high-K Calc-alkaline Magmatism Research Articles

Deeply Derived Magma Controlling the Polymetallic Mineralization at Shuikoushan, South China: Constraints from Mineral U–Pb Dating and Whole-Rock Geochemistry

Various magmatic–hydrothermal activities have resulted in different styles of polymetallic mineralization in South China. Shuikoushan is a large Fe-Cu-Pb-Zn-Au-Ag orefield situated in fold-and-thrust belts within the South China Block. Two types of granodiorite have been identified in recent drilling work. The early-stage, coarse-grained granodiorite has developed magnetite-bearing skarns in the deep level. The late-stage, fine-grained granodiorite is associated with garnet-hematite–magnetite–pyrite–sphalerite–chalcopyrite-bearing skarns in its contact zone. Away from the garnet-bearing skarn are calcite–quartz–pyrite–sphalerite–galena veinlets in faulted breccia. Fieldwork has identified iron mineralization in both skarns, whereas copper mineralization was only discovered in the garnet-bearing skarns. Lead, zinc, gold, and silver mineralization were observed in the garnet-bearing skarns and faulted breccia. Zircon U–Pb analyses suggested the emplacement of two granodiorite at 167.8 ± 0.8 Ma (MSWD = 1.1, N = 31) and 163.6 ± 0.7 Ma (MSWD = 1.3, N = 32). Apatite and garnet U–Pb dating further indicated the magnetite-bearing skarns of 166.2 ± 1.9 Ma (MSWD = 4.5, N = 27), the hematite–magnetite–sulfide-bearing skarns of 158.6 ± 2.8 Ma (MSWD = 1.3, N = 34), and the calcite–quartz–sulfide veinlets of 159.5 ± 5.2 Ma (MSWD = 1.7, N = 24). The time–space relationship between the two intrusions and hydrothermal activities suggests that the fine-grained granodiorite is responsible for polymetallic mineralization. Whole-rock geochemistry analyses demonstrated the enrichment of LILEs and the depletion of Nb and Ta in two granodiorites, with a slight enrichment in LREEs and flat HREE patterns. These granodiorite bodies therefore belong to high-K calc-alkaline magma generated via the crust’s partial melting. The fine-grained granodiorite generally has a lower HREE and higher Dy/Yb, Sr/Y ratios than coarse-grained granodiorite, corresponding to the source of magma in garnet stable lower crust. The residual garnet keeps ferric iron in melts, leaving the fine-granodiorite more oxidized for copper and gold concentration. Through these analyses and our drilling work, a continuous skarn–hydrothermal–epithermal system has been identified for Cu-Pb-Zn-Au-Ag targeting in Shuikoushan.

Petrogenesis of Andesite Rocks in Datae Area, Sidenreng Rappang Regency, South Sulawesi Province

The research area is in the Datae Area, Watangpulu District, Sidenreng Rappang Regency, South Sulawesi Province. This study aims to determine the distribution of volcanic rocks, determine the crystallization phase based on petrographic analysis, and determine the type, magma affinity and tectonic environment based on geochemical data. The method used in this study was field data collection and rock sampling for analysis through petrographic analysis and geochemical analysis using the X-Ray Fluorescence (XRF) method by analysing the main elements, trace elements and rare earth elements (REE). The results of the petrographic analysis show that the rocks found in the field are volcanic breccia and ignimbrite. Volcanic breccia showed coarse-grained texture composed of angular to rounded andesite fragments and pyroclastic material fused together in a matrix. Meanwhile, ignimbrite showed fine grained texture with lapilli to boulder-sized fragments, poor sorting, open-packed and non-layered structure. Based on the Total Alkali Silika (TAS) diagram, AFM diagram, and binary diagram, the results of the geochemical analysis showed that the rocks found in the study area were andesite and trachy-andesite, while the magma affinity area is high-K calc-alkaline and shoshonitic. High-K calc-alkaline magmas are associated with subduction zones and are characterized by elevated levels of potassium and aluminum, while shoshonitic magmas are typically found in intraplate or back-arc settings, characterized by their distinctive potassium, sodium, and barium-rich compositions. The results from ternary diagram and geochemical Spider plots proved that the magma tectonic environment is island arc—continental arc basalt, indicating that the rock was formed in a subduction area. This research supports previous research regarding the tectonics of the western arm of Sulawesi, which stated that this area was formed by subduction.

Kinematics and geochronology of the Lancang metamorphic complex: Implications for the evolution of the Paleo-Tethys region

The Lancang metamorphic complex is a key component of the Three River Tethys Orogen in the SE Tibetan Plateau, with typical rock assemblages and deformation fabrics recording the subduction of the Paleo-Tethys Ocean and subsequent continental collision. In this study, we present new petrographic and structural observations, together with zircon U-Pb and mica 40Ar/39Ar geochronologic data, to reveal the deformation and kinematics of the Lancang metamorphic complex, thus providing insights into the Permian−Triassic evolution of the eastern Paleo-Tethys domain. The subduction of the Paleo-Tethys Ocean and subsequent collision resulted in a range of structural features, including penetrative regional foliations, thrusts, asymmetric folds at various scales, and ductile deformation fabrics such as asymmetric boudins and porphyroclasts. Zircon U-Pb dating of foliated gabbro and 40Ar/39Ar dating of mica schist and mylonite, which preserve shortening fabrics, suggest that the Paleo-Tethys Ocean was subducted during the Late Carboniferous to Permian−Early Triassic, and the collision of the Baoshan and Simao blocks mainly occurred during ca. 237−230 Ma in the SE Tibetan Plateau. Regional deformation likely shifted from shortening to extension ca. 230 Ma, as reflected by post-collision high-K calc-alkaline magmatism. Our results document regional structural patterns and place timing constraints on the evolution of the Paleo-Tethys Ocean.

Three stages of early Paleozoic magmatism in the Tibetan-Himalayan orogen: New insights into the final Gondwana assembly

Earth’s evolution involves deep, hot rocks rising upward by convection to near-surface environments, as well as the unique scenarios such as the formation and breakup of Gondwana and Pangea . These processes have been well recorded by the widely distributed magmatism . To understand the tectonic evolution and Gondwana assembly, we compiled early Paleozoic zircon U–Pb ages (n = 67), in-situ zircon Hf isotopes (n = 1011), and bulk-rock elemental compositions (n = 293) and Sr–Nd isotopes of magmatic rocks in the Tibetan–Himalayan orogen. Three stages of Paleozoic magmatism were identified here, including early (>490 Ma) to middle (490–470 Ma) to late (<470 Ma) stages, in response to the final assembly of the Gondwana supercontinent . Early-stage magmatic rocks are characterized by highly variable SiO 2 (48.0–80.0 wt%) and MgO (0.02–9.65 wt%) contents with Mg# range from 5.4 to 78, K 2 O/Na 2 O ratios ranging from 0.14 to 2.81, and whole-rock Sr–Nd ( 87 Sr/ 86 Sr(i) (0.7035–0.7340), ε Nd (t) (-9.5–+1.0)) and zircon Hf (ε Hf (t) = –15 to + 8.0) isotopic compositions with significant mantle contributions; they could be generated in an Andean-type arc setting along the active northern continental Gondwana margin. Middle-stage magmas were dominated by fertile continental crustal signatures (SiO 2 > 70 wt%, A/CNK > 1.10, MgO < 2.69 wt%) in a crustal thickening setting. Late-stage magmas also have highly variable Si, Mg and isotopic components, with coeval mantle-derived magmas developing in an extensive setting. Importantly, the widespread presence of early Cambrian to late Ordovician peraluminous high-K calc-alkaline magmatism in the Tibetan–Himalayan orogen indicates that the reworking of ancient continental crustal materials played a key role in reconstructing and stabilizing the final Gondwana assembly.

U–Pb geochronology and geochemistry of grenville-age plutons in the Sunsas Belt - Bolivia, SW Amazonian Craton: Tectonic and magmatic implications

The Sunsas syn-to post-orogenic high-K calc-alkaline magmatism is crucial to understand the tectonic and thermodynamic history of the Sunsas Orogeny in the southwestern part of the Amazonian Craton. This orogeny is correlated with the Grenville orogenic cycle (c. 1.3 to 0.95 Ga) of Laurentia. Three granitic intrusions from Sunsas belt were classified as fractionated I-type and hybrid A-type granites. The first, the Nomoca granodiorite presents calc-alkaline affinity with peraluminous-magnesian composition (Mg0 = 1.61 wt%), and typical characteristics of intermediate magmas (SiO2 = 67.3 w%). The La Asunta and Nocemano syenogranites have calc-alkaline affinity with peraluminous-ferrous composition (FeO = 2.26–3.31 wt%) and characteristics of silica-rich magmas (SiO2 = 70.4–74.9 w%). Geochemical fractionation patterns suggest that the granites were derived from the reworking of two crustal protolith sources in the same tectonic environment. The Nomoca, La Asunta and Nocemano intrusions yield crystallization ages between 1.17 and 1.08 Ga. Inherited zircon cores with 3.63 and 2.91 Ga Archean ages from Nomoca and Nocemano intrusions may be correlated to the Superior Province evolution, which is located in the south-central part of the Canadian Shield. These U–Pb ages strengthen the geotectonic model for the Rodinia supercontinent with Laurentia-Baltica-Amazonia configuration. Paleoproterozoic (2.12–1.69 Ga) and Mesoproterozoic (1.4–1.3 Ga) U–Pb inherited zircon ages from these intrusions support intensive reworking of the Paraguá basement. A concordant age of 555 Ma for zircon rims suggests reworking of the Sunsas Province during the Neoproterozoic Brasiliano Orogeny.

The age and geochemistry of the mid-Cretaceous volcanic rocks in the Jinan Basin: Implications for the mid-Cretaceous tectonic environments of the Korean Peninsula and Northeast Asia

Most of the mid to late Cretaceous igneous rocks in the southeastern margin of the Northeast Asian continent are interpreted to be formed due to upwelling of asthenospheric mantle caused by slab rollback and associated back-arc extension. However, the tectonic environments for the mid-Cretaceous igneous rocks in the Korean Peninsula is uncertain. The Jinan Basin is one of the Cretaceous pull-part basins in the southern Korean Peninsula. The mid-Cretaceous volcanic rocks occur in association with the Jinan Basin. In this study, we investigated whole-rock major and trace element geochemistry and Sr-Nd-Pb isotope compositions of the mid-Cretaceous volcanic rocks in the Jinan Basin to understand their petrogenesis and tectonic environments. Also, U-Pb zircon age of sedimentary and volcanic rocks in the Jinan Basin was determined to constrain the age of sedimentation and igneous activities. The results show that sedimentation started at least from 97.7 Ma and continued until 89.5 Ma. The sedimentary sequences were intermittently extruded by rhyolitic and andesitic magma 90–89 Ma, and later intruded by basaltic trachyandesite 84 Ma. The volcanic rocks in the Jinan Basin show geochemical features of alkaline to high-K calc-alkaline magma series with strong enrichment in large ion lithophile elements and light rare earth elements relative to high field strength elements. The mafic and intermediate volcanic rocks are distinguished from the typical continental arc magmas by enrichment in incompatible elements such as Y and Zr with high Zr/Y, suggesting that they originated from an enriched source. The basaltic trachyandesites and andesite have Sr isotope ratios (87Sr/86Sri) of 0.708769–0.709484 and Nd isotope ratios (143Nd/144Ndi) of 0.511782–0.511886, which indicate that they formed from mantle which was contaminated with crustal component in their petrogenesis. The Pb isotope data (206Pb/204Pb = 17.572–18.158, 207Pb/204Pb = 15.535–15.640 and 208Pb/204Pb = 38.366–38.921) suggest that the crustal component should have experienced a prolonged evolution with a low μ value. The Mg# (46–57) and Cr contents (40–180 ppm) in the mafic to intermediate rocks higher than typical crustal melts at a given range of SiO2, showing that they evolved from a mantle-derived primary magma. We attribute the crust-like geochemical and isotopic signature of the Jinan mafic and intermediate igneous rocks to the partial melting of enriched lithospheric mantle metasomatized by subduction components and subsequent crustal assimilation during magma ascent and pooling at the mid-crustal depth of ~9–10 km. The geochemical and isotopic features of the Jinan volcanic rocks are similar to those of the mid-Cretaceous basaltic volcanic rocks in the Yeongdong and Gyeongsang Basins, South Korea and the southeastern margin of South China Craton (SCC). This may suggest that the partial melting of the enriched lithospheric mantle, induced by slab rollback of the paleo-Pacific plate and upwelling of the asthenospheric mantle, was widespread underneath the southeastern Korean Peninsular as well as the southeastern margin of SCC.

Trace Element Composition of Igneous and Hydrothermal Magnetite from Porphyry Deposits: Relationship to Deposit Subtypes and Magmatic Affinity

AbstractThe trace element composition of igneous and hydrothermal magnetite from 19 well-studied porphyry Cu ± Au ± Mo, Mo, and W-Mo deposits was measured by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and then classified by partial least squares-discriminant analysis (PLS-DA) to constrain the factors explaining the relationships between the chemical composition of magnetite and the magmatic affinity and porphyry deposit subtypes. Igneous magnetite can be discriminated by relatively high P, Ti, V, Mn, Zr, Nb, Hf, and Ta contents but low Mg, Si, Co, Ni, Ge, Sb, W, and Pb contents, in contrast to hydrothermal magnetite. Compositional differences between igneous and hydrothermal magnetite are mainly controlled by the temperature, oxygen fugacity, cocrystallized sulfides, and element solubility/mobility that significantly affect the partition coefficients between magnetite and melt/fluids. Binary diagrams based on Ti, V, and Cr contents are not enough to discriminate igneous and hydrothermal magnetite in porphyry deposits.Relatively high Si and Al contents discriminate porphyry W-Mo hydrothermal magnetite, probably reflecting the control by high-Si, highly differentiated, granitic intrusions for this deposit type. Relatively high Mg, Mn, Zr, Nb, Sn, and Hf but low Ti and V contents discriminate porphyry Au-Cu hydrothermal magnetite, most likely resulting from a combination of mafic to intermediate intrusion composition, high chlorine in fluids, relatively high oxygen fugacity, and low-temperature conditions. Igneous or hydrothermal magnetite from Cu-Mo, Cu-Au, and Cu-Mo-Au deposits cannot be discriminated from each other, probably due to similar intermediate to felsic intrusion composition, melt/fluid composition, and conditions such as temperature and oxygen fugacity for the formation of these deposits.The magmatic affinity of porphyritic intrusions exerts some control on the chemical composition of igneous and hydrothermal magnetite in porphyry systems. Igneous and hydrothermal magnetite related to alkaline magma is relatively rich in Mg, Mn, Co, Mo, Sn, and high field strength elements (HFSEs), perhaps due to high concentrations of chlorine and fluorine in magma and exsolved fluids, whereas those related to calc-alkaline magma are relatively rich in Ca but depleted in HFSEs, consistent with the high Ca but low HFSE magma composition. Igneous and hydrothermal magnetite related to high-K calc-alkaline magma is relatively rich in Al, Ti, Sc, and Ta, due to a higher temperature of formation or enrichment of these elements in melt/fluids.Partial least squares-discriminant analysis on hydrothermal magnetite compositions from porphyry Cu, iron oxide copper-gold (IOCG), Kiruna-type iron oxide-apatite (IOA), and skarn deposits around the world identify important discriminant elements for these deposit types. Magnetite from porphyry Cu deposits is characterized by relatively high Ti, V, Zn, and Al contents, whereas that from IOCG deposits can be discriminated from other types of magnetite by its relatively high V, Ni, Ti, and Al contents. IOA magnetite is discriminated by higher V, Ti, and Mg but lower Al contents, whereas skarn magnetite can be separated from magnetite from other deposit types by higher Mn, Mg, Ca, and Zn contents. Decreased Ti and V contents in hydrothermal magnetite from porphyry Cu and IOA, to IOCG, and to skarn deposits may be related to decreasing temperature and increasing oxygen fugacity. The relative depletion of Al in IOA magnetite is due to its low magnetite-silicate melt partition coefficient, immobility of Al in fluids, and earlier, higher-temperature magmatic or magmatic-hydrothermal formation of IOA deposits. The relative enrichment of Ni in IOCG magnetite reflects more mafic magmatic composition and less competition with sulfide, whereas elevated Mn, Mg, Ca, and Zn in skarn magnetite results from enrichment of these elements in fluids via more intensive fluid-carbonate rock interaction.

The geology of the Bozymchak Cu-Au skarn deposit, Tien Shan belt, Central Asia: emphasis on the geochemical characteristics of the granitoids

ABSTRACTThe Bozymchak Cu-Au skarn deposit is located in the Chatkal – Kurama region, approximately 130 km east from the Almalyk Cu-Au porphyry mine camp. The current paper provides the results from geochemical study and shows that geochemical characteristics of the Bozymchak area granitoids, including the rare-earth elements, are essentially similar to high-K calc-alkaline series magmatism of the Almalyk area. Systematic sampling of the Bozymchak granitoids has revealed the zoned distribution of several elements relative to the Cu-Au skarn. Most markedly, this is expressed by P2O5, MgO, Fe2O3 and V, whose contents decrease in the granitoids located closest to the skarns. The zoned distribution of base metals Cu, Zn, Pb, Mo, and also As, is less distinct, however, in general, their content decreases away from the skarns. This revealed geochemical zoning appears to represent a hydrothermal halo of Cu-Au bearing skarns and can potentially be used for guiding exploration in the region.

Petrogenesis of Volcanic Arc Granites from Bayah Complex, Banten, Indonesia

This research aimed to reveal the petrogenesis of granitic rocks of Bayah Complex starting from magma differentiation to exposing event, this research also intended to determine the tectonic environment. The methods carried out in this research include field observation, petrographic analysis using polarized light microscopy, and geochemical analysis using X-Ray Fluorescence (XRF) and Inductively Coupled Mass Spectrometry (ICP-MS).&#x0D; Petrographic analysis shows that Bayah granitic rocks are composed of quartz, plagioclase, and K-feldspar while the rest are amphibole, biotite, sericite, chlorite, epidote, and opaque. Based on its major oxide concentrations, Bayah granitic rocks classified as granite and diorite-quartz which have high-K calc-alkaline magma. 4 samples of granitic rocks showed the A/N+K+C &gt; 1 molar ratios belonging to the peraluminous S-type granite index while the remaining 1 sample showed a molar ratio of A/N+ K+C &lt; 1 and A/N+K &gt; 1 which classified as metaluminous I-type granite. Accordingly, Bayah granitic rocks are S-type granite which crystallized from sediment-derived magma, the sediments itself estimated sourced from continental especially Malay Peninsula, Indonesian Tin Island, and Schwaner Mountains. During differentiation, the magma undergone crustal contamination reflected by the increase in both SiO2 0.51 wt% and Al2O3 1.95 wt%, and decrease in Fe2O3 + MgO 0.61 wt% from the pure composition of sediment-derived magma. Furthermore, the occurrence of crustal contamination also recognized from high concentrations of Rb and Ba which indicate the interaction of magma with the materials of continental crust.&#x0D; Regard to the exposing event, Bayah granitic rocks approximated to be exposed due to regional tectonic activity which caused Orogenesa I in the Early Oligocene to the Late Oligocene. Moreover, based on the plot of trace elements especially Rb, Y, Nb, Ta, and Yb on Harker and tectonic discriminant diagrams, Bayah granitic rocks are formed on volcanic-arc active continental margins in accordance with regional tectonic setting.

Calc-alkaline magmatism associated with salt diapirs in the Shurab and Garmsar back-arc areas (Central Basin, Iran): magma genesis and tectonic implications

Medium- and high-K calc-alkaline magmatism of the Shurab (southeast Qom city) and Garmsar (northwest Garmsar city) areas occurred within the Lower Red Formation in the Central Basin behind the Urumieh-Dokthar Magmatic Arc. In terms of whole-rock geochemical analyses and in agreement with the petrographic features, all representative samples of the Shurab area are classified into three groups: group 1 with mainly intergranular texture comprises basalt/trachybasalt, while groups 2 and 3 with trachytic and porphyritic textures, respectively, have basaltic trachyandesite composition. The overall major constituents are plagioclase with composition in the range from An 49 Ab 23 to An 75 Ab 47 , clinopyroxene with composition in the range Wo 43-45 En 39-45 Fs 9-15 , and olivine with composition in the range from Fo 58 Fa 31 to Fo 67 Fa 40 . Minor minerals consist of opaque minerals and K-feldspar in the range Or 41-65 Ab 33-50 An 0.69-8 . The characteristic accessories are apatite and sphene. In the Garmsar area, rocks are seen as subvolcanic with mafic (basalt) and intermediate (trachybasalt/basaltic trachyandesite) compositions. The Garmsar area rocks represent intergranular, granular, ophitic, and subophitic textures. In these rocks, major mineral phases are plagioclase and clinopyroxene. The minor constituents are olivine, opaque minerals, amphibole, biotite, and quartz. Apatite is the most important accessory mineral. The rocks of both areas display REE patterns characterized by LREE-enriched and HREE-depleted segments typical of arc lavas. Primitive mantle-normalized trace element patterns for samples of both areas exhibit high ratios of strongly incompatible elements with similar bulk partition coefficients (e.g., Th/ Ta and Th/Ce), enrichment in large-ion lithophile elements (LILEs: Cs, Ba, Rb, Th) relative to the high field-strength elements (HFSEs: Ti, Hf, Zr, and REEs), and troughs for Nb, Ta, Ti, and Zr and peaks for Cs, Th, K, and Sr, all of which are indicators for subductionrelated magmatism. Subduction of the Neo-Tethys beneath the Eurasian margin led to upper mantle deformation and metasomatism. Once the Arabian plate collided with the Eurasian margin, subduction ended through a slab breakoff process, and thermal flux of asthenospheric origin uprising through the slab tear induced the thermal erosion of the mantle metasomatized during the previous subduction event and triggered its partial melting. Also, the late Eocene-early Oligocene collision of Eurasian with Arabian plates led to the subsidence and formation of faults and extensions in the Central Basin (i.e. the Shurab and Garmsar areas) such that eruption of medium- and high-K metasomatic magmatism along these faults and extensions caused postcollision volcanism in the Central Basin.

Neoproterozoic granitoids in the basement of the Moroccan Central Meseta: Correlation with the Anti-Atlas at the NW paleo-margin of Gondwana

Field observations and U–Pb LA–ICP–MS zircon ages of magmatic outcrops in the Goaïda area, south-eastern part of Moroccan Central Massif (Meseta domain), provide firm evidence of Neoproterozoic silicic magmatism in the basement of the Moroccan Variscan belt. This magmatic activity produced three distinct plutons —dark, pink and white granitoids—, which form a Neoproterozoic basement strongly reworked in the Carboniferous and intruded by Hercynian gabbro, dolerite and rhyolite bodies. The Goaïda dark granitoids are syeno–granodiorites, whereas the pink and white granitoids are granites sensu stricto. All the facies of Goaïda granitoids have I-type, high-K and calc-alkaline affinities. Concordant U–Pb zircon data yield Lowermost Ediacaran mean age for white granites (625±9Ma) and Ediacaran mean ages for dark granitoids (600±10Ma) and pink granites (552±10Ma). White granites record old high-K calc-alkaline magmatism that started in the Anti-Atlas belt at ca. 620Ma, coinciding with the end of the second period of the Pan-African orogenesis. On the other hand, the dark and pink granitoids formed in subduction-related to post-collisional regimes during the final stage of the Pan-African orogenesis, namely the WACadomian orogeny. We combine new field, geochronological and geochemical data with results from the literature to propose a new lithostratigraphic reconstruction of the Precambrian to Early Cambrian times in the Moroccan Meseta front at the NW margin of the West African Craton. The presence of Precambrian outcrops —including Paleoproterozoic and Neoproterozoic rocks— in the Moroccan Variscan belt demonstrates the continuity of the peri-Gondwanan Panafrican basement at least from the eastern Anti-Atlas to the Central Meseta domain. Along with the lack of Paleozoic ophiolitic suture and subduction-related metamorphic rocks, this continuity supports the hypothesis that the Moroccan Variscan mountains were part of the NW margin of Gondwana in the Paleozoic.

Late Mesozoic high-K calc-alkaline magmatism in Southeast China: the Tongling example

ABSTRACTWe report new zircon U–Pb ages, Hf isotopic and geochemical results for the Tongling granitic plutons of Southeast China. SHRIMP U–Pb ages for the Miaojia quartz monzodiorite porphyrite，the Tianebaodan and Tongguanshan quartz monzodiorites, the Xinqiaotou granodiorite porphyry, and the Shatanjiao and Nanhongchong granodiorite are 143 ± 2, 141 ± 1 and 142 ± 1, 147 ± 1, and 145 ± 1 and 139 ± 1 Ma, respectively. Combined with previous geochronological data, our results indicate that the porphyritic rocks are older than rocks of the same type lacking porphyritic texture. Geochemically, these high-K calc-alkaline intrusive rocks are characterized by arc-like trace element distribution patterns, with significant enrichment in LILE and LREE but depletion in HFSE. Lu–Hf isotopic compositions of zircons from the high-K calc-alkaline (HKCA) rocks have εHf(t) values of magmatic 139–147 Ma zircons from −8.1 to −25.6, with two-stage model ages (tDM2) of 1.71–2.67 Ga, whereas εHf(t) values of inherited 582–844 Ma zircons range from 5.4 to −9.5, with tDM2 of 1.39–2.22 Ma, younger than tDM2 values of igneous zircon, indicating that newly formed mantle material was added to the continental crust of the Yangtze Block. Moreover, εHf(t) values of inherited zircon cores older than 1000 Ma are from −7.8 to −26, similar to magmatic zircons, and the tDM2 values are all greater than 3.0 Ga (3.16–3.75 Ga), reflecting partial melting of ancient sialic material. We conclude that the plutonic melts were derived from both the enriched mantle and the ancient crust. The HKCA Tongling intrusions coincide temporally with the J3–K1 magmatic event that was widespread in Southeast China. This igneous activity may have accompanied sinistral slip along the Tan-Lu fault due to oblique subduction of the Palaeo-Pacific plate.

U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil

Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U–Pb age patterns coupled with Lu–Hf data for 18 samples, representing different stages of the Minas Basin evolution (∼2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in turn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca. 2600Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after the 2730–2600Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is younger than 2600Ma, most likely coinciding with the great oxygenation event between 2400 and 2200Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca. 2120Ma with the deposition of the synorogenic Sabará Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton. The εHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly built by crust–mantle mixing processes, with a successive decrease of εHf values in zircons crystallized after 3250Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports previous interpretations of a long-lived evolution of the southern São Francisco Craton comprising a succession of convergent island arcs, small microplate collisions, and development of Archean convergent and divergent basins that evolved between Archean and Paleoproterozoic times.

Long-lived, stationary magmatism and pulsed porphyry systems during Tethyan subduction to post-collision evolution in the southernmost Lesser Caucasus, Armenia and Nakhitchevan

The composite Meghri–Ordubad and Bargushat plutons of the Zangezur–Ordubad region in the southernmost Lesser Caucasus consist of successive Eocene to Pliocene magmatic pulses, and host two stages of porphyry Cu–Mo deposits. New high-precision TIMS U–Pb zircon ages confirm the magmatic sequence recognized by previous Rb–Sr isochron and whole-rock K–Ar dating. A 44.03±0.02Ma-old granite and a 48.99±0.07Ma-old granodiorite belong to an initial Eocene magmatic pulse, which is coeval with the first stage of porphyry Cu–Mo formation at Agarak, Hanqasar, Aygedzor and Dastakert. A subsequent Oligocene magmatic pulse was constrained by U–Pb zircon ages at 31.82±0.02Ma and 33.49±0.02Ma for a monzonite and a gabbro, and a late Miocene porphyritic granodioritic and granitic pulse yielded ages between 22.46±0.02Ma and 22.22±0.01Ma, respectively. The Oligo-Miocene magmatic evolution broadly coincides with the second porphyry-Cu–Mo ore deposit stage, including the major Kadjaran deposit at 26–27Ma.Primitive mantle-normalized spider diagrams with negative Nb, Ta and Ti anomalies support a subduction-like nature for all Cenozoic magmatic rocks. Eocene magmatic rocks have a normal arc, calc-alkaline to high-K calc-alkaline composition, early Oligocene magmatic rocks a high-K calc-alkaline to shoshonitic composition, and late Oligocene to Mio-Pliocene rocks are adakitic and have a calc-alkaline to high-K calc-alkaline composition. Radiogenic isotopes reveal a mantle-dominated magmatic source, with the mantle component becoming more predominant during the Neogene. Trace element ratio and concentration patterns (Dy/Yb, Sr/Y, La/Yb, Eu/Eu*, Y contents) correlate with the age of the magmatic rocks. They reveal combined amphibole and plagioclase fractionation during the Eocene and the early Oligocene, and amphibole fractionation in the absence of plagioclase during the late Oligocene and the Mio-Pliocene, consistent with Eocene to Pliocene progressive thickening of the crust or increasing pressure of magma differentiation. Characteristic trace element and isotope systematics (Ba vs. Nb/Y, Th/Yb vs. Ba/La, 206Pb/204Pb vs. Th/Nb, Th/Nb vs. δ18O, REE) indicate that Eocene magmatism was dominated by fluid-mobile components, whereas Oligocene and Mio-Pliocene magmatism was dominated by a depleted mantle, compositionally modified by subducted sediments.A two-stage magmatic and metallogenic evolution is proposed for the Zangezur–Ordubad region. Eocene normal arc, calc-alkaline to high-K calc-alkaline magmatism was coeval with extensive Eocene magmatism in Iran attributed to Neotethys subduction. Eocene subduction resulted in the emplacement of small tonnage porphyry Cu–Mo deposits. Subsequent Oligocene and Miocene high-K calc-alkaline and shoshonitic to adakitic magmatism, and the second porphyry Cu–Mo deposit stage coincided with Arabia–Eurasia collision to post-collision tectonics. Magmatism and ore formation are linked to asthenospheric upwelling along translithospheric, transpressional regional faults between the Gondwana-derived South Armenian block and the Eurasian margin, resulting in decompression melting of lithospheric mantle, metasomatised by sediment components added to the mantle during the previous Eocene subduction event.

Geochronology, geochemistry, and petrogenesis of the Eocene Bayburt intrusions, Eastern Pontides, NE Turkey: Evidence for lithospheric mantle and lower crustal sources in the high-K calc-alkaline magmatism

Eocene I-type plutons are widespread in the Eastern Pontides, Northeastern Turkey. Geochemical and isotopic results on two Eocene intrusive bodies located in the southern zone of the Eastern Pontides were utilized to achieve a proper reconstruction of their origin. Based on laser ablation ICP-MS U–Pb zircon dating, Kılıçkaya and Kozluk intrusions present similar 206Pb/238U versus 207Pb/235U concordia ages of 46.75±0.79 and 46.9±0.68 Ma, respectively. Both intrusions exhibit similar petrographical, geochemical, and isotopical features, and contain abundant mafic microgranular enclaves (MMEs). The intrusive rocks are composed of diorite, tonalite, and granodiorite, whereas MMEs are composed of diorite. Both the intrusive rocks and the MMEs are I-type, high-K calc-alkaline in composition and display a metaluminous character. They are enriched in large-ion lithophile and light rare-earth elements and are depleted in high-field strength elements. The intrusive rocks show moderate variation in 87Sr/86Sr(i) (0.70531–0.70576), εNd(i) (+0.3 to −0.5), and δ18O values (+6.6 to +6.9), as well as Nd model ages (0.73–0.82Ga). Their Pb isotopic ratios are 206Pb/204Pb=18.67–18.86, 207Pb/204Pb=15.61–15.62, and 208Pb/204Pb=38.62–39.03. Although the isotope signatures of MMEs (87Sr/86Sr(i)=0.70528–0.70561; εNd(i)=+0.7 to −0.3; δ18O=+6.7 to +6.8) are significantly similar to those of the host rocks, the MMEs are characterized by relatively low contents of SiO2 (57–59wt.%), low aluminum saturation index (0.8–0.9), and high Mg numbers (31–36). All of these data suggest magma generation by mixing of enriched lithospheric mantle- and lower crustal-derived melts. Moreover, Sr–Nd isotopic modeling reveals ∼17% to 23% lower crustal magma contribution to the mantle component.

Geology and origin of Ag–Pb–Zn deposits occurring in the Ulaan-Jiawula metallogenic province, northeast Asia

Located at the conjunction area of China, Mongolia and Russia in NE Asia, the Ulaan-Jiawula (also referred as UJ) region, with an area of 400,000km2, is one of the most important Ag–Pb–Zn, U, Sn, W, Nb–Ta, and Au metallogenic provinces in Asia. At present, 2126 deposits and showings including 500 Ag–Pb–Zn deposits have been discovered, explored and mined since the late 1960s. These Ag–Pb–Zn occurrences can be subdivided into three types according to their geological setting, texture, alteration and mineral assemblages: (1) low sulfidation epithermal Ag–Pb–Zn deposits; (2) intermediate sulfidation epithermal Ag–Pb–Zn deposits; (3) mixed-type Ag–Pb–Zn deposit consisting of vein-like and tabular ore bodies. The Eren Tologoi and Tsagenbulagen deposits are representative of low-sulphidation type Ag–Pb–Zn mineralization in the UJ region, and are associated with intensive adularization and sericitization. Ore occurs as mineralized quartz veins, veinlet groups and altered-fracture zones within Mesozoic alkaline and high-K calc-alkaline volcanic rocks, Ore mineralogy includes native silver, electrum, pyrite, galena, sphalerite, arsenopyrite, pyrargyrite and chalcopyrite. The Tsav and Jiawula deposits are typical of intermediate sulfidation Ag–Pb–Zn mineralization. The δ34S value of sulfide (pyrite and galena) separates from groups 1 and 2 varies from 1.5‰ to 3.5‰ and 2.0‰ to 4.5‰, respectively. The δ34S values of the Mesozoic volcanic host rocks for groups 1 and 2 deposits also show the positive δ34S values of 1.5–4.8‰, while the δ34S value of pyrite separate from the pre-Jurassic schist range from −6‰ to −8‰ which are much lower than Mesozoic volcanic host rocks and their associated ore deposits. There is no difference between the δ34S value of sulfide (pyrite and galena) separates from vein-like ore bodies of the group 3 deposits and their wall rocks, having δ34S value of 1.0–5.0‰ and 1.2–4.5‰ which are similar to that of groups 1 and 2 deposits. For the Mesozoic monzogranite porphyry dykes and their associated tabular skarn ore bodies, the pyrite separates show δ34S values of 2–5‰ and 1.8–3‰. All of these deposits show relatively radiogenic lead isotopic compositions compared to mantle or lower crust curves. Most lead isotope data of sulfides from the Ag–Pb–Zn ores plot between the Mesozoic volcano–hypabyssal rocks and pre-Jurassic metamorphic rocks. Monzogranite dykes at Ulaan and Noyon Tologoi have εNd (T) values ranging from 1.5 to 4.5 that are similar to most of the Mesozoic granite with positive εNd (T) values in the Great Hinggan Mountains-Mongolia orogenic belt. Data are interpreted as indicative of a mixing of ore-forming materials from mantle-derived alkaline and high-K calc-alkaline magma with these from pre-Jurassic metamorphic wall rocks. Isotopic age data, geological and geochemical evidence suggest that the ore fluids for the Ag–Pb–Zn deposits were generated during eruption or emplacement of the Mesozoic alkaline and high-K calc-alkaline magma. The Mesozoic magmas may provide heat, volatiles and metals for the group 1 and 2 deposits. Evolved metamorphic fluids produced by devolatilization, circulated the wall rocks, were also progressively involved in the magmatic hydrothermal system, and may have dominated the ore fluids during late stage ore-forming processes. Most of the Ag–Pb–Zn bodies that occur along the contact of the pre-Jurassic marble and Cretaceous monzogranite porphyry dykes at Ulaan and Noyon Tologoi are closely associated with skarn. The ore fluid of these group 3 deposit may have resulted from the mixing of Mesozoic magmatic water and evolved metamorphic fluids. Ore deposition in this instance would be the product of the interaction of the Mesozoic intrusions and pre-Jurassic carbonate rocks.

Early to Late Paleoproterozoic magmatism in NE Brazil: The Alto Moxotó Terrane and its tectonic implications for the Pre-West Gondwana assembly

The Alto Moxotó Terrane is a Paleoproterozoic inlier within the Transversal Domain of the Neoproterozoic Borborema Province (NE Brazil). An isotopic and whole-rock geochemistry study has been performed in the Sucuru region (Paraiba State, NE Brazil) which revealed a long-lived evolution for this terrane. The first event is Siderian-aged, dated on 2.44 Ga, being represented by granitic to granodioritic banded orthogneisses and migmatites of the basement. They correspond to meta to peraluminous high-K calc-alkaline series, where geochemical patterns besides zircon features and Nd isotopic data indicate that they were formed in a convergent tectonic environment with reworking of an older Archean continental crust. This basement was intruded by different magmatic suites through two distinct tectono-magmatic events. The older one is Rhyacian-aged recorded by emplacement of the Carmo mafic-ultramafic suite and Pedra d'Água granitic suite, with ages varying from 2.15 to 2.0 Ga. The Carmo Suite shows compositions similar to tholeiitic and minor calc-alkaline series and geochemical patterns of a depleted source. These general chemical characteristics are compatible with an arc-related magmatism in early stages of subduction. The Pedra d'Água suite corresponds to middle to peraluminous high-K calc-alkaline magmatism which presents a typical magmatic arc geochemical signature. The negative εNd (t) values suggest a strong continental component for genesis of these magmas. The last tectonomagmatic episode occurred in the Statherian-Calymmian boundary and is represented by bimodal magmatic association of the Serra da Barra Suite, dated around 1.6 Ga. The dominant felsic rocks present an evolved composition and correspond to typical metaluminous sub-alkaline suite. The trace-element and REE patterns of both mafic and mainly felsic rocks suggest a within-plate setting. The attributed source is of crustal derivation, which is supported by the negative εNd (t) values. A mantle plume can be invoked for mechanism of generation of the Serra da Barra magmatism. This polycyclic Paleoproterozoic evolution observed at Alto Moxotó terrane is also well documented in orogenic terranes worldwide, mainly those related to Atlantica supercontinent amalgamation. On the other hand, Statherian-Calymmian extensional event is also coherent with worldwide descriptions and are commonly referred to early break-up stage of the large Paleoproterozoic land masses.

Petrogenesis of the Archean tonalite–trondhjemite–granodiorite (TTG) and granites in the Lushan area, southern margin of the North China Craton: Implications for crustal accretion and transformation

Tonalite–trondhjemite–granodiorite (TTG) assemblages and abundant high-K calc-alkaline magmatism are considered to be closely related to craton stabilization, and usually record a tectonic transition. Three episodes of granitic magmatism are identified in the Lushan area, at the southern margin of the North China Craton (NCC) on the basis of new LA-ICP-MS zircon U–Pb ages and whole-rock geochemical data. They are TTG gneisses, sodic–potassic granite (SPG) suite and potassic granite dated at ∼2840Ma, ∼2760Ma and ∼2570Ma, respectively. The TTG gneisses have high SiO2, variable Mg#, Cr and Ni contents with high (La/Yb)N and Sr/Y ratios, suggesting that the parental magmas were derived by partial melting of subducted oceanic crust. They show no obvious correlations between Sr/Y and Dy/Yb or (La/Yb)N and Dy/Yb, and all have negative Nb and Ta but positive Zr and Hf anomalies and variable Dy/Yb, Nb/Ta, Zr/Hf and Zr/Sm ratios, suggesting melting of a deep source (>45km) with rutile eclogite and garnet amphibolite in the residue. The TTG samples have positive ɛHf(t) values (+2.6 to +7.0) with the youngest TDMC (2896Ma) close to the crystallization age, indicating that they were produced by partial melting of juvenile crustal materials in an arc setting. Rocks of the SPG suite have high SiO2 contents, variable Na2O/K2O ratios (0.41–10.91), and low Y and Yb contents with high Sr/Y ratios, indicating an affinity to I-type granites. They display depleted and concave-upward REE patterns between middle and heavy REEs and higher Zr/Sm than TTG gneisses, possibly resulting from amphibole removal by fractional crystallization or as a residual phase during melting. Meanwhile, the rocks have a large variation of Dy/Yb without obvious correlations between Sr/Y and Dy/Yb, and (La/Yb)N and Dy/Yb, in combination with variable but uniformly low Y contents. Therefore, we suggest that the SPG samples were derived from partial melting with garnet in the residue. Magmatic zircons have ɛHf(t) values from −4.3 to +4.2 with TDMC ages from 3200Ma to 2877Ma, indicative of older mafic lower crustal sources. The rocks formed within a short time interval with the TTG, and their emplacement was accompanied by regional granulite and amphibolite metamorphism, implying that they may also have formed in an arc setting. The potassic granite has high SiO2 (74.79wt.%) and K2O+Na2O (9.22wt.%) contents with a low 10,000Ga/Al (1.89) ratio and TZr (670°C). Magmatic zircons have a narrow range of ɛHf(t) values (−2.0 to +4.1) with TDMC ages (2942–2692Ma) older than the formation age, but consistent with the formation age (ca. 2760Ma) of the Lushan SPG suite. The potassic granite has a Hf isotope composition identical to that of the SPG suite and is enriched in LREE and depleted in Y with a positive Eu anomaly, suggesting that the SPG suite is the main source. One zircon yielded an inherited age of 2837±36Ma consistent with the age of the TTG gneisses, indicating that the gneisses could also be the source of the potassic granite. The two types of source rocks indicate a shallow crust depth. Hence the heat required for partial melting of granodioritic rocks to form the potassic granite could have been provided by the upwelling of mantle or mantle-derived melts in an extensional setting. Therefore, the TTG gneisses, SPG suite and potassic granite in the Lushan area record a tectonic transition from a compressive to an extensional setting in the southern margin of the NCC between 2.85 and 2.50Ga.

First Evidence of Lamprophyric Magmatism from the Konya Region, Turkey: a Genetic Link to High‐K Volcanism

AbstractIn the vicinity of Konya (Turkey), mafic, micro‐porphyritic sub‐volcanic rocks intrude into the Mesozoic units, which represents the only example of such a rock type in the region. 40Ar/39Ar dating of two whole rock samples from the sub‐volcanics gave ages of 13.72±0.13 and 12.40±0.11 Ma, suggesting temporal association to the Late Miocene‐Pliocene high‐K calc‐alkaline volcanism in the region. The mineral chemistry and geochemical data permit us to classify the rocks as “minette” lamprophyres. They include diopside and phlogopite phenocrysts in a microcrystalline groundmass composed of sanidine, phlogopite, diopside and titano‐magnetite. Segregation and ocelli‐like globular structures occur commonly in the samples. In terms of major elements, the lamprophyres are calcalkaline, and potassic to ultrapotassic rocks. All the lamprophyres display strong enrichments in LILE (Rb, Ba, K, Sr), radiogenic elements (Th, U) and LREE (La, Ce) and prominent negative Nb, Ta, and Ti anomalies on primordial mantle‐normalized trace element diagrams. Geochemical data suggest that the lamprophyres and high‐K calc‐alkaline rocks in the region derived from a subduction‐modified lithospheric mantle source affected by different metasomatic events. Lamprophyric magmatism sourced phlogopite‐bearing veins generated by sediment‐related metasomatism via subduction, but high‐K calc‐alkaline magmas are possibly derived from a mantle source affected by fluid‐rich metasomatism.

The Mazarrón basin, SE Spain: a study of mineralization processes, evolving magmatic series, and geothermal activity

The Miocene to Present Mazarrón basin provides a window on the metallogenic role of an evolving magmatic series. High-K calc–alkaline magmas gave rise to an important cluster of Pb–Zn–Ag–Cu vein and stockwork deposits emplaced in dacitic to rhyodacitic domes, part of a complex volcanic–metallogenic province (Au, Hg, Pb–Zn–Cu–Ag, Sn) stretching for ∼150 km along the Mediterranean coast of SE Spain. By Pliocene time the former magmatic series had been replaced by intraplate alkaline basaltic volcanism, thus becoming the southern branch of the Western/Central Europe alkaline province. In terms of base metal sulphide deposits, this European province is barren, although it triggered widespread, CO2-rich geothermal activity. Modern geothermal activity at El Saladillo (Mazarrón) resulted in the deposition of carbonate sinter deposits and formation of microbial mats. Proximal facies consist of millimetric to centimetric multicoloured layers of microbial mats, including yellow-orange thin bands of calcified bacteria and mineral growths of aragonite and calcite; green layers of live thermophilic Lyngbya-type cyanobacteria; black, degraded organic matter; and pyrite as the sole sulphide phase. Except for arsenic (37–63 μg g−1), all of the studied trace elements (Ag, Ba, Bi, Cd, Cu, Pb, Sb, Se, and Sn) appear in remarkably low concentrations in the geothermal sinters. This is consistent with compositional data for the El Saladillo waters, with no significant metal concentrations. We present the first conceptual model (Miocene to Present) for the ore-forming processes, magmatism, CO2 degasification, and geothermal activity for this realm. We argue that the time- and space-limited character of this volcanism (small, scattered outcrops), the deep magma emplacement level, the metal sulphide behaviour in alkaline basaltic magmatic chambers, and the dry character of these magmas prevented any metallogenic interaction between the chambers and the much shallower meteoric waters that drove the El Saladillo geothermal system and others of the same kind in Spain and elsewhere in Europe.