high-K Calc-alkaline Granites Research Articles

Petrology and geochemistry of Late Triassic rapakivi-type granites in the Dupangling area, South China: Role of fluid-rock interaction in the origin of rapakivi texture

Rapakivi-type granites not only document magmatic processes but also archive subsolidus interactions between granitic rock and fluid, and thereby provide crucial information about fluid infiltration in the Earth's crust. However, the key process to generate rapakivi texture is still debated. Here, we report comprehensive mineralogical, geochemical and Hf isotopic compositions of the Dupangling rapakivi granites (210.4–214.9 Ma) in the South China Block to investigate the effect of fluid-rock interaction on the origin of rapakivi feldspar. Dupangling rapakivi granites have high SiO2 (72.63–78.21 wt%) and alkali contents (Na2O + K2O = 6.14–9.06 wt%) with high K2O/Na2O ratios (1.37–2.64), characteristic of weakly peraluminous (A/CNK = 1.04–1.10) high-K calc-alkaline granites. Samples have weakly fractionated REE patterns with negative Eu anomalies (δEu = 0.05–0.38). They have negative whole-rock εNd(t) (−8.45 to −7.91), variable zircon εHf(t) (−9.7 to −1.0) and two-stage Hf isotope model ages (1.32–1.84 Ga), due to their derivation from a major early Mesoproterozoic crustal source with a subordinate late Paleoproterozoic component. Rapakivi feldspars in Dupangling granites are composed of an alkali-feldspar core and a plagioclase mantle. Fractures, pores and secondary inclusions (biotite, sericite, epidote and hematite) are closely associated with the mantles and oligoclase patches within alkali-feldspar cores. These pervasive microtextural features and variations of Be, Rb, Ba, Sr and LREE within rapakivi feldspars are interpreted to have formed through subsolidus fluid-induced dissolution-reprecipitation replacement processes. This study highlights that fluid-rock interaction plays an important role in generating rapakivi texture.

Multiple stages of continental rifting in Eastern Peninsular Malaysia: new insights from Jurassic–Cretaceous granitoids

Mesozoic granitoids in Peninsular Malaysia provide crucial information on the temporal–spatial relationship between the Tethyan and Palaeo-Pacific domains. This paper presents new ages and geochemical data for newly identified Jurassic–Cretaceous granites and meta-granites from East Malaya. These granitoids can be divided into three groups. Group 1 consists of high-K calc-alkaline granites and granodiorites (171–162 Ma) with variable ε Nd ( t ) values of −7.4–+0.5, zircon ε Hf ( t ) values of −7.4–+8.6, and high initial ratios for 206 Pb/ 204 Pb (20.04–20.65), 207 Pb/ 204 Pb (15.73–15.79) and 208 Pb/ 204 Pb (39.80–40.20). The melting of metasedimentary rocks with a juvenile mafic component formed Group 1 samples. Group 2 granite porphyries ( c. 131 Ma) with A-type affinities and Group 3 granitic gneisses ( c. 130 Ma) with I-type affinities share similar ε Nd ( t ) values (−7.2 to −5.5), zircon ε Hf ( t ) values (−10.1–+6.5), and initial ratios for 206 Pb/ 204 Pb (18.81–19.02), 207 Pb/ 204 Pb (15.71–15.77) and 208 Pb/ 204 Pb (38.95–39.59). Although Group 2 and 3 samples were derived from an ‘ancient’ meta-mafic source region, Group 2 shows evidence for the involvement of a juvenile mafic component. All these granitoids are akin to the Permian–Triassic igneous rocks in East Malaya. The Jurassic–Cretaceous igneous rocks in Eastern Peninsular Malaysia were formed during multiple stages of continental rifting in response to Palaeo-Pacific slab rollback pulses rather than by Tethyan evolutionary processes. Supplementary material : Data for the Middle Jurassic–Early Cretaceous granitoids of East Malaya are available at https://doi.org/10.6084/m9.figshare.c.6689085 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Granite thermal reservoirs in Lingshui area of Hainan Island and their significance to geothermal resources, China

Hainan Island located at the southernmost tip of the continental crust of the South China Plate, has high terrestrial heat-flow values, widely-distributed hot springs, and rich geothermal resources. Intensified researches on the origin and potentials of geothermal resources can promote Hainan Island's development into a clean energy island. To determine the geological conditions for the formation of geothermal resources in southern Hainan Island, we collected core samples of granites from the Baocheng batholith in southern Hainan Island and conducted systematic analysis in respect of petrology, geochronology, geochemistry, and petrophysical property. The results of this study are as follows. The Baocheng batholith in the southern Hainan Island has a crystallization age of 98.42 ± 0.56 Ma, making it the product of magmatism in the early stage of the Late Cretaceous. It mainly consists of high-K calc-alkaline granites, which were intruded by intermediate-to-mafic veins. The Baocheng batholith has a high radioactive heat generation rate of 2.712–6.843 μW/m3, with an average of 3.846 μW/m3, a radioactive heat-flow value of 30.768 mW/m2 and a heat-flow contribution rate of 38.95%–43.95%. As shown by the results of their thermophysical property analysis, the granites have high thermal conductivity and can serve as high-quality geothermal reservoirs. In combination with previous geological and geophysical data, the geothermal model of the Lingshui area was established in this study. The deep structure indicates the presence of high-conductivity and low-resistivity layers in the basement of the Baocheng batholith. It can be inferred thereby that asthenospheric upwelling may occur and that there exist two magma vents at depth in the batholith. Therefore, magmatic heat at depth and granites with high radioactive heat generation rate serve as the main heat sources in the Lingshui area.

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

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

Geochemistry, Geochronology, and Prospecting Potential of the Dahongliutan Pluton, Western Kunlun Orogen

Triassic granitoids are abundant on the northwestern margin of the Tibetan Plateau. The Dahongliutan pluton, located in the eastern Western Kunlun orogen, formed in the Late Triassic.Previous field studies have identified potential mixing of crustal and mantle magmas. In this study, we used zircon U–Pb ages and major and trace elemental analyses to investigate the tectonic evolution of the pluton, and to determine whether any exchange of mantle-derived material occurred between the pluton and the source area. We found that the pluton has relatively high SiO2 contents, and the aluminum saturation index is consistent with peraluminous high-K calc-alkaline granite. The pluton is enriched in light rare earth elements; both light and heavy rare earth elements are highly fractionated. The magma that formed the pluton was predominantly derived from the crust; however, a small amount of upper mantle material was involved in the early stages of magma formation. The pluton underwent composite emplacement as a result of tectonic extension and magmatic emplacement, which may have occurred in the late Triassic post-collisional orogenic stage. Late Triassic magmatism provided heat and ore-forming material for Pb–Zn, Cu, Fe, and rare metal mineralization, which is of considerable importance for geological prospecting.

Petrogenesis of Early Cretaceous granitoids in Liyang volcanic basin, eastern China: Geodynamic implications for Paleo-Pacific slab rollback

Late Mesozoic magmatism in eastern China was extensive and closely related to the subduction of the Paleo-Pacific plate, but genetic relationship between magmatism and subduction remains unclear. Cretaceous magmatic rocks distributed along the eastern coast of China can provide an opportunity to evaluate the influence of subduction on the evolution of the magmatism. Here, a combined study of whole-rock major-trace elements and Sr-Nd-Pb-Hf isotopes as well as zircon U-Pb ages was carried out for the Cretaceous granitoids in Liyang volcanic basin, eastern China. Zircon U-Pb dating results indicate that the Liyang granitoids were emplaced in the Early Cretaceous (ca. 130–125 Ma). These samples (SiO2 = 70.8–75.3 wt%) are mainly composed of high-K calc-alkaline granite and granite porphyry. Their geochemical characteristics are similar to I-type granites, with enrichment in LREEs, Rb, Th and U, and negative Eu (δEu = 0.04–0.51), Ba, Sr, P and Ti anomalies. All samples show negative whole-rock εNd(t) (−9.8 to −5.7) and zircon εHf(t) (−15.7 to −3.60) values (corresponding crustal Hf model ages of 1.40–2.17 Ga), and high radiogenic Pb isotopic compositions. The integrated interpretation of geochemical data reveal that rollback of the Paleo-Pacific subducted slab resulted in lithospheric extension and thinning, and the upwelling of hot asthenosphere in eastern China, which induced more intensive underplating of the mantle-derived mafic magma. The ascent of heat and mafic magma, intruded in Meso-Neoproterozoic crust, and triggered partial melting of the Meso-Neoproterozoic crust. The Liyang I-type granitoids were the result of the Meso-Neoproterozoic crustal components mixing with a small number of mantle-derived magmas in the extensional tectonic setting, which was response to slab rollback of the Paleo-Pacific plate.

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

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

Geochemistry and Hf–O–Pb isotopes of the Hongniangshan complex, Inner Mongolia, China: Constrains on petrogenesis and mineralization of the Quanzigou porphyry Mo deposit

The Quanzigou porphyry molybdenum deposit is located in Fengzhen County, Inner Mongolia, China, belonging to the northern margin of the North China Craton. A Yanshanian granitic complex, namely the Hongniangshan complex, is exposed in the deposit, mainly composed of medium–coarse-grained granite, porphyritic granite, and quartz porphyry. The Mo orebodies occur mainly in the porphyritic granite as ore-bearing quartz veins or veinlets. Previous study on molybdenite Re–Os and zircon U–Pb dating suggests that the Hongniangshan complex emplaced during 173–160 Ma and that the Quanzigou Mo deposit formed at ca. 160 Ma. Geochemical analyses in this study show that all these Middle–Late Jurassic granites are peraluminous, high-K calc-alkaline granite, featured by enrichment in Rb, Th, U, Hf, and Zr and depletion of Ba, P, and Ti, with high K2O/Na2O ratios. Nearly all the samples from the medium–coarse-grained granite and the porphyritic granite show weakly negative Eu anomalies, whereas the negative Eu anomalies of the quartz porphyry are moderate or strong. The Hongniangshan complex has low zircon εHf(t) values (−14.4 to − 6.7), old single-stage and two-stage model ages (1099–1471 Ma and 1637–2124 Ma, respectively), and low K-feldspar Pb isotopic compositions (206Pb/204Pb = 17.019–17.590, 207Pb/204Pb = 15.365–15.489, 208Pb/204Pb = 37.002–37.670), with K-feldspar δ18O values of 8.0–10.4‰, suggesting that the granitic complex was predominantly originated from a Paleoproterozoic lower crust source. Geochemical characteristics, combined with results from previous studies, show that the Quanzigou Mo mineralization was closely related to the quartz porphyry. The Middle Jurassic medium–coarse-grained granite was likely formed in the back-arc extension environment triggered by the subduction of the Mongol–Okhotsk Ocean and the Paleo-Pacific plate, and the formation of the Late Jurassic porphyritic granite and the quartz porphyry was controlled by both the post-collisional process of the Mongol–Okhotsk orogenic belt and the coeval subduction of the Paleo-Pacific plate.

Zircon U–Pb geochronology and Sr–Nd–Hf–O isotopic constraints on the relationship between Mo and Pb–Zn mineralization in the Haisugou pluton in the southern Great Xing’an Range, northeast China

The Haisugou pluton and its contact zones with Middle Permian strata contain Cu–Mo and Pb–Zn ore deposits, providing an excellent example to study the relationship between Pb–Zn–Ag and Mo mineralization in the southern Great Xing’an Range (SGXR). Here we present U–Pb zircon ages and Sr–Nd–Hf–O isotope data for biotite monzogranite in the Xiaojingzi Pb–Zn deposit and Mo-bearing biotite monzogranite in the Xiaojingzi Cu–Mo deposit. These rocks yield zircon U–Pb ages of 136.2 ± 1.1 and 135.5 ± 1.3 Ma, respectively. The biotite monzogranites are enriched in SiO2 (average = 68.9 wt%) and Na2O + K2O (average = 7.7 wt%), contain 14.3–15.1 wt% Al2O3 (average = 14.7 wt%), and have A/CNK values of 0.97–1.05, indicating the biotite monzogranites are high-K calc-alkaline granites, and peraluminous. The biotite monzogranites are also characterized by negative Eu anomalies (Eu/Eu* = 0.78–0.45), enrichments in Rb, Th, U, Nd, and Hf, and depletions in Ba, Sr, P, Ti, and Nb. The biotite monzogranites have (87Sr/86Sr)i ratios of 0.70519–0.70457, εNd(t) values of + 0.37 to –0.39, and TDM2 ages of 978–915 Ma. They also have zircon εHf(t) values of 3.6–9.1, TDM2 model ages of 959–608 Ma, and δ18O values of 6.68‰–7.42‰. The Mo and Pb–Zn mineralization around the Haisugou pluton were genetically related to the granitic pluton and occurred simultaneously, forming a porphyry system. Geochemical and Sr–Nd–Hf–O isotope data indicate the Haisugou pluton was probably formed by partial melting of juvenile crust and mixing with mantle-derived components. In the Early Cretaceous, the SGXR was in an extensional setting, which was related to asthenospheric upwelling after the closure of the Mongol–Okhotsk Ocean.

Extensive mineralization in the eastern segment of the Xingmeng orogenic belt, NE China: A regional view

• There are four types of EXOB deposits: porphyry , skarn , hydrothermal vein, and epithermal types. • There are five stage mineralizations in EXOB: 480–440, 300–220, 200–165, 155–130, and 125–100 Ma. • The five metallogenic periods correspond to different geological setting. The eastern segment of the Xingmeng orogenic belt (EXOB) hosts numerous Mo, polymetallic Ag, Pb–Zn , Sn, Cu, Au (Ag), and rare-earth element (REE) deposits and is one of the most important polymetallic-ore regions globally. The mineralization type includes i) porphyry Cu (Mo, Au), Mo (Cu, Pb–Zn, W), Sn (Cu–Ag) deposits, ii) skarn Cu–Au, polymetallic Pb–Zn and Fe–Sn deposit, and iii) veined polymetallic Ag, Pb–Zn, Sn, Cu deposits and W, Mo deposits, with an REE deposit related to magmatic hydrothermal fluid; and iv) epithermal Ag and Au (Ag, Te) deposits, respectively. The mineralization-related rocks in the EXOB are mainly high-K calc-alkaline granites together with minor alkaline granites that were derived from the melting of juvenile crust. The mineralizations in the EXOB are typically related to magmatic-hydrothermal events. In this study we attempt a systematic analysis of the temporospatial distribution of ore deposits in the EXOB, in order to constrain the geodynamic setting of mineralization. Based on available geochronological data, we suggest five mineralization stages for the EXOB at 480–440, 300–220, 200–165, 155–130, and 125–100 Ma, respectively. The porphyry Cu–Mo mineralization occurred during the early Paleozoic (480–440 Ma). The extensive Mo (W, Sn), and Ag (Pb–Zn) polymetallic mineralization was formed during the Mesozoic. The Ordovician–Triassic mineralization (480–220 Ma) is related to the Paleo-Asian Ocean tectonism and developed in an island arc setting. The Permian–Triassic mineralization (300–220) was formed in a post-collisional tectonic setting related to the development of Hegenshan suture. The early–middle Jurassic deposits (200–165 Ma) are related to the subduction of the Paleo-Pacific oceanic plate on the East Asian continental margin. The Late Jurassic–Early Cretaceous deposits (155–130 Ma) were formed in an extensional setting related to rollback of the Paleo-Pacific Plate. The Jurassic–Cretaceous mineralization (200–100 Ma) in the northern segment of the Da Hinggan Mountains is associated with the subduction and post-collisional tectonic setting of the Mongol–Okhotsk oceanic plate. The latest stage of epithermal deposits (125–100 Ma) were developed in a continental margin back-arc setting associated with subduction of the Paleo-Pacific Plate beneath the Eurasia.

Zircon U–Pb ages and geochemical characteristics of granites in the Yaoertu deposit: Implications for Pb–Zn–Ag mineralization in the southern Great Xing’an Range, NE China

Abstract The newly discovered Yaoertu Cu–Pb–Zn–Ag deposit in the southern Great Xing’an Range (SGXR), NE China, is spatially associated with late Yanshanian intrusions. The Cu mineralization occurs within a fine-grained granite, whereas the Pb–Zn–Ag orebodies are developed within country rocks of the Linxi Formation, and are spatially associated with monzogranite or fine-grained granite. The monzogranite and fine-grained Cu-bearing granite have zircon ages of 137.1 ± 0.4 and 137.4 ± 0.5 Ma, indicating that mineralization occurred in the Early Cretaceous, consistent with the formation of extensive skarn or hydrothermal Pb–Zn–Ag deposits in the SGXR. The monzogranite is enriched in SiO2 (69.91–67.87 wt%) and Na2O + K2O (8.43–7.92 wt%), contains 15.20–14.85 wt% Al2O3, and has a mean A/CNK value of 1.01, indicating the monzogranites are weakly-peraluminous high-K calc-alkaline granites. The fine-grained granites contain 77.18–75.14 wt% SiO2, 5.44–4.73 wt% K2O, 13.14–12.16 wt% Al2O3, 0.62–0.52 wt% CaO, and belong to the high-K calc-alkaline series. The monzogranite is enriched in light rare earth elements (REEs), exhibits fractionation of light over heavy REEs (LREE/HREE = 10.58–9.78), and has Eu/Eu* values of 0.74–0.61, whereas the fine-grained granite has LREE/HREE of 8.34–7.07 and more marked negative Eu anomalies (Eu/Eu* = 0.17–0.11). Zircon δ18O values in the monzogranite range from 6.61‰ to 6.87‰, and from 6.67‰ to 7.14‰ in the fine-grained Cu-bearing granite. The chemical composition and zircon Hf–O isotopic data suggest that the Early Cretaceous granites are formed by mixing between the juvenile crust and mantle-derived materials. Post-orogenic extensional settings related to the closure of the Mongol–Okhotsk Ocean resulted in extensive magmatism and large-scale mineralization.

Release of Uranium from Uraninite in Granites Through Alteration: Implications for the Source of Granite-Related Uranium Ores

Abstract Uraninite is the main contributor to the bulk-rock uranium concentration in many U-rich granites and is the most important uranium source for granite-related uranium deposits. However, detailed textural and compositional evolution of magmatic uraninite in granites during alteration and associated uranium mobilization have not been well documented. In this study, textures and geochemistry of uraninites from the Zhuguangshan batholith (South China) were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The geochemical data indicate that the Longhuashan and Youdong plutons are peraluminous leucogranite, the Changjiang pluton is highly fractionated high-K calc-alkaline granite, and the Jiufeng pluton belongs to a high-K calc-alkaline association. Uraninites from the Longhuashan and Youdong granites have lower concentrations of ThO2 (0.9–4.0 wt %) and rare earth elements (REE)2O3 (0.1–1.0 wt %) than those from the Changjiang and Jiufeng granites (ThO2 = 4.4–7.6 wt %, REE2O3 = 0.7–5.1 wt %). Uraninites observed in the Longhuashan, Youdong, Changjiang, and Jiufeng granites yielded chemical ages of 223 ± 3, 222 ± 2, 157 ± 1, and 161 ± 2 Ma, respectively. The samples (including altered and unaltered) collected from the Longhuashan, Youdong, and Changjiang granites are characterized by highly variable whole-rock U concentrations of 6.9 to 44.7 ppm and Th/U ratios of 0.9 to 7.0, consistent with crystallization of uraninite in these granites being followed by uranium leaching during alteration. Alteration of uraninite, indicated by altered domains developing microcracks and appearing darker in backscattered electron (BSE) images compared to unaltered domains, results in the incorporation of Si and Ca and mobilization of U. In contrast, the least altered samples of the unmineralized Jiufeng granite have low U concentrations (5.3–16.4 ppm) and high ΣREE/U (13.6–49.4) and Th/U ratios (2.1–5.6), which inhibit crystallization of uraninite, as its crystallization occurs when the U concentration is high enough to exceed the substitution capacity of other U-bearing minerals. These results indicate that the Longhuashan, Youdong, and Changjiang granites were favorable uranium sources for the formation of uranium deposits in this area. This study highlights the potential of uraninite alteration and geochemistry to assist in deciphering uranium sources and enrichment processes of granite-related uranium deposits.

Nature and (in-)coherent metamorphic evolution of subducted continental crust in the Neoproterozoic accretionary collage of SW Mongolia

In continental subduction complexes minor volumes of high-pressure mafic rocks (eclogites) often co-exist with much more abundant felsic (granitic) and metasedimentary rocks, which are vital for resolving the origin and metamorphic evolution of subducted continental crust. In SW Mongolia, the Alag Khadny eclogite-bearing accretionary complex (AKC) is assumed to represent either a remnant of oceanic slab, or a continental margin, subducted in the Early Cambrian. Here we present geochronological, geochemical and petrological evidence of subduction records for the three major types of lithologies that host mafic eclogites, including Mesoproterozoic and Neoproterozoic granitic basement and overlying Neoproterozoic continental-margin sediments. Variably deformed, ferroan and peraluminous metagranitoids compose a major part of AKC and are interlayered with eclogites in its southern and eastern margins. They have geochemical features of post-collisional/intraplate high-K calc-alkaline granites. LA-ICP-MS U-Pb zircon geochronology of three distinct metagranite samples show uniform protolith crystallization ages of ca. 0.96 Ga and uncertain re-crystallization in the Late Neoproterozoic or Early Paleozoic metamorphic event, whereas abundant zircon inheritance indicates older, Mesoproterozoic to Paleoproterozoic crustal substrate during granite generation. The existence of Mesoproterozoic crust is highlighted by finding of distinct metagranitoids with the U-Pb zircon crystallization age of ca. 1.6 Ga. Hafnium isotope signatures (TDMC 2.88–1.85 Ga) of zircons from all lithologies preserved the evidence of reworked Neoarchean to Paleoproterozoic crust, similar to that of the Baidrag block (southern Mongolia), for both Mesoproterozoic and Neoproterozoic rocks. Regardless of the specific lithology, the rocks display indicators of high-pressure metamorphic re-equilibration, including garnet (XCa up to 0.65) + epidote + phengite (Si p.f.u. up to 3.56) ± rutile assemblage in metagranitoids, garnet + phengite (Si p.f.u. up to 3.42) in quartz-rich semi-pelites and garnet + phengite (Si p.f.u. up to 3.39) + medium-Mg chloritoid (XMg up to 0.25) + kyanite + rutile in metapelites. Corresponding P-T conditions recovered from different lithologies reveal incoherent subduction of rocks, which could be shallow for granitic basement (1.1–1.4 GPa and 600–670 °C) and clastic metasediments (1.4–1.6 GPa, 570–620 °C), but deeper for metapelites (2.1–2.3 GPa, 500–570 °C). consistent with that of eclogites, The combined data show that the Alag Khadny complex represents a remnant of a rifted Mesoproterozoic to Neoproterozoic (ca. 1.6–0.96 Ga) continental margin consequently metamorphosed under HP conditions during Late Neoproterozoic–Early Cambrian evolution of the southern Central Asian Orogenic Belt. Acquired P-T estimates imply that high-pressure metagranitoids and metasedimentary rocks equilibrated at different depths, but most likely shared a common subduction-related metamorphic evolution.

Geochronology, petrogenesis and tectonic significance of Dahongliutan pluton in Western Kunlun orogenic belt, NW China

The Dahongliutan granitic pluton, in the eastern part of the West Kunlun orogenic belt, provides significant insights for studying the tectonic evolution of West Kunlun. This paper presents a systematic study of LA-ICP-MS zircon U-Pb age, major and trace elements, Sr-Nd-Hf isotopes, and the first detailed Li isotope analysis of the Dahongliutan pluton. LA-ICP-MS zircon U-Pb dating shows that the Dahongliutan granites were emplaced in the Late Triassic ((213±2.1) Ma). Geochemical data show relatively high SiO2 contents (68.45 wt%–73.62 wt%) and aluminum saturation index (A/CNK=1.11–1.21) indicates peraluminous high-K calc-alkaline granite. The Dahongliutan granites are relatively high in light rare earth elements (LREE) and large ion lithophile elements (LILEs) (e.g., Rb, K, Th), and relatively depleted in high field strength elements (HFSEs) (e.g., Nb, Ta, P, Ti). The eNd(t) values range from −8.71 to −4.73, and (87Sr/86Sr)i=0.7087–0.71574. Zircons from the pluton yield 176Hf/177Hf values of 0.2826181 to 0.2827683, and eHf(t) values are around 0; the two-stage Hf model ages range from 0.974 to 1.307 Ga. The δ7Li values are 0.76‰–3.25‰, with an average of 2.53‰. Isotopic compositions of the pluton suggest a mixed trend between the partial melting of the Middle Proterozoic ancient crustal material and a juvenile mantle-derived material. This study infers that the Dahongliutan rock mass is formed in the post-collisional extension environment, when the collision between South Kunlun and the Tianshuihai terranes results in the closure of the Palaeo-Tethys. The mantle-derived magma results in partial melting of the lower crust.

SHRIMP U-Pb zircon dating of Neoproterozoic granites from the easternmost São Roque Domain, Ribeira Belt

Four granitic plutons from the easternmost portion of the São Roque Domain (SRD) were dated by U-Pb zircon SHRIMP; the results indicate that the peak of granitic magmatism was concentrated in a short interval (606–589 Ma), the same as in the central portion of the SRD. The two porphyritic biotite granites (Morro Azul and Imbiruçu) yield the oldest ages (respectively, 601.0 ± 4.9 Ma and 606.3 ± 4.8 Ma) and have inherited zircons with similar ages (~2.1–2.0 Ga), but are not comagmatic. The Morro Azul granite has geochemical signature similar to other high-K calc-alkaline (HKCA) granites from the SRD, while the Imbiruçu granite has much higher Sr/Zr and other chemical features that demand different sources. Other two dated samples are very different from each other and from the HKCA granites. The age of the Morro do Pão tonalite (589.1 ± 5.5 Ma) indicates that, in spite of its more deformed character, it is younger; a similar value, although with large uncertainty, is shown by the Serra dos Índios peraluminous leucogranite (593 ± 12 Ma). Our analytic data combined with field relationships suggest that soon after the main episode of HKCA magmatism, the SRD witnessed the emplacement of granites of varied composition forming small bodies that recorded deformation associated with transcurrent tectonics.

O Stock Serra da Acauã: um exemplo de granito tipo I fracionado oxidado no Domínio Rio Piranhas-Seridó, NE do Brasil

O Stock Serra da Acauã está inserido no contexto da atividade plutônica ediacarana, uma das mais importantes feições geológicas na Província Borborema, Nordeste do Brasil. O corpo está dividido em duas fácies: uma equigranular fina a média e outra inequigranular média a fracamente porfirítica com fenocristais de K-feldspato. Determinações U-Pb em zircão apontaram uma idade ediacarana de c.a 578 Ma para a sua cristalização. Petrograficamente, o stock consiste de um biotita monzogranitos hololeucocráticos a leucocráticos (M = 1,3 – 9,9%), com biotita sendo o máfico principal (0,5 a 8,1%). Minerais opacos, titanita, allanita, apatita e zircão são acessórios e as fases minerais mais precoces. As rochas que formam o stock são geoquimicamente similares, de caráter fracamente peraluminoso (1,00 ≤ A/CNK ≤ 1,04), com coríndon normativo e de assinatura transicional entre rochas alcalinas e calcioalcalinas. A variação do conteúdo de óxidos e elementos traço sugere o fracionamento de plagioclásio, biotita, titanita, apatita e magnetita durante a cristalização do magma. O diagrama para elementos terras raras mostra enriquecimento dos elementos terras raras leves em relação aos elementos terras raras pesados, com razões LaN/YbN entre 16,10 e 54,75, e anomalias negativas de Eu (Eu/Eu* de 0,66 a 0,90) compatíveis com fracionamento de plagioclásio. Dados referentes à temperatura de saturação de zircão somados a diagramas discriminantes geoquímicos permitem associar essas rochas a granitos tipo I altamente fracionados. O conjunto de dados permite correlacionar o magmatismo no contexto de granitoides calcioalcalinos de alto potássio, tardi a pós-tectônicos do Domínio Rio Piranhas-Seridó.

Intraplate extension of the Indochina plate deduced from 26 to 24 Ma A-type granites and tectonic implications

ABSTRACTIn recent years, abundant Cenozoic potassic magmatic rocks from eastern Tibet and the Indochina Block have been studied extensively; however, until now, knowledge of Cenozoic A-type granites from the interior of the Indochina Block has been limited. U–Pb zircon ages for six samples of the Salei granite pluton within the Indochina Block range from 26 to 24 Ma. In situ Lu–Hf and Sr–Nd isotope data indicate that the Salei pluton was sourced mostly from Mesoproterozoic basement rocks of the Indochina Block, mixed with a small volume of juvenile crust derived from the underplated mantle. Whole-rock major element geochemistry indicates that the six samples are peraluminous high-K calc-alkaline granites. The trace and rare earth element patterns are typical of within-plate A-type granites. In combination with previous research, the present results suggest that the late Oligocene Salei granite formed from the convective removal of thickened lower continental lithospheric mantle. Moreover, the presence of 26–24 Ma A-type granites in the Indochina Block indicates within-plate extension in the interior of the block during the late Oligocene.

On the crystallization conditions of the Neoproterozoic, high-K calc-alkaline, Bragança Paulista-type magmatism, southern Brasília Orogen, SE Brazil

Syn-orogenic Neoproterozoic granitic magmatism (ca. 630–600 Ma) in southern Brasilia Orogen includes large batholiths of compositionally expanded high-K calc-alkaline granites (lato sensu) and small occurrences constituted by anatetic leuco-granites associated to the regional metamorphism. We present petrographic, mineralogical and geochemical data for a representative sample of the Braganca Paulista-type granite and estimates for magmatic crystallization conditions. The sample corresponds to a porphyritic hornblende-biotite monzogranite (CI ≈ 20) comprising perthitic microcline megacrysts within a medium-grained matrix with plagioclase (An 30 Ab 70 ), quartz, microcline and mafic minerals. The main mafic minerals are biotite (0.51 ≤ mg# ≤ 0.57) and Ca-amphibole (potassic-magnesio-hastingsite, 0.47 ≤ mg# ≤ 0.52), with similar volumes; accessory phases (ca. 2 vol.%) are Fe-Ti oxides (ferrian ilmenite, titanohematite, hematite and magnetite), allanite, apatite, zircon, titanite and sulphides. Our results indicate crystallization at 510 ± 60 MPa and temperatures from ca. 970oC (close-to-liquidus) to 755 ± 45oC (close-to-solidus), under oxidizing conditions, compatible with 0 ≤ ΔNNO ≤ +1. Estimated water and halogen fugacity ratios are ƒ H2O /ƒ HF ≥ 10 5.8 , 10 3.5 ≤ ƒ H2O /ƒ HCl ≤ 10 3.8 and ƒ HF /ƒ HCl ≤ 10 -2.2 . The obtained pressure, integrated with available regional geobarometric data, suggests a relative uplift rate about 0.2–0.3 (km/Ma) from the main regional metamorphism to the post-orogenic magmatism in the area.

Geochronology and geochemistry of Early Devonian intrusions in the Qimantagh area, Northwest China: evidence for post-collisional slab break-off

ABSTRACTThe Qimantagh area of Northwest China lies in the western part of the East Kunlun Orogenic Belt and is characterized by extensive magmatism, particularly in the Triassic. However, recent research has shown that Devonian magmatism was also widespread in this area and has a genetic relationship with mineralization. This article presents a detailed study of three types of Early Devonian intrusions: high-K calc-alkaline granites, A-type granites, and mafic intrusions, all from the Qimantagh region. These rocks were subjected to precise zircon U–Pb dating, major and trace element analyses, and Sr–Nd isotope measurements, focusing on the Lalingzaohuo (eastern Qimantagh) and Yemaquan (central Qimantagh) monzogranites, as well as the coeval Tanbeixuefeng (western Qimantagh) mafic dike swarm. To better understand the Early Devonian igneous activity in the Eastern Kunlun, data for other coeval granitoids were compared with our data. The Yemaquan monzogranite yielded a mean zircon U–Pb age of 400.5 ± 1.4 Ma. These rocks are metaluminous to slightly peraluminous, with Al2O3 contents of 13.10–14.16 wt.%, high alkali contents (total K2O + Na2O) of 6.89–7.68 wt.%, relatively low Sr contents (79–192 ppm), and high (La/Yb)N ratios, all of which indicate an I-type granite affinity. The Lalingzaohuo monzogranites yielded mean zircon U–Pb ages of 396.2–402.2 Ma. These rocks have higher SiO2 and alkali contents than the Yemaquan monzogranite, with high 10,000 Ga/Al ratios, high Zr + Nb + Ce + Y contents, high Fe2O3T/MgO ratios, and high Y contents, indicating an A-type granite affinity. These two monzogranites have initial 87Sr/86Sr ratios of 0.703–0.706 and εNd(t) values of –0.1 to –0.7. The Sr–Nd isotopic data require a significant input of a mantle component in the petrogenesis of these granites. The Tanbeixuefeng diabase dikes formed at ~396 Ma and have a continental tholeiitic affinity, as evident from small Ti–Nb–Ta anomalies and high contents of light rare earth and large-ion lithophile elements. We propose that post-collisional slab break-off was responsible for the generation of these Early Devonian intrusions in the Qimantagh area.

U–Pb and Re–Os geochronology and geochemistry of the Donggebi Mo deposit, Eastern Tianshan, NW China: Insights into mineralization and tectonic setting

The Donggebi Mo deposit located in NW China is a newly discovered, large, stockwork-type Mo deposit with ore reserves of 441Mt @ 0.115%Mo. Ore bodies occur along faults and fractures at the external contact zone of a concealed porphyritic granite and volcaniclastic rocks of Gandun Formation, spatially associated with a fine-grained granite. Mo-bearing veins are mainly assemblages of volatile-rich K-feldspar-quartz-oxide, K-feldspar-quartz, polymetallic sulfides and calcite-quartz. Zircon LA-ICP-MS U–Pb dating yielded concordant ages of 234.6±2.7Ma and 231.8±2.4Ma for the porphyritic granite and the fine-grained granite, respectively; molybdenite Re–Os dating gave an isochron age of 234.0±2.0Ma. These ages further confirm an important and extensive magmatic-metallogenic event in Eastern Tianshan during the Triassic Indosinian orogeny. Whole-rock major and trace element analyses indicate that the granitic rocks associated with Mo mineralization are high in Si, K, Rb, Th, Nb, Ta, Ga and LREE, but low in P, Ti, Sr and Ba, belonging to high-K calc-alkaline granites with A-type features. Magma was likely derived from the re-melting of thickened lower crust in a post-collision compression environment in the Late Permian, experienced strong crystal fractionation and formed the large Donggebi Mo deposit under an intra-plate extension setting in the Early to Middle Triassic.