I-type Magmas Research Articles

Petrogenesis and tectonic setting of igneous rocks from the Dongbulage porphyry Mo deposit, Great Hinggan Range, NE China: Constraints from geology, geochronology, and isotope geochemistry

The Dongbulage porphyry Mo deposit is a recently discovered deposit located in the Huanggang–Ganzhuermiao polymetallic metallogenic belt of Inner Mongolia, NE China. Here, we present zircon U–Pb ages and Hf isotopic compositions, and whole-rock geochemical and Sr–Nd–Pb isotopic data, for magmatic rocks associated with Mo mineralisation to constrain the age and petrogenesis of these rocks. The rocks are dominated by mineralised granite porphyries, quartz-monzonites, and rhyolite. Zircon U–Pb dating shows that the ore-bearing granite porphyries have ages of 154.4 ± 3.5, 155.4 ± 1.1, and 158.7 ± 0.6 Ma, the quartz-monzonites have ages of 157.8 ± 1.6 and 166.5 ± 1.3 Ma, and the rhyolite has an age of 172.9 ± 3.0 Ma. The granite porphyries and rhyolites are characterised by high K2O and SiO2 contents, enrichment in light rare-earth elements, strong negative Eu anomalies, and pronounced depletion in Ba, Nb, Ta, Sr, P, and Ti. The quartz-monzonites show enrichment in large-ion lithophile elements (Rb and K), are depleted in heavy rare-earth elements, Nb, Ta, Sr, P, and Ti, and exhibit weak negative Eu anomalies. All of the rocks have low initial 87Sr/86Sr (0.7022–0.7064) and εNd(t) values (−3.62 to + 3.99), positive εHf(t) values (+1.1 to + 13.8), and young two-stage Nd and Hf model ages (TC DM(Nd) = 623–1240 Ma and TC DM(Hf) = 305–1108 Ma, respectively). Whole-rock Pb isotopic compositions show a narrow range of values, with 206Pb/204Pb = 18.314–19.116, 207Pb/204Pb = 15.573–15.595, and 208Pb/204Pb = 38.731–39.296, which, together with their Sr–Nd–Hf isotopic compositions, indicate the dominance of a mantle source component. The isotopic data suggest that the Dongbulage magmatic rocks were derived from partial melting of juvenile lower crust. The granite porphyries are highly evolved I-type magmas with geochemical characteristics similar to those of porphyry granitoids associated with Mo mineralisation in the Great Hinggan Range. On the basis of the regional geology and geochemistry, we suggest that the Dongbulage porphyry Mo deposit formed in a subduction setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.

3D distribúcia minerálnych inklúzií v granátoch z lokalít Lesné - Potičky a Beňatinská voda (Slovenská republika)

Visualization of garnets and their mineral inclusions was performed by X-ray microtomography by reconstructing 3D image from 1800 measured 2D X-ray projections. Visualization procedure of 3D distribution of mineral inclusions was based on the different absorption of X-ray radiation between the host garnet and mineral inclusions. 3D visualization provided a realistic picture of a distribution of the 126 identified mineral inclusions in garnet from rhyolite and rhyodacite Beňatinská voda and 21 inclusions in garnet from Lesné - Potičky (Slovak Republic). Composition of garnet from locality Lesné - Potičky is Alm71.0-73.7Prp8.3-9.0Grs14.7-16.6 and from locality Beňatinská voda is Alm72.1-73.2 Prp5.5-5.9Grs18.3-19.4. Mineral inclusions in garnets from locality Lesné - Potičky are represented by fluorapatite, zircon, ilmenite, annite and magmatic melts preserved in the form of glass inclusions trapped in apatite inclusions. Mineral inclusions in garnets from locality Beňatinská voda are represented by fluorapatite, zircon and plagioclase An78.53-57.12. Chemical composition of zircons and fluorapatites are similar from both localities. Based on the chemical composition, the high-pressure origin of garnets associated with I-type magmas was confirmed.

Nd isotope mapping of a Pinwarian-age composite arc belt in the Quebecia terrane of the central Grenville Province, Canada

There continues to be confusion in the geological community concerning the ages of crustal formation and crustal accretion within the central Grenville Province of Quebec. To clarify the geological history of crustal growth in the eastern part of the Quebecia terrane, sixty new Nd isotope analyses are presented from a 60,000 km2 area northwest of Baie Comeau. Most samples yield Pinwarian Nd model ages that suggest them to be derived from juvenile oceanic arc terranes. However, two large slivers with Paleoproterozoic TDM ages attest to the existence of hidden blocks of old crust, which divide the area of juvenile Pinwarian crust into a composite arc belt of smaller accreted terranes. The old crustal blocks probably do not reach the present surface, but represent an igneous crustal protolith of younger I-type magmatism. By comparison with a Mesozoic tectonic analogue, it is proposed that accreted juvenile arc crust with attached slivers of older crust were rifted away from an active margin to the west, and translated eastwards until blocked by the previously accreted Labradoria terrane. Although the Quebecia composite arc belt consists of over 95% of Pinwarian juvenile arc crust, the age of arc accretion was post-Pinwarian. The proposed oblique nature of the accretion process may explain the lack of a major collisional orogen at that time. This paper shows the usefulness of large-scale Nd isotope mapping of Precambrian crustal terranes to clarify complex processes of crustal formation and arc accretion.

Eocene I-type magmatism in the Eastern Pontides, NE Turkey: insights into magma genesis and magma-tectonic evolution from whole-rock geochemistry, geochronology and isotope systematics

ABSTRACT The Eastern Pontides orogenic belt in NE Turkey hosts numerous I-type plutons of Eocene epoch. Here, we report new U–Pb SHRIMP zircon ages and in situ zircon Lu-Hf isotopes along with bulk-rock geochemical and Sr-Nd-Pb-O isotope data from the Kemerlikdağı, Aydıntepe and Pelitli plutons and mafic microgranular enclaves (MMEs) to constrain their parental melt source(s) and evolutionary processes. U-Pb SHRIMP zircon dating yielded crystallization ages between 45 and 44 Ma for the studied plutons and their MMEs. The plutons range from gabbro to granite and have I-type, medium to high-K calc-alkaline, and metaluminous to slightly peraluminous characteristics. On the primitive mantle-normalized multi-trace-element variations, the plutons and their MMEs are characterized by significant enrichment in LILE/HFSE. Chondrite-normalized REE patterns of the plutons and their MMEs are close to each other and show moderate enrichment with variable negative Eu anomalies. The studied plutons have fairly homogeneous isotope composition (87Sr/86Sr(i) = 0.70502 to 0.70560; εNd(i) = +0.9 to – 1.4; δ18O = +5.0 to +8.7‰, εHf(i) = – 2.2 to +13.5). The MMEs show medium to high-K calc-alkaline and metaluminous character. Although the isotope signatures of the MMEs (87Sr/86Sr(i) = 0.70508 to 0.70542; εNd(i) = +0.9 to −1.1; δ18O = +5.8 to +8.0, εHf(i) = +4.3 to +10.4) are very similar to those of the host rocks. Fractionation of plagioclase, amphibole, pyroxene and Fe-Ti oxides played an important role in the evolution of the plutons. The isotopic composition of the studied plutons and MMEs are similar to I-type plutons derived from mantle sources. The MMEs show incomplete magma mixing/mingling, representing small bodies of mafic parental magma. The parental magma(s) of the studied plutons were generated from the enriched lithospheric mantle and then modified by fractional crystallisation, and lesser assimilation and mixing/mingling in the crustal magma chambers.

Mineral and bulk–rock chemistry of Shadli bimodal metavolcanics from Eastern Desert of Egypt: Implication for tectonomagmatic setting and Neoproterozoic continental growth in the Arabian–Nubian Shield

The Neoproterozoic Shadli metavolcanics in the Eastern Desert of Egypt have been conventionally categorized as a bimodal island-arc association. The present study deals with Shadli metavolcanics of three areas: Hamama in the central and Darhib and Atshan in the southern Eastern Desert of Egypt. They contain both mafic and felsic compositions and display a bimodal nature. Geochemical classification indicates that the mafic end-members are tholeiitic basalt and basaltic andesite whereas the felsic ones comprise calc-alkaline dacite and rhyolite.Mafic end-members show flat to slightly LREE-depleted patterns comparable to normal MORB produced from a depleted mantle source. Major element data indicates affinity to arc-related non-cumulative mafic rocks. The obvious negative Nb and positive Pb anomalies, the nearly flat REE patterns together with pyroxene chemistry are characteristic of island-arc tholeiitic suite. Accordingly, we suggest that their primary magma was derived from partial melting of a depleted mantle source metasomatized by subduction-related slab fluids/melts.Felsic end-members exhibit magnesian character consistent with a relatively hydrous, oxidizing magma and subduction-related source. Their weakly peraluminous character and calc-alkalic to calcic compositions are characteristics of arc-related magmas. Moreover, the negative Nb and Ti anomalies suggest an influx of subduction-related slab fluids/melts. Their SiO2 contents are too high to represent magmas directly derived by partial melting of a mantle source. So, the high SiO2 and Al2O3 and the low MgO contents suggest melting crustal source. The high Y/Nb ratios (> 1.2) confirm that they were generated from crustal source. Actually, their Ce/Pb ratios (average of 2.66) are affiliated to those of continental crust and contrast typical mantle values. The weakly peraluminous and sodic nature is a typical feature of I-type magma. Therefore, their magmas were most likely derived by partial melting of thickened low-K mafic lower crust.Several lines of evidence let us speculate a genetic relationship between mafic and felsic end-members and that the felsic rocks were possibly evolved from the mafic melts that derived from metasomatized mantle. These comprise the close proximity and a coeval nature; the subalkaline character with approximately continuous trend; the similarity of trace element patterns; the arc-like signature, and the well fitness of major element data of the felsic rocks with melts derived from low-K mafic lower crust. The general tendency of silica increase with alkalis from mafic to felsic end-members may indicate that the felsic rocks were generated by fractional crystallization processes of the mafic magmas in the area.

Crustal reworking at convergent margins traced by Fe isotopes in I-type intrusions from the Gangdese arc, Tibetan Plateau

Voluminous magmatism at active continental margins and collision zones is marked by I-type intrusions. Paleocene-Eocene intrusions, exposed in the Lhasa terrane of the Tibetan Plateau, are part of the Gangdese arc that operated during Neo-Tethyan ocean subduction and subsequent India-Asia collision. Arc-like geochemical trace element signatures and radiogenic isotope systematics are indicative of juvenile I-type magmatism with variable silica contents consequent to igneous differentiation. Here, we present the first Fe isotope data for this fossil arc terrane, which have highly variable δ57Fe values (relative to IRMM-014) of −0.05 to +0.57‰. The data show no obvious correlations with major and trace element systematics, except for highly evolved rocks with >70 wt% SiO2. Based on trace element systematics, deuteric fluid exsolution is excluded as a cause for the isotope variations in less evolved rocks. Furthermore, there is no apparent relation between Fe isotope values and the established tectonic evolution from syn- to post-collisional magmatism. Comparison with I-type granites of the Australian Lachlan Fold Belt and Cordilleran Snake River Plain reveals an, on average, lighter δ57Fe in the Gangdese suite in primitive lavas, yet distinctively heavier than intra-oceanic arcs. The heavier δ57Fe values for primitive Lachlan Fold Belt and Snake River Plain rocks are interpreted here as crustal contribution in the form of S-type magmas derived from crustal anatexis, which are absent in the Gangdese arc. Gangdese Belt data yield an average δ57Fe of +0.13 ± 0.02‰ (2σ), which is proposed as the best estimate for juvenile crust at active continental margins.Rhyolite-MELTS modelling suggests that the Gangdese Belt data can be reproduced through fractional crystallization along a liquid line of descent at oxygen fugacity between FMQ = 0 to +2, typical for arc-related melts. Crucially, the majority of data is coherent with partial melts of existing mafic crust as the major contributor to the juvenile component in the intrusions, with minor mantle-derived melts, evidenced through heavier primitive Fe isotopes. This indicates that for the Gangdese Belt samples, the primitive, parental melts are derived from lower crustal successions through predominantly crustal reworking with only subordinate crustal growth. Hence, the Fe isotope data indicates a two-step evolution with melting of underplated mafic material sometime in the geologic past. Although juvenile in nature, these successions are part of the existing crust, supporting scenarios in which crustal reworking in convergent margin intrusions is an important process in evolved magma generation.

Late Cretaceous I- and A-type magmas in eastern Turkey: Magmatic response to double-sided subduction of Paleo- and Neo-Tethyan lithospheres

We provide geochronological (zircon UPb) and geochemical data (whole rock major and trace elements, Sr-Nd-Pb isotopes, mineral compositions, zircon trace elements) for Late Cretaceous I- and A-type granitoids and associated gabbros from three areas (Dereli, Şebinkarahisar, Divriği), along a north-south traverse in eastern Turkey from the northern part of the Eastern Pontides Orogenic Belt to the Anatolide-Tauride Block, and from two locations (Sökmen and Pırnallı) that are situated away from the traverse line. Our aim is to interpret the tectonic environment in which the granitoids formed. Late Cretaceous plutonic activity began ~ 90 Ma and continued uninterruptedly for about 20 my. The Dereli suite and the Asarcık intrusion at Şebinkarahisar are I-type granitoids; the others are A-type granitoids. The A-type classification of these rocks is ambiguous; they are A-typerelative to other coeval granitoids in eastern Turkey. The Şebinkarahisar, Murmana (Divriği), and Pırnallı granitoids evolved primarily by closed-system fractional crytallization. At Şebinkarahisar, I- and A-type intrusions are isotopically indistinguishable, and must share the same source. Open system, AFC processes affected the other granitoids. Crustal components contributed to all of the granitoids. The Dereli granitoids have an old component (1.2 < TDM < 1.75 Ga) that is unusual among Turkish igneous rocks. No mantle component is recognizable in the A-type granitoids, but the low SiO2 content of some granitoids requires a mantle-derived component. Arc-like geochemical features may be inherited from a mid-crustal source component, in addition to contributions from the arc environment active at the time of magmatism. A petrogenetic relation cannot be demonstrated between the Divriği gabbros and their contemporaneous granitoids. The gabbros require a subcontinental lithospheric mantle source. Trace elements in zircon track fractional crystallization paths within suites, and faithfully map the arc-related petrogenesis of the granitoids, but do not mirror trace element distributions in zircons from other A-type suites. Available data indicate that Late Cretaceous plutonic activity began at about ~90 Ma in both the northern part of the Eastern Pontides Orogenic Belt and the southern part of the Anatolide-Tauride Block. Magma compositions began to change at ca. 80 Ma, and transformed successively into high-K I-type and shoshonitic A-type activity, and magmatism continued until ~ 70 Ma. We interpret this 20 my interval to be the subduction-dominated, arc-construction phase in the Eastern Pontides. The distribution of I-type magmas in eastern Turkey is best explained by double-sided, initially shallow-angle subduction of Paleo- and Neo-Tethyan lithospheres, with subsequent steepening of the subducted slabs leading to an extensional regime and the generation of A-type magmas. This hypothesis also explains the origin of Late Cretaceous I- and A-type Central Anatolian granitoids.

Generation of I-type granitic rocks by melting of heterogeneous lower crust

[Extract]: Granite generation is a fundamental process for the growth and evolution of Earth’s continental crust. I-type granitic rocks, nominally derived from infracrustal sources, are the most common granite type and are voluminously emplaced in convergent margin settings. A puzzling feature is that many I-type granites show isotopic evidence for reworking of older supracrustal material, in conflict with the I-type designation. How the supracrustal component was incorporated by I-type magmas is a matter of deduction, particularly given difficulties in recognizing the putative infracrustal source region in the exposed geology. We report a case study of I-type granitic magma generation by hybridization between metasedimentary-derived partial melt and intercalated mafic granulite units during extraction of silicic magma from the lower crust in the Hidaka Metamorphic Belt (HMB), Japan (Hammerli et al., 2018). Isotopic data (Nd, Hf, O) obtained by microanalysis of accessory minerals in former melt networks (leucosomes) suggest that hybridization operates on a (sub-) grain scale, where repeated injections of externally derived melt attempt to approach local equilibrium with the host mafic granulites during transfer through complex melt pathways (see our figure 3; and also Hasalova et al. [2011] and references therein).

Co-development of Jurassic I-type and A-type granites in southern Hunan, South China: Dual control by plate subduction and intraplate mantle upwelling

Two types of spatially and temporally associated Jurassic granitic rocks, I-type and A-type, occur as pluton pairs in several locations in southern Hunan Province, South China. This paper aims to investigate the genetic relationships and tectonic mechanisms of the co-development of distinct granitic rocks through petrological, geochemical and geochronological studies. Zircon LA-ICPMS dating results yielded concordant U–Pb ages ranging from 180 to 148 Ma for the Baoshan and Tongshanling I-type granodiorites, and from 180 to 158 Ma for the counterpart Huangshaping and Tuling A-type granites. Petrologically, the I-type granodiorites consist of mafic minerals such as hornblende whereas the A-type granites are dominated by felsic minerals (e.g., quartz, K-feldspar and plagioclase). Major and trace element analyses indicate that the I-type granodiorites have relatively low SiO2 (64.5–71.0%) and relatively high TiO2 (0.28–0.51%), Al2O3 (13.8–15.5%), total FeO (2.3–4.7%), MgO (1.3–2.6%) and P2O5 (0.10–0.23%) contents, and the A-type granites are characterized by high concentrations of Rb (212–1499 ppm), Th (18.3–52.6 ppm), U (11.8–33.6 ppm), Ga (20.0–36.6 ppm), Y (27.1–134.0 ppm) and HREE (20.3–70.0 ppm), with pronounced negative Eu anomalies (Eu/Eu* = 0.01–0.15). Moreover, the I-type granodiorites are classified as collision-related granites emplaced under a compressional environment, whereas the A-type granites are within-plate granites generated in an extensional setting. Zircon Hf isotopic compositions vary substantially for these granitic rocks. The I-type granodiorites are characterized by relatively young Hf model ages (TDM1 = 1065–1302 Ma, TDMC =1589–2061 Ma) and moderately negative εHf(t) values (–5.9 to –11.5), whereas the A-type granites have very old model ages (TDM1 = 1454–2215 Ma, TDMC = 2211–2974 Ma) and pronounced negative εHf(t) values (–15.8 to –28.3). These petrochemical and isotopic characteristics indicate that the I-type granodiorites may have been derived from a deep source involving mantle-derived juvenile (basaltic) and crustal (pelitic) components, whereas the A-type granites may have been sourced from melting of meta-greywacke in the crust. This study proposes that the pressure and temperature differences in the source regions caused by combined effects of intra-plate mantle upwelling and plate subduction are the major controlling factors of the co-development of the two different types of magmas. Crustal anatexis related to lithospheric delamination and upwelling of hot asthenosphere under a high pressure and temperature environment led to the formation of the I-type magmas. On the other hand, the A-type magmas were formed from melting of the shallower part of the crust, where extensional stress was dominant and mantle-crust interaction was relatively weak. Rifts and faults caused by mantle upwelling developed from surface to depth and successively became channels for the ascending I- and A-type magmas, resulting in the emplacement of magmas in adjacent areas from sources at different depths.

Early Cretaceous diorites in the Kenbale Cu mineralization occurrence, Tibet, China, and its geological significance

The Kenbale Cu mineralization occurrence related to the diorite is a newly discovered Cu mineralization event in the Bangong-Nujiang metallogenic belt, Tibet, China. The Cu mineralization is hosted in the contact between the monzogranite or biotite quartz diorite and the fine-grained diorite, which is the mineralization related intrusion. In order to constrain the Kenbale mineralization age, petrogenesis and tectonic setting, we conducted LA-ICP-MS zircon U-Pb dating and Hf isotopic analyses of the biotite quartz diorite and fine-grained diorite and also the whole-rock geochemical study of the biotite quartz diorite. Zircon UPb dating show that weighted mean 206Pb/238U ages of the biotite quartz diorite and fine-grained diorite are 123.5 ± 1.9 Ma (MSWD = 2.3, n = 16) and 118.9 ± 1.3 Ma (MSWD = 2.5, n = 18), respectively. The biotite quartz diorite is a high-K calc-alkaline I-type magma rock and was controlled mainly by partial melting process during the magma formation and evolution. This intrusion is characterized by positive eHf(t) values (2.6 to 5.8) and old Hf crustal model ages (813 to 1016 Ma), indicating that the magma was sourced from partial melting of the Mesoproterozoic to Neoproterozoic juvenile crust of the northern Lhasa Terrane. Compared with the biotite quartz diorite, the mineralization associated fine-grained diorite has much higher zircon eHf(t) values (8.2 to 11.4) and younger Hf crustal model ages (450 to 650 Ma). These characteristics are similar with those of the coeval magmatic rocks induced by slab break-off of the southward subducted Bangong-Nujiang Ocean. The geochronology and geochemical results show that the Kenbale Cu mineralization was controlled by the slab break-off of the southward subducted Bangong-Nujiang Ocean.

Geochemistry of garnet in pegmatites from the Boroujerd Intrusive Complex, Sanandaj-Sirjan Zone, western Iran: implications for the origin of pegmatite melts

Pegmatite-hosted garnets from four localities in the Boroujerd region, Lorestan (Western Iran), have been analysed for major and selected trace element compositions. The mineral assemblage of the granitic pegmatites is primarily quartz, plagioclase (albite), and alkali feldspar (orthoclase-microcline), as well as garnet, muscovite, fluorapatite, tourmaline (schorl-foitite), andalusite and zircon. The mineralogical and geochemical characteristics of the pegmatites indicate that they are peraluminous to slightly metaluminous I-type granites. Based on mineral assemblages and whole-rock geochemistry, the pegmatites are classified as muscovite-type pegmatites. Electron-probe micro-analysis reveals that garnets have concentric compositional zoning and are almandine-spessartine solid solutions with lesser pyrope, grossular and andradite components. Concentric zoning of major elements in the garnet is attributed to magmatic growth from a melt. On a MnO + CaO versus FeO + MgO (wt%) plot, the composition of garnet is consistent with crystallisation from weakly to moderately evolved melts. The garnets from the Boroujerd pegmatites are characterised by decreasing Y, HREE, Ti, Zr, Nb, Ta, Hf, and U abundances from core to rim. The garnets also have high chondrite normalized HREE abundances with nearly flat patterns (YbN/SmN = 0–508), lower LREE contents, and negative Eu anomalies (Eu/Eu* < 0.3). Variation in these elements from core to rim is attributed to increasing magma fractionation. The composition and major and trace element zoning patterns in the garnet of the Boroujerd pegmatites are compatible with a magmatic origin and crystallisation from variably fractionated I-type magmas demonstrating that garnet crystal-chemistry is an important tool for deciphering the origins of pegmatite magmas.

Hybridization between I-type and S-type granites in the Ordovician Famatinian magmatic arc, Tafí del Valle, Tucumán, NW Argentina.

In the Tafi del Valle region, in northwestern Argentina, several intrusive bodies of lower Paleozoic age were emplaced in the metasedimentary Puncoviscana Formation, belonging to the Sierras Pampeanas. Four intrusive bodies outcrop in the study area: La Ovejeria, El Infiernillo, Loma Pelada and Los Cuartos. La Ovejeria and El Infiernillo intrusive bodies represent the I-type magmatism according to their major element contents and show cotectic evolutions similar to those described by Famatinian I-type batholiths. These moderately peraluminous adakitic trondhjemites have characteristic high Sr/Y ratios and low Fe 2 O 3 +MgO+MnO+TiO 2 contents. They are related to high-pressure conditions at the source, where dehydration melting of basaltic rocks may be involved and garnet is retained in the residue leading to generation of HREE depleted melts. The Loma Pelada granites show characteristics of S-type magmatism (low CaO and MgO, and high SiO 2 and K 2 O contents) typical of granites segregated in the last stages of magmatic differentiation, or anatectic granites. They show an increasing peraluminosity due to garnet entrainment and they are related to the anatectic melts generated in the Puncoviscana Formation. Both the Loma Pelada and Los Cuartos granitoids include samples with intermediate geochemical characteristics that range between those of the El Infiernillo and La Ovejeria and the regional metasedimentary rocks. These characteristics could be explained by assimilation processes involving the I-type intrusive magmas and the metasedimentary host rocks or by hybridization processes between trondhjemitic I-type magmas as La Ovejeria and El Infiernillo and anatectic S-type melts.

Latest Cretaceous “A2-type” granites in the Sakarya Zone, NE Turkey: Partial melting of mafic lower crust in response to roll-back of Neo-Tethyan oceanic lithosphere

An integrated study of comprehensive geochronological, geochemical, and Sr-Nd-Hf isotopic data was undertaken for the A-type Topcam pluton that intruded within the Sakarya Zone (NE Turkey) with the aims of elucidating its origin and tectonic significance and gaining new insights into the generation of aluminous A-type granites. New LA-ICP-MS zircon U-Pb crystallization ages of 72 and 73Ma indicate emplacement in the Late Cretaceous time, just after extensive metaluminous I-type magmatism in the area. The pluton consists mainly of alkali feldspar, quartz, plagioclase, amphibole, and biotite with accessory minerals such as magnetite, apatite, and zircon. The outcrop is composed of granite, syenite, monzonite, and quartz monzonite and possesses a wide range of SiO2 content (57–70wt%) with elevated Ga/Al ratios and low Mg# (mostly <43). The pluton is metaluminous to weakly peraluminous, with aluminium saturation index (ASI) (molar Al2O3/[CaO+K2O+Na2O]) values of 0.82 to 1.18, and belongs to the shoshonitic and ultra-potassic series. All the samples exhibit relative enrichment in light rare earth elements (LREE) and significant negative Eu (Eu/Eu*=0.31 to 0.86) anomalies on the chondrite-normalized REE diagram. The rocks are enriched in some large ion lithophile elements (e.g., Rb, Th and Ba), and spidergrams show a relative depletion in Nb, Ti, and Sr. The granitic rocks of the pluton have identical 87Sr/86Sr(i) ratios ranging from 0.70518 to 0.70716, relatively low εNd (t) values varying from −5.5 to −0.4, and TDM ages (0.82–1.19Ga). In situ zircon analyses show that the rocks have variable negative and positive εHf (t) values (−5.5 to 5.9) and Hf two-stage model ages (742 to 1468Ma), which are indicative of minor addition of juvenile material. Sr-Nd isotope modelling suggests mixing of 70–90% of lower crustal-derived melt with ~10–30% of mantle-derived melt at lower crust depths. The heat source for partial melting is provided by upwelling of hot asthenosphere triggered by slab roll-back events. Geochemical and isotopic data reveal that metaluminous A2-type granites were derived from partial melting of the Paleozoic lower continental crust dominated by mafic rocks in amphibolitic composition, with minor input of subcontinental lithospheric mantle-derived magma followed by subsequent limited fractional crystallization to generate a variety of rock types. From integrating all available data with the regional tectonic evolution in the Sakarya Zone and adjacent regions, we attribute generation of aluminous A2-type granites to a back-arc extension in the subduction zone, which is induced by the roll-back of the Neo-Tethyan oceanic slab around 72Ma. Consequently, we conclude that these A-type granites were related to intensive extension tectonic, which peaked during the late Cretaceous (Maastrichtian) in response to the roll-back of the Neo-Tethyan oceanic slab, which is indicative of the final-stage subduction-related magmatism in the Sakarya Zone.

Petrogenesis of Jurassic granitoids in the west central Lhasa subterrane, Tibet, China: the Geji example

ABSTRACTThe Jurassic magmatic and volcanic rocks are widespread along the west central Lhasa subterrane. However, the petrogenesis of these rocks is poorly understood because of lacking high-quality geochronology and geochemical data. Here, we present new zircon U–Pb age and Hf isotopic data, whole-rock geochemical and Sr–Nd–Pb isotopic data for the Songduole and Qiangnong plutons in Geji area. LA-ICP-MS dating of zircon yield crystallization ages of 172.1 ± 1.9 and 155.9 ± 1.2 Ma for the Songduole and Qiangnong plutons, respectively. Geochemically, Songduole and Qiangnong granodiorite are characterized by high MgO (2.63–3.49 wt%), high Mg# (49–50), and low TiO2 (0.48–0.57 wt%). Besides, all rocks show metaluminous, calc-alkaline signatures, with strong depletion of Nb, Ta, and Ti, enrichment of large-ion lithophile (e.g. Rb, Th, K), and a negative correlation between SiO2 and P2O5. All these features are indicative of arc-related I-type magmatism. Five samples from the Songduole granodiorite have whole rock (87Sr/86Sr)i of 0.71207–0.71257, εNd(t) values of −15.1 to −13.9, zircon εHf(t) values of −17.4 to −10.5, (206Pb/204Pb)t ratios of 18.402–18.854, (207Pb/204Pb)t ratios of 15.660–15.736, and (208Pb/204Pb)t ratios of 38.436–39.208. Samples from the Qiangnong granodiorite have (87Sr/86Sr)i of 0.71230–0.71252, εNd(t) values of −15.1 to −14.2, zircon εHf(t) values of −12.6 to −6.4, (206Pb/204Pb)t ratios of 18.688–18.766, (207Pb/204Pb)t ratios of 15.696–15.717, and (208Pb/204Pb)t ratios of 38.546–39.083. These geochemical signatures indicate that the two plutons most likely originated from partial melting of the ancient Lhasa lower crust with obvious inputs of mantle-derived melts. Combined with regional geology, our results indicate that the Jurassic magmatism in the west central Lhasa subterrane most likely resulted from the southward subduction of the Bangong Ocean lithosphere beneath the central Lhasa terrane.

Formation of Hadean granites by melting of igneous crust

The oldest known samples of Earth, with ages of up to 4.4 Gyr, are detrital zircon grains in meta-sedimentary rocks of the Jack Hills in Australia. These zircons offer insights into the magmas from which they crystallized, and, by implication, igneous activity and tectonics in the first 500 million years of Earth’s history, the Hadean eon. However, the compositions of these magmas and the relative contributions of igneous and sedimentary components to their sources have not yet been resolved. Here we compare the trace element concentrations of the Jack Hills zircons to those of zircons from the locality where igneous (I-) and sedimentary (S-) type granites were first distinguished. We show that the Hadean zircons crystallized predominantly from I-type magmas formed by melting of a reduced, garnet-bearing igneous crust. Further, we propose that both the phosphorus content of zircon and the ratio of phosphorus to rare earth elements can be used to distinguish between detrital zircon grains from I- and S-type sources. These elemental discriminants provide a new geochemical tool to assess the relative contributions of primeval magmatism and melting of recycled sediments to the continents over geological time. The formation process for the oldest mineral grains on Earth has remained elusive. A comparison of trace element concentrations of these ancient zircons with known material suggests melting of igneous crust as their source.

The auriferous ore mineralization and its zonal distribution around the Variscan Kłodzko-Złoty Stok granitoid pluton in the Sudetes (SW Poland) – an overview

Due to a low level of erosion the Variscan (Carboniferous–Mississippian) Klodzko–Zloty Stok (KZS) granitoid pluton and its metamorphic rock cover are unique examples of the ore mineralisation distribution pattern around a pluton. The KZS pluton formed from I-type magmas. It is composed mostly of high-K, metaluminous, biotite- and hornblende-rich granitoids of various compositions ranging from granodiorite to monzonite. The ore mineralisation in the KZS shows specific zonation that reflects interaction between post-magmatic mineralising fluids and country rocks of different composition. In the KZS pluton and its surroundings the mineralisation reveals high-temperature Ti-W oxides and As-Fe sulphide-arsenides plus Fe-oxides which are replaced outwards by Cu-Fe-Pb-Zn sulphides and subsequently, in the marginal parts of the pluton, by the Pb-Sb-Fe sulphide mineralisation. The specific elements and the isotopic composition of sulphur in ore minerals indicate that the metal-bearing postmagmatic-metamorphic hydrothermal fluids, despite their strong affinities to the KZS hybrid magmatic fluids, show also an influence of variable composition of country rocks. Variable alteration processes: hornfelsitisation, skarnisation, dolomitisation, serpentinitisation, pyroxenisation, biotitisation, K-feldspatisation, silicification, berezitisation, carbonatisation, prehinitisation, chloritisation, epidotisation, sericitisation, albitisation and sulphidisation developed along contacts of various rock types within the country rocks. In more fractured zones, transported elements were preferentially trapped by calcareous (Ca-rich) metamorphic rocks. Moreover, along the direct contact between granitoids and calcareous rocks a high temperature auriferous skarns with magnetite-pyrrhotite or/and lollingite-arsenopyrite mineralisation were formed. There are positive correlations between organic matter and Fe 2 O 3 and MgO contents in skarns, suggesting remobilization of organic matter by hydrothermal fluids released during serpentinisation. The organic matter and carbonate samples have very variable δ 13 C and δ 18 O values. Most probably these are the result of isotopic re-equilibration between minerals under high temperatures. On the intimate contact of granitoids with less permeable amphibolitic hornfelses a high temperature titanite-scheelite mineralisation of veinlet-impregnation type occurred, while thermal and metasomatic alteration of the enveloping more permeable sandstones developed away from direct contact with granites, causing the formation of pyrite-rich beresites. As a rule, different types of sulphide ore mineralisation contain refractory gold captured by arsenopyrite, lollingite and/or pyrite. Moreover, the formation of contact-metasomatic ore mineralisation was accompanied by ore precipitation in veins and stockworks at a wide temperature range from 480 to 150°C during early and late fracturing stages. The younger stages also revealed variable concentration of gold. All those observations strongly indicate that the whole KZS pluton and its aureole was fertile in gold.

Geochronology, geochemistry, and Sr–Nd–Pb isotopes of Cretaceous granitoids from western Tibet: petrogenesis and tectonic implications for the evolution of the Bangong Meso-Tethys

New zircon U–Pb age data, whole-rock major and trace elemental data, and Sr–Nd–Pb isotopic data of granitoids from the Woruo and Bailong areas in the southern margin of the Qiangtang Block (western Tibet, China) provide important evidence for northward subduction of the Bangong Meso-Tethyan oceanic lithosphere. Five granitoid samples are dated at 120.7–112.7 Ma. These granitoids mostly belong to calc-alkaline and high-K calc-alkaline series, and show strong enrichments in large-ion lithophile elements (e.g. Rb, Ba, and Th), depletions in Nb and Ta, and negative correlations between P2O5, TiO2, MgO, and SiO2 contents, consistent with the evolution trend of I-type magmas. The samples are characterized by a wide range of Sr–Nd–Pb isotopic compositions (initial εNd values from −0.06 to 5.84, initial 87Sr/86Sr from 0.704458 to 0.705596, (206Pb/204Pb)0 from 18.5436 to 19.2465, (207Pb/204Pb)0 from 15.6115 to 15.6712, and (208Pb/204Pb)0 from 38.6427 to 39.6942). The trace elemental and Sr–Nd–Pb isotopic data suggest that these samples are derived from a mixture of lower crust and mantle materials. Together with the published data, these Early Cretaceous magmatic rocks represent a continental arc setting formed by the northward subduction of the Bangong Meso-Tethys during the Early Cretaceous (120–112 Ma).

How tectonics controlled post-collisional magmatism within the Dinarides: Inferences based on study of tectono-magmatic events in the Kopaonik Mts. (Southern Serbia)

In this study, we report evidence about coupling between tectonic and magmatic processes in a complex orogenic system. The study focuses on the Kopaonik Mts. situated between the Dinarides and the Carpatho-Balkanides (Southern Serbia), and a perfect area for investigating tectono-magmatic evolution. We combine a new data set on tectonic paleostress tensors with the existing information on Cenozoic magmatic rocks in the wider Kopaonik Mts. area. The paleostress study revealed the presence of four brittle deformational phases. The established link between fault mechanism and igneous processes suggests that two large tectono-magmatic events occurred in this area. The Late Eocene–Early Miocene tectono-magmatic event was generally characterized by transpressional tectonics that provided conditions for formation of basaltic underplating and subsequent lower crustal melting and generation of I-type magmas. Due to predominant compression in the first half of this event, these magmas could not reach the upper crustal levels. Later on, limited extensional pulses that occurred before the end of this event opened pathways for newly formed mantle melts to reach shallower crustal levels and mix with the evolving I-type magmas. The second event is Middle–Late Miocene in age. It was first associated with clear extensional conditions that caused advancing of basaltic melts to mid-crustal levels. This, in turn, induced the elevation of geotherms, melting of shallow crust and S-type granite formation. This event terminated with transpression that produced small volumes of basaltic melts and finally closed the igneous scene in this part of the Balkan Peninsula. Although we agree that the growth of igneous bodies is usually internally controlled and can be independent from the ambient structural pattern, we have strong reasons to believe that the integration of regional scale observations of fault kinematics with crucial petrogenetic information can be used for establishing spatial–temporal relationships between brittle tectonics and magmatism.

Geochronology and geochemistry of granitoids related to the giant Dahutang tungsten deposit, middle Yangtze River region, China: Implications for petrogenesis, geodynamic setting, and mineralization

Porphyry and skarn deposits in the middle Yangtze Valley within the Northern Yangtze Craton have a combined tungsten resource of ~3milliontonnes (Mt) and represent one of the most important tungsten regions in the world. The Dahutang porphyry tungsten deposit, with reserves of >1Mt, is one of the largest deposits. Uranium–Pb analyses for the ore-related granitoids yield ages of 147.4±0.58Ma–148.3±1.9Ma for porphyritic biotite granite, 144.7±0.47Ma–146.1±0.64Ma for fine-grained granite, and 143.0±0.76Ma–143.1±1.2Ma for granite porphyry, a progressive youngling of ages that is consistent with field observations. Geochemical data show that the three types of granite are characterized by enrichments in Rb, Pb, and U, and depletion in Ba, Nb, P, and Ti, with ASI [molar Al2O3/(CaO+Na2O+K2O)]>1.1 that is characteristic of a peraluminous melt. The P2O5 contents of the granites are 0.13–0.37% and have a positive correlation with SiO2, and they are thus S-type intrusions. They exhibit initial 87Sr/86Sr of 0.721 to 0.731 and εNd(t) of −5.06 to −7.99 for porphyritic biotite granite, 0.7196 to 0.7289 and −6.29 to −6.74 for fine-grained granite, and 0.7153 to 0.7365 and −5.09 to −7.64 for granite porphyry. Chondrite-normalized rare earth element (REE) patterns for the granites are characterized by enrichment in the light REE and a strong negative Eu anomaly, indicating that they were derived from the Proterozoic pelitic and psammitic basement strata and experienced strong fractional crystallization of plagioclase. Our ca. 150–140Ma age for the Dahutang S-type magmatism and W mineralization is identical to that of the I-type magmatism related to Cu–Au–Mo–Fe-bearing porphyry and skarn deposits along the middle to lower Yangtze River Valley. We propose that the latest Jurassic to earliest Cretaceous granitoids and ores formed during a tearing of the subducting Izanagi slab, which caused the upwelling of asthenosphere and resulting mantle–crust interaction. The S-type granitoids and related W ore systems resulted from the re-melting of the Proterozoic crust, whereas the I-type granitic rocks and related ores are attributed to the partial melting of the subducted slab.

Geochronology, geochemistry, and zircon Hf isotopic compositions of Mesozoic intermediate–felsic intrusions in central Tibet: Petrogenetic and tectonic implications

Abstract Mesozoic intermediate–felsic intrusions are widely distributed in the southern Qiangtang terrane, central Tibet. Zircon U–Pb dating shows that these intrusions formed in two periods in the Jurassic (169–150 Ma) and Cretaceous (127–113 Ma). They mostly belong to the high-K calc-alkaline series, and show strong enrichments in large ion lithophile elements (e.g., Cs, Rb, and K), depletions in Nb, Ta, and Ti, and negative Ba anomalies on primitive mantle-normalized diagrams. P2O5 contents decrease with increasing SiO2 content, and Th contents increase with increasing Rb content, consistent with the evolution trend of I-type magmas. These intrusions show a wide range of zircon eHf(t) values from − 19.4 to 11.2, including in rocks with similar SiO2 contents, suggesting variable contributions from mantle and Qiangtang crustal sources. Fine-grained mafic to intermediate igneous enclaves in Jurassic intrusions have similar zircon U–Pb ages and similar or slightly higher zircon eHf(t) values to the host rocks, suggesting that the enclave magmas were derived from mixed magmas at depth and injected into more evolved magmas in upper crustal magma chambers. Magma mixing is also supported by the wide range of zircon Hf isotopic compositions (eHf(t) = − 19.4 to 2.5) from within individual Jurassic and Cretaceous intrusions, and Jurassic enclaves. The Jurassic–Cretaceous magmas likely formed in a continental arc setting during subduction of the Bangong–Nujiang ocean between 170 and 110 Ma, and evolved in the upper plate crust by MASH processes.