Calc-alkaline I-type Granites Research Articles

Early Triassic high-K granitoids and enclaves of the Daheba pluton, West Qinling (China): Implications for relative contributions of crust and mantle

Early Triassic granitoids are widespread in the northwestern West Qinling Orogen, China, but their petrogenesis and geodynamic implications remain unclear. In this study, we integrated new field and petrological observations, mineralogical compositions, zircon U-Pb dating, Hf isotopic and whole-rock geochemical analyses for the early Triassic granitic pluton in the Daheba area to determine its magma source and geodynamic scenario. The pluton is composed of granodiorite and syenogranite and carries microgranular enclaves (MEs) which formed at ca. 253–249 Ma. The granitoids show wide SiO2 contents of 63.73–77.49 wt% (av. 69.89), high K2O contents of 3.4–5.4 wt% (av. 4.1) and moderate Mg# of 16–51 (av. 36), belonging to high-K, calc-alkaline I-type granites. These rocks have high radiogenic but uniform Hf isotopic compositions with 176Hf/177Hf and ɛHf(t) of 0.282511–0.282658 and −3.85 – +1.25, respectively. The MEs hosed within the granite are characterized by high Mg# of 35–58 (av. 46) and variable εHf(t) of −4.64 – +9.35, which likely represent a hybridized melt derived from a slab-modified mantle and lower crust. In combination with coeval magmatic rocks in the western Gonghe-East Kunlun area, we propose a genetic model where mafic magmas derived from an enriched mantle and underplated beneath the overlying lower crust are considered to have produced the high-K felsic magma. Further, the hybridized melt ascended to shallower crustal levels to generate a series of rocks ranging from dioritic MEs to granodiorite to syenogranite. Mass balances modeling suggests that the generation of these rocks involved 36 % of the lower crustal-derived melt and 64 % of the SCLM (R2 = 0.9). Our new data, in tandem with published results suggest that the Daheba pluton formed during the subduction stage of the Paleo-Tethyan Ocean and that a local extensional episode occurred at 253–249 Ma in the western Gonghe area.

Linking beryllium enrichment to crystal-melt separation in granitic magmatic systems: Insights from high-silica granites in the southern Great Xing’an Range, NE China

High-silica granites are significant carriers of highly incompatible elements and are closely associated with mineralization of the rare metal beryllium. Thus, understanding their origin and evolution is of paramount importance for comprehending the evolution of the continental crust and enrichment processes of beryllium. This study presents zircon U-Pb ages, whole-rock major and trace element compositions, and Nd-Hf-O isotopic data for Early Cretaceous high-silica granite porphyries, monazite U-Pb ages and Nd isotopic data for beryllium-rich quartz veins, and whole-rock and apatite Nd isotopic data for Permian tuffs in the Dongshanwan W-Mo-Be deposit in the southern Great Xing’an Range, northeastern China. Our aim is to elucidate the link between mineralization and magmatism and to further our insight into the processes of crystal-melt separation and the mechanisms driving beryllium enrichment in granitic magmatic systems. Zircon U-Pb dating of the high-silica granite porphyry yields a weighted mean 206Pb/238U age of 141 ± 1 Ma, which is consistent with the age of hydrothermal monazite (ca. 140 Ma) from the beryllium-rich quartz veins. Hydrothermal monazite from the intra-granite porphyry quartz vein has positive εNd(t) values (+0.76 to +1.63) that overlap broadly with whole-rock Nd isotopic compositions of the host granite porphyry [εNd(t) = +1.24 to +1.61]. These characteristics indicate that the Dongshanwan beryllium mineralization was temporally and genetically associated with magmatic-hydrothermal activity of the Dongshanwan high-silica granite porphyries. Our systematic studies suggest that both the Dongshanwan high-silica granite porphyries and coeval Be-barren high-silica granites in the study area are high-K calc-alkaline I-type granites. They originated from a shared magmatic system and formed by the partial melting of a predominantly juvenile medium- to high-K basaltic crustal source, with a minor addition of old crustal components. Rayleigh fractionation modeling indicates that the granitic magma underwent a two-stage crystal-melt separation process. During the first stage, the fractional crystallization of a large proportion of plagioclase, in which beryllium is compatible, not only effectively inhibited beryllium enrichment in the differentiated melt, but also removed a large amount of Ca. During the second stage, minerals in which beryllium is incompatible dominated the fractionating assemblage owing to the low Ca contents in the magma, resulting in a surge in beryllium concentration in the differentiated melt. Our findings reveal that beryllium cannot be appreciably enriched in calc-alkaline granitic magmatic systems until plagioclase fractionation has substantially removed Ca from the system.

Petrogenesis and Tectonic Implication of Jurassic Granites in Central Guangdong, SE China: Constraints from Zircon U-Pb-Hf-O and Whole-Rock Geochemical and Sr-Nd Isotopic Data

Abstract The origin and tectonic regime responsible for the inland Jurassic granites in Southeast (SE) China remain controversial. This study presents zircon secondary ion mass spectrometry (SIMS) U-Pb ages, in situ zircon Hf-O isotopes, and whole-rock geochemical and Sr-Nd isotopic data for the Fogang and Xinxing Batholiths in central Guangdong. Mineralogical and geochemical features indicate that these granites are high-K (>4.8 wt% K2O at 72 wt% SiO2), calc-alkaline I-type granites. SIMS U-Pb analyses on magmatic zircons yield consistent ages ranging from 158 to 163 Ma, suggesting that the Fogang and Xinxing granites were emplaced in the period of 163–158 Ma. In addition, these granites have whole-rock initial Sr87/Sr86 ratios of 0.6802–0.7072 and negative εNd(t) values of −9.5 to −8.2, zircon negative εHf(t) values of −12.34 to −0.56, and high δ18O values of 7.64‰–10.08‰. The above features imply that the granites were most likely generated through the mixture of supracrustal sedimentary components with minor addition of mantle-derived magmas. Granites from the Fogang and Xinxing Batholiths in SE China should be derived from the Proterozoic crustal reworking due to asthenosphere upwelling or underplating and intrusion of mafic magmas. These Jurassic granites reflect anorogenic magmatism probably formed in an intraplate extensional setting resulted from the foundering of the flat slab beneath SE China.

Origin of late Carboniferous highly fractionated high-K calc-alkaline I-type granites from the eastern Pontides (Şiran, northern Turkey)

ABSTRACT The Sakarya Zone (northern Turkey) is characterized by the emplacement of voluminous granitoids during the late Carboniferous. In this study, we present geological, U-Pb zircon age, elemental abundance and Sr-Nd-Pb isotopic data on two highly evolved Carboniferous granite bodies within the Early to Late Jurassic volcaniclastic rocks in the Şiran region. The largest body forms a roughly E-W trending ~30 km long and 0.5–2.5 km wide stripe the southern boundary of which is a southvergent thrust, and the other one a subcircular outcrop, ~5 by ~3 km, unconformably overlain by Lower Jurassic volcaniclastic rocks. Their emplacement ages are constrained by LA-ICP-MS U-Pb zircon dating to 310–313 ± 7 Ma (2σ, late Carboniferous). The granitic rocks consist of quartz, microperthitic K-feldspar, plagioclase, and minor biotite, and are characterized by highly evolved compositions with high concentrations of SiO2, Na2O, K2O and Ba, and low concentrations of TiO2, Fe2O3*, MgO, CaO, P2O5 and Sr. Geochemical characteristics indicate a highly fractionated high-K calc-alkaline peraluminous I-type affinity. Chondrite-normalized rare-earth element (REE) patterns are slightly fractionated, with light REEs enriched with respect to middle and heavy ones, and showing variable negative Eu anomalies. On the N-MORB-normalized multi-element variation diagrams, samples display negative anomalies of Ba, Nb, Sr, P, Zr, Eu, and Ti, and positive anomalies of K, and Pb. Initial 87Sr/86Sr and εNd values are 0.70432–0.70610 and −6 to −11, respectively, similar to other Carboniferous high-K calc-alkaline granites and mafic-ultramafic intrusions in the region. The compositional characteristics of the Şiran granites can be explained mainly by fractional crystallization involving hornblende, plagioclase, and biotite and without the involvement of significant amounts of garnet. There is no need to invoke magma mixing and/or melting of a heterogeneous source to account for the geochemical variation. We propose that the late Carboniferous granites formed by remelting of middle- to high-K calc-alkaline mafic rocks at lower crustal depths, followed by extensive fractionation at the upper crustal depths. A thorough review of data from the literature reveals that highly fractionated granites constitute a significant component of the late Carboniferous granites in the Eastern Pontides.

Mesozoic crustal reworking at different depths in the North China Craton: Insight from the coexisting Early Cretaceous high and low Sr/Y granitoids

Crustal reworking, an important part of continental evolution, can occur in cratons even though they are generally rigid and stable. However, the reworking mechanisms are still debated. Here, we present detailed zircon UPb ages, mineral compositions, major and trace elements, and Sr–Nd–Pb–Hf isotopic data for the coexisting high and low Sr/Y granitoids in the Liaodong Peninsula to decipher the reworking mechanism in the eastern North China Craton (NCC). Mafic microgranular enclaves (MMEs) are common in the studied granitoids, and both the granitoids and their MMEs have consistent emplacement ages of 128–126 Ma. The low and high Sr/Y granitoids are characterized by high-K calc-alkaline I-type granites. They are enriched in light rare earth elements (REEs) and large ion lithophile elements (e.g., Rb, K, and Pb), with depletions in high field strength elements (e.g., Nb, Ta, P, and Ti). The low Sr/Y granitoids have homogeneous Sr–Nd–Pb-Hf isotopic compositions, indistinguishable from those of their MMEs, indicating that they are of cognate origin. Their high (87Sr/86Sr)i (0.713759–0.715341), low εNd(t) and εHf(t) values (−19.2 to −18.1 and − 20.9 to −15.0, respectively), and old two-stage Nd and Hf model ages (ca. 2.50 Ga) suggest that they are derived from partial melting of the ancient lower crust at a normal crustal depth. In contrast, the high Sr/Y granitoids show more depleted heavy REEs and higher Sr/Y (21.1–80.2) and (La/Yb)N (19.2–50.2) ratios, with very low Y (≤ 12.5 ppm) and Yb (≤ 1.11 ppm) contents and negligible Eu anomalies. Their enriched and variable Sr–Nd–Pb-Hf isotopes (e.g., εNd(t) = −20.8 to −14.9, εHf(t) = −24.3 to −9.2) are distinctly different from those of their MMEs (e.g., εNd(t) = −17.6 to −13.2, εHf(t) = −20.8 to −0.3), implying a magma mixing process. These features suggest that the high Sr/Y granitoids and their MMEs are formed by mixing of the thickened ancient lower crustal and lithospheric mantle-derived magmas, with minor contributions of the asthenospheric mantle. Combined with the coeval (129–114 Ma) high-Mg adakitic and A-type granitoids, the coexisting high and low Sr/Y granitoids may indicate intensive crustal reworking at variable depths in the NCC. The reworking is attributed to the asthenosphere upwelling and lithospheric delamination induced by the rollback of the subducting Paleo-Pacific plate.

Paleo-Pacific subduction in Southeast Vietnam: Evidence from Late Cretaceous intrusive rocks in the Dalat zone

The Dalat zone in Southeast Vietnam forms a key component of the Paleo-Pacific subduction system, which stretches from the Coastal South China to West Borneo. Petrology, zircon UPb geochronology and in-situ LuHf isotopes, and whole-rock geochemical analyses for gabbros and granitoids in this zone might define details of its role in the Pacific subduction. The gabbros in this region yield an age of ca. 93 Ma, and are enriched in large-ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) with remarkable negative anomalies in NbTa and Ti, similar to the Cretaceous mafic rocks in the Coastal South China. Their initial 87Sr/86Sr ratios range from 0.70531 to 0.70615, εNd(t) values range from −0.8 to +1.4, (206Pb/204Pb)i ratios range from 18.58 to 18.67 and zircon in-situ εHf(t) values range from +0.4 to +9.7. These characteristics suggest that the gabbros originated from a mantle wedge that had modified by sediment-derived melts. The granitoids found in the Deoca, Dinhquan, Ankroet (Cana) suits of the Dalat zone formed at 103–93 Ma. They exhibit significant variations in major oxide content (SiO2 = 58.84–78.61 wt%; MgO = 0.04–2.66 wt%), classifying them as high-K calc-alkaline I-type granites. In comparison with coeval gabbros, the granitoids show similar whole-rock Sr-Nd-Pb and zircon in-situ LuHf isotopic compositions, arguing for a juvenile crust with arc-like geochemical affinities. The Cretaceous igneous rocks in the Dalat zone of Southeast Vietnam give collectively two age-clusters of ca. 122–112 Ma and ca. 108–75 Ma, resembling those in the Coastal South China and West Borneo. Consequently, these rocks are considered the part of the Cretaceous Paleo-Pacific subduction system, providing a connection between South China in the north and West Borneo in the south.

Devonian continental arc magmatism in the southern Central Asian Orogenic Belt: Evidence from the Dunhuang Block, NW China

Reconstruction of periods and sources of continental arc magmatism provides critical insights for deciphering the thermal evolution and geodynamics of the continental lithosphere and unveiling subduction-related episodes of accretion and orogeny. The Dunhuang Block, located in the southern Central Asian Orogenic Belt, is built upon a Precambrian metamorphic crystalline basement that is intruded by numerous Paleozoic granitoids. In this paper, we present new zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes from the Hanxiakouzi and Shuangta granodiorite plutons outcropped in the central and northern Dunhuang Block, respectively. The U-Pb zircon dating indicate that the Hanxiakouzi and Shuangta granodiorites were emplaced at ca. 366–363 Ma, i.e., in the late Devonian. Geochemically, the Hanxiakouzi granodiorites are medium- to high-K, I-type granites possessing high Sr and Sr/Y, i.e., similar to adakites. The Hanxiakouzi granodiorites show negative εNd(t) values (−8.2 to −6.6), significant positive εHf(t) values (+0.7 to +8.1), and evolved Pb isotope features suggesting their derivation by melting of subducted terrigenous sediments, interaction of melts with mantle peridotite, and assimilation of ancient crust during magma ascent. The Shuangta granodiorites belong to high-K calc-alkaline I-type granites with medium Sr and low Sr/Y. The Shuangta granodiorites yield negative εNd(t) values (−2.9 to −3.1) and negative to positive zircon εHf(t) values (−1.8 to +3.6), suggesting their formation by partial melting of ancient mafic crust with addition of minor mantle-derived melt and subducted terrigenous sediments. In general, Hf-in-zircon isotopes characteristics of the late Paleozoic granitic rocks in the Dunhuang Block indicate that the southern Dunhuang area carries more ancient crust materials than the central and northern Dunhuang areas, indicating a lateral heterogeneity of the middle Paleozoic crust. Conclusively, the middle Paleozoic granitoids of the Dunhuang Block were emplaced at an active continental margin of the southern Paleo-Asian Ocean.

Permian-Triassic tectonic evolution of the Ailaoshan orogenic belt in SW China: insights from magmatic records

ABSTRACT The Ailaoshan orogen in SW China records the evolution of the Ailaoshan Paleo-Tethyan ocean and the amalgamation history between the South China and Indochina blocks, an important process for the formation of Southeast Asia. However, its tectonic evolution remains ambiguous with various competing models. We have carried out an integrated geochronological–petrological–geochemical study for the granites, dacites-rhyolites, granodiorites and trachyandesites in this orogen to give new constraints on this issue. The 255–254 Ma granites and the 250–248 Ma dacites-rhyolites show similar geochemical features and are characterized by strongly peraluminous nature, continental crust-like trace element patterns and negative zircon εHf(t) values (−14.4 to −6.6), indicating they derived from partial melting of ancient crust. The 229 Ma hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.96–1.01) and belong to high-K calc-alkaline I-type granites. They show depleted whole-rock Sr-Nd and zircon Hf isotope compositions (initial 87Sr/86Sr = 0.7027 to 0.7038, εNd(t) = 4.0 to 4.1, εHf(t) = 9.3 to 11.5), suggestive of derivation from partial melting of juvenile mafic crust. The 226 Ma trachyandesites are characterized by high MgO (4.1–4.6 wt.%), high Mg# (56) and arc-type geochemical affinities with enriched isotope compositions (initial 87Sr/86Sr = 0.7108 to 0.7111, εNd(t) = −7.7 to −7.5, εHf(t) = −6.3 to −3.5). These features indicate that their parental magmas derived from partial melting of enriched lithospheric mantle metasomatized by oceanic sediment-derived melts. These new data, in conjunction with spatial-temporal-temperature variations of igneous rocks, metamorphic records and stratigraphic changes in the region, suggest that the Ailaoshan Paleo-Tethyan ocean closed at the Early Triassic (ca. 250 Ma) which was followed by the Late Triassic postcollisional slab breakoff, and the ocean experienced westward unipolar subduction during its evolution with no assumed eastward subduction.

Carboniferous mafic-ultramafic intrusions in the Eastern Pontides (Pulur Complex): Implications for the source of coeval voluminous granites

This study deals with the age and petrogenesis of mafic-ultramafic intrusions ranging in size from a few meters to 10 km within the Early Carboniferous high-grade gneisses of the Pulur Complex in the Eastern Pontides. The intrusions comprise dunite, wehrlite, gabbronorite, leucogabbro, anorthosite and ilmenite-bearing gabbronorite of cumulus origin, and are crosscut by dikes of ilmenite-bearing gabbronorite, leucogranite and microdiorite. U Pb dating on zircons from gabbronorite, anorthosite and leucogranite yielded igneous crystallization ages of 322–326 Ma, indicating that the intrusions were emplaced ca. 5–7 Ma after the peak of high-grade metamorphism, and form part of the Late Carboniferous high-volume magmatism in the region. In most cumulate rocks, Cr Al spinel, olivine and plagioclase were early crystallizing phases, followed by orthopyroxene, clinopyroxene and hornblende. Whole rock geochemical data suggest that wehrlite, gabbronorite, leucogabbro and anorthosite stem from a common magma, and ilmenite-bearing gabbronorite and dikes of leucogranite and microdiorite from different magmas. Application of mineral/melt partition coefficients to trace element compositions of clinopyroxene and hornblende in cumulate rocks suggests that the main cumulate body was derived from middle- to high-K calc-alkaline basic melts, and relatively late ilmenite-bearing gabbronorites from hypersthene-normative Ca-rich melts. All the rock types display radiogenic Sr and Pb isotopic signatures, and unradiogenic Nd isotopic ratios, which are indistinguishable from those of the coeval voluminous high-K calc-alkaline I-type granites in the region; the isotopic ratios are probably related to the metasomatism of the lithospheric mantle by sediment-derived melts. We suggest that the parental melts of the mafic-ultramafic intrusions and those of the high-K calc-alkaline granites were genetically related, and melts of the high-K calc-alkaline granites were probably derived from the melting of newly underplated calc-alkaline basic material at lower crustal depths, that were compositionally comparable to the parental magmas of the mafic-ultramafic intrusions. • The Pulur mafic-ultramafic intrusions (NE Turkey) formed at 326–322 Ma. • They are part of the Late Carboniferous high-volume magmatism. • Parental melts of the mafic-ultramafic intrusions were middle- to high-K calc-alkaline basic melts. • The high-volume magmatism probably resulted from the convective thinning of the lithosphere.

Geochronology and Petrogenesis of Ahetala Granodiorite in South Tianshan Orogenic Belt, Xinjiang: New Constraints on the Tectonic Evolution of the South Tianshan Ocean

The Ahetala granodiorite is located in the western section of the South Tianshan Orogenic Belt (STOB), which is of great significance regarding the dispute on the closing date of the South Tianshan Ocean (STO) and the tectonic evolution of STOB. To determine the tectonic setting and petrogenesis, the study of petrography, electron probe microanalysis (EPMA), LA-ICP-MS zircon U–Pb geochronology, and major and trace elements analyses are carried out for Ahetala granodiorite. Based on LA-ICP-MS U–Pb zircon dating, the granodiorite was emplaced at 282.1 ± 1.3 Ma (MSWD = 1.11). Geochemically, Ahetala granodiorite is characterized by metaluminous (A/CNK = 0.86–0.87), rich alkali (K2O + Na2O = 6.80–7.13), which belongs to high-K calc-alkaline I-type granite. They are enriched in LREE and depleted in HREE (LREE/HREE = 9.02–13.89) and exhibit insignificant Eu anomalies (δEu = 0.94–0.97). Ahetala granodiorite is enriched in large ion lithophile elements (e.g., K, Sr, Ba) and depleted in high field-strength elements (e.g., Ta, Ti, Nb, P). The Nb/Ta values (10.97–18.10), Zr/Hf values (39.41–40.19), and Mg# (54.87–56.02) of the granodiorite and the MgO content of biotites (13.42–14.16), the M value (M = Mg/(Mg + Fe2+)) of amphiboles (0.68–0.75), suggest that granodiorite originates from the crustal contamination of the mantle-derived magmas. Combined with regional geological background, previous research, and the nature of the Ahetala granodiorite, we suggest that Ahetala granodiorite was emplaced at a transitional stage of the volcanic arc (syn-collision) to post-collision setting and the South Tianshan Ocean was closed in the Early Permian.

Permian arc magmatism in southern Tibet: Implications for the subduction and accretion of the Zhikong–Sumdo Paleo-Tethys Ocean

The tectonic evolution of the Zhikong–Sumdo Paleo-Tethys Ocean (Hereafter referred to as Zhikong–Sumdo Ocean) in southern Tibet is controversial due to the limited records of arc magmas. Here, the newly discovered Zhangda complex in the Zhikong area of Tibet is selected as the research object. Zircon U–Pb geochronology, zircon Hf isotopes, whole-rock geochemistry and Sr-Nd isotope analyses performed based on field geological surveys show that the Zhangda complex is composed of Early Permian hornblende gabbro (278.3 ± 1.1 Ma), cumulate gabbro (277.4 ± 1.7 Ma), tonalite dike (281.1 ± 1.9 Ma), Middle–Late Permian gabbro diorite (267.8 ± 2.9 Ma, 269.0 ± 3.1 Ma), and tonalite (258.0 ± 2.7 Ma). The Zhangda mafic rocks show weak fractionation of light and heavy rare earth elements, and they are enriched in large ion lithophile elements and depleted in high field strength elements. Meanwhile, the Zhangda tonalites show the characteristics of metaluminous calc-alkaline I-type granite. They are enriched in light rare earth and large ion lithophile elements and are depleted in heavy rare earth and high field strength elements. The ɛHf(t), ɛNd(t) and the initial 87Sr/86Sr values of the mafic rocks are + 9.3–+14.4, +4.2–+5.9 and 0.702803–0.704264, respectively, while the ɛHf(t), ɛNd(t) and initial 87Sr/86Sr values of the tonalites are + 9.8–+16.3, +5.5–+6.1 and 0.703105–0.704071, respectively. Combined with the regional geological survey results, the Permian Zhangda complex was found to be formed in a tectonic setting of subduction north of the Zhikong–Sumdo Ocean. The Zhangda mafic rocks were formed by partial melting of the depleted mantle modified by subducted metasomatic fluids, while the Zhangda tonalites were the products of partial melting of the juvenile crust. During the Zhikong–Sumdo Ocean subduction, mantle-derived magma underplating led to the growth of juvenile crust in southern Tibet.

The Early Cretaceous Granitoids and Microgranular Mafic Enclaves of Sanguliu Pluton, the Liaodong Peninsula: Implications for Magma Mixing and Decratonic Gold Mineralization in the Eastern North China Craton

Some Early Cretaceous granitoids characterized by abundant mafic microgranular enclaves (MMEs) formed by magma mixing have been associated with gold deposits in the eastern North China Craton (NCC). However, the genetic connection of magma mixing with gold mineralization remains unclear. The zircon U–Pb ages and in situ Lu-Hf isotopic compositions, whole-rock major- and trace-element and Sr–Nd–Pb isotopic compositions, as well as EPMA biotite compositions, were presented for the Sanguliu granodiorite and enclaves in the Liaodong Peninsula in order to obtain insights into the spatial and temporal distribution, and internal connection of magma mixing with the decratonic gold deposits in the eastern NCC. The Sanguliu granodiorite yielded coeval formation ages with the enclaves (~123 Ma), and their acicular apatites and plagioclase megacrysts suggest that the enclaves were formed by mixing between mafic and felsic magmas. Geochemically, the Sanguliu granodiorite is high-K calc-alkaline I-type granite, with an initial 87Sr/86Sr ratio of 0.70552 to 0.71470 and strongly negative εNd(t) (−11.4 to −21.3) and zircon in situ εHf(t) values (−15.1 to −25.4), indicating that the felsic magmas were ancient lower crust with the involvement of mantle-derived materials. Meanwhile, the enclaves have high MgO (4.18 to 6.17 wt.%), Cr (45.91 to 290.04 ppm), and Ni (19.65 to 88.18 ppm) contents, with high Mg# values of 50 to 57 at intermediate SiO2 contents (53.68 to 55.78 wt.%), highly negative εNd(t) values (mostly −18.42 to −22.03), and in situ zircon εHf(t) values (−18.6 to −22.7), indicating that the mafic magma was mainly derived from the enriched lithospheric mantle. Furthermore, the biotites from the Sanguliu granodiorite clustered between the MH and NNO buffers in the Fe2+–Fe3+–Mg diagram. This, combined with the high Ce/Ce* ratios (1.30 to 107.18) of the zircons, indicates that the primary magmas forming the Sanguliu granodiorite had a high oxygen fugacity, which is favorable for gold mineralization. These findings, together with previous studies of the Early Cretaceous granitoids with enclaves in the eastern NCC, suggest that magma mixing commonly occurred during 110–130 Ma and is temporally, spatially, and genetically related to decratonic gold systems in eastern NCC.

Late Carboniferous intrusions along the Kalamaili suture zone, southwestern Central Asian Orogenic Belt (CAOB): implications for a tectonic switch from subduction to collision

ABSTRACT A tectonic switch from subduction to collision and/or arc–arc collision is a key issue for understanding accretionary orogenic processes. We present new U-Pb ages, geochemistry, whole-rock Nd and zircon Hf isotope data for a suite of late Carboniferous intrusive rocks along the Kalamaili suture zone of the southwestern Central Asian Orogenic Belt (CAOB) and demonstrate their petrogenesis and the transition of their tectonic settings. Zircon U-Pb dating for the gabbros, diorites, granodiorites, and monzogranites yields ages of 317–301 Ma. The gabbros (311 Ma) were likely derived from partial melting of a mixed source of depleted MORB-like asthenospheric mantle with minor old crustal material; the diorites (301 Ma) from the mixed depleted lithospheric mantle and crustal components; the granodiorites (303 Ma) from the mixed mantle- and crust-derived magmas; and the monzogranites (317 Ma) from melting of the newly underplated basaltic lower crust. Combined with previous data, we have grouped all the intrusive rocks along the Kalamaili suture zone into three phases: 350–340 Ma, 330–320 Ma, and 320–300 Ma. The first phase consists of tholeiitic and high-K calc-alkaline granites, the second phase is composed of high-K calc-alkaline I-type granites with strong deformation, and the third phase comprises voluminous and various rock types (mainly mafic and felsic, including many A-type granites), revealing a magmatic flare-up. The magmatic associations and evolution from the first to the third phase, together with regional geology, suggest a tectonic transition from subduction/accretion (350–340 Ma) through syn-collision (330–320 Ma) to post-collision (or post-accretionary, 320–300 Ma), respectively. This study provides new magmatic evidence for the switch from subduction to collision (arc-arc collision) along the Kalamaili suture zone in the southwestern CAOB.

Late Carboniferous extension-related magmatism in the southwestern Alxa block of NW China: geochronology, geochemistry, and tectonic implications

ABSTRACT Whether the northern margin of the North China Craton (NCC) was a continental arc or in a lithospheric extensional setting during the Carboniferous is the primary divergence among different tectonic models about the terminal evolutionary history of the southeastern Central Asian Orogenic Belt (CAOB). The Alxa block is the western segment of the northern NCC and contiguous to the southeastern CAOB, and therefore the tectonic setting of the Carboniferous magmatic intrusions in this block can shed light on this controversy. In this contribution, new zircon U–Pb ages, elemental geochemistry, and Sr-Nd isotopes are presented for thirteen Late Carboniferous (~318–300 Ma) magmatic intrusions in the southwestern Alxa block. Among them, seven calc-alkaline I-type granites and one aluminous A2-type granite were probably generated by the partial melting and crystallization differentiation of various crustal sources (perhaps including earlier orogenic materials) under different temperature conditions. Four quartz diorites and one hornblende gabbro may be the partial melts of subduction-modified basaltic lower crust sources and sub-continental lithospheric mantle sources, respectively. According to the integration of the new results and regional geological correlations, the Alxa block and the southeastern CAOB were most likely in a uniform tectonic regime during the Carboniferous. At that time, this region was characterized by the lithospheric extension-related magmatic rock associations, the increasing mantle inputs over time, the clockwise P–T paths of high temperature-low pressure metamorphic rocks, and the transgression sedimentary sequences. All these lines of evidence suggest an intra-continental lithospheric extensional setting rather than a continental arc setting for the southeastern CAOB during the Carboniferous.

Petrogenesis and Tectonic Implications of the Triassic Granitoids in the Ela Mountain Area of the East Kunlun Orogenic Belt

The East Kunlun Orogenic Belt is located in the western part of the Central Orogenic Belt of China, with a large number of Triassic igneous rocks parallel to the Paleo-Tethys ophiolite belt, which provides a large amount of geological information for the tectonic evolution of the Paleo-Tethys Ocean. The granitoids studied in this paper are located in the Ela Mountain area in the eastern part of the East Kunlun Orogenic Belt. Zircon U-Pb dating results show that these different types of granitoids were crystallized in the Triassic. The 247.5 Ma porphyritic granites from Zairiri (ZRR) displayed calc-alkaline I-type granite affinities, with the zircon εHf(t) values being mainly positive (−0.5 to + 3.8, TDM2 of 1309–1031 Ma), indicating that they are derived from the partial melting of the juvenile crust and mixed with ancient crustal components. The 236.8 Ma Henqionggou (HQG) granodiorites and 237.5 Ma Daheba (DHB) granodiorites are high-K calc-alkaline I-type granite, and both have mafic microgranular enclaves (MMEs), showing higher and more varied Mg# (39.73–62.73), combined with their negative Hf isotopes (εHf(t) = −2.6 to −1.6, TDM2 = 1430–1369 Ma), suggesting that their primary magmas were the products of partial melting of the Mesoproterozoic lower crust that mixed with mantle-derived rocks. The 236.4 Ma DHB porphyritic diorites showed characteristics of high-K calc-alkaline I-type granitoids, with moderate SiO2 contents, medium Mg# values (40.41–40.65), with the Hf isotopes (εHf(t) = −2.9 to −0.5; TDM2 = 1451–1298 Ma) indistinguishably relative to contemporaneous host granodiorites and MMEs. The petrographic and geochemical characteristics indicate that the porphyritic diorites are the product of well-mixed magma derived from the Mesoproterozoic lower crust and lithospheric mantle. Based on the results of this paper and previous data, the chronology framework of Late Permian–Triassic magmatic rocks in the eastern part of the East Kunlun Orogenic Belt was constructed, and the magmatic activities in this area were divided into three peak periods, with each peak representing an extensional event in a particular tectonic setting, for example, P1 (slab roll-back in subduction period; 254–246 Ma), P2 (slab break-off in transition period of subduction and collision; 244–232 Ma), P3 (delamination after collision; 230–218 Ma).

Geochronology and Geochemistry of the Granite Porphyry from the Qinglingou Gold Deposit, South Qinling, China: Implication for Petrogenesis and Mineralization

The Zhashui-Shanyang ore cluster area is one of the most important gold polymetallic ones in northwestern China. The Qinglingou gold deposit is a newly discovered small-scale deposit in the Zhashui-Shanyang area. Gold mineralization closely related to acid intrusive rocks has been found for the first time in this area. In this paper, the geochronology, whole-rock geochemistry, and isotope signature of the granite porphyries in the deposit are studied. They are characterized by variable medium SiO2 (67.22–71.72 wt.%), high K2O + Na2O contents (6.54–10.34 wt.%), and variable Al2O3 (14.47–15.10 wt.%) values. The A/CNK ratios range from 0.90 to 1.23, and the A/NK ratios vary from 1.14 to 1.48. These rocks also contain biotite and amphiboles and are similar to peraluminous and high-K calc-alkaline I-type granites. The Qinglingou granite porphyries show relative enrichment of Rb, Th, and K, and depletion of Nb, Ta, P, Ti, and other high field strength elements. These porphyries are enriched in light rare earth elements relative to heavy rare earth elements with weak negative Eu anomalies (δEu = 0.63–0.89), which is interpreted to be the best age of crystallization of the Qinglingou porphyries. LA–ICPMS zircon U–Pb dating yields an age of 211 ± 1.2 Ma (n = 16, MSWD = 0.39). The close spatial relationship between the ore bodies and granite porphyry dikes indicates that this age may represent the metallogenic age in this area. The zircons have 176Hf/177Hf ratios ranging from 0.282625 to 0.282702, the εHf(t) values are near 0 and the two-stage zircon Hf model ages range from 1121 to 1296 Ma. These data indicate that the Qinglingou granite porphyries were derived from the interplay between mantle- and crustal-derived magmas. We therefore propose that there is potential gold in carbonate rocks at the periphery of porphyry-skarn copper-molybdenum deposits.

Thermo-mechanical destruction of Archean cratonic roots: Insights from the Mesozoic Laiyuan granitoid complex, North China Craton

Igneous complexes with diverse magmatic suites provide essential targets for investigating magma differentiation processes and crust-mantle interaction. The North China Craton (NCC) is a crucial window to gain insights into craton destruction through voluminous magmatism during the Mesozoic involving extensive crust-mantle interaction. Here we investigate the granitoid suite from the Laiyuan complex in the central NCC to constrain the magmatic evolution and petrogenetic linkages and to gain insights into the process of crust-mantle interaction related to craton destruction. The Laiyuan granitoid complex comprises syenogranite, monzogranite, quartz monzonite and monzonite with mafic magmatic enclaves (MMEs). The granitoids were formed during the Early Cretaceous (137–128 Ma) with εHf(t) values and TDMC ages ranging from −21.8 to −16.8 and 2564 to 2255 Ma, respectively. The compositional variations of the different rock types suggest distinct magmatic evolution and petrogenesis. Geochemical and isotopic data indicate that the enriched lithospheric mantle-derived mafic magmas underwent early-stage plagioclase-dominated and late-stage hornblende-dominated fractional crystallization to form the monzonites and quartz monzonites. Geochemical modeling results suggest that the magma of the MMEs originated through mixing between lithospheric mantle-derived mafic magma and crust-derived felsic magma with post-injection hybridization to generate MMEs with variable compositions. The monzogranites are classified as high-K calc-alkaline I-type granites with higher SiO2 contents (69–71 wt%) and lower Mg# (41–44) than intermediate rocks. They were generated by partial melting of the basaltic lower crust, with the addition of mafic magma from an enriched mantle. The highly fractionated syenogranites with lower Mg# (18–27) were evolved from the monzogranitic magma through plagioclase-dominated crystal removal. The adakitic affinities of the monzonites and monzogranites were generated by crystallization of mantle-derived magmas and partial melting of continental crust of normal thickness (~40 km), respectively. The bottom-up crust-mantle interaction accounts for the compositional diversity of the Laiyuan granitoids, and suggests that thermo-mechanical destruction played a dominant role in the destruction of the central NCC as compared with the continental delamination process in the eastern NCC.

Constraints of magmatism on the Ergu Fe–Zn polymetallic metallogenic system in the central Lesser Xing’an Range, NE China: evidence from geochronology, geochemistry and Sr–Nd–Pb–Hf isotopes

AbstractThe medium-sized Ergu Fe–Zn polymetallic skarn deposit is located in the central Lesser Xing’an Range, NE China. The ore bodies are mainly hosted in the contact zone between granodiorite intrusions and lower Cambrian dolomitic crystalline limestones or skarns. To reveal the magmatic influence on the mineralization, resource potential and metallogenic geodynamic process of this deposit, a systematic study of the geology, petrology, zircon U–Pb dating, element geochemistry, amphibole geochemistry and Sr–Nd–Pb–Hf isotopes of the Ergu deposit intrusives was conducted. The results show the following: (1) The major rock types in the mine area are medium-grained granodiorite and porphyritic granite, and the rock related to mineralization is medium-grained granodiorite. Zircon U–Pb dating suggests that the granodiorite and porphyritic granite formed at 181.9–183.8 Ma and 182.7 Ma, respectively. Thus, an Early Jurassic magmatic event led to the formation of the Ergu deposit. (2) The granodiorite and porphyritic granite are high-K calc-alkaline I-type granites that formed by comagmatic evolution with varying degrees of fractional crystallization and were likely derived from partial melting of the lower crust. The Ergu deposit occurred in an active continental-margin tectonic setting. (3) The high water content (5.69 wt % H2O), high oxygen fugacity (ΔFMQ = +1.75 to +1.82) and intermediate-plutonic emplacement (3.13 km) of the granodioritic magma are key factors in the formation of the Ergu deposit. The porphyry granite is characterized by high water content (>4 wt % H2O), reduced oxygen fugacity (ΔFMQ = −0.47) and shallow emplacement (<3 km).

Correction to: Geochemical and isotope evidence for mantle-derived source rock of high-K calc-alkaline I-type granites, Pernambuco–Alagoas Domain, northeastern Brazil

Unfortunately, Fig. 14 shows vectors pointing in the wrong direction.

Magmatic constraints on the Ermi porphyry copper mineralization, Northeast China: Evidence from zircon U-Pb geochronology, whole-rock geochemistry and Sr-Nd-Hf isotopic geochemistry

The Ermi porphyry Cu deposit (PCD), located on the northeastern margin of the North China Craton (NCC), is a medium-sized PCD with a reserve of > 0.11 Mt and an average grade of 0.6% Cu. Copper mineralization occurs mainly within the intrusions of quartz diorite, granodiorite, granodiorite porphyry and granite porphyry. To reveal the magmatic contributions to mineralization, we conducted zircon U-Pb dating and element geochemical and Sr-Nd-Hf isotope analyses of mineralized intrusions at Ermi on the basis of field and petrographic observations. The zircon LA-ICP-MS U-Pb ages of quartz diorite, granodiorite, granodiorite porphyry and granite porphyry are 95.0 ± 1.0 Ma (n = 16, MSWD = 0.97), 94.2 ± 1.4 Ma (n = 15, MSWD = 0.93), 93.9 ± 1.2 Ma (n = 19, MSWD = 0.22) and 92.0 ± 1.2 Ma (n = 18, MSWD = 0.41), respectively. All of these intrusive rocks belong to metaluminous, calc-alkaline I-type granites. They exhibit high 87Sr/86Sr(t) values (0.7075 to 0.7084), low negative εNd(t) values (-16.7 to −12.6), and variable but mainly negative εHf(t) values (-12.4 to −6.4), with corresponding TDM2(Hf) ages of 2.1 ~ 2.7 Ga. These findings indicate that the initial magma originated from the partial melting of the Archean lower crust of the NCC. Combined with the dynamic background of the study area, we believe that they formed in an active continental margin environment related to the rollback of the subducting Paleo-Pacific slab in the Cretaceous. The oxygen fugacity (fO2) values estimated from rare earth element (REE) and Ti concentrations in zircons show that: The fayalite-magnetite-quartz buffer (ΔFMQ) values of the quartz diorite and granodiorite are −2.6 and 0.87, respectively. The ΔFMQ values of the granodiorite porphyry and granite porphyry are 2.68 and 2.13, respectively. The high oxygen fugacity promoted the enrichment of Cu and other ore-forming elements in the magma. However, the results of estimating crustal thickness from the (La/Yb)N ratio of magma show that the Ermi PCD formed under the condition of a thinned or shallow lower crust (<25 km). Thinned continental crust may lack massive sulfide accumulation and is not conducive to the large-scale storage and accumulation of fertile magmas in the middle or upper crust, which may limit the mineralization scale of the Ermi PCD.