Partial Melting Of Mantle Wedge Research Articles

Subduction retreating caused the external breakup of Rodinia: Constraints from the Neoproterozoic igneous rocks in the western Yangtze Block, South China

The western Yangtze Block is an ideal place for investigating the Precambrian tectonic evolution of the South China Craton and the geodynamic mechanism responsible for the breakup of Rodinia. However, the Neoproterozoic tectonic evolution of the western Yangtze Block has not been fully elucidated; in particular, the driving mechanism has changed from an arc setting to a rift setting. Here, we present new zircon U–Pb geochronology and O–Hf isotopic compositions, whole-rock geochemistry, and Sr–Nd isotope data for Yanbian andesites and Shimian gabbros from the western Yangtze Block, South China. The ca. 850–840 Ma Yanbian andesites are high-Mg andesites with moderate SiO2 (56.75–60.21 wt%) and high MgO (4.24–6.44 wt%) and Mg# (52–66). These rocks show enrichments in large-ion lithophile elements (LILEs; e.g., Rb, Ba, Sr, and K) and light rare earth elements (LREEs) and depletions in high-field strength elements (HFSEs; e.g., Nb, Ta and Ti) and display decoupled Nd–Hf isotopes (εNd(t) = +3.9 to + 5.0, εHf(t) = +9.7 to + 13.1) and relatively high zircon δ18O values (5.82–7.72 ‰); these findings indicate that these rocks were derived from a mantle wedge enriched by slab fluids and sediment melts. The ca. 820–810 Ma Shimian calc-alkaline gabbros are characterized by enriched LREEs and LILEs (e.g., Rb, Sr, and K) and depleted HFSEs (e.g., Nb, Ta and Ti). These rocks show decoupled Nd–Hf isotopes (εNd(t) = +3.2 to + 4.2, εHf(t) = +3.1 to + 7.5) and relatively low zircon δ18O values (4.28–5.31 ‰), indicating that they were formed by partial melting of mantle wedge metasomatized by sediment and oceanic slab melts. Compiled geochronological data suggest that Neoproterozoic subduction-related magmatism along the western Yangtze Block formed a long-term active arc system. Slab retreat in this subduction zone led to a shift in the tectonic setting from a compressional setting to an extensional setting in the Yangtze Block during the middle to late Neoproterozoic. Moreover, the temporal link between retreating subduction zone and extensional tectonics in the Yangtze Block suggests that protracted subduction retreating resulted in external rifting in Rodinia.

The Paleocene high-silica granites and their associated diorite enclaves in central Lhasa subterrane, Xizang, China: Insights to crust-mantle mixing and crustal reworking

The history of crustal growth in the western Central Lhasa (CL) subterranean during India-Eurasian collision remains unclear. The crucial problem is lack of suitable and ideal magmatism recorded information of the early stages of continental collision. Here, we report the newly discovered high-silica granites (K-feldspar granite with aplite granite) hosting diorite enclaves from the Geji area in western CL subterrane. This suite of magmatic rocks is of great significance to reveal the crustal growth of CL during the India-Eurasia collision. Zircon U-Pb dating results show that the K-feldspar granite, aplite granite, and diorite enclaves were formed at 57.2–57.9 Ma, 58.7 Ma and 58.2 Ma, respectively. Petrology, mineralogy, and mineral chemistry of the plagioclase from the diorite enclave indicates that it was generated by magma mixing between mafic and felsic magmas. The mafic melt was sourced from partial melting of mantle wedge and metasomatized by subduction fluid and sediment melt. This has been supported by the positive zircon εHf(t) values (+0.6 to + 4.9), enrichment of large ion lithophile elements (Rb, K, Th, and U) and depletion of high field strength elements (Nb and Ta), and the high Th/Ce ratios of diorite enclaves. The K-feldspar granite also has positive zircon εHf(t) values (+1.3 to +6.2), arc magma geochemical features, and a lower crust Nb/Ta ratio (8.3). These indicate that the K-feldspar granite was originated from the juvenile lower crust. In conclusion, we think that the crust-mantle magma mixing has a substantial impact on the crustal growth of the western CL subterrane during the subduction slab roll-back of the Paleocene Neo-Tethys Ocean when paired with other research and the context of regional tectonic development.

Temporal evolution of the early−late Neoarchean granitoid magmatism in the eastern North China Craton: Transition of geodynamic regime from mantle plume to continental marginal arc system

A study of tonalite−trondhjemite−granodiorite (TTG) suite and sanukitoids emplaced at different ages in the Archean can constrain the transition of early Earth’s tectonic regime, which remains a subject of debate. In this contribution, we report a systematic investigation of an early Neoarchean and late Neoarchean TTG-sanukitoid association from the eastern North China Craton based on mineralogical, petrological, and geochemical evidence. The geochemical features of the 2.7 Ga TTG rocks studied suggest that their magma was primarily generated by partial melting of garnet-amphibolite and eclogite. Moreover, they are characterized by relatively low values of MgO, Mg#, Cr, and Ni, and zircon ɛHf(t) that varies mostly with evolved signature, which suggests that the primary magma of the TTGs was generated in a setting of thickened lower crust. The 2.5 Ga high-K calc-alkaline granitoids studied show an affinity to Archean sanukitoids. Their representative major and trace elemental and isotopic features suggest that they were derived from partial melting of mantle wedge metasomatized by subducted fluids and slab- and sediment-derived melts, followed by varying degrees of mineral fractional crystallization. The eastern North China Craton may have developed a continental marginal arc system in the late Neoarchean attached to another craton in the global Kenorland supercontinent, which might have eventually resulted in its final cratonization. The distinct tectonic settings of the two types of granitoids may indicate a transition of the tectonic regime from vertical in the early Neoarchean to horizontal at the end of the late Neoarchean. Moreover, the low δ18O values found in this study as well as those in other areas of the globe suggest that they were probably related to cold climatic conditions and/or elevated latitudes or altitudes.

Magma-mixing origin for the Early Jurassic intrusive rocks in the eastern Songnen–Zhangguangcai Range Massif, NE China: Evidence from geochronology, geochemistry and Hf–O–Sr–Nd isotopes

Granites containing abundant dioritic enclaves are widespread in the Songnen–Zhangguangcai Range Massif (SZRM). However, the role of mantle- and crust-derived magmas in the petrogenesis of the dioritic enclaves is debated. We present new zircon U–Pb–Hf–O isotopic compositions, whole-rock geochemistry, mineral geochemistry, and Sr–Nd isotopic compositions of hornblendites and dioritic enclaves and their host granites to elucidate their origins and investigate crust–mantle hybridization. Zircon U–Pb dating suggests that these intrusive rocks were emplaced during the Early Jurassic (197–186 Ma). The geochemical characteristics of hornblendites are similar to those of the Early Jurassic mafic–ultramafic rocks in the Lesser Xing’an–Zhangguangcai Range. They yield low (87Sr/86Sr)i ratios (0.704266–0.704324), high εNd(t) values (3.87–3.91), and are enriched in Ba, Sr, and K and depleted in Nb, Ta, and Ti, suggesting that they were derived from the partial melting of mantle wedge metasomatized by sediment melt. The host granites have high SiO2 (>65.12 wt%) and low MgO (<1.92 wt%) and Al2O3 (<16.23 wt%) contents and are to metaluminous–peraluminous high-K calc-alkaline rocks. In addition, they yield positive zircon εHf(t) values (3.42–7.58), zircon δ18O values (4.87‰–5.85‰) and whole-rock εNd(t) values (0.10–0.44), suggesting that the granitic magma originated from the partial melting of continental crust with the involvement of mantle-derived melts. The field and petrographic observations and geochemical analyses indicate that the enclaves were derived from magma mixing and mingling. The dioritic enclaves contain K-feldspar megacrysts and back-veins, and plagioclase crystals within them are reversely zoned and have ocellar textures. The weighted mean ages of the host granites (186 ± 3 and 188 ± 2.3 Ma) are similar to those of the dioritic enclaves (186 ± 1.8 and 188 ± 1.1 Ma). The major element contents of the intrusive rock are linearly correlated with the SiO2 contents, and the whole-rock geochemical and isotopic characteristics of the hornblendites and host granites show that they are the mafic and felsic end-members, respectively, involved in the magma mixing. Therefore, we propose that underplating by mantle-derived magma likely triggered partial melting of the continental crust to produce felsic magma, and the dioritic enclaves were formed by the mixing and mingling of mantle- and crust-derived magma alongside melting, assimilation, storage, and homogenization. This suggest that the Mudanjiang Oceanic crust was subducted westward beneath the SZRM during the Early Jurassic.

Petrogenetic and tectonic implications of Neoproterozoic igneous rocks from the western Yangtze Block, South China

Spatiotemporal variations in magma sources and the petrogenetic types of igneous rocks generally record major changes in tectonic styles and crustal growth mechanisms and thus play vital roles in tectonic reconstruction. In this study, we present new petrological, geochronological, geochemical and Sr-Nd-Hf isotopic data for Neoproterozoic igneous rocks in the Western Yangtze Block (WYB), South China, aiming to constrain their petrogenesis and tectonic implications. Geochronological and geochemical data compilations indicate a prolonged (ca. 910 to 730 Ma) Andean-type magmatic arc system in the WYB; however, the initial magmatism and subsequent magmatic flare-up events in different regions of the WYB are asynchronous. Petrogenetic study reveals that most Tonian mafic rocks exhibiting typical arc-related geochemical affinities and depleted Nd-Hf isotopes are generated by the partial melting of mantle wedge that is metasomatized by subduction-related fluids and/or melts. Elemental and isotopic studies suggest that the newly identified ca. 880–851 Ma adakitic rocks in the WYB are derived from melting of thickened juvenile or ancient continental crust, while the studied A2-type and I-type granitoids originate from differentiation of mantle-derived magma or reworking of continental crust, which are the key mechanisms of crustal evolution in the WYB. This study indicates that the Yangtze Block probably lies on the periphery of the Rodinia supercontinent, and long-lived arc magmatism including mafic magma underplating and crustal reworking, and episodic magmatic flare-up that occur due to slab rollback play key roles in Neoproterozoic continental evolution of the WYB.

Episodic magmatism in the Dananhu arc, eastern Tianshan: Implications for the Late Palaeozoic tectonic evolution of the North Tianshan Ocean

ABSTRACT The North Tianshan Ocean represents a critical southwestern segment of the Paleo-Asian Ocean and is crucial for understanding accretionary and collisional processes of the southwestern Central Asian Orogenic Belt. The Dananhu arc belt, an important porphyry Cu deposit metallogenic belt in the eastern North Tianshan, records Paleozoic episodic magmatism. However, the tectonic affinity and evolution processes of the Dananhu arc belt are still open to debate. Here, geochronology, major and trace elements, and Sr-Nd-Hf isotope compositions for magmatic rocks are conducted to reveal the ages, petrogenesis, and tectonic settings of these magmatic rocks in the Dannanhu arc belt. The Carboniferous dacite (328 Ma) and gneissic granite (310 Ma) show high-K calc-alkaline, enriched in large ion lithophile elements (LILEs; e.g. Rb, Th, and U), depleted in high field strength elements (HFSEs; e.g. Nb, Ta, and Ti), depleted isotopic compositions (εNd(t) = 1.3-3.4; εHt(t) = 0.5-12.5) and juvenile Nd-Hf model ages. Combining these Carboniferous magmatic rocks with the features of high Sr-Ba granitoid and Sr-Nd isotopic decoupling, we suggest that these Carboniferous rocks were probably formed through fractional crystallization of partial melting of mantle wedge that had been metasomatized by melts from subducted sediments in a forearc setting. The early Permian granites (289-276 Ma) show high K2O+Na2O (6.9-8.9 wt.%), low MgO (0.06-0.15 wt.%) contents, high positive zircon εHt(t) (10.5 to 12.1) and whole-rock εNd(t) (4.4-5.5) values, suggesting that the early Permian granites were derived from juvenile lower crust in a post-collisional setting. Our geochronological and geochemical data, together with published data, reveal that high flux arc magmatism with age peaks at ca. 431 and 332 Ma is consistent with porphyry copper mineralization in the Dananhu arc belt, implying a close genetic relationship. The final closure of the North Tianshan Ocean was constrained to the late Carboniferous and early Permian.

Geochemical, zircon U–Pb–Hf–O isotopic evidence and molybdenite Re–Os dating from the Cuojiaoma batholith, eastern Tibetan Plateau: Implications for molybdenum potential and tectonic evolution

Subduction of oceanic plates beneath continental lithosphere is critical for understanding tectonic evolution and evaluation of prospecting and exploration. Within the Yidun Terrane (YDT) of southwestern China, a number of Mesozoic to Cenozoic granitoid intrusions are exposed and they are useful for investigating the tectonic evolution of the Paleo-Tethys system. However, Mesozoic magmatism of the northern portion of the YDT, remains ambiguous regarding to their magmatic spatial–temporal evolution and their mineralization potential. As the largest pluton in the northern YDT, the Cuojiaoma batholith mainly consists of monzogranite and granodiorite. In this study, we present new zircon U–Pb and molybdenite Re–Os ages, whole-rock geochemical, and zircon Hf–O isotopic data for the Cuojiaoma batholith. LA-ICP-MS zircon U-Pb dating of granodiorite and monzogranite exhibit ages of 221.8 ± 1.4 Ma (n = 22, MSWD = 2.4) and 216.7 ± 2.2 Ma (n = 14, MSWD = 0.03), respectively. A total of 9 molybdenite samples differing Re-Os model ages of 205.4 ± 3.3 and 220.6 ± 5.5 Ma, yield a robust weighted mean model age of 209.9 ± 1.8 Ma (MSWD = 2.4, n = 9) representing the depositional age of molybdenite. The monzogranite and granodiorite’s mineralogical and geochemical characteristics indicate they are classified as (medium-) high-K calc-alkaline and metaluminous to weakly peraluminous I-type granite. Geochemically, they are enriched in large-ion lithophile elements (LILEs, e.g., Rb, U, K) and light rare earth elements (LREEs), and depleted in high-field-strength elements (HFSEs, e.g., Nb, Ta, Ti and P) and heavy rare earth elements (HREEs), and contain distinctly or slightly negative Eu anomalies and no significant Ce anomalies, indicating an affinity to classical island arc magma. Combined with their negative zircon εHf(t) values (−16.24 to −2.49 and −16.41 to −1.43) and two-stage Hf model ages (2019–1255 Ma and 2027–1200 Ma), plus their zircon δ18O values, which range from 5.96 to 8.01 and from 5.05 to 7.61 for monzogranite and granodiorite, respectively, these geochemical indexes indicate that the Cuojiaoma batholith shares similar petrogenesis to other intrusions within the YDT. The formation of the early granodiorite may be genetically related to the slab subduction and is most likely formed by mixture of lower crustal melts and mafic magma derived from partial melting of mantle wedge induced by the influx of slab derived melt (fluid). Subsequent slab break-off and the upwelling asthenosphere at ∼ 216 Ma to 210 Ma led to high heat flow and extensive melting of the overlying mantle wedge, followed by the highly crystallization differentiation, which finally contributed to the monzogranite and the subsequential disseminated molybdenite in a post-subduction extension setting. The northern YDT possesses high Mo metallogenic prospectivity, especially for the magmatic activity that dominantly by lower crustal melt and genetically related to the slab break-off occurred at ∼ 216 Ma and represented by the highly fractionated granite derived from the large Cuojiaoma granitic batholith.

The Transitional Gabbroic Rocks in Bayah Geological Complex, Western part of Java, Indonesia, Inferred from XRF, ICP-MS, and Microprobe Analysis

Gabbro, is a fossil remnant of oceanic crust in western part of Java, found at Bayah Geological Complex (BGC) and Ciletuh Melange Complex (CMC), Indonesia. It has been studied by using petrographic, X-Ray Fluorescence (XRF), and inductively coupled plasma-mass spectrometry (ICP-MS) and mineralogical (microprobe) analyses. Mineral and geochemical composition of these rocks provide important clues to their origins since the rocks have been deformed and gone through auto metamorphism, beside they contain the economic mineral and or rare earth elements (REE). Gabbroic rocks in these two areas generally shows phaneritic to porphyritic texture, granular texture. These rocks in CMC are dominated by plagioclase (oligoclase to albite), hornblende, pyroxene, partly altered to tremolite, actinolite, chlorite, epidote, and sericite; meanwhile those of BGC dominantly consist of plagioclase, pyroxene, hornblende, some present of chlorite, actinolite, epidote and biotite as secondary minerals. In multi-element diagrams, gabbroic rocks in CMC show strong negative Sr and Zr, but positive Nb anomaly, while those of BGC show strong negative anomaly of Nb and Zr. In addition, based on rare earth elements (REE) diagrams, gabbroic rocks in CMC show depleted of light rare earth elements (LREE) with negative Eu anomaly, while gabbro’s in BGC show enrichment of LREE. These characteristics indicate that GBC’s and CMC’s gabbroic rocks came from different magma sources, one was formed by partial melting of depleted upper mantle reservoir while the other one was formed by partial melting of mantle wedge with active participation of subducted slab in an arc tectonic setting, suprasubduction zone which were formed at started Upper Cretaceous to Paleogene, and they had retrograde metamorphism to epidote amphibolite facies.

Origin, Accretion, and Reworking of Continents

AbstractThe continental crust is unique to the Earth in the solar system, and controversies remain regarding its origin, accretion and reworking of continents. The plate tectonics theory has been significantly challenged in explaining the origin of Archean (especially pre‐3.0 Ga) continents as they rarely preserve hallmarks of plate tectonics. In contrast, growing evidence emerges to support oceanic plateau models that better explain characteristics of Archean continents, including the bimodal volcanics and nearly coeval emplacement of tonalite‐trondjhemite‐granodiorite (TTG) rocks, presence of ∼1600°C komatiites and dominant dome structures, and lack of ultra‐high‐pressure rocks, paired metamorphic belts and ophiolites. On the other hand, the theory of plate tectonics has been successfully applied to interpret the accretion of continents along subduction zones since the late Archean (3.0–2.5 Ga). During subduction processes, the new mafic crust is generated at the base of continents through partial melting of mantle wedge with the addition of H2O‐dominant fluids from subducted oceanic slabs and partial melting of the juvenile mafic crust results in the generation of new felsic crusts. This eventually leads to the outgrowth of continents. Subduction processes also cause softening, thinning, and recycling of continental lithosphere due to the vigorous infiltration of volatile‐rich fluids and melts, especially along weak belts/layers, leading to widespread continental reworking and even craton destruction. Reworking of continents also occurs in continental interiors due to either plate boundary processes or plume‐lithosphere interactions. The effects of plumes have proven to be less significant and cause lower degrees of lithospheric modification than subduction‐induced craton destruction.

Multiple enrichment of subcontinental lithospheric mantle with Archean to Mesozoic components: Evidence from the Chicheng ultramafic complex, North China Craton

Numerous Late Paleozoic to Early Mesozoic mafic-ultramafic intrusions occur along the northern margin of the North China Craton (NCC). The timing, magma source, genetic types and tectonic evolution of these intrusions still remain controversial. Here we conduct a systematic petrological, mineral chemical, whole-rock geochemical, isotopic (zircon Lu–Hf and whole-rock Sr–Nd isotopes) and geochronological study on representative samples from the Chicheng ultramafic complex in the northern NCC, our results provide new insights into multiple melt-fluid interactions in the subcontinental lithospheric mantle through time. Zircon U–Pb data from the ultramafic rocks (pyroxenite and serpentinized dunite) show a wide range of ages (2721–129 Ma), indicating zircon growth within an evolving and metasomatized mantle wedge during multi-stage melt-fluid interactions. The youngest zircon population (145–129 Ma) possibly marks the timing of formation of the Chicheng ultramafic complex at the Early Cretaceous. Moreover, these ultramafic rocks also witnessed tectonic transition from Paleo-Asian Ocean to Paleo-Pacific Plate subduction during the Paleozoic to Early Mesozoic and subsequent progressive lithospheric thinning and craton destruction at the northern margin of the NCC, which is also attested by the newly discovered diorite porphyry dyke from this complex reported in this study with zircon U–Pb ages in the range of 447 to 128 Ma. Zircon Lu–Hf isotopic data show εHf(t) values in the range of −19.9 to +15.4 with TDM of 219–3012 Ma and TDMC of 240–3650 Ma. Whole-rock Sr–Nd isotopic data display εNd(t) values ranging from −12.3 to −1.6, indicating heterogenous sources involving both depleted mantle and reworked ancient crustal components. Whole-rock geochemical data show enrichment in LILEs (Rb, Sr, Ba, Pb) and depletion in HFSEs (Nb, Ta, Ti), with positive anomalies at Ba, K, Pb and Nd and strongly negative Zr and Ti anomalies, suggesting geochemical affinities related to subduction-related island arc setting within an active continental margin. Mineral chemical data on clinopyroxenes do not correspond to “Alaskan-type” affinities. Integrating geochemical, geochronological and isotopic studies from this study and those from previous studies related to the mafic-ultramafic complexes in the northern Hebei Province along the northern margin of the NCC, we propose that these complexes might be composite plutons formed during the Early Cretaceous, which were derived from the interaction of melts and fluids released from subducted slab with metasomatized mantle peridotite, triggering different degree of partial melting of mantle wedge.

Contribution of an Eastern Indochina-derived fragment to the formation of island arc systems in the Philippine Mobile Belt

AbstractThe Philippine Mobile Belt is a complex plate boundary with multiple terranes in Southeast Asia, yet its early tectonic evolution is still not fully understood due to a scarcity of solid evidence. Here we report new whole rock geochemical, Sr-Nd isotopic, and zircon U-Pb-Hf isotopic data for Cretaceous-Miocene arc magmatic rocks from the Cebu and Bohol Islands, Philippine Mobile Belt. Bulk geochemical data display arc affinities with enriched large ion lithophile elements (e.g., Sr and Ba) and depleted high field strength elements (e.g., Nb, Ta, and Ti). The high positive εNd(t) (+4.6 to +9.1) values and low initial 87Sr/86Sr ratios (0.7032–0.7048) suggest that these igneous rocks were generated by partial melting of mantle wedge in an arc setting. U-Pb dating of zircons revealed Cretaceous (ca. 120–90 Ma), middle Eocene to early Oligocene (ca. 43–30 Ma), and middle Miocene (ca. 14 Ma) crystallization ages for the arc magmatism with abundant Permian-Triassic zircon xenocrysts clustering at ca. 250 Ma. The Permian-Triassic grains show dominantly negative εHf(t) values ranging from −16.2 to −6.6, which are similar to those of coeval rocks in Eastern Indochina. Combined with previous paleomagnetic studies, we propose that an Eastern Indochina-derived continental fragment was involved during the formation of arcs in the Cebu and Bohol Islands, which highlights the potential contribution of ancient continental materials in the formation of intra-oceanic arcs. This scenario does not support the previously proposed model that the Cretaceous arc in the Philippine Mobile Belt formed in the northern margin of the proto-Philippine Sea Plate and Australian margin.

Middle Paleoproterozoic tectonic evolution of the Trans-North China Orogen, North China Craton: Constraint from the intermediate-acid magmatism in the Lüliang area

The excellent middle-Paleoproterozoic tectono-thermal activities from the Lüliang Complex can provide pivotal constraints on the tectonic evolution of the Trans-North China Orogen between Eastern and Western blocks of North China Craton. LA-ICP-MS zircon dating gives emplacement ages of 2189 ± 16 Ma for gneissic diorite, 2188 ± 11 Ma for gneissic quartz monzonite, 2153 ± 9 Ma for gneissic granite in Chijianling area, respectively. The gneissic diorites have high Al2O3 (15.89–16.69 wt%), MgO (3.35–4.96 wt%), low Sr/Y (11.3–16.6), (La/Yb)N (7.40–8.44), enrichment of LILE and depletion in HFSE, especially Nb, Ta, indicating partial melting of mantle wedge fluxed by the fluids. The gneissic quartz monzonites and gneissic granites belong to high K calc-alkaline and shoshonitic series and show right inclined REE patterns, consisting with I-type granite. Zircon Hf and whole-rock Nd isotopic compositions (εHf(t) = +0.1 to +5.3 and − 7.8 to −1.7; εNd(t) = −0.4 to +0.4 and − 1.8 to −0.6) of the gneissic quartz monzonites and gneissic granites are identical to those of dominant Neoarchean basement materials with addition of Mesoarchean vestiges to a certain extent. The diversity of source material (including continental and volcanic arc materials) resembles to magmatism in normal continental arc margins. The spatial distribution, rock assemblage and decreasing rock formation pressure further hint the tectonic transformation from compression to extension regime in local areas. Taking into account the prevalence magmatic records and contemporaneous deposition of middle-Paleoproterozoic in the Trans-North China Orogen, it suggests an active continental arc setting at ~2.2 Ga and local tectonic extension regime with back-arc basin at ~2.1 Ga for a consequence of the Paleoproterozoic subduction between the Eastern block and Western block of the NCC.

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The excellent middle-Paleoproterozoic tectono-thermal activities from the Lüliang Complex can provide pivotal constraints on the tectonic evolution of the Trans-North China Orogen between Eastern and Western blocks of North China Craton. LA-ICP-MS zircon dating gives emplacement ages of 2189 ± 16 Ma for gneissic diorite, 2188 ± 11 Ma for gneissic quartz monzonite, 2153 ± 9 Ma for gneissic granite in Chijianling area, respectively. The gneissic diorites have high Al2O3 (15.89–16.69 wt%), MgO (3.35–4.96 wt%), low Sr/Y (11.3–16.6), (La/Yb)N (7.40–8.44), enrichment of LILE and depletion in HFSE, especially Nb, Ta, indicating partial melting of mantle wedge fluxed by the fluids. The gneissic quartz monzonites and gneissic granites belong to high K calc-alkaline and shoshonitic series and show right inclined REE patterns, consisting with I-type granite. Zircon Hf and whole-rock Nd isotopic compositions (εHf(t) = +0.1 to +5.3 and − 7.8 to −1.7; εNd(t) = −0.4 to +0.4 and − 1.8 to −0.6) of the gneissic quartz monzonites and gneissic granites are identical to those of dominant Neoarchean basement materials with addition of Mesoarchean vestiges to a certain extent. The diversity of source material (including continental and volcanic arc materials) resembles to magmatism in normal continental arc margins. The spatial distribution, rock assemblage and decreasing rock formation pressure further hint the tectonic transformation from compression to extension regime in local areas. Taking into account the prevalence magmatic records and contemporaneous deposition of middle-Paleoproterozoic in the Trans-North China Orogen, it suggests an active continental arc setting at ~2.2 Ga and local tectonic extension regime with back-arc basin at ~2.1 Ga for a consequence of the Paleoproterozoic subduction between the Eastern block and Western block of the NCC.

The Ediacaran Rio Doce magmatic arc in the Araçuaí – Ribeira boundary sector, southeast Brazil: Lithochemistry and isotopic (Sm–Nd and Sr) signatures

The Rio Doce magmatic arc, developed from ca. 630 to ca. 580 Ma on an active continental margin, linking the Araçuaí and Ribeira orogens in southeastern Brazil. The arc plutonic portion comprises the G1 supersuite, a calc-alkaline, magnesian, I-type pre-collisional rock-assemblage, mostly composed of tonalite to granodiorite, frequently containing dioritic to mafic enclaves, and their metamorphosed equivalents. We carried out field, petrographic, lithochemical and isotopic (Sm–Nd and Sr) studies on a segment of the Rio Doce arc located in the transition region between the Araçuaí and Ribeira orogens. The studied samples include metamorphozed granitic rocks (referred to by their igneous names in the QAP diagram), consisting of syenogranite, monzogranite, granodiorite, tonalite, quartz diorite, orthopyroxene-bearing tonalite and orthopyroxene-bearing quartz diorite. This rock assemblage defines an I-type, magnesian, metaluminous to slightly peraluminous, medium-to high-K, expanded calc-alkaline series. The numerous mafic to dioritic enclaves and related features indicate magma mixing processes. Isotopic data show moderately to strongly negative εNd(t) values (−2.9 to −13.6) and intermediate to high 86Sr/87Sr ratios (0.7067–0.7165) suggests assimilation of older crustal material (i.e., the Juiz de Fora and Pocrane complexes, enclosing paragneisses), which is also indicated by Nd TDM model ages from 1.19 Ga to 2.13 Ga. Magmatic orthopyroxene and high content of CaO in garnet suggest magma crystallization in the deep crust. Together, our data point out to a combination of partial melting of mantle wedge in the subduction zone, deep crustal anatexis, host rock assimilation, and crystal fractionation for magma genesis in the southeastern Rio Doce arc.

Correlation of Quaternary Volcano Clusters With Partial Melting of Mantle Wedge, Northeast Japan: A Numerical Model Study

AbstractThe Quaternary volcano clusters in Northeast Japan and the no‐volcano zones between them imply extensive and scarce melting, respectively, in the mantle wedge, but no quantitative study on the heterogeneous melting has been conducted. Here, we constructed two‐dimensional numerical models by considering along‐arc temperature variations in the mantle wedge expressed as high‐ (hot fingers) and low‐temperature anomalies (deterred corner flow) with the slab dehydration, porous flow of aqueous fluid, and partial melting of the mantle wedge. The results show that the high‐ and low‐temperature anomalies in the mantle wedge result in extensive and negligible melting beneath the volcano clusters and no‐volcano zones, respectively, consistent with geochemical and geophysical estimations. Contrary to the near‐complete slab dehydration beneath the volcano clusters, the partially dehydrated subducting slab beneath the no‐volcano zones transports the remaining water into the mantle transition zone, which has implications for intraplate volcanoes in Northeast Asia.

Prolonged Neo-Tethyan magmatic arc in Myanmar: evidence from geochemistry and Sr–Nd–Hf isotopes of Cretaceous mafic–felsic intrusions in the Banmauk–Kawlin area

Cretaceous mafic–felsic intrusions are extensively distributed in the West Burma terrane (Myanmar), but their petrogenesis and tectonic setting still remain unclear. In this study, whole-rock geochemical and Sr–Nd as well as zircon U–Pb and Hf isotopic data for the Cretaceous mafic–felsic intrusions from the Banmauk–Kawlin area (northern Myanmar) are presented. Precise zircon U–Pb dating results indicate that they emplaced at Cretaceous (~ 110–90 Ma) and likely belong to an eastward extension of the coeval Gangdese magmatic belt in the southern Lhasa terrane (Tibet). The studied Cretaceous intrusions (SiO2 = 41.97 to 74.54 wt%) mostly have calc-alkaline and Na-rich characteristics, and strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb and Ta on primitive mantle-normalized diagrams, consistent with geochemical characteristics of arc-type magmas. Most of Cretaceous gabbroic and dioritic intrusions with relatively depleted mantle Sr–Nd–Hf isotopic compositions (87Sr/86Sri = 0.7041–0.7048, eNd(t) = 0.2–6.8, and eHf(t) = 4.3–15.1) and high Ba/La ratios were possibly derived from partial melting of mantle wedge metasomatized by slab-derived fluids and underwent a certain degree of fractional crystallization. Whereas Cretaceous granodiorite and granite probably formed by partial melting of juvenile arc lower crust on the basis of positive eNd(t)–eHf(t) values (− 2.4 to 6.6 and − 2.8 to 15.3) and low initial Sr isotopic ratios (87Sr/86Sri = 0.7045–0.7063). A wide range of Th/Nb ratios and Sr–Nd–Hf isotopic values in these intrusions suggests that their juvenile arc lower crust possibly formed by melting of slab-derived fluids and/or sediment melts metasomatized mantle. Overall, Cretaceous (~ 110–90 Ma) mafic–felsic intrusions in the West Burma terrane may have formed in an arc setting during subduction of the Neo-Tethyan oceanic lithosphere, suggesting a prolonged Neo-Tethyan magmatic arc system from southern Tibet to Southeast Asia.

Paleoproterozoic subduction within the Yangtze Craton: Constraints from Nb-enriched mafic dikes in the Kongling complex

Niobium-enriched mafic rocks constitute a rare suite of rocks formed in the subduction-related settings and provide important insights into mantle sources and geodynamic processes associated with plate subduction. In this contribution, we report newly-defined Nb-enriched mafic rocks from the Archean-Paleoproterozoic Kongling complex within the northern Yangtze Craton, which shed new light on the Paleoproterozoic subduction process of the craton. LA-ICP-MS zircon U-Pb dating reveals two episodes of Paleoproterozoic intermediate-mafic magmatism: (1) the ca. 2.15 Ga dioritic dikes and the younger Nb-enriched mafic dikes formed in 2.05–2.03 Ga. The ca. 2.15 Ga diorites have high Nb contents of 14.7–18.0 ppm but low Nb/LaPM (0.27–0.31), Nb/U (9.0 to 13.5) and Nb/ThPM values (0.24 to 0.31). The enriched zircon Hf isotope (ɛHf (t) = −4.8 ~ −1.1) and whole-rock Nd isotope (ɛNd (t) = −4.2 ~ −3.7) of the older diorites are similar to those of the coeval high-Mg andesites (~2.12 Ga) from the northern Huangling dome, indicate an enriched mantle source. The geochemical and isotopic data collectively suggest that they were derived from partial melting of a metasomatized sub-arc lithospheric mantle at the initial stage of subduction. The younger mafic rocks (ca. 2.05–2.03 Ga) possess high Nb contents (10.9–24.2 ppm) and lower magnitude of negative Nb anomalies with Nb/U (17.2–51.6), Nb/ThPM (0.40–0.88) and Nb/LaPM (0.49–0.97), which is different from those of normal island arc rock suites. The mafic dikes have negative zircon ɛHf (t) values (−12.6 ~ −10.5), dominantly negative ɛNd (t) values (−4.9 to −1.0, except one with +2.5), indicate an enriched mantle source. The Nb-enriched mafic rocks were likely produced by partial melting of mantle wedge that has been modified by the recycled continental sediments along the subduction zone. We infer that a slab window regime likely prevailed in the Kongling complex at ca. 2.05 Ga during the subduction termination. The opening of a slab window and asthenosphere upwelling possibly triggered partial melting of the enriched mantle wedge, and account for the generation of the younger Nb-enriched mafic dikes.

Late Cretaceous Neo-Tethyan slab roll-back: Evidence from zircon U-Pb-O and whole-rock geochemical and Sr-Nd-Fe isotopic data of adakitic plutons in the Himalaya-Tibetan Plateau

Abstract Late Cretaceous (ca. 100–80 Ma) magmatism in southern Lhasa subterrane records critical geological events, which can provide important insights into the regional tectonic evolution and geodynamic process of South Tibet. This study presents new zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Fe and zircon U-Pb-O isotopic data for two dioritic plutons in the southern Lhasa subterrane. Secondary ion mass spectrometry U-Pb dating on magmatic zircons from these rocks yielded a consistent age at ca. 90 Ma. The rocks exhibit variable SiO2 contents (52–59 wt%), high Fe2O3T contents (7.1–10.0 wt%), and low K2O/Na2O ratios (0.18–0.48). Most samples have high Al2O3 (17.0–19.5 wt%) and Sr (493–678 ppm), but low Yb (0.9–2.4 ppm) and Y (9–25.2 ppm) concentrations, and thus high Sr/Y (23–74) ratios, typical of adakite-like geochemical features. The adakitic rocks have relatively uniform initial 87Sr/86Sr isotopic ratios (0.7043–0.7046) and εNd(t) values (+3.67 to +4.16), indicating derivation from similar parental magmas. The δ56Fe values of whole-rock samples vary from 0.011 to 0.091‰ with an average of 0.045 ± 0.046‰ (two standard deviations), reflecting a homogeneous Fe isotopic composition, which is associated with melt-mantle interaction. In addition, the rocks are characterized by relatively high zircon δ18O values of 5.72–7.19‰, indicating the involvement of an 18O-enriched component during magma formation. The calculation of Al-in-hornblende barometer indicates that the adakitic rocks were emplaced at pressures of 6.4–9.8 kbar. Therefore, it is proposed that the adakitic rocks were most likely generated by partial melting of mantle wedge that had been previously modified by slab-melts at a relatively shallow depth, followed by minor fractional crystallization of hornblende. Taking into account previously published data in the southern Lhasa subterrane, we suggest that the ca. 90 Ma magmatism could be related to a period of Neo-Tethyan oceanic slab roll-back, which can provide new insights into the revolution process of the Neo-Tethyan ocean realm and the accretion of the Himalaya-Tibetan Plateau.

Newly discovered early Neoproterozoic (ca. 900 Ma) andesitic rocks in the northwestern Tarim Craton: Implications for the reconstruction of the Rodinia supercontinent

The Tarim Craton, one of the largest continental blocks in China, has been considered as a constituent block of the Rodinia supercontinent. However, the early Neoproterozoic tectonic evolution and the role of the Tarim Craton in the reconstruction of Rodinia remain controversial. Here, we present zircon U-Pb and Lu-Hf isotopic and whole-rock geochemical data for the newly discovered andesitic rocks in the Aksu area of northwestern Tarim Craton. LA-ICP-MS zircon dating results show that they were formed at ca. 908–903 Ma. These andesites have arc-type geochemical features such as enrichment in LREEs with (La/Yb)N ratio of 4.4–6.9 and obviously negative Nb, Ta, Ti anomalies. The high positive zircon εHf (t) (+7.5 to +11.9) values, integrated with trace element signatures, indicate that the magma source of the andesitic rocks were derived from partial melting of mantle wedge that was metasomatized by the sediment/slab-derived fluids through subduction, with possibly insignificant contributions from crustal materials. These geochronological and geochemical data suggest that subduction-related arc magmatism occurred in the northwestern Tarim Craton as early as ca. 900 Ma. Combined with a compilation of previous published data, these results therefore indicate that active continental margin probably widely occurred along the northwestern and southeastern margins of the Tarim Craton and adjacent microcontinents during the early Neoproterozoic, which may be linked to the Neoproterozoic circum-Rodinia subduction-accretion system.

Petrogenesis of gabbroic intrusions in the Valerianov-Beltau-Kurama magmatic arc, Uzbekistan: The role of arc maturity controlling the generation of giant porphyry Cu—Au deposits

Arc maturity is considered to play an important role in the mineralization of porphyry Cu—Au deposits. However, the early stage of arc is rarely preserved leading to controversies over arc evolution. Here we investigate gabbroic intrusions from the Akcha, Beleuti and Kalmakyr arc in relation to the Almalyk porphyry Cu—Au orefield in Uzbekistan. The Akcha biotite gabbro shows medium to fine grained texture, and is composed of plagioclase and biotite with minor clinopyroxene, orthopyroxene, quartz and magnetite. The Beleuti and Kalmakyr gabbros display coarse-grained texture, and are dominated by plagioclase, amphibole and clinopyroxene. Zircon LA-ICP-MS U—Pb dating yields ages of 339.9 ± 2.0 Ma for Akcha biotite gabbro, 339.0 ± 3.3 Ma for Beleuti gabbro and 335.0 ± 2.4 Ma for Kalmakyr gabbro. The emplacement ages of these intrusions are older than those of ore-bearing porphyries in the Almalyk orefield, indicating that the gabbros were emplaced during early stage of the arc evolution. The gabbroic rocks are characterized by high Mg# [100 × molar Mg2+/(Mg2++Fe2+), 41–61], low SiO2 contents (41.6–50.9 wt%), enrichment in large-ion lithophile elements and negative anomalies for high field strength elements, together with relatively depleted Sr-Nd-Hf isotopic compositions (0.7044–0.7057, −1.59-1.96, 3.38–9.96, respectively). The geochemical features suggest that these rocks were mostly derived from the partial melting of mantle wedge modified by subduction-related fluids. Estimates on water contents based on the composition of amphibole show 4.9–5.3 wt% for the Akcha biotite gabbro, and 5.6–6.8 wt% for the Beleuti gabbro. The oxygen fugacity estimated by zircon Ce/Nd, Ce4+/Ce3+ ratios are lower than those of porphyries from the giant porphyry deposits in the Central Asian Orogenic Belt. Our results, together with previously reported data on porphyries in the Almalyk orefield suggest that the gabbro was formed in an immature arc setting associated with the northward subduction of the Paleo-Turkestan oceanic plate, whereas the ore-bearing porphyries were formed in a mature arc.