Negative eHf Research Articles

The geochronology, geochemistry, and petrogenesis of the Leimengou porphyries, Qinling Orogen: A case study of intrusions associated with a Dabie-type porphyry Mo deposit

The Leimengou giant Mo deposit is a porphyry system in the northeastern Qinling Orogen along the southern margin of the North China Craton, comprising orebodies hosted mainly in a multiphase porphyritic granitic to monzonitic pluton emplaced in the Taihua Supergroup. Zircons from the syn-ore porphyritic monzogranite (PMG) and the porphyritic K-feldspar granite (PKG) yielded U − Pb ages of 131.3 ± 1.0 Ma and 130.6 ± 0.9 Ma, respectively. The post-ore, quartz monzonite porphyry (QMP), has a weighted mean 206Pb/238U age of 124.6 ± 1.0 Ma (n = 14, 1σ, MSWD = 0.13). These ages constrain the Leimengou porphyry system to have formed between 132 and 124 Ma. The PMG and PKG have similar geochemical characteristics, i.e., high-K calc-alkaline affinity, negative εHf(t) values of − 25.1 to − 22.0 and − 25.1 to − 19.2, and TDM2 ages of 2.77–2.57 Ga and 2.76–2.40 Ga, respectively. The PKG has lower concentrations for Sr, Ba, and negative anomalies of δEu, and also has higher total REE values compared to the PMG. These anomalies are interpreted to reflect fractional crystallization involving plagioclase and biotite. The characteristics of the PKG support its derivation from an evolved magma, which likely facilitated the enrichment of Mo. Additionally, the Hf isotope data suggest that the Leimengou porphyry system had a composite source, with inputs from the North Qinling Accretion Belt, the North China Craton, and the mantle. Compared to the syn-ore PMG, the post-ore QMP exhibits lower (La/Yb)N ratios of 20.5–22.8, higher zircon εHf(t) values of − 19.7 to − 9.0, and younger TDM2 ages of 2.42–1.75 Ga. This suggests that the Leimengou porphyry Mo system formed during thinning of an overthickened orogenic crust during the tectonic transition from collisional compression to post-collisional extension. The productive intrusions at Leimengou and other porphyry Mo deposits of Dabie-type have average Nb/Zr ratios that are typically below 1. Moreover, the Rb/Sr ratios range from 0.1 to 1, further distinguishing these intrusions from the intrusions associated with Climax- and Endako-type Mo deposits.

Geochemistry and Zircon U–Pb Geochronology of the Wugongshan Granites in the Northwestern Jiangxi Area, China: Implications for the Paleozoic Tectonic Development of South China

The properties of the Caledonian orogeny along the transition belt of the Yangtze and Cathaysia blocks have received much attention in recent years. The widespread Early Paleozoic granites provide critical geological clues for unraveling the tectonic evolution and geodynamic processes of the South China Continent (SCC). Here we present new zircon U–Pb chronology, whole-rock major and trace elements, in situ Hf isotopes for Paleozoic granites, i.e., the Wugongshan granites in the northwest Jiangxi province, and aim to explore the magmatism and properties of the Caledonian orogeny involved in their formation. Our new data show that the Wugongshan granites were emplaced during the Early Silurian Period (442–438 Ma). The Paleozoic Wugongshan granites belong to S-type muscovite-bearing peraluminous granites (MPG) and show a single origin. The Wugongshan granites exhibit negative εHf(t) values (−11.56 to −6.19) and TDM2 model ages of 2148–1809 Ma, indicating their derivation from an ancient crustal source, through partial melting of ancient crustal material. The Wugongshan granitic magmatism is probably being generated in an extensional environment related to an intracontinental orogeny setting. It is inferred that the Paleozoic tectonic–magmatic event in the Wugongshan area was associated with the oceanic–continental convergence of the Paleo-Tethys Ocean. The Wugongshan granites highlight the intracontinental magmatism in the Early Paleozoic orogeny in the SCC.

Zircon U–Pb ages and O–Hf isotopes of Quaternary trachytes from the East Sea: Implications for the genesis of low-δ18O magmas

Quaternary intraplate magmatism formed several volcanic islands and seamounts, including Dokdo (DD), Ulleungdo (UD), Simheungtack (ST), Anyongbok, and Isabu in the southwest of the East Sea back-arc basin. In this study, we present whole-rock geochemical, zircon U–Pb age, and in situ O–Hf isotope data for the submerged volcanic rocks from DD, UD, and ST to provide new insights into the eruption timing of these volcanoes and constrain the magma evolution processes. All samples used in this study were trachytes and exhibited ferroan, alkalic, and metaluminous to weakly peraluminous characteristics. They showed light rare earth element (REE)-enriched patterns with (La/Yb)N ratios of 25.3–31.7 and mostly negative Eu anomalies in a chondrite-normalized REE plot. In addition, they were enriched in large-ion lithophile elements and high field strength elements; they exhibited positive Pb anomalies and strongly negative Ba, Sr, P, and Ti anomalies. The zircons yielded a weighted-mean 206Pb/238U age of 2.61, 0.348–0.704, and 2.76–2.94 Ma for the DD, UD, and ST trachytes, respectively. All zircons exhibited lower δ18O values than normal depleted mantle values, regardless of the crystallization age and spatial distribution of volcanoes. The δ18O values showed no correlation with U contents or Th/U ratios, indicating that the low δ18O signatures were of primary magmatic origin. The Hf isotopic compositions of the zircons were relatively heterogeneous but predominately characterized by positive εHf values. Binary O–Hf mixing modeling revealed that low-δ18O rocks with positive εHf values from the UD and ST volcanoes were derived from a hybrid source of recycled juvenile crustal materials with low-δ18O and positive εHf signatures and an enriched mantle source with normal δ18O and negative εHf values. The juvenile oceanic crust in the source was likely metasomatized by seawater at high temperatures prior to melting. In contrast, the felsic magma that formed the DD volcanoes may have assimilated with regional basement rocks (Triassic–Jurassic granitoids), resulting in increased δ18O values and decreased εHf values relative to those of the UD and ST volcanoes. Our study highlights the significant contribution of recycled oceanic crust materials to the generation of the Quaternary magmas.

Mid-Mesoproterozoic (ca. 1.37 Ga) anorogenic magmatism in the Dabie orogen, northern Yangtze Craton: Response to the breakup of Columbia

It is evident that the Yangtze Craton was involved in the formation and breakup of the Columbia supercontinent. However, due to the scarcity of Mesoproterozoic geological records and reliable paleomagnetic data, little is known about the timing, paleogeographic position, and geological processes of the Yangtze Craton. We conducted detailed geological mapping, petrographic, geochemical, and in situ zircon U-Pb and Lu-Hf isotopic investigations on newly recognized Mesoproterozoic quartz syenite and monzogranite in the Dabie orogen, northern Yangtze Craton. The results show that the quartz syenite and the monzogranite were emplaced at 1369 ± 12 Ma and 1372 ± 5 Ma, respectively. Both rocks are high in total alkali (K2O + Na2O) content and FeOt/(FeOt + MgO), with elevated diagnostic 10,000*Ga/Al ratios and Zr + Nb + Ce + Y concentrations, and enrichment in light rare earth elements. They are also depleted in heavy rare earth elements with significant negative Eu anomalies but remarkably low Sr, Cr, and Ni contents. These compositions define affinity to A1-type granite. In addition, the quartz syenite displays variable zircon Hf and homogeneous whole-rock Nd isotopic compositions with positive εHf(t) values of +0.7 to +5.7 (average +2.4) and εNd(t) values of −0.1 to +2.5 (average +1.0). In contrast, the monzogranite has homogeneous zircon Hf and whole-rock Nd isotopic compositions with negative εHf(t) values of −5.7 to −2.6 (average −4.8) and εNd(t) values of −3.5 to −1.5 (average −2.2). We propose that the quartz syenite was likely generated by the partial melting of juvenile, crust-derived melt with involvement of minor mantle-derived material, while the monzogranite was likely derived from the partial melting of ancient crust in an extensional tectonic regime (e.g., continental rift). Based on the newly recognized ca. 1.37 Ga granitic magmatism and previously reported magmatic events, we argue that the mid-Mesoproterozoic (ca. 1.37 Ga) magmatism in the Yangtze Craton occurred in response to the breakup of Columbia, and represents the separation of the Yangtze Craton from Columbia. Furthermore, according to comparable magmatic and sedimentary events, we propose that the Yangtze Craton, along with central Hainan Island, may have been linked to northwestern Laurentia, southwestern Siberia, and northeastern Australia during 1.6−1.4 Ga.

Devonian to Early Carboniferous Retreating—Advancing Subduction Switch in the Northwestern Patagonia Accretionary Orogen: U‐Pb and Lu‐Hf Isotopic Insights

AbstractIn this contribution, we present new early middle Devonian igneous and metaigneous units with a major juvenile magmatic source input in the North Patagonian Massif, which were discovered through U‐Pb and Lu‐Hf zircon analyses. Afterward, we assessed their tectonic implications for northwestern Patagonia and then for southern South America, combining our results with available database information consisting of igneous crystallization ages and isotopic data of the Devonian to early Carboniferous magmatic units, tectonic‐metamorphic analyses, and thermochronologic record. This study allows for distinguishing retreating and advancing subduction switching in northwestern Patagonia (38°30′ to 44°S) and a contrasting coetaneous evolution for basement outcrops exposed further north (27°30′ and 37°30′S). The early middle Devonian (400–380 Ma) northwestern Patagonian magmatism is characterized by widespread magmatism and positive εHf–εNd linked to forearc and backarc magmatism that evolved within a retreating subduction stage. A tectonic switching toward advancing orogeny stage began in the late Devonian, evidenced by a lull in magmatic activity with a negative εHf–εNd trend, possibly contemporaneous with the first tectonic‐metamorphic event in western Patagonia. An early Carboniferous magmatic gap, followed by the subsequent development of the main foliation in the basement during the Carboniferous‐Permian period, denotes the acme of this contractional stage. In contrast, the Devonian period in the northern segment is characterized by mostly negative εHf–εNd values, reverse shear zone activity in the foreland, and an inboard magmatism migration, evidencing a compressive tectonic setting that changed to an extensional configuration in the early Carboniferous with widespread arc magmatism development.

Geodynamic evolution in the post-collisional stage of the East Kunlun Orogenic Belt: constraints from the Late Triassic intermediate–felsic igneous rocks

The Late Triassic igneous rocks associated with post-collision are widely distributed in the East Kunlun Orogenic Belt (EKOB), but their specific dynamic mechanism and evolutional process are still controversial. To address these key issues, we investigated the geochronology and geochemistry of intermediate–felsic igneous rocks from the EKOB, including trachyandesite, rhyolite, porphyritic monzogranite, syenogranite, granite porphyry and crystalline tuff. Zircon U–Pb isotopes of these rocks indicate that they were formed between 231.1 and 215.8 Ma (i.e. Late Triassic). These igneous rocks have moderate to high SiO2 (60.29–79.56 wt%) and low mantle compatible element contents (e.g. Co: 0.37–12.62 ppm; Ni: 1.55–15.59 ppm), suggesting that continental crustal-derived material played an important role in their formation. Porphyritic monzogranite (231.1 Ma), syenogranite (228.1 Ma), trachyandesite (227.4 Ma) and rhyolite (215.8 Ma) have Nb/U (1.41–4.71) and Ce/Pb (1.48–6.19) ratios like that of the crust, with εHf(t) values (–1.31 to 2.26) and old two-stage model (TDM2) ages of 1340–1119 Ma, suggesting that they originated from the partial melting of a Mesoproterozoic crust with minor mantle material involved in their source. Crystalline tuff (224.6 Ma) and granite porphyry (222.3 Ma) have Nb/U (1.93–3.81) and Ce/Pb (0.30–3.18) ratios, negative εHf(t) values (–7.04 to −5.12) and old TDM2 ages (1703–1581 Ma) closer to those of crust, suggesting that they were derived from the partial melting of a Paleo–Mesoproterozoic continental crust without addition of mantle material. Based on our new data and published data, the Late Triassic igneous rocks from the EKOB can be divided into three stages, 236–227, 226–218 and 216–208 Ma, corresponding to slab break-off, lithospheric mantle delamination and thickened lower crust delamination, respectively.

Geochronology and geochemistry of early Paleozoic magmatism in the Qilian orogen: Constraints on closure of the Proto-Tethys Ocean

The Proto-Tethys Ocean was a Neoproterozoic to early Paleozoic ocean that opened upon the breakup of Rodinia and closed by Paleozoic oceanic and continental subduction. The Qilian orogenic belt is the northernmost orogen of the Proto-Tethys domain and consists of the North Qilian belt, the Central Qilian block and the South Qilian belt. The processes responsible for extensive early Paleozoic magmatism in the Qilian orogen are crucial to understanding the closure of the ocean. This paper presents a systematic investigation of early Paleozoic mafic and felsic rocks in the Qilian orogen. Gabbroic dikes from the Central Qilian block have LA-ICP-MS zircon U-Pb ages of 499–497 Ma with a wide range of εHf(t) values of −9.94 to + 4.28 and TDM1 model ages of 1557–929 Ma, and dioritic dikes have a LA-ICP-MS zircon U-Pb age of 489 ± 3 Ma, positive εHf(t) values of +7.61 to +10.53, TDM1 model ages of 684–790 Ma, and an amphibole 40Ar/39Ar age of 486.3 ± 4.3 Ma. Both sets of dikes were derived from partial melting of a heterogeneous spinel-facies lherzolite lithospheric mantle that was modified by fluids and melts from a subducted slab. The protolith of amphibolites from the Hualong block in the South Qilian belt was a mafic intrusion of 454 ± 2 Ma with negative εHf(t) values of −9.69 to −7.79 and TDM1 model ages of 1390–1478 Ma. Its trace element signature indicates that sediment-derived melts were involved in the magma formation. An amphibole 40Ar/39Ar age of 418.7 ± 3.8 Ma from an amphibolite records the timing of amphibolite facies metamorphism. Felsic volcanic tuffs and granitic intrusions from the Central Qilian block have zircon U-Pb ages of 507–440 Ma with a broad range of zircon εHf(t) values of −9.60 to + 11.87 and TDM2 model ages of 2037–584 Ma. They have geochemical characteristics similar to I-type and S-type granites that were sourced from partial melting of juvenile and ancient continental crust with minor input of mantle materials. The formation of the felsic rocks indicates the transition from an arc-related setting to a post-collisional setting. Combining our results with existing data, we suggest that the Central Qilian block was affected by both southward subduction of the North Qilian ocean and the northward subduction of the South Qilian ocean, resulting in the formation of an Andean-type continental arc along the northern margin of the Central Qilian block and a subduction-accretion system along the southern margin of the Hualong block at ca. 530–440 Ma. Collision of the Central Qilian, Hualong, Quanji and Qaidam blocks at ca. 440–418 Ma marks the final closure of the Proto-Tethys Ocean.

Magmatic controls on Pb-Zn and W-Sn metallogenic variations in the Nanling Metallogenic Belt, South China: Difference in sources, oxygen fugacity and differentiation degree

The Nanling Metallogenic Belt (NMB) in South China contains huge amounts of Middle to Late Jurassic granitoid-related polymetallic Pb-Zn and W-Sn deposits. Whether there is a link between granitoid genesis and mineral species and what specific factors control the metallogenic specialization remained unclear. Herein, we presented a systematic investigation on the Dafang Pb-Zn ore-causative intrusion, and then placed it into the compiled comprehensive dataset of the NMB ore-hosting granitoids aiming to reveal the magmatic control on the Pb-Zn and W-Sn metallogenic variations in South China. Our results illustrate that the Dafang granitoid is potassic, alkaline (Na2O + K2O: 5.84 % to 7.87 wt%) and meta-luminous (A/CNK: 0.75 to 1.01), with middle SiO2 content (60.59–65.15 wt%), displaying an analogous nature of I-type granitoids. Trace elements of all samples are characterized by a significant enrichment in LREEs, Pb, and K, and a strong depletion of HREEs, HFSEs as well as Ba. Further zircon U-Pb dating yields a concordant age of 157.0 ± 0.8 Ma (MSWD = 1.1), consisting with the Jurassic magmatic-hydrothermal activities in the NMB. Their negative εHf(t) values (−6.7 to −10.2) and two-stage Hf model ages (1.6 to 1.7 Ga) suggest that the Dafang granitoid intrusion was generated from the partial melting of a Paleoproterozoic middle-lower crust. By comparing the Dafang with other NMB ore-causative granitoids in the comprehensive dataset, we investigated two types of ore-causative granitoids, i.e., the Pb-Zn- and W-Sn-mineralized granitoids, with distinct magmatic source, redox state and evolution degree. The Pb-Zn-bearing granitoids predominantly generated from amphibolite with a high oxygen fugacity (Ce4+/Ce3+: average 104.8, n = 55) and low differentiation degree (Rb/Sr: average 0.8, n = 60; Nb/Ta: average 12.5, n = 62). In contrast, the W-Sn metallogenic granitoids originated from metasedimentary rocks with a relatively lower oxygen fugacity (Ce4+/Ce3+: average 46.7, n = 258) and higher differentiation degree (Rb/Sr: average 59.0, n = 139; Nb/Ta: average 5.3, n = 156). Collectively, we conclude the Pb-Zn and W-Sn metallogenic variations in the NMB (South China) are jointly determined by magmatic sources, oxygen fugacity and differentiation degree.

Modification of Archean lower crust of the North China Craton by magma underplating during the Mesozoic: Evidence from zircon U-Pb-Hf-O isotopes of granulite xenoliths

Previous studies of felsic granulite and pyroxenite xenoliths have confirmed the existence of the Archean lower crust beneath the Fuxin region which experienced magma underplating in the Phanerozoic. U-Pb-Hf-O isotopes of zircons in felsic granulite xenoliths from the Fuxin late Cretaceous basalts in the North China Craton were analyzed to evaluate the role of magma underplating in the modification of the Archean lower crust during the Phanerozoic. The felsic granulites recorded a uniform upper intercept age of 2.5 Ga and a spread of concordant Mesozoic zircons from 177 to 105 Ma, with a peak at 118 Ma. Most Precambrian zircons show discordant U-Pb ages and obvious core-rim structure. The Mesozoic zircons from the granulite xenoliths can be divided into two groups: zircons with an age of >106 and those with an age of ≤106 Ma. Zircons with ages older than 106 Ma are characterized by an unzoned or core-rim structure and enriched Hf-O isotopic compositions, whereas zircons with ages of ≤106 Ma mainly exhibit oscillatory zoning and have depleted Hf-O isotopic compositions. Some >106 Ma zircons with strongly negative εHf(t) values of −40.4 to −24.9 are considered to be age resets of ancient zircons. The relatively higher Hf-O isotopic values for the rest of the >106 Ma zircons indicate that various proportions of underplated magmas with high εHf(t) and δ18O values contributed to their formation. The underplated magmas may have originated from the lithospheric mantle, metasomatized by melts/fluids from subducted Paleo-Asian and Paleo-Pacific oceanic crusts. The ≤106 Ma zircons probably crystallized in a melt from the depleted mantle. These observations suggest that long-lived magma underplating occurred beneath the Fuxin region during the Mesozoic, and the derivation of underplated magmas changed from an enriched lithospheric mantle to a depleted asthenospheric mantle at ∼106 Ma. Combined with our previous studies, we conclude that magma underplating not only provided heat for remelting, but also added exotic material in the modification of ancient lower crust beneath the Fuxin region during the Mesozoic. Furthermore, continuous modifications of cratonic lower crust by magma underplating weaken its refractory and made it more susceptible to chemical erosion and partial melting, which played an important role in the lower crust destruction of the craton.

Formation of columnar/tabular and vermicular kaolinite in the crystal tonsteins within the Late Carboniferous Coal in the Datong Coalfield, Shanxi Province, North China

The Datong Coalfield, Shanxi Province, North China, is rich in high-grade coal-measure kaolin, primarily occurring as partings within the Late Carboniferous–Early Permian coal seams. There is a type of kaolinite-dominant coarse-grained parting similar to sandstone in appearance, whereas the phanerocrystalline minerals are columnar/tabular and vermicular kaolinite rather than terrigenous detrital minerals. The origins of the coarse-grained partings and the formation mechanism of the columnar/tabular and vermicular kaolinite remain ambiguous. Herein, petrographical, mineralogical, whole-rock geochemical, and zircon U–Pb–Hf isotopic studies of the coarse-grained partings were conducted to explore these issues. The zircons in the coarse-grained partings show typical features of magmatic origin and yield a single age group of very latest Carboniferous at ca. 300 Ma, indicating they were transformed from air-fall volcanic ash. Therefore, the coarse-grained partings are essentially crystal tonsteins. The wide range of negative εHf(t) values and arc-related tectonic affinity of the zircons genetically link the primary volcanic ash to the Late Paleozoic continental arc volcanoes that existed in the Inner Mongolia Paleo-Uplift, related to the southward subduction of the Paleo-Asian oceanic plate beneath the North China Block. Two orthogonal cleavages are generally observed on the columnar/tabular and vermicular kaolinite in the crystal tonsteins, contradicting the crystalline structure of kaolinite that belongs to a 1:1 type phyllosilicate with only one cleavage along its (001) lattice plane. These columnar/tabular and vermicular kaolinite are considered to be pseudomorphic kaolinite after plagioclase in the crystal-rich volcanic ash. When the crystal-rich volcanic ash fell into open and acidic peat-forming environments (mires), the low-pH water containing abundant organic acids and good water circulation conditions facilitate dissolution of plagioclase along the chemically unstable (001) lattice planes and leaching out of Na+, Ca2+, and much of silica. Simultaneously, the Al3+ or hydroxides of aluminum and silica recrystallized along the (001) lattice planes of plagioclase as the substrate, constraining layer-by-layer growth of large kaolinite platelets to eventually form pseudomorphic kaolinite. The cleavages perpendicular to the exclusive (001) cleavage of pseudomorphic kaolinite should be inherited from the twin planes and (010) cleavage cracks (if present) of plagioclase.

The Early–Middle Triassic Supervolcano in the Yangtze Block, South China and associated obstacles to biotic recovery

The end–Permian mass extinction was one of the major global crises spanning the entire Early Triassic or longer. Eruptions of volcanos were one of the factors that delayed the biotic recovery after this event. Supervolcano eruptions can cause catastrophic effects on global environment, climate, and life. Here we investigate the tuff layers from Early–Middle Triassic boundary in the Yangtze Block and identify a supervolcano eruption event. The zircon U–Pb ages of the section–Langdai, section–Daijiagou and section–Longmendong tuff samples are 247.1 ± 1.9 Ma, 247.6 ± 2.0 Ma and 247.7 ± 1.7 Ma, respectively. These ages mark the Olenekian–Anisian boundary. The zircon grains from the tuff layers have negative εHf(t) (−15.3 to −0.8), two–stage Hf model (TDM2) ages (1.7 to 2.2 Ga) and display high–δ18O values (mostly > 10‰). Clay minerals and quartz dominate the rock composition. The whole rock compositions show that the tuff layers were derived from magma of intermediate to felsic composition, which formed by the remelting of Paleoproterozoic materials of continental crust. The volcanic eruption site is located in the Jinshajiang–Ailaoshan–Song Ma suture zone in the southwestern margin of the Yangtze Block. A combination of the closure of the Paleo–Tethys Ocean Basin and the collision of the Indochina Block and South China contributed to the eruption, which was a supervolcano eruption under the active continental margin arc settings. We speculate that this supervolcano eruption might have contributed to the delayed biotic recovery after the end–Permian mass extinction.

Pre-Eocene Arabia-Eurasia collision: New constraints from the Zagros Mountains (Amiran Basin, Iran)

Abstract The timing of continental collision between Arabia and Eurasia is a highly controversial issue, on which new constraints are here provided from the Amiran Basin (Zagros Mountains, Iran). Upper Cretaceous carbonate ramps grown along the Arabian northern margin are overlain by the siliciclastic deep-water Amiran and shallow-water Kashkan Formations, dated biostratigraphically as 64–60 Ma (Paleocene) and 56–52 Ma (earliest Eocene), respectively. Abundant ophioliticlastics, detrital Cr-spinel geochemistry, and detrital zircons with positive εHf(t) values dated as 110–80 Ma, 180–160 Ma, and 260–200 Ma indicate that the Amiran Formation was derived from the obducted Kermanshah ophiolite and Sanandaj-Sirjan zone. Besides sharing similar composition and zircon-age spectra, the overlying Kashkan Formation contains recycled detritus and one new zircon-age component with negative εHf(t) values dated as 250–200 Ma, suggesting supply from additional sources in Central Iran. The Amiran Formation thus indicates that the Kermanshah ophiolite, obducted in the Late Cretaceous, was subaerially exposed to erosion in the Paleocene. The Kashkan Formation testifies to the establishment of a new fluvial system, sourced from Central Iran and flowing across the Zagros suture zone. This implies that continental collision between Arabia and Eurasia took place before the beginning of the Eocene (56 Ma) in the Lorestan region (Iran).

Geochronology and Geological Implications of Paleoproterozoic Post-Collisional Monzogranitic Dykes in the Ne Jiao-Liao-Ji Belt, North China Craton

Hardly any previous studies have focused on the granitic dykes which intrude into the Paleoproterozoic Liaohe Group in the Liaodong Peninsula, northeast of the North China Craton. In situ zircon U-Pb dating, Lu-Hf isotopic and geochemical analyses on three representative monzogranite dykes were taken in this study. These dykes have relatively high content of SiO2 (72.20%–74.78%) and K2O (2.83%–6.37%), and have characteristics of high-K calc-alkaline to shoshonite series. Two dyke samples have I-type granite features and have high Sr/Y ratios and positive Eu anomalies, showing an adakitic feature. Another dyke has a high ratio of Ga/Al, but has a low Zr saturation temperature, which differs from the typical A-type granite. Zircon grains from these three dykes have typical magmatic zoning in CL images and yield consistent U-Pb ages of ~1859–1852 Ma, which are interpreted as the crystallization ages of these dykes. Hf isotopic analyses yield mainly negative εHf(t) values and TDM2 ages of 2782–2430 Ma, similar to those of the 2.2–2.1 Ga granitoids and meta-sedimentary rocks (the Liaohe Group), indicating these monzogranitic dykes may have been sourced from melting of Paleoproterozoic granitoids and meta-sedimentary rocks. The monzogranitic dykes were generated under a post-collisional geological setting after the Jiao-Liao-Ji orogeny process.

Petrogenesis and tectonic implications of the early Paleozoic granites in the Lincang granitic batholith, southwestern China: Constraints from geochronology, geochemistry and Hf isotopes

This study presents the recently discovered Wulao Shan Ordovician granite within the Lincang granitic batholith, discusses its geochemical affinity, genesis, and tectonic significance, and interprets the proto-Tethys orogenic model in southwest Yunnan. LA-ICP-MS zircon U-Pb analyses indicate a crystalline age of 473.0 ± 2.9 Ma for the Wulaoshan gneissic granite. Geochemical analyses show that the Wulaoshan granite exhibits relatively high SiO2 concentrations (73.4–77.3 wt.%), strong peraluminous properties (ASI > 1.1), strongly Eu-negative anomalies, light and heavy rare earth fractionation, and relative Ba, Nb, Ta, Sr, P, and Ti depletion. SiO2 and P2O5 exhibit a strong negative correlation, whereas Rb and Y-Th with a positive correlation. The magmatic zircons have negative εHf(t) values of -5.47∼2.74. Petrographic observations and whole-rock geochemical and isotopic analyses imply no aluminum-rich minerals such as cordierite, indicating that the Wulaoshan granite is a highly fractionated, high-temperature I-type granite, which may have formed via partial melting of the magnesian-iron igneous crust. Additionally, K-feldspar, plagioclase, and biotite within the granite samples may have undergone intense fractional crystallization. The Wulao Shan gneissic granite is an arc granite associated with subduction, indicating that the Lincang Block underwent proto-Tethys subduction. This finding provides evidence for proto-Tethys subduction down to the Lincang-Simao block and further supports the bidirectional subduction model of the proto-Tethys.

Southwest Borneo, an autochthonous Pangea-Eurasia assembly proxy: Insights from detrital zircon record

Abstract The current tectonic model for Borneo in SE Asia suggests that the SW Borneo block rifted from NW Australia at ca. 190 Ma and drifted across the Tethyan Ocean to collide with Eurasia in the Early Cretaceous. But, the global zircon Hf trend after 200 Ma indicates that circum-Pacific-style accretionary orogens prevail. The SW Borneo detrital zircon data set, which combines our new data with previous data, shows consistent age peaks (ca. 250 Ma, 1.9–1.8 Ga, and 2.5–2.4 Ga) in late Permian to Early Cretaceous samples. The Banda terranes, a notable block derived from NW Australia, have distinct detrital zircon age peaks for pre-breakup and post-breakup. Available Borneo detrital zircon εHf(t) values for ca. 1.8 Ga and 2.4 Ga are indistinguishable from those of NW Australia sources, but εHf(t) values for 300–200 Ma are more negative than those from the Gondwanide orogen and are more similar to those from the Peninsular Malaysia Indosinian orogen. We suggest SW Borneo is a Triassic accretion zone at eastern Cimmeria that rifted from NW Australia in the Permian. The ca. 250 Ma negative εHf(t) values present in samples are characteristic of Tethyan-style collisional orogens and show participation in Pangea assembly. SW Borneo underwent further autochthonous accretion along its SE margin (ca. 186 Ma and ca. 140 Ma) in a Jurassic Meso-Tethys and Paleo-Pacific supra–subduction zone setting. Our revision locates SW Borneo with other SE Tethysides blocks in Eurasia where accretionary orogens have influenced rises after 200 Ma.

Petrography, geochemistry and geochronology of igneous rocks from the Jiangnan Orogen, South China: constraints on the Early Paleozoic tectonic evolution of the South China Block

The Early Paleozoic tectonic evolution of the South China Block (SCB) remains controversial related to intracontinental orogenic and oceanic subduction processes. We present whole-rock major and trace elemental data, LA-ICP-MS zircon U-Pb age and Lu-Hf isotopic data for the Early Paleozoic igneous rocks including granodiorites from the Yuechengling pluton and volcanic breccias from the Damingshan pluton from the western segment of the Jiangnan Orogen in the SCB. LA-ICP-MS zircon U-Pb dating yielded emplacement ages for the Yuechengling S-type granitoids of 438–436 Ma and the deposited age for the Damingshan volcaniclastic rocks to be later than 451 Ma. The Yuechengling granitoids have consistent SiO2, TiO2, Fe2O3T, MgO, and P2O5 contents, higher Al2O3 contents, and Na2O + K2O values, but lower Mg# values, compared with those of the Damingshan volcaniclastic rocks. All the studied samples exhibit enrichment in LREEs and moderate negative Eu anomalies (δEu = 0.63–0.75), with negative Ba, Sr, Nb, Ta, P, and Ti anomalies, and positive Rb, Th, U, Pb, and K anomalies. The granitoids have variable CaO/Na2O ratios of 0.22–1.11, negative εHf(t) values of −11.98 to −0.90, and corresponding TDM2 ages distributed from 2.37 to 1.55 Ga. The petrographic and geochemical characteristics of the Yuechengling granitoids indicate that their parental magma was derived from a crustal meta-greywacke and meta-pelite components in the Paleoproterozoic basement, and have undergone some degree of fractional crystallization. The volcaniclastic rocks have mostly negative εHf(t) values with partially positive (−27.54 to 8.73), and zircons with negative εHf(t) values (−27.54 to −0.14) show TDM2 ages of 3.79 to 1.63 Ga. Combined with petrographic and geochemical data, we suggest that the Damingshan volcaniclastic rocks were derived from Neoarchean-Neoproterozoic crustal materials and the felsic parental magma has undergone some degree of magma mixing with mantle material, and deposited soon after a Late Ordovician volcanic eruption (later than 451 Ma). Integrated with previous studies, our new data support the intracontinental orogenic model to account for the Early Paleozoic tectonic evolution. Thus, we suggest that the Early Paleozoic tectonic setting of the SCB was intracontinental orogeny rather than oceanic subduction-collision.

A Devonian Shoshonitic Appinite–Granite Suite in the North Qinling Orogenic Belt: Implications for Partial Melting of a Water-Fluxed Lithospheric Mantle in an Extensional Setting

AbstractAppinite–granite suites commonly occur in the final stage of collisional orogenic processes, providing a unique opportunity to reveal the properties of continental lithospheric mantle and crust–mantle geodynamics. In this paper, we present a systematic study of the petrology, mineral chemistry, whole-rock geochemistry and geochronology of the Xiong’erling pluton and adjacent appinite dikes in the northern margin of the North Qinling orogenic belt. The pluton is mainly composed of diorites, quartz monzonites and minor granites. The diorites and appinites have LA-ICP-MS zircon U–Pb ages of c. 389 Ma with variable εHf(t) values of −5.58 to +3.36 and TDM1 model ages peaking at c. 1133 Ma. These rocks belong to the shoshonitic series with high Ba–Sr content and were emplaced in an intraplate extensional environment. The quartz monzonites and granites are oxidized A-type granites and have zircon U–Pb ages of c. 396 and c. 378 Ma with negative εHf(t) values of −11.99 to −1.18 and TDM2 model age peaks at 1434, 1720, and 1888 Ma. The in situ87Sr/86Sr ratios of plagioclase from the mafic and felsic rocks are 0.70565-0.70752 and 0.70695-0.71008, respectively. The Xiong’erling pluton and the coeval appinite dikes represent a Devonian appinite–granite suite in the North Qinling orogenic belt. Asthenospheric upwelling during the intraplate extension triggered partial melting of a phlogopite- and amphibole-bearing garnet lherzolite mantle source that had been previously metasomatized by the subducted oceanic slab, leading to the formation of a primitive hydrous mafic magma. The rapid ascent of the water-rich magma along deep-seated active faults with fast crystallization of amphibole resulted in emplacement of the c. 389 Ma appinite dikes. Replacement of anhydrous minerals by amphibole and biotite via hydrous reaction during magma cooling resulted in the formation of the coeval diorites. The mafic magma underplating triggered episodic remelting of a late Paleoproterozoic to early Mesoproterozoic crustal source, leading to the generation of the c. 396–378 Ma quartz monzonites and granites. Combining our results with existing data, we identify a sequence of (1) northward subduction of the Shangdan oceanic crust beneath the Qinling block at c. 524–438 Ma resulting in island-arc calc-alkaline magmatism, (2) closure of the Shangdan Ocean indicated by collision between the Qinling block and the South Qinling terrane and slab failure magmatism at c. 438–410 Ma, and (3) post-collisional to intraplate extension with alkaline magmatism at c. 410–370 Ma. The Devonian extensive intraplate magmatism marks the end of the Paleozoic orogenesis in the North Qinling belt.

Zircon U–Pb ages and Hf–O isotopes of Xiaomasa Miocene granite in the Ximeng area, western Yunnan, southwest China: Constraints on petrogenesis and tectonic setting

Characteristic granites of the East Tethyan Tectonic Domain (ETTD) are primarily exposed along the Himalayan orogenic belt and Gangdese batholith in the north, extend from western Yunnan in the centre, and through the Burma batholith to Peninsular Malaysia in the south. Western Yunnan is an important part of the ETTD magmatic arc, featuring characteristic granites that mainly developed between the Jurassic and Paleogene. Nonetheless, compared to other regions of the ETTD, Miocene magmatism has been poorly documented in western Yunnan. The Xiaomasa granite occurs in the Ximeng area of western Yunnan. In this study, we present U–Pb ages, and Hf–O isotope data for zircon crystals from the Xiaomasa granite pluton. Laser Ablation–Multicollector–Inductively Coupled Plasma–Mass Spectrometry (LA–MC–ICP–MS) zircon U–Pb dating yields precise emplacement ages of 15.8–16.1 Ma for the Xiaomasa granite, indicating that Miocene granitic magmatism occurred in western Yunnan. Zircons from the Xiaomasa granite have negative εHf(t) values ranging from −6.6 to −11.6, relatively high δ18O values (6.8%–10.2‰), and two‐stage Hf isotopic model ages (1.51–1.83 Ga). Zircon Hf–O isotopic characteristics indicate that the Xiaomasa granite was mainly derived from partial melting of ancient continental crust. The Ximeng Precambrian metamorphic basement is a probable material source for the granite. The Xiaomasa granite was probably produced by partial melting of the thickened Ximeng ancient metamorphic basement under a reduced pressure environment, reflecting a cumulative effect of the escape of Sundaland caused by the dynamics of the continuous India–Asia collision.

Positioning the Yangtze Block within Nuna: Constraints from Paleoproterozoic granitoids in North Vietnam

There is no consensus on the Precambrian paleogeographic reconstructions of Yangtze Block through the various supercontinent cycles and its linkage to other continental blocks. New data on the Paleoproterozoic tectonic history of the block enables linkage with other major Nuna-forming continents to be constrained. Zircon U-Pb-Hf isotopic and whole-rock elemental data highlight three episodes of Paleoproterozoic granitoids, dated at 2.30–2.27 Ga, 1.85–1.83 Ga, and 1.75 Ga from the Phan Si Pan Complex of the Phan Si Pan Zone, a southeast extension of the Yangtze Block in north Vietnam. The older two episodes of granitoid emplacement have negative εHf(t) values with similar TDM2 ages of 3.3–2.9 Ga, which suggest reworking of Archean basement rocks possibly at syn- to post-collisional settings. The 1.75 Ga A-type trondhjemite with positive εHf(t) values (0 to + 9) formed by partial melting of Paleoproterozoic juvenile crustal materials along with some mantle addition, most likely related to an intra-plate rift setting. Integrating the new results with compilations throughout the Yangtze Block, we suggest that the northern and southwestern Yangtze have different Archean and earliest Paleoproterozoic histories. Furthermore, correlations of Archean-Paleoproterozoic tectono-thermal and detrital zircon signatures between southwestern Yangtze and north Laurentia, and between northern Yangtze and southern Siberia, suggest they were close neighbors at these times. The collision between the northern and southwestern Yangtze in the late Paleoproterozoic is inferred to have led to the assembly of Laurentia and Siberia along a cryptic suture in central Yangtze and widespread crustal magmatism. Thus, we tentatively reconstruct the Yangtze Block as a key tie point between northern Laurentia and southern Siberia within the Nuna Supercontinent.

Provenance of multi-stage volcanic ash recorded in the Late Carboniferous coal in the Jungar Coalfield, North China, and their contribution to the enrichment of critical metals in the coal

The origins of partings within the Late Carboniferous No. 6 coal in the Jungar Coalfield, North China, and their relationship to the enrichment of critical metals in the coal, is poorly understood. This study combines UPb ages and LuHf isotope data of zircon, whole-rock geochemistry, LA–ICP–MS elemental mapping, and selective chemical extraction experiments to investigate the provenance of the partings and the occurrence mode of critical metals in the partings collected from the exploration area in the northwest of the Jungar Coalfield. It was found that the zircons in the kaolinite-dominant partings yielded a single age group of ca. 300 Ma at the latest Carboniferous (Gzhelian), indicating that the partings are alteration products of air-fall volcanic ash (tonsteins). The zircons are characterized by negative εHf(t) values and a continental arc tectonic setting, suggesting a genetic connection between the volcanic ash and the Late Paleozoic continental arc that existed in the Inner Mongolia Paleo-Uplift, related to the southward subduction of the Paleo-Asian oceanic plate beneath the northern margin of the North China Block. During the devitrification of volcanic glasses to kaolinite in the mires, the incompatible elements, such as Nb, Ta, Zr, Hf, and rare earth elements (REEs and Y, REY), preserved in the volcanic glasses were leached out as they are incompatible with the crystal lattice of kaolinite. Niobium and Ta, similar to Ti in ionic radii, were preferentially incorporated into fine-grained Ti oxides as reprecipitated products in the alteration process of volcanic ash. The enrichment of Nb, Ta, and Ti in organic matter in the tonsteins suggests that they have some mobility during alteration of volcanic ash and could be, to some extent, transported into the enclosing peats. Zirconium, Hf, and REY were fixed by organic matter admixed with the volcanic ash after their deposition in the mires. Meanwhile, they could also be transported into the enclosing peats, as no secondary minerals formed could substantially retain them. Although Li and Ga were able to be incorporated into the crystal lattice of kaolinite during their crystallization, they could also be transported into the enclosing peats due to their fluid-mobile nature. Both the leaching of a voluminous amount of volcanic ash contacting with the peats and the input of the volcanic ash as an admixture into the peats contributed to the enrichment of critical metals in the Late Carboniferous coal in the Jungar Coalfield.