K-feldspar Granite Research Articles

Magma Mixing Genesis of the Mafic Enclaves in the Qingshanbao Complex of Longshou Mountain, China: Evidence from Petrology, Geochemistry, and Zircon Chronology

The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. In order to investigate the origin and formation of mafic enclaves observed in the Qingshanbao body and the implications for magmatic-tectonic dynamics, we systematically studied the mineralogy, petrography, and geochemistry of these enclaves. Our results showed that the enclaves contain plagioclase enwrapped by early dark minerals. These enclaves also showed round quartz crystals and acicular apatite in association with the plagioclase. Electron probe analyses showed that the plagioclase in the host rocks (such as K-feldspar granite, adamellite, granodiorite, etc.) show normal zoning, while the plagioclase in the mafic enclaves has a discontinuous rim composition and shows instances of reverse zoning. Major elemental geochemistry revealed that the mafic enclaves belong to the calc-alkaline rocks that are rich in titanium, iron, aluminum, and depleted in silica, while the host rocks are calc-alkaline to alkaline rocks with enrichment in silica. On Harker diagrams, SiO2 contents are negatively correlated with all major oxides but K2O. Both the mafic enclaves and host rock are rich in large ion lithophile elements such as Rb and K, as well as elements such as La, Nd, and Sm, and relatively poor in high field strength elements such as Nb, Ta, P, Ti, and U. Element ratios of Nb/La, Rb/Sr, and Nb/Ta indicate that the mafic enclaves were formed by the mixing of mafic and felsic magma. In terms of rare earth elements, both the mafic enclaves and the host rock show right-inclined trends with similar weak to medium degrees of negative Eu anomaly and with no obvious Ce anomaly. Zircon LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) U-Pb concordant ages of the mafic enclaves and host rock were determined to be 431.8 5.2 Ma (MSWD (mean standard weighted deviation)= 1.5, n = 14) and 432.8 4.2 Ma (MSWD = 1.7, n = 16), respectively, consistent with that for the zircon U-Pb ages of the granite and medium-coarse grained K-feldspar granites of the Qingshanbao complex. The estimated ages coincide with the timing of the late Caledonian collision of the Alashan Block. This comprehensive analysis allowed us to conclude that the mafic enclaves in the Qingshanbao complex were formed by the mixing of crust-mantle magma with mantle-derived magma due to underplating, which caused partial melting of the ancient basement crust during the collisional orogenesis between the Alashan Block and Qilian rock mass in the early Silurian Period.

Tracing magma mixing and crystal–melt segregation in the genesis of syenite with mafic enclaves: Evidence from in situ zircon Hf–O and apatite Sr–Nd isotopes

Alkaline rocks contain essential information on post-collisional/intraplate extensional magmatic processes within the continental lithosphere. The Erhulai syenitic pluton in the Liaodong Peninsula, North China Craton, consists of quartz syenite, mafic enclaves, and porphyritic K-feldspar granite. Field observations and zircon U–Pb dating reveal that the quartz syenite and the hosted mafic enclaves were coeval (with identical emplacement ages of 129–126 Ma), and slightly older than the porphyritic K-feldspar granite (ca. 123 Ma). The mafic enclaves have relatively low SiO2 and high MgO contents (up to 3.0%), and lack Ba or Eu anomalies. Whole-rock analyses of the mafic enclaves and accessory minerals in the enclaves show relatively low initial 87Sr/86Sr ratios (0.7056 to 0.7078) and variable εNd(t) (−11.2 to −2.0) and εHf(t) (−15.8 to −5.5) values. Large proportion of zircons from the mafic enclaves possess mantle-like δ18O values. These geochemical features suggest an enriched mantle source, with the addition of crustal material. The quartz syenites have relatively high SiO2 and low CaO and MgO contents, as well as significantly positive K, Ba, and Eu anomalies. All the quartz syenites show variable (87Sr/86Sr)i ratios (0.7073 to 0.7081) and εNd(t) values (−10.4 to −8.6) for the whole-rocks and apatites, εHf(t) values of −12.4 to −3.6 for the zircons, and zircon δ18O values of +4.4‰ to +7.0‰ (mainly greater than +5.3‰). All these features can be isotopically produced by the partial melting of ancient crustal material, with the involvement of mantle-derived magma. Crystal fractionation process, such as K-feldspar crystallization and accumulation, played an important role in the formation of the quartz syenite. The porphyritic K-feldspar granites possess relatively evolved geochemical compositions with high silica contents (SiO2 > 69 wt%) and remarkable negative Ba and Eu anomalies, which are chemically complementary to the quartz syenite. A crystal mush model was employed to establish the genetic link between the porphyritic K-feldspar granite and the quartz syenite, with the granite representing the interstitial melt extracted from the crystal mush and the quartz syenite representing the residual accumulation of crystals. The variable isotopic compositions of the quartz syenite and the porphyritic granite were mainly the result of extensive interaction of isotopes between mantle- and crust-derived magmas during magma mixing.In situ analyses of the Sr, Nd, Hf, and O isotopes of accessory minerals, coupled with field observations and whole-rock geochemical data for the Erhulai syenitic pluton, indicate a complex multi-stage magmatic process involving magma mixing, crystal–melt segregation, and wall-rock assimilation. Our study also shows that in situ isotopic analyses of accessory minerals provide unique information on, and are powerful geochemical tracers of, mantle–crust interactions and magmatic processes.

Petrogenesis of Late Paleozoic diorites and A-type granites in the central Eastern Tianshan, NW China: Response to post-collisional extension triggered by slab breakoff

Geological evolution of the Eastern Tianshan in the Late Paleozoic is significant to understanding the multiple accretions and final formation of the southern Central Asian Orogenic Belt. Here, we report new whole-rock geochemical and Sr–Nd isotopic data, and in situ zircon U–Pb ages for three typical A-type granitic intrusions (syenogranite, K-feldspar granite and monzonitic granite) and one dioritic pluton in the central Eastern Tianshan, NW China, in order to constrain their petrogenesis, tectonic setting and geodynamic evolution. Zircon LA-ICP-MS U–Pb ages indicate that the syenogranites and K-feldspar granites were both formed during a short time interval in the Early Permian (284–286 Ma), whereas the diorites were crystallized at 293 ± 6 Ma. The monzonitic granites were generated at 307 ± 3 Ma, earlier than the other two granitic intrusions. The three kinds of granites (syenogranite, K-feldspar granite and monzonitic granite) have high HFSE, HREE and Y/Nb ratios (1.68–2.84), and remarkably low Sr and Ba contents, with the absence of aluminium-rich minerals and show metaluminous to weakly peraluminous natures, indicating geochemical characteristics of aluminous A2-type granites. These granites show negative εNd(t) (−3.32 to −4.40) values and Mesoproterozoic two stage Nd model ages (TDM2 = 1.36 to 1.43 Ga), which suggest a relatively old crustal source for these rocks. The Sr–Nd isotopic compositions imply that the Mesoproterozoic metamorphic basement of the Central Tianshan Block can be considered as a potential magmatic source for these aluminous A2-type granites. In addition, they have geochemical characteristics similar to the experimental melt that was derived from partial melting of crustal metaigneous rocks at the depth of middle to lower crust levels. Therefore, the granites were most likely produced by partial melting of metaigneous rocks in a post-collisional extensional setting. The diorites have low SiO2 and high MgO, with uniform (87Sr/86Sr)i values (~0.7055), negative εNd(t) values (−4.11 to −4.59) and Mesoproterozoic two stage Nd model ages (TDM2 = 1.41 to 1.45 Ga). They have higher Ti/Zr (42.8–46.7) and Ti/Y (280–359) ratios than continental crust and show negative Nb-Ta-Ti anomalies, which can be explained by partial melting of a relatively fertile mantle modified by old crustal materials of the Central Tianshan Block. The formation of the dioritic pluton was induced by an upwelling asthenosphere in an extensional geodynamic setting. Based on the zircon saturation temperatures of these A-type granites and the distribution of Late Carboniferous to Early Permian mantle-derived intrusions, a slab breakoff model is suggested to interpret the formation of the studied A-type granites and diorites. We infer that the slab breakoff was initiated in the Late Carboniferous and ended in the Early Permian.

Genetic relationship between granitic magmatism and W mineralization recorded in the Nanling Scientific Drilling (SP-NLSD-2) in the Pangushan W mining district, South China

The Nanling Region in South China hosts numerous W-dominated polymetallic deposits that are related to Mesozoic granites. Although considerable amounts of age data have been obtained, the genetic relationship between granitic magmatism and W mineralization remains unclear. The Nanling Scientific Drilling (SP-NLSD-2) in the Pangushan W deposit has penetrated Upper Devonian sedimentary rocks (4.1–721.9 m), Sinian sedimentary rocks (721.9–1287.9 m) and Mesozoic granite (1287.9–2012.1 m). The drill hole clearly reveals a zonation including exocontact W-bearing quartz veins, alkali autometasomatic zone and primary K-feldspar granite. The K-feldspar granite at the depth of 1880 m, and rocks of potassium autometasomatic zone at 1414 m and greisenized zone at 1288 m have magmatic zircon grains with U–Pb ages of 164.8 ± 1.4 Ma, 161.7 ± 1.6 Ma, and 153.8 ± 1.2 Ma, respectively. Molybdenite Re–Os ages of endocontact mineralization at the depths of 1302 m and 1291 m are 155.9 ± 3.1 Ma and 155.0 ± 2.3 Ma, respectively. Muscovite Ar–Ar ages of exocontact mineralization at the depths of 1050 and 885 m are 154.9 ± 1.5 Ma and 154.0 ± 3.0 Ma, respectively, and molybdenite Re–Os age of exocontact quartz-vein type mineralization at 860 m is 152.0 ± 2.6 Ma. These new ages indicate that the granite emplacement, potassium autometasomatism, greisenization, and W mineralization occurred at ∼164.8 Ma, ∼161.7 Ma, ∼153.8 Ma, and 155.9–152 Ma, respectively. The W mineralization was approximately 9–13 Myr younger than the hosting granite. The whole-rock and feldspar chemical compositions of K-feldspar granite, potassium autometasomatic zone, greisenized zone, and feldspar-quartz veins indicate the sequence of metal transportation and concentration to form the zonation. The granite crystallized from high-K calcalkaline, metaluminous to peraluminous, highly differentiated magmas that were enriched in W and Bi. During crystallization, the magmas underwent potassium autometasomatism caused by post-magmatic fluids which were rich in K, Fe, W, and rare-earth elements (REE) but poor in Na and Ca, and formed the potassium autometasomatic zone. The evolved post-magmatic fluids became rich in K, Si, Ca, REE, and W but poor in Na and Fe and initiated greisenization to generate the greisenized zone, which almost exhausted Ca, REE, Na, and Fe of the fluids. The later crystallization of feldspar quartz veins exhausted K and caused the residual post-magmatic fluids to be rich in Si and W. The fluids formed W-bearing quartz veins with decreasing temperature and pressure. The main reason for W enrichment in the hydrothermal fluids was due to the successive crystallization of minerals rather than autometasomatism.

Late Cretaceous granitic magmatism and mineralization in the Yingwuling W–Sn deposit, South China: Constraints from zircon and cassiterite U–Pb geochronology and whole-rock geochemistry

Numerous Late Cretaceous W–Sn deposits associated with granitic rocks were developed in the southern part of South China. However, the relationship among granitic magma, mineralization and tectonic setting remains disputed. The Yingwuling W–Sn deposit is spatially associated with K-feldspar granite and biotite granite in the southwestern part of Guangdong province, South China. LA-ICP-MS zircon U–Pb dating of K-feldspar granite, biotite granite and weathered ore-bearing granites yielded ages of ∼79 Ma, which agree well with the LA-ICP-MS cassiterite U–Pb age of 79.6 ± 0.9 Ma, indicating a close genetic link between the Yingwuling pluton and W–Sn mineralization. Geochemically, both K-feldspar granite and biotite granite show high SiO2, Na2O + K2O and low CaO, P2O5 contents, and they belong to shoshonitic series and high-K calc-alkaline series, respectively. High Rb/Sr ratios and low Nb/Ta and Zr/Hf ratios of the Yingwuling pluton indicate strong magmatic differentiation. Compared with K-feldspar granite, biotite granite experienced a higher degree of fractional crystallization as indicated by lower Fe2O3, TiO2, LREE, Sr, Eu, Ba and Zr contents and higher SiO2, HREE, Rb, Cs and Y contents. Their Sr and Nd isotope compositions (initial 87Sr/86Sr = 0.7027 and 0.7097; εNd(t) = −5.6 and −5.7) are less radiogenic than that of the South China basement. Thus, it is likely that some juvenile materials were involved in the formation of these granitic intrusions. This is also favored by the wide range of zircon Hf isotope values (εHf(t) = −6.6 to 0.8), which indicates mixing processes. A-type granite affinity of the Yingwuling pluton shows that it was possibly formed in an extensional setting. Late Cretaceous W–Sn deposits constitute an EW-trending belt from Guangdong to Yunnan provinces, which was compatible with the northward subduction of the Neo-Tethys plate rather than the northwestward subduction of the Pacific plate during Late Cretaceous. Combined with previous studies on magmatic rocks and tectonic activities during Late Cretaceous in South China, this study suggests that the subduction of the Neo-Tethys plate was most possibly responsible for the Late Cretaceous Yingwuling granitic intrusion and associated W–Sn mineralization.

Isotope Chronology and Geochemistry of the Lower Carboniferous Granite in Xilinhot, Inner Mongolia, China

Geochronological and geochemical analyses were performed on K-feldspar granites and monzonitic granites from the Xilinhot area, Inner Mongolia, China. Zircon U/Pb ages indicate that the two types granites were emplaced during the Lower Carboniferous. The K-feldspar granites (332 Ma) have the typical A-type granite characteristics of a post-collision setting. The monzonitic granites have an emplacement age of 323 Ma. Zircon eHf values of the former range from +12.8 to +14.2, with an average TDM2 of 453 Ma. The latter have lower zircon eHf values, ranging from +5.4 to +10.7, with an average TDM2 of 798 Ma. The strong, positive eHf values of the zircon indicate that both sets of samples are from a juvenile crust formed in an oceanic crust subduction stage, although the monzonitic granite may have undergone a hybridization of crustal materials. These results indicate a younger post orogenic event. The Paleo-Asian Ocean had closed before the Early Carboniferous and the Xilinhot area started its post-orogenic evolution with an extensional tectonic environment during the Early Carboniferous.

Late Carboniferous to Early Permian magmatic pulses in the Uliastai continental margin linked to slab rollback: Implications for evolution of the Central Asian Orogenic Belt

The Paleo Asian Ocean underwent a protracted closure history during Late Paleozoic. Here we investigate the magmatic evolution during this process based on a detailed study in the Baiyinwula region along the Uliastai continental margin. The major rock types in this area are Late Carboniferous-Early Permian volcanic sequences and coeval intrusions. We identified four stages of magmatic evolution based on the diverse assemblages and their precise isotopic ages. The first stage is represented by andesites with a zircon 206Pb/238U age of ca. 326±12Ma. These rocks are metaluminous to weakly peraluminous, high-K calc-alkaline, and possess high Na2O/K2O ratios in the range of 1.23 to 2.45. They also display enrichment of large ion lithophile elements (LILE) and depletion of high field strength elements (HFSE), with markedly positive zircon εHf (t) varying from 8.1 to 15.6.The geochemical features of these andesites are similar to those of typical arc volcanic rocks. The second stage includes granodiorites emplaced at 318.6+1.8Ma. The rocks are high-K calc-alkaline with A/CNK values ranging from 0.95 to 1.06, and show enrichment in LILE and depletion in HFSE. They show geochemical affinities to adakites, with high Sr and low Y and Yb contents, indicating magma derivation from thickened lower crust. Zircon grains from these rocks display positive initial εHf (t) values ranging from 11.1 to 14.6 with corresponding two-stage Hf model ages (TDM2) of 394–622Ma. The third stage consists of syenogranite together with a volcanic suite ranging in composition from rhyolite todacite, which formed during 303.4±1.2 to 285.1±2.2Ma. They possess elevated silica and alkali contents, high FeOt/MgO and Ga/Al ratios, low Al2O3, MgO and CaO contents, and high Rb, Y, Nb, Ce, Zr, Y, and Ga contents, strong negative Ba, Sr and Eu anomalies, showing I- to A-type granitic affinities. Zircons in these rocks show elevated Hf isotopic compositions (εHf (t)=9.9 to 14.6) with TDM2 varying from 324 to 673Ma. The fourth magmatic pulse is represented by K-feldspar granite with zircon U-Pb ages from 283.2±1.9Ma to 280.0±1.4Ma, and typical alkalic A-type granite geochemistry. These rocks possess positive εHf (t) values in the range of 9.7 to15.2, and a restricted range of Hf model age from 327 to 684Ma. The magmatic rocks from the four stages show comparable εHf (t) and T2DM, suggesting that the magmas were derived from the same evolving mantle-derived source. We propose a tectonic model linking the evolution of the magmatism with the closure of the Paleo Asian Ocean that involved the following stages. The andesites were formed during the initial oceanic subduction stage with magma sourced from the metasomatized lithospheric mantle. Stage 2 adakite-like rocks were derived from subduction-induced thickened crust. Subsequent slab rollback resulted in asthenospheric upwelling and melting of residual juvenile crust to generate the I- and A- type syenogranite, rhyolite and dacite suite, finally followed by the A-type K-feldspar granite.

Evolution of Middle-Late Triassic granitic intrusions from the Badaguan Cu-Mo deposit, Inner Mongolia: Constraints from zircon U-Pb dating, geochemistry and Hf isotopes

The Great Xing’an Range in the eastern part of the Central Orogenic Belt is one of the major polymetallic metallogenic belts in China. The Badaguan Cu-Mo deposit, in the Erguna massif forms part of this belt and is a typical porphyry deposit associated with multiple granitic intrusions, which are temporally and genetically related to the formation of this deposit. In this paper, we present new zircon U–Pb ages, Hf isotopic data, and whole-rock major and trace element geochemistry on the Badaguan granitoids. Zircon U–Pb data indicate that the intrusions formed during two major phases: ca. 244–237 Ma and ca. 232–229 Ma. The Middle Triassic (ca. 244–237 Ma) phase is represented by a suite of medium-K calc-alkaline granite, K-feldspar granite, biotite granite, and porphyritic granite with I-type affinities. In general, they are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high field strength elements (HFSEs). Their zircon εHf (t) values and two-stage model ages (TDM2) range from −1.5 to +8.5 (with a mean value of +4.9) and from 732 to 1366 Ma (with a mean value of 959 Ma), respectively. In contrast, the Late Triassic (ca. 232–229 Ma) intrusions dominantly comprise a suite of high-K calc-alkaline I-type granite porphyry and granodiorite porphyry. These rocks are enriched in LILEs and LREEs but depleted in HREEs and HFSEs, such as Nb, Ta and Ti. Their εHf (t) and TDM2 values range from +3.4 to +6.2 (with a mean value of +5.0) and from 865 to 1047 Ma (with a mean value of 942 Ma), respectively. These results suggest that the primary magmas of the Middle and Late Triassic intrusive rocks were co-magmatic and were mainly derived from the partial melting of juvenile thickened lower crust. In addition, the primary magma forming the Middle Triassic complex also assimilated a small amount of ancient crustal material and experienced a remarkable degree of fractional crystallization prior to its emplacement. In contrast, the source magma of the Late Triassic complex probably underwent interaction between of minor mantle-derived melt and crustal components prior to emplacement. The Cu in Badaguan deposit was likely sourced from the mantle-derived melt, whereas the Mo was contributed by the host rocks with high Mo contents.

Early Silurian to Early Carboniferous ridge subduction in NW Junggar: Evidence from geochronological, geochemical, and Sr-Nd-Hf isotopic data on alkali granites and adakites

The Central Asian Orogenic Belt (CAOB) evolved through a long-lived orogeny involving multiple episodes of subduction and accretion marking a major phase of continental growth during the Paleozoic. The northern part of the Western Junggar region (NW Junggar) offers a window into these processes, particularly to constrain the timing of closure of the Paleo-Asian Ocean. Here we report geochemical, geochronological, and isotopic data from K-feldspar granites and adakitic rocks from the NW Junggar region. Zircon U-Pb ages suggest that the granites were emplaced during Early Silurian to the Early Carboniferous (434–328Ma). The granites show geochemical characteristics similar to those of A-type granites, with high SiO2 (71.13–76.72wt%), Na2O+K2O (8.00–9.59wt%), and Al2O3 (12.28–14.08wt%), but depleted Sr, Nb, Ta and Eu. They display moderate to high positive εNd(t) and εHf(t) values (4.26–8.21 and 7.69–14.60, respectively) and young Nd and Hf model ages (T2DM-Nd=489–740 Ma and T2DM-Hf=471–845 Ma), suggesting magma derivation through partial melting of lower crust in the Boshchekul-Chingiz and Zharma-Saur arcs. The adakites are characterized by high Sr content (406.5–751.6ppm), and low Y (13.8–16.4ppm) and Yb (1.5–1.8ppm) content, yielding relatively high Sr/Y ratios (25.38–49.41) similar to those of modern adakites. They have high positive εNd(t) and εHf(t) values (7.85–8.25 and 13.23–15.97, respectively) and young Nd and Hf model ages (T2DM-Nd=429–535Ma and T2DM-Hf=355–550Ma), indicating that their source magmas were likely derived from partial melting of the oceanic crust beneath the Boshchekul-Chingiz arc. The petrogenesis and distribution of the A-type granites and adakites, as well as the tectonic architecture of the region, suggest that a ridge subduction event might have occurred during the Early Silurian to Early Carboniferous. In combination with previous studies in the Chinese Altai, we suggest a two-sided ridge subduction model for the Junggar-Altai region.

The formation of the Late Cretaceous Xishan Sn–W deposit, South China: Geochronological and geochemical perspectives

The Xishan Sn–W deposit is spatially related to K-feldspar granites in the Yangchun basin, western Guangdong Province, South China. LA-ICP-MS zircon U–Pb dating for the Xishan pluton defines an emplacement age of ~79Ma (78.1±0.9Ma; 79.0±1.2Ma; 79.3±0.8Ma), consistent with the mineralization age of the Xishan Sn–W deposit constrained by molybdenite Re–Os isochron age (79.4±4.5Ma) and LA-ICP-MS cassiterite U–Pb ages (78.1±0.9Ma and 79.0±1.2Ma) for the cassiterite-quartz vein. These indicate a close genetic relationship between the granite and Sn–W mineralization. The Xishan K-feldspar granites have geochemical characteristics of A-type granites, e.g., high total alkali (Na2O+K2O=7.88–10.07wt.%), high Ga/Al ratios (10000*Ga/Al>2.6) and high Zr+Nb+Ce+Y concentrations (>350ppm). They are further classified as A2-type granites. The whole-rock isotopic compositions of K-feldspar granites (initial 87Sr/86Sr=0.705256–0.706181; εNd(t)=−5.4 to −4.8) and zircon εHf(t) values (−7.8 to 2.0) suggest a mixed magma source. The low zircon Ce4+/Ce3+ ratios (12–88) of K-feldspar granites suggest low oxygen fugacities, which is key for enrichment of tin in primary magmas. The K-feldspar granites have experienced strong differentiation as indicated by their high Rb/Sr and K/Rb ratios, and low Nb/Ta and Zr/Hf ratios, which play an important role in ore-forming element transportation and concentration. A-type granite characteristics of the Xishan pluton show that it formed in an extensional environment. The high F and low Cl characteristics of the K-feldspar granite are most probably attributed to slab rollback. In the Late Cretaceous, the Xishan Sn–W deposit was located near the interaction of the circum-Pacific and the Tethys tectonic realms. Late Cretaceous Sn–W deposits, including the Xishan deposit, form an EW-trending belt from Guangdong to Yunnan Province in South China. This belt is in accordance with the direction of the Neo-Tethys slab rollback in the Late Cretaceous. In addition, the NS-trending extension has been recognized in the Late Cretaceous in South China. We propose that the Xishan Sn–W deposit should be attributed to the Neo-Tethys slab rollback in the Late Cretaceous.

Pulses of Late Mesozoic magmatism: Zircon ages and Hf-O isotopic composition of the Qingyang-Jiuhuashan granitic complex, southern Anhui province, eastern China

Late Mesozoic magmatic rocks are widely distributed in southern Anhui province, and are represented by the Qingyang-Jiuhuashan granitic complex, which consists dominantly of the Qingyang pluton of granodiorite and monzogranite, and the Jiuhuashan pluton of K-feldspar granite. These two plutons have zircon U-Pb ages of 138Ma–128Ma. Combining the new data with previously reported age data, the magmatism in southern Anhui province can be subdivided into three stages: early stage of ∼152–136Ma, middle stage of ∼136–130Ma, and latest stage of ∼130–120Ma. Granodiorite (early stage) and monzogranite (middle stage) of the Qingyang pluton have SiO2 contents of 66–68wt%, total alkali contents of 7.5–8.6wt%, K2O/Na2O ratios of 1.1–1.3, A/CNK ratios of 0.9–1.1, and low FeOT/(FeOT+MgO) values of 0.71–0.73. These rocks show depletion in Nb, Ta, and Zr and slightly negative Eu anomalies. K-feldspar granite (late stage) of the Jiuhuashan pluton is characterized by high SiO2 contents (>75wt%), K2O/Na2O ratios of 1.1–1.3, and A/CNK ratios of 0.9–1.2, and high FeOT/(FeOT+MgO) values of 0.88–0.93. They have high concentrations of Nb, Ta, and Zr, and strongly negative Eu anomalies. Initial εHf values of zircon grains from the granodiorite and monzogranite range from −8.01 to −6.71 and −11.40 to −9.43, with δ18O values varying from 7.16‰ to 8.04‰ and 7.26‰ to 8.06‰, respectively. Zircon grains from K-feldspar granites have relatively high initial εHf values of −7.62 to −4.78, but similar δ18O values of 7.03–8.84‰. Geochemical features of granodiorite and monzogranite point to an I-type signature, whereas those of K-feldspar granite show an A-type affinity. We propose that the granodiorite and monzogranite originated from mixing melts produced by partial melting of lithospheric mantle metasomatized by fluids and crustal rocks induced by underplating basaltic magmas, related to subduction of the Paleo-Pacific oceanic crust, whereas the K-feldspar granite formed from crustal anatexis in an extension setting caused by rollback of the subduction.

Continental crust melting induced by subduction initiation of the South Tianshan Ocean: Insight from the Latest Devonian granitic magmatism in the southern Yili Block, NW China

The Tianshan belt of the southwestern Central Asian Orogenic Belt was generated by Paleozoic multi-stage subduction and final closure of several extinct oceans, including the South Tianshan Ocean between the Kazakhstan-Yili and Tarim blocks. However, the subduction initiation and polarity of the South Tianshan Ocean remain issues of highly debated. This study presents new zircon U-Pb ages, geochemical compositions and Sr-Nd isotopes, as well as zircon Hf isotopic data of the Latest Devonian to Early Carboniferous granitic rocks in the Wusun Mountain of the Yili Paleozoic convergent margin, which, together with the spatial-temporal distributions of regional magmatic rocks, are applied to elucidate their petrogenesis and tectonic linkage to the northward subduction initiation of the South Tianshan Ocean. Our zircon U-Pb dating results reveal that these granites were emplaced at the time interval of 362.0±1.2–360.3±1.9Ma, suggesting a marked partial melting event of the continental crust in the Latest Devonian to Early Carboniferous. These granites, based on their mineral compositions and textures, can be categorized as monzogranites and K-feldspar granites. Geochemically, both monzogranites and K-feldspar granites have characters of I-type granites with high K2O contents (4.64–4.83wt.%), and the K-feldspar granites are highly fractionated I-type granites, while the monzogranites have features of unfractionated I-type granites. Whole-rock Sr-Nd isotopic modeling results suggest that ca. 20–40% mantle-derived magmas may be involved in magma mixing with continental crust partial melts to generate the parental magmas of the granites. The mantle-derived basaltic magmas was inferred not only to be a major component of magma mixture but also as an important heat source to fuse the continental crust in an extensional setting, which is evidenced by the high zircon saturation temperatures (713–727°C and 760–782°C) of the studied granites. The Latest Devonian to Early Carboniferous extensional setting in the Wusun Mountain region of the Yili Paleozoic convergent margin is addressed by the subduction initiation of the South Tianshan Ocean and constituted a late Paleozoic nascent arc- back-arc system in the southwestern CAOB.

Petrogenesis of the Huashanguan A-type granite complex and its implications for the early evolution of the Yangtze Block

An integrated study of petrography, zircon U-Pb ages, Hf-O isotope compositions, as well as whole rock geochemistry was carried out for a Paleoproterozoic granite complex in the northern Yangtze Block, to investigate its petrogenesis and geological significances. Petrographically, the Huashanguan complex is a granite complex comprised of monzogranite in the marginal facies and K-feldspar granite in the central facies. U-Pb dating of magmatic zircons from the monzogranite and K-feldspar granite yielded ages of 1816±50Ma and 1843±9Ma respectively. The more precise age of 1843±9Ma is suggested to represent the formation age of the Huashanguan complex. The granites have uniform negative zircon εHf(t) values of −20.2 to −15.8, with corresponding TDM2 ages of ca. 3.6–3.5Ga. The δ18O values average at 6.80±0.09‰. These indicate that the granites were generated by partly melting of Archean rocks, implying the widespread of Archean basement in the Yangtze Block. The monzogranites display low FeOT and MgO contents and evolved trace element features, suggesting their formation by more fractional crystallization from similar parent magma of the K-feldspar granites. The occurrence of the Huashanguan granite complex indicates that the Yangtze Block has experienced a tectonic transition from tectonic convergence to extension at ca. 1.85Ga, possibly due to the collapse of the ca. 2.0Ga orogeny.

The geochemical evolution of the granitoid rocks in the South Qinling Belt: Insights from the Dongjiangkou and Zhashui intrusions, central China

Widespread Late Triassic granitoid rocks in the South Qinling Belt (SQB) represent excellent subjects to study the geochemical and geodynamic evolution of magmatic rocks during the collision between the North China Craton and South China Block. In this study, we report new geological, geochemical, zircon U–Pb geochronology and zircon Hf isotopic data for the Dongjiangkou and Zhashui intrusions, two large igneous complexes typical of the SQB. We also summarize published geochemical data of similar granitoid rocks. Our results show that the Dongjiangkou intrusion is composed of ca. 223–214Ma quartz diorites, tonalites and granodiorites with abundant coeval mafic magmatic enclaves (MME), and the Zhashui intrusion consists of ca. 203–197Ma monzogranites and K-feldspar granites with rare MME. The Dongjiangkou granitoid rocks are characterized by high K2O, MgO, Rb, and Mg# values, but low TiO2, Sc, and A/CNK (molar Al2O3/(CaO+Na2O+K2O)) values, with εHf(t) values of −18.1 to −0.4 and TDM2(Hf) values of 1141–2117Ma. We suggest that the Dongjiangkou granitoid rocks are formed by magma mixing between 70%–90% melts derived from partial melting of the Neoproterozoic basement rocks of the SQB and 10%–30% mantle-derived mafic melts with minor involvement of Archean to Paleoproterozoic old basement materials of the SQB. The Zhashui granitoid rocks exhibit high K2O, Rb, A/CNK, AMF(Al2O3/(MgO+FeOT)), Al2O3/TiO2 and Rb/Sr values, but low MgO, TiO2, Sc, CaO/Na2O values, with εHf(t) values of −3.5 to +2.3 and TDM2(Hf) values of 979–1300Ma, suggesting they are mainly produced by partial melting of Neoproterozoic metamorphic greywackes mixed with minor amounts of mantle-derived melts. The MME are characterized by low SiO2, Sr/Y ratio, but high MgO, K2O, and Rb contents, with εHf(t) values of −0.8 to +4.3 and TDM(Hf) values of 732–905Ma, suggesting they are produced by partial melting of metasomatized continental lithospheric mantle. A flare-up event is recognized during 225–205Ma and the lower SiO2 and Sr/Y of the granitoid rocks during this period indicate prominent involvement of mantle-derived melts mixed with crustal melts. The granitoid rocks with higher SiO2 and Sr/Y during 225–205Ma, however, suggest they are formed under a greater pressure than those of previous period (235–225Ma) granitoid rocks. Few granitoid intrusions are formed after 205Ma, and they display high SiO2 with low Sr/Y reflecting that they may be produced by low pressure partial melting of crustal materials or may represent highly fractionated magmas in the upper crust. These geochemical variations show a regular change with their formation ages, reflecting the possible variation in petrogenesis and crustal thickness. We propose that the granitoid rocks may have been formed in a transitional setting from subduction to collision during ca. 235–225Ma, and a slab break-off event followed during ca. 225–205Ma. Slab detachment was completed during ca. 205–190Ma. We propose that no intensive delamination/convective removal of lower crust occurred in the SQB.

Petrogenesis of the Huili Paleoproterozoic leucogranite in the Jiaobei Terrane of the North China Craton: A highly fractionated albite granite forced by K-feldspar fractionation

A Paleoproterozoic leucogranite has been identified petrologically as highly fractionated granite near Huili in the Jiaobei Terrane of the North China Craton. This granite occurs as a 3×10km pluton in the metamorphic Paleoproterozoic Jingshan Group and was dated at 1.86Ga using zircon LA-ICP-MS U-Pb ages. The Huili leucogranite can be subdivided into three groups: groups I and II have normal leucogranite abundances with 2.22–2.57wt.% Na2O, 6.10–6.92wt.% K2O, and 71.68–73.07wt.% SiO2 and group III has a remarkably high Na2O concentration of 6.45–7.23wt.%, a low K2O content of 0.82–1.05wt.%, and 74.21–74.79%wt.% SiO2. Moreover, group III leucogranite comprises slightly lower Th, U, and Sr contents and considerably lower K-feldspar compatible elements, such as Rb, Ba, Pb, and Cs than those of groups I & II. All of these features strongly indicate the K-feldspar fractionation during the magma evolution from groups I and II to group III, which is strongly supported by the Pb isotope analysis. Group III leucogranite has a notably high U/Pb ratio of 0.30 to 0.45 with a normal U content of 1.42 to 2.21ppm and very low Pb content of 4 to 5ppm, indicating a significant K-feldspar fractionation of the magma. Group III leucogranite has high radiogenic Pb isotopes (i.e., 206Pb/204Pb=37.407–116.31), demonstrating that the rocks must have existed in a high U-Pb system for a notably long time. Fortunately, the whole rock Pb isotope values roughly define the Pb-Pb isochrons, not only when all three groups of samples are considered together but also when any individual group is considered. The ages are very close to the formation time of ~1.86Ga indicating the high U/Pb system required by these Pb isotopes must have been initiated during the formation of the Huili leucogranite, which has perfectly confirmed the K-feldspar fractionation during the magma evolution.All samples have consistent εNd values (t=1.86Ga) of −4.0 to −6.2 with two-stage Nd model ages (TDM2) of 2.67 to 2.85Ga. It is concluded that the 1.86Ga Huili leucogranite is highly fractionated, derived from ancient crustal material extracted from the depleted mantle at 2.7–2.8Ga, and experienced significant fractionation of K-feldspar in association with biotite and monazite fractionation during the magmatic evolution. Group III leucogranite is albite granite with albite phenocrysts, whereas groups I & II are K-feldspar granites with K-feldspar phenocrysts. It is here argued that the Huili albite granite (group III leucogranite) is derived from a highly differentiated residual melt separated from the K-rich magma represented by groups I and II leucogranite due to Kf fractionation during magma evolution.

A Silurian-early Devonian slab window in the southern Central Asian Orogenic Belt: Evidence from high-Mg diorites, adakites and granitoids in the western Central Beishan region, NW China

The Beishan orogenic belt is a key region for deciphering the accretionary processes of the southern Central Asian Orogenic Belt. Here in this paper we present new zircon U–Pb ages, bulk–rock major and trace element, and zircon Hf isotopic data for the Baitoushan, and Bagelengtai plutons in the western Central Beishan region to address the accretionary processes.The Baitoushan pluton consists of quartz diorites, monzonites and K-feldspar granites, with zircon LA–ICP–MS U–Pb ages of 435Ma, 421Ma and 401Ma, respectively. The Baitoushan quartz diorites and quartz monzonites exhibit relatively high MgO contents and Mg# values (63–72), display enrichments in LILEs and LREEs, and exhibit high Ba (585–1415ppm), Sr (416–570ppm) and compatible element (such as Cr and Ni) abundances, which make them akin to typical high-Mg andesites. The Baitoushan quartz diorites and quartz monzonites were probably generated by the interaction of subducted oceanic sediment-derived melts and mantle peridotites. The Baitoushan K-feldspar granites are ascribed to fractionated I-type granites with peraluminous and high-K calc-alkaline characteristics. They exhibit positive εHf(t) values (2.43–7.63) and Mesoproterozoic–Neoproterozoic zircon Hf model ages (0.92–1.60Ga). Those early Devonian granites, including Baitoushan K-feldspar granite and Gongpoquan leucogranites (402Ma), are derived from melting of the mafic lower crust and/or sediments by upwelling of hot asthenospheric mantle. The Bagelengtai granodiorites exhibit similar geochemical signatures with that of typical adakites, with a zircon SHRIMP U-Pb age of 435Ma. They exhibit relatively high Sr (502–628ppm) and Al2O3 (16.40–17.40wt.%) contents, and low MgO (1.02–1.29wt.%), Y (3.37–6.94ppm) and HREEs contents, with relatively high Sr/Y and (La/Yb)N ratios. The Bagelengtai granodiorites were derived from partial melting of subducted young oceanic crust, with significant contributions of subducted sediments, subsequently hybridized by the mantle peridotite.On the basis of our data and combined with previous data, we conclude that a Silurian–early Devonian slab window model accounts for all geological records in the western segment of the Central Beishan. We further propose that magmatic events associated with a slab window played an important role in crustal growth of the Central Asian Orogenic Belt.

Geochronology and geochemistry of the TTG and potassic granite of the Taihua complex, Mts. Huashan: Implications for crustal evolution of the southern North China Craton

Tonalite-trondhjemite-granodiorite (TTG) suite and potassic granite volumetrically expose in the Neoarchean to Paleoproterozoic Taihua complex, Mts. Huashan region, southernmost segment of the Trans-North China Orogen (TNCO). Zircon U–Pb dating on the trondhjemite, granitic gneiss, K-feldspar granite and coarse-grained granite samples show three episodes of magmatism (2.55–2.49Ga, 2.33–2.25Ga and 1.87–1.80Ga) with distinct geochemical features in this area during the Paleoproterozoic. The trondhjemite samples have high SiO2 (67.46–71.73wt%), Na2O (4.83–5.95wt%), low Mg# (31–40) and HREE contents, with moderate (La/Yb)N values (16.8 to 35.3) and Sr/Y ratios (15.8 to 34). The potassic granite samples show high SiO2 (65.2–75.43wt%), K2O (3.9–8.6), low Na2O (1.74–4.17wt%), Mg# (2–46) and HREE contents, with moderate to high (La/Yb)N values (10.3 to 226) and Sr/Y ratios (12.8 to 208). All these granitoid samples are characterized by high SiO2 and low Mg#, Cr, Ni with moderate to high (La/Yb)N values and Sr/Y ratios. The absence of evidence of any pre-existing high Sr/Y and La/Yb sources in this region led to that the granitoids probably generated from partial melting of hydrous mafic rocks with garnet and amphibole in the residue. Therefore, partial melting of thickened lower curst is the most likely origin. Combined with previous studies, the first episodic magmatism (2.55–2.49Ga) represented by TTG and granitic gneisses with positive whole rock ƐNd(t) and zircon ƐHf(t) values is interpreted as melts from partial melting of juvenile thickened lower crust. The second episodic magmatism (2.33–2.25Ga) represented by TTG, granitic gneisses and K-feldspar granite with positive to negative whole rock ƐNd(t) and zircon ƐHf(t) values is suggested as the product of partial melting of both juvenile and pre-existing crustal material. The third episodic magmatism (1.87–1.80Ga) is represented by these potassic granites, which is synchronism with the metamorphism recorded in this region and probably resulted from partial melting of pre-existing crustal materials in a syn-orogenic or post-orogenic setting during the collision between the Eastern and Western Blocks of the North China Craton. Multistage continental accretion (at 2.84–2.72Ga, 2.57–2.43Ga and 2.36–2.25Ga) and reworking (at 2.36–2.25Ga, 2.19–2.07Ga and 1.87–1.80Ga) occurred in the southern segment of the TNCO from Neoarchean to Paleoproterozoic. Transformation from an Andean-type continental margin arc setting on the western margin of the Eastern Block to continent-arc-continent collision in the southern TNCO during Late Neoarchean to Late Paleoproterozoic is suggested in this paper.

Early to late Yanshanian I-type granites in Fujian Province, SE China: Implications for the tectonic setting and Mo mineralization

The Cathaysia Block is the southeastern part of the South China Block in Southeast (SE) China, and it hosts voluminous late Mesozoic I-, S-, and A-type granitoids, as well as minor highly fractionated granites. We present here zircon U–Pb age data and Nd–Hf isotopic data for the Dayang and Juzhou granites, together with new petrological and geochemical analyses. The Dayang pluton consists of fine-grained two-mica monzonitic granites in which the plagioclases exhibit zoning and poikilitic textures. In contrast, the Juzhou pluton consists of medium- to coarse-grained biotite K-feldspar granites that lack zoning and poikilitic textures. The emplacement ages are 143±2.3Ma for the Dayang pluton and 133±2.1Ma for the Juzhou pluton according to zircon U–Pb isotope analyses. The Dayang and Juzhou granites are both metaluminous and belong to the shoshonitic series. The Dayang granite exhibits very flat REE patterns, showing the tetrad effect, and the spidergrams show striking negative Ba, Sr, Nb, and Ti anomalies and a positive Ta anomaly. In contrast, the Juzhou granite has sloping REE patterns, but like the Dayang granite it also has striking negative Ba, Sr, Nb, Ta, and Ti anomalies. Petrographic and geochemical evidence indicates that the Dayang granite is a highly fractionated I-type granite and that the Juzhou granite is a typical I-type granite. The tetrad effect in the Dayang granite can be interpreted in terms of melt–rock interactions at a late stage of magma evolution, whereas the main mechanism during the evolution of the Juzhou magma was fractionation of plagioclase, biotite, hornblende, apatite, zircon, and allanite. Nd–Hf isotope data suggest that the Dayang and Juzhou granites were both formed partial melting of Paleoproterozoic basement rock and juvenile material (underplating basalts or Mayuan Group amphibolites), with the Juzhou granite having a greater contribution from juvenile material than the Dayang granite. Our new data, together with existing data, suggest that the tectonic setting of the early Yanshanian (∼143Ma) highly fractionated I-type Dayang granite was a back-arc that formed in response to the westward subduction of the Paleo-Pacific Plate, and that the late Yanshanian (∼133Ma) Juzhou granite formed in a continental arc setting in response to rollback of the Paleo-Pacific Plate toward the coastline. The Mo mineralization in the Makeng ore area was probably the result of the exsolution of Mo-bearing fluids from the Dayang granitic magmas due to extensive fractional crystallization.

Late Triassic syn-exhumation magmatism in central Qiangtang, Tibet: Evidence from the Sangehu adakitic rocks

The geodynamic setting of Late Triassic magmatic activity along the Longmu Co–Shuanghu suture zone (LSSZ) in central Qiangtang, Tibet is a matter of debate. This paper presents zircon LA–ICP–MS U–Pb ages, zircon Hf isotopic compositions, and whole-rock geochemical data for the Sangehu (SGH) granitic intrusion in central Qiangtang, and addresses the petrogenesis of Late Triassic magmatism, and the history of collision between the northern and southern Qiangtang terranes. The SGH pluton consists mainly of biotite adamellite with mafic microgranular enclaves (MMEs), and small amounts of K-feldspar granite. The biotite adamellite, MMEs, and K-feldspar granite give ages of 207.8±3.0Ma, 212.4±31Ma, and 211.6±3.8Ma, respectively. The MMEs show magmatic textures and acicular apatite, and are coeval with the host biotite adamellite, suggesting they were produced by magma mixing. All samples from the SGH pluton show high Sr and low Y contents, and positive Eu anomalies, similar to adakitic rocks. The high K2O contents and low Mg#, Cr, and Ni contents, and enriched Hf isotopic characteristics of the zircons indicate that these magmas were derived from the partial melting of thickened crust. However, the whole-rock geochemical data and zircon Hf isotopic compositions also reveal heterogeneity at the source. The combined magmatic and metamorphic records suggest that Triassic magmatic activity in central Qiangtang was closely related to the collision of the northern and southern Qiangtang terranes. The large-scale Late Triassic (225–200Ma) magmatic event in central Qiangtang may have resulted from the breakoff of the Longmu Co–Shuanghu Tethys Ocean lithospheric slab in the early Late Triassic (236–230Ma). The Late Triassic magmatic rocks, including adakitic rocks, are coeval with retrograde high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in central Qiangtang, and show characteristics of syn-exhumation magmatism. The early adakitic rocks (>220Ma) were generated by melting of the edge of the slab, which was heated by upwelling asthenospheric mantle after subduction slab breakoff, and the late adakitic rocks (<220Ma) were generated by partial melting of the thickened crust.

Petrology and geochemistry of charnockites (felsic ortho-granulites) from the Kerala Khondalite Belt, Southern India: Evidence for intra-crustal melting, magmatic differentiation and episodic crustal growth

The Kerala Khondalite Belt (KKB) of the southern India encompasses volumetrically significant magmatic components. Among these, orthopyroxene-bearing, felsic ortho-granulites, popularly known as charnockites in Indian context, constitute an important lithology. In contrast to the well-known phenomena of arrested charnockitization, the geochemical characteristics and petrogenesis of these ortho-granulite suites remain poorly studied, leaving geodynamic models envisaged for the KKB highly conjectural. In this paper, we try to bridge this gap with detailed results on orthopyroxene-bearing, felsic ortho-granulites spread over the entire KKB and propose a new petrogenetic and crustal evolution model.Based on geochemical characteristics, the orthopyroxene-bearing, felsic ortho-granulites (charnockites sensu lato) of KKB are classified into (1) tonalitic (TC), (2) granitic (GC), and (3) augen (AC) suites. Members of the TC follow sodic (characterized by decreasing CaO/Na2O), whereas those of the GC and AC follow calc-alkaline trends of differentiation. Geochemical patterns of the TC resemble those of the Archaean tonalite–trondhjemite–granodiorite (TTG) suites, with slightly magnesian character (average Mg#=33), moderate LREE (average LaN=154), low HREE (average YbN=6) and Y (1–53ppm; average 11ppm). The TC is also characterized by positive to slightly negative europium anomalies (Eu/Eu*=0.7 to 1.67). The GC and AC suites, on the other hand, resemble post-Archaean arc-related granites. The GC displays ferroan nature (average Mg#=22), low to moderate degrees of REE fractionation (average [La/Yb]N=34.84), high contents of Y (5–128ppm; average 68), and low Sr/Y (1–98) ratios. Significant negative Eu anomalies (Eu/Eu*=0.18–0.91; average 0.50) and low Sr (65–690ppm) are also noted in the GC. Similar chemical characteristics are shown by the AC, with ferroan nature (average Mg#=21), low to moderate degrees of REE fractionation (average [La/Yb]N=26), high contents of Y (71–99ppm; average 87), and low Sr/Y (average 2) ratios with significant negative Eu anomalies (Eu/Eu*=0.03–0.31; average 0.23) and low Sr (average 160ppm) contents. The protoliths of the TC are interpreted as being derived from partial melting of thickened oceanic-arc crust composed of Archaean mafic composite source rocks (i.e., eclogite and/or garnet amphibolite) with a garnet amphibolite residue. Geochemical features of the GC, such as high Rb/Sr (average 1.80) and Ba/Sr ratios (average values >6), are considered as evidence for crustal reworking in their genesis, suggesting remelting of a quartzo-feldspathic (TTG) source, within the plagioclase stability fields.The geochemical features of the felsic ortho-granulite suite, substantiated with published geochronological data on members of the TC, GC, and AC suites, suggest a four-stage crustal evolution of the KKB. The first stage is marked by the formation of an over-thickened oceanic-arc. Zircon Hfc model ages of the TC and GC suites constrain the time of this juvenile magmatic crust-forming event as Meso- to Neoarchaean (2.8 to 2.6Ga). The second stage corresponds to the production of TTG magmas by melting of the over-thickened oceanic-arc crust, subsequent to basaltic underplating during Palaeoproterozoic (ca. 2.1Ga). The third stage was initiated by a transition in subduction style from shallow to steep due to continent-arc accretion. This stage is marked by the formation of granitic magmas through partial melting of the TTG crust and their differentiation into GC and TC. The zircon crystallization ages (1.89 and 1.85Ga) of the GC indicate arc accretion occurred during the Palaeoproterozoic. The fourth stage of crustal evolution is correlated with the Mesoproterozoic (~1.5Ga) emplacement of megacrystic K-feldspar granites (protoliths to the AC and augen gneisses). The distinct petrography, geochemistry and crystallization ages of the AC suggests recurrence of megacrystic, high-K calc-alkaline granitoids as the product of final phases of crustal-remelting marking subduction cessation. All these magmatic events are fairly well correlated with the major episodes of crustal growth observed in the once contiguous continental fragments (Sri Lanka and Madagascar) and worldwide events (2.7, 1.9, and 1.2Ga) implying similar episodic nature in the lower crustal evolution of the KKB.