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The increase in initial Hf isotopes identified in early Mesoarchean detrital zircon is commonly interpreted as a reflection of the geodynamic transition from stagnant‐lid to mobile‐lid tectonics. However, given the lack of petrogenetic context, interpreting detrital zircon may lead to spurious conclusions. In this contribution, we use zircon U‐Pb‐Hf‐O isotopic and bulk rock compositions of newly identified 3.05–2.9 Ga granitoids from the SW Yangtze Block to posit petrogenesis within an isotopically juvenile magmatic system. A statistical analysis of these data with a global igneous zircon Lu‐Hf isotopic compilation reveals an increase in average initial radiogenic Hf isotopes during the Paleoarchean to Mesoarchean transition. We posit that the Earth's continental crust underwent a global rejuvenation across the Paleo‐Mesoarchean transition. This rejuvenation can be explained by an independently observed increase in mantle temperatures resulting from mantle thermal evolution and does not require a change in tectonic style. Plain Language Summary: In this study, we explore the Earth's continental crust evolution before 3.0 billion years ago, a period characterized by limited preserved ancient rocks. We focus on zircon from igneous rocks, which provides a more reliable petrogenetic record than detrital zircon. Our study challenges the widely observed increase in detrital zircon initial Hf isotopes during the Paleo‐to Mesoarchean transition, often interpreted as a shift in tectonic regimes. We present new data from 3.05 to 2.9 billion‐year‐old granitoids in the Yangtze Block, suggesting isotopically juvenile magmatic activity. Statistical analysis of a global database of igneous zircon Hf isotopes reveals a state‐shift increase in εHf(t) across the Paleo‐to Mesoarchean transition, indicating global crustal rejuvenation at that time. Contrary to prevailing theories, we propose that this rejuvenation can be attributed to elevated mantle temperatures, challenging the notion of a significant geodynamic change during this period. Our findings emphasize the need to consider mantle thermal evolution in understanding continental crust growth on early Earth. Key Points: 3.05 and 2.9 Ga granitoids derived from juvenile crust are identified in the SW Yangtze BlockGlobal crust rejuvenation occurred across the Paleo‐to Mesoarchean transitionThis period of rejuvenation resulted from the effects of peak mantle temperatures [ABSTRACT FROM AUTHOR]

• 2.25 Ga A 2 -type granites are identified in the SW Yangtze Block. • The Paleo-Mesoproterozoic A 2 -type granites yield a secular increase in δ18O. • Diverse high-δ18O materials contribute to this secular increase. The elevation of δ18O in zircon through Earth history has been previously identified as being coeval with the assembly of post-Archean supercontinents. This was interpreted to result from the increasing incorporation of high-δ18O sediments into magmas due to enhanced crustal thickening and reworking during supercontinent assembly. However, little attention has been paid to the variations of δ18O in igneous rocks during the extensional phases of the supercontinent cycle. Given the scarcity of early Paleoproterozoic granites due to the ca. 2.3–2.2 Ga tectono-magmatic lull, we first report a suite of ca. 2.25 Ga granites from the SW Yangtze Block by providing zircon U-Pb-Hf-O isotopes, whole-rock geochemical, and Sm-Nd isotopic analyses to constrain their petrogenesis. The results demonstrate that they are A 2 -type granite and originated from the partial melting of Meso-Neoarchean igneous crust in a post-collision extensional setting. Integrating these data with a global compilation of Paleo-Mesoproterozoic A 2 -type granites allows us to further explore secular changes in elemental and isotopic compositions of these granite types. The A 2 -type granites in this study exhibit mantle-like zircon δ18O values, in accord with those from the compiled pre-1.85 Ga A 2 -type granites. Additionally, the data show a secular increase in zircon δ18O for the compiled Paleo-Mesoproterozoic A 2 -type granites. Similar increasing trends are also observed in various compositional proxies that imply the increasing addition of mafic igneous rocks into magma sources that are likely associated with the back-arc extensional settings of the Great Proterozoic Accretionary Orogen (GPAO). Considering that the compiled post-1.8 Ga A 2 -type granites have depleted Nd-Hf isotopes, we posit that they were mainly derived from mafic rocks with arc-like geochemical compositions. In this context, the secular increase in zircon δ18O for the post-1.8 Ga A 2 -type granites might reflect the increasing assimilation of altered oceanic crust into the back-arc and inboard magmatic systems of retreating accretionary orogens. In contrast, the compiled ca. 1.85 Ga A 2 -type granites possess non-radiogenic Hf and elevated O isotopes, indicative of the incorporation of ancient sediments in their magma sources. We suggest that they are most likely generated in a post-collision extensional setting associated with the very early stages of assembly of the Columbia/Nuna supercontinent. [ABSTRACT FROM AUTHOR]

Granulite-facies xenoliths entrained within igneous rocks shed a light on poorly understood yet critical questions about age, origin and history of the lower continental crust. Here, we present the first coupled in-situ U-Pb, Lu-Hf and O isotope data for the Precambrian zircons from fourteen deep-crustal xenoliths from the North China craton. The geochronological data demonstrates that the oldest lower crustal remnants formed at ∼3.82 Ga and related magmatism continued until ∼3.55 Ga. The Eo-Paleoarchean zircons, with exception of one analysis, have subchondritic initial Hf isotopes with negative ε Hf (t) and are characterized by normal mantle to elevated δ18O values (5.37–6.90‰), indicating a development of a low Lu/Hf reservoir and hydrosphere-crust interactions in the early Earth. Magmatic zircons from lower crustal xenoliths of North China define a strongly episodic distribution of ages at 3.82–3.55 Ga, ∼2.7 Ga, ∼2.5 Ga and 1.95–1.85 Ga and a non-linear Hf isotope-age array for nearly 2 Gyr, indicating episodic crustal generation and reworking through time. The lower crustal xenoliths record a change in zircon O isotope compositions from a restricted range at 3.8–2.6 Ga to more variable after ∼2.5 Ga. Both heavier (δ18O up to 10.25‰) and lighter (δ18O low to 2.16‰) O isotope compositions than the normal mantle are observed in ∼2.5 Ga magmatic zircons. The secular change in zircon O isotopes documents an increase in recycling rate of surface-derived materials (including high-δ18O sediments, weathered and altered rocks and low-δ18O altered oceanic crust) into magma sources at the end of Archean, which, in turn, is possibly linked to modern style subduction processes and maturation of the crust at that time. [ABSTRACT FROM AUTHOR]

Strictly speaking, since Tang I et al. i [[3]] focused on continental arc magmatism which was generated under a pre-existing continental crust, their results are more relevant to the evolution, I rather than i the origin, of continental crust. For instance, if garnet fractionation is the primary driver in increasing Mg# of continental calc-alkaline magmas, the process would also concomitantly raise the La/Yb ratio and decrease Yb due to garnet being a major carrier of heavy rare earth elements. The formation of continental crust is pivotal to understanding the evolution of the earth and its habitability. [Extracted from the article]

Abstract Low Nb Ta rhyolites from the Permian Tarim Large Igneous Province (LIP) represent the melting products of continental crust above a mantle plume. Zircon U Pb dating reveals that the Kuchehe and Dawanqi rhyolites were erupted at 292.6 ± 0.5 Ma and 274 ± 2 Ma respectively. Both rhyolite groups are characterized by pronounced negative Nb Ta anomalies, crust-like trace element ratios and negative ε Nd-Hf (t) values, consistent with a crustal origin. Newly acquired data, combined with available data in the literature, clearly show that there is an increasing trend of zircon saturation temperature (T Zr) from 794 to 827 °C to 886–936 °C for the early to middle stage (293–287 Ma), followed by a decreasing T Zr of 803–908 °C for the late stage (287–274 Ma) of the Tarim magmatism. The temporal changes in T Zr for the Tarim rhyolites are interpreted to reflect the crustal melting behavior above a mantle plume, such that fusible materials in the crust melt at an earlier stage and refractory materials melt at a later stage. The gradual decrease in T Zr , towards the final stage of the Tarim rhyolitic magmatism, reflects the gradual 'decay' of thermal input from mantle plume to the lithosphere in the region. This thermal model is also applicable to describe the crustal melting behavior in the Chon Aike silicic LIP of Patagonia and the Snake River Plateau-Yellowstone Plateau volcanic provinces. Highlights • The Tarim low Nb Ta rhyolite are partial melting products of crustal materials. • The low Nb Ta rhyolites exhibit a temporal variation in T Zr • The temporal changes in T Zr reflect crustal melting behavior above a mantle plume [ABSTRACT FROM AUTHOR]

The composition of lower crust of the Tarim Craton in NW China is essential to understand the petrogenesis of the ~290-275 Ma Tarim basalts and associated intermediate-felsic rocks. However, it remains poorly constrained because extremely sparse granulite terrains or granulite xenoliths have been found in the Tarim Craton. New trace element and Sr-Nd-Pb isotopic data are reported for the Neoarchean and Neoproterozoic igneous rocks widely distributed in the northern margin of the Tarim Craton. The Neoarchean granitic gneisses show fractionated REE (rare earth element) patterns [(La/Yb) = 12-58, Yb = 10.6-36] with pronounced negative Nb-Ta and Ti anomalies. These features, together with negative εNd (−0.7 to −3.2) suggest that they were derived from melting of mafic lower crust. The Neoproterozoic biotite granodiorites are strongly depleted in HREE with (La/Yb) up to 55. They are characterized by high Sr (671-789 ppm) but very low Y (7.10-8.06 ppm) and Yb contents (0.47-0.58 ppm), showing typical features of adakitic rocks. The samples with different SiO contents display identical Sr/Sr (0.7101-0.7103), εNd (−14.1 to −15.7) and Pb isotopes (Pb/Pb = 36.94-37.07). These features together with arc-like trace element patterns suggest that they were derived from melting of thickened lower crust. In comparison, the Neoproterozoic hornblende-biotite granodiorites have similar trace element compositions except for weaker depletion in HREE and have lower Sr/Sr (0.7078) and initial Pb isotopes, and higher εNd (−12.3 to −12.7). This suggests that they were formed by melting of old lower continental crust at a shallower depth than the biotite granodiorites. These rocks were derived from the lower crust, thus providing valuable information on the nature of the lower crust beneath northern Tarim. Combined with published data, the Sr/Sr, εNd, Pb/Pb and εHf of the northern Tarim lower crust ranges from 0.7055 to 0.7103, from −12 to −17, from 16.20 to 16.65, and from −7 to −19, respectively, at ~785 Ma. These data also suggest vertical compositional heterogeneity of the northern Tarim lower crust. [ABSTRACT FROM AUTHOR]

Abstract: The ~260Ma Emeishan Large Igneous Province (ELIP) in southwest China has previously been demonstrated to provide compelling evidence for pre-volcanic crustal doming in support of the mantle plume hypothesis. However this has been questioned by Ukstins-Peate and Bryan (2008) by showing hydrothermal magmatic activity at the Daqiao section. To solve this argument, a detailed characterization of the contact between the Emeishan basalts and the Maokou Formation was carried out. The contact is shown to be an unconformity, which is characterized by paleokarst on top of the Maokou Formation, including paleokarst relief, sinkholes, caves, tower karst and its corresponding rocks (such as kaolinite, bauxite and ferruginous duricrust and collapsed breccias, etc.). This paleokarst unconformity was in turn covered or infilled by the Emeishan basalts and tuffs, suggesting that uplift and erosion occurred prior to the eruption of the ELIP. The extent of erosion of the Maokou Formation indicates the ELIP can be divided into three roughly concentric zones: the inner, intermediate, and outer zones. The paleokarst features on the top of Maokou Formation vary across the ELIP. In the inner zone, a likely sinkhole and an incision valley with 450m relief in height are found. In the intermediate zone, various paleokarst landforms such as karst relief, sinkholes and tower karsts are well developed. Some sinkholes that developed in the Qixia Formation below the Maokou Formation imply that the paleorelief is more than 350m in height. In the outer zone, the paleokarstic surface is a paleo-weathering layer with minor karstification and development of caves at 10–50m. This spatial variation of the paleokarst reflects variation of uplift height across the ELIP. The extent of minimal uplift is estimated to be at least 450m in the inner zone, 350m in the intermediate zone, whereas uplift is minor (tens-50m) in the outer zone. The magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models. The paleokarst was formed after the deposition of the Maokou Formation and the eruption of the Emeishan basalts at the end-Guadalupian and indicates a short duration of uplift. Thus this study lends further support to domal uplift prior to the Emeishan flood volcanism, but also to the mantle plume initiation model for the generation of the ELIP. [Copyright &y& Elsevier]

Abstract: The Emeishan large igneous province in SW China comprises a bimodal mafic–silicic suite with the silicic rocks occurring at the uppermost part of the thick lava sequence. The silicic rocks have an age of 257–263Ma, and are thus roughly coeval with the Guadalupian–Loping (G–L) boundary event. Most silicic rocks (trachyte and rhyolite) from the Emeishan province have rather uniform ε Nd values (+1 to +2.9) that are comparable with the uncontaminated high-Ti basalts. This fact and the remarkably narrow ranges of incompatible element ratios (e.g., Zr/Nb) of the basalt–silicic suite indicate a genetic relationship between basalt and silicic members. The significant difference between the Emeishan rocks and the experimental melts of hydrated basaltic crust, suggests the fractional crystallization of basaltic magma, rather than crustal melting, as the major petrogenetic process for the formation of silicic rocks. Indeed, their major and trace element trends can be modeled by fractionation of the observed mineral phases (feldspar, clinopyroxene, Fe–Ti oxide and apatite). In contrast to the virtually closed system differentiation processes associated with trachytes, the rhyolites may have experienced interaction with upper crustal material during ascent. The geochemical characteristics and recent assessment of timing of the Emeishan volcanism suggest the Emeishan rhyolites as the potential source of the widespread clay bed at the G–L boundary in south China. This enhanced the causal link between the Emeishan eruption and the end-Guadalupian biological crisis. [Copyright &y& Elsevier]

Abstract: Nd–Hf isotopic decoupling has frequently been observed in the continental and oceanic mantle, but its origin remains controversial. Here we present combined elemental and Sr–Nd–Hf isotopic study on peridotite xenoliths entrained in Cenozoic basalts from Shuangliao and Jiaohe in Northeast China, which provides insight into this issue. The data reveal a heterogeneous lithospheric mantle beneath Northeastern China, consisting of fertile (type I) to strongly refractory (type II) peridotites. Type I peridotites are largely shielded from late metasomatism, thus preserving information of depletion events. Nd model age suggests a Proterozoic lithospheric mantle beneath NE China. Type II peridotites are mostly refractory harzburgites and show ubiquitous enrichment of incompatible elements. They are further divided into two sub-groups. Clinopyroxenes from type IIa samples have high and wide Lu/Hf (0.34–1.3) and very radiogenic Hf isotopic ratios (ε Hf =44.4–63.8). Hf concentration is generally low (0.12–0.43ppm) and plots along or slightly above the modeled partial melting depletion trend. In contrast, Nd content in type IIa clinopyroxenes is significantly higher than the modeled concentrations in residues at a given degree of melt depletion. The difference in enrichment of Hf and Nd translates to decoupling of Lu/Hf–Sm/Nd ratios and of Nd–Hf isotopes (ε Nd =−1.3 to 8.4). Clinopyroxenes from most of type IIb peridotites have relatively low Lu/Hf ratios (0.04–0.24) and coupled Nd–Hf isotopes. Both Hf and Nd plot significantly above the depletion trend; their concentrations are governed by the equilibrium partitioning between percolating melt and peridotites. The distinct geochemical characteristics of type IIa and type IIb clinopyroxenes may have resulted from chromatographic percolation of small volumes of silicate melts, in which percolation fronts of incompatible elements are dependent on their relative incompatibilities. [Copyright &y& Elsevier]

Abstract: Diapirism as a crustal magma ascent and emplacement mechanism has been increasingly questioned due to lack of unambiguous natural examples. In this paper we report the structure of the Cretaceous Fangshan pluton in the hinterland of the North China Craton, ca. 40km southwest of Beijing, China. This pluton is a compositionally and texturally concentrically zoned granodiorite with an approximately circular shape. Our detailed structural and petrological investigations reveal a high-temperature shear aureole with pluton-side-up kinematic indicators and a rim syncline around the pluton. In addition, an intensely deformed Archean complex occurs at the northern and southern margins of the pluton requiring at least 4km upward movement through the 4–5km thick overlying cover sequence during magma ascent. Based on comparison of stratigraphic units inside and outside the aureole, the bulk wall-rock shortening by ductile flow is estimated to be about 4km, which is roughly the same as the radius of the pluton. These features are consistent with results of numerous modeling studies and diagnostic criteria of magmatic diapirism, indicating that the Fangshan pluton is a magmatic diapir intruded into a ductile upper crust. [Copyright &y& Elsevier]

Abstract: SHRIMP zircon U–Pb dates, combined with in-situ Hf isotopic data, provide new constraints on the petrogenesis and protolith of peralkaline, metaluminous and peraluminous intrusions and rhyolitic tuffs in the Emeishan large igneous province, with significant bearing on crustal melting associated with mantle plumes. Syenite and A-type granitic intrusions from Huili, Miyi and Taihe in the center of this large igneous province yield U–Pb dates at ∼260Ma, consistent with the ages obtained for mafic layered intrusions in the same province. Zircon from these rocks exhibits a wide range of initial Hf isotope ratios (ε Hf(t)=−1.4 to +13.4), with corresponding T DM1 of 400–900Ma. The highest ε Hf(t) value is only marginally lower than that of depleted mantle reservoir at 260Ma, suggesting that their source is primarily juvenile crust added during Emeishan volcanism, with incorporation of variable amounts of Neoproterozoic crust. The trigger of crustal melting is most likely related to advective heating associated with magmatic underplating. In contrast, the 255–251Ma peraluminous granites from Ailanghe and 238Ma rhyolitic tuff from Binchuan, have negative initial ε Hf values of −1.3 to −4.4, and of −7.7 to −14, respectively. Hf isotopic model ages and presence of inherited zircons indicate their derivation from Mesoproterozoic and Paleoproterozoic crust, respectively. Given the time lag relative to the plume impact (∼260Ma) and insignificant mantle contribution to 255–238Ma magmatism, conductive heating is suggested as the trigger of crustal melting that resulted in formation of delayed felsic magmas. The involvement of older crust in younger felsic magmas is consistent with upward heat transfer to the lithosphere during plume impregnation, if the age of crust is inversely stratified, i.e., changes from Paleoproterozoic to Mesoproterozoic to Neoproterozoic to Permian with increasing depth. Such crust may have resulted from episodic, downward crustal growth during the evolution of the western Yangtze Craton. [Copyright &y& Elsevier]

Metasomatism of the lithospheric mantle by subduction-related fluids/melts is recorded in the Early Cretaceous Xinkailing high magnesium andesites (HMAs) from Western Liaoning. Olivine-hosted melt inclusions within the Xinkailing HMAs are alkaline and record a much lower SiO 2 content and higher Al 2 O 3 and CaO contents than the sub-alkaline bulk rock compositions. These observed compositional differences between bulk rocks and melt inclusions suggest that a crustally derived, high-SiO 2 melt was incorporated in the Xinkailing HMAs within the pre-eruptive magma chamber. The process of this incorporation accounts for the compositional differences between upper (HMAs) and lower (high magnesium basalts) successions of the Yixian Formation. Olivine phenocrysts also record unusually high Ni and Ni/MgO contents with high Fo values. Based on the fact that bulk rocks record low Ni contents, whereas olivine crystals record a steep correlation between Fo and Ni and low CaO and CaO/FeO contents, in addition to the likely considerable depression of the olivine liquidus temperature, we argue that a hydrous (2–6% H 2 O) orthopyroxene-rich pyroxenite source was formed by the reaction between subducted slab-released SiO 2 -rich fluids and overlying mantle peridotite. We further propose that during a series of Phanerozoic successive subduction events around the Eastern NCC, a significant amount of water may have been transported to the lithospheric mantle, thus lowering its viscosity and ultimately destabilizing the cratonic lithosphere. [ABSTRACT FROM AUTHOR]

This paper reports new zircon LA–ICP–MS and SIMS U–Pb ages and Hf isotope data, and whole-rock major and trace element data for Late Triassic igneous rocks of eastern Heilongjiang Province, NE China. These data provide new insights into the timing of the initiation of subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The zircon U–Pb age data indicate that a suite of Late Triassic (228–202 Ma) igneous rocks is present within the Songnen–Zhangguangcai Range Massif and within the western margin of the Khanka Massif. The Late Triassic igneous rocks within the Songnen–Zhangguangcai Range Massif consist of basalts, basaltic andesites, gabbro-diabases, and rhyolites, whereas coeval igneous rocks in the western margin of the Khanka Massif consist of hornblende gabbros and syenogranitic porphyries. These Late Triassic rocks constitute a geochemically bimodal igneous rock association that contains mafic rocks enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE) such as Nb, Ta, Zr, Hf, and Ti. Zircons from these mafic rocks have ε Hf ( t ) values and T DM1 ages of +2.8 to +9.8 and 477–733 Ma, respectively, suggesting that they formed from a primary magma generated by the partial melting of depleted lithospheric mantle material that had been previously modified by subduction-related fluids. The coeval felsic rocks are characterized by enrichments in LREEs and LILEs, and depletions in HREEs and HFSEs (including Nb, Ta, and Ti), and their zircons have ε Hf ( t ) values and T DM2 ages of +0.6 to +7.9 and 766 to 1461 Ma, respectively, implying that these rocks were generated during the partial melting of juvenile crustal material. The Late Triassic bimodal igneous rocks in eastern Heilongjiang Province, combined with the regional geologic information, therefore record a post-orogenic extensional environment related to the final late Permian–Early Triassic closure of the Paleo-Asian Ocean. In addition, the presence of Late Triassic bimodal igneous rocks within the eastern margin of the Eurasian continent suggests that the subduction of the Paleo-Pacific Plate beneath the Eurasian continent began after the Late Triassic. [ABSTRACT FROM AUTHOR]

Abstract: The nature of the source of continental flood basalts (CFB) is a highly debated topic. Proposed mantle sources for CFBs, including both high- and low-Ti basalts, include subcontinental lithospheric mantle (SCLM), asthenospheric mantle, and deep, plume-related mantle. Re–Os isotope systematics can offer important constraints on the sources of both ocean island basalts (OIB) and CFB, and may be applied to distinguish different possible melt sources. This paper reports the first Re–Os isotope data for the Late Permian Emeishan large igneous province (LIP) in Southwest China. Twenty one CFB samples including both low- and high-Ti basalts from five representative sites within the Emeishan LIP have been analyzed for Os, Nd, and Pb isotopic compositions. The obtained Os data demonstrate that crustal assimilation affected Os isotopic compositions of some Emeishan basalt samples with low Os concentrations but not all of the samples, and the Emeishan basalts with high Os contents likely experienced the least crustal contamination. The low and high-Ti basalts yield distinct Os signatures in terms of 187Os/188Os and Os content. The low-Ti basalt with the highest Os concentration (400ppt) has a radiogenic Os isotopic composition (γOs(t), +6.5), similar to that of plume-derived OIB. Because the Os isotopic composition of basalts with relatively high Os concentrations (typically >50ppt) likely represents that of their mantle source, this result implies a plume-derived origin for the low-Ti basalts. On the other hand, the high-Ti basalts with high Os concentration (over 50ppt) have unradiogenic Os isotopic signatures (γOs(t) values range from −0.8 to −1.4), suggesting that a subcontinental lithosphere mantle (SCLM) component most likely contributed to the generation of these magmas. Combining Pb and Nd isotopic tracers with the Os data, we demonstrate that the low-Ti basaltic magmas in the Emeishan CFB were mainly sourced from a mantle plume reservoir, whereas the high-Ti basaltic magmas were most likely derived from a SCLM reservoir or were contaminated by a significant amount of lithospheric mantle material during plume-related magma ascent through the SCLM. [Copyright &y& Elsevier]

The Early Permian Tarim large igneous province (Tarim LIP) consists mainly of basaltic lavas, mafic–ultramafic intrusions including dikes and, syenite bodies in the Tarim Basin, NW China. A major unit of the Tarim LIP, the Wajilitag intrusive complex, consists of olivine pyroxenite, clinopyroxenite and gabbro units (from bottom to top), diorite and syenite rocks occurred in the upper part of the complex and alkali mafic dikes intrude the clinopyroxenite phase. Here we report the zircon U–Pb age and Hf isotopes, geochemical characteristics and Sr–Nd–Pb isotopic data of the alkali mafic dikes, and diorite, aegirine–nepheline syenite and syenite porphyry units in the Wajilitag intrusive complex. Zircons from the diorite and alkali mafic rocks yield concordant crystallization ages of 275.2 ± 1.2 Ma and 281.4 ± 1.7 Ma, respectively. The diorite and syenitic rocks in Wajilitag area have a narrow range of SiO 2 contents (51.9–57.3 wt.%), and are enriched in total alkalis (Na 2 O + K 2 O = 8.3–14.3 wt.%), among which the aegirine–nepheline syenite and syenite porphyry have the geochemical affinity of A-type granites. The alkali mafic rocks and syenitic rocks have high Al 2 O 3 (19.4–21.1 wt.%), Zr, Hf, Ba contents, total rare earth element abundances and LREE/HREE ratios and low Mg# value, K, P and Ti contents. Diorites have lower Al 2 O 3 contents, total REE abundances and LREE/HREE ratios and higher Mg# values than the alkali mafic rocks and syenitic rocks. The diorites and syenitic rocks have low initial 87 Sr/ 86 Sr ratios (0.7034–0.7046), and high εNd( t ) values (0.1–4.1) and zircon εHf( t ) values (− 0.9–4.4). All the diorites and syenitic rocks show the 206 Pb/ 204 Pb ratios ranging of 18.0–19.5, 207 Pb/ 204 Pb of 15.4–15.6 and 208 Pb/ 204 Pb of 38.0–39.9. Sr–Nd isotopic ratios indicate a FOZO-like mantle source for the diorite and syenitic rocks, similar to that of the mafic–ultramafic rocks in the Wajilitag complex. In contrast, zircon Hf isotopes of basalt and syenite elsewhere in the Tarim LIP indicate a FOZO-like component may also contribute to Tarim LIP magmatism. Geochemical and Sr–Nd–Pb–Hf isotopic features reflect that diorites and syenitic rocks are probably derived from a FOZO-like mantle source, consistent with a plume mantle origin and then underwent crystal fractionation process. [ABSTRACT FROM AUTHOR]

Abstract: Late Carboniferous igneous rocks are widespread in the western Tianshan, but the tectonic settings for these rocks remain controversial. We report a plagioclase 40Ar/39Ar age, and geochemical, Sr–Nd isotope and LA–ICPMS clinopyroxene trace element data for gabbros in the Luotuogou region. The tholeiitic Luotuogou gabbros give a Late Carboniferous (312±1Ma) 40Ar/39Ar age and are characterized by high and variable εNd(t) values ranging from +3.7 to +7.8. They have geochemical features of both intra-plate and island arc magmatic rocks, i.e., relatively high TiO2 (0.6–2.2wt.%), Nb (4.2–24ppm) and Zr (51.4–283ppm) contents combined with variable and slightly high Nb/La ratios (0.24–1.8, mostly>0.7), and negative to positive Nb anomalies. The gabbros contain zoned clinopyroxenes, with Mg- and Cr-rich cores. Their parental magmas, as calculated using trace element data from Cr-rich (>3000ppm) clinopyroxene cores and clinopyroxene/basaltic liquid partition coefficients, show enrichments in incompatible elements, and prominent negative to slightly positive Nb anomalies, indicative of the influence of subduction-related compositions in their mantle source. These features indicate that the Luotuogou gabbros were most likely formed by interactions between asthenospheric and metasomatized lithospheric mantle. They were most plausibly formed by mixing between the asthenospheric mantle-derived and metasomatized lithosphere mantle-derived melts. Mixing was the result of asthenosphere upwelling triggered by roll-back of the subducted Paleo-Junggar Oceanic Plate rather than mantle plume-related rifting or post-collisional break-off during the Late Carboniferous. [Copyright &y& Elsevier]

Abstract: A suite of picrites and basalts from the Muli area, in the northwestern part of the Emeishan continental flood basalt province, provides new and valuable information on the geochemistry of the Emeishan Large Igneous Province (LIP) and its source. The Muli picrites can be classified as type-1 or type-2. The former shows ocean–island basalt-like trace element characteristics, with γOs (260Ma) values and εNd (260Ma) values ranging from +7.5 to +11.5 and from +6.0 to +7.8, respectively. This is the first time that picrites with highly radiogenic Os and high Os contents (up to 3.3ppb) have been recognized in the Emeishan LIP. These characteristics probably reflect a relatively enriched component in the Emeishan LIP source. The type-2 picrites are characterized by non-radiogenic γOs (260Ma) values ranging from −4.2 to −0.3, and they may be further subdivided into type-2A and type-2B picrites. Type-2A picrites contain moderate amounts of the light rare earth elements (LREEs), have low CeN/YbN values (1.1–2.0), and a relatively high initial εNd (+5.0 to +6.6). In terms of Os and Nd isotopes, the Muli type-2A picrites are similar to the Song Da komatiites of Vietnam and the Gorgona Island picrites, revealing the existence of a depleted mantle component in the Emeishan LIP source. In contrast with the type-2A picrites, type-2B lavas exhibit a negative Nb anomaly and relatively lower initial εNd and γOs values (Nb/La>1.8; εNd (260Ma)=−5.5 to +6.4; γOs (260Ma)=−4.2 to −1.9), suggesting that the type-2B lavas have a depleted mantle source, similar to type-2A, but that the type-2B lavas are also influenced by various degrees of mixing of depleted plume-derived melt, sub-continental lithospheric mantle, and/or continental crust. Given that the basalts in the Muli area show similar geochemical features to those of the type-2B picrites, their origins are inferred to be similar. [Copyright &y& Elsevier]

Abstract: There are several places in the Emeishan Large Igneous Province (ELIP) where highly magnesian volcanic or intrusive rocks accompany more abundant flood basalts. The high-Mg rocks vary in composition from LREE-depleted, low-Ti komatiites to LREE-enriched, high-Ti picrites. These magmas carried cognate olivine phenocrysts with Fo content higher than 91mol% indicating that these olivines crystallized and equilibrated with high-Mg melts. The maximum measured Fo content from the Dali area is 93.5mol% which, depending on the K D value used, indicates a MgO content of 23–25wt.% for the parental melt. The high estimated MgO wt.% values provide evidence for a hot portion of the Emeishan mantle-plume head with a potential mantle temperature of ca. 1700°C. Melt inclusions trapped within olivine phenocrysts have compositions similar to those of the host lavas but with a higher variability in the abundance of incompatible trace elements. The inclusions yield a calculated maximum MgO content of ca. 22wt.% for the melt. The compositional and isotopic variability of the high-Mg magmas in the ELIP is akin to that observed in basaltic rocks, which are divided into low-Ti and high-Ti types, suggesting that most of the basalts were developed in deep crustal magma chambers by fractional crystallization and mixing processes from primitive magmas. [Copyright &y& Elsevier]

Igneous rocks related to abnormal high heat flow preserved in ancient convergent margins provide direct clues to identify fossil ridge-subduction. The Khanka Massif, as a witness of the final termination of the Paleo-Asian Ocean in Late Paleozoic, provides an ideal opportunity to trace the fossil ridge-subduction. Different types of Permian igneous rocks (282–255 Ma) were identified in composition from mafic to felsic. The mantle-derived mafic rocks are further subdivided into two groups. Group I are arc-featured rocks with normal mantle-like features in Mg isotopes. Permian subduction setting was therefore proposed within western margin of Khanka Massif, supported by the coeval arc-featured granitoids and the detrital zircon cumulative proportion curves. By contrast, Group II are tholeiitic and have more depleted Sr-Nd-Pb-Hf isotopic compositions similar to MORB of Paleo-Asian Ocean. In addition, the decoupling between Sr-Nd-Pb-Hf and Mg isotopes indicate isotope exchange between MORB and magnesite. High heat condition is therefore required because of the decomposition reactions of magnesite. The crust-derived felsic rocks exhibit the prominent difference in Sr-Nd-Pb-Hf-Mg isotopic compositions, implying synchronous melting of the continental and oceanic crusts, which are supported by the high zircon saturation temperatures (855–935 °C). Consequently, an 'abnormal high-heat condition' caused by ridge subduction and resultant slab window is the most likely model to reconcile the diversiform magmatism and tectonic evolution along the west margin of the Khanka Massif in the Permian. Sr-Nd-Pb-Hf-Mg isotopes are therefore verified as an integrated tracer to decipher the magmatic response to the ridge-subduction in ancient subduction zone. • 'Abnormal' Permian igneous rocks were identified in easternmost CAOB. • Permian Ridge subduction was responsible for these 'abnormal' igneous rocks. • Integrated Sr-Nd-Pb-Hf-Mg isotopes were valid to trace fossil ridge-subduction. [ABSTRACT FROM AUTHOR]

The Wuda Tuff Flora in the North China Craton (NCC) is a "vegetational Pompeii" and one of the most completely preserved marsh ecosystems of the late Paleozoic Northern Hemisphere. However, the precise age, geochemistry, and petrogenesis of the thick tuff containing this peat-forming flora have not been established. We conducted a comprehensive petrographic, mineralogical, whole-rock geochemical, and zircon U Pb and Hf O isotopic investigation of five samples from a vertical section through the tuff bed. Our results confirm that the material that buried the flora is a volcanic tuff bed that has undergone intensive post-deposition alteration. Whole-rock Al 2 O 3 /TiO 2 ratios (65.8–103.5) and negative Eu/Eu* values (0.27–0.38) further suggest a felsic volcanic origin. Secondary ion mass spectrometry zircon U Pb dating of the altered tuff bed yielded a weighted mean 206Pb/238U age of 295.9 ± 1.4 Ma (1σ, MSWD = 0.94, n = 39), constraining the age of the Wuda Tuff Flora to the earliest Permian. Depletions of Nb and Ta in both the whole-rock and zircon compositions indicate an arc-related setting for the volcanism. The positive εHf(t) values (0.0 to +5.0) and δ18O values (5.05‰–6.17‰) of zircon grains from the Wuda Tuff suggest a juvenile crust origin of the volcanic magma. Geochemical comparisons with contemporaneous igneous rocks suggest that the volcanic eruption that led to the formation of the Wuda Tuff and associated vegetational Pompeii was most probably caused by arc volcanism along the western margin of the NCC related to subduction of Paleo-Asian Ocean oceanic crust, implying that the Alxa Terrane had not yet amalgamated with the NCC during the early Permian. • The Wuda Tuff was felsic arc-originated with juvenile crust. • The age of Permian Tuff Flora at Wuda Coalfield is 295.9 ± 1.4 Ma. • A magmatic arc may exist to the west of North China Craton during early Permian. [ABSTRACT FROM AUTHOR]