Search

The Imourkhssen porphyry Cu±Mo±Au±Ag deposit is located at the Ouzellagh-Siroua Salient (OSS) straddling the boundary between the central Anti-Atlas and the central High Atlas. It is characterized by a typical porphyry-style mineralization. The volcanic rocks are intruded by numerous magmatic rocks of the Ouarzazate Group (580–539 Ma), referred to as the Late Ediacaran magmatic suites (LEMS). Of these, the Askaoun, Imourkhssen, and Imourgane granites are the most significant as they are related to the porphyry mineralization. The entire set is intruded by the Zaghar mafic dyke swarms. Zircon U-Pb dating of the Imourkhssen granite and the ore-bearing granite porphyry shows that these intrusive rocks were emplaced at 558 ± 1 and 550 ± 2 Ma, respectively. Moreover, the whole-rock major and trace element geochemistry reveal a high-K calc-alkaline I-type composition, consistent with an emplacement in a post-collisional setting under a trans-tensional tectonic regime. Ore bodies are hosted by the Askaoun granodiorite as well as the Imourgane granite. The mineralization occurs as fine-grained dissemination and infills of hydrothermally altered NNE–SSW to N–S trending veins and veinlets. Ore-related hydrothermal alteration consists of potassic, chlorite-sericite, serecitic, and propylitic mineral assemblages along with pervasive silicification and pyritization, providing a porphyry-style alteration pattern. The ore periods comprise supergene and magmatic-hydrothermal periods. The latter includes primary dissemination and secondary NNE–SSW to N–S ore-bearing system stages. The occurrence of molybdenite is either restricted to the potassic and chlorite-sericite alteration zones of the ore-bearing granite as fine disseminations or alternatively as veinlet infills within the propylitic halos. The molybdenite occurrences along with pyrite, chalcopyrite, galena, and tennantite dissemination are assigned to the primary ore stage, while the NNE–SSW to N–S ore-bearing system is related to the secondary ore stage. It consists of pyrite, chalcopyrite, bornite, covellite, diagenite, sphalerite, hematite, galena, gold, and chenguodaite. The predominance of cockade and crack-and-seal textures suggest multiple episodes of ore-forming fluid circulations under epithermal conditions. The supergene stage is achieved by subordinate malachite, azurite, barite, hematite, epsomite, and chrysocolla. From the descriptions above, we argue that the Imourkhssen Cu±Mo±Au±Ag mineralization shares many mineralogical and paragenetic attributes of porphyry-copper deposits. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study including LA-ICP-MS zircon U-Pb dating, geochemical, zircon Hf isotope, and whole rock Sr-Nd isotope analysis of magmatic rocks from the Yitong County, Jilin Province, NE China. These data are used to better constrain the Middle Silurian–Middle Devonian tectonic evolution in the eastern segment of the northern margin of the North China Craton (NCC). Zircon U-Pb dating results show that the Ximangzhang tonalite formed in the Late Silurian (425 ± 6 Ma); the basalt, andesite, and metamorphic olivine-bearing basalt in the Fangniugou volcanic rocks formed in the Middle Silurian (428 ± 6.6 Ma) and Middle Devonian (388.4 ± 3.9 Ma, and 384.1 ± 4.9 Ma). The Late Silurian tonalites are characterized by high SiO2 and Na2O and low K2O, MgO, FeOT, and TiO2, with an A/CNK ratio of 0.91–1.00, characteristic of calc-alkaline I-type granite. They are enriched in Rb, Ba, Th, U, and K, and depleted in Nb, Sr, P, and Ti, with positive εNd(t) (+0.35) and εHf(t) (+0.44 to +6.31) values, suggesting that they mainly originated from the partial melting of Meso–Neoproterozoic accretionary lower crustal material (basalt). The Middle Silurian basalts are characterized by low SiO2, P2O5, TiO2, and Na2O and high Al2O3, FeOT, and K2O, enriched in Rb, Ba, Th, U, and K and depleted in Nb, Ta, Sr, P, and Ti, indicative of shoshonitic basalt. The Late Silurian tonalites have positive εNd(t) (+4.91 to +6.18) values and primarily originated from depleted mantle magmas metasomatized by subduction fluids, supplemented by a small amount of subducted sediments and crustal materials. The Middle Devonian volcanic rocks exhibit low SiO2, TiO2, and Na2O and high K2O, and MgO, enriched in Rb, K, and LREEs and depleted in Nb, Ta, Sr, and HREEs, characteristic of shoshonitic volcanic rocks. Their εNd(t) (+2.11 to +3.77) and εHf(t) (+5.90 to +11.73) values are positive. These characteristics indicate that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction fluids, with the addition of crustal materials or subducted sediments during their formation. Based on regional geological data, it is believed that the study area underwent the following evolutionary stages during the Silurian–Devonian period: (1) active continental margin stage of southward subduction of the Paleo–Asian Ocean (PAO) (443–419 Ma); (2) arc-continent collision stage (419–405 Ma); (3) post-collision extension stage (404–375 Ma); (4) active continental margin stage, with the PAO plate subducting southward once again (375–360 Ma). [ABSTRACT FROM AUTHOR]

Fozi Mountain National Geopark is located in Zhenghe County in the northern region of Fujian Province, where the volcanic rocks of the Zhaixia Formation of the Shimaoshan Group are exposed. Zircon U-Pb dating and geochemical analysis were carried out to constrain its age and tectonic environment. The results show that three zircon U-Pb dating samples have attained ages of 99.2 ± 1.0 Ma, 99.6 ± 0.8 Ma, and 99.7 ± 2.0 Ma. Volcanic rocks in the core scenic area of Fozi Mountain were formed during the Late Cretaceous period. Elemental analysis showed that these volcanic rocks were dominated by the shoshonite series. They include gray dacite porphyry, grayish-white breccia tuff, volcanic agglomerate, and gray tuffaceous sandstone. These rocks were characterized by high silicon, high alkali content, and rich potassium levels. Lu-Hf isotope analysis of zircons revealed that their εHf(t) values varied from −8.7 to −6.8. The corresponding TDM2 values were primarily distributed in the range of 1.71 Ga to 1.59 Ga. These findings indicated that the magma primarily originated from the partial melting of the Mesoproterozoic crystalline basement, accompanied by a small number of mantle-derived materials. Tectonic environment analysis indicated that these rocks were formed in the post-orogenic intraplate extensional environment, which was associated with the back-arc extension or lithospheric thinning caused by the subduction of the paleo-Pacific plate beneath the Eurasian plate. The formation of these volcanic rocks was attributed to post-orogenic magmatism. [ABSTRACT FROM AUTHOR]

The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province. LA‐ICP‐MS zircon U‐Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8 ± 1.6 and 246.5 ± 1.3 Ma, coeval with peraluminous granites of the Qinzhou Bay Granitic Complex. The studied rhyolites and dacites are characterized by high SiO2, K2O, and Al2O3, and low MgO, CaO, and P2O5 contents and are classified as high‐K calc‐alkaline S‐type rocks, with A/CNK = 0.98–1.19. The volcanic rocks are depleted in high field strength elements, e.g., Nb, Ta, Ti, and P, and enriched in large ion lithophile elements, e.g., Rb, K, Sr, and Ba. Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions (εHf(t) = –29.1 to –6.9), source discrimination indicators and high calculated Ti‐in‐zircon temperatures (798–835°C) reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S‐type silicic magma. The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo‐Tethys Ocean in this region, as the associated subduction would have generated an extensional setting in which the mantle‐derived upwelling and volcanic activity occurred. [ABSTRACT FROM AUTHOR]

The influence of the paleo-Tethys or paleo-Pacific oceanic plate subduction on Early Triassic South China has long been debated. We have studied the zircon U-Th-Hf isotopes, trace elements, and whole-rock geochemistry of Early Triassic peraluminous granitoids in the Qinzhou Bay area, South China Block. LA–ICP–MS zircon U–Pb dating has revealed the Jiuzhou granodiorites and Dasi-Taima granite porphyries formed between 248.32 ± 0.98 and 246.6 ± 1.1 Ma. These rocks are characterized by high K2O and Al2O3, and low MgO, CaO, and P2O5 contents with A/CNK = 1.06–1.17, showing high-K calc-alkaline S-type affinities. The Early Triassic intrusive rocks and adjacent silicic volcanic rocks in the Qinzhou Bay area were found to be comagmatic and derived from a common magma pool, detached in an undifferentiated melt instead of indicating remarkable crystal—melt separation. Although the analyzed granitoids have highly enriched zircon Hf isotopic compositions (εHf(t) = −23.9 to −7.8), they cannot originate solely from metasedimentary protoliths. Source discrimination indicators have revealed enriched lithospheric mantle-derived magma was also an endmember component of the S-type silicic magma, which provided a heat source for the crustal anatectic melting as well. We inferred the studied Early Triassic granitoids formed under the paleo-Tethys tectonic regime before the collision of South China and Indochina blocks, as the oceanic plate subduction would have created an extensional setting which further caused the mantle-derived upwelling and volcanic eruption. [ABSTRACT FROM AUTHOR]

This investigation reports the first discovery of more than 70 tuff intervals in the Upper Triassic, South Qilian Basin. Petrographic and geochemical analyses were carried out on ten tuff samples and zircon U-Pb dating were on three. Thin section and X-ray diffraction (XRD) results indicate that the tuffs were composed of crystal shards and altered glass shards; crystal shards include plagio-clase and quartz. Most of the tuffs had been transformed into illite/smectite mixed-layers (I/S). In addition, calcite, pyrite, dolomite and siderite were also identified in some of the tuff samples. Analysis of major elements suggests that the tuffs are peraluminous high-K calcalkaline series. Trace elements indicate that the tuffs are enriched in high field strength elements (HFSE), including Th, U, Ta, Zr and Hf. Geochemical characteristics suggest that the tuffs originated from comendite pantellerite and rhyolite from within plate setting. Zircon U-Pb dating (236.0 ± 1.7, 231.4 ± 1.6, and 223.1 ± 3.9 Ma) indicate that the tuffs were erupted in the Late Triassic. Comparative chronology and geochemical analyses suggest that the West Qinling belt and the East Kunlun belt are the potential source regions of these tuffs, and they originated from the within plate magma during a post-collisional period. [ABSTRACT FROM AUTHOR]

The early Paleoproterozoic (ca. 2.2–2.1 Ga) tectonic evolution of the Jiao–Liao–Ji belt (JLJB) is a continuous hot topic and remains highly controversial. Two main tectonic regimes have been proposed for the JLJB, namely arc-related setting and intra-continental rift. Abundant ca. 2.2–2.1 Ga volcanic rocks were formed in the JLJB, especially in the Liaodong Peninsula. These ca. 2.2–2.1 Ga volcanic rocks therefore could host critical information for the evolution of the JLJB. In this study, we report a suit of ca. 2.2–2.1 Ga felsic metavolcanic rocks in the Liaodong Peninsula of the JLJB to provide new insights into the above issue. Zircon U-Pb dating reveals that the felsic metavolcanic rocks were erupted at 2185–2167 Ma. They have variable εHf(t) values (−0.70 to +9.69), high SiO2 (66.30–75.30 wt.%) and relatively low TiO2 (0.03–0.78 wt.%), tFe2O3 (0.55–5.03 wt.%), MgO (0.17–8.76 wt.%), Cr (9.16–67.30 ppm), Co (2.01–7.00 ppm) and Ni (3.90–25.70 ppm) contents with enrichments in light rare earth element (REE) and large ion lithophile element (LILE), and depletions in heavy REE and high field strength element (HFSE). Geochemical and isotopic results indicate that the felsic metavolcanic rocks were sourced from partial melting of ancient Archean TTG rocks and juvenile lower crustal materials. Combined with coeval A-type granites, bimodal volcanic rocks and the absence of typical arc magmatism, the most likely tectonic regime at ca. 2.2–2.1 Ga for the JLJB is an intra-continental rift. [ABSTRACT FROM AUTHOR]

The Nanyuan Formation contains information related to the Mesozoic tectonic transformation. In this study, three representative profiles were surveyed from the Nanyuan Formation, and multiple analyses were conducted. Zircon U‐Pb dating yielded their ages as approximately 158–146 Ma. The volcanic rocks are enriched in Rb, Th, U, K, and Pb and depleted in Nb, Ta, P, and Ti, implying their affinity for I‐type granites. The εNd(t) values (–8.3 to −6.0), (87Sr/86Sr)i values (0.7077–0.7094) of the volcanic rock, and εHf(t) values (–8.71 to 0.12) of the Mesozoic zircons suggest that the Nanyuan Formation magma originated in the lower crust with the involvement of depleted mantle materials. The parent rocks of the rhyolitic and dacitic volcanic rocks formed by partial melting of basement rocks in South China and the andesitic volcanic rocks were derived from partial melting of the metasomatites generated by slab‐mantle interaction. The fractional crystallization also played an important role in later stage. Discrimination diagrams of the volcanic rocks indicated that they formed in a volcanic arc environment. Combined with previous data, the Nanyuan Formation recorded subduction of the Paleo‐Pacific Plate before regional tectonic transformation. The compressive stress field endured until the end of the Late Jurassic. [ABSTRACT FROM AUTHOR]

The Wanbaogou granitic plutons are exposed along with coeval volcanic rocks, and provide an opportunity to investigate Silurian tectonism in the South Kunlun belt, northwest China. This study presents new whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for Silurian intrusive rocks of the Wanbaogou area. We analysed four samples: a porphyritic monzogranite and dioritic dike from the Wanbaogou pluton and a granodiorite and monzogranite from the Wudaogou pluton. Zircon U–Pb dating yielded similar ages of 423.8 ± 1.9, 422.9 ± 1.9, 424.9 ± 2.0, and 425.3 ± 2.6 Ma, respectively. indicating that the intrusions were coeval. The granitic samples are mostly transitional between the high-K and shoshonite series. The Wanbaogou monzogranite is metaluminous and has features typical of A-type granites in terms of trace element geochemistry, whereas the Wudaogou granitoids are metaluminous to weakly peraluminous I-type granites. The Wanbaogou dikes are intermediate to mafic in composition and belong to the low- to medium-K series. The four intrusive samples have εHf(t) values of −10.62 to +0.99 (average = −2.52), similar to the εHf(t) values of intraplate volcanic rocks (−6.35 to +2.89; average = −1.82) and, combined with the geochemical data, indicate the 430–420 Ma magmatism could have been generated by crustal melting with input from mantle-derived materials, followed by crustal contamination. Data for the Wanbaogou and Wudaogou plutons, dikes, and volcanic rocks from the same area suggest rapid orogenic uplift at 430–420 Ma. Our data and the results of previous research on the Kunlun high- to ultra-high-pressure metamorphic belt and coeval volcanic and intrusive rocks elsewhere in the region suggest that collisional tectonism ceased abruptly at 430–420 Ma. Slab break-off may be responsible for this termination of tectonism and rapid uplift. [ABSTRACT FROM AUTHOR]

Copyright of Geology & Resources is the property of Geology & Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Lhasa terrane records voluminous magmatism related to the subduction of the Neo-Tethyan oceanic lithosphere, the study of which constrains the tectonomagmatic evolution of the region. We report zircon U-Pb ages, whole-rock compositions and Sr-Nd isotopic data from volcanic rocks in the Bangba district within the central Lhasa subterrane to constrain their magmatic source and petrogenesis. Zircon U-Pb dating of two volcanic rock samples yields End Cretaceous ages of 70.0 ± 0.8 and 74.3 ± 1.2 Ma. The rocks have high SiO2 (65.41 wt.%–68.45 wt.%), Al2O3 (16.16 wt.%–16.59 wt.%) and K2O (5.00 wt.%–6.73 wt.%) contents, and low TFe2O3 (2.33 wt.%–2.79 wt.%), MgO (0.64 wt.%–1.44 wt.%) and TiO2 (0.61 wt.%–0.65 wt.%) contents, with aluminium saturation indices (A/CNK) of 0.99–1.06. The major- and trace-element compositions of the rocks show they are metaluminous to slightly peraluminous high-K calc-alkaline trachydacite. The relatively high SiO2 and Sr-Nd isotopic compositions ((87Sr/86Sr)i = 0.722 654, 0.722 038 and 0.725 787 and εNd(t) = −12.27, −12.36 and −6.09, respectively) indicate that the trachydacites formed by partial melting of crustal material. The trachydacites are relatively enriched in light rare earth elements, depleted in heavy rare earth elements, have high (La/Yb)N and (Gd/Yb)N ratios (>61 and >6, respectively), and low Y (<18 ppm) and Yb (<18 ppm) contents, indicating they most likely formed from partial melting of lower crust in the garnet stability field. Considering the geodynamic setting of the region during this period, partial melting of the ancient Lhasa crust was likely triggered by underplating mafic magmas during rollback of the Neo-Tethyan slab. [ABSTRACT FROM AUTHOR]

Whole-rock geochemistry, zircon U–Pb ages and Hf–O isotopes of the volcanic rocks from Tegusiaobao, north of Sonid Youqi, southeast Central Asian Orogenic Belt, were presented to trace their origin and the associated crustal evolution process. The Tegusiaobao volcanic rocks are composed of trachyandesite and per-aluminous rhyolites. Precise SHRIMP and LA-ICP-MS zircon U–Pb dating of rhyolite samples reveal that the Tegusiaobao volcanic rocks erupted during the Latest Permian to Triassic (c. 257–231 Ma), which is coeval with the emplacement of post-collision-related dikes and granites in the southeast Central Asian Orogenic Belt. Geochemical and isotopic analysis implies that a crust-mantle magma mixing model is likely responsible for the genesis of the Tegusiaobao trachyandesite-rhyolite suite. Nine zircon grains from a rhyolite sample exhibit variable δ18O values, with one mantle-like value (5.10‰) and eight values (6.42–8.77‰) that are akin to the supra-crustal materials. Zircons from this sample show depleted Hf isotopic composition (εHf(t) = + 10.91 to + 15.81). The high δ18O values of the rhyolite reveal the interaction of their protolith and surface water at low temperatures, and the preceding subduction caused the recycling of the supra-crustal materials and the closure of the Solonker–Linxi Ocean. The generation of the Tegusiaobao volcanic rocks also suggests that reworking of the supra-crustal materials is a potential way to operate the crustal evolution in the Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

The Aqishan lead‐zinc deposit, located in the Jueluotag metallogenic belt of eastern Tianshan, Xinjiang, Northwest China, has a stratiform occurrence in the marine volcanic tuff of the Yamansu Formation. The ore body has a typical double‐layer structure, having a stratified, stratoid, lenticular upper part and a veined, stockwork‐like lower part. The occurrence of the upper orebody is consistent with that of the volcanic tuff wall rock. The ore minerals are mainly chalcopyrite, pyrite, sphalerite, galena and magnetite, the altered minerals mainly being silicified, such as sericite, chlorite, epidote, garnet. The garnetized skarn, being stratiform and stratoid, is closely related to the upper part of the orebody. Geological observations show that the limestone in the ore‐bearing Yamansu Formation is not marbleized and skarnized. Spatially, it is associated with the ferromanganese deposits in the marine volcanic rocks of the Yamansu Formation. These geological features reflect the likelihood that the Aqishan lead‐zinc deposit is a hydrothermal exhalation sedimentary deposit. The results from the EPMA show that the garnet is mainly composed of grossular–andradite series, contents being in a range of 34.791–37.8% SiO2, 32.493–34.274% CaO, 8.454–27.275% FeO, 0.012–15.293% Al2O3, 0.351–1.413% MnO, and lower values of 0.013–1.057% TiO2. The content of SiO2 vs. CaO and FeO vs. Al2O3 has a significant positive correlation. The results of ICP‐MS analysis for the garnet show that the REE pattern is oblique to right in general. The total amount of rare earth elements is relatively low, ΣREE = 71.045–826.52 ppm, which is relatively enriched for LREE and depleted for HREE. LREE/HREE = 8.66–4157.75, LaN/YbN = 23.51–984.34, with obvious positive Eu and Ce anomalies (δEu = 2.27–76.15, δCe = 0.94–1.85). This result is similar to the REE characteristics of ore‐bearing rhyolite volcanic rocks, showing that the garnet was formed in an oxidizing environment and affected by clear hydrothermal activity. The U‐Pb isotopic dating of garnet by fs‐LA‐HR‐ICP‐MS gives an age of 316.3 ± 4.4 Ma (MSWD = 1.4), which is consistent with the formation time of the Yamansu Formation. According to the study of deposit characteristics and geochemical characteristics, this study concludes that the Aqishan lead‐zinc deposit is a hydrothermal exhalation sedimentary deposit, the garnet being caused by hydrothermal exhalative sedimentation. [ABSTRACT FROM AUTHOR]

Felsic tuff as a direct fallout deposit is known from one small area in the Kyrenia Range, north Cyprus, within deep-sea terrigenous turbidites. Nearby tuffaceous siltstones contain compositionally similar felsic volcanic rocks (c. 5–10%), mixed with terrigenous material. Sedimentary evidence indicates that the fallout tuff was variable reworked locally, whereas the tuffaceous siltstones are interpreted as turbidites mixed with terrigenous material derived from Anatolia. U–Pb dating of zircons that were extracted from a sample of relatively homogeneous tuff yielded a dominant age of 16.64 ± 0.12 Ma (Burdigalian). Zircon trace-element analysis indicates predominant derivation from within-plate-type felsic magma. Whole-rock chemical analysis of the tuffaceous sediments as a whole is compatible with a felsic arc source, similar to the post-collisional magmatism within Anatolia. Regional comparisons suggest that the nearest volcanism of similar age and composition is located c. 500 km away, within the Kırka area (Eskişehir region) of the Western Anatolia Volcanic Province. Evidence of tephra dispersal in the western Mediterranean region and climatic modelling suggests E-wards prevailing winds and therefore tephra transport over southern Anatolia and adjacent areas during early Miocene time. The north Cyprus tuffs could represent powerful Minoan (Plinian)-type eruptions in western Anatolia, coupled with SE-wards tephra transport during and soon after the onset of post-collisional magmatism. [ABSTRACT FROM AUTHOR]

Late Paleozoic volcanic rocks are well exposed in the Yining Block, NW China, and are predominately composed of andesites, rhyolites and volcaniclastics as well as minor basalts. Study of the petrology, whole‐rock geochemistry and zircon U‐Pb dating for the Early Carboniferous alkaline basalts from Wusun Mountain, western Yining Block, constrains their petrogenesis and tectonic evolution. The alkaline basalts consist mainly of plagioclases, mostly albite and labradorite, as well as clinopyroxenes and olivines; zircon U‐Pb dating indicates their formation at ca. 350 Ma. Geochemically, the basaltic samples have low SiO2 contents, and high TiO2, Al2O3 and alkaline contents, coupled with high Na2O/K2O ratios, displaying an alkaline basalt affinity. They show remarkable LILE enrichment and HFSE depletion. Meantime, these samples have relatively high TFe2O3, MgO, and Mg# values as well as Ni and Cr, relatively high Sm/Yb and U/Th, suggesting origination from a mantle source metasomatized by slab fluids. They formed in a transitional tectonic setting from arc to intraplate, showing a typical affinity of back‐arc basin basalts. The alkaline basalts were likely generated in a nascent back‐arc extension setting resulting from slab rollback of the southern Tianshan oceanic lithosphere. A bi‐directional subduction model seems more reasonable for the evolution of the southern Tianshan Ocean. These new data will provide a new tectonic model for Late Paleozoic tectonic evolution of the western Yining Block. [ABSTRACT FROM AUTHOR]

The Elashan magmatic belt is located at the eastern margin of the East Kunlun orogenic belt (E‐KOB) in northwestern China, where voluminous magmatism occurred during the Late Permian to Late Triassic. Mid‐Triassic volcanism produced the Xilikete Formation, which shows a geochemistry similar to that of highly fractionated I‐type (HFI) volcanic rocks. These rocks are characterized by high SiO2 (73.82–74.97 wt%), differentiation index (DI; 91.01–94.69), and alkalis (e.g., high K2O + Na2O, with K2O/Na2O ratios greater than 1.0) and by enrichment in some large‐ ion lithophile elements (LILEs; e.g., Rb, K, and Pb) and depletion in other LILEs (e.g., Ba and Sr) as well as some high‐field‐strength elements (HFSEs; e.g., Nb, Ta, and Ti); these features confirm that they are HFI volcanic rocks. Zircon U–Pb ages indicate that the volcanic rocks were emplaced at ~239 Ma. These zircons have εHf(t) values ranging from −2.26 to +0.36, with two‐stage model ages (TDM2) of 1,441–1,221 Ma, indicating a magma source that involved partial melting of Mesoproterozoic lower crust accompanied by a minor juvenile mantle component. The ~240 Ma magmatism in the E‐KOB was probably developed in response to subduction of the Palaeo‐Tethys oceanic plate. Previous studies indicate that a tectonic transformation from subduction to continental collision occurred at ~240 Ma. Combining these data with regional geological observations, we conclude that the Daheba volcanic rocks formed in an active continental margin setting related to the subduction of the Palaeo‐Tethys oceanic plate beneath the E‐KOB. [ABSTRACT FROM AUTHOR]

U-Pb dating of magmatic zircons from the Permian basaltic metaandesites/metabasalts of the Tribeč Mts. yielded the Concordia ages of 263.1±2.6 Ma, which correspond to the Guadalupian Epoch in the time span of the uppermost Wordian/Capitanian Stages. These magmatic zircon ages clearly document the timing of the Mid-Permian lithospheric extension in the internal zone of the Variscan fragments in the Western Carpathians. The studied volcanic rocks with the associated metasediments belong to the Veporic Unit that overthrusts the Tatric Unit. The considered sequence was correlated with the Northern Veporic Permian rocks from the Čierťaž Mts. From the geochemical point of view, the studied volcanic rocks have a calc-alkaline magmatic trend with an affinity to continental within-plate tectonic setting, linked to the post-orogenic lithospheric extension. The detrital zircon population, obtained from the associated arkosic metagreywackes, displays mainly Tournaisian and Ediacaran zircon ages in the range of 342-367 and 546-631 Ma, respectively. Only a small number of Cambrian/Ordovician (499-466 Ma), Tonian (720-1000 Ma) and Paleoproterozoic/Neoarchean (~1.9 Ga and ~2.5 Ga) zircon ages were determined. The similar association of zircon ages was found within the xenocrystic cores in the studied volcanic rocks. The presented detrital and xenocrystic zircon ages specify the provenance of the Tribeč Permian deposits from the Western Carpathian Crystalline Basement crust, characteristic of derivation from the Variscan magmatic rocks and reworked fragments of Cadomian crust. [ABSTRACT FROM AUTHOR]

Post‐collisional volcanic rocks of Mesozoic age occur in the regions adjacent to Gerze, part of the southern Qiangtang Terrane of northern Tibet, China. Geochronological, geochemical, and whole‐rock Sr‐Nd isotopic analyses were performed on the volcanic rocks to better characterize their emplacement age and models for their origin. Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U‐Pb zircon analyses yielded consistent ages ranging from 123.1±0.94 Ma to 124.5±0.89 Ma for six volcanic rocks from the study area. The intermediate volcanic rocks belong to the alkaline and sub‐alkaline magma series in terms of K2O+Na2O contents (5.9%–9.0%), and to the shoshonitic and calc‐alkaline series on the basis of their high K2O contents (1.4%–3.3%). The Gerze volcanic rocks are characterized by the enrichment of light rare earth elements [(La/Yb)N=34.9–49.5] and large–ion lithophile elements (e.g., Rb, Ba, Th, U, K, Pb, and Sr), slightly negative Eu anomalies (Eu/Eu*=0.19–0.24), and negative anomalies in high field strength elements (e.g., Nb, Ta, Hf and Ti), relative to primitive mantle. The samples show slightly elevated (87Sr/86Sr)i values that range from 0.7049 to 0.7057, and low ∊Nd(t) values from –0.89 to –2.89. These results suggest that the volcanic rocks studied derived from a compositionally heterogeneous mantle source and that their parent magmas were basaltic. The more mafic, parental magmas to the Gerze volcanic rocks likely underwent fractional crystallization of clinopyroxene, hornblende, biotite, and potassium feldspar, during ascent, with little to no crustal contamination, prior to their eruption/emplacement. While these volcanic rocks exhibit geochemical signatures typical of magmas formed in a destructive plate‐margin setting, it is plausible that their mantle source might also have acquired such characteristics in an earlier episode of subduction. [ABSTRACT FROM AUTHOR]

This paper presents new geochemical, U–Pb geochronological, and Sm–Nd isotopic data for early Paleozoic granitoids and acidic volcanic rocks within the Mamyn Terrane that constrain the early Paleozoic tectonic evolution of the eastern central Asian orogenic belt (CAOB). The Mamyn Terrane is usually considered part of the Argun Massif, although our new geochronological data indicate the presence of two magmatic events within the terrane that occurred at the Ediacaran–Cambrian boundary (∼541 Ma) and the late Cambrian–Early Ordovician boundary (507–488 Ma). Field observations indicate that all of the late Ediacaran–Early Cambrian (∼541 Ma) volcanic rocks are deformed whereas the Late Cambrian–Early Ordovician (507–488 Ma) intrusive and volcanic rocks are either deformed or undeformed. The ∼541 Ma magmatic event in the study area produced rhyodacite, trachyrhyodacite, and trachyrhyolite units that are either high-K calc-alkaline or shoshonitic. These units have ε Nd(t) values from −7.4 to −8.7, t Nd(DM) ages of 1.9–1.8 Ga, and formed from primary magmas generated by the partial melting of Mesoproterozoic continental crustal material in a suprasubduction zone setting. The Late Cambrian–Early Ordovician (507–488 Ma) magmatic event in this area formed gabbrodiorite, diorite, granodiorite, granite, trachyrhyodacite, and rhyodacite units that are medium-K and calc-alkaline, and have arc-like trace element compositions that are enriched in the large ion lithophile elements (LILEs) and depleted in the high field strength elements (HFSEs). These units have initial 87 Sr/ 86 Sr (i) ratios and ε Nd(t) values that range from 0.7048 to 0.7067 and from −3.3 to −0.2, respectively, yielding t Nd(DM) ages of 1.6–1.1 Ga. These features indicate that the magmas that formed these units were generated in a subduction zone setting, most likely by the partial melting of Mesoproterozoic crustal material with the addition of some younger juvenile material. In addition, the Late Cambrian–Early Ordovician trachyrhyodacite and rhyodacite units in this area are high-K and calc-alkaline or are shoshonitic and are enriched in K, Rb, the rare earth elements (REE), Y, Nb, Ta, and Zr, and are depleted in Sr and have A-type granite affinities. However, these units do not contain alkali amphibole or pyroxene and have high FeO tot /MgO ratios (6.7–12.7) that indicate they formed from highly fractionated magmas. Therefore, these volcanic rocks represent extreme melt differentiates that also formed the coeval granites. The early Paleozoic magmatic events within the Mamyn Terrane have also been identified in the Argun, Bureya, and Jiamusi areas of the eastern CAOB, suggesting that all of these areas have a common geodynamic history. [ABSTRACT FROM AUTHOR]

Limited geochronological and geochemical data from Early Cretaceous igneous rocks of the Gangdese Belt have resulted in a dispute regarding the subduction history of Neo-Tethyan Ocean. To approach this issue, we performed detailed in-situ zircon U–Pb and Hf isotopic, whole-rock elemental and Sr–Nd isotopic analyses on Late Mesozoic volcanic rocks exposed in the Liqiongda area, southern Lhasa terrane. These volcanic rocks are calc-alkaline series, dominated by basalts, basaltic andesites, and subordinate rhyolites, with a bimodal suite. The LA–ICPMS zircon U–Pb dating results of the basaltic andesites and rhyolites indicate that these volcanic rocks erupted during the Early Cretaceous (137–130 Ma). The basaltic rocks are high-alumina (average > 17 wt.%), enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs), showing subduction-related characteristics. They display highly positive zircon ε Hf (t) values (+ 10.0 to + 16.3) and whole-rock ε Nd (t) values (+ 5.38 to + 7.47). The silicic suite is characterized by low Al 2 O 3 (< 15.4 wt.%), Mg # (< 40), and TiO 2 (< 0.3 wt.%) abundances; enriched and variable concentrations of LILEs and REEs; and strongly negative Eu anomalies (Eu/Eu* = 0.08–0.19), as well as depleted Hf isotopic compositions (ε Hf (t) = + 4.9 to + 16.4) and Nd isotopic compositions (ε Nd (t) = + 5.26 to + 6.71). Consequently, we envision a process of basaltic magmas similar to that of MORB extracted from a source metasomatized by slab-derived components for the petrogenesis of mafic rocks, whereas the subsequent mafic magma underplating triggered partial melting of the juvenile crust to generate acidic magma. Our results confirm the presence of Early Cretaceous volcanism in the southern Lhasa terrane. Combined with the distribution of the contemporary magmatism, deformation style, and sedimentary characteristics in the Lhasa terrane, we favor the suggestion that the Neo-Tethyan oceanic lithosphere was flat-lying beneath the Lhasa terrane during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

An integrated study of zircon U-Pb ages and Hf-O isotopes, whole rock and apatite geochemistry, and whole rock Sr-Nd-Hf isotopes were conducted for the Jurassic adakitic volcanic rocks from the Tiaojishan Formation in the Yanshan Fold and Thrust Belt (YFTB) of the North China Craton, to investigate their genesis, with attention to the role of crust thickness in achieving the adakitic traits. Zircon U-Pb dating gives eruption ages of 162–158 Ma for these rocks. These rocks have variable SiO 2 (55.7–68.1 wt%) and MgO (0.35–4.0 wt%), and adakitic trace element signatures including high Sr/Y (27.9–100) and (La/Yb) N ratios (9.6–27.6). Chemical variations in whole rock and apatite suggest a feldspar-dominated fractional crystallization, superimposed by variable mineral accumulation on whole rock compositions. Together with isotopic compositions that include evolved whole rock (87Sr/86Sr) i = 0.70447–0.70591, ε Nd (t) = −17.5 to −12.1, and ε Hf (t) = −22.2 to −11.2, and zircon ε Hf (t) = −26.8 to −11.2 and δ18O = 5.7–7.0 ‰, we attribute these rocks are sourced from mafic lower continental crust. By comparing the trace element signatures between the examined samples and modern continental arc magmatic rocks formed at variable crustal thickness, it is suggested that these rocks are most likely originated from a thickened crust. A further estimate based on whole rock Sr/Y and La/Yb gives a crust thickness of 56 ± 7 km. The crust thickening and associated uplift of the YFTB could be attributed to the westward subduction of the Paleo-Pacific plate. This led to a high altitude (∼3.8 ± 0.9 km) and cool climate habitat (a mean annual paleotemperature of 7 ± 7 °C) for the Yanliao Biota lived therein during this period, which may have played an important role in the earliest appearance of the feathered characteristic of dinosaurs. • A thickened lower continental crust source is responsible for the volcanic rocks. • Crust thickening and uplift are related to the subduction of the Paleo-Pacific plate. • Uplift-induced cooling may be important for the appearance of feathered dinosaurs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Sanhe represents the initial phase of Mesozoic Pb–Zn–Ag mineralization at Argun Massif. • Incursion of unusually metal-rich fluid was critical to the Sanhe ore formation. • The deposit belongs to intermediate sulfidation (IS)-epithermal type. • Fluid mixing was likely the main trigger for mineralization. The Sanhe is a typical medium-size Pb–Zn–Ag deposit in the Argun Massif, NE China. Its Pb–Zn–Ag orebodies are mainly hosted in the Jurassic Tamulangou Formation volcanic rocks. The orebodies occur as quartz vein clusters. The ore-forming quartz porphyry is LA–ICP–MS zircon U–Pb dated to be 165.2 ± 1.2 Ma, and the ore sphalerite yielded a Rb–Sr age of 162.5 ± 4.3 Ma. These ages indicate that the Sanhe represents the oldest Pb–Zn–Ag mineralization in the Argun Massif. Combined with published age data, the Pb–Zn–Ag mineralization of the Argun Massif occurred in three phases at ca. 160 Ma, 140 Ma and 130 Ma. The quartz porphyry shows right-inclining REE ((La/Yb) N = 22.92–40.69) patterns and negative Eu anomalies (δEu = 0.68–0.81), together with enrichments in K, La, Ce, Nd, Zr and Hf but depletions in Ba, Ta, Nb, Sr, P and Ti. Whole-rock geochemistry and Hf isotopes suggest that the quartz porphyry was derived from partial melting of juvenile lower crustal materials during the post–collision extension of the Mongol–Okhotsk orogenic belt. Sulfide S–Pb isotope compositions indicate that the ore-forming materials were derived from the deep magma, whilst He isotopes indicate that the ore fluids were dominantly crustal-derived. Fluid chemical compositions obtained from LA–ICP–MS single fluid inclusion analyses support that mixing of magmatic fluids with meteoric water was an important mineralization trigger at Sanhe. Our new data show that the involvement of unusually metal-rich fluids is a prerequisite to form abundant Pb–Zn–Ag mineralization at Sanhe. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Cretaceous Sn mineralization in SGXR is formed under slab roll-back setting. • Cu-rich Sn granites are characterized by higher fO 2 , lower differential degree and ASI than those of Sn-W granites. • Ore-forming process experienced the cooling, increasing volatile contents and fluid-rock reaction. • Injection of oxidized fluids exsolved from mafic magma contributes to the Sn-Cu mineralization. Primary tin deposits usually contain little or no copper due to the distinct geochemistry of Sn and Cu. However, examples of copper-rich tin deposits in many tin provinces around the world are also well known. The genesis of copper-rich tin deposits remains controversial. The Maodeng Sn-Cu polymetallic, a typical Cu-rich Sn deposit in the southern Great Xing'an Range (SGXR) Northeast China, offers an excellent opportunity to reveal the genesis of coupled copper-tin deposits. The ore mineralization is associated with the granite porphyry, complement phase of the Alubaogeshan complex, which emplaced into the volcanic rocks of the Lower Permian Dashizhai Formation. Herein, we report new zircon and cassiterite U-Pb ages and their trace elements compositions, with the aim of constraining the metallogenic chronology framework, and clarifying the indicative effects of the ore-forming fluids on mineralization in different ore-forming stages, and thus establishing the genetic model for the Sn-Cu deposit. LA-ICP-MS U-Pb dating of zircon from the granite porphyry yields a weighted mean U-Pb age of 134.6 ± 0.4 Ma, which consistent to the zircon U-Pb age (ca. 138 Ma) of porphyry monzogranite (main phase of the Alubaogeshan complex) and cassiterite U-Pb ages (137–140 Ma), suggesting an Early Cretaceous Sn-Cu mineralization under the Paleo-Pacific plate slab roll-back setting. Granite porphyry displays more evolved characterisrics, with higher SiO 2 contents (71.5 ∼ 77.4 wt%), Rb/Sr ratios (3.39 ∼ 10.33) and lower Nb/Ta ratios (10.86 ∼ 13.06) compared to those of porphyry monzogranite (SiO 2 contents of 70.4 ∼ 72.1 wt%; Rb/Sr and Nb/Ta ratios of 1.03 ∼ 1.72 and 13.34 ∼ 15.83, respectively). This is further supported by the trace elements contents of zircons from granite porphyry and porphyry monzogranite, because the former has a stronger Eu anomaly, higher Hf concentrations, lower Zr/Hf and Th/U ratios than the latter. Our new data, integrated with previously published geochemical data, suggest that the granites associated with Cu-rich Sn deposits are characterized by higher oxygen fugacity, lower differential degree and aluminum saturation index (ASI) than those of Sn-W deposits. This could also use to address the Sn-Cu deposits usually have relatively small Sn mineralization potential. The trace elements of the cassiterites are characterized by high Fe (up to 3358 ppm), Ti (up to 1894 ppm) and abnormal high In (∼2500 ppm) concentrations, but low Nb, Ta contents. From early to late stage, the W and U contents and Nb/Ta and Zr/Hf ratios are increased, reveal that the ore-forming process experienced the cooling, increasing volatile contents and fluid-rock reaction. Finally, a new metallogenic model was established, which highlight oxidized Cu-rich fluids exsolved from the upwelling mantle magma would add to the reduced, Sn-rich magma chambers. This contribution indicate that, the Cu and Sn metals come from the mantle magma and crustal granitic magma, respectively, and that Cu-rich Sn deposits are more likely a product of spatial coupling. [ABSTRACT FROM AUTHOR]

The volcanic rocks from the Sayabouli area in northwestern Laos have been poorly studied. These volcanic rocks are traditionally mapped as the Permian-Early Triassic sequences on the geological map. One basaltic-andesite from the Sayabouli area yields a zircon U-Pb age of 237.7±1.7 Ma, suggesting a Middle Triassic origin. All basalt and basaltic-andesite samples from the Sayabouli area show depletions in HFSEs (e.g., Nb, Ta, Ti) and have high LILE/HFSE ratios, and exhibit the geochemical affinity to the continental arc volcanic rocks and are geochemically similar to the continental arc volcanic rocks from the Phetchabun belt in northeastern Thailand, suggesting a Late Permian-Middle Triassic continental margin in the Sayabouli area of northwestern Laos and Phetchabun area of northeastern Thailand. Our data indicate that the Phetchabun arc volcanic belt through the western Loei sub-belt can be linked to the Sayabouli area in northwestern Laos. [ABSTRACT FROM AUTHOR]

The Khunik prospecting area is located 106 km south of Birjand in eastern Iran, and is considered as an epithermal gold prospecting area. The mineralization is related to subvolcanic rocks. There are several outcrops of subvolcanic intrusions in the area which intruded into Paleocene–Eocene volcanic rocks (andesite, trachy-andesite and pyroclastic rocks). Petrographic studies indicate that subvolcanic rocks consist mainly of diorite, monzonite, quartz-monzonite, monzodiorite and quartz-monzodiorite. Mineralogically, these rocks contain plagioclase, K-feldspar, amphibole, pyroxene, biotite and quartz. Geochemically, they have features typical of high-K calk-alkaline to shoshonitic and are metaluminous, and also belong to magnetite granitoid series (I-type). Primitive mantle normalized trace element spider diagrams display enrichment in LILE, such as Rb, Ba, and Cs, compared to HFSE. Chondrite-normalized REE plots show moderately LREE enriched patterns (7.45 < La N /Yb N < 10.54), and no significant Eu anomalies. Tectonic discrimination diagrams also show affinities with modern convergent margin magmas, suggesting that magmas of Khunik area formed in volcanic arc setting related to subduction of the oceanic crust under the Lut Block plate . The initial 87 Sr/ 86 Sr ratios (0.704196–0.704772) and εNdi values (+1.3 to +3.3) are compatible with an origin of the parental melts in a supra-subduction mantle wedge. Zircon U–Pb dating by LA-ICP-MS indicates the age of 38 ± 1 Ma (late Eocene) for subvolcanic units that are related to mineralization. A biotite granodiorite porphyry is the testimony of the youngest magmatic activity in the area, with an age of 31 ± 1 Ma (early Oligocene). The represented dates are interpreted as magmatic crystallization ages of subvolcanic intrusions. [ABSTRACT FROM AUTHOR]

Zircon U–Pb chronological and geochemical research has been undertaken on the volcanic rocks of the Tamulangou Formation in the Zhalantun area, middle part of the Great Xing’an Range in NE China. The volcanic rocks yield ages of ∼147 Ma (the Late Jurassic), 14–17 Myr younger than volcanic rocks of the same formation in the northern part of the Great Xing’an Range, indicating that volcanism spanned the Middle–Late Jurassic. The Tamulangou volcanic rocks, together with the JixiangFeng Formation and rhyolite of the Shangkuli Formation, constitute bimodal volcanics related to widespread coeval A-type granites, suggesting the Tamulangou Formation volcanics formed in an extensional environment. Spatial variations in petrological, geochronological, and geochemical features of the volcanic rocks of the Tamulangou Formation indicate subduction to the southeast following orogenesis and closure of the Mongol–Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

The Early–Mid-Devonian Ashele Formation of the southern margin of the Chinese Altay hosts the Ashele Cu–Zn volcanogenic massive sulfide (VMS) deposit and consists of intercalated volcanic and sedimentary rocks that have experienced regional greenschist-facies metamorphism. We studied the petrography, zircon U–Pb geochronology, geochemistry, and Sr–Nd isotopes of dacites and basalts in order to understand the petrogenesis of these rocks and the regional tectonic evolution. Two dacites yielded LA-MC-ICP-MS zircon U–Pb ages of 402 ± 6 Ma and 403 ± 2 Ma. The dacites are calc-alkaline, and characterized by high Na 2 O/K 2 O ratios (3.6–9.3), and high Mg# values (47–63), enrichment in large ion lithophile elements (LILE) and light rare earth elements (LREE), depletion in Nb, Ta, Ti, and P, and relatively positive ε Nd ( t ) values (+3.6 to +7.5), collectively suggesting a sanukitic magma affinity. The variations in the major and trace elements of the dacites indicate that Fe–Ti oxide, plagioclase, and apatite were fractionated during their petrogenesis. The basalts are tholeiitic, and are characterized by high Mg# values (66–73), and negative Nb and Ta anomalies. The geochemical characteristics of the basalts are similar to those of N-MORB. Those characteristics together with the positive ε Nd ( t ) values (+6.8 to +9.2) of the basalts, indicate that the precursor magma was derived mainly from an N-MORB-type depleted asthenospheric mantle in an island arc setting. The geochemical similarities between the basalts and dacites indicate that they both originated from a similar depleted mantle source via partial melting under different magmatic conditions in each case, possibly related to ridge subduction. [ABSTRACT FROM AUTHOR]

The Philippine island arc system is a collage of amalgamated terranes of oceanic, continental and island arc affinities. Here we investigate a volcanic suite in Cebu Island of central Philippines, including basalt, diabase dike, basaltic pyroclastic rock and porphyritic andesite. LA-ICP-MS U–Pb geochronology of zircon grains from the porphyritic andesite and pyroclastic rock yielded ages of 126 ± 3 Ma and 119 ± 2 Ma, respectively, indicating an Early Cretaceous age. The age distribution of the detrital zircons from river sand in the area displays a peak at ca. 118 Ma, close to the age of the pyroclastic rock. The early Cretaceous volcanic rocks in the central Philippines were previously regarded as parts of ophiolite complexes by most investigators, whereas the Cebu volcanics are distinct from these, and display calc-alkaline affinity and island arc setting, characterized by high LREE/HREE ratios and low HFSE contents. These features are similar to the Early Cretaceous arc basalts in the Amami Plateau and east Halmahera in the northernmost and southernmost West Philippine Basin respectively. Zircon Hf isotopes of the pyroclastic rocks show depleted nature similar to those of the Amami Plateau basalts, implying the subducted Pacific-type MORB as probable source. Zircon Hf isotopes of the porphyritic andesite show slight enrichment relative to that of the pyroclastic rocks and MORB, indicating subducted sediments as a minor end-member in the source. The Hf isotopic compositions of the volcanic rocks are also reflected in the detrital zircons from the river sands. We propose that the volcanic rocks of Cebu Island were derived from partial melting of sub-arc mantle wedge which was metasomatized by dehydration of subducted oceanic crust together with minor pelagic sediments. Within the tectonic environment of Southeast Asia during Early Cretaceous, the volcanic rocks in Cebu Island can be correlated to the subduction of paleo-Pacific plate. The Early Cretaceous volcanic suites in Cebu Island along with the Early Cretaceous arc volcanic rocks, ophiolites and boninites in the southern–western–northern margin of West Philippine Basin are inferred to have formed within single subduction zone before the opening of the Philippine Sea Plate. [ABSTRACT FROM AUTHOR]

Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U-Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios (0.43-1.18), indicating an igneous origin. Geochronological results of LA-ICP-MS U-Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma (MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations (96.04-265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc-continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic. [ABSTRACT FROM AUTHOR]

• The Bailingshan dacitic tuffs formed at 312 Ma. • Bailingshan dacitic tuffs were derived from melting of juvenile lower crust mixed with mantle materials. • The dacitic tuffs and iron mineralization were generated by the subduction of the Paleo-Tianshan oceanic plate. The Bailingshan deposit is an economically important Fe deposit in Eastern Tianshan, located in the southern margin of the Central Asian Orogenic Belt, Xinjiang, northwest China. The orebodies at Bailingshan are mainly hosted in the Carboniferous volcanic rocks. In this study, new secondary ion mass spectrometry (SIMS) zircon U-Pb dating, whole rock geochemistry, zircon Hf-O isotopic analyses and Sr-Nd isotopic analyses were carried out on the Bailingshan dacitic tuff. New SIMS zircon U-Pb dating results indicate that the dacitic tuff occurred in the Late Carboniferous (312.1 ± 3.3 Ma and 312.4 ± 4.4 Ma). The geochemistry of the dacitic tuff is consistent with calc-alkaline arc magmatism, characterized by high SiO 2 (70.33–74.70 wt%) and (La/Yb) N values of 1.06 to 3.47. In addition, the Bailingshan dacitic tuff displays variable ε Hf (t) values (+8.2 to + 14.1), low δ18O values (4.70 to 6.35 ‰), high Mg# values (30–59), together with relatively uniform ε Nd(t) values from + 2.1 to + 5.8 and (87Sr/86Sr) i ratios ranging from 0.703818 to 0.707168, suggesting a fractional crystallization dominated origination from melting of a juvenile lower crust that mixed with the depleted mantle materials was most likely responsible for genesis of the Bailingshan dacitic tuffs. Combined with regional tectonic evolution and our new data, we infer that the change of subduction angle led to the rupture of magma chamber and the release of the Fe-rich fluids from magma chamber, causing the iron mineralization and relevant alteration of Bailingshan deposit in the Aqishan-Yanmansu arc. [ABSTRACT FROM AUTHOR]

Abstract: U–Pb zircon SHRIMP geochronology and Lu–Hf zircon LA–MC–ICPMS isotope geochemistry are used to constrain the ages of Paleoproterozoic felsic magmatism and their crustal sources in the Aillik Group, Makkovik Province of Labrador. This information is important for understanding the extent of crustal reworking vs. juvenile crustal growth in subduction-related magmatism during the Paleoproterozoic and improves framework knowledge for uranium exploration in the Central Mineral Belt of Labrador. U–Pb SHRIMP zircon geochronology from four felsic tuff samples collected from two different areas of the Aillik Group yield magmatic 207Pb/206Pb ages of 1852±7Ma (2σ), 1854±7Ma (2σ), 1861±7Ma (2σ), and 1862±7Ma (2σ). The ages fall within the range of previous U–Pb zircon dates reported for felsic volcanic rocks of the Aillik Group. Altogether these dates indicate that felsic volcanism spanned at least 30m.y. and was perhaps most intense during the last 10m.y. of that interval. A foliated syn-deformational monzogranite in the Aillik Group (Cross Lake granite) yields a 207Pb/206Pb zircon date of 1805±6Ma (2σ), which indicates that development of a pervasive planar fabric associated with northwestward thrusting of the Aillik Group continued after this time. Initial values for magmatic zircons from the four felsic tuffs (−4.8 to −1.9, −1.7 to +2.2, −11.8 to +3.8, −9.0 to −4.6) and monzogranite (−4.8 to −1.5) exhibit significant variability, which indicates heterogeneous sources. Most of the zircon grains have negative initial values and calculated crust formation Hf-isotope T DM model ages point to substantial contributions from melts of ancient crust, ranging in age from ca. 2200 to 2900m.y. and clustering at ca. 2500m.y. Inherited zircon grains in the felsic tuffs and monzogranite, mainly have U–Pb ages of ca. 1880–1920Ma, though others are older, up to ca. 2743Ma. Hf-isotope T DM model ages for the inherited zircons are similar to those of the magmatic zircons. The Hf-isotope results indicate that subduction-related felsic magmatism in the Makkovik Orogen involved significant crustal reworking (∼80%) during formation of the Aillik Group. [Copyright &y& Elsevier]

Abstract: Submarine tholeiitic and calc-alkaline basalt and andesite with subordinate dacite, metamorphosed to greenschist facies, are exposed at Wadi Kareim and Wadi El Dabbah, Central Eastern Desert of Egypt. These metavolcanic sequences are representative of early stages of Neoproterozoic crust formation in the northern part of the Arabian-Nubian Shield. The magmas were primitive to moderately fractionated, as indicated by average Mg# (54), Cr (191ppm) and Ni (69ppm). Their REE patterns are slightly fractionated [(La/Yb)N =1.3–3.9], and multi-element diagrams show Ba, Sr, K and Rb enrichments and Nb and Ta depletions, typical of modern convergent margin igneous rocks. Tectonic discrimination diagrams also show affinities with modern convergent margin magmas, suggesting that Wadi El Dabbah lavas formed in a volcanic arc that experienced cryptic crustal contamination, whereas Wadi Kareim lavas formed in a back-arc basin. Positive initial ɛNd (+5.1 to +8.9) and Nd model ages (0.64–0.79Ga) indicate that the crust is juvenile and was extracted from a depleted mantle source. Wadis Kareim and El Dabbah metavolcanic rocks are dated at ∼750Ma (U–Pb SHRIMP) but contain abundant pre-Neoproterozoic zircons which might be derived from underlying sediments or perhaps older continental crust. These results indicate that a major ∼750Ma crust-forming event involving ophiolite generation and eruption of juvenile melts was important for the formation of the crust. [Copyright &y& Elsevier]

Abstract: Analyses of zircon grains from the Queureuilh Quaternary tephras (pumice) provide new information about their pre-eruptive history. U–Pb dating was performed in situ using two methods: SHRIMP and LA-MC-ICPMS equipped with a multi-ion counting system. Both methods provided reliable 207Pb/206Pb and 206Pb/238U ratios as well as U and Th abundances required for U–Pb Concordia intercept age determination, after initial 230Th disequilibrium correction. The new LA-MC-ICPMS method was validated by dating a reference zircon (61.308B) and zircons from a phonolitic lava dated independently with the two techniques. A time resolution of about 20kyr for 1Ma zircon crystals was achieved for both methods. The clear euhedral zircon population from Queureuilh tephras is quite complex from several points of view: (1) some grains are reddish or yellowish while others are colorless; (2) the U and Th composition changes by more than an order of magnitude and Th/U is generally high (∼1–2); (3) there are three discrete ages recorded at 2.35±0.04, 1.017±0.008 and 0.640±0.010Ma. From the previously determined 40Ar/39Ar age at 0.571±0.060Ma [Duffell H. (1999) Contribution géochronologique à la stratigraphie volcanique du Massif des Monts Dore par la méthode 40Ar/39Ar. D.E.A. Univ. Clermont-Ferrand, 56 p.], the discontinuous zircon age populations, the color of the grains and their composition, we favor the following model as explanation: The oldest, less numerous group of reddish zircons represents xenocrystic grains resulting from assimilation of the local material during magma ascent. A primitive magma chamber, perhaps deep in crustal level, was formed at 1.0Ma. The related magma, previously characterized by high Th/U ratio (2.2±1.1), underwent rejuvenation during ascent to a new chamber at shallow depth and/or during injection of more mafic magmas. During this stage, at 0.64Ma, the colorless zircon grains of lower Th/U ratio (1.3±0.5) crystallized. This last stage defined the magma residence time of 70kyr prior to eruption dated by the 40Ar/39Ar method. However, if the primitive magma is considered, the magma residence time as a whole from this first stage reached 446kyr. In the light of the complex history of such magmas, which commonly involves recycling of zircon grains that precipitated tens to hundreds of kyr earlier than eruptions, the use of Zr concentration in geochemical modeling of whole rock compositional data can be problematic. [Copyright &y& Elsevier]

The northwestern Erguna Block, where a wide range of volcanic rocks are present, provides one of the foremost locations to investigate Mesozoic Paleo-Pacific and Mongol-Okhotsk subduction. The identification and study of Late Jurassic mafic volcanic rocks in the Badaguan area of northwestern Erguna is of particular significance for the investigation of volcanic magma sources and their compositional evolution. Detailed petrological, geochemical, and zircon U-Pb dating suggests that the Late Jurassic mafic volcanic rocks formed at 157–161 Ma. Furthermore, the geochemical signatures of these mafic volcanic rocks indicate that they are calc-alkaline or transitional series with weak peraluminous characteristics. The rocks have a strong MgO, Al2O3, and total alkali content, and a SiO2 content of 53.55–63.68 wt %; they are enriched in Rb, Th, U, K, and light rare-earth elements (LREE), and depleted in high-field-strength elements (HFSE), similar to igneous rocks in subduction zones. These characteristics indicate that the Late Jurassic mafic volcanic rocks in the Badaguan area may be derived from the partial melting of the lithospheric mantle as it was metasomatized by subduction-related fluid and the possible incorporation of some subducting sediments. Subsequently, the fractional crystallization of Fe and Ti oxides occurred during magmatic evolution. Combined with the regional geological data, it is inferred that the studied mafic volcanic rocks were formed by lithospheric extension after the closure of the Mongol-Okhotsk Ocean. [ABSTRACT FROM AUTHOR]

The paper presents new geochemical data of the basic to intermediate volcanic rocks from the Hronic unit. The studied rocks are strongly altered and the primary mineral composition (clinopyroxenes, amphiboles, spinels, biotites, and plagioclases) is preserved only in some localities. The clinopyroxene corresponds to augite and primary amphiboles to pargasites. Spinels have a chemical composition similar to spinels from volcanic rocks. According to chemical composition, the studied basalts correspond to rift-related continental tholeiites. 143Nd/144Nd vs. 87Sr/86Sr isotopic ratios of the basalts are scattered around the value of 143Nd/144Nd for CHUR, where 143Nd/144Nd ratios are relatively stable and 87Sr/86Sr values are relatively varied. According to isotopic ratio of 207Pb/204Pb vs. 206Pb/204Pb, the basalt analyses lie in the field of EMII (mantle source enriched with crustal materials). The new results of U-Pb LA-ICP-MS dating of apatite point to an age 254 ± 23 Ma (Lopingian). [ABSTRACT FROM AUTHOR]

VMS deposits in the Iberian Pyrite Belt (IPB), Spain and Portugal, constitute the largest accumulation of these deposits on Earth. Although several factors account for their genetic interpretation, a link between volcanism and mineralization is generally accepted. In many VMS districts, research is focused on the geochemical discrimination between barren and fertile volcanic rocks, these latter being a proxy of VMS mineralization. Additionally, the volcanological study of igneous successions sheds light on the environment at which volcanic rocks were emplaced, showing an emplacement depth consistent with that required for VMS formation. We describe a case on the El Almendro–Villanueva de los Castillejos (EAVC) succession, Spanish IPB, where abundant felsic volcanic rocks occur. According to the available evidence, their geochemical features, εNd signature and U–Pb dates suggest a possible link to VMS deposits. However, (paleo)volcanological evidence here indicates pyroclastic emplacement in a shallow water environment. We infer that such a shallow environment precluded VMS generation, a conclusion that is consistent with the absence of massive deposits all along this area. We also show that this interpretation lends additional support to previous models of the whole IPB, suggesting that compartmentalization of the belt had a major role in determining the sites of VMS deposition. [ABSTRACT FROM AUTHOR]

Cretaceous volcano-sedimentary basins and successions in the Korean Peninsula are located along NE-SW- and NNE-SSW-trending sinistral strike–slip fault systems. Soft-sediment deformation structures (SSDS) of lacustrine sedimentary strata occur in the Wido, Buan, and Haenam areas of the southwestern Korean Peninsula. In this study, systematic geological, geochronological, and geochemical investigations of the volcanic-sedimentary successions were conducted to constrain the origin and timing of SSDS-bearing lacustrine strata. The SSDS-bearing strata is conformably underlain and overlain by volcanic rocks, and it contains much volcaniclastic sediment and is interbedded with tuffs. The studied SSDSs were interpreted to have formed by ground shaking during syndepositional earthquakes. U-Pb zircon ages of volcanic and volcaniclastic rocks within the studied volcano-sedimentary successions were ca. 87–84 Ma, indicating that active volcanism was concurrent with lacustrine sedimentation. Geochemical characteristics indicate that these mostly rhyolitic rocks are similar to subduction-related calc-alkaline volcanic rocks from an active continental margin. This suggests that the SSDSs in the study area were formed by earthquakes related to proximal volcanic activity due to the oblique subduction of the Paleo-Pacific Plate during the Late Cretaceous. [ABSTRACT FROM AUTHOR]

The Western Liaoning area, where a large number of Jurassic-Cretaceous volcanic rocks are exposed, is one of the typical areas for studying the Mesozoic Paleo-Pacific and Mongolia-Okhotsk subduction process, and lithospheric destruction of North China Craton. The identification and investigation of Early Jurassic adakitic volcanic rocks in the Xintaimen area of Western Liaoning is of particular significance for exploring the volcanic magma source and its composition evolution, tracking the crust-mantle interaction, and revealing the craton destruction and the subduction of oceanic plates. Detailed petrography, zircon U–Pb dating, geochemistry, and zircon Hf isotope studies indicate that the Early Jurassic intermediate-acidic volcanic rocks are mainly composed of trachydacites and a few rhyolites with the formation ages of 178.6–181.9 Ma. Geochemical characteristics show that they have a high content of SiO2, MgO, Al2O3, and total-alkali, typical of the high-K calc-alkaline series. They also show enrichment of light rare earth elements (LREEs) and large ion lithophile elements (LILEs), depletion of heavy rare earth elements (HREEs) and high field strength elements (HFSEs), and have a high content of Sr and low content of Y and Yb, suggesting that they were derived from the partial melting of the lower crust. The εHf(t) values of dated zircons and two-stage model ages (TDM2) vary from −11.6 to −7.4 and from 1692 to 1958 Ma, respectively. During the Early Jurassic, the study area was under long-range tectonic effects with the closure of the Mongolia-Okhotsk Ocean and the subduction of the Paleo-Pacific plate, which caused the basaltic magma to invade the lower crust of the North China Craton. The mantle-derived magma was separated and crystallized while heating the Proterozoic lower crust, and part of the thickened crust melted to form these intermediate-acidic adakitic volcanic rocks. [ABSTRACT FROM AUTHOR]