Quartz Monzonite Research Articles

High- and low-Mg adakitic rocks in southern Tibet: Implication for the crustal thickening and geodynamic process in the late Cretaceous

The history of crustal thickening is critical for comprehending the evolution process of the Tibetan plateau. The genetic relationship and spatiotemporal distribution of adakitic rocks with high Sr/Y, (La/Yb) N ratios may impose fundamental constraints on specific geodynamic and crustal thickening processes. The Songka intrusive suite consists of adakitic rocks with high-Mg adakite (monzonites), low-Mg adakitic rocks (quartz monzonites), and gabbroic-diorites. Their geochemical characteristics, petrogenesis, and geodynamic implication is discussed in this paper. Songka high-Mg adakites formed when subducting Neo-Tethyan oceanic slab melts were assimilated by mantle peridotite at elevated temperatures (average Ti-in-zircon temperatures of sample SK1319 are 830 °C). Low-Mg adakitic rocks exhibit markedly different geochemical characteristics than those formed in the juvenile thickened lower crust. The least-squares mass balance and trace element simulations indicate that Songka low-Mg adakitic samples were formed at a degree of 60–65% fractional crystallization of melts resembling Songka high-Mg adakites. Songka gabbroic diorites are formed in the metasomatic mantle wedge. The genetic relationship between these rocks indicates that the crust of the southern Tibet did not appear to thicken obviously during the early stage of late Cretaceous (100–90 Ma). The intensive emplacement of late Cretaceous high-Mg adakites (Mg # > 50) and mafic rocks (SiO 2 < 52%) in the southern Lhasa terrane around 95–90 Ma, together with the slow convergence velocity of the Indian-Asian continent, can be explained by the response of rapid crustal thickening and Neo-Tethyan slab rollback at 95–90 Ma. • High-Mg adakitic rocks were formed from partial melting of Neo-Tethyan slab. • Coeval low-Mg adakitic rocks were produced by fractional crystallization. • Rapid crustal growth and Neo-Tethyan slab rollback occurred at 95–90 Ma.

Compositional Attributes of the Deep Continental Crust Inferred From Geochemical and Geophysical Data

AbstractThis study provides a global assessment of the abundance of the major oxides in the deep continental crust. The combination of geochemistry and seismology better constrains the composition of the middle and lower continental crust better than either discipline can achieve alone. The inaccessible nature of the deep crust (typically &gt;15 km) forces reliance on analog samples and modeling results to interpret its bulk composition, evolution, and physical properties. A common practice relates major oxide compositions of small‐ to medium‐scale samples (e.g., medium to high metamorphic grade terrains and xenoliths) to large scale measurements of seismic velocities (Vp, Vs, Vp/Vs) to determine the composition of the deep crust. We provide a framework for building crustal models with multidisciplinary constraints on composition. We present a global deep crustal model that documents compositional changes with depth and accounts for uncertainties in Moho depth, temperature, and physical and chemical properties. Our 3D compositional model of the deep crust uses the USGS Global Seismic Structure Catalog (Mooney, 2015) and a compilation of geochemical analyses on amphibolite and granulite facies lithologies (Sammon &amp; McDonough, 2021, https://doi.org/10.1029/2021JB022791). We find a SiO2 gradient from 61.2 ± 7.3 to 53.3 ± 4.8 wt.% from the middle to the base of the crust, with the equivalent lithological gradient ranging from quartz monzonite to gabbronorite. In addition, we calculate trace element abundances as a function of depth from their correlations with major oxides. From here, other lithospheric properties, such as Moho heat flux ( mW/m2), are derived.

Petrogenesis and Geological Significance of the Quartz Monzonites in the Jinling Area, Western Shandong Province

Jinling complex pluton is a key part of the Mesozoic magmatic belt in the eastern North China Craton. However, its petrogenesis is still being debated. The Jinling complex, mainly composed of biotite diorites, hornblende diorite, augite diorites, (quartz) monzonites, and quartz diorites, is outcropped in Huashan and Heitieshan. This paper studies the zircon geochronology, zircon Hf isotope, and Sr-Nd-Pb isotope of quartz monzonites. The samples have high contents of Cr, Ni, V, Al2O3, Ba, Sr, and are enriched in LREEs, LILEs (K, Ba, Sr), depleted in HREEs, and HFSEs (Nb, Ta, Ti). The samples with captured zircons of ~2.5 Ga yield a weighted mean age of ~127 Ma, and the zircons have negative values of εHf(t) from −3.2 to −9.4 while the ratios of 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb 37.75~38.15, 15.41~15.43, 17.59~17.98, respectively. The ratios of Th/U are from 3.77 to 3.82, while the values of μ and ω are 9.18 and from 35.72 to 36.15. Meanwhile, the ratios of 87Sr/86Sr are higher than the ones of the mantle. Geochemical and isotopic features indicate that the quartz monzonites derived from the subcontinental lithospheric mantle that probably assimilated ancient NCC upper crust materials (~15–20%) during the magma ascent in a lithospheric extension setting.

Major and trace element geochemistry of Permo-Triassic granitoids from NW Sonora, Mexico: Constraints on the origin of the Late Paleozoic-early Mesozoic Cordilleran magmatic arc along SW Laurentia

Permo-Triassic granitoids (PTGs) (284–224 Ma) crop out in Sierra Los Tanques (SLT) and surrounding areas in NW Sonora, Mexico. Based on mineralogical and geochemical characteristics, the PTGs are subdivided into three main suites: melanocratic (MS), leucocratic (LS) and pegmatitic-aplitic (PAS) suites. MS has I-type signatures (mostly metaluminous: biotite and hornblende), while LS is weakly peraluminous with biotite, muscovite, and garnet. PAS is composed of garnet-bearing pegmatite-aplite dikes of Permo-Triassic age. MS is slightly older than LS based upon field relations and age dating. PAS cut both granitoid suites and local Paleoproterozoic banded gneisses. PTGs are petrologically and geochemically classified as granodiorites, granites, and quartz monzonites, with medium-to high-K calc-alkaline affinity, and volcanic-arc granite (VAG) signatures. The enrichment in LILE (such as K, Rb, Ba, Sr, and Pb) and LREE over HFSE and HREE, respectively, together with negative Nb, Ta, P, and Ti anomalies, suggest derivation from a crustal source in a continental arc setting. Trace-element ratios of Ba/Ta≫1000, Th/Yb > 1, and Th/Ta>6–20 also support a setting in an active continental margin. All these geochemical features imply that crustal assimilation did play a major role in magma genesis. Crustal contamination is supported by field evidence, including xenoliths, stoped blocks, and roof pendants of Proterozoic basement rocks (Yavapai-type? crust). We propose that the PTGs from NW Sonora formed in a continental arc setting likely derived from the heat-fluxed melting of crustal material induced by mafic (basaltic?) underplating, thus the PTGs record the initiation of subduction and the generation of the early magmas in the nascent Late Paleozoic Cordilleran arc in SW Laurentia.

Hydrous Juvenile Lower Crust at the Western Yangtze Craton Margin as the Main Source of the Beiya Porphyry‐skarn Au Deposit

AbstractThe Beiya porphyry‐skarn Au deposit is one of the largest gold deposits in China, temporally and spatially associated with Eocene intrusions in a post‐collisional setting in western Yunnan, China. In this study, we report new whole‐rock geochemistry, Sr‐Nd isotope, zircon U‐Pb geochronology and in situ zircon Hf‐O isotopes of quartz‐monzonite and biotite‐monzonite porphyries from the Beiya deposit. The porphyry‐skarn mineralization at the Beiya deposit is mainly associated with the quartz monzonite porphyry (35.8 ± 0.6 Ma), while the biotite‐monzonite porphyry (34.3 ± 0.5 Ma) represents a post‐mineralization intrusion crosscutting the main orebodies and the quartz‐monzonite porphyry. Both intrusions have high‐K and adakitic composition and are characterized by high Sr/Y ratios, high SiO2 and Al2O3 concentrations (SiO2 = 69.80–73.86 wt%; Al2O3 = 14.11–15.19 wt%), and low MgO, Cr, and Ni concentrations (MgO = 0.2–1.0 wt%; Cr = 1.76–11.13 ppm; Ni = 2.52–11.72 ppm). Their Sr‐Nd isotope compositions (87Sr/86Sr = 0.7066–0.7077; εNd(t) = –5.3 to –1.5) are consistent with the lower crustal‐derived amphibolite xenoliths (87Sr/86Sr = 0.7060–0.7100; εNd(t) = –10.0 to 0.0), indicating that they might be derived from a thickened juvenile lower crust beneath the Yangtze Craton. The biotite‐monzonite porphyry has lower zircon δ18O values of +5.3‰ to +6.8‰ and higher εHf(t) values of –2.3 to +5.5 than those of the quartz‐monzonite porphyry with δ18O values of +7.1‰ to +8.2‰ and εHf(t) values of –3.8 to +1.5, implying that they were derived from different parts of the lower crust. High Ba/La and Pb/Ce ratios suggest that the quartz‐monzonite porphyry is derived from a volatiles‐rich reservoir. Relatively higher La/Yb, Sm/Yb and Dy/Yb ratios of the biotite‐monzonite porphyry indicate residual garnet in the source, indicating a deeper source than that of the quartz‐monzonite porphyry. The hydrous components should be represented by the amphibole‐rich lithologies, which has relatively shallower depth than that of the garnet‐bearing mafic thickened lower crust. Our data suggest that the mineralized quartz‐monzonite porphyry at the Beiya deposit is derived from partial melting of amphibole‐rich lithologies in the upper part of the thickened juvenile lower crust beneath the Yangtze Craton, while the post‐mineralization biotite‐monzonite porphyry is derived from the basal, and volatiles‐poor, part of the juvenile lower crust.

Partial Melting of Lithospheric Mantle and Formation of the Early Cretaceous Alkaline Rocks in the Guandimiao REE Deposit, Luxi Terrane, Eastern China

The Luxi Terrane (eastern China) exposes widespread Early Cretaceous alkaline rocks, whereas their petrogenesis remains controversial, including fractional crystallization, partial melting and crustal contamination regime. Here, we present petrology, geochemistry, sphene U-Pb geochronology and trace element data from the syenogranite, quartz syenite and quartz monzonite of the Guandimiao alkaline complex rocks to investigate their petrogenesis. Geochemical data suggest that these alkaline rocks show alkalic and peralkaline characters, and high Ga/Al ratios, SiO2, light rare-earth element (LREE), Zr and Nb, and low MgO, CaO, Eu contents, corresponding to A-type granites. Sphene trace elements in syenogranite and quartz monzonite show obvious fractionation between LREE and heavy rare-earth element (HREE) and high Th/U ratios, indicating a magmatic origin. They yield U-Pb lower intercept ages of 128 ± 2.3 Ma and 127 ± 1.3 Ma, representing the crystallization ages of these alkaline rocks. The negative correlations between CaO, Fe2O3 (Total), MgO, P2O5, TiO2, MnO and the pronounced depletion in Nb, Ta and Ti suggest that the alkaline rocks were formed by fractional crystallization. Additionally, the positive correlation between La/Hf and La, Th and Th/V, Ce/Yb and K2O, and Tb/Yb and Yb suggest that the alkaline melts are generated by partial melting. Such high Rb/Nb, (Th/Nb)N and Nb/Th ratios indicate crustal contamination during the magma emplacement. We, therefore, propose the magma source of the alkaline rocks in the Guandimiao complex originated by partial melting of lithospheric mantle, which experienced fractional crystallization and crustal contamination processes during its emplacement. Such complex alkaline rocks were probably formed in an extensional back-arc setting induced by the retreat of the subducting Izanagi plate.

Research on Metallogenic System and Deposit Genesis: With Zhacun Goldmine in Weishan County of Yunnan as an Example

This paper mainly takes Zhacun goldmine as the research object and carries out research on the metallogenic system and genesis of the deposit in the area. The research methods are as follows: according to the geological characteristics of the metallogenic mining area in the Zhacun goldmine, combined with the comparative analysis of the metallogenic age, alteration characteristics and lithology between the Zhacun goldmine and the Lianhuashan alkali rich rock mass, and the analysis of the isotopic data in the Zhacun goldmine, this paper demonstrates that the magmatic activity of the Lianhuashan quartz monzonite porphyry plays an important role in the mineralization of this area, which is both an important ore source and fluid source. It is also the main heat source driving the circulation of ore-forming fluid. On this basis, through the analysis of the metallogenic elements in the area, the metallogenic system model of Zhacun goldmine is constructed. It is considered that under the action of long-term horizontal compressive stress, the atmospheric precipitation infiltrated into the formation continued to penetrate along the fractures and fissures to deep crust and finally mixed with the magmatic water sealed in the thick formation. During this period, a series of shallow and ultrashallow porphyry mass intruded, providing heat source and part of the ore-forming materials and resulting in incomplete homogenization under high temperature and high pressure, which formed highly mineralized mixed water. Under the combined action of long-term compressive stress and various deep thermal dynamics, these mineral fluids migrated along the buried deep faults near the core of the duplex anticline to the upper part of the crust. When the metal elements in these ore fluids migrated over long distances to the nappe fault zone of the gold-bearing fracture zone, the gold began to precipitate, and the native gold and the coarse-grained pyrite and quartz formed at the same time or earlier started to fill the fracture zone along the fissures and accumulate into minerals. Then, through the analysis of metallogenic conditions, gold mineralization process, and genetic mechanism of the deposit, it is proposed that the genetic type of the ore deposit in this area is magmatic mesothermal-epithermal gold deposit. The establishment of metallogenic system model in Zhacun goldmine will provide theoretical and practical guidance for deep and peripheral prospecting prediction in the area, carry out targeted and reasonable prediction, and improve prospecting effectiveness.

Geochronology, geochemistry, and isotopic composition of the early Neoproterozoic granitoids in the Bikou Terrane along the northwestern margin of the Yangtze Block, South China: Petrogenesis and tectonic implications

The early Neoproterozoic granitoids exposed in the Bikou Terrane preserve vital information for understanding the Tonian tectonic evolution along the northwestern margin of the Yangtze Block, South China. However, their accurate forming age, petrogenesis, and tectonic attributes remain ambiguous. This study reports new results on zircon U–Pb geochronology, zircon Hf isotopes, whole-rock geochemistry, and Sr–Nd isotopes of the Baiquesi and Bahaihe quartz monzonite, Shilingou monzogranite, and Maliupu granodiorite from the Bikou Terrane. Detailed zircon U–Pb dating results reveal that the quartz monzonite and monzogranite were formed at ca. 860 Ma, whereas the granodiorite was emplaced at ca. 825 Ma. The quartz monzonite and monzogranite samples exhibit certain linear correlations in the Harker diagram, congruent distribution patterns of rare earth elements, and consistent isotopic compositions, indicating that they shared the same magma source, whereas the monzogranite was formed by differentiation crystallization of primitive quartz monzonite melt. The quartz monzonite samples are calc-alkaline in composition and have high ratios of Sr/Y and (La/Yb)N, coinciding well with the adakitic rocks. The relatively high contents of MgO, Ni, Cr, and Sr, low contents of Yb and Y, low ratios of La/Ce, Rb/Sr, and Th/La, and positive values of εHf(t) (+4.8–+6.7) and εNd(t) (+1.7–+2.1) indicate that they were formed by the interaction between slab-derived melt and mantle wedge. This mechanism may be triggered by a slab rollback process in an arc-related setting. The Maliupu granodiorite samples are classified as calc-alkaline I-type granitoids, and have low concentrations of MgO, Cr, Ni, and Y, and low ratios of Sr/Y and (La/Yb)N. They are featured by highly evolved εHf(t) values from −15.0 to −10.9 and εNd(t) values from −11.8 to −11.9, with Hf and Nd model ages ranging between 2.63 and 2.20 Ga, implying they were derived from partial melting of the ancient lower mafic crust and were formed in a subduction-related setting. Therefore, the new data, combined with those from previous studies in the Bikou Terrane, provide an essential link in the evidence chain for the hypothesis that the northwestern periphery of the Yangtze Block was in a persistent subduction-related tectonic regime in the early Neoproterozoic.

Zircon U–Pb age, whole-rock geochemistry and Nd–Sr–Pb isotope constraints on petrogenesis of the Eocene Zajkan gabbro–monzogranite intrusion, Tarom-Hashtjin magmatic belt, NW Iran

The late Eocene high-K to shoshonitic Zajkan intrusion, situated in the Tarom-Hashtjin magmatic belt (THMB), NW Iran, ranges in composition from gabbro to pyroxene quartz monzodiorite, pyroxene quartz monzonite and monzogranite, and is classified as an I-type metaluminous granitoid. On the primitive mantle-normalised spider diagram, these rocks demonstrate negative high field strength element (HFSE) anomalies, large-ion lithophile element (LILE) enrichment, and positive Pb anomaly, indicating a subduction-related signature. Furthermore, the granitoids are characterised by coherent chondrite-normalised rare earth element patterns with high light rare earth elements/heavy rare earth elements (LREE/HREE) and moderate to weakly negative Eu anomalies (Eu/Eu* = 0.6–0.86). LA-ICP-MS zircon U–Pb dating demonstrates that the Zajkan intrusion crystallised at ca 36.5 Ma. Relatively low to moderate 87Sr/86Sr ratios (0.7046–0.7061) and positive εNd(t) values (1.52–1.88) of the Zajkan samples are consistent with an enriched lithospheric mantle source that was metasomatised by an earlier subducted slab. Geochemical features show that the parental magma of the Zajkan intrusion likely resulted from a partial melting of metasomatised amphibole-bearing mantle source. Sr–Nd isotope modelling is consistent with the Zajkan intrusion formed from a mix of ∼80% of a mantle-derived magma and ∼20% of a juvenile lower crustal-derived magma. Partial melting of the metasomatised mantle may have resulted from late Eocene lithospheric thinning and hot asthenospheric upwelling through slab roll-back or lithospheric delamination. KEY POINTS The late Eocene high-K to shoshonitic Zajkan intrusion is located within the Tarom-Hashtjin magmatic belt, NW Iran. U–Pb zircon dating revealed an age of ca 36.5 Ma for emplacement of the Zajkan intrusion. Sr–Nd isotope modelling is consistent with the Zajkan intrusion formed from a mix of ∼80% of mantle-derived magma and ∼20% of juvenile lower crustal-derived magma.

Origin of the Bada porphyry Cu–Au deposit, eastern Tibet: Geology and isotope geochemistry (C–O–S–Pb) constraints

Bada is a newly discovered Cu–Au deposit located in the south part of the Yulong porphyry Cu (–Mo–Au) belt (YPCB), eastern Tibet. The Cu–Au mineralization, mainly hosted by the alkali-rich quartz monzonite porphyry (QMP), with minor by the fine-grained monzonitic porphyry (MP) and surrounding strata of the Nanxin Formation. The hydrothermal alteration assemblages recognized at Bada mainly include potassic, phyllic, propylitic, and argillic. The Cu–Au mineralization occurs within the potassic and phyllic alteration zones. Three main metallogenic stages have been identified: stage I ore-barren quartz ± dolomite ± K-feldspar ± pyrite veins, stage IIa dolomite ± quartz + pyrite veins, stage IIb dolomite ± quartz + polymetallic sulfide veins, and stage III dolomite ± calcite veins. The dolomite δ13CPDB values from stage I to III range from –2.2 – –1.8 ‰, –6.8 – –3.4 ‰, to –4.2 – 1.9 ‰. Their δ18OSMOW values vary from 7.7 – 9.8 ‰, 6.5 – 11.9 ‰, to 7.8 – 11.4 ‰, respectively. The corresponding calculated δ18Ofluid values ranging from 6.0 to 6.3 ‰ for stage I, and –1.1 to 4.3 ‰ for stage II, and –1.7 to 1.9 ‰ for stage III. The C–O isotopic compositions imply that the ore-forming fluids were dominated by magmatic water with the input of meteoric water. The narrow δ34S value range of sulfides (1.43 to 6.61 ‰, mean 4.64 ‰) reflects a predominantly magmatic origin for the sulfur. The Pb isotopic compositions of most sulfide samples coincide with the alkali-rich porphyries in the region, indicating that the alkalic porphyries provided the main source of Pb. Combined with the zircon U–Pb age of the ore-bearing porphyry (ca. 35.0 Ma), the Bada deposit is defined as a porphyry Cu–Au deposit in a late-collisional setting. The study of the genesis of Bada provides a better understanding of the Cu–Au mineralization potential of the southern YPCB.

Connected volcanic and plutonic association by crystal-melt segregation in the Daiyunshan volcanic field, SE China

The Daiyunshan volcanic field is one of the largest volcanic fields in the volcanic-plutonic complex belt along the coast of SE China, which records a long volcanic activity history from the Late Jurassic to the Late Cretaceous. In this paper, we conduct comprehensive petrological, geochemical, isotopic and zircon trace element analyses for two representative calderas (Shiniushan and Yunshan) to reveal the crystal-melt segregation and magma recharge processes of the Daiyunshan volcanic field. Systematic LA-ICP-MS zircon U-Pb dating and isotope analyses reveal that the porphyritic quartz monzonite, porphyritic granite and rhyolite of the Shiniushan caldera have identical crystallization ages (97–94 Ma) and consistent Nd-Hf isotope compositions [εNd(t) = −3.6 to −2.8; zircon εHf(t) = −2.7 to 1.8], which are consistent with those of the porphyritic quartz monzonite and rhyolites in the nearby Yunshan caldera, indicating that the magmas of the two calderas were derived from a common magma source region. Volcanic-plutonic rocks from two calderas display metaluminous to peraluminous features and have low MgO, FeOT, Ni and Cr contents. We thus suggest that their parental magmas were derived by remelting of pre-existing crust with contributions of juvenile components. The Shiniushan porphyritic granite and rhyolite and the Yunshan rhyolites are characterized by distinctly negative Eu anomalies and depletions of Ba, Sr, P and Ti, while the porphyritic quartz monzonites from both calderas show complementary geochemical signatures, such as positive Ba anomalies and neglectable Eu anomalies. The back-scattered electron (BSE) images and energy-dispersive X-ray spectrometry (EDS) phase mapping of the Shiniushan porphyritic quartz monzonite reveal textural indicators of crystal accumulation, such as imbrication and synneusis of plagioclase phenocrysts. Their interstitial assemblages of K-feldspar, quartz and plagioclase commonly resemble the phenocryst assemblages of porphyritic granite. We believe that the Shiniushan porphyritic granite and rhyolite and Yunshan rhyolites represent extracted melts from the mush reservoir, while porphyritic quartz monzonites in both calderas are inherent cumulates that have lost interstitial melts. Therefore, our study shows that the Late Cretaceous volcanic-plutonic rocks in the Daiyunshan volcanic field should be connected by crystal-melt segregation processes. Furthermore, a typical zigzag variation in zircon εHf(t) values is shown by the Late Jurassic to Late Cretaceous volcanic-plutonic rocks from the Daiyunshan volcanic field, indicating variable contributions of asthenospheric mantle-derived melts and the multistage slab rollback of the subducting paleo-Pacific plate beneath SE China.

The importance of Confocal Raman Spectroscopy and mineral chemistry studies in the magma crystallization processes: Strandja Intrusives, NW Turkey

The Strandja Massif cropping out in NW Turkey is cut by Late Cretaceous intrusives. These are called Strandja Intrusives and they are felsic and mafic coeval intrusives. Felsic intrusives consist of granite, granodiorite, quartz monzonite and syenite, while mafic intrusives consist of diorite and gabbro composition. Main composition of felsic intrusives consists of quartz, alkali feldspar, plagioclase, biotite, amphibole ±pyroxene mineral association, while main composition of mafic ones consists of plagioclase, biotite, amphibole ±pyroxene ±olivine mineral association. Amphiboles hydrated double-chain mineral of the Strandja Intrusives observed in all rocks used as an index mineral in this study to understand the petrological evolution of the rocks. According to Confocal Raman Spectroscopy studies amphiboles were actinolite type and exhibited similar spectrum and results of mineral chemistry reveals that they were calcic/Mg-hornblende types. According to geothermobarometer calculations, amphiboles crystallize in felsic intrusives at a pressure range of 0.49-0.94 kbar and a temperature of 757.52-814.49oC temperature at a depth of approximately 1.34-4.93 km, while in mafic ones at 2.59 kbar pressure and 892.82oC temperature at 9.97 km depth. Different temperatures-depth conditions and overlaps in Raman shift obtained from amphiboles indicate that these intrusives are derived from different sources but crystallized in the same environment.

Late Paleozoic Shoshonitic Magmatism in the Southwestern Middle Tianshan (Tajikistan) of the Southwestern Altaids: Implications for Slab Roll-Back With Extensional Arc-Related Basins After Flat Subduction

Paleozoic magmatic rocks are widespread in the western Middle Tianshan. Their petrogenesis can provide important insights into the geodynamic evolution of the southwestern Altaids. Here, we present an integrated study of U–Pb zircon geochronology and geochemical and Lu–Hf isotopic compositions for the Late Paleozoic shoshonitic Chorukhdairon pluton and genetically and spatially related quartz porphyry in the southern Chatkal–Kurama terrane, western Middle Tianshan. The Chorukhdairon pluton mainly comprises monzodiorite and quartz monzodiorite (first phase), quartz monzonite (second and main phase), monzogranite (third phase), and leucomonzogranite (fourth phase). LA–ICP–MS zircon dating yielded magma crystallization ages of 294–291 Ma and 286 Ma for the Chorukhdairon pluton and quartz porphyry, respectively. All the rocks possess high K2O content (3.29–5.90 wt.%) and show an affinity with shoshonite series rocks. They display similar trace element compositions characterized by the enrichment of large ion lithophile elements (e.g., Rb, Th, U, and K) and depletion of high-field strength elements (e.g., Nb, Ta, P, and Ti), compatible with typical arc magmatism. Combined with zircon Lu–Hf isotopic data, we suggest that the Chorukhdairon pluton was produced by partial melting of the enriched mantle, followed by fractional crystallization of pyroxenes, amphibole, plagioclase, biotite, and accessory Fe–Ti oxides, apatite, and zircon. The quartz porphyries are similar to highly fractionated I-type granitic rocks, and their parental magma could result from the mixing of different batches of mantle-derived magmas or magmas derived from the mantle and juvenile lower crust. Considering the continuousness of the Middle Carboniferous to Early Permian magmatism in the western Middle Tianshan and other regional geological data, we suggest that the Chorukhdairon pluton and related quartz porphyry probably formed in an oceanic subduction setting. Furthermore, the temporal and spatial evolution of the Paleozoic magmatism imply that the flat-slab subduction that was induced by the subduction/accretion of seamounts probably occurred beneath the Middle Tianshan during the Middle Devonian to Early Carboniferous, after which the southeastward slab roll-back occurred during the Middle Carboniferous to Early Permian. The late slab roll-back was responsible for the southeastward arc magmatism migration and magmatic flare-up in the Chatkal–Kurama terrane, western Tianshan, and led to the formation of arc-related extensional basins and significant crustal growth in the southwestern Altaids.

Evaluation of magnetite as an indicator mineral for porphyry Cu exploration: a case study using bedrock and stream sediments at the Casino porphyry Cu–Au–Mo deposit, Yukon, Canada

The trace element composition of detrital magnetite grains recovered from six local streams around the Casino high-grade porphyry Cu–Au–Mo deposit, west-central Yukon, is compared with igneous and magmatic-hydrothermal magnetite recovered from mineralized and unmineralized host rocks at the deposit. Linear discriminant analysis of 12 elements (Mg, Al, Ti, V, Mn, Co, Cr, Ni, Cu, Zn, Ga and Ge) and plots of Ti v. Ni/Cr are used to discriminate between magmatic-hydrothermal magnetite from the potassic alteration zone and igneous magnetite from granodiorite and quartz monzonite hosting the deposit. Magmatic-hydrothermal magnetite with a trace element composition similar to that from the potassic alteration zone at Casino is identifiable in stream sediments draining the deposit. Copper in magmatic-hydrothermal magnetite, present as minute inclusions of sulfide minerals such as chalcopyrite or substituted within the magnetite crystal lattice, is a strong indicator of Cu mineralization. We show that the chemical compositions of magnetite recovered from stream sediments can be used to explore for porphyry systems. Thematic collection: This article is part of the Applications of Innovations in Geochemical Data Analysis collection available at: https://www.lyellcollection.org/cc/applications-of-innovations-in-geochemical-data-analysis Supplementary material: Laser ablation data for major, minor and trace elements in magnetite from bedrock and stream sediment samples from Casino are available at https://doi.org/10.6084/m9.figshare.c.5896900

Age and petrology of Eocene-Oligocene calc-alkaline volcanism in Biga Peninsula (NW Turkey): Implications for magma origin and geodynamic evolution

In NW Anatolia, Eocene-Oligocene post-collisional volcanism is represented by K-rich volcanic rocks, including high K calc-alkaline products. Magmatic rocks in the Dededağ area (Biga Peninsula, NW Turkey) can be classified into 6 different groups with lithostratigraphic and chronostratigraphic data using 40Ar/39Ar methods (Eocene-early Oligocene, 42.08 ± 0.09 to 29.02 ± 0.29 Ma). From the Eocene period, there are calc-alkaline Laledağ granodiorite, Beyçayır volcanics with andesite and dacite composition, and also Kızıldam volcanics with alkaline and basic character (basaltic trachyandesite, trachybasalt). Furthermore, in the Oligocene period, calc-alkaline volcanism started with Dededağ volcanics with dacite and rhyolite intermediate-acidic composition, continued with Kırcalar volcanics consisting of basalt and basaltic andesite, and Harmancık volcanics ranging from basalt to rhyolite. The calc-alkaline Çamyayla pluton with quartz monzonite composition intruded into Oligocene Dededağ and Harmancık volcanics in the region. Alkaline lavas in the region are classified as high-K and shoshonitic, and calc-alkaline lavas are medium-high-K. On N-type mid-ocean ridge basalt and chondrite-normalized trace element diagrams, enrichment was observed for all volcanic units with regard to large ion lithophile elements and light rare earth elements. High field strength elements and heavy rare earth elements were depleted in all volcanic units. These compositions reveal the participation of a mantle source that was enriched by subduction components. Using geochemical data, all the volcanic rocks differentiated as a result of magma mixing/replenishment and contamination/assimilation processes. Consequently, the source of volcanism is thought to derive from the compressional regime associated with collision during the Eocene-Oligocene, and from a previously-enriched lithospheric mantle source with subsequent effects of the extensional regime.

Petrogenesis and Geodynamic Implications of Late Triassic Mogetong Adakitic Pluton in East Kunlun Orogen, Northern Tibet: Constraints from Zircon U–Pb–Hf Isotopes and Whole-Rock Geochemistry

Adakites or adakitic rocks usually show special geochemical signatures and are petrological probes to reveal the tectono–magmatic evolutionary history of paleo–orogenic belts. Here, we present a comprehensive study on the zircon U–Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotopes of Mogetong adakitic pluton in East Kunlun orogen, Northern Tibetan Plateau, to constrain its petrogenesis and tectonic setting, and thus to reveal its implications for the Paleo–Tethyan orogeny. The studied pluton comprises of quartz monzonite porphyry with zircon U–Pb crystallization age of ca. 215 Ma, which is coeval to their diorite enclaves (ca. 212 Ma). The quartz monzonite porphyries have intermediate SiO2 (63.31–65.74 wt%), relatively high Al2O3 (15.52–16.02 wt%), K2O (2.83–3.34 wt%), and Sr (462–729 ppm), but low Y (9.14–15.7 ppm) and Yb (0.73–1.39 ppm) with high Mg# (47–55), Sr/Y (30–57) and La/Yb ratios resembling typical high–K calc-alkaline and high Mg# adakitic rocks. Zircon Lu–Hf isotopes show that the studied samples have weakly juvenile zircon Lu-Hf isotopes (εHf(t) = 1.80–4.03) with older model age (1.00–1.14 Ga). The relative low content of Cr (14–59 ppm) and Ni (8–30 ppm), as well as the petrological, geochemical, and Lu-Hf isotopic data, indicates that the Mogetong adakitic rocks were generated by partial melting of thickened lower crust with a certain contribution of the underplated mantle-derived magma in slab break-off setting. This study shows that the Late Triassic adakitic magmatism in East Kunlun orogen may be the response of tectonic transition from oceanic subduction to post–subduction extension, and the reworking of ancient continental crust with subsequent variable crust-mantle magma mixing is the major mechanism of continental crust evolution in the Paleo–Tethyan orogenic belt.

Petrology, zircon U–Pb geochronology and tectonic implications of the A1-type intrusions: Keban region, eastern Turkey

The Southeast Anatolian Orogenic Belt (SAOB), the most extensive segment of the Alpine-Himalayan Orogenic Belt, resulted from the northward subduction of the southern branch of the Neotethys oceanic crust beneath the Anatolian micro-plate. We present new whole-rock geochemistry, zircon U–Pb ages, and Lu–Hf isotope data from the stocks and dykes with a length of up to tens of meters belonging to the Keban magmatic rocks, eastern Turkey. These rocks are represented by syenite and quartz monzonite intruded into the Keban metamorphic complex. The geochemistry data indicates that the samples bear mostly metaluminous, variably high alkalines (K2O + Na2O), Ga/Al ratios and zircon saturation temperature, and typically the A-type granite characters. According to the Y/Nb vs Yb/Ta diagram, the Keban magmatic rocks show A1-type geochemical signatures modified by crustal melts. Syenite and quartz monzonite samples from Keban magmatic rocks give zircon U–Pb ages of 77.4 ± 0.34 Ma, 76.3 ± 0.3 Ma and 76.36 ± 0.34 Ma, respectively. On the primitive mantle-normalised trace element patterns, the Keban magmatic rocks show enrichment in large-ion lithophile elements (LILEs) relative to high field strength elements (HFSEs). They are coupled with slightly negative Nb–Ta anomalies. Chondrite-normalised rare earth-element patterns show strong enrichment in LREEs relative to HREEs, a typical A-type granites feature. The zircons have negative εHf(t) values that vary from −2.68 to −0.41, and Hf model ages (TDM2) range from 1171.54 to 1329.26 Ma, indicating the enriched lithospheric mantle sources and crustal contribution. The sources and evolution of the alkaline magmas might be related to the post-collisional tectonic setting.

First report on zircon U-Pb age (125.9 Ma) of the quartz monzonite from the Pandian skarn iron deposit in the Luxi area, Eastern China

First report on zircon U-Pb age (125.9 Ma) of the quartz monzonite from the Pandian skarn iron deposit in the Luxi area, Eastern China

The origin of microgranular enclaves in the Early Cretaceous Shuangjianzishan granites in southern Great Hinggan Range, NE China

The microgranular enclaves (MEs) and their host granitoids contain vital information on the genesis and evolution of the magma, especially for those which have close relationship with mineralization, yet remains a hot debate on their origin. Here, we investigate the MEs and their host granitoids in the Shuangjianzishan (SJZ) deposits, southern Great Hinggan Range, NE China, using ziron U–Pb dating and Hf isotopes, along with a systematic analysis of whole‐rock geochemical and Sr‐Nd isotopic compositions. The SJZ MEs mainly consist of monzonites and quartz monzonites, and the SJZ granitoids comprise a suite of fine‐grained syenogranites and coarse‐grained monzogranites. The zircon U–Pb dating results suggest that the SJZ granitoids and the SJZ MEs were emplaced at approximately 143–141 Ma. Geochemical features and isotopic compositions of the SJZ granitoids indicate that they are mainly generated by partial melting of juvenile lower‐crustal basaltic rocks. The fine‐grained syenogranites and the coarse‐grained monzogranites have a gradual contact relationship, similar crystallization age, Sr‐, Nd‐, and Hf‐isotopic compositions, suggesting that they were derived from a similar silicic magma reservoir. According to the geochemical compositions and petrographic characteristics (aggregates of coarse‐grained euhedral plagioclase crystals) of the SJZ granitoids, we infer that the monzogranites (SiO2 = 69.24–74.95 wt%) are regarded as the residual cumulate and the fine‐grained syenogranites (SiO2 = 74.83–77.97 wt%) are high silica melts segregated from a crystal mush. The SJZ MEs are characterised by low SiO2 (50.03–64.20 wt%) and MgO (1.08–2.63 wt%) contents, high P2O5 contents and contain acicular apatite, which are consistent with the products of intermediate magma. Combining with the MEs have comparable crystallization age, mineral assemblage, whole‐rock Sr‐Nd and zircon Hf‐isotopic compositions with their host granitoids, implying the MEs were autoliths related to their host monzogranites. Collectively, we infer that the SJZ MEs were generated by the rapid cooling and crystallization of the hot ascending intermediate magmas contacted with the cooler wall rocks, then those sub‐solid fine‐grained crystal‐rich margins were fragmented and injected into the progressive evolved mush chamber, leading to the extraction and upward percolation of high silicic melts from the compacting crystal‐rich mush in the shallow crust.

Fractional Crystallization and Partial Melting of the Paleoproterozoic Gneisses and Pegmatite in the Giant Husab Uranium Deposit, Namibia

The giant Husab uranium deposit is located in the Paleoproterozoic Abbabis Metamorphic Complex, which was highly partially melted and metamorphosed during the Damara Orogenic Event. The timing of magma emplacement has been investigated; however, the petrogenesis is unclear. Here we reported petrology, geochemistry, and monazite U-Pb age data from biotite granitic gneisses, syeno-granite, syeno-granitic pegmatites, syeno-granitic gneiss, granitic syenite and biotite quartz monzonites of this complex. Geochemical data suggest that these Paleoproterozoic rocks show high SiO2, Al2O3, and K2O, moderate Na2O, low CaO and Fe2O3, and MgO abundance. The alkali-calcic to alkalic, peraluminous, low Fe-number, depletion in HFSE (Nb-Ta, Ti) and enrichment in LILE (e.g., Rb, Pb) characteristic correspond with I- and S-type granite. Major and trace elements are strongly fractionated with the increase of SiO2, which, together with strongly fractionated LREE patterns and high (La/Yb)N ratios of the biotite granitic gneiss and syeno-granitic gneiss, suggest that the magma was highly evolved and fractionated. Monazite U-Pb data show three metamorphic age groups of 581–535 Ma, 531–522 Ma and 518–484 Ma. The increasing trend of La/Sm and La/Yb with the increase of La, suggest these rocks most likely experienced a partial melting process during the late Palaeozoic metamorphism. We, thus, propose a fractional crystallization model for the generation of the Paleoproterozoic Abbabis Metamorphic Complex basement rock, which was metamorphosed and melted during the late Palaeozoic Damara Orogenic Event and provided the magma sources for primary uranium mineralization.