a continuous large-scale linear magnetic anomaly and contains long-wavelength constituents which could still be detected on satellites. However, Sichuan Basin is covered by 4 to 10 km thick non-magnetic sedimentary layers from Neoproterozoic to Cenozoic, which conceals the magnetic sources in the Precambrian basement and makes it difficult to explore the geological origin of the Sichuan Basin magnetic anomaly. In this study, we applied 3D inversion to the magnetic data, and then compared our inverted susceptibility model with geological maps. We found that the spatial distribution of the Sichuan Basin magnetic anomaly controls the range of the rigid basement beneath Sichuan Basin and it is surrounded by the widespread Neoproterozoic magmatic complexes. Based on our analysis, we proposed that the geological origin of the Sichuan Basin magnetic anomaly might be related to the craton-scale Neoproterozoic magmatic event, which has played an important role in the stabilization of the basement and the evolution of the deep crust in Sichuan Basin.

Late Neoproterozoic mafic sills in the Suizhou area of the South Qinling block: constraints for the tectonic evolution of the northern margin of the Yangtze craton

ABSTRACT Late Neoproterozoic gabbroic-diabasic sills are widely distributed in the eastern part of the South Qinling block. Here, a comprehensive geochronological and geochemical study of these mafic sills has been conducted. LA-ICP-MS zircon U-Pb results indicate that the gabbroic-diabasic sills were formed at 632 ± 2 Ma. The sills consist mainly of tholeiitic basaltic rocks with relatively low TiO2 contents (0.81–1.07 wt.%) and high Fe2O3 T/MgO ratios. These rocks display relatively flat to moderate light rare earth elements (LREE) enrichment patterns and positive Eu anomalies (Eu/Eu* = 1.15–1.41). On the primitive mantle normalized spider diagram, the samples show E-MORB-like geochemical features. All of the studied samples display similar Sm-Nd isotopic compositions with negative εNd (t) values ranging from −6.2 to −5.5. Most clinopyroxenes from the mafic sills have relatively low Al/Ti ratios similar to those of typical rift-related cumulates. Therefore, Whole-rock and mineral geochemical features of the studied samples suggest that the mafic sills might have been derived from partial melting of a metasomatised subcontinental lithospheric mantle source in a continental rift setting. It can be advocated that the break-up of the Rodinia supercontinent in the northern part of the Yangtze craton might have been a long-lasting process. By comparison of the coherent Neoproterozoic magmatic events in the northern Yangtze craton and the Tarim block, it can be suggested that the Yangtze craton might have been adjacent to the Tarim block in the reconstruction model of the Rodinia supercontinent.

Early Neoproterozoic granitic gneisses in the Amdo micro-continent, Tibet: petrogenesis and geodynamic implications

ABSTRACT The palaeogeographic locations of ancient continental blocks in the Tibetan Plateau, especially of micro-continental blocks during the Neoproterozoic supercontinent cycle, remain enigmatic. To clarify the petrogenesis of Neoproterozoic granitic gneisses and the early evolution of the Amdo micro-continent, we conducted an integrated study of the petrography, geochronology, and geochemistry of biotite monzonitic gneisses from the Precambrian metamorphic basement. The biotite monzonitic gneiss sample yielded a weighted mean zircon U–Pb age of 820 ± 11 Ma, indicating an early Neoproterozoic magmatic event. All gneiss samples show enrichment in light rare-earth elements and depletion in high-field-strength elements in N-MORB-normalized spider diagrams, which suggests that their precursor magma was generated in a subduction-related active continental margin. In addition, these rocks have mostly positive εHf(t) values (−1.0 to 7.0) and corresponding crustal model ages of 1.3 − 1.8 Ga. Zircon Hf isotopes and whole-rock geochemistry indicate that the gneisses were derived from partial melting of juvenile crust material. Recently published age spectra of detrital zircons from different blocks suggest that the Amdo micro-continent had a closer affinity to the Lhasa terrane than to the Qiangtang terrane prior to and during the break-up of the Rodinian supercontinent. However, the gneisses are geochemically distinct from back-arc magmatic rocks in the Lhasa terrane and similar to coeval Andean-type magmatic rocks in blocks that constituted the northwestern margin of Rodinia (including Madagascar, Seychelles, and Malani). This study therefore provides new constraints on the Neoproterozoic palaeogeographic location and evolution of the Amdo micro-continent.

U–Pb (zircon) geochronologic constraint on tectono-magmatic evolution of Chaur granitoid complex (CGC) of Himachal Himalaya, NW India: implications for the Neoproterozoic magmatism related to Grenvillian orogeny and assembly of the Rodinia supercontinent

Many elongated, lenticular intrusive granitoids of various ages are scattered within the Lesser Himalayan metamorphic belt, all along the ~ 2500 km length of the Himalaya. The Neoproterozoic Chaur granitoid complex (CGC) of Chaur area is characterized by foliated and non-foliated peraluminous granites occurring as an isolated granitoid body within the Jutogh group. In this work, we present the whole-rock geochemical data of six samples and U–Pb (zircon) geochronology of two different granites of the CGC and one granitic gneiss sample of Jutogh group from Himachal Pradesh of NW Himalaya. Our newly obtained results of U–Pb (zircon) geochronological age populations from all granitoid sample yield age between 766 and 1080 Ma with few younger phases and older inherited ages. We obtained U–Pb (zircon) ages from two sample of the CGC, out of which one gives the two prominent age spectra for 206Pb/238U with weighted mean age of 826 ± 4.97/9.74 Ma, MSWD = 0.65, n = 8) and 868 ± 6.21/12.17 Ma, MSWD = 1.28, n = 7). Similarly, another granite of CGC gives the weight mean age of 929 ± 6.48/12.70 Ma (MSWD = 1.28, n = 11). The granitic gneiss of the Jutogh group also gives two prominent age spectra for 206Pb/238U, with weighted mean age of 861 ± 8.27/16.21 Ma (MSWD = 0.31, n = 10) and 932 ± 10.0/19.6 Ma (MSWD = 1.57, n = 8). The whole-rock geochemical data show calc-alkaline composition of all six samples and suggest a subduction-related accretion setup. The depletion in the Nb, Sr, P and Ti in CGC indicates a magmatic arc type magma. U–Pb (zircon) ages of all three samples have a similar phase of crystallization and we defined as ~ 930 Ma age of crystallization of CGC. The whole-rock geochemical data suggest that all the three samples possibly came from the same magma source during the Neoproterozoic magmatic events in the northern marginal part of the Indian plate. It is envisaged that the unknown microcontinents present in the northern margin collide with the Indian plate and the subduction process coincides with the onset of the Grenvillian orogeny during the Neoproterozoic. The extension of these minor collision orogen may have been connected with Lhasa, Trim as well as Greater India blocks. In this collisional process, the crustal melt was generated and intruded in the form of CGC within the pre-existing Paleoproterozoic crust of Indian plate. The whole process indicates that the subduction of unknown microcontinent under the Indian plate may be correlated with the Grenvillian orogeny and formation of the Rodinia supercontinent during Neoproterozoic.

Zircon U–Pb ages and Hf isotope compositions of the Neoproterozoic magmatic rocks in the Helan Mountains, North China

AbstractThe periodic dispersal and assembly of continental fragments has been an inherent feature of the continental crust. Based on the discovery of large-scale supercontinent cycle and the theory of plate tectonics, several supercontinents have been identified, such as Columbia/Nuna, Rodinia, Gondwana and Pangaea. Neoproterozoic magmatic events related to the break-up of Rodinia are globally well preserved. Although Neoproterozoic magmatic events were very weak in the North China Craton (NCC), they are crucial in reconstructing the geometries of the NCC and could facilitate the completion of the Neoproterozoic configuration of the supercontinent. In this study, c. 853–835 Ma magmatic rocks are identified in the western margin of the NCC. Precise zircon U–Pb age determination yields 206Pb/238U average ages of 835.5 ± 5.3 Ma (HL-39) and 853.7 ± 4.5 Ma (HL-30). In situ zircon Hf isotope compositions of the samples reveal that their parental magma was formed by the reworking of ancient crust evolved from Mesoproterozoic mantle. In summary, the discovery of Neoproterozoic magmatic rocks in the western margin of the NCC, and reported synchronous rocks in other parts of the NCC indicate that the NCC might be conjoined with the supercontinent Rodinia during the Neoproterozoic. This discovery is of significant help in unravelling the early Neoproterozoic history of the NCC and the evolution of the supercontinent Rodinia.

Ages and nature of the protolith of the Tulovchikha metamorphic complex in the Bureya Massif, Central Asian Orogenic Belt, Russia: Evidence from U–Th–Pb, Lu–Hf, Sm–Nd, and 40Ar/39Ar data

The Bureya Massif is located in the eastern segment of the Central Asian Orogenic Belt (CAOB) and its tectonic affinity and Precambrian evolution is highly controversial. Here we present mineralogical, whole-rock geochemical (major and trace elements and Sm–Nd isotopes) and zircon Hf isotopic data, together with zircon geochronological and mica 40Ar/39Ar dating of the biotite and amphibole gneisses from the Tulovchikha metamorphic complex (previously considered as Archean or Paleoproterozoic basement) in the Bureya Massif, in order to investigate their protolith, metamorphic and deformation ages, petrogenesis, and tectonic implications. LA-ICP-MS U–Pb dating of magmatic zircons from the biotite gneiss, the amphibole–biotite gneiss, and the amphibolite yields single zircon age populations cluster at ~950 Ma, ~920 Ma and ~940 Ma, respectively. The narrow zircon age ranges, together with the morphological features of the zircon crystals and the geochemical data, indicate that the studied metamorphic rocks have a magmatic origin and their protoliths were formed in the early Neoproterozoic (i.e., 950–920 Ma). The consistent formation ages further suggest that the Neoproterozoic gabbro–granitic rocks within the Nyatygran Complex in the Bureya Massif probably represent the protolith of the studied metamorphic rocks. The biotite and amphibole-biotite gneisses of the Tulovchikha metamorphic complex yield whole-rock Nd model ages (tNd(DM)) of 2.4–1.5 Ga and Hf zircon crustal model ages (tHf(C)) of 1.7–1.2 Ga, indicating that the precursors of the Tulovchikha Complex gneisses formed from the reworking of Meso–Paleoproterozoic rocks or mixed Neoproterozoic juvenile and Meso–Paleoproterozoic crustal sources. Considering that the Bureya and Jiamusi massifs experienced similar Neoproterozoic magmatic events, we suggest that these massifs form a contiguous crustal unit and share a common geological history. The rocks of Tulovchikha metamorphic complex in the studied area experienced epidote-amphibolite to amphibolite facies metamorphism probably in the early Paleozoic, as evidenced by the 471 ± 19 Ma age of a metamorphic zircon with a low Th/U ratio (<0.1). According to 40Ar/39Ar biotite dating of the biotite gneiss, the Tulovchikha Complex experienced a youngest thermal event at 227 ± 3 Ma. This event may be related to the final closure of the Paleo-Asian Ocean, or may have been caused by the deformation of the blocks of East Asia in connection with the initial stages of the closure of the Mongol–Okhotsk Ocean.

Early Neoproterozoic gneissic granitoids in the southern Yili Block (NW China): Constraints on microcontinent provenance and assembly in the SW Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) was built by amalgamation of diverse geologic units including several microcontinents. The nature and geodynamic evolution of the Precambrian basement of these units are essential to constrain their origin, and thus the geodynamic and paleogeographic reconstruction of the accretionary system. The Yili Block, located in the west of the Chinese Tianshan Orogen, is one of these Precambrian-based continental constituents. Field investigations, zircon U-Pb dating and Lu-Hf isotopic analysis, whole-rock geochemical and Sr-Nd isotopic studies were conducted on the gneissic granitoids from the Giergelang area, southern Yili Block. These rocks yielded early Neoproterozoic zircon U-Pb ages (962–934 Ma), containing substantial number of Paleo- to Mesoproterozoic inherited zircons (2403–1268 Ma); their protoliths belong to peraluminous high-K granite series displaying right-declining REE patterns and Eu negative anomalies together with LILE (K, Rb, U, Th) enrichment and depletions in Ba, Nb, Sr, P, Ti; they have negative εNd(t) values ranging from −2.5 to −4.7, and old Nd model ages varying from 1650 Ma to 1910 Ma; they also exhibit highly variable zircon εHf(t) values (−12.1 to 4.4), and Hf-in-zircon model ages (1558–2574 Ma). Integrating all these results, it is suggested that the primary magma of gneissic granitoids was generated by partial melting of supracrustal rocks with involvement of old crustal materials.A comparison of data from the Yili Block and its neighboring continental units reveals that the Neoproterozoic magmatic event is an important episode of crustal reworking for the major continental blocks within the CAOB. Similar Neoproterozoic magmatic events and comparable upper Neoproterozoic to lower Paleozoic stratigraphic sequences of the Yili, Chinese Central Tianshan and Tarim blocks, suggest that they had a similar crustal evolution and close tectonic and paleogeographic relation during Neoproterozoic, and were likely derived from one single continental plate.

Middle Neoproterozoic magmatic event in the western Nam Tso area, Tibetan Plateau: Constraint on the origin of the North Lhasa terrane

Middle Neoproterozoic magmatic event in the western Nam Tso area, Tibetan Plateau: Constraint on the origin of the North Lhasa terrane

Provenance and tectonic implications of Cambrian sedimentary rocks in the Bureya Massif, Central Asian Orogenic Belt, Russia

In this paper we present new detrital zircon U–Pb ages and Lu–Hf isotopic data as well as whole-rock geochemical data for siltstones of the Cambrian Chergilen and Allin formations in the Mel’gin Trough of the Bureya Massif, Russia. Our aim is to constrain the provenance and tectonic settings of these strata. The detrital zircons in these rocks are dominantly Neoproterozoic in age (∼80% of all zircons), along with some Mesoproterozoic and Paleoproterozoic zircons, and the main age peaks are at ca. 1.78, 1.64, 1.45, 1.18, 0.94, and 0.82 Ga. The zircon Hf and whole-rock Sm–Nd isotopic compositions, together with geochronological data, show that the main sources of the Cambrian sediments were Neoproterozoic and Mesoproterozoic igneous complexes formed by the reworking of Paleoproterozoic rocks. The main age populations of detrital zircons from the Cambrian siltstones in the Bureya Massif are similar to those of detrital zircons from the Neoproterozoic and early Paleozoic deposits within the Jiamusi Massif, suggesting that they share a common history. However, the crustal basements of the Bureya and Jiamusi massifs are different from those of other massifs in the eastern part of the CAOB, such as the Erguna, Khanka, Khingan, and Songnen–Zhangguangcai Range massifs. The wide Neoproterozoic magmatic events suggest that the Bureya and Jiamusi massifs have an affinity to the Tarim Craton or the northern Tian Shan block, different from the North Asian and North China cratons.

Precambrian tectonic affinity of theNorthQinlingMicrocontinent: Constraints from the discovery ofMesoproterozoic magmatic zircons in theQinlingGroup

This paper presents new results on zircon U–Pb dating of a two‐mica schist from the Qinling Group in the core of the North Qinling Orogenic Belt (NQB), Central China, with the aim of constraining the formation time of the Qinling Group, and the tectonic affinity of the North Qinling Microcontinent. Zircon U–Pb dating indicates that the protolith of the metasedimentary rock in the Qinling Group was deposited later than ~1502 Ma. The Qinling Group in the NQB represents a long‐lived unit, and its formation age can be constrained to the period between the Paleoproterozoic and early Neoproterozoic. The zircon age populations of the studied sample can be divided into two major populations of 1559–1642 and 1470–1548 Ma, and one subordinate population of 1717–1794 Ma, indicating their provenances were mainly attributed to the NQB and subordinately from the North China Craton (NCC) and the Yangtze Craton (YZC). And the distribution of the early Neoproterozoic magmatic events and the Nd–Pb whole‐rock isotopes, zircon Hf isotopes, and trace element compositions of the Precambrian basement rocks in the NQB is significantly different from those in the NCC and YZC, indicating that the NQB cannot be a southern sector of the NCC, or a northern sector of the YZC, and was an independent microcontinent from the Paleoproterozoic to the early Neoproterozoic.

Provenance of Ediacaran (Sinian) sediments in the Helanshan area, North China Craton: Constraints from U–Pb geochronology and Hf isotopes of detrital zircons

The tectonic relationship between the Alxa Block and the North China Craton has long been controversial. The Helanshan area lies at the western margin of the Ordos Block and to the east of the Alxa Block, and it contains Eidacaran Zhengmuguan Formation and Tuerkeng Formation. The Zhengmuguan Formation is made up of tillites, limestone and dolomine, and the Tuerkeng Formation consists of silty slate. A parallel unconformity marks the boundary between the Tuerkeng Formation and the Early Cambrian Suyukou Formation, which is composed mainly of phosphatic pebbly sandstone and sandstone. U–Pb dating ages of detrital zircons in the Zhengmuguan and Suyukou Formations reveal two Neoproterozoic age peaks of 818±4Ma (n=88) and 905±8Ma (n=20). Neoproterozoic magmatic events have yet been reported in the basement of the Ordos Block, while some Neoproterozoic igneous rocks have been found in the basement of the Alxa Block. Moreover, the two Neoproterozoic age peaks correspond well with the ages of Neoproterozoic igneous rocks in Alxa Block. The Hf isotopic characteristics of a part of Neoproterozoic zircons from the Ediacaran Zhengmuguan Formation in the Helanshan area (εHf(t)=–7.812 to 3.274, TDMC=2211–1578Ma, n=10) are similar to those Neoproterozoic igneous zircons from the Langshan area (εHf(t)=–1.105 to 5.928, TDMC=1.75–1.38Ga, n=23) and Bayinnuoergong area in the Alxa Block. The parental magmas had a long residency time in the crust. It seems, therefore, that Alxa Block provenance provided Neoproterozoic clastics for Helanshan area in Ediacaran, and Alxa Block had already been a part of the North China Craton by the late Neoproterozoic, even earlier.

Discovery and Geological Significance of Neoproterozoic Metamorphic Granite in Jimo, Shandong Province, Eastern China

AbstractDuring the 1:50000 regional geological survey in Jimo, east Shandong Province, Paleoproterozoic metamorphic supracrustal rocks and Neoproterozoic metamorphic plutonite were newly discovered. These rocks displayed inclusions which had occurred in the Mesozoic granite, and the main lithologies are schist, granulite, marble, and granitic gneiss. Geochemical analyses suggest that Neoproterozoic metamorphic plutonite are characterized by high‐K, metaluminous to weakly peraluminous. They are enriched in LILE and depleted in HFSE, with moderately enrichment of LREE, weak fractionation of LREE from HREE and negative Eu anomalies. The surface age of plutonic rocks in the survey area is 770.2±2.4 Ma, representing the age of magma crystallization, which is agreement with the the Neoproterozoic magmatic event after Rodinia supercontinent in the northern margin of Southern China continental block. In addition, the age of sporadic distribution (298 Ma and 269 Ma) is mixed zircon age, representing the rocks experienced metamorphism in Indosinian period. According to the associated mineral assemblages, and the characteristic metamorphic minerals and temperature pressure conditions, four metamorphic facies were identified, including amphibolitic, epidote amphibolite, greenschist, and mid‐high pressure greenschist. Analysis of tectonic setting suggests that granitic gneiss is formed in an extensional environment and was involved from the continental margin magmatic arc to intraplate environment. Jimo is distributed in the east of Zhuwu fault, and has the same Spatial distribution location with the Weihai uplift UHP metamorphic belt rocks. The metamorphic rocks in Jimo area have similar geochemical characteristics of elements, tectonic setting and retrograde metamorphism with that in the Sulu UHP metamorphic belt. Therefore, Zhuwu fault may be the boundary fault of Sulu UHP metamorphic belt.

Neoarchean–Early Paleoproterozoic and Early Neoproterozoic arc magmatism in the Lützow–Holm Complex, East Antarctica: Insights from petrology, geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes

The Lützow–Holm Complex (LHC) of East Antarctica forms part of the Neoproterozoic–Cambrian high-grade metamorphic segment of the East African–Antarctic Orogen. Here we present new petrological, geochemical, and zircon U–Pb and Lu–Hf isotopic data for meta-igneous rocks including charnockite, felsic gneiss, metagabbro, and mafic granulite from the LHC and evaluate the Neoarchean to Early Paleoproterozoic (ca. 2.5Ga) and Early Neoproterozoic (ca. 1.0Ga) arc magmatic events. The trace element geochemical signatures reveal a volcanic arc affinity for the charnockites from Sudare Rocks and Vesleknausen and felsic gneiss from Rundvågshetta, suggesting that the protoliths of these rocks were derived from felsic arc magmas. In contrast, metagabbros from Skallevikshalsen and Austhovde, occurring as boudins in metasediments, show non-arc signatures (within-plate basalt or mid-oceanic ridge basalt). The upper intercept ages of magmatic zircons in charnockite plotted on concordia diagrams yielded 2508±14Ma (Sudare Rocks) and 2490±18Ma (Vesleknausen), clearly suggesting a Neoarchean to Early Paleoproterozoic arc magmatic event. A subsequent thermal event during Early Neoproterozoic traced by 206Pb/238U age of oscillatory-zoned core of zircon in mafic granulite from Langhovde (973±10Ma) is consistent with a similar Early Neoproterozoic magmatic event reported from the LHC, suggesting a second stage of arc magmatism. The timing of peak metamorphism has been inferred from 206Pb/238U mean ages of structureless zircons in metagabbros from Skallevikshalsen and Austhovde, mafic granulite from Langhovde, and felsic gneiss from Rundvågshetta in the range of 551±5.4 to 584±5.0Ma. Zircon Lu–Hf data of Neoarchean charnockites from Sudare Rocks and Vesleknausen indicate that the protolith magma was sourced from Paleo- to Neoarchean juvenile components mixed with reworked ancient crustal materials. Protolith magmatic rock of the felsic gneiss from Rundvågshetta might have been sourced from reworked Paleoarchean crust. In contrast, metagabbros from Skallevikshalsen and Austhovde were derived from the Paleoproterozoic reworked crust. The results of this study suggest the occurrence of several discrete crustal fragments of ca. 2.5Ga and ca. 1.0Ga juvenile magmatic arcs in the southwestern part of the LHC, which amalgamated during the latest Neoproterozoic collisional event related to the final stage of assembly of the Gondwana supercontinent.

Neoproterozoic magmatic events in the South Qinling Belt, China: Implications for amalgamation and breakup of the Rodinia supercontinent

Neoproterozoic magmatic rocks in the South Qinling Belt of China provide important clues for understanding the mechanism and timing of the amalgamation and breakup of the Rodinia supercontinent. Here we report new geochemical and high-precision LA-ICP-MS zircon U–Pb–Hf isotopic analyses on magmatic suites from the Liuba and Zhashui areas in the South Qinling Belt. Our data show that the crystallization ages of the granitic intrusions from Tiefodian and Tangjiagou in the Liuba area are 863±22Ma and 794±11Ma, respectively, whereas those of the dioritic and gabbroic intrusions at Chishuigou in the Zhashui area are 925±28Ma and 832.6±4.0Ma, respectively. The diorites at Chishuigou display arc-related geochemical affinity, characterized by strong depletion in Nb, Ta, P and Ti, and enrichment in large-ion lithophile elements (i.e., Rb, Ba, Th and U), indicating a subduction-related arc setting at ca. 925Ma. The Tiefodian granitic rocks have high SiO2 (68.46–70.98wt.%), Na2O (3.87–4.51wt.%), and low K2O (1.34–2.61wt.%) contents with TTG affinity. However, their Cr, and Ni contents and Cr/Ni, Nb/Ta ratios are similar to those of continental crust, and together with high negative εHf(t) values (−4.87 to −14.84), suggesting a continental margin arc at ca. 863Ma. The gabbros at Chishuigou have high TiO2 content (2.74–3.14wt.%), Zr/Y (3.93–4.24), Ta/Yb (0.19–0.25) ratios and low Zr/Nb ratios (11.37–13.17), similar to the features of within-plate basalts, indicating an intra-continental rift setting at ca. 833Ma. The granitoids at Tangjiagou exhibit enrichment of LREE, K and Pb, and depletion of Nb, Ta, P and Ti, suggesting an extensional tectonic environment at ca. 794Ma.The results indicate that Neoproterozoic magmatic rocks in the South Qinling Belt formed before ca. 833Ma and might represent the amalgamation of the Rodinia supercontinent in an arc-related subduction environment, whereas the magmatic events with the peak ages at ~740Ma during ca. 833–680Ma represent the breakup of Rodinia. Integrating our new data with those from previous works, we propose a new tectonic model for the evolutionary history of the South Qinling Belt in the Neoproterozoic, including four key stages: 1) an ocean that separated the South Qinling Belt and the Yangtze Block in the Early Neoproterozoic (ca.1000–956Ma); 2) bidirectional subduction of the oceanic lithosphere during ca. 956–870Ma; 3) subduction and collision between the South Qinling Belt and the Yangtze Block during ca. 870–833Ma, thus suggesting that the South Qinling Belt was as a part of the Yangtze Block from this period; and 4) intra-continental rifting during ca. 833–680Ma, although the blocks were not entirely rifted apart.

Early Neoproterozoic arc magmatism in the Lützow-Holm Complex, East Antarctica: Petrology, geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes and tectonic implications

The Lützow-Holm Complex (LHC) in East Antarctica has prominently figured in Proterozoic supercontinent reconstructions and is an important region to address subduction-collision process. Here we present petrological, geochemical and zircon U–Pb geochronological and Lu–Hf data on a suite of meta-igneous rocks from the LHC. The rocks that we investigated include hornblende-biotite gneiss (Bt+Hbl+Pl+Kfs+Qtz), charnockite (Pl+Qtz+Kfs+Opx+Hbl+Grt), and amphibolite (Hbl+Pl+Bt±Cpx). Metamorphic temperature based on Hbl-Pl assemblage increases from the western part (710–740°C) to the eastern part (780–820°C) of the complex. The REE and trace element patterns as well as Rb-Y-Nb and Rb-Yb-Ta plots reveal volcanic arc affinity for the Hbl-Bt gneiss from Kasumi Rock, Tama Point, and Innhovde, suggesting that the protoliths of the rocks were derived from felsic to intermediate arc magmas. The amphibolite sample from Kasumi Rock also suggests subduction-related volcanic arc affinity. In contrast, the protolith of charnockite from Futatu-iwa is inferred as within-plate granite, as its geochemical signature is distinct from that of the other granitic to dioritic rocks in the LHC. The protolith of amphibolite from Tama Point is inferred as ocean-island basalt, suggesting the accretion of remnant oceanic lithosphere along with the arc components during the subduction-collision event. Zircon grain morphology and internal structure as examined from CL images indicate that the oldest population in all the samples preserves magmatic crystallization history, as also supported by their high Th/U ratios. The 206Pb/238U mean ages of the oldest population of magmatic zircons in the four rocks show 984±6.9Ma (Kasumi Rock), 965±7.7Ma (Tama Point), 981±18Ma (Innhovde), and 999±6.3Ma (Futatu-iwa) clearly marking a prominent Early Neoproterozoic magmatic event. Subsequent thermal events during the mid Neoproterozoic are also indicated by the concordant ages of a distinct population of zircons with high Th/U values, and 206Pb/238U ages in the range of 899–753Ma from Futatu-iwa charnockite and Tama Point Hbl-Bt gneiss. The youngest population of zircons in these rocks is evidently metamorphic, characterized by structureless overgrowth domains with low Th/U values that yield 206Pb/238U mean ages in the range 582±11–574±9.5Ma, probably related to late Neoproterozoic collisional event and high-grade metamorphism. Zircon Lu–Hf data indicate juvenile sources that contributed to the Neoproterozoic magmatism in the study area. A continental arc-type setting is suggested with magma sourced from Late Paleoproterozoic to latest Mesoproterozoic components, which might have formed during an earlier subduction cycle. Such Early Neoproterozoic arc magmatism has been inferred from other Gondwana fragments such as the Kadugannawa Complex in Sri Lanka, which is regarded as an extension of the LHC. The results of this study therefore suggest that the magmatic arcs in the LHC and the Kadugannawa Complex might have formed under a similar continental arc-setting during Early Neoproterozoic, and that the LHC is a collage of several crustal blocks including Early Neoproterozoic (ca. 1Ga) juvenile volcanic arcs and Neoarchean (ca. 2.5Ga) basement, which were amalgamated during the latest Neoproterozoic related with the final stage of amalgamation of the Gondwana supercontinent.

Geochronology and geochemistry of tuff beds from the Shicaohe Formation of Shennongjia Group and tectonic evolution in the northern Yangtze Block, South China

Meso- to Neoproterozoic magmatic events are widespread in the Yangtze Block. The geochronology and tectonic significance of the Shennongjia Group in the Yangtze Block are still highly controversial. An integrated geochronology and geochemistry approach provides new insights into the geochronological framework, tectonic setting, magmatic events, and basin evolution of the northern Yangtze Block. Our new precise sensitive high-resolution ion microprobe U–Pb data indicate a deposition age of 1180 ± 15 Ma for the Shicaohe Formation subalkaline basaltic tuff that is geochemically similar to modern intracontinental rift volcanic rocks. The integration of available geochemical data together with our new U–Pb ages indicates the Shicaohe Formation subalkaline basaltic tuff formed ca. 1180 in a continental rift-related setting on a passive continental margin. The Shennongjia Group is topped by the Zhengjiaya Formation volcanic sequence, indicating arc-related igneous events at 1103 Ma. The transition of the late Mesoproterozoic tectonic regime from intracontinental extension to convergence occurred between ca. 1180 and 1103 Ma in the northern Yangtze Block. Tectonic evolution in the Neoproterozoic led to accretion along the northern margin of the Yangtze Block. These results provide geochronological evidence, which is of utmost importance for reconfiguration of the chronostratigraphic framework and for promoting research on Mesoproterozoic strata in China, thereby increasing understanding of magmatic events and basin evolutionary history in the northern Yangtze Block.