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The Amdo microcontinent which separates the Qiangtang terrane to the north and the Lhasa terrane to the south is a key terrane for reconstructing the tectonic evolution of Central Tibet. We report the new finding of retrograde eclogites within the Amdo microcontinent in this study. The eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, rutile and quartz and underwent a four‐stage metamorphic evolution, including a peak eclogite facies stage (M1) at ~20–24 kbar and 580–620°C, followed by an HP granulite facies decompression stage (M2) at ~13–15 kbar and 750–780°C, a subsequent MP‐UHT granulite facies heating stage (M3) at 8–10 kbar and >840°C and a final amphibolite facies retrogression (M4) at 5.3–6.0 kbar and 560–580°C. The eclogites exhibit rare earth element distribution patterns and trace element abundances similar to those of N‐MORB and arc‐related volcanics, with depleted whole‐rock εNd(t) values of 3.4 to 4.2, and are inferred to have formed in a back‐arc basin tectonic setting. Zircon and rutile U–Pb dating yields a protolith age of 226 ± 5 Ma, a peak eclogite facies metamorphic age of 190 ± 1 Ma, an HP granulite facies metamorphic age of 179 ± 1 Ma and an amphibolite facies retrograde age of 172 ± 1 Ma. The clockwise P–T–t paths and the oceanic protolith signature of retrograde eclogites suggest that part of the back arc basin was subducted to depths of ~80 km. Tectonic erosion associated with the subduction of the Amdo microcontinent beneath the Tethys Ocean accounts for the deep subduction of the back‐arc basin and the absence of arc magmatic rocks in the northern Amdo microcontinent. [ABSTRACT FROM AUTHOR]

The Amdo microcontinent located within the Bangong–Nujiang Suture Zone (BNSZ) holds one of the important keys to understand the tectonic evolution of Central Tibet before the Qiangtang‐Lhasa terrane collision during the Mesozoic. Newly discovered eclogites were reported within the Amdo microcontinent in this study, and their metamorphic evolution is deciphered by petrographic observations, pseudosection modelling, geochemistry, and zircon U–Pb dating. The eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, rutile, and quartz, and underwent a four‐stage metamorphic evolution, including eclogite facies stage (M1) at ~20–24 kbar and 580–620°C, followed by HP granulite facies decompression stage (M2) at ~13–15 kbar and 750–780°C, subsequent MP–HT granulite facies heating stage (M3) at 8–10 kbar and >840°C, and final amphibolite facies retrogression (M4) at 5.3–6.0 kbar and 560–580°C. The eclogites exhibit rare earth element (REE) distribution patterns and trace element abundance similar to those of N‐MORB and arc‐related volcanics, which are inferred to have formed in a back‐arc Basin tectonic setting. Zircon U–Pb dating yields eclogite facies metamorphic age of 190 ± 1 Ma. The clockwise P–T–t paths and the oceanic protolith signature of retrograde eclogites suggest that part of the back‐arc Basin was subducted to the depths of ~80 km. The subsequent ultra‐high temperature metamorphic overprinting may be related to the upwelling of the asthenosphere. Tectonic erosion associated with the subduction of the Amdo microcontinent beneath the Tethys Ocean accounts for the deep subduction of the back‐arc Basin and the absence of arc magmatic rocks in the northern Amdo microcontinent. [ABSTRACT FROM AUTHOR]

The Bangor area is located in the middle part of the Bangong–Nujiang Suture Zone (BNSZ), where a large number of Middle Jurassic‐Early Cretaceous magmatic rocks are exposed, and is a key area for studying the tectonic evolution of the Bangong–Nujiang Tethys Ocean (BNO). However, the arc magmatic system triggered by the southward subduction of the BNO has not been systematically identified in the northern margin of the Lhasa Terrane, and the timing of initial subduction and closure is still controversial. In this study, four granite, two amphibolite, and one gabbro samples from the Bangor area yield two clusters intrusive ages of 162–168 Ma and 121–133 Ma. The Stages I and II granites show whole‐rock geochemistry similar to those of continent arc magmatism, characterized by enrichment in large ionic lithophile elements (LILEs; e.g., Th, Rb, K) and depletion in high field strength elements (HFSEs; e.g., Nb, Ta, P, Ti). The Stage I magmatic rocks consist of granodiorite, amphibolite, and gabbro and have similar zircon εHf(t) values of −10.1 to −3.5, which may be formed by partial melting of enriched mantle wedge related to the southward subduction of the BNO. The Stage II highly differentiated I‐type granites show positive zircon εHf(t) values of +1.5 to +9.9, which are considered the product of highly differentiated processes via the mixed magma derived from depleted mantle and lower crustal rocks. The Stage II I‐type granites show negative zircon εHf(t) values of −9.2 to −0.7, which are derived from a mixed magma source generated by partial melting of lower crust and enriched lithospheric mantle. On the basis of data from this study and previous research studies, a four‐stage tectonic evolutionary model of the Bangong–Nujiang Tethys Ocean is constructed: Stage 1 (190–145 Ma), the northward and southward subduction of BNO formed a series of arc magmatism; Stage 2 (145–135 Ma), a magmatism lull occurred on the north side due to the subduction effect of the ocean plateau, while the southward subduction still continued; Stage 3 (135–116 Ma), the roll‐back of subducted slab enhanced the magmatism in this stage; and Stage 4 (<116 Ma), the closure of BNO lead to the formation of syn‐collisional magmatism. [ABSTRACT FROM AUTHOR]

Eclogites in the high‐pressure (HP) and ultrahigh‐pressure (UHP) belt record important information about the subduction process and evolution history of the orogenic belt. The Luliangshan eclogites surrounded by granitic gneiss or paragneiss as lenses are exposed in the western segment of the North Qaidam UHP metamorphic belt, northwestern China. Petrology, mineral chemistry, and P–T pseudosection modelling show that the eclogites have experienced a multi‐stage metamorphic process. The peak eclogite‐facies metamorphic stage, is characterized by omphacite in matrix and as inclusion in garnet, with the peak mineral assemblages of garnet + omphacite + rutile + quartz at T > 790°C and P > 25.5 kbar. The initial HP granulite‐facies retrogression is characterized by the symplectite of diopside + plagioclase around omphacite, with P–T conditions of 911°C and 16.9 kbar. The subsequent amphibolite‐facies stage is characterized by amphibole + plagioclase symplectite around the clinopyroxene, with the metamorphic conditions of 674–686°C and 6.4–6.9 kbar. Zircon U–Pb analyses yielded two metamorphic age clusters: (a) HP granulite‐facies metamorphic age of 422–425 Ma, and (b) amphibolites‐facies retrograde age of 397–420 Ma. The protolith of eclogite have geochemical characteristics similar to those of normal mid‐ocean ridge basalt (N‐MORB); and the varying εNd(t) values (−6.3 to 2.1) indicate that the Luliangshan eclogites were derived from a mantle source with rare crustal contamination. Combining these data with previous studies, a multi‐stage tectonic model can be proposed: In the Early Neoproterozoic, the protolith of the Luliangshan eclogites were emplaced into ancient continental crust; during 460–430 Ma, following the oceanic subduction, the subduction of continental crust was dragged by the oceanic slab and continue to subduct towards the Qilian Block, and metamorphosed at the depth of at least 75 km. After a long and slow exhumation process, it returned to the shallow crust. [ABSTRACT FROM AUTHOR]

Earth's first continental crust is formed by Archaean and mainly consisted of tonalite–trondhjemite–granodiorite with a small amount of diorites (DTTGs), which has an essential role in probing early crust–mantle dynamic regime and in understanding the formation mechanism of continental crust. Here, we present zircon U‒Pb dating and Lu‒Hf isotopes, whole-rock geochemistry, and petrography on DTTGs rocks in the Dunhuang Block. Three episodes of DTTGs were emplaced circa 2.67 Ga, 2.60 Ga, and 2.50 Ga. The circa 2.67 Ga TTGs exhibit high SiO2 contents (68.14–71.70 wt%), low MgO contents (0.65–1.31 wt%), and high ratios of (La/Yb)N (146 on average), with their enriched Nd-Hf isotopes [ƐHf (t) = -5.48–3.19 and ƐNd (t) = -5.77–0.53], indicating origination from partial melting of amphibolites at thickened lower crust. In contrast, the circa 2.60 Ga transitional TTGs exhibit relatively high MgO contents (2.80–3.39 wt%), flat REE (Rare earth element) patterns with moderate ratios of (La/Yb)N (20.49 on average), and dispersed Nd-Hf isotopes [ƐHf (t) = -5.48–3.19 and ƐNd (t)= −3.99–3.08]. Accordingly, circa 2.60 Ga transitional TTGs melts were produced by partial melting of the shallower crust induced by mantle-derived magma upwelling. The circa 2.50 Ga diorites exhibit low SiO2 (55.72–59.11 wt%) but high MgO (3.51–4.52 wt%) contents with positive Nd-Hf isotopes [ƐHf (t) = -0.16–4.17 and ƐNd (t) = 2.00–4.45], suggesting that they originated from partial melting of mantle wedges metasomatized by fluid from subduction slabs. Combined with the detailed petrogenetic studies and crustal thickness variation, we conclude that the complex crust–mantle interaction may be an essential reason for the Neoarchaean diversity of DTTGs from the Dunhuang Block, which experienced prolonged arc accretion before Neoarchaean, followed by delamination between 2.67 and 2.60 Ga and subsequently transitioned to subduction. [ABSTRACT FROM AUTHOR]

The Qilian orogenic system in the northern Tibetan Plateau records the complete tectonic cycle from opening of Proto-Tethys Ocean, initial subduction, to continental subduction and collision, and extensional collapse during Neoproterozoic to Devonian. Based on a compilation of recently published high-quality data, this contribution provides an overview of the composition, distribution, nature and ages of the principal tectonic elements, including ophiolites, multiple magmatic rocks, as well as high-grade metamorphism and anatexis, with a view to trace the tectonic evolution of the Qilian orogenic system with respect to the opening, subduction, accretion and closure of Proto-Tethys Ocean. Three main suture zones resulting from amalgamation involving microcontinental blocks within the Proto-Tethys Ocean are identified in the Qilian orogenic system, including the North Qilian subduction-accretion suture (NQLS), South Qilian subduction-accretion suture (SQLS) and North Qaidam subduction-collision zone (NQDS) from north to south that sandwich the Alxa, Qilian, Oulongbuluke and Qaidam Blocks. Two contrasting types of convergent orogeny in the Early Paleozoic includes the accretionary orogeny between Alxa, Qilian and Oulongbuluke Blocks (NQLS and SQLS), and the collisional orogeny between the Oulongbuluke Block and Qaidam Block (NQDS). Both Mariana-type and Andean-type subduction systems were identified in the NQLS based on the occurrence of Early Paleozoic accretionary complexes, ophiolites, high-pressure/low temperature metamorphic rocks and arc-related volcanic rocks and intrusions. The northward subduction beneath a Mariana-type intra-oceanic subduction system is represented by the Cambrian-Ordovician island-arc related volcanic rocks, back-arc volcanic rocks and ophiolite complex, and the southward subduction of the Proto-Tethys North Qilian Ocean beneath the Qilian Block generated an Andean-type continental arc, characterized by coeval arc magmatism and high-temperature metamorphism. Although oceanic subduction-related high-pressure metamorphism has not yet been recognized, the SQLS is also a typical accretionary orogen composed of island arc rocks, back-arc magmatic assemblages, ophiolite and accretionary complexes. The NQDS is a typical collisional orogen, characterized by ultrahigh pressure pelitic/granitic gneisses intercalated with minor eclogites and garnet peridotite blocks, although the previous subduction of oceanic crust can not yet be precluded, supported by the existence oceanic-type eclogite and arc-related magmatism and high-temperature metamorphism. Integrating the geological, petrological, geochemical and geochronological evidence, we reconstruct the Neoproterozoic-Paleozoic tectonic history of the Qilian orogenic system with respect to Proto-Tethys Ocean, which includes opening of the Proto-Tethys Qilian Ocean (580-550 Ma), subduction (520-460 Ma), and closure with subsequent deep continental subduction (455-430 Ma), and multi-stage exhumation of deeply subducted continental slab (425-400 Ma), as well as final extensional collapse (400-360 Ma) [ABSTRACT FROM AUTHOR]

The tectono-magmatic evolution of the Bangong-Nujiang Tethyan Ocean (BNO) plays a crucial role in understanding the Tibetan Plateau accretion before the Cenozoic India-Asia collision. The microcontinents and oceanic plateau recognized recently within the BNO provide important clues for constructing the subduction process between BNO and the Qiangtang terrane. In this contribution, we provide a comprehensive overview of the multidisciplinary information from magmatism, metamorphism, stratigraphy, geochronology, geochemistry, Hf isotopic data, ophiolite suites, and paleomagnetism to gain insights into the spatially and temporally related geodynamic processes of the BNO. A compilation of geochronological data indicates that the emplacement of the diverse igneous suites occurred mainly during three stages: stage 1 (190–150 Ma), stage 2 (130–110 Ma), and stage 3 (110–70 Ma). The igneous suites, including granitoids, mafic intrusions and volcanic rocks, formed two arcuate E–W trending belts that parallel the Bangong-Nujiang suture zone and are correlated to the double sided subduction of the BNO. We infer that the BNO initially opened at ~270Ma between the Lhasa terrane and Qiangtang terrane, although the relationship between the BNO and Longmu Tso-Shuanghu paleo-Tethyan ocean is still unclear. Age data related to metamorphism, arc magmatism, supra-subduction zoneophiolites, and sedimentary strata indicate that the northward subduction of the BNO started at ~190 Ma, followed by the subduction of microcontinents beneath the Qiangtang terrane at 195 Ma. In contrast, the subsequent southward subduction of the BNO started at ~170 Ma, resulting in the opening of the Shiquanhe-Namuco ocean. As indicated by the high Mg volcanic suite, intra-ocean subduction within the BNO also occurred during 170-145Ma, possibly related to the resistance from subduction of ocean plateau and slab retreat. Based on evidence from petrology, isotope geochronology, and isotopic geochemistry, we also infer that the magmatic lull during 145-130Ma is related to the slab subduction of ocean plateau beneath the southern Qiangtang subterrane. The closure of the BNO was most likely diachronous, which started as early as Late Jurassic and continued to the late Early Cretaceous (120-110Ma). • Initial opening of BNO at ~270 Ma and northward subduction at ~190 Ma. • Southward subduction started at ~170 Ma, leading to the opening of SNO. • Ocean plateau mechanism for intra-ocean subduction of BNO and magmatic lull during 145–130 Ma. • Diachronous closure of the BNO initiated at 150 Ma and the final closure during 110–100 Ma. [ABSTRACT FROM AUTHOR]

• Five stages of magmastism occurred along both sides of the BNS. • The Early Jurassic and the Late Cretaceous granitoids are produced by roll back and extension-collapse of the Tongka micro-block, separately. • The collision between Lhasa and Qiangtang terranes may continue to the latest Cretaceous (<74 Ma). • Ophiolites north of Amdo, Baqing and Dengqen were possiable lithospheric remanants of the LSO. The Tongka micro-block, located in the eastern section of the Bangong-Nujiang suture, and characterized by Mesozoic granitoids and high grade metamorphic rocks, holds the key to the evolution of the Bangong-Nujiang ocean (BNO). Here we present a systematic petrologic, geochemical, zircon U-Pb-Hf, and whole rock Sr-Nd-Pb isotopic investigation on six new granitoids in Tongka. The results suggest these granitoids yielded two stages of crystallization (171–177 Ma and 74 Ma) and two stages of metamorphism (201–215 Ma and 170–175 Ma). Combined with the existing work within BNS, the magmatism along the BNS can be divided into five stages: stage 1 (240–250 Ma), stage 2 (200–230 Ma), stage 3 (150–190 Ma), stage 4 (100–135 Ma) and stage 5 (73–100 Ma). Both the Early Jurassic and Late Cretaceous Tongka granitoids in this study are high-K calc-alkaline series, with enrichments in large ion lithophile elements (e.g., Cs, Rb, and K) and depletions of large ion lithophile elements (e.g., Nb, Ta, and Ti). The variable ε Hf (t) values (−17.3 to −7.6), ε Nd (t) values (−12.08 to −11.15) and ancient T DM2 (1.48–2.00 Ga) for the Early Jurassic granitoids and weakly negative ε Hf (t) values (−6.3 to −1.5), ε Nd (t) values (−8.75 to −8.60) and old T DM2 ages (1.07–1.33 Ga) for the Late Cretaceous granitoids, suggest that they are both mainly derived from the melting of ancient crust with minor mantle material input. However, the formation of the Early Jurassic and Late Cretaceous granitoids in Tongka is related to different tectonic settings: roll back after the Tongka micro-block subducted beneath the southern Qiangtang subterrane and extension-collapse after the Tongka micro-block collided with the northern Lhasa subterrane. The initial subduction of the BNO may start from 190 Ma, and the collision between the Lhasa and Qiangtang terranes may continute to the latest Cretaceous (<74 Ma). Ophiolites north of Amdo, Baqing and Dengqen were possiable lithospheric remanants of the Longmu Tso-Shuanghu ocean (LSO) rather than the BNO. [ABSTRACT FROM AUTHOR]

• The Altun block, Qilian block, North Qaidam and East Kunlun block show strong affinity in the Meso-Paleoproterozoic. • The assembly of Rodinia in AQK may start as early as 1030 Ma with a peak convergent time of ∼918 Ma. • The initial breakup of Rodinia in AQK may have started from 860 Ma until to 660 Ma with the peak time of ∼765 Ma. • The separation of AQK from the South China craton may occur until the opening up of Qilian ocean after 660 Ma. The Altun-Qilian-Kunlun Mountain (AQK), located on the northeastern margin of the Qinghai-Tibet Plateau, experienced multiple Neoproterozoic magmatic and metamorphic events which are correlated to the Rodinia supercontinent history. Here we present results from a systematic petrologic, geochemical, and zircon U Pb and Hf isotopic study on Neoproterozoic granitoids and mafic rocks from the AQK. In conjunction with a review of the available age data, we divide the early Neoproterozoic magmatism in AQK into two stages: the first stage at ca. 1030–846 Ma and the second stage at ca. 860–660 Ma. The new Lu Hf isotopic data coupled with published Lu Hf and Sm Nd results indicate that the stage 1 mafic rocks were mainly derived from a depleted mantle source with minor contamination with crustal materials or subducted sediments. The stage 2 mafic rocks were mainly derived from the depleted mantle with limited crustal contamination. Combined with whole-rock geochemical compositions and Sr Nd isotopic data, the stage 1 granitic magmas are inferred to have been derived from reworked Paleoproterozoic-Mesoproterozoic crust and the stage 2 granitoid magmas mainly came from reworked continental crust with minor mantle magma input. The AQK experienced arc magmatism in a compressional environment on an active continental margin during the late Mesoproterozoic-early Neoproterozoic (1030–846 Ma), followed by rift-related magmatism in an extensional setting in the middle to late Neoproterozoic (860–660 Ma). Similarities in basement compositions, magmatism and metamorphism between the Qilian block (QL) and surrounding blocks suggest that the AQK was with a composite block at early Neoproterozoic. The assembly of AQK started as early as 1030 Ma with peak convergence at ca. ∼918 Ma. The initial breakup might have started from 860 Ma and lasted until to 660 Ma with the peak at ca. ∼765 Ma. These timings correspond well with those of the assembly and breakup of the Neoproterozoic supercontinent Rodinia. The breakup of AQK from the South China Craton might have occurred in the late Neoproterozoic, not until the opening of the Qilian ocean at around 660 Ma. [ABSTRACT FROM AUTHOR]

The North Qaidam subduction-collision zone is a typical Alpine-type ultra-high pressure (UHP) metamorphic zone due to the Early Palaeozoic subduction of the Qaidam Block beneath the Oulongbuluke Block, with an integrated record of oceanic subduction, continental subduction, collision, and exhumation to post-collisional extensional collapse. In this study, systemic petrology, zircon U-Pb geochronology, Hf isotopic data and whole-rock geochemical analyses have been carried out for granitoids in the North Qaidam UHP metamorphic units to determine their petrogenesis and further reveal the tectonic evolution of the continental collision orogen. Zircon U-Pb dating yields weighted mean ages of 433 ± 2 Ma, 351 ± 8 Ma, 416 ± 4 Ma, 389 ± 3 Ma and 383 ± 1 Ma, with the εHf(t) values of the latter three ages ranging from −2.4 to 3.3, −5.9 to 1.1 and −3.3 to 2.4, respectively. Based on field relationship, petrological, geochronological, and geochemical results, these granitoids could be divided three groups. The early group granodiorites (~433 Ma) show a marked chemical resemblance to adakites: (1) high La/Yb and Sr/Y ratios, with low Y and HREE values; (2) high Al2O3 and low Mg#, Cr, and Ni values with obvious positive Eu anomalies. Petrological and geochemical characters indicate that the early group adaktic granodiorites may be derived from partial melting of metabasite in a thickened mafic lower crust. The middle group granites (~416 Ma) have an affinity to I-type granitoids, characterized by high Na2O contents (>4.18 wt.%) and low A/CNK values, which were probably generated by partial melting of felsic gneiss of subducted continental crust. The late group granites (389 ~ 351 Ma) are also I-type granitoids, which were originated from partial melting of Mesoproterozoic crust, with minor mantle material input. According to a comprehensive study of these granitoids, along with regional geological background and HP-UHP metamorphism, a four-stage evolutionary process of the North Qaidam UHP metamorphic belt from oceanic subduction, continental subduction, collision to extensional collapse is proposed. After the final closure of the Proto-Tethys Ocean, the subducted continental crust experienced HP-UHP eclogite-faces metamorphism (460 ~ 430 Ma), and thickening of the lower crust lead to generation of adakites and S-type granites. Following break-off of the subducting oceanic slab (425 ~ 400 Ma), the reduction in negative buoyancy caused the exhumation of deeply subducted continental crust accompanied by associated anataxis and syn-collisional I-type granitoids, representing the transition in tectonic regime from compression to extension. Due to the tectonic transition, mantle-derived intrusions and post-collisional granitoids were emplaced during 400 ~ 350 Ma. Simultaneously, the pronounced decreasing in La/Yb and Sr/Y ratios of magmatic rocks (age of 460 ~ 350 Ma) suggested that the crustal thickness decreased gradually from syn-collisional to post-collisional stage. [ABSTRACT FROM AUTHOR]

• The metamafic rocks can be classified into high-Fe and low-Fe groups, and the former is similar to N-MORB and the latter is similar to E-MORB. • The high-Fe and low-Fe groups may have been derived from different parts of a mantle plume. • The Tarim Craton, North China Craton, and North Australia Craton may potentially dominated by the same superplume. In the Mesoproterozoic, there was an epic transition on Earth, the final breakup of the Columbia supercontinent. Understanding the dynamic mechanism responsible for the final breakup of Columbia supercontinent is crucial for establishing Earth's evolution that includes geology, environment and life. However, there is little research on what drove the breakup of the Columbia supercontinent. Here we focus on this issue by integrating new zircon U-Pb ages, Lu-Hf isotopes, and whole-rock geochemical data for metamafic rocks from the Oulongbuluke Block in the southeast of Tarim Craton. These data show that the protoliths of these metamafic rocks were emplaced at ca. 1.37–1.35 Ga and were divided into high-Fe and low-Fe groups. The high-Fe and low-Fe groups show geochemical character similar to normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB), respectively. The high-Fe group was formed by high degree (7%-9%) partial melting of spinel-phase lherzolite mantle source, whereas the low-Fe group was derived from low degree (5%-6%) partial melting of spinel-phase lherzolite mantle source. We propose that the high-Fe and low-Fe groups may have been derived from magmas from different parts of a mantle plume. The formation of the 1.37–1.35 Ga metamafic rocks in the Oulongbuluke Block may be related to the separation of the Tarim Craton into North and South Tarim cratons, which resulted in the opening of the initial Middle Tarim Ocean Basin. By comparison with the plume-induced Yanliao Rift of North China Craton and McArthur Basin of North Australia Craton, we present that these three cratons may potentially dominated by a superplume, forming circular rift zone and radiating dykes. This superplume triggered the continuous extension to most parts of Columbia and led to the final breakup of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Tonalitic–trondhjemitic–granodiorite (TTG)-like leucosomes, which are formed from anatectic melts, record crustal growth and evolution and thus provide constraints on the process of anatexis. However, potential Mg isotope disequilibrium during crustal anatexis makes interpreting the genesis of anatectic melts challenging, thereby potentially hindering the application of the Mg isotope system in investigations of crustal evolution and crustal anatexis. A key factor in Mg isotope fractionation during anatexis is the behaviour of garnet, which becomes preferentially enriched in light Mg isotopes compared with other Mg-hosting minerals during partial melting processes. In this study, a combination of petrography, whole-rock geochemistry, and mineral microanalysis reveals that garnets in leucosomes from the Dulan area of the North Qaidam orogen, were formed by dehydration melting of hornblende. Garnet-bearing leucosomes yield low δ26Mg values (−0.70‰ to −0.33‰) compared with garnet-free leucosomes (−0.19‰ to −0.16‰) and global arc rocks (−0.35‰ to 0.06‰). The different Mg isotopic compositions are attributed to the effect of peritectic garnets on the Mg isotope system in anatectic melts. Quantitative modelling further indicates that the lower Mg isotopic values of garnet-bearing leucosomes require the incorporation of ∼5% peritectic garnets into anatectic melts during magma ascent. Our results demonstrate the influence of peritectic garnets on the Mg stable isotope system and highlight that this influence on the Mg isotopic compositions of peritectic minerals during crustal anatexis must be considered in interpretations of crustal evolution using the Mg isotope system. • The Grt-bearing TTG-like leucosomes show low δ26Mg values than Grt-free ones. • The Grt-bearing leucosomes could be explained by incongruent melting and garnet entrainment. • Garnet entrainment is first-order factor of δ26Mg values of TTG-like melts. [ABSTRACT FROM AUTHOR]

• The South Orogen underwent early post-collision during 1.90–1.85 Ga, followed by late post-collision during 1.80–1.73 Ga. • The North Orogen experienced early post-collision at 1.80–1.73 Ga and then entered the late post-collision at 1.67–1.60 Ga. • Finally, the South Orogen and North Orogen simultaneously entered the initial breakup stage during 1.55–1.47 Ga. The Tarim Craton located in the northwest of China, where the Paleo-Mesoproterozoic extensional magmatism related to the Columbia supercontinent is widely developed. However, the process and time of the extension and initial breakup of the Tarim Craton are still controversial during Paleo-Mesoproterozoic era. In this contribution, we present a systematic petrographic, geochemical, and zircon U-Pb-Hf investigation on Aketashitage granite dykes, Wulan granitic gneisses and Astingbulake metadiabases from the Tarim Craton. Results from our study indicate that the ca. 1.88–1.86 Ga Aketashitage granite dykes belong to I-type granites, which were probably derived from low degree partial melting of thickened Archean crust during early post-collisional setting. The ca. 1.55 Ga Wulan granitic gneisses also show the characteristics of I-type granites, which mainly came from partial melting of mafic lower crust with minor mantle-derived magma input during the rift setting. The ca. 1.55 Ga protoliths of Astingbulake metadiabases show affinity to ocean island basalts and/or continental flood basalts and were produced by partial melting of enriched continental lithospheric mantle under continental rifting setting. In conjunction with previous studies, it can be concluded that the Tarim Craton experienced episodic extension to initial breakup: the South Orogen underwent early post-collisional extension during ca. 1.90–1.85 Ga, followed by late post-collisional extension during ca. 1.80–1.73 Ga; the North Orogen experienced early post-collisional extension at ca. 1.80–1.73 Ga and then entered the late post-collisional extension at ca. 1.67–1.60 Ga; finally, the South Orogen and North Orogen simultaneously entered the initial breakup stage during ca. 1.55–1.47 Ga. Based on a comparison of the global Mesoproterozoic (ca. 1.58–1.45 Ga) magmatic activities as a response to the initial break up of the Columbia supercontinent, we suggest that the Tarim Craton (including the Oulongbuluke Block) and North China Craton were close to India, Australia, Yangtze, Siberia, Congo, São Francisco and West African. [ABSTRACT FROM AUTHOR]

Compared with the statement of the mantle plume hypothesis for large-scale plus high-volume intraplate magmatism, a series of OIB-like mafic rocks which are low-volume and spatially closely related to subduction zones still remain mysterious and inapposite to be explained by using traditional mantle plume hypothesis. In the North Qaidam, most previous studies have focused on ultra-high pressure metamorphic rocks and have paid little attention to mafic magmatism as a mechanism of generating magma with a mantle signature. The Kendelong (KDL) metagabbro with consistently intrusive ages of 485–490 Ma within the Olongbuluke microblock that is overriding plate above the subduction zone is analogous to Oceanic Island Basalts (OIBs) in geochemistry and formed contemporaneously with oceanic subduction. Analyzed samples of the KDL metagabbro have sporadic (87Sr/86Sr) i ratios of 0.7008–0.7063 that have been influenced by paulopost alteration, relatively uniform positive ε Nd (t) values of +0.3 to +1.4, zircon ε Hf (t) values of +1.5 to +6.8, and coupled Nd–Hf isotopes that lie on the terrestrial array. After ruling out the possibility of contributions from subducted enriched components and mantle metasomatites, geochemical features and isotopic compositions indicate that the magmas were derived from a relatively primitive asthenosphere without prior large-volume melt extraction. Rare earth element modeling shows that a low degree of partial melting (<10%) of an asthenospheric mantle source in the garnet stability field should be responsible for the magmatic origin of the KDL OIB-like metagabbro. Considering the temporal and spatial correlations between the KDL metagabbro and other types of mafic rock in adjacent regions, we propose that decompression melting of upwelling asthenosphere triggered by rollback of subducted oceanic slab is a plausible regime to explain the petrogenesis of the early Paleozoic KDL OIB-like metagabbro and to trace a fortuitous tectonic transition event. Moreover, even if the OIB-like magmatism is spatially related to subduction zones, the participation of subduction materials could not be an exclusive prerequisite to sentence its genesis. [Display omitted] • OIB-like magmation is reported in the North Qaidam. • OIB-like magmation in the North Qaidam is related to plate tectonics. • Magmas were derived from decompression-induced melting of upwelling asthenosphere. • Slab only provided geodynamic regime for the Kendelong OIB-like metagabbro. [ABSTRACT FROM AUTHOR]

• The ~3.67 Ga TTGs from Aketashitage area derived from the melting of a thickened oceanic plateau crust or island-arc crust. • Two Paleoproterozoic orogenic belts along the southern and northern margins of the Dunhuang Block. • The Southern Orogen is ~150 m.y. earlier than the Northern Orogen. • In the Paleoproterozoic, Dunhuang Block was assembled into the Columbia supercontinent. The evolution of the Dunhuang Block associated with the assembly of the Columbia supercontinent is poorly constrained. The geochemical composition and temporal evolution of magmatic and metamorphic rocks may hold key information regarding critical geodynamic processes that occurred during the evolution of the Dunhuang Block. In this paper, we present a systematic petrographic, geochemical, and zircon U-Pb and Hf isotopic investigation on tonalitic gneiss, carbonatite, granitic dyke, mafic granulite and A-type granite in the Dunhuang Block. The results suggest that tonalitic gneiss was derived from partial melting of a thickened oceanic plateau crust or island-arc crust at ~3.67 Ga and then it recorded an important subduction-collision orogenesis in the Paleoproterozoic (~2.02 Ga to ~1.96 Ga). The ~1.94 Ga carbonatite and ~1.85 Ga granitic dyke were formed by partial melting of marble and Meso- to Neoarchean basement rocks, respectively. Both of them were formed in post-collisional setting. The ~1.82 Ga mafic granulite recorded high-pressure granulite facies metamorphism followed by a medium–low pressure granulite facies metamorphic overprint, suggesting a clockwise P-T path and implying an environment of collisional orogenesis. The ~1.76 Ga A-type granite resulted from the reworked Neoarchean crust and was most likely related to a post-collisional episode. Combined with previous studies, we identify two Paleoproterozoic orogenic belts of the Dunhuang Block: the ~2.00–1.96 Ga South Orogen and ~1.85–1.80 Ga North Orogen. According to the coupling of these two orogenies with the Columbia orogeny, we conclude that the Dunhuang Block was associated with the assembly of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Mafic granulite, garnet peridotite, and garnet pyroxenite occurred as slices or lenses within dominant felsic granulite, and they together constitute a high‐pressure metamorphic terrane in the Bashiwake unit, South Altyn Tagh, Northern Tibet, China. Previous studies focused on the metamorphic evolution, and geothermobarometry results indicated that the mafic granulite has experienced high pressure/(ultra‐)high temperature (HP/(U)HT) metamorphism, followed by a medium pressure (MP) granulite‐facies overprint. However, the nature and petrogenesis of the mafic granulite in the dominant felsic granulite are poorly known. Combining the previous geothermobarometry results with the petrographic observations, mineral chemistry, and pseudosection modelling in this study, at least four stages were suggested for the metamorphic evolution of the mafic granulites in the South Altyn Tagh, including the eclogite‐facies stage (3–4 GPa, 910–1000°C), high pressure–ultrahigh temperature (HP–UHT) metamorphism, an isothermal decompression, and subsequent MP granulite‐facies overprint. The U–Pb dating of zircons yielded two age clusters: one age cluster at ca. 500 Ma, representing the retrograde age of HP–UHT metamorphism after the eclogite‐facies stage, and another age cluster of ca. 900 Ma that represented the age of the protolith for the mafic granulite. This indicated that the protolith of the mafic granulite was formed in the early Neoproterozoic and then was taken to extreme temperatures and pressures during the early Palaeozoic orogenic event. The elemental abundances of the mafic granulites in the Bashiwake area clearly indicated that they were higher in FeO and TiO2, but were significantly lower in MgO, Cr, and Ni than those of associated garnet peridotites/pyroxenites, and they showed LREE‐enriched patterns with slightly positive Eu anomalies. Sr–Nd isotopic data suggested a basaltic magmatic origin with crust contamination for the protolith of the mafic granulite. Integrating these results together with previous studies, we suggest that the mafic granulites were derived from the basaltic magma intrusion in the continental crust during the Neoproterozoic and subsequently suffered a common HP/UHT metamorphism with felsic crust rocks in the early Palaeozoic (ca. 500 Ma) after the eclogite‐facies metamorphism related to the continental collision (>500 Ma). [ABSTRACT FROM AUTHOR]

Abstract The North Qaidam ultra-high pressure (UHP) metamorphic belt in the northern Tibetan Plateau is considered as a typical Alpine-type UHP metamorphic belt due to the Early Paleozoic subduction of the Qaidam Block beneath the Qilian Block. The well-preserved Paleozoic metatexite migmatite, diatexite migmatite, felsic sheet/dyke and anatectic granite in the North Qaidam UHP metamorphic belt provide us with an excellent opportunity to study the generation, transport and final fate of crustal melt and geodynamic processes associated with orogenesis. Based on structural relationships, petrology, geochronology, whole-rock geochemistry and Sr Nd isotope data, the Early Paleozoic anatexis during oceanic subduction to continental collision in the North Qaidam UHP metamorphic belt can be further divided into three stages of development ~470 Ma, 446–428 Ma and 432–420 Ma. The first-stage granitic leucosomes are rich in K, poor in Na with low Sr/Y and enrichment of large ion lithophile elements (LILEs), which were probably derived from partial melting of ancient felsic gneiss in continental arc circumstances during oceanic subduction. The second-stage Na-rich leucosomes and tonalite plutons are characterized by high Na, Sr, Sr/Y and La/Yb and low heavy rare earth elements (HREEs), with positive ε Nd (t) values of 0.1–4.3 and zircon ε Hf (t) values of 8.3–10.2, similar to typical tonalite-trondhjemite-granodiorites (TTGs). These TTG-like magmas were produced through partial melting of newly emplaced gabbroic rocks with arc affinity under high-pressure (HP) granulite-facies conditions in a thickened lower crust during continental collision. The volumetrically significant migrated plutons evolved from TTG-like melt will become segments of continental crust and contribute to crustal growth, with partial residual products of HP granulite and/or garnet pyroxenite to the mantle by delamination. The third stage of anatexis was preserved in both migmatitic UHP gneiss and eclogite in the Xitieshan and Luliangshan terranes. The Kfs-rich felsic leucosomes inside UHP gneisses in the third stage are characterized by high alkali contents and low mafic component with FeO T + MgO + TiO 2 <2%. In trace element distribution diagrams, these Kfs-rich leucosomes exhibit parallel patterns to their host gneisses but lower element contents and slightly positive Eu and Sr anomalies. The Pl-rich leucosomes within the retrograde eclogite have geochemical features as follows: (1) rich in CaO, Na 2 O and poor in K 2 O, with Na 2 O/K 2 O ratios >2.0; (2) high La/Yb and Sr/Y, and low Y and HREEs; (3) high Al 2 O 3 and low Mg# values; and (4) enriched in LILEs(e.g., Rb, Ba, K, Sr, Pb) and poor in high field strength elements (HFSEs). Partial melting of UHP eclogite and felsic gneiss during the initial retrogression stage with Pl-rich and Kfs-rich leucosome formation was triggered by dehydration melting involving predominant zoisite and muscovite. The anatectic melts from partial melting of deeply subducted UHP gneiss have accumulated and migrated outside the deeply subducted crustal slice in the form of syn -collisional plutons. The melt evolution from the leucosomes produced at the early exhumation stage to syn-collisional granitoids produced at the late exhumation, might contribute greatly to the exhumation of the North Qaidam UHP metamorphic belt from mantle depths to the lower crustal levels. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang Suture Zone (BNSZ) is one of the main suture zones in the Tibetan Plateau and indicates the existence of the Bangong–Nujiang Neo‐Tethys Ocean (BNO). It was formed by the collision between the Qiangtang and Lhasa blocks after the closure of the BNO. However, its evolutionary processes and subduction polarity remain controversial. Research on the BNSZ is of great significance for exploring plate tectonic evolution and ocean–continent connection. The scarcity of the BNSZ structural data is one of the most important reasons for the debate of the BNO tectonic evolution. Based on structural analysis in the field and combined with previous petrology and palaeomagnetic data, this paper has determined that the closure time of the BNO is progressive and scissor‐like, from Middle Jurassic in the east to Early Cretaceous in the middle and late Early Cretaceous to early Late Cretaceous in the west. There was a three‐stage deformation in the BNSZ: (a) N–S‐directed compression induced by the initial collision; (b) WNW–directed transpression related to the stress adjustment; and (c) NE–SW‐directed compression caused by the low‐angle NE‐directed subduction of the Indus–Yarlung Zangbo Ocean. The different structural pattern along the eastern segment of the BNSZ may have resulted from orogenic bending due to the later Himalayan Orocline caused by the India–Eurasia collision in the Cenozoic. [ABSTRACT FROM AUTHOR]

Highlights • Grenvillian orogeny of Rodinia in Oulongbuluke Block systematically investigated. • Metabasite, augen granitic gneiss, paragneiss ages of 1132 ± 33, 1118 ± 9, 1124 ± 12 Ma. • Peak metamorphic P-T conditions of 4.8–5.8 kbar and 652–700 °C. • Metabasites resemble the geochemical characteristics of Andean arc magmatism. • Oulongbuluke Block likely temporarily connected to Qilian Block and Tarim Craton. Abstract A systematic petrologic, geochemical, and zircon U-Pb and Lu-Hf isotopic investigation of an ∼1.1 Ga arc magmatism and metamorphism was studied to evaluate the Grenvillian orogeny and assembly of Rodinia in the Oulongbuluke Block in NW China. The peak metamorphic P-T conditions of the paragneiss were restricted to 4.8–5.8 kbar and 652–700 °C based on P-T pseudosection and conventional geothermobarometry. Zircon U-Pb ages of 1132 ± 33 Ma, 1118 ± 9 Ma, and 1124 ± 12 Ma were determined for the metabasite, augen granitic gneiss, and paragneiss, respectively, indicating magmatic intrusion and a metamorphism event in the late Mesoproterozoic. The metabasites exhibited enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), resembling the geochemical characteristics of Andean arc magmatism. The whole-rock geochemistry and in-situ zircon ε Hf (t) values of 4.3 and 11.2 suggested that the protolithic mafic magma originated from a subduction-modified lithospheric mantle. The low zircon ε Hf (t) values of −5.2 and −0.5 also suggested that the calc-alkaline augen granitic gneisses were derived from the partial melting of a late Paleoproterozoic crustal source. The ∼1.1 Ga arc-related magmatism and metamorphism in the Oulongbuluke Block indicated the occurence of a tectonic-thermal event in an Andean-type active continental margin in the late Mesoproterozoic. In this regard, the Oulongbuluke Block was likely temporarily connected to the Qilian Block and Tarim Craton, forming a single continuous block with similar Grenville age during the late Mesoproterozoic to early Neoproterozoic (1.1–0.9 Ga). [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is located in the eastern part of the Tethys-Himalayan megatectonic domain and consists of a series of microplates that successively accreted to the southern edge of the Eurasian Continent. These microplates have undergone complex evolutionary processes during rifting, drift and collision. The gravity and magnetic anomalies show that the anomaly characteristics on the Tibetan Plateau is significantly different in the north-south direction, from the Qaidam Microplate to the Lhasa Microplate. In this paper, we apply an improved Logistic Filter method, combined with the upward continuation of gravity anomalies, to identify multi-scale tectonic boundaries in the Tibetan Plateau region. The results show that the edge detection results correspond well in space with fracture zones and suture/ophiolite zones. Also, there are clear discontinuities along both sides of the middle and western sections of the Bangong-Nujiang Suture Zone and the eastern section of the Jinshajiang-Ailaoshan Suture Zone. We refined the boundaries of five microplates, including the South and North Qiangtang and the South, Central and North Lhasa, in the southern Tibetan Plateau. Then, we analyzed the evolutionary processes of these microplates and the transformation of the types to which the microplates belonged during different historical periods by combining relevant evidences from other geological records and plate reconstruction. These microplates are strongly related to the evolutionary history of the Tethys Ocean. The closure of the Neo-Tethys Ocean triggered a large-scale orogeny between the Indo-Asian continents, and these microplates were eventually accreted in the orogenic belt. We analyze the formation patterns and boundary types of microplates in the evolutionary process and then divide into three stages, i.e., rifting-derived, accretion-derived, and subduction-derived stages. The transformation patterns of microplate types at different stages provide a new perspective for the study of the evolution of mega-orogenic belts. • Tectonic interpretation and microplate division of the Tibetan Plateau with gravity and magnetic data. • Multi-scale edge detection at different depths on the Tibetan Plateau by the improved Logistic Filter method. • A transformation pattern of microplate types during the evolution of Qiangtang and Lhasa microplates. [ABSTRACT FROM AUTHOR]

Southeast China is characterized by widespread Mesozoic igneous rocks, which have drawn a great deal of attention in recent decades because of their tectonic significance and related large-scale mineralization. Among these igneous rocks, The Tangquan pluton in Southwest Fujian Province is the only adakitic pluton that has been discovered within the Cathaysian Block. It is mainly composed of a central unit of granodiorite with peripheral granodioritic porphyries. Two medium-grained granodiorite samples have zircon U-Pb ages of 162.2 ± 2.0 Ma and 163.0 ± 1.4 Ma, indicating intrusion in Middle Jurassic times. Adakite-like geochemical features of the pluton include high Sr/Y (46.7) and (La/Yb)N (25.5) values, and low Y (12.2 ppm) and Yb (1.04 ppm) abundances. All samples have low εNd(t) values (average −9.49) and high initial 87Sr/86Sr ratios (average 0.708242). These results suggest that the adakitic rocks were generated by partial melting in thickened crust. The Tangquan pluton probably formed during the extrusion collision of microcontinents within the Cathaysian Block related to subduction of the Pacific Plate, which caused crustal thickening and partial melting of Neoproterozoic crust with arc-like magmatic characteristics. Because the extrusion collision occurred between microcontinents in an intraplate (Cathaysian Block) setting, the effects of the extrusion collision were not as strongly felt as those involved in the Jiangshan-Shaoxing Fault along which numerous adakitic rocks were emplaced with related porphyry-type copper deposits. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Magma mingling between mafic and felsic magmas is a plausible mechanism for the formation of mafic microgranular enclaves (MMEs) which are common worldwide. Through dissecting the MMEs with parentage of magma mingling, it can be ascertained how two types of magmas with contrasting physicochemical properties interplay and what implicit information magma mingling records in crust-mantle interaction. Here we present petrography, geochronology, major and trace elements, Sr-Nd-Hf isotopes, and mineral geochemistry for rock associations from the North Qaidam orogen, which provides new insights into the processes of magma mingling, petrogenesis of large-volume host plagiogranites and crust-mantle magmatic interaction. MORB (mid-ocean ridge basalt)-like and arc-like magmas can be distinguished from mantle-derived mafic samples with zircon U Pb ages ranging from 480 to 465 Ma. MORB-like magmas originated from a MORB-type asthenospheric mantle, whereas arc-like magmas were derived from an ultra-depleted asthenospheric mantle as a result of consecutive extraction of MORB-like magmas and late-stage metasomatism by subduction-related aqueous fluids. Given the content discrepancies for major oxides, gabbro-dioritic MMEs are formed by incipient mechanical mingling between gabbro-diorite magmas and felsic plagiogranite magmas. MMEs and host plagiogranites yield coincident crystallization ages of 478 Ma and overlapped whole-rock Sr Nd ((87Sr/86Sr) i = 0.7044–0.7052; ε Nd (t) = +4.6 ∼ +5.6) and zircon Hf isotopes (ε Hf (t) = +13 ∼ +16). The host plagiogranite magmas are most likely derived by partial melting of pre-existing analogues of gabbro-diorite intrusions under the condition of consecutive underplating of different batches of cognate magmas over short time scales, which in turn determine the consistent isotope compositions between MMEs and host plagiogranites. As for mineral geochemistry, the plagioclases with the highest An% value and the hornblendes implying the highest melt water content, appear within the MME-bearing plagiogranites next to the chilled margin of MMEs, illustrating that aqueous fluid and heat transfer play a pioneering but finite role in incipient magma mingling. The consecutive underplating of cognate mantle-derived magmas as an ultimate engine leads to the partial melting of newly emplaced basites to form massive plagiogranite magmas and geochemically stratified crust. With magma ascent into a shallow level of crust, magma mingling between underplated mafic magmas and resultant plagiogranite magmas is finally realized. • Enclaves originated from an ultra-depleted mantle metasomatized by subduction fluids. • Finite transfer of fluid and heat appeared from enclaves to hosts in magma mingling. • Consecutive underplating of cognate magmas resulted in overlapped isotopic signatures between enclaves and hosts. • Large-volume host plagiogranites derived from partial melting of antecedent basites. [ABSTRACT FROM AUTHOR]

The Oulongbuluke Block, which is located in the northeastern margin of the Tibet Plateau, has traditionally been considered to be a fragment of the Tarim Craton. Here we present a systematic petrologic, geochemical, and zircon U-Pb and Hf isotopic investigation on mafic granulite and migmatite in the Oulongbuluke Block. The mafic granulite is mainly composed of clinopyroxene, orthopyroxene, plagioclase, amphibole and quartz, with peak metamorphic P-T contions of 6.5–8.8 kbar, 745–770 °C. Macroscopic and microscopic observations provide strong evidence for in situ partial melting of the felsic gneiss involving breakdown of biotite within the Oulongbuluke Block. The Pl-rich leucosomes with positive Eu anomalies and higher Sr contents were generated as the early-formed feldspar cumulate, and the Kfs-rich pegmatite with negative Eu anomalies and lower Sr contents may represent percolating fractionated melt that was trapped during cooling. Zircon U–Pb dating and Hf isotopic analyses on the mafic granulite and migmatite of the Oulongbuluke Block reveal two distinct age populations: the early Paleoproterozoic (∼2.37 Ga) and late Paleoproterozoic (1.93–1.92 Ga). The ∼2.37 Ga magmatic zircon cores of the migmatite have ε Hf (t) values between −4.3 and 0.4, with two-stage Hf model ages (T DMC ) mainly between 2.82 Ga and 3.05 Ga. The age of 1.93–1.92 Ga obtained from the mafic granulite and migmatite is interpreted as the age of Late Paleoproterozoic metamorphism and anatexis. Most of the 1.93–1.92 Ga metamorphic and anatectic zircons have significantly lower 176 Lu/ 177 Hf ratios but higher 176 Hf/ 177 Hf (t) values than the inherited magmatic zircon cores, which demonstrates that both the zircon U–Pb and Lu–Hf isotope compositions were significantly reset during metamorphism and anatexis. The late Paleoproterozoic metamorphic and anatectic event coincided with global orogenic events that are recorded in many continental fragments, which suggests their link to the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Paleozoic syn-collisional I-type granitoids in the North Qaidam orogen reflect crustal reworking rather than growth. • Early Paleozoic granitoid magmas originated from Proterozoic and Paleozoic crustal sources in the North Qaidam orogen. • Inhomogenous thicknesses of overriding plate triggered by syn-collision induced hot mantle convection and granitoid incubation. Granitoids constitute the major theme in evaluating the growth and reworking of continental crust on Earth. Here we present U-Pb geochronology, geochemistry and Sr-Nd-Hf isotopes of the early Paleozoic granitoids emplaced during pre- and syn-collisional stages in the North Qaidam orogen to gain insights on the granitoid typology, genetic mechanism, as well as the implications for the evolution of continental crust. The pre- and syn-collisional granitoids in this region all belong to I-type granite and are derived from different continental crustal sources including late Mesoproterozoic to early Neoproterozoic metamorphic crystalline basement, and juvenile continental crust formed during early Paleozoic oceanic subduction. Granitic magmas derived from the two sources underwent a series of magmatic processes such as mixing or assimilation, which lead to the transitional geochemical and isotopic features, suggesting that besides source components, magmatic processes from melt extraction to granitoid emplacement also exerted an important influence on the formation of these granitoids and crustal maturation. Although S-type granitoids are commonly taken as the fingerprint for continental collision, our study emphasizes that the role of I-type granites formed in syn-collisional setting should not be underestimated. Besides subducted slab processes such as roll-back, retreat, or break-off, we propose a novel geodynamic model which envisages that the lateral inhomogeneity in lithospheric thickness triggered by continental collision within the overriding plate above subduction zone controlled the magmatism. Both growth and reworking of continental crust occur during oceanic subduction, whereas syn-collision setting is dominated by continental crust reworking as in the North Qaidam orogen. [ABSTRACT FROM AUTHOR]

• The Baibuziwan area has experienced three stages of metamorphism and anatexis at ~1.95 Ga, ~1.90 Ga, ~1.85 Ga, respectively. • It is confirmed for the first time that Baibuziwan migmatites were formed via Late-Paleoproterozoic fluid-fluxed melting. • The lithosphere after collisional orogeny of the Khondalite Belt may have experienced repeated asthenospheric upwelling. The metamorphism and anatexis of the Khondalite Belt may provide key information for the Late-Paleoproterozoic collisional orogeny of the North China Craton (NCC). Migmatites formed by anatexis are widely developed in the Daqingshan Complex, central Khondakite Belt. However, the timing and anatectic regime of these migmatites have not been constrained. In this paper, we present systematic petrographic, whole-rock geochemical, Sr-Nd isotopic, zircon U-Pb and Hf isotopic investigation of the Baibuziwan stromatic migmatite and different types of leucosome in the northwestern Daqingshan Complex. The results show that: (1) the metamorphic rocks in Baibuziwan underwent in-situ to in-source partial melting, and the anatectic melts migrated and gathered in different degrees; (2) the ∼2.37 Ga Bt-Hbl-Pl gneiss in the Daqingshan Complex is possible protolith of the Baibuziwan migmatites; (3) the Baibuziwan migmatites have experienced three stages of metamorphism and anatexis in the Late-Paleoproterozoic, i.e., ∼1.95 Ga, ∼1.90 Ga, ∼1.85 Ga; (4) the anatectic regime of the Baibuziwan migmatites is fluid-fluxed melting, which has been proposed for the first time in Daqingshan Complex. Combined with previous studies, we suggest that following the collisional orogeny, the thinned lithosphere of the Khondalite Belt may have experienced asthenospheric upwelling. The lower crust of the Daqingshan complex was heated and dehydrated repeatedly, and the generated fluid poured into the overlying crust, which eventually led to the episodic metamorphism and fluid-fluxed melting in the Baibuziwan area. [ABSTRACT FROM AUTHOR]

Kyanite eclogites can provide insights into global orogenic processes within subduction-collision zones. Here we present an integrated study of the petrography, mineral chemistry, zircon U-Pb geochronology, and whole-rock geochemistry of granulitized kyanite eclogites from South Altyn Tagh, located at the northern margin of the Qinghai-Tibet plateau, China. Our results suggest that the rocks experienced eclogite-facies metamorphism (27–37 kbar, 1030–1068 °C), followed by a high pressure-ultra-high temperature (HP-UHT) stage (17–20 kbar, 945–1033 °C), isothermal decompression, and a medium pressure-(ultra)-high temperature (MP-(U)HT) (10–12 kbar, 810–950 °C) granulite-facies overprint. Zircon U-Pb dating yielded a weighted mean U-Pb age of ca. 500 Ma for the metamorphic domains, which is interpreted as the timing of HP-UHT metamorphism. In contrast, the age of ca. 800 Ma recorded by the inherited cores of zircon grains is considered to represent the protolith formation age. High Al 2 O 3 and CaO and relatively low MgO and FeO contents, LREE enrichment and nearly flat HREE patterns, and enriched Sr-Nd isotopic compositions suggest that the protoliths of the granulitized kyanite eclogites were likely derived from an enriched mantle source affected by crustal contamination. These results, together with previous research on these associations suggested that the protoliths of granulitized kyanite eclogites and associated garnet peridotite in the Bashiwake area are derived from mafic-ultramafic intrusions composed of plagioclase-rich gabbroic rocks and olivine-rich cumulates. These mafic-ultramafic intrusions were possibly generated by plume-induced melting related to the rifting of the Rodinia supercontinent during the Neoproterozoic, and were later subjected to early Paleozoic metamorphism. The geodynamic model proposed envisages continental subduction followed by relamination of felsic and mafic-ultramafic associations at the base of the lower crust, which were subsequently exhumed, forming diapir-like bodies. Our results, combined with those from previous studies, not only provide insights into the processes of continental collision to exhumation, but also provide significant constraints on the geotectonic processes leading to the formation of HP rocks within subduction-collision orogens. • The U-Pb dating of metamorphic zircons at ca. 500 Ma represented the HP-UHT stage. • The distinct metamorphic events were documented by Y+REEs concentrations in the garnet grain. • REE-based thermobarometer suggests the granulitized kyanite eclogite has recorded the UHP metamorphism. • A tectonic model of subduction-relamination is proposed for the geodynamic evolution of the granulite-peridotite unit. [ABSTRACT FROM AUTHOR]

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

The article focuses on the study with the relationship between metamorphism, anatexis, deformation and exhumation mechanism of ultra high-pressure (UHP) metamorphic rocks in collisional orogen. It mentions microscopic evidence for in situ partial melting, as well as the geochemistry, zircon and isotopic results of migmatite from the North Qaidam. It also mentions zircon crystallization from anatectic melt for petrogenesis and the dynamic mechanism of anatexis.