Zircon ages and Hf isotopic compositions of Permian and Triassic A-type granites from central Inner Mongolia and their significance for late Palaeozoic and early Mesozoic evolution of the Central Asian Orogenic Belt

ABSTRACT

This work presents zircon ages and Hf-in-zircon isotopic data for Permian and Triassic A-type granitoids and reviews the evolution of central Inner Mongolia, China, during the early Permian and Late Triassic. SHRIMP U–Pb dating of zircons of peralkaline granites yielded ²⁰⁶Pb/²³⁸U ages of 294 ± 4 Ma and 293 ± 9 Ma that reflect the time of Permian magmatism. Zircon ages were also obtained for Late Triassic granites (226 ± 4 Ma, 224 ± 4 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia.

The Permian peralkaline granites show typical geochemical features of A-type granites, which also have highly positive zircon ε_Hf(t) values (+4.9 – +17.1), indicating a significant contribution of an isotopically depleted source, likely formed from mantle-derived magmas. Late Triassic A-type granitoids, however, in central Inner Mongolia show large variations and mostly positive in zircon ε_Hf(t) values (?1.3 – +13.5), suggesting derivation from a mixture of crust and mantle or metasomatized lithospheric mantle with crustal contamination. The geochemical characteristics of the Permian peralkaline granites and Late Triassic A-type granitoids are consistent with a post-collisional setting and were likely related to asthenosphere upwelling during the evolution of the Northern Block and Central Asian Orogenic Belt (CAOB).     

Sulfur Isotope Variations of Metallic Ore Deposits in the Gyeongsang Basin,South Korea

Many metallic ore deposits of the Late Cretaceous to Early Tertiary periods are distributed in the Gyeongsang Basin. Previous and newly analyzed sulfur isotope data of 309 sulfide samples from 56 ore deposits were reviewed to discuss the genetic characteristics in relation to granitoid rocks. The metallogenic provinces of the Gyeongsang Basin are divided into the Au–Ag(–Cu–Pb–Zn) province in the western basin where the sedimentary rocks of the Shindong and Hayang groups are distributed, Pb–Zn(–Au–Ag–Cu), Cu–Pb–Zn(–Au–Ag), and Fe–W(–Mo) province in the central basin where the volcanic rocks of the Yucheon Group are dominant, and Cu(–Mo–W–Fe) province in the southeastern basin where both sedimentary rocks of the Hayang Group and Tertiary volcanic rocks are present. Average sulfur isotope compositions of the ore deposits show high tendencies ranging from 2.2 to 11.7‰ (average 5.4‰) in the Pb–Zn(–Au–Ag–Cu) province, ?0.7 to 11.5‰ (average 4.6‰) in the Cu–Pb–Zn(–Au–Ag) province, and 3.7 to 11.4‰ (average 7.5‰) in the Fe–W(–Mo) province in relation to magnetite‐series granitoids, whereas they are low in the Au–Ag(–Cu–Pb–Zn) province in relation to ilmenite‐series granitoids, ranging from ?2.9 to 5.7‰ (average 1.7‰). In the Cu(–Mo–W–Fe) province δ³⁴S values are intermediate ranging from 0.3 to 7.7‰ (average 3.6‰) and locally high δ³⁴S values are likely attributable to sulfur derived from the Tertiary volcanic rocks during hydrothermal alteration through faults commonly developed in this region. Magma originated by the partial melting of the ³⁴S‐enriched oceanic plate intruded into the volcanic rocks and formed magnetite‐series granitoids in the central basin, which contributed to high δ³⁴S values of the metallic deposits. Conversely, ilmenite‐series granitoids were formed by assimilation of sedimentary rocks rich in organic sulfur that influenced the low δ³⁴S values of the deposits in the western and southeastern provinces.     

Petrochemistry of Granitoids Along the Loei Fold Belt,Northeastern Thailand

Petrochemical characteristics of Permo‐Triassic granitoids from five regions (i) Mung Loei, (ii) Phu Thap Fah – Phu Thep, (iii) Phetchabun, (iv) Nakon Sawan – Lobburi, and (v) Rayong – Chantaburi along the Loei Fold Belt (LFB), northeastern Thailand were studied. The LFB is a north–south trending 800 km fold belt that hosts several gold and base‐metal deposits. The granitoids consist of monzogranite, granodiorite, monzodiorite, tonalite, quartz‐syenite, and quartz‐rich granitoids. These are composed of quartz, plagioclase, and K‐feldspar with mafic minerals such as hornblende and biotite. Accessory minerals, such as titanite, zircon, magnetite, ilmenite, apatite, garnet, rutile, and allanite are also present. Magnetic susceptibilities in the SI unit of granitoids vary from 6.5 × 10⁻³ to 15.2 × 10⁻³ in Muang Loei, from 0.1 × 10⁻³ to 29.4 × 10⁻³ in Phu Thap Fah – Phu Thep, from 2.7 × 10⁻³ to 34.6 × 10⁻³ in Petchabun, from 2.4 × 10⁻³ to 14.1 × 10⁻³ in Nakon Sawan – Lobburi, and from 0.03 × 10⁻³ to 2.8 × 10⁻³ in Rayong – Chantaburi. Concentration of major elements suggests that these intermediate to felsic plutonic rocks have calc‐alkaline affinities. Concentration of REE of the granitoids normalized to chondrite displays moderately elevated light REE (LREE) and relatively flat heavy (HREE) patterns, with distinct depletion of Eu. Rb versus Y/Nb and Nb/Y tectonic discrimination diagrams illustrate that the granitoids from Muang Loei, Phu Thap Fah – Phu Thep, Phetchabun, Nakon Sawan – Lobburi, and Rayong – Chantaburi formed in continental volcanic‐arc setting. New age data from radiometric K‐Ar dating on K‐feldspar from granodiorite in Loei and Nakhon Sawan areas yielded 171 ± 3 and 221 ± 5 Ma, respectively. K‐Ar dating on hornblende separated from diorite in Lobburi yielded 219 ± 8 Ma. These ages suggest that magmatism of Muang Loei occurred in the Middle Jurassic, and Nakon Sawan – Lobburi occurred in Late Triassic. Both Nb versus Y and Rb versus (Y + Nb) diagrams and age data indicate that Nakon Sawan – Lobburi granitoids intruded in Late Triassic at Nong Bua, Nakon Sawan province and Khao Wong Phra Jun, Lobburi province in volcanic arc setting. Muang Loei granitoids at the Loei province formed later in Middle Jurassic also in volcanic arc setting. The negative δ³⁴S_CDT values of ore minerals from the skarn deposit suggest that the I‐type magma has been influenced by light biogenic sulfur from local country rocks. The Au‐Cu‐Fe‐Sb deposits correlate with the magnetite‐series granitoids in Phetchabun, Nakon Sawan – Lobburi and Rayong – Chantaburi areas. Metallogeny of the Au and Cu‐Au skarn deposits and the epithermal Au deposit is related to adakitic rocks of magnetite‐series granitoids from Phetchabun and Nakon Sawan areas. All mineralizations along the LFB are generated in the volcanic arc related to the subduction of Paleo‐Tethys. The total Al (^TAl) content of biotite of granitoids increases in the following order: granitoids associated with Fe and Au deposit < with Cu deposit < barren granitoids. X_Mg of biotite in granitoids in Muang Loei indicates the crystallization of biotite in magnetite‐series granitoids under high oxygen fugacity conditions. On the other hand, low X_Mg (<0.4) of biotite in magnetite‐series granitoids in Phu Thap Fah – Phu Thep and Rayong – Chantaburi indicates a reduced environment and low oxygen fugacity, associated with Au skarn deposit (Phu Thap Fah) and Sb‐Au deposit (Bo Thong), respectively. The magnetite‐series granitoids at Phu Thap Fah having low magnetic susceptibilities and low X_Mg of biotite were formed by reduction of initially oxidizing magnetite‐series granitic magma by interaction with reducing sedimentary country rocks as suggested by negative δ³⁴S_CDT values.     

Rb‐Sr geochronology and Sr isotopic composition of Devonian granitoids,eastern Tasmania

Biotite igneous ages and well‐defined isochron ages of plutons from the composite Blue Tier Batholith and the Coles Bay area in northeastern Tasmania range from 395 to 370 Ma. The older limit of this range, for the George River granodiorite, is considerably older than any age previously recorded for NE Tasmania. The ages of the youngest plutons (Mt Paris and Anchor granites), which host cassiterite ores, record pervasive hydrothermal alteration events. The initial ⁸⁷Sr/⁸⁰Sr ratios of the granitoids range from 0.7061 to 0.7136 and suggest different protolith compositions, consistent with mineralogical and geochemical characteristics of each pluton. The S‐type garnetbiotite granites (Ansons Bay and Booby alia granites) have initial ratios greater than 0.7119, indicative of enriched, high Rb/Sr ratio, crustal source‐rocks of Proterozoic age (1700–800 Ma). The S‐type biotite granites (Poimena and Pearson granites) have relatively high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7070, 0.7105) but overlap with those of the I‐type granodiorites (George River, Scamander Tier, Pyengana and Coles Bay granodiorites) which are in the range of 0.7061 to 0.7073. The initial ratios of the enriched altered plutons are poorly constrained, and on both hand‐specimen and thin‐section scales, reveal open‐system Sr isotopic patterns.

Isochron ages for the arenite‐lutite and lutite sedimentary associations of the Mathinna Beds, which are intruded by the granitoids, reflect an approach to Sr isotopic equilibrium during regional metamorphism. The metamorphic age (401 ± 7 Ma) of the early Pragian arenite‐lutite association indicates a relatively small time interval between deposition, regional metamorphism and granitoid intrusion. The isotopic age for the lutite sedimentary association (423 ± 22 Ma) is tentatively correlated with a Benambran‐age burial metamorphic event that has not previously been recorded in Tasmania.     

Petrogenesis of Mesoproterozoic K‐rich granitoids,southern Mt Angelay igneous complex,Cloncurry district,northwest Queensland

The K‐rich granitoids of the southern Mt Angelay igneous complex belong to the younger phases of the Williams and Naraku Batholiths (<1540 Ma) in the Cloncurry district. Granitoids of the complex form a series of I‐type, K‐rich, metaluminous monzodiorite to subaluminous syenogranite. These intrusions have geochemical affinities akin to ‘A‐type’ granites and contain plagioclase, alkali feldspar, quartz, biotite, hornblende and typically accessory magnetite, titanite, apatite and zircon. With increasing SiO₂ the granitoids vary from alkaline to subalkaline, and exhibit a decrease in TiO₂, Al₂O₃, Fe₂O₃*, MnO, MgO, CaO, P₂O₅, Cu, Sr, Zr, LREE and Eu, with an increase in Na₂O, K₂O, Rb, Pb, Th, U, Y and HREE. This suite of relatively oxidised granitoids (<1.0 log units above NNO) were emplaced after the peak of metamorphism and pre‐ to post‐D₃, a major east‐west horizontal‐shortening event. The synchronous emplacement of high‐temperature mafic (>960°C) and foliated felsic (>900°C) granitoids formed zones of mingled and mixed monzonite and quartz monzonite to monzogranite containing abundant rapakivi K‐feldspar. These intrusions are interpreted to have been derived from source rocks of different compositions, and probably by different degrees of partial melting. The unfoliated felsic granitoids are considered to represent the fractionated equivalents of older foliated felsic granitoids. All granitoids possess a Sr‐depleted and Y‐undepleted signature, which suggests that the source material probably contained plagioclase and no garnet, restricting magma production to <800–1000 MPa (～24–30 km). Underplating of mantle‐derived mafic material into mid‐crustal levels is considered the most viable mechanism to produce these high‐temperature K‐rich granitoids at these pressures. The composition of the felsic granitoids is consistent with derivation from a crustal source with a tonalitic to granodioritic composition. However, the mafic granitoids require a more mafic, possibly gabbroic source, which may have been supplemented with minor mantle‐derived material. These granitoids are also enriched in Th, U, LREE and depleted in Ba, Ti, Nb and Sr and compare closely to the Mesoproterozoic granitoids of the Gawler Craton. The economic significance of these styles of granitoids may also be highlighted by the close spatial relationship of hematitic K‐feldspar, magnetite, fluorite and pyrite‐rich veins, alteration and filled miarolitic cavities with the least‐evolved felsic intrusions. This style of veining has a probable magmatic origin and is similar to the gangue assemblage associated with Ernest Henry‐style Fe‐oxide‐(Cu–Au) mineralisation, which suggests that these granitoids represent prospective sources of fluids associated with Cu–Au mineralisation in the district.     

Source Diversity of Ore Sulfur from Mesozoic-Cenozoic Mineral Deposits in the Korean Peninsula Region

Abstract: Sulfides from the Daebo Jurassic granitoids and some ore deposits from Korean Peninsula and Sikhote Alin occurring in different basement settings were analyzed for δ³⁴S values. Highly positive values were obtained from Jurassic Mo skarn deposit at Geumseong of the Ogcheon belt (average +13. 0%), Au‐quartz vein deposits at Unsan, North Korea (+6. 7%), and late Paleozoic Sn‐F deposit at Votnesenka (+8. 2%), Khanka massif, Russia. Together with published data of that region, regional variation of δ³⁴S values is shown across Korean Peninsula. Sulfur isotopic data published are compiled on 88 ore deposits, whose mineralization epochs belong to Cretaceous (58 deposits), Jurassic (25 deposits) and Precambrian (4 deposits) in South Korea. Average sulfur isotopic values vary across South Korea as follows: Cretaceous deposits in the Gyeongsang basin, +4. 8% ranging +1.2 ? +12.7‰ (n=28); Jurassic and Cretaceous deposits in the Sobaegsan massif, +3. 5% ranging 0.0 ? +7.8‰ (n=20); those of the Ogcheon belt, +6. 4% ranging ‐0.5 ? +15.4‰(n=19); those of the Gyeonggi massif, +5. 5% ranging +2.1 ? +9.0‰(n = 21). The δ³⁴S values of South Korea tend to be concentrated around +5. 5 permil, exhibiting little, if any, a systematic variation across the geotectonic belts. This tendency is seen also in North Korea and Northeast China within the Cino‐Korean Block, and may be called as Cino‐Korean type. Sulfur of this type is derived mostly from the crystalline basement. Khanka massif of Russia seems to have features of the Cino‐Korean type. In contrast, paired positive/negative belts corresponding to magnetite‐series/ilmenite‐series granitic belts are overwhelming in the Japanese Islands, especially in Southwest Japan. The similar trend is also seen in southern Sikhote Alin and northern Okhotsk Rim, which may be called as Japanese type. Source of the sulfur in this type is likely in the subducting oceanic slab for positive value and accreted sedimentary complex for the negative value, respectively. The Daebo granitoids have an average rock δ³⁴S value of +5. 3 permil, which should have reflected that of the source rocks in the continental crust. The ore sulfur heavier than this value may have been originated in other granitoids having even higher δ³⁴S values, or the ore fluids interacted directly with sulfate sulfur of the host evaporites or carbonate rocks. Rock isotopic values of granitoids and basement rocks need to be examined in future from the above point of view in mind.     

Paleoproterozoic Granitoids on Liaodong Peninsula,North China Craton

Paleoproterozoic granitoids are an important constituent of the Jiao–Liao–Ji Belt(JLJB). The spatial-temporal distribution and types of Paleoproterozoic granitoids are closely related to the evolution of the JLJB. In this paper, we review the field occurrence, petrography, geochronology, and geochemistry of Paleoproterozoic granitoids on Liaodong Peninsula, northeast China. The Paleoproterozoic granitoids can be divided into pre-tectonic(～2.15 Ga; peak age=2.18 Ga) and post-tectonic(～1.85 Ga) granitoids. The pre-tectonic granitoids are magnetite and hornblende–biotite monzogranites and granodiorites. Pre-tectonic monzogranites are widespread in the JLJB and have A_2-type affinities. In contrast, pretectonic granodiorites are only present in the Simenzi area and have adakitic affinities. The post-tectonic granitoids consist of porphyritic monzogranite, syenite, diorite, granodiorite, quartz monzonite, monzogranite, and granitic pegmatite, which are adakitic rocks and I-, S-, and A_2-type granitoids. The assemblage of pre-tectonic A_2-type granitoids and adakitic rocks indicates the initial tectonic setting of the JLJB was a continental back-arc basin. The assemblage of post-tectonic adakitic rocks and I-, S-, and A_2-type granitoids indicates a post-collisional setting. The 2.20–2.15 Ga A_2-type granitoids and adakitic rocks were associated with the initial stage of back-arc extension, and the peak of back-arc extension is inferred from the subsequent(2.15–2.10 Ga) mafic intrusive activity. The ～1.90 Ga adakitic rocks mark the beginning of the postcollisional stage, which was followed by the intrusion of low-temperature S-and I-type granitoids. High-to low-pressure granitoids(S-type) were generated during the peak of post-collisional lithospheric delamination and asthenospheric upwelling. The emplacement of later granitic pegmatites occurred during the waning of the orogeny.     

Redox Condition,Nature and Tectono-magmatic Environment of Granitoids and Granite gneisses from the Karbi Anglong Hills,Northeast India: Constraints from Magnetic Susceptibility and Biotite Geochemistry

The Karbi Anglong hills (erstwhile Mikir hills) in northeast India are detached and separated from the Meghalaya plateau by a NW-SE trending Kopili rift. The Karbi Anglong hills granitoids (KAHG) and its granite gneissic variants belong to Cambrian plutons formed during Pan-African orogenic cycle, which commonly intrude the basement granite gneisses and Shillong Group metasediments. The KAHG can be broadly classified into three major granitoid facies viz., coarse grained porphyritic granitoid, medium grained massive non-porphyritic granitoid, and granite gneiss, which share a common mineral assemblage of plagioclase-K-feldspar-quartz-biotite±hornblende-apatite-titanite-zircon-magnetite but differ greatly in mineral proportion and texture. Modal mineralogy of KAHG, granite gneiss and basement granite gneiss largely represents monzogranite and syenogranite. The magnetic susceptibility (MS) of the KAHG, granite gneiss and basement granite gneiss varies widely between 0.11×10^-3 and 43.144×10^-3 SI units, corresponding to ilmenite series (<3×10^-3 SI; reduced type) and magnetite series (>3×10^-3 SI; oxidized type) of granitoids respectively. The observed MS variations are most likely intrinsic to heterogeneous source regions, modal variations of orthomagnetic and ferromagnetic minerals, and tectonothermal and deformational processes that acted upon these rocks. The primary and re-equilibrated compositions of biotites from the KAHG, granite gneiss and basement granite gneiss suggest calcalkaline, metaluminous (I-type) nature of felsic host magma formed in a subduction or post-collisional to peraluminous (S-type) host magma originated in syn-collisional tectonic settings, which were evolved and stabilized between FMQ and NNO buffers typically corresponding to reducing and oxidising magma environments respectively.     

Temporal, Spatial and Geochemical Discriminations of Granitoids in South Korea

Abstract: Five groups of the Phanerozoic granitoids in South Korea can be deduced from their temporal and spatial distributions: (1) Jurassic granitoids in the Gyeonggi massif, (2) Permo-Jurassic granitoids in the Ogcheon belt, (3) Permo-Jurassic granitoids in the Yeongnam massif, (4) Cretaceous granitoids in the Ogcheon belt, and (5) Cretaceous granitoids in the Gyeongsang basin. Though the granitoids of each group generally show calc-alkaline and orogenic natures, the petrological, geochemical and genetical features are different with each other. The Permo-Jurassic granitoids in the Ogcheon belt have lower contents of Al₂O₃, Fe₂O₃, CaO, P₂O₅, but higher of FeO, FeOT, MgO, K₂O than those in the Yeongnam massif. From higher feature of K₂O, Na₂O+K₂O and K₂O/Na₂O, the Ogcheon belt seems to have been located at closer continent side relative to the Yeongnam massif during Permo-Jurassic time. From lower values of Fe₂O₃/FeO and magnetic susceptibility the granitoids of the Ogcheon belt had been solidified under more reducing environment than those of the Yeongnam massif. The Cretaceous granitoids in the Ogcheon belt have lower contents of TiO₂, Fe₂O₃, FeO, FeOT, CaO and P₂O₅, but higher of MgO, K₂O, Na₂O+K₂O and K₂O/Na₂O than those in the Gyeongsang basin. This feature indicates that the Ogcheon belt would correspond to the continental environment of magma genesis during Cretaceous time. Higher values of Fe₂O₃/FeO and magnetic susceptibility in the Cretaceous granitoids in the Gyeongsang basin suggest that the granitoids had been solidified under highly oxidizing environment. From the particular chemical features of K₂O, Na₂O+K₂O and K₂O/Na₂O, the Permo-Jurassic granitoids in the Ogcheon belt, the Yeongnam massif as well as the Cretaceous ones in the Gyeongsang basin can be categorized to the continental margin type granite. The Jurassic granitoids in the Gyeonggi massif are possibly of collision type, and the Cretaceous granitoids in the Ogcheon belt of post–orogenic, intra–conti–nent type. The Jurassic granitoids in the Gyeonggi massif had been possibly generated by crustal melting during the collision of Gyeonggi massif to the northern Pyeongnam basin block. The Cretaceous granitoids in the Ogcheon belt had been emplaced at the hinterland of the continental margin during post-orogenic stage of the Honam Shear Zone. The Cretaceous granitoids in the Gyeongsang basin are often compared with Japanese Cretaceous?Paleogene granitoids in their geochemical and genetical natures. For the granitoid composition, the granitoids in the Gyeongsang basin are higher in Fe₂O₃, Fe₂O₃/FeO, Na₂O, K₂O, Na₂O+K₂O and K₂O/Na₂O, but lower in Al₂O₃, FeO, MnO, CaO and P₂O₅ than the Japanese granitoids. The contents of TiO₂, FeOT and MgO are similar in both granitoids. This geochemical contrast would imply that the Cretaceous granitoid magmas in the Gyeongsang basin had been originated at closer place to the continent side under more tensional field, and solidified under more oxidizing environment than the coeval Japanese granitoid magmas.     

Apatite Composition of Representative Magnetite‐series and Ilmenite‐series Granitoids in Japan

Apatites of representative magnetite‐series and ilmenite‐series granitoids were studied in the Japanese Islands. Concentrations of the volatile components F, Cl and SO₃ are differently distributed in apatites of these granitoid series. Apatites are always fluoroapatite. They have weakly higher F content in the ilmenite series than in the magnetite series. In contrast, Cl and SO₃, are significantly concentrated in apatites of the magnetite series compared to the ilmenite series. These characteristics reflect the original concentrations of these components in the host granitic magmas. A high fO₂ seems most important for the S‐concentration as sulfate in apatite of the magnetite series. REE and Y are only erratically high in the studied apatites.     

Petrogenetic Appraisal of Early Palaeozoic Granitoids of Kinnaur District, Higher Himachal Himalaya, India

The Early Palaeozoic felsic magmatism of Kinnaur district is represented by more-or-less equivalent Akpa granitoids (477±29 Ma) and Rakcham granitoids (453±9 Ma), which form an integral part of the Central Crystalline Zone in the southern portion of the Tethys Himalayan Tectogen. Both, Akpa granitoids (AG) and Rakcham granitoids (RG), intrude the rocks of the Vaikrita Group. Substantially low magnetic susceptibility values (c = 0.016-0.187 × 10⁻³ SI) of these Early Palaeozoic granitoids suggest their nature similar to as ilmenite series (reduced-type) granitoids emplaced in a syn-collisional tectonic setting. The modal compositions of AG mainly correspond to two-mica (muscovite-biotite) monzogranite belonging to the granitoids generated by crustal fusion. Based on mineral assemblage (Ms+Bt+Tur+Ap), associated skarn-type tungsten mineralization, occurrence of metasedimentary enclaves, and whole-rock geochemistry (SiO₂ = 70.75-72.95 wt.%, TiO₂ = 0.02-0.17 wt.%, K₂O/Na₂O = 1.05-2.32, molar A/CNK = 0.93 to 1.33, CIPW corundum 0.17 to 3.82 wt.%, Av. Sr = 304ppm, initial ⁸⁷Sr/⁸⁶Sr = 0.7206±0.00235), the AG can be typically characterized as peraluminous (S-type) granite as similarly noted for RG. Higher Rb/Sr ratio and initial ⁸⁷Sr/⁸⁶Sr = 0.737±0.002 of RG compared to that of AG however indicate involvement of relatively more crustal component in generation of RG. The AG is enriched in Ba and light rare earth elements (LREE). The chondrite normalized REE patterns of AG appear weakly fractionated (La_N/Lu_N= 1.06-6.43) and show pronounced negative Eu-anomaly (Eu_N/Eu^* = 0.03). The AG and RG represent typical S-type granite suites that largely evolved due to differential degree of anatexis (partial fusion) of sedimentary protoliths, prior to Caledonian but after the Pan-Indian thermal orogenic event.     

Granitoid Series in Terms of Magnetic Susceptibility: A Case Study from the Barberton Region,South Africa

Magnetic susceptibilities were measured on a representative collection of Archaean granitoids of the Barberton region using a portable KT5 magnetic susceptibility meter. The studied granitoids comprise, (1) syn-tectonic tonalite-trondhjemite-granodiorite (TTG) granitoids (132 samples), (2) late-tectonic calc-alkaline granitoids (402 samples) and (3) post-tectonic low-Ca and high-Ca granitoids (12 samples). Most of the early-stage syn-tectonic granitoids (∼3450 Ma) have low magnetic susceptibilities, less than 3 × 10⁻³ SI units, and correspond to ilmenite-series granitoids. The late-stage Kaap Valley tonalite pluton (∼3230 Ma) contains sporadically distributed higher magnetic susceptibility values (greater than 3 × 10⁻³ SI units), which are less than one-third in magnetic susceptibility of typical magnetite-series TTG of the Japanese Island Arc and thus strictly belong to an intermediate series. The Barberton TTG suite is essentially derived from reduced amphibolitic lower crust that reflects the anoxic nature of the Earth surface during the Archaean Eon. The more oxidized nature of the Kaap Valley tonalite may be generated in an oxidized lower crust by fluids squeezed out of the subducting plate.Late-tectonic granodiorite - adamellite batholithic complexes (∼3105 Ma) belong mostly to the magnetite series, and seem to suggest that relatively oxidized continental crust, reflecting oxic atmosphere and subduction mechanism operating, had evolved it by this time. Post-tectonic granitic plutons formed largely between circa 2900 Ma and 2700 Ma can be subdivided into low-Ca ilmenite series and high-Ca magnetite series.     

Early Proterozoic granitoids of the Olenek complex (northern Siberian craton): petrogenesis and geodynamic setting

The paper deals with geological and geochemical studies of granitoids of the Olenek complex in the Olenek uplift of the basement of the northern Siberian craton. The age of these granitoids was earlier estimated at 2036 ± 11 Ma. The granitoids of the Olenek complex correspond in composition to high-alumina quartz diorites, granites, and leucogranites of the normal petrochemical series. According to geochemical and mineralogical characteristics, the quartz diorites can be assigned to granites of the transitional I-S type, and the granites and leucogranites, to S-type granites. The 8_Nd(T values in the granites of the Olenek complex vary from -0.2 to + 1.4, and the Nd model age is 2.4-2.5 Ga. The quartz diorite is characterized by 8_Nd(T) = + 3.0 and a Nd model age T(DM) = 2.2 Ga. The geochemical characteristics of the granites and leucogranites indicate their formation through the melting of a source of graywacke composition, whereas the quartz diorites resulted, most likely, from the mixing of granitic and basaltic melts. The fact that the granitoids of the Olenek complex intruded the folded rocks of the Eekit Formation but stay virtually undeformed massive bodies suggests that they formed at the postdeformation stage of the regional evolution after the completion of the Paleoproterozoic orogenic events. The intrusion of granitoids marks the completion of the formation of the Early Proterozoic Eekit fold belt on the western (in the recent coordinates) margin of the Birekta terrane of the Olenek superterraine and the final formation of the superterrane structure. At the next stage of magmatism (1.98-1.96 Ga), best pronounced in the uplifts of the basement of the northern Siberian craton, all terranes forming the Anabar and Olenek superterranes assembled into a single structure.     

Neoproterozoic calc‐alkaline peraluminous granitoids of the Deleihimmi pluton,Central Eastern Desert,Egypt: implications for transition from late‐ to post‐collisional tectonomagmatic evolution in the northern Arabian–Nubian Shield

The widely distributed late‐collisional calc‐alkaline granitoids in the northern Arabian–Nubian Shield (ANS) have a geodynamic interest as they represent significant addition of material into the ANS juvenile crust in a short time interval (∼630–590 Ma). The Deleihimmi granitoids in the Egyptian Central Eastern Desert are, therefore, particularly interesting since they form a multiphase pluton composed largely of late‐collisional biotite granitoids enclosing granodiorite microgranular enclaves and intruded by leuco‐ and muscovite granites. Geochemically, different granitoid phases share some features and distinctly vary in others. They display slightly peraluminous (ASI = 1–1.16), non‐alkaline (calc‐alkaline and highly fractionated calc‐alkaline), I‐type affinities. Both biotite granitoids and leucogranites show similar rare earth element (REE) patterns [(La/Lu)_N = 3.04–2.92 and 1.9–1.14; Eu/Eu* = 0.26–0.19 and 0.11–0.08, respectively) and related most likely by closed system crystal fractionation of a common parent. On the other hand, the late phase muscovite granites have distinctive geochemical features typical of rare‐metal granites. They are remarkably depleted in Sr and Ba (4–35 and 13–18 ppm, respectively), and enriched in Rb (381–473 ppm) and many rare metals. Moreover, their REE patterns show a tetrad effect (TE_1,3 = 1.13 and 1.29) and pronounced negative Eu anomalies (Eu/Eu* = 0.07 and 0.08), implying extensive open system fractionation via fluid–rock interaction during the magmatic stage. Origin of the calc‐alkaline granitoids by high degree of partial melting of mafic lower crust with subsequent crystal fractionation is advocated. The broad distribution of late‐collisional calc‐alkaline granitoids in the northern ANS is related most likely to large areal and intensive lithospheric delamination subsequent to slab break‐off and crustal/mantle thickening. Such delamination caused both crustal uplift and partial melting of the remaining mantle lithosphere in response to asthenospheric uprise. The melts produced underplate the lower crust to promote its melting. The presence of microgranular enclaves, resulting from mingling of mantle‐derived mafic magma with felsic crustal‐derived liquid, favours this process. The derivation of the late‐phase rare‐metal granites by open system fractionation via fluid interaction is almost related to the onset of extension above the rising asthenosphere that results in mantle degassing during the switch to post‐collisional stage. Consequently, the switch from late‐ to post‐collisional stage of crustal evolution in the northern ANS could be potentially significant not only geodynamically but also economically. Copyright © 2011 John Wiley & Sons, Ltd.     

Petrogenesis of the Nanling Mountains granites from South China: Constraints from systematic apatite geochemistry and whole-rock geochemical and Sr–Nd isotope compositions

The widespread Mesozoic granitoids in South China (135,300 km²) were emplaced in three main periods: Triassic (16% of the total surface area of Mesozoic granitoids), Jurassic (47%), and Cretaceous (37%). Though much study has been conducted on the most abundant Jurassic Nanling Mountains (NLM) granites, their rock affinities relative to the Triassic Darongshan (DRS) and Cretaceous Fuzhou–Zhangzhou Complex (FZC) granites which are typical S- and I-type, respectively, and the issue of their petrogenetic evolution is still the subject of much debate. In this study, we discuss the petrogenesis of NLM granites using apatite geochemistry combined with whole-rock geochemical and Sr–Nd isotope compositions. Sixteen apatite samples from six granite batholiths, one gabbro, and three syenite bodies in the NLM area were analyzed for their major and trace element abundances and compared with those collected from DRS (n = 7) and FZC (n = 6) granites. The apatite geochemistry reveals that Na, Si, S, Mn, Sr, U, Th concentrations and REE distribution patterns for apatites from DRS and FZC granites basically are similar to the S and I granite types of the Lachlan Fold Belt (Australia), whereas those from NLM granites have intermediate properties and cannot be correlated directly with these granite types. According to some indications set by the apatite geochemistry (e.g., lower U and higher Eu abundances), NLM apatites appear to have formed under oxidizing conditions. In addition, we further found that their REE distribution patterns are closely related to aluminum saturation index (ASI) and Nd isotope composition, rather than SiO₂ content or degree of differentiation, of the host rock. The majority of apatites from NLM granites (ASI = 0.97–1.08 and εNd(T) = −8.8 to −11.6) display slightly right-inclined apatite REE patterns distinguishable from the typical S- and I-type. However, those from few granites with ASI > 1.1 and εNd(T) < −11.6 have REE distribution patterns (near-flat) similar to DRS apatites whereas those from granites with ASI < 1.0 and εNd(T) > −6.6 and gabbro and syenite are similar to FZC apatites (strongly right-inclined). In light of Sr and Nd isotope compositions, magmas of NLM intrusives, except gabbro and syenite, and few granites with εNd(T) > −8, generally do not involve a mantle component. Instead, they fit with a melt derived largely from in situ melting or anatexis of the pre-Mesozoic (mainly Caledonian) granitic crust with subordinate pre-Yanshanian (mainly Indosinian) granitic crust. We suggest that an application, using combined whole-rock ASI and εNd(T) values, is as useful as the apatite geochemistry for recognizing possible sources for the NLM granites.     

Granitic magmatism,basement ages,and provenance indicators in the Malay Peninsula: Insights from detrital zircon U–Pb and Hf-isotope data

The Malay Peninsula lies on two continental blocks, Sibumasu and East Malaya, which are intruded by granitoids in two provinces: the Main Range and Eastern. Previous models propose that Permian–Triassic granitoids are subduction-related and syn-to post-collisional. We present 752 U–Pb analyses that were carried out on zircons from river sands in the Malay Peninsula; of these, 243 grains were selected for Hf-isotope analyses. Our data suggest a more complex Sibumasu–East Malaya collision history. ¹⁷⁶Hf/¹⁷⁷Hf_i ratios reveal that Permian–Triassic zircons were sourced from three magmatic suites: (a) Permian crustally-derived granitoids, (b) Early-Middle Triassic granitoids with mixed mantle–crust sources, and (c) Late Triassic crustally-derived granitoids. This suggests three Permian–Triassic episodes of magmatism in the Malay Peninsula, two of which occurred in the Eastern Province. Although the exact timing of the Sibumasu–East Malaya collision remains unresolved, current data suggest that it occurred before the Late Triassic, probably in Late Permian–Early Triassic. Our data also indicate that Sibumasu and East Malaya basements are chronologically heterogeneous, but predominantly of Proterozoic age. Some basement may be Neoarchaean but there is no evidence for basement older than 2.8 Ga. Finally, we show that Hf-isotope signatures of Triassic zircons can be used as provenance indicators.     

Triassic Granitic Magmatism at the Northern Margin of the North China Craton: Implications of Geochronology and Geochemistry for the Tectonic Evolution of the Central Asian Orogenic Belt

The early Mesozoic marked an important transition from collisional orogeny to post-orogenic extension at the northern margin of the North China Craton(NCC). In this study, we undertook zircon U-Pb dating and whole-rock majorand trace-element geochemical analyses of early Mesozoic granitic rocks in the Chifeng area to establish their geochronological framework, petrogenesis, and implications for the tectonic evolution of the eastern Central Asia Orogenic Belt(CAOB). Zircon U-Pb dating results show that these rocks were emplaced in three stages during the Triassic:(1) syenogranites during 250–248 Ma,(2) granodiorites during 244–243 Ma, and(3) monzogranites and granodiorites during 232–230 Ma. These Triassic granitoids belong to the high-K calc-alkaline series and are evolved I-type granites. They have high SiO_2 and low Mg O contents with enrichments in light rare-earth elements, Zr, Hf, Rb, Th, and U, and depletions in Ba, Nb, Ta, Sr, and Eu. These geochemical data indicate that the granitoids were derived from partial melting of a lower-crustal source under relatively low-pressure conditions and subsequently underwent extensive fractional crystallization. Considering both the geochemical data and regional geological information, we propose that the 250–248 Ma syenogranites were emplaced in an extensional environment linked to slab break-off after closure of the Paleo-Asian Ocean(PAO) along the Solonker-Xra Moron-Changchun suture zone. The 244–243 Ma granodiorites were formed in a compressional orogenic setting during collision between the Erguna-Xing'an-Songliao composite block and the NCC. The 232–230 Ma granodiorites and monzogranites were emplaced during the transition from compressional orogeny to post-orogenic extension. Overall, the early Mesozoic tectonic evolution of the Chifeng area can be divided into three main stages:(1) closure of the Paleo-Asian Ocean and extension related to slab break-off during the Early Triassic;(2) continuous collisional compression during the Middle Triassic after closure of the PAO; and(3) post-orogenic extension during the Late Triassic, most probably due to lithospheric delamination after amalgamation of the Erguna-Xing'an-Songliao composite block and the NCC.     

Sulfur Isotopic Variation of Yanshanian Magmatic-hydrothermal Deposits in Southern China

Abstract: Sulfur isotope data (δ³⁴S) of sulfides of more than 6700 samples from 157 ore deposits associated with Early and Late Yanshanian granitic and volcanic activities in South China are reviewed and summarized. Averaged δ³⁴S values of individual deposits vary from ‐9. 3 to +20. 6%, and show a normal distribution pattern with the average of +2%. About 88 % of the ore deposits have values within the range, ?2.5 ? +13.6‰, of associated Yanshanian granitoids. There is a temporal‐spatial variation of δ³⁴S values of the ore deposits. However, no clear zonal distribution parallel to geotectonic NNE lineaments was observed. Spatial distribution of ore sulfide δ³⁴S values in most of the NE part of the whole studied area coincides with that of Yanshanian granitoids and volcanic rocks. A downward tendency of the average values in time is: +3. 0% (n=7, J₁) → +1. 6% (n=29, J₂) → +1. 7% (n=68, J₃) → +1. 8% (n=37, K₁) → ?1. 5% (n=16, K₂). There is an “island” of high and variable δ³⁴S values (0? +16.5‰) occurring within a generally low trough zone (?8 ? 0%) of N‐S about 800 km and E‐W 100 to 300 km, bounded by 110°E ? 116°E longitudes and 22°N ? 31°N latitudes. The island occurs at the junction of three tectonic units and a NE‐trending crustal matching line implying a variety of magmatism occurred at the junction. The low trough zone coincides with a low ferric/ferrous ratio zone of Early Yanshanian granitoids, indicating their genetic relationship. Different genetic types of ore deposits show different histogram patterns suggesting different relationships to magmatic rocks and host strata. Granite/greisen/pegmatite type deposits are most closely associated with granitoids, with average ore sul‐fide δ³⁴S values for individual ore deposits ranging between ‐2. 0 and +4. 1%, and an average of +0. 5% (n = 15) close to type meteoric value of 0%. Porphyry‐type deposits have also narrow range of ?2.2 ? + 4.9‰, with an average value of +1. 1% (n = 18). Skarn‐type dominated ore deposits have a nearly normal distribution pattern with an average of +1. 6% (n = 62), ranging from ‐5. 3 to +11. 5%. Volcano‐subvolcanic ore deposits range between ‐3. 1 and +5. 9% with an average of +2. 3% (n = 19). Other types of hydrothermal ore deposits have averaged δ³⁴S values of individual ones from ‐9. 3 to +20. 6%, with average value of +1. 3% (n=43). Vertical and horizontal zonations of δ³⁴S values of ore deposits around their associated granitoid plutons are observed in several localities. Such zonations may be caused by interaction between magma and/or magmatic fluids and host sedimentary rocks, as well as the evolution of physico‐chemical conditions of ore‐forming fluids. Spatial distribution of ore sulfur isotope compositions is also clearly controlled by tectonics and deep faults. Ore sulfur isotope composition is sometimes strongly affected by host sedimentary rocks, especially by evaporite sulfur with much higher δ³⁴S value and partly by biogenic sulfur with low δ³⁴S value. The δ³⁴S values of Yanshanian granitoids are from ‐2. 5 to +13. 6% for both rock samples and pyrite/pyrrhotite separates from granitic rocks, with similar spatial distribution pattern to those of associated ore deposits. The ore deposits associated with ilmenite‐series granitoids have δ³⁴S values ranging between ‐7. 5 and +10. 4% with an average of +1. 0%, while the ore deposits associated with magnetite‐series granitoids ranging between ?8.0 ? +11.5‰ with an average of +1. 1%. δ³⁴S values of ore deposits tend to converge to +3% as the Fe₂O₃/FeO ratio of associated granitoids increases from 0. 45 to 8. 7.     

Geochemistry and Origin of Megacrystic Granitoid Rocks from Eastern Ghats Granulite Belt

The Eastern Ghats Granulite Belt (EGGB) forms part of a continuous Precambrian metamorphic terrain in Gondwana. It is characterised by widespread development of an Archaean khondalite suite of metasedimentary rocks, Archaean to Late-Proterozoic charnockites and Late Proterozoic anorthositic, granitic and syenitic emplacements. A 1900 Ma megacrystic granitoid suite, containing varying proportions of charnockites and granites, forms an important and widely distributed litho-unit in the central khondalite and eastern migmatite zones of the EGGB. It contains metasedimentary enclaves, megacrystic K-feldspar, quartz, plagioclase ovoids, biotite, garnet (porphyroblasts and coronas), apatite, zircon, ilmenite, magnetite, etc. Hypersthene is present in the charnockite phase. Monazite is present in some garnet-free granites. It is characterised by low Na₂O/K₂O ratios, high alumina saturation index, CaO, MgO, and ÝREE, negative correlation of TiO₂, Al₂O₃, Fe₂O₃^t, MgO, MnO, CaO, P₂O₅, Ba, Sr, Zr and V with SiO₂, positive correlation of K₂O, REE, Th and Rb with SiO₂, fractionated LREE, relatively flat HREE and negative Eu anomalies.The data suggest S-type nature of the suite. Fractionation of the granitic magma and local variations in pH₂O and fCO₂ caused the formation of megacrystic charnockites. Formation of the corona garnet is related to the reworking of the suite during late Proterozoic (ca. 1250 Ma) isothermal decompression associated with channelised CO₂-rich fluid flux along narrow shear zones.     

Magnetic susceptibility mapping of felsic magmatic lithounits in the central part of Bundelkhand Massif,central India

Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central part of Bundelkhand massif comprises of multiple felsic magmatic pulses (∼2600–2200 Ma), commonly represented by coarse grained granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG), grey and pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10⁻³ SI with an average of 6.35×10⁻³ SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials. CPG (av. MS=3.95×10⁻³ SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10⁻³ SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites, which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10⁻³ SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized type, magnetite series granite. FPG (av. MS= 0.666×10⁻³ SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources. FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31–10.22×10⁻³ SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system. Grey (av. MS=10.30×10⁻³ SI) and pink (av. MS=6.72×10⁻³ SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic) protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by hydrothermal and tectonic processes acting upon them.