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Multiple models exist for forming continental crust (e.g. mantle plumes, relamination, arc magmatism), each with different implications for water budget and distribution. Arc systems produce garnet-pyroxene rich rocks within lower crust and these are generally defined as eclogite (metamorphosed basalt) or arclogite (igneous cumulate). The former should be dehydrated and the latter hydrated. By quantifying water content and trace elements of nominally anhydrous minerals (NAMs) from lower crustal rocks we may assess the mode of their formation. Analyses of Proterozoic, kimberlite-hosted two-pyroxene garnet granulite xenoliths from State Line, CO suggest an igneous origin. Using energy dispersive spectroscopy (EDS) maps and average mineral water contents, we find that whole rocks contain 100 to 650 ppm H2O, with clinopyroxene as the main water-bearing NAM. Analyses of Paleozoic amphibole gabbronorites from the exhumed Famatinia Arc, Argentina indicate secondary mineralization of hydrous phases with amphibole being the primary carrier for water. Additionally, comparison of observed trace element partitioning between NAMs in xenoliths shows that 1) reconstructed bulk rocks can “see through” the host magma contamination, but 2) care must be taken to account for accessory minerals, which may incorporate significant trace elements, in reconstructing bulk compositions. Comparison of xenolith vs. exhumed arc lower crust suggests that the latter may experience retrogression and re-equilibration of NAM water content, resulting in re-partitioning that is not representative of the original hydration state at depth.

The Himalaya Terrane of southern Tibet exposes successive shallow-marine carbonate deposits from the Lower to Upper Triassic, and is a key region for studying the Triassic conodont biostratigraphy at the northern margin of the Indian Plate. On the basis of newly collected samples from the Kangshare and Laibuxi formations at the Tulong section, 11 conodont species of 7 genera were identified, and four conodont zones were established, namely, the Novispathodus abruptus Zone (lower Spathian, first reported in Tibet), the Columbitella jubata Zone (middle Spathian), the Triassospathodus symmetricus Zone (upper Spathian), and the Chiosella timorensis Zone (lowermost Anisian) in ascending order. The first occurrence (FO) of Chiosella timorensis indicates the Olenekian–Anisian boundary (OAB) at Bed 25, upper part of the Kangshare Formation. The regional and global correlation of these conodont zones is synthesized.

South China, India, and their derivative blocks preserve many similar magmatic and sedimentary records related to the tectonic transition from Rodinia to Gondwana. They provide crucial insights into not only the paleogeographic correlation between them but also the geodynamic mechanism for such a transition. Our new results, combined with published data from these blocks, reveal that South China remained linked with India at least from ca. 830 Ma to ca. 510 Ma and formed the South China–India Duo, which is located at the western margin of Rodinia. The identical magmatism and sedimentation reflect that double late Neoproterozoic rift systems in the South China–India Duo developed owing to the rollback of subducting oceanic slab beneath them. For example, an intracontinental rift developed along the Jiangnan–Aravalli–Delhi fold belt, which separated the Yangtze-Marwar block from the Cathaysia-Bundelkhand block. Another intra-arc rift developed contemporaneously along the northern and western margins of the Yangtze block, through the Marwar terrane of western India, and then into the Seychelles and Madagascar terranes. Such an intra-arc rift is the most feasible explanation for the common development of coeval arclike and extension-related magmatic rocks and extensional sedimentary sequences on the western margin of the South China–India Duo, in Seychelles and Madagascar, and even at other subduction zones. South China was finally separated from Indian Gondwana at ca. 510 Ma due to the opening of the Proto-Tethys Ocean.

Diachronous opening of the Rheic Ocean and separation of Avalonian–Cadomian terranes from Gondwana began with a change from an active to passive margin in the late Ediacaran to early Cambrian. During the Cambrian, extension within these terranes was recorded by magmatism and by the development of sedimentary basins. However, the timing, style, and kinematics of this transformation still remain poorly understood and plate-scale models vary significantly. To address this issue, the Přibram–Jince basin in the Bohemian Massif was chosen as a case study since it preserves an excellent record of Cambrian rifting. Here, after Cadomian subduction ceased at ∼527 Ma, extension initiated and a thick pile of continental siliciclastics was deposited in the basin between ∼515 Ma and ∼499 Ma, interrupted by marine transgression at ∼506–503 Ma. Our field, paleocurrent, and rock-magnetic data suggest that the source areas were located to the ∼ESE and to the ∼SW of the basin during the deposition of the lower and upper formations, respectively. Sediment sources changed accordingly from distant metamorphic basement (Gondwana?) and Cadomian volcanic arcs and an accretionary wedge underlying the basin. This redirection marked a change in the tectonic evolution of the basin from orthogonal to dextral oblique extension that enlarged the basin into a pull-apart structure. Integrating this depositional and tectonic record into a large-scale picture, we suggest that strike-slip movements along the former Avalonian–Cadomian belt controlled the diachronous opening of the Rheic Ocean. An inherited suture in the Avalonian ribbon terrane facilitated complete rifting and rift–drift transition while the Cadomian terranes remained attached to Gondwana. The kinematics of this event remains controversial. Either it was opposite along the westerly (sinistral) and easterly (dextral) segments of the belt, which may be explained by interaction with an intervening spreading center, or it was the same dextral transtension.

Terranes are passengers within drifting oceanic plate, and ride with the plate to subduction plate boundaries. Although oceanic lithosphere readily subducts into the mantle at the plate boundary, terranes may resist sinking or not, depending on a variety of controlling factors that are not very well understood. Further, the tectonic development of terranes prior to their arrival at a subduction zone is not well documented. We performed numerical experiments to explore these unknowns of terrane geodynamics during the whole pre- to post-collisional period. Our analyses reveal that terranes can undergo considerable extension prior to their arrival to subduction plate boundaries owing to the pull force exerted by sinking oceanic slabs. Increasing terrane crustal thickness, decreasing terrane width or imposed convergence velocity, and an intra-oceanic subduction setting aggrandizes the pre-collisional terrane extension. The numerical models identify increasing terrane crustal thickness and width, and decreasing imposed convergence velocity as factors that promote terrane accretion. Additionally, having a continental overriding plate at the subduction boundary increases the propensity for terrane accretion. Some intra-oceanic subduction experiments demonstrate ablative subduction and subduction polarity reversal events in connection with terrane collisions/subduction. We compare our models to the evolution of a controversial Tethyan terrane, the Nilufer oceanic plateau. Our models suggest that the Nilufer terrane may have undergone pre-collisional extension owing to the pull of the sinking Tethys Ocean plate. Further, uninterrupted subduction of the Tethys Ocean, despite the accretion of the Nilufer terrane, is illustrated by our results which have implications on other regions along the Tethyan orogenic belt.

Ophiolite nappes, encompassing dismembered oceanic lithosphere sections, in the Eastern Desert of Egypt are mainly confined to Tonian-Cryogenian inter-terrane sutures. A cohesive geodynamic model of these ophiolites remains elusive in light of the variably obliterated field relationships and lack of ample geochronological information. Available geochemical data of the well-studied ophiolites lead to different interpretations of mid-ocean ridge, back-arc and/or fore-arc affinities. Relevant geochronological data are likewise heterogeneous in terms of methods and the dated lithologic units. Here, we attempt to constrain the timing and genesis of some Eastern Desert ophiolites by using new SIMS zircon U-Pb and oxygen isotope data of gabbros from four different ophiolites. The new zircon U-Pb ages and oxygen isotope values integrated with available geochemical data constrain ages of 737 ± 6 Ma and 720 ± 6 Ma and fore-arc origin of the Wadi El-Sid and Gabal Abu Dahr-Abu Siayil ophiolites, respectively. The δ18O(Zrn) values of these fore-arc ophiolites (+2.5 to +8.5‰) deviate significantly from primitive mantle values, suggestive of substantial degrees of subduction-induced metasomatism. The Gabal El-Rubshi and Wadi Ghadir back-arc ophiolites returned younger and mutually similar ages (702 ± 5 Ma and 698 ± 4 Ma, respectively) and less heterogeneous δ18O(Zrn) values (+3.1 to +6.1‰). Excluding outliers, most measured δ18O(Zrn) values are indistinguishable from the unaltered MORB values and the restricted mantle-like δ18O range. Results of the present study suggest multiple arc-fore-arc accretion events and an extensive late Tonian back-arc basin opening event in the evolution of the Eastern Desert accretionary belt. Subduction tectonics continued to stabilize the immature arc crust ∼750–720 Ma and a tapered back-arc spreading ridge engendered at ∼700 Ma. The final terrane accretion and suturing could have been associated with subduction-related melts that circulated and locally metasomatized back-arc ophiolites. This model is in broad agreement with the recently advocated ∼720 Ma plate reorganization in the closure of the Mozambique Ocean during the course of Gondwana assembly.

Precambrian metamagmatic complexes of the Zhingeldy and Kendyktas blocks of the Zheltau and Chu-Kendyktas terranes of the SW part of the Central Asian Orogenic Belt (CAOB) consist of predominant Neoproterozoic orthogneisses with the estimated protolith ages of ca. 790–800 Ma, and subordinate epidote and garnet amphibolites, metabasalts and metadolerites of the lower metamorphic grades. The orthogneisses are characterized by negative eNd(t) values of −12 to −4 with Nd model ages of 2.3–1.7 Ga, indicating their protoliths could have formed by a reworking of the Palaeoproterozoic crustal materials. Precambrian metavolcanic rocks in the studied region are rhyolites with the estimated crystallization ages of ca. 800–830 Ma, and are associated with metabasalts. Metasedimentary complexes in the studied region consist of intensively retrogressed garnet-mica schists interlayered with marmorized limestones, metasilicic rocks, epidote and garnet amphibolites and strongly altered eclogites. The inferred protoliths of the garnet-mica schists are terrigenous rocks accumulated during the latest Ediacaran – middle Cambrian and formed from Mesoproterozoic (ca. 1.0 Ga) and to a lesser extent Palaeoproterozoic felsic source rocks (ca. 1.6–1.7 Ga and ca. 2.5 Ga). The garnet-mica schists of the Kendyktas block have negative eNd(t) of −13.4 and a model age tNd(DM) of 2.2 Ga, implying formation of their protolith from Palaeoproterozoic crustal source. The studied Zheltau and Chu-Kendyktas terranes from the SW part of the CAOB have much in common in terms of Precambrian and Early Palaeozoic evolution and chemical compositions of the key rock types. The presence of the Early Precambrian rocks (Zheltau terrane), an abundance of the Late Mesoproterozoic (1000–1100 Ma) detrital zircons in the Ediacaran-Cambrian metasedimentary complexes and a wide distribution of the Late Neoproterozoic magmatism, are distinctive features of the studied terranes. We refer such Precambrian terranes of the western CAOB to the Ulutau-Moyunkum group where tectono-magmatic evolution is consistent with that observed from the northern part of the Tarim craton. Our results also aid comprehensive correlation of metamorphic complexes of the Precambrian terranes from the SW CAOB.

Mechanisms of syn-collision magma generation are unclear due to the uncertainty in defining the term collision. We address this issue by presenting detailed petrographic, chronological, and geochemical data for the Tanggula Batholith located immediately to the north of the Longmu Tso–Shuanghu suture zone (LSSZ) in northern Tibet. Zircon LA–ICPMS U–Pb dating suggests that the Tanggula Batholith was emplaced at 235–226 Ma. Samples from the batholith show variable SiO2 of 66.6–80.6 wt% and are characterized by high normative corundum (1.09–4.35 wt%) and high aluminum saturation index (A/CNK = 1.05–1.40). These samples exhibit high initial 87Sr/86Sr (0.7165–0.7214), negative whole-rock eNd(t) (−10.1 to −8.5), eHf(t) (−8.7 to −6.3), enriched Pb isotope compositions, and variable zircon eHf(t) values (−29.9 to +5.6), as well as variable zircon δ18O value (6.90–9.22‰). These signatures are characteristic of S-type granites, and were derived from anataxis of metasedimentary rocks from the Qiangtang Terrane with input from mantle-derived components. We propose that the Tanggula Batholith was emplaced in a syn-collisional setting following closure of the Longmu Tso–Shuanghu Ocean along a north dipping subduction zone based on: the timing of high-pressure, low-temperature metamorphism at 244–221 Ma marking collision between Southern and Northern Qiangtang; the timing of exhumation of metamorphic rocks at ~223–204 Ma; and, bimodal volcanism (225–202 Ma) associated with slab breakoff at 220–215 Ma.

Resolving the time of rifting of the Black Sea basin is critical to reconstructing the tectonic evolution of the Pontides arc in northern Turkey. U–Pb geochronology of detrital zircons from Middle Jurassic, Upper Cretaceous, and lower Eocene formations in the Eastern Pontides (NE Turkey), as well as published data from circum-Black Sea terranes, reveals that sediments preserved along with the northern (East European Craton-Scythian Platform) and southern (Eastern and Central Pontides-southern flank of the Greater Caucasus-Transcaucasus) margins of the Eastern Black Sea basin display distinct detrital provenances. The U–Pb detrital zircon ages of the sedimentary samples from the Eastern Pontides have distinct populations with ages of ~650–540, ~200, ~170, ~80, and ~50 Ma. In contrast, the ages of the sedimentary samples from the northern Black Sea terranes are characterized by age peaks of ~1400 and ~1100 Ma compared to those of the Eastern Pontides. Only a few detrital zircons in the range of ~650–540 Ma and

South Altyn Tagh contains ultrahigh-pressure (UHP) terranes that have been exhumed from ~300 km mantle depth. Previous zircon U–Pb geochronology has yielded an eclogite-facies age of ca. 500 Ma and a high-pressure (HP) granulite-facies retrograde age of ca. 450 Ma in the Jianggalesayi area in the western segment of South Altyn Tagh. However, in the eastern segment (Yinggelisayi and Danshuiquan localities), an age range of 500–480 Ma has been determined, and it remains uncertain as to whether this age range represents the timing of the peak metamorphic stage or the retrograde overprint. Our study of newly discovered retrograde eclogite in the Danshuiquan locality shows that it underwent three stages of metamorphism, under eclogite-facies, HP granulite-facies and amphibolite-facies P–T conditions of 2.5–4.0 GPa and 870–1050 °C, 2.0–1.4 GPa and 830–940 °C, and 0.7–1.3 GPa and 704–880 °C, respectively. The decompression-dominated P–T path evolved mainly after crossing the solidus, indicating marked retrograde modification under melt-bearing conditions. LA–ICP–MS and SIMS zircon U–Pb dating yielded ca. 500 Ma eclogite-facies and ca. 484 Ma granulite-facies retrograde ages and a later retrograde age of ca. 452 Ma. The clockwise P–T–t path indicates rapid exhumation from eclogite-facies to granulite-facies within around 16 Myr, which is faster than that of the UHP rocks in the western segment. Thus, the HP–UHP rocks in South Altyn Tagh suggest a differential exhumation process for the eastern and western segments. The distinct HP–UHT metamorphism and rapid exhumation of (U)HP rocks in the eastern segment likely resulted from local mantle heating. The continuing P–T evolution of the (U)HP rocks under UHT conditions during exhumation led to a pervasive granulite-facies overprint in the eastern segment of the South Altyn Tagh. The rapid exhumation recorded in the eastern segment provides valuable insights into the exhumation mechanism of ultra-deep subducted UHP terranes.

Due to the high density at mantle depths, subducted oceanic crust rarely exhumes to the surface of Earth, making it challenging to determine the evolution and dynamic behavior of oceanic crust. The Sumdo eclogite-bearing metamorphic belt, located between the north and south Lhasa terranes in Tibet, is a natural laboratory for studying the metamorphic evolution of oceanic eclogites. We combined phase equilibrium modeling with detailed petrological investigations for the newly discovered Xilang eclogite from this belt and obtained near-peak metamorphic conditions of 539 °C at 1.84 GPa and a steep exhumation P–T path. These values are much lower than published for the other areas of this belt. Quartz inclusions sealed in garnet from high-pressure rocks are known to preserve residual pressures during exhumation, which can be used to reexamine the peak metamorphic conditions of eclogites in the Sumdo metamorphic belt. We analyzed quartz from three different areas in the belt, including Xilang, Jilang, and Xindaduo, with laser Raman micro spectroscopy. Xilang eclogite preserved the highest residual pressure of 0.53 ± 0.07 GPa in the quartz stability field. A systematic comparison of the residual pressures of different eclogites revealed that not only the peak metamorphic conditions but also the exhumation rate of the host rocks controlled the residual pressure. Hence, the Xilang eclogite may record lower peak P–T conditions, because it exhumed differently than the eclogites from the other areas in the Sumdo metamorphic belt. Combined with numerical modeling, the residual pressures obtained by Raman spectroscopy may be a new way to compare the metamorphic conditions of eclogites and to obtain geochronological information in addition to isotopic investigations.

The evolution of the Mozambique Ocean spans the Rodinia and Gondwana supercontinent cycles playing a key role in Earth history. Integrated petrological, geochronological, geochemical, and isotopic data on the Neoproterozoic units from the Lhasa terrane, Tibet, constrain the magmatic and metamorphic evolution of the ocean. Our results reveal two magmatic (ca. 695 Ma and ca. 671 Ma) and two metamorphic (ca. 700 Ma and ca. 650 Ma) pulses. Gabbros define the first magmatic suite. They have within-plate affinities and experienced crustal contamination. Their positive zircon eHf(t) (+1.6 to +9.6) and whole-rock eNd(t) (+2.7 to +6.1) values are indicative of a depleted mantle source. Gabbros from the second magmatic event belong to the tholeiitic series, lack evidence for crustal contamination, and are geochemically similar to E-MORB. They have negative to positive zircon eHf(t) (−3.2 to +1.5) and low positive whole-rock eNd(t) (+1.4 to +2.0) values, and were probably derived from an E-MORB-type enriched mantle source, slightly modified by subduction components. Evidence for the metamorphic events (ca. 700 and ca. 650 Ma) was obtained from U Pb dating of zircon rims of marbles and gabbros, which are characterized by low Th/U ratios (0.01–0.07) indicative of a metamorphic origin. Integrating previous studies with the data presented in this contribution, we suggest that the history of the Lhasa terrane was linked to the evolution of the Mozambique Ocean. The older mafic magmatism (ca. 695 Ma) and metamorphism (ca. 700 Ma) formed during terrane accretion processes along an active continental margin to the ocean. The relatively younger mafic magmatism (ca. 671 Ma) provides a record from an oceanic fragment that was metamorphosed (ca. 650 Ma) during closure of the Mozambique Ocean.

The timing of ocean closure and thermal evolution of the crust in the Bangong–Nujiang suture zone (BNSZ) in central Tibet, which separates the Qiangtang terrane to the north and the Lhasa terrane to the south, are controversial. In this study, we combine petrology, zircon U–Pb geochronology and phase equilibrium modeling to determine the P–T–t paths of newly discovered retrograde eclogites and retrograde granulites from the Amdo complex in the central part of BNSZ. Retrograde eclogites, which occur in the north as lenses in the orthogneisses with a prominent migmatitic texture, record decompression with heating P–T paths from medium-temperature eclogite-facies P–T fields at ~23–24.5 kbar and ~610–655 °C to high-pressure granulite-facies P–T fields at ~10.5–16.5 kbar at ~680–775 °C, followed by nearly isothermal decompression to the P of ~9 kbar at c. 182–181 Ma and further decompression. By contrast, the south orthogneisses without any migmatitic structure host lenses of retrograde granulites. They record “hairpin” clockwise P–T path characterized by compression and heating from ~5 kbar at ~450 °C to peak granulite-facies P–T conditions of 11.5–13 kbar at 640–725 °C, followed by an isothermal decompression to the P of ~8–10 kbar at c. 182 Ma and near isobaric cooling. The spatial relations (retrograde eclogites in the north) and higher peak P–T conditions of the retrograde eclogites, suggest the Amdo complex was a product of northward subduction beneath the Qiangtang terrane. Based on the protolith age for retrograde granulites (c. 184 Ma) and one young gabbro from the Amdo ophiolite (c. 184 Ma) that represents the intra-oceanic arc–backarc basin complex between the Qiangtang terrane to the north and the Amdo complex, we propose that both retrograde eclogites and granulites experienced fast burial to ~13–24 kbar before exhumation to ~9 kbar within 2–3 Ma.

Collision-induced subduction transference may have triggered subduction of the Neo-Tethys oceanic lithosphere. To verify this proposition, we present an integrated geochemical and geochronological studies of new and published data of the Permian-Triassic magmatism in the Lhasa Terrane. The newly identified Chongni mafic intrusions (gabbros and diorites) in the North Lhasa Terrane (NLT) were emplaced during the Early Permian (ca. 275 Ma). The mafic rocks have (87Sr/86Sr)t ratios between 0.7037 and 0.7042, and eNd(t) values between + 5.2 and + 5.8. The zircons of the Chongni mafic rock samples have eHf(t) values from + 9.1 to + 12.9. The isotopic data in conjunction with trace element features suggest that the Chongni mafic intrusions have been derived mainly by partial melting of a metasomatized mantle wedge source. The newly identified Quxu granodiorites and hornblende gabbros in the South Lhasa Terrane (SLT) were emplaced in the Late Triassic (ca. 228–203 Ma). The granodiorites are characterized by (87Sr/86Sr)t ratios of 0.7036–0.7037 and eNd(t) values of +6.6 to +6.7, while the hornblende gabbro samples have (87Sr/86Sr)t ratios of 0.7033–0.7035 and eNd(t) values of +7.3 to +7.4. The zircons of the granodiorite and hornblende gabbro samples revealed eHf(t) values of +10.3 to +14.0 and +10.8 to +16.4, respectively. The isotopic data in combination with trace element signatures suggest that the granodiorites were derived from a juvenile basaltic lower crust with a minor input of mantle components, while the hornblende gabbros are interpreted to have formed during partial melting of a formerly metasomatized depleted mantle wedge source. The Early Permian and Late Triassic magmatic rocks consistently show arc-related signatures, which probably record the northward subduction of the Sumdo Paleo-Tethys and the Neo-Tethys oceanic slabs, respectively. This evidence, in combination with that of other studies on the Permian-Triassic magmatism across the Lhasa Terrane, indicates that arc magmatism within the NLT switched to collisional magmatism at ca. 260 Ma due to the collision of oceanic islands/plateaus and, further on, the collision of the SLT with the NLT. Furthermore, the change from ca. 265–255 Ma alkaline magmatism to ca. 240–200 Ma calc‐alkaline magmatism within the SLT may reflect the geodynamic transition from lithospheric extension to Andean-style orogenesis. Therefore, we propose that subduction initiation of the Neo-Tethys oceanic lithosphere in the Tibetan Plateau resulted from the southward transference of the Sumdo Paleo-Tethys subduction zone, involving the collision of oceanic islands/plateaus and, subsequently, the collision of the SLT with the NLT. Additionally, the geological records of the Tethyan orogenic system suggest that the subduction initiation of the Neo-Tethys oceanic lithosphere is a uniform response to the collision between Cimmeria and Eurasia.

The continental collision-induced far-field intraplate deformation may be topographically separated from or coherent with the collision front, the mechanism of which is poorly constrained. Here, we build a series of 2D thermo–mechanical models to explore the controlling factors of distal orogenesis in the framework of a composite terrane sandwiched between two strong continental blocks. The model results suggest that the development of distal orogenesis requires a strong rheological heterogeneity in the overriding lithosphere. Two types of far-field collisional effects with distinct patterns of topographic evolution are identified, characterized by (I) a delayed and discrete distal orogenesis separated from the collision front by a low-relief, less-deformed terrane interior, and (II) an instant distal orogenesis subsequently integrated into a progressively growing plateau. These two types of far-field orogenesis are revealed to be analogous to the development of the Kopet Dagh and northern Tibet. The comparisons between model results and geological observations provide significant constraints on the dynamics of crustal-scale deformation propagation and the formation of distinct lithospheric architectures.

Bedded chert and siliceous shale successions previously regarded as the Silurian–Devonian rock units, distributed in the Nong Prue area, northwest of Kanchanaburi, western Thailand, yielded Lopingian (upper Permian) and Lower–Middle Triassic radiolarians. We found chert breccia layers in northern Nong Prue area, mainly consisting of angular to sub-angular chert clasts with matrices of silt-sized chert grains and clay minerals. We discriminated uppermost Pennsylvanian–Lopingian (upper Carboniferous–upper Permian) and Middle Triassic radiolarian-bearing chert clasts from four different levels of the chert breccia; 28 species of 15 genera with one radiolarian gen. et sp. indet. are identified. On the basis of sedimentary characteristics of the chert breccia, we suggest that the chert breccia is of sedimentary origin. The radiolarian assemblages reported here, together with previously known lithological and paleontological evidence, further indicate that the chert breccia was deposited in the Paleotethys with chert clasts derived from fine grained siliceous rocks in the continental margin to deep ocean basin of the Sibumasu Terrane.

The Tibet Plateau is a key region to understand the evolution of the Tethys Oceans. The finding of Permian–Triassic eclogites and Carboniferous–Triassic ophiolites indicated the existence of a Paleo–Tethys Ocean in the Lhasa terrane, although the mechanism of subduction and exhumation mechanism of the high–pressure rocks remains equivocal. Here we focus on deformation, metamorphism, and geochronology of key rocks in the Sumdo area with a view to constrain the tectonic evolution of the Tethys Ocean and the geodynamic mechanism of eclogite exhumation. Structural analysis indicates two main stages of deformation (D1 and D2) in the study area. The D1 deformation (264–235 Ma) is dominated by penetrative Sn+1 foliation and solid rheological folds, resulted from the first type eclogites (~260 Ma), with exhumation at ~240 Ma along the subduction channel. The D2 deformation (213–180 Ma) is characterized by the tight and isoclinal overturned folds and thrust faults, related with the collisional exhumation (~200 Ma) of the second type eclogite (~230 Ma). Spreading of the Bangong–Nujiang and Indus–Yarlung Zangbo Tethys Oceans triggered the closure of Sumdo Tethys Ocean, as well as their initial subduction.

The northeastern of the South China Sea (SCS) has undergone tectonic inversion from a Mesozoic convergent continental margin to a Cenozoic divergent continental margin. The remnant subduction-related structures, such as volcanic arc and forearc basin, likely preserve key clues to reveal the dynamic mechanism of this tectonic inversion. We applied ocean bottom seismometers (OBS) data, combining with multi-channel seismic data, gravity data, drilling data, and petrologic observations, to reveal geophysical and structural features of the Dongsha Basin, a Mesozoic basin in the northeastern SCS. The Mesozoic strata are characterized by large thickness (~1–8 km), relatively high P-wave velocities (3.5–5.5 km/s), high densities (2.55–2.65 g/cm3), alternating folds, and thrust faults, which are significantly different from the features of Cenozoic strata. The Dongsha Basin is flanked by a Mesozoic granitic arc to the northwest and an inferred Palaeo-Pacific subduction zone to the southeast, indicating that it is geographically located in the Mesozoic forearc region. Considering the similar Mesozoic strata detected in the southern margin of the SCS and the contemporaneous accretionary complex outcrops observed in the Palawan Continental Terrane, we propose that the Mesozoic strata in these two regions originated from a common Mesozoic forearc basin, which was broken by the forearc rifting and subsequently separated by the spreading of Cenozoic SCS. Accordingly, a continuous Palaeo-Pacific subduction system is reconstructed, including the “arc-forearc-accretionary wedge” tectonic sequences. Reviewing the mechanisms of forearc rifting globally and the retreat of volcanic arcs onshore South China, we speculate that rollback of the Palaeo-Pacific subduction slab might be one of the causes for the forearc rifting and the initial extension of the SCS.

The occurrence of pre-existing crust in orogenic belts has important implications for constraining and testing models of orogenic processes and for making paleogeographic reconstructions. Asynchronous magmatic–metamorphic rocks provide an opportunity to reconstruct the positions and constituent blocks of certain Precambrian fragments. Here we report Neoarchean to Neoproterozoic crustal rocks preserved in the North Wulan Terrane (NWT), northwestern China. Our new zircon geochronological data reveal the ca. 2.57 Ga magmatic and 2.0–1.72 Ga metamorphic events in the NWT, implying its involvement in the formation of Columbia supercontinent. Meanwhile, the NWT also recorded the 1.5–1.3, 1.1, 0.9–0.8 and 0.51–0.48 Ga magmatic-metamorphic activities, corresponding to the involvement of regional Precambrian fragments in cyclic supercontinent-related processes from Columbia to Greater Gondwana. Most of the ca. 2.57 and 0.9–0.8 Ga granites are characterized by enriched zircon eHf(t) values of –5.7 to +0.9 and –5.2 to +7.1. Moreover, some of these granites show fractionated characteristics, with high silica contents (80.3–82.3 wt% and 73.9–75.2 wt%), indicating that these rocks were derived mainly from remelting of 3.6–2.7 Ga mature crustal materials and 1.6–2.0 Ga crustal materials without or with minor contribution of juvenile materials, respectively. On the basis of these new results, regional stratigraphy, and previously determined geochemical data and tectonic signatures, it is concluded that the Quanji Massif and the Central Qilian, Hualong and North Wulan terranes probably formed a coherent Qilian–Quanji block as the southeastern extension of the Tarim Craton initiated from the Neoarchean. We propose that from the Neoarchean to early Paleoproterozoic, the primal Qilian–Quanji block was formed by long-term arc-related magma emplacement and reworking of ancient mature crustal materials in southeastern Tarim Craton. Subsequently, the juvenile Tarim–Qilian–Quanji continent was involved in tectonic cycles during its involvement in the supercontinents of Columbia and Rodinia.

Long-lived subduction and accretion of the Paleo-Asian Ocean (PAO) led to the formation of the Central Asian Orogenic Belt (CAOB). The central part of the southern CAOB is crucial to understand the tectonic evolution of the entire CAOB. However, the Paleozoic evolution and the final closure of the central PAO are controversial, and the nature of the Early Paleozoic basins is confusing. The relatively complete Paleozoic strata are well-preserved in Zhusileng area in the central part of the southern CAOB and provide an ideal object to constrain the Paleozoic tectonic setting of the PAO. In this study, detrital zircon U-Pb dating and sedimentological and paleocurrents analyses are conducted on the Cambrian-Devonian strata and Lower Permian strata. Most detrital zircons from the Cambrian-Devonian strata have Precambrian ages, while the detrital zircons from the Lower Permian strata are mainly of Paleozoic age. The North China Craton, Alxa Block and Tarim Craton are not the provenances of the Cambrian-Devonian strata. The central part of the southern CAOB was located in a passive continental margin setting during the Cambrian to Ordovician and received the detritus from the Beishan Orogenic Belt. During the Silurian to Middle Devonian, a nearly east-west-trending foreland basin that resulted from the collision between the Zhusileng-Hangwula terrane and southern Mongolian microcontinent developed. From the Late Devonian to Early Permian, bidirectional subduction of the PAO occurred between the Alxa Block and Zhusileng-Hangwula terrane, resulting in numerous arc-related magmatic rocks. Detritus in the Lower Permian strata was mainly from the Paleozoic magmatic rocks and Cambrian-Devonian strata in Zhusileng and surrounding areas. The Late Paleozoic shortening deformation and the switch of the tectonic setting from subduction/collision to post-collision occurred in the central part of the southern CAOB imply that the central PAO closed between the Early and Late Permian.

The Gangdese orogenic belt in southern Tibet records a succession of arc-trench-basin assemblages formed by the Neo-Tethyan subduction and the subsequent India-Asian collision. However, the geochronology and geodynamics of S-type granites in the northern part of the Gangdese belt are disputed. This paper describes ~190 Ma S-type granitoids outcropped in the Nyainqentanglha Range, South Tibet, focusing on their petrogenesis and their relationship with contemporaneous magmatism. There are three distinct groups of granitoids, based on field relationships, petrology, and geochemistry. The coarse-grained Group I and II granitoids are large, sheet-like bodies and exhibit high contents of incompatible elements and negative Eu anomalies. The fine-grained Group III granites form small laccoliths and have low REE contents and positive Eu anomalies. The negative eNd(t) and eHf(t) values, abundant inherited zircons, moderately light REE and LILE enrichment, and HFSE depletion indicate that the Damxung granitoids were derived mainly by the partial melting of a metapelitic source. Further studies proposed that group I and II samples with high contents of incompatible elements and negative Eu anomalies represent fractionated melts, whereas group III samples with low REE contents and positive Eu anomalies represent cumulates. The age distribution pattern of inherited zircons supports the interpretation that the Lhasa terrane rifted away from the northern margin of the Indian plate. Considering previously published data in the Lhasa terrane, we suggest that the Early Jurassic magmatism could be related to a period of subducted oceanic slab roll-back, which provides new insights into the evolution process of the Neo-Tethyan ocean realm.

The Lancang Group in SW Yunnan constitutes a pivotal component of the continental margin bounding the Proto- and Paleo-Tethys oceans, yet its formation timing, composition and tectonic affinity remain ill-defined. In this contribution, we present new zircon U-Pb age and whole-rock geochemistry data from volcanic and sedimentary rock units, which are compiled with published data, to refine the depositional age, provenance and nature of the group and its host terrane. The Lancang Group consists of five formations, two of which (Manlai and Huimin) contain abundant metavolcanic rocks. The metavolcanic rocks show a secular change in geochemistry, from EMORB-like calc-alkaline series of the ca. 495 Ma Manlai Formation, to arc-like high-K series of the Huimin Formation. Five metavolcanic samples from the Huimin Formation yielded zircon U-Pb ages between 478 ± 5 Ma and 442 ± 5 Ma. The late Cambrian-Ordovician arc magmatism is related to an active continental margin setting associated with subduction of the Proto-Tethys Ocean. The time-integrated geochemical variation shown by the volcanic rocks likely reflects evolving maturity of the arc system. The youngest detrital zircon ages of the five formations, in conjunction with age constraints from the interbedded volcanic rocks, suggest that the Lancang Group was largely accumulated during the early Paleozoic. The Lancang Terrane is reconstructed as a continental block, which formed part of the magmatically-active margin of the Proto-Tethys during the early Paleozoic. Provenance analysis based on detrital zircon age spectra and Hf isotope data indicates Gondwana affinities of the terrane. Furthermore, xenocrystic zircon ages and zircon Hf and whole-rock Nd model ages from igneous rocks support presence of Neoarchean-Mesoproterozoic basement underlying the terrane. The reconstructed Lancang Terrane bears important implications for understanding the configuration of the northern margin of Eastern Gondwana and the relationship between the Proto- and Paleo-Tethys oceans.

New palaeogeographical reconstructions for the earlier Ordovician (480 Ma), and later Ordovician (450 Ma) integrate revised longitude-calibrated palaeomagnetic reconstructions and the inclusion of synthetic plate margins within the now-vanished oceanic areas. There are substantial published differences from the previous placing of some of the continents and terranes in Asia; for example, Siberia and Gondwana have previously been placed at varied distances and relative positions in relation to the Kazakh terranes, South and North China, and Tarim. But there are only minor changes for most of the world, particularly in the North American and European areas. The global distributions of benthic trilobites and brachiopods within faunal provinces and their changes through the Ordovician are plotted, including the new term Cathay-Tasman Province for some pan-equatorial brachiopod faunas from China and Australia, and key sites and provinces are shown on the revised maps. The 30 Myrs from 470 to 440 Ma (mid Ordovician to early Silurian) saw some of the most varied and changeable climates of the whole Phanerozoic culminating in the ‘Hirnantian’ ice age. Those changes in turn much affected the rates of evolution of many benthic and pelagic animal groups which were driven by both biological and environmental causes. Global cooling during the Ordovician was a prime factor by reducing sea surface temperatures which challenged life to evolve faster and more substantially than before. That cooling was driven by decreasing atmospheric CO2, for reasons that are not fully resolved, but probably included reduced sourcing (reduced continental arc activity) combined with increased silicate weathering due to the advent of land plants and perhaps the progressive exhumation of low-latitude collisional arcs. Since long-term CO2 sinks are largely controlled by palaeogeography, the general increase in the concentration of continents in the tropics during the Ordovician increased the overall global weathering.

The theory of plate tectonics is widely accepted by scientists and provides a robust framework with which to describe and predict the behavior of Earth’s rigid outer shell – the lithosphere – in space and time. Expressions of plate tectonic interactions at the Earth’s surface also provide critical insight into the machinations of our planet’s inaccessible interior, and allow postulation about the geological characteristics of other rocky bodies in our solar system and beyond. Formalization of this paradigm occurred at a landmark Penrose conference in 1969, representing the culmination of centuries of study, and our understanding of the “what”, “where”, “why”, and “when” of plate tectonics on Earth has continued to improve since. Here, we summarize the major discoveries that have been made in these fields and present a modern-day holistic model for the geodynamic evolution of the Earth that best accommodates key lines of evidence for its changes over time. Plate tectonics probably began at a global scale during the Mesoarchean (c. 2.9–3.0 Ga), with firm evidence for subduction in older geological terranes accounted for by isolated plate tectonic ‘microcells’ that initiated at the heads of mantle plumes. Such early subduction likely operated at shallow angles and was short-lived, owing to the buoyancy and low rigidity of hotter oceanic lithosphere. A transitional period during the Neoarchean and Paleoproterozoic/Mesoproterozoic was characterized by continued secular cooling of the Earth’s mantle, which reduced the buoyancy of oceanic lithosphere and increased its strength, allowing the angle of subduction at convergent plate margins to gradually steepen. The appearance of rocks during the Neoproterozoic (c. 0.8–0.9 Ga) diagnostic of subduction do not mark the onset of plate tectonics, but simply record the beginning of modern-style cold, deep, and steep subduction that is an end-member state of an earlier, hotter, mobile lid regime

Yanshanian (ca. 200–100 Ma) metallogeny of eastern Asia was dominantly controlled by oblique subduction and rollback of the Izanagi plate, and also, more locally in the north, by closure of the Mudanjiang Ocean basin and accretion of the Bureya-Jiamusi-Khanka block and the Sikhote-Alin terranes. Although exact distances are difficult to estimate due to Early Cretaceous crustal extension, ores related to Yanshanian subduction certainly developed for more than 1500 km landward from the active trench, such as exemplified by those deposits overprinting the Paleoproterozoic Trans-North China orogen. In the northern part of the Yanshanian orogen, and thus hosted within the eastern edge of the Central Asian orogenic belt, Endako-type porphyry Mo deposits related to subduction of the Mudanjiang slab formed throughout northeast China from 200 to 135 Ma. Extensional magmatism related to rollback of the slab led to widespread Au-Ag epithermal vein development and a scattering of small Cu-Au porphyry occurrences across the same area from 125 to 100 Ma. Sinistral strike-slip motion along the continental margin in adjacent Russia, caused by the NNW motion of the Izanagi plate, led to formation of 115–95 Ma post-collisional Cu-Au porphyries, Sn-W ores associated with reduced intrusions, and orogenic gold deposits in the central Sikhote-Alin region. In the North China block, whereas early Yanshanian ore formation was relatively limited, 130–120 Ma extension-related basement uplifts were associated with formation of two of China’s most important orogenic gold provinces on the Jiaodong Peninsula and in the East Qinling; in the latter, the entire period of late Yanshanian extension may be defined by widespread 148–107 Ma Mo-rich porphyry and skarn deposit formation. To the south along the Asian margin, the oblique NW-directed subduction of the Izanagi slab was responsible for the adakitic porphyry Cu deposit formation on the eastern side of the South China block at 175–155 Ma, which continued inland for as much as 500 km to the Cathaysia-Yangtze suture. The transition at 160–150 Ma to development of the Nanling W-Sn belt in the interior of Cathaysia roughly overlaps the time of tectonic switch to slab retreat, which gradually led to seaward migration of the extension-related magmatism forming the 145–133 Ma Sn ores and 110–100 Ma high to low sulfidation epithermal deposits along the Southeast Coast belt. A period of sinistral strike-slip along the southern end of the Tan-Lu fault system was possibly responsible for a tear in the Izanagi plate and consequential S-type magmatism forming W porphyry-skarn ores of the Jiangnan belt at 145–133 Ma and I-type magmatism leading to Fe-Cu-Au skarns at the northern edge of the Yangtze block. In summary, the early Yanshanian of eastern Asia was dominated by widespread subduction-related porphyry Mo formation in the north and localized porphyry Cu formation to the south, followed by late Yanshanian development of world-class Au, Mo, Sn, and W resources during subsequent slab retreat, continental-scale extension, and strike-slip events along continental margin transform faults.

The fault-bounded Nashoba–Putnam terrane, a metamorphosed early Paleozoic, Ganderian arc/back-arc complex in SE New England, lies between rocks of Avalonian affinity to the southeast and middle Paleozoic sedimentary rocks, interpreted as cover on Ganderian basement, in the Merrimack belt to the northwest. U–Pb detrital zircon laser ablation inductively coupled plasma mass spectrometry analysis were conduced on six samples from the Nashoba terrane in Massachusetts and seven samples associated with the Merrimack belt in Massachusetts and SE New Hampshire to investigate their depositional ages and provenance. Samples from the Nashoba terrane yielded major age populations between ~560 and ~540 Ma, consistent with input from local sources formed during the Ediacaran–Cambrian Penobscot orogenic cycle and its basement rocks. Youngest detrital zircons in the terrane, however, are as young as the Early to Middle Ordovician. Six formations from the Merrimack belt were deposited between ~435 and 420 Ma based on youngest zircon age populations and crosscutting plutons, and yielded large ~470–443 Ma age populations. Three of these formations show only Gondwanan provenance. Three others have a mixed Gondwanan-Laurentian signal, which is known to be typical for younger and/or more westerly sedimentary rocks and may indicate that they are the youngest deposits in the Merrimack belt (late Silurian to early Devonian) and/or have been deposited in the equivalent of the more westerly Central Maine basin. Detrital zircon age populations from the Tower Hill Formation, along the faulted contact between the Merrimack belt and Nashoba terrane, are different from either of these tectonic domains and may indicate that the boundary is complex., Le terrane limité par des failles de Nashoba-Putnam, un complexe d’arc/arrière-arc métamorphisé gandérien du Paléozoïque précoce dans le sud-est de la Nouvelle-Angleterre, se trouve entre des roches ayant une affinité avalonienne au sud-est et des roches sédimentaires du Paléozoïque moyen, interprétées comme une couverture du socle gandérien, dans la ceinture de Merrimack au nord-ouest. Six échantillons provenant du terrane de Nashoba au Massachusetts et sept échantillons associés à la ceinture de Merrimack au Massachusetts et dans le sud-est du New Hampshire ont fait l’objet d’une analyse par spectrométrie de masse avec plasma à couplage inductif et par ablation par laser de datation U–Pb sur zircon détritique aux fins de l’examen de leurs âges sédimentaires et de leur provenance. Les échantillons provenant du terrane de Nashoba ont révélé des populations principalement âgées entre environ 560 et 540 Ma, ce qui correspond à la contribution des sources locales apparues durant le cycle orogénique édiacarien-cambrien de Penobscot et aux roches de son socle. Les zircons détritiques les plus récents dans le terrane remontent cependant seulement à l’Ordovicien précoce à moyen. Six formations de la ceinture de Merrimack se sont déposées à peu près entre 435 et 420 Ma selon les populations des âges les plus récents sur zircon et les plutons transversaux, et elles ont présenté de vastes populations âgées d’environ 470 à 443 Ma. Trois de ces formations témoignent uniquement d’une provenance gondwanienne. Trois autres évoquent de façon mixte le Gondwanien et le Laurentien, ce qui est reconnu comme un trait typique des roches sédimentaires plus récentes ou plus à l’ouest et qui pourrait révéler qu’il s’agit de dépôts plus récents dans la ceinture de Merrimack (du Silurien tardif au Dévonien précoce) ou qui se seraient mis en place dans l’unité équivalente du bassin plus occidental du centre du Maine. Les populations d’un âge sur zircon détritique de la Formation de Tower Hill le long de la zone de contact faillé entre la ceinture de Merrimack et le terrane de Nashoba diffèrent de l’un et l’autre de ces domaines tectoniques et pourraient indiquer que leur limite est complexe.

The boundary between tropical Permian faunas of the Inthanon Zone and Gondwana faunas in far NW Thailand has been long debated. Both the Late Devonian and the Permian Gondwanan platform margins lie a few kilometres west of the Mae Yuam/Mae Sariang Fault (MYMS FZ). In the Permian, the margin grades eastwards into hemipelagic radiolarites along the MYMS FZ and westwards into the Thitsiphin carbonate platform of Myanmar. The area west of the MYMS FZ is the Northern part of the West Thailand Region (NWTR). Quartz-rich limestones of Roadian age in the NWTR are succeeded by deep-water platform limestones in the NWTR and shallow-water carbonates in Myanmar and contain a distinctive fusulinid fauna including Monodiexodina which does not occur in palaeotropical terranes. A 300-m section of limestone 10 km west of the MYMS FZ contains Wordian microfauna and is placed in a deep shelf to slope environment. Carboniferous to Triassic continental margin, hemipelagic, non-hydrothermal, radiolarian cherts outcrop on either side of the Mae Yuam valley and were deposited on the upwelling margins of an ocean separating the Inthanon Zone and Sibumasu Terrane. The widely accepted allochthon model proposes that the Inthanon Zone Devonian-Triassic radiolarites were pelagic and deposited on a subducting ocean that supported seamounts with Visean to Permian tropical shallow-water carbonates lasting at least 90 my. We suggest an alternative hypothesis where the radiolarites of the Inthanon Zone were continental margin as shown by their geochemistry and deposited in deeper parts of small extensional basins with limited volcanism between long-lived, isolated carbonate platforms.

A large amount of high-quality teleseismic data is used for common conversion point (CCP) stacking of receiver functions in the Longmenshan area. The results show that a large-scale high-velocity anomaly or lithospheric delamination can completely destroy upper mantle discontinuities or erase the phase boundary of olivine, which is a very important finding and can be used to assess stagnant slabs in the mantle transition zone globally. The deepening region of the 660 km discontinuity beneath the Songpan-Ganzi terrane might indicate that the large-scale high-velocity anomaly in the mantle transition zone is a cold domain and can affect the topography of upper mantle discontinuities.

Granitoids with diverse composition and tectonic settings provide important tools for exploring crustal evolution and regional geodynamic history. Here we present an integrated study using petrological, mineralogical, zircon U-Pb geochronological, whole-rock geochemical, and isotopic data on the Late Triassic Daocheng batholith in the Yidun Terrane with a view to understanding the petrogenesis of a compositionally diverse batholith and its implications for the evolution of the Paleo-Tethys Ocean in the eastern Tibetan Plateau. The different lithological units of the batholith, including granodiorite, monzogranite, and quartz diorite, with abundant mafic microgranular enclaves in the granodiorite (MME I) and monzogranite (MME II), show identical crystallization ages of 218–215 Ma. The mineral assemblage and chemical composition of the granodiorite are identical to those of tonalitic-granodioritic melts generated under water-unsaturated conditions. The insignificant Eu anomalies and low magmatic temperatures indicate hydrous melting in the source. The relatively narrow range of whole-rock chemical and Sr-Nd isotopes, as well as the zircon trace element and Hf isotopic compositions of the granodiorite, suggest a homogeneous crustal source for the magma. Our modeling suggests that the rock was produced by 20–50% of lower crustal melting. The Daocheng monzogranites display more evolved compositions and larger variations in Sr-Nd-Hf isotopes than the granodiorite, which are attributed to assimilation and the fractional crystallization process. This is evidenced by the presence of metasedimentary enclave and inherited zircon grains with Neoproterozoic and Paleozoic ages, a non-cotectic trend in composition, and the trend shown by the modeling of initial 87Sr/86Sr ratios and Sr. The quartz diorites and MMEs showing composition similar to that of andesitic primary magma have high zircon εHf(t) values and are characterized by enrichment in LILEs and depletion of HFSEs. They were derived from the partial melting of lithospheric mantle that had been metasomatized by slab melts and fluids. The MMEs in both rocks display typical igneous texture and higher rare earth element (REE) and incompatible element concentrations than their host granites. The presence of fine-grained margins, acicular apatite, and plagioclase megacrysts suggests a magma mingling process. The overgrowth of amphibole around the pyroxene, quartz ocelli rimmed by biotite, and oscillatory zones of plagioclase are all indicative of chemical diffusion. Their enriched Sr-Nd isotopes imply isotopic equilibrium with the host granites. Based on a comparison with the coeval subduction-related magmatism, we propose that subduction and subsequent rollback of the Paleo-Tethys (Garzê-Litang Ocean) oceanic slab was the possible mechanism that triggered the diverse Triassic magmatism within the eastern Tibetan Plateau.

A careful petrologic analysis of mylonites’ mineral assemblages is crucial for a thorough comprehension of the rheologic behaviour of ductile shear zones active during an orogenesis. In this view, understanding the way new minerals form in rocks sheared in a ductile manner and why relict porphyroblasts are preserved in zones where mineral reactions are generally supposed to be deformation-assisted, is essential. To this goal, the role of chemical potential gradients, particularly that of H2O (µH2O), was examined here through phase equilibrium modelling of syn-kinematic mineral assemblages developed in three distinct mylonites from the Calabria polymetamorphic terrane. Results revealed that gradients in chemical potentials have effects on the mineral assemblages of the studied mylonites, and that new syn-kinematic minerals formed in higher-µH2O conditions than the surroundings. In each case study, the banded fabric of the mylonites is related to the fluid availability in the system, with the fluid that was internally generated by the breakdown of OH-bearing minerals. The gradients in µH2O favoured the origin of bands enriched in hydrated minerals alternated with bands where anhydrous minerals were preserved even during exhumation. Thermodynamic modelling highlights that during the prograde stage of metamorphism, high-µH2O was necessary to form new minerals while relict, anhydrous porphyroblasts remained stable in condition of low-µH2O even during exhumation. Hence, the approach used in this contribution is an in-depth investigation of the fluid-present/-deficient conditions that affected mylonites during their activity, and provides a more robust interpretation of their microstructures, finally helping to explain the rheologic behaviour of ductile shear zones.

Mare volcanics on the Moon are the key record of thermo-chemical evolution throughout most of lunar history1–3. Young mare basalts—mainly distributed in a region rich in potassium, rare-earth elements and phosphorus (KREEP) in Oceanus Procellarum, called the Procellarum KREEP Terrane (PKT)4—were thought to be formed from KREEP-rich sources at depth5–7. However, this hypothesis has not been tested with young basalts from the PKT. Here we present a petrological and geochemical study of the basalt clasts from the PKT returned by the Chang’e-5 mission8. These two-billion-year-old basalts are the youngest lunar samples reported so far9. Bulk rock compositions have moderate titanium and high iron contents with KREEP-like rare-earth-element and high thorium concentrations. However, strontium–neodymium isotopes indicate that these basalts were derived from a non-KREEP mantle source. To produce the high abundances of rare-earth elements and thorium, low-degree partial melting and extensive fractional crystallization are required. Our results indicate that the KREEP association may not be a prerequisite for young mare volcanism. Absolving the need to invoke heat-producing elements in their source implies a more sustained cooling history of the lunar interior to generate the Moon’s youngest melts., Isotopic analysis of basalt clasts returned from the Moon by the Chang’e-5 mission indicates that the rocks were derived from a mantle source that lacked potassium, rare-earth elements and phosphorus.

The Mesoproterozoic MARA terrane of western South America is a composite igneous-metamorphic complex that is important for Paleozoic paleogeographic reconstructions and the relative positions of Laurentia and Gondwana. The magmatic and detrital records of the MARA terrane are consistent with a Laurentian origin; however, the metamorphic and deformation records lack sufficient detail to constrain the correlation of units within the MARA terrane and the timing and mechanisms of accretion to the Gondwana margin. Combined regional mapping, metamorphic petrology, and garnet and monazite geochronology from the Sierra de Maz of northwest Argentina suggest that the region preserves four distinct litho-tectonic units of varying age and metamorphic conditions that are separated by middle- to lower-crustal ductile shear zones. The Zaino and Maz Complexes preserve Barrovian metamorphism and ages that are distinct from other units within the region. The Zaino and Maz Complexes both record metamorphism ca. 430–410 Ma and show no evidence of the regional Famatinian orogeny (ca. 490–455 Ma). In addition, the Maz Complex records an earlier granulite facies event at ca. 1.2 Ga. The Taco and Ramaditas Complexes, in contrast, experienced medium- and low-pressure upper amphibolite to granulite facies metamorphism, respectively, between ca. 470–460 Ma and were later deformed at ca. 440–420 Ma. The Maz shear zone that bounds the Zaino and Maz Complexes records sinistral oblique to sinistral deformation between ca. 430–410 Ma. The data suggest that at least some units in the MARA terrane were accreted by translation, and the Gondwana margin of northwest Argentina transitioned from a dominantly convergent margin to a highly oblique margin in the Silurian.

New U-Pb zircon geochronology using high-spatial resolution secondary ion mass spectrometry fills a data gap and provides crystallization ages for granitoids from the Asir composite terrane in the ...

SUMMARY A series of terranes were accreted to Eurasia in the region of what is now the Tibetan Plateau, including the Qaidam-Qilian, the Songpan-Ganzi, the Qiangtang, the Lhasa and the Tethyan Himalaya terranes. The drift history of the Qiangtang Terrane and the timing of the Lhasa–Qiangtang collision are controversial. To contribute to this topic, here, we palaeomagnetically investigate the Middle-Upper Jurassic limestones of the Yanshiping group in the Zaduo area (32.5°N, 95.2°E), in the Estern Qiangtang Terrane. Twelve sites (133 samples) were processed. A major challenge in palaeomagnetism is the possibility of remagnetization that interferes with palaeogeographic reconstructions. Both thermal and alternating field demagnetizations were carried out to isolate the characteristic remanent magnetization (ChRM). Despite the positive reversals test, rock magnetic information points to a remagnetized ChRM. The ChRM is residing in stable single-domain (SSD) magnetite grains with cogenetic superparamagnetic (SP) particles. The co-occurreance of SSD and SP magnetites generates distinct rock-magnetic properties often refer to as the ‘remagnetized fingerprint’ in limestones. This remagnetization process is also manifested by the widespread occurrence of gypsum veinlets in the limestones. The site-mean direction of the 12 sites after tilt-correction is Ds = 30.6°, Is = 35.6°, κs = 182.9, α95 = 3.2°, corresponding to a palaeolatitude of ∼19.7°± 2.8°N for the study area. The corresponding palaeopole (59.8°N, 202.7°E with A95 = 2.8°) points to an NRM acquired after the India–Eurasia collision. The original sediments were likely anoxic because of the high organic carbon fluxes that prevailed during their deposition. After the India–Eurasia collision, it is envisaged that conditions became more oxic, giving rise to oxidation of iron sulphides to authigenic magnetite and the CRM acquisition. The Zaduo area in the Eastern Qiangtang Terrane has experienced ∼15.7° ± 3.2° (∼1740 ± 350 km) of latitudinal crustal shortening since the Eocene. In addition, the clockwise rotation responding to the India–Eurasia collision is also detected in the Zaduo area.