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The temporal and spatial distribution of enriched source components at sites of continent–continent collision provides critical insights into mantle dynamic processes associated with subduction- and collision-related events. However, determining the origin of such enriched components remains a significant challenge. We report a comprehensive dataset of the Linzizong volcanic succession (LVS) from four locations with varying distance across-strike to the Indus–Yarlung suture in southern Tibet, which marks the exposed surface expression of the India–Asia collision zone. The LVS rocks in this study can be divided into two groups: a calc-alkaline Group 1 (69–55 Ma), mainly including basaltic–andesitic varieties, and a shoshonitic Group 2 (52–50 Ma), consisting predominantly of silicic rocks with minor mafic compositions. Group 1 samples are likely derived from the fractional crystallization of primitive basaltic melts as a result of the partial melting of a metasomatized mantle wedge. These samples are decoupled in Nd–Hf isotopic compositions, suggesting an incorporation of subducting sediment-derived melts into the mantle wedge. The influence of sediment-derived melt on the mantle source increases away from the suture zone toward Asia (i.e. from the south to the north) as indicated by the more enriched Sr, Nd, Pb, and Hf isotopic compositions, as well as elevated Th/La and La/Sm ratios. The heavy δ26Mg values, and high Ba/Th and Sr/Th ratios of samples close to the suture coincide with the dehydration of the subducting Neo-Tethyan slab. Group 2 mafic samples have depleted and coupled εNd–εHf isotopic compositions and are characterized by elevated (La/Yb)N and Dy/Yb ratios as well as low Zr/Nb ratios, indicating an origin of enriched garnet-bearing lithospheric mantle with contributions from asthenosphere-derived materials. Group 2 silicic samples are isotopically enriched both near and far away from the suture, which can be attributed to the involvement of ancient lower crust-derived melt from Tethyan Himalaya and central Lhasa subterrane basement, respectively. Our results show that the LVS are the magmatic response to late subduction (Group 1), and to initial India–Asia collision and slab breakoff (Group 2). Negative trends in the whole-rock Nd and zircon Hf isotopic compositions at ~51 Ma should be treated with caution for geodynamic interpretations, depending on the distance between the samples and the India–Asia suture. [ABSTRACT FROM AUTHOR]

A o ations between tholeiitic and calc-alkaline arc magmatism with close spatial and temporal relationships can provide critical constraints on magma genesis and allow the reconstruction of subduction polarity at convergent margins. This study identifies two compositionally distinct intrusive series from the Yusufeli region in the Eastern Pontides arc, NE Turkey. The intrusive rocks from the Yusufeli intrusive complex were emplaced at 179–170 Ma and are dominated by the low- to medium-K tholeiitic series, with depleted Hf isotopic compositions. In contrast, the intrusive rocks from the Camlikaya intrusive complex were emplaced at 151–147 Ma and are characterized by the medium- to high-K calc-alkaline series, with relatively enriched Hf isotopic compositions. The Al-in-hornblende geobarometer reveals that the magmas of both intrusive complexes crystallized at upper crustal levels (∼150–250 MPa, ∼5–8 km). The presence of patchy-textured plagioclase and the widespread occurrence of coeval dykes and magmatic mafic enclaves indicate that the two intrusive complexes are derived from multiple magma pulses in open magmatic systems. The mineral crystallization order of amphibole and plagioclase, the trace elemental signatures (e.g. Sr/Y and Y), and rare earth element modeling collectively suggest that the Yusufeli intrusive complex was dominated by plagioclase and clinopyroxene fractionation with earlier plagioclase crystallization than amphibole, whereas the Camlikaya intrusive complex was dominated by the fractionation of amphibole accompanied by co-crystallization of plagioclase. Such significant differences in the fractionating mineral assemblages at comparable intrusion pressures can be attributed to different initial H2O contents of the Yusufeli and Camlikaya parental magmas, which ultimately control their distinct liquid lines of descent. In accord with thermodynamic modeling results derived using the Rhyolite-MELTS software, we propose that the Yusufeli intrusive rocks are derived from damp (∼1–2 wt% H2O) parental magmas formed dominantly by decompression melting of mantle wedge in a back-arc setting. In contrast, the wet parental magmas (>∼2 wt% H2O) of Camlikaya intrusive rocks are more hydrous and formed through flux melting of suprasubduction-zone mantle wedge. This conclusion, combined with the back-arc basin related Jurassic sedimentary and structural records previously determined in the Southern Zone of the Eastern Pontides, indicates that the geochemical compositions and spatial relationship of the Yusufeli and Camlikaya intrusive complexes are preferably explained by the southward subduction of the Paleotethys oceanic lithosphere in the Early to Late Jurassic. [ABSTRACT FROM AUTHOR]

Voluminous Early Cretaceous volcanic rocks in the central Lhasa subterrane provide an ideal opportunity for understanding the mantle–crust interaction and tectonic‐magmatic evolution of the Lhasa Terrane. Here, we report zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic data for the Early Cretaceous volcanic rocks, including high‐silica rhyolites (117.2 ± 1.1 Ma) and contemporaneous andesites (114.1 ± 0.8 Ma) in the Sailipu area, central Lhasa subterrane. All these rocks show enriched light rare earth elements (LREE), and radioactive heat‐generating elements (e.g., Th, U, K, and Pb) but depleted high‐field‐strength elements (HFSEs, e.g., Nb, Ta, P, and Ti). The different bulk‐rock Sr–Nd–Pb and zircon Hf isotopic compositions of the rhyolites and andesites suggest that these rocks have distinct magma sources and petrogenetic history rather than an identical source involving assimilation‐fractional crystallization process. The Sailipu high‐silica rhyolites exhibit the characteristics of fractional crystallization and have varying zircon εHf(t) values (−12.2 to +5.2), negative εNd(t) values (−9.5 to −1.6), high and variable initial Sr isotopic compositions ([87Sr/86Sr]i = 0.7047–0.7116) and radiogenic Pb isotopic signatures (206Pb/204Pb = 18.784–18.802, 207Pb/204Pb = 15.722–15.737, and 208Pb/204Pb = 39.382–39.492). A combined process of magma mixing (involving crustal‐derived felsic melts and mantle‐derived mafic melts) and subsequent fractional crystallization were mainly responsible for the formation of these high‐silica rhyolites. The Sailipu andesites show more enriched Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.7088–0.7154, εNd(t) = −9.9 to −6.7] relative to rhyolites, and less radiogenic Pb isotopic compositions (206Pb/204Pb = 18.632–18.669, 207Pb/204Pb = 15.686–15.689, 208Pb/204Pb = 39.140–39.201). They were likely derived from partial melting of an enriched mantle wedge previously metasomatized by melts derived from subducted sediments. We interprete these Early Cretaceous volcanic rocks as the product of slab break‐off during the southward subduction of the Bangong‐Nujiang Tethyan oceanic seafloor. The dominantly positive εHf(t) and ancient TDMC ages (0.85–1.90 Ga) of Sailipu high‐silica rhyolites further imply that, under the stress relaxation regime, the mantle‐derived melts locally reworked the ancient basement of the central Lhasa subterrane. [ABSTRACT FROM AUTHOR]

Abstract: The petrogenesis and geodynamic implications of the Cenozoic adakites in southern Tibet remain topics of debate. Here we report geochronological and geochemical data for host granites and mafic enclaves from Wolong in the eastern Gangdese Batholith, southern Tibet. Zircon LA-ICP-MS dating indicates that the Wolong host granites and enclaves were synchronously emplaced at ca. 38Ma. The host granites are medium- to high-K calc-alkaline, metaluminous (A/CNK=0.93–0.96), with high Al2O3 (15.47–17.68%), low MgO (0.67–1.18%), very low abundances of compatible elements (e.g., Cr=3.87–8.36ppm, Ni=3.04–5.71ppm), and high Sr/Y ratios (127–217), similar to those typical of adakite. The mafic enclaves (SiO2 =51.08–56.29%) have 3.83–5.02% MgO and an Mg# of 48–50, with negative Eu anomalies (δEu=0.59–0.79). The Wolong host granites and enclaves have similar Sr–Nd isotopic compositions (initial 87Sr/86Sr=0.7053–0.7055, ε Nd(t)=−2.7 to −1.4), with varying zircon ε Hf(t) values, ranging from +6.0 to +12.6. A comprehensive study of the data available for adakitic rocks from the Gangdese Batholith indicates that the Wolong adakitic host granites were derived from partial melting of a thickened lower crust, while the parental magmas of the mafic enclaves were most likely derived from lithospheric mantle beneath southern Tibet. The Wolong granitoids are interpreted as the result of mixing between the thickened lower crust-derived melts and lithospheric mantle-derived mafic melts, which are likely the protracted magmatic response to the break-off of the Neo-Tethyan oceanic slab at about 50Ma. Our results suggest that the crustal thickening in southern Tibet occurred prior to ~38Ma, and support the general view that the India–Asia collision must have occurred before 40Ma. [Copyright &y& Elsevier]

[Display omitted] • Kohistan and Gangdese (garnet) hornblendites and/or garnet gabbros are of cumulate origins. • Amphiboles in these lower crust cumulates have high Nb/Ta but low Nb and Ta concentrations. • Amphibole fractionation will not change Nb/Ta ratio of arc magmas significantly. • Rutile likely plays an important role in Nb/Ta fractionation in continental crust formation. Earth's continental crust has a lower Nb/Ta ratio than that of its building blocks –basaltic melts from the mantle. This Nb/Ta mass imbalance implies the existence of a complementary high Nb/Ta reservoir in deep crust. Amphibole-rich arc cumulates have been proposed to be one such candidate due to the preferential partitioning of Nb over Ta into amphibole. To test this proposal, we carried out in-situ analyses of amphibole and rutile in the lower crustal rocks from Kohistan arc and Gangdese arc. Petrological observations and geochemical results suggest that these rocks in both Kohistan arc and Gangdese arc are of magmatic origins and formed by crystal accumulation, i.e. of cumulate. The Kohistan garnet-bearing hornblendite cumulates were formed at 952–1009 ℃; the garnet-free hornblendite cumulates in Kohistan arc and Gangdese arc were formed at 941–992 ℃ and 955–1027 ℃, respectively. We find that, although the amphibole of the Kohistan and Gangdese cumulates have high Nb/Ta ratios (average 18.2 and 17.0, respectively), their Nb and Ta concentrations are far lower than mantle-derived volcanics (Nb < 1.1 ppm, Ta < 0.11 ppm). We show that, with such low concentrations of Nb and Ta, amphibole fractionation will not change arc magma Nb/Ta ratios significantly. Instead, the rutile in Kohistan cumulates has high Nb/Ta ratios and high Nb-Ta concentrations. The calculation shows that rutile may play a more important role in Nb/Ta fractionation during arc magma differentiation in thickened arc crust. Our study provides a mineralogical perspective to understand the formation of continental crust, and improves our understanding how Nb or Ta becomes enriched in arc setting. [ABSTRACT FROM AUTHOR]

• The Kashala Formation deposited during Late Triassic age. • Archean to late Paleozoic detrital zircon grains in sediments of the Kashala Formation. • U-Pb age and Hf isotopes suggest secular and episodic continental reworking and growth from Paleoarchean to Early Paleozoic. • Detrital zircon grains suggest proximal sources by second cycle of transportation and deposition during accumulation of the Kashala Formation. Detrital zircon analysis of the Triassic Kashala Formation of the Alpurai Group in Swat, Pakistan, west of Indus syntaxis, record Archean to Paleozoic ages. The U-Pb age spectra show distinctive age clusters at 3510–3100 Ma, 2700–2400 Ma, 1750–1500 Ma, 1350–750 Ma, 700–600 Ma and 580–470 Ma, with one youngest age of 229 Ma, suggesting secular and episodic continental growth. The prominent negative εHf (t) values indicate dominantly crustal reworking together with a minor contribution from a juvenile crust. The age pattern is similar to the detrital zircon from Tethyan Himalaya and South India, showing two major peaks at 926 Ma and 532 Ma, and corresponding to Greenville and Pan-African orogenies, respectively. The U-Pb age peaks between ca. 1750–1600 Ma and 900–750 Ma are correlated well with the peaks of detrital zircon from Precambrian and Ordovician rocks in the Hazara region. Detrital zircon analysis suggests proximal source areas. Based on combined U-Pb and Hf isotope analysis and grain morphology, Paleoproterozoic detrital zircon grains were derived from basement rocks of the Besham Complex, which is presently exposed in the Indus syntaxis. The zircon trace element geochemistry reveals mainly felsic and mafic igneous rocks of the continental crust, suggesting that proximal Proterozoic-Paleozoic intrusions in the Swat and Hazara regions as a possible source. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) was established in response to multiple subduction-accretion-collision processes. However, the origin and evolution of the accreted arc terranes remain unclear, as exemplified by the question how ancient and juvenile materials were accreted and constructed in the accretionary belts. This question is addressed here by presenting in-situ zircon U Pb and Hf isotopic, whole-rock elemental and Sr Nd isotopic analyses of the four Late Paleozoic igneous rock units from Xilinhot in the southeastern CAOB. The new geochronological and geochemical data support the existence of two Late Carboniferous to Permian magmatic arc systems — Ulistai active continental margin and Baolidao arc belt. These arc systems are characterized by magmatic activity extending from 330 to 250 Ma, with two magmatic "flare-ups" (325–295 Ma vs. 295–270 Ma). The first magmatic "flare-up" (325–295 Ma) includes high-K calc-alkaline rhyolites, dacites and alkali-feldspar granites, which can be interpreted to have originated from re-melting of the juvenile lower crust beneath a continental arc induced by the Paleo-Asian oceanic ridge subduction. The second magmatic "flare-up" (295–270 Ma) reveals a seaward migration of magmatism due to slab rollback subsequent to ridge subduction. The Middle to Late Permian shoshonitic andesites witnessed the closure of the Hegenshan ocean during this period. In combination with previously reported Sr-Nd-Hf isotopic data, we suggest that the Baolidao arc belt and some other arc terranes (e.g., Bainaimiao arc) in the southeastern CAOB were built upon Precambrian microcontinents that have been largely fragmented and significantly reworked. In summary, ridge subduction accompanied by slab rollback played an important role in the rejuvenation of microcontinents and accretion of arc terranes in the southeastern CAOB. • The 325–270 Ma magmatism in SE CAOB was linked to ridge subduction & slab rollback. • The 262–250 Ma andesites witnessed the closure of the Hegenshan ocean. • The Baolidao arc belt was built upon a Precambrian terrane during the Late Paleozoic. • Ridge subduction & slab rollback played a key role in crustal growth in SE CAOB. [ABSTRACT FROM AUTHOR]

• The juvenile lower crust enriched in sulfides and hydrous minerals is necessary to the formation of collision-related PCDs. • The evolution processes of fertile magmas determine the metal associations of collision-related PCDs. • Contemporaneous regional tectonics can affect the tonnage of collision-related PCDs. Porphyry Cu deposits (PCDs) in continental collision settings are new targets for modern mineral exploration, and the relationships among locations, tectonic environments, tonnages, and metal associations are not yet understood. The Gangdese PCD belt formed in a typical continental collision setting between the Indian and Asian plates. In the present study, new elemental and isotopic data from fertile porphyries (Cu–Mo, Cu–Mo–Pb–Zn, and Cu–W–Mo) and barren coeval and pre-ore porphyries of the Gangdese PCD belt were combined with previously published data to provide new insights into the metallogenesis of PCDs in continental collision settings. Factors that contributed to the formation of collision-related PCDs in the Lhasa terrane, Tibet, include the nature of the magmatic sources, magmatic evolution during ascent through the crust, and regional tectonics. These PCDs were not formed by partial melting of ancient lower crust. Instead, attributed to the subduction of Neo-Tethyan oceanic slab, arc magmas and slab-derived fluids resulted in the accumulation of sulfides and hydrous minerals at the base of the continental crust. Partial melting of this refertilized juvenile lower crust produced oxidized water- and Cu-rich magmas with the potential to produce large PCDs, although only under favorable regional tectonic conditions. Regional compressional stress is not conducive to the formation of large magma chambers, so the collision-related adakite-like magmas that developed during the early stages of India–Asia collision commonly lack alteration and associated mineralization. In contrast, relatively large magma chambers can develop in extensional settings within the continental collision orogen, which facilitates the formation of large and giant PCDs. Small Cu–W–Mo deposits formed during the transition between compressional and extensional settings. Thus, the regional tectonic setting and structural framework of the host orogen influenced the tonnage of PCDs. The metal associations of collision-related PCDs in the Lhasa terrane were controlled mainly by the extent of assimilation of the upper crust and the degree of fractional crystallization of the ore-forming magmas. Lead–zinc mineralization in Cu–Mo deposits is attributed to the assimilation of metapelites by fertile magmas in the upper crust, and highly fractionated fertile magmas are required to produce W mineralization. [ABSTRACT FROM AUTHOR]

Post-collisional potassic and high Sr/Y magmatism in the Lhasa terrane provides critical constraints on the timing and mechanism of subduction of Indian lithosphere and its role in the uplift of the Tibetan Plateau. Here, we report whole-rock geochemistry, mineral geochemistry, zircon U Pb ages, and in situ zircon Hf isotope ratios for the Nyemo pluton, a representative example of such magmatism. The Nyemo pluton is composed of high Sr/Y host rocks and coeval shoshonitic mafic microgranular enclaves (MMEs). Whole-rock compositions of the host rocks and MMEs form linear trends in Harker diagrams, consistent with modification of both end-members by magma mixing. Although the main high Sr/Y phase of the pluton formed by partial melting of the lower crust of the thickened Lhasa terrane, the MMEs display abnormally enriched light rare earth elements, low whole-rock ε Nd (t) and low zircon ε Hf (t) that suggest derivation from low degree melting of hydrous and enriched mantle. Based on the occurrence of shoshonitic magma and high La/Yb and high Sr/Y with adakitic affinity host rocks around 30 Ma, the Nyemo pluton is best explained as a record of onset of extension that resulted from convective removal of the mantle lithosphere beneath Tibet in the Oligocene. • High Sr/Y host rocks of Nyemo pluton are derived from thickened lower crust. • Coeval shoshonitic enclaves were produced from enriched lithospheric mantle. • Lithospheric mantle convective removal, onsets of extension may have occurred during Oligocene. [ABSTRACT FROM AUTHOR]

• The quartz albite porphyry emplaced at 318.6 ± 3.0 Ma in a subduction environment. • The I-type granite quartz albite porphyry originates from the juvenile lower crust. • The northward subduction of oceanic crust generated these intrusions and mineralization. The Linglong porphyry Cu deposit is located in the Dananhu–Tousuquan Arc Belt, adjacent to the large Tuwu–Yandong Cu deposits in Eastern Tianshan, northwest China. In this study, zircon U–Pb, whole rock geochemistry, and zircon Hf–O isotopic analyses were carried out on the Linglong intrusions (i.e., quartz albite porphyry and diorite porphyry). New SIMS zircon U–Pb dating and previous data indicate that the quartz albite porphyry occurred in the Late Carboniferous (318.6 ± 3.0 Ma), younger than emplacement of the diorite porphyry (338–340 Ma) and tonalite porphyry (332–335 Ma) in this area, as well large-scale copper mineralization (331–335 Ma) in Eastern Tianshan. The geochemistry of the quartz albite porphyry intrusions is consistent with calc-alkaline normal arc magmatism, characterized by high SiO 2 (74.82–77.89 wt%), obvious Eu anomalies (0.42–0.52), high Y (21–25.9 ppm) and Yb (2.98–3.67 ppm) concentrations, moderate Mg# values (35–40), but relatively low Sr/Y (6.86–9.52)and low 10,000 Ga/Al values. In situ Hf–O isotopic analyses on zircons show that the quartz albite porphyry rocks have variable ε Hf (t) (+9.0 to + 13.9) and low δ18O values (4.72 to 5.84‰), suggesting a juvenile lower crust derived composition. However, the diorite porphyry intrusions show features of low SiO 2 (57.51–61.12 wt%), minor Eu anomalies (0.82–1.15), strong depletion in high field strength elements (e.g., Nb, Ta, P and Ti), but enrichment in large ion lithophile elements (e.g., Rb, Ba, K and Pb). They also exhibit normal island arc magma geochemical signatures, with high Y (20.9–40.2 ppm), and Yb (2.75–4.64 ppm) concentrations, high Mg# (40–51), and relatively low (La/Yb) N (2.07–4.10) and Sr/Y (5.75–12.13) values, suggesting the melt was derived from the subduction-modified mantle mafic to ultramafic materials. Combined with regional tectonic evolution and our new data, we suggest that the Late Carboniferous magma was generated during the period of the northward subduction of the Paleo-Tianshan ocean plate beneath the Dananhu–Tousuquan island arc. [ABSTRACT FROM AUTHOR]

Generation of continental crust in collision zones reflect the interplay between oceanic subduction and continental collision. The Gangdese continental crust in southern Tibet developed during subduction of the Neo-Tethyan oceanic slab in the Mesozoic prior to reworking during the India-Asia collision in the Cenozoic. Here we show that continental arc magmatism started with fractional crystallization to form cumulates and associated medium-K calc-alkaline suites. This was followed by a period commencing at ~70 Ma dominated by remelting of pre-existing lower crust, producing more potassic compositions. The increased importance of remelting coincides with an acceleration in the convergence rate between India and Asia leading to higher basaltic flow into the Asian lithosphere, followed by convergence deceleration due to slab breakoff, enabling high heat flow and melting of the base of the arc. This two-stage process of accumulation and remelting leads to the chemical maturation of juvenile continental crust in collision zones, strengthening crustal stratification., (© 2022. The Author(s).)