Triassic Magmatism Research Articles

Permian post-collisional basic magmatism from Corsica to the Southeastern Alps

Post-Variscan Early Permian magmatism is widespread from Corsica to the Eastern Alps. After the formation of the Variscan orogenic belt between Laurussia and Gondwana, felsic and mafic bodies were emplaced during an extensional tectonic phase. This study focuses on a mafic dyke swarm that intruded in the region of Ajaccio (Corsica, France) and on a gabbroic intrusive complex outcropping in the Eastern Alps (Bressanone/Brixen, South Tyrol, Italy) both of which were emplaced during this extensional event. New U-Pb data from zircon show that both of these intrusions were emplaced at ca. 282 Ma. Most Ajaccio dykes display a calc-alkaline affinity and are characterized by enrichment of LILE (Large Ion Lithophile Elements) and LREE over HREE (Light and Heavy Rare Earth Elements) and HFSE (Nb, Ta, Hf, Zr; High Field Strength Elements). Two dykes show tholeiitic affinity and are characterized by marked LREE and Th-U depletion and by minor negative Nb-Ta anomalies on multi-element diagrams, which is typical for within-plate basalts. Bressanone/Brixen gabbros display similar geochemical features to the Ajaccio calc-alkaline samples with LREE enrichment over MREE (Medium Rare Earth Elements) and HREE, and HFSE depletion. Such characteristics are also confirmed by trace element data obtained by LA-ICP-MS on clinopyroxene and plagioclase crystals.The calc-alkaline to tholeiitic dykes are characterized by enriched to depleted Sr-Nd-Pb isotopic compositions, respectively. Some Ajaccio dykes and the Bressanone/Brixen gabbros are clearly affected by crustal contamination. However, the combination of trace element and isotopic variations suggests that mantle source heterogeneities were also involved. Isotopic compositions of the Ajaccio dykes reveal the presence of two distinct mantle source signatures: an enriched mantle (EM) component, which dominates the composition of the calc-alkaline-like suite, while a DMM (Depleted MORB Mantle) component dominates the source of the tholeiitic suite. The EM mantle source likely formed during Variscan subduction, however the composition of the tholeiitic suite requires a source composed dominantly of depleted mantle, with a minor contribution from both the subducting slab and supra-subduction mantle wedge. The mantle source of the tholeiitic magmas possibly originated from greater depths (compared to the calc-alkaline-like suite) during the post-orogenic extensional phase potentially due to break-off and/or roll-back of the Variscan slab or mantle flow from the front or margins of the subducted slab.Notably, coeval Permian mafic intrusive bodies from throughout Corsica (Bocca di Tenda, Porto, Pila Canale) and from the Australpine and Southalpine Alps intruded at a similar time and have geochemical features that are very similar to the Ajaccio dyke swarm and Brixen gabbro. This indicates that a widespread Permian magmatic province developed in a post-orogenic extensional tectonic setting at the margin of the former Variscan belt. During the Middle-Late Triassic magmatism with similar enriched geochemical signatures occurred in the Southern Alps, Dinarides, Australpoine domains and at the end of the Triassic over central Pangea (Central Atlantic Magmatic Province). This would highlight the importance that the Variscan orogeny had in the development of a more fertile mantle.

Triassic magmatism and metamorphism in the Antarctic Peninsula: Identifying the extent and timing of the Peninsula Orogeny

The mid to Late Triassic marks an episode of magmatism, deformation and metamorphism along the proto-Pacific margin of the Antarctic Peninsula and Patagonia. Calc-alkaline magmatism at ~227 Ma developed in a convergent margin setting across the central Antarctic Peninsula and North Patagonian Massif. Two distinct deformation and metamorphic events have been identified at ~221 Ma and ~207 Ma based on new U–Pb zircon ages from a metamorphic orthogneiss complex, investigated for the first time, from the elevated plateau region of central Palmer Land. These two events are interpreted to date the timing of the multi-phase Peninsula Orogeny, which correlates with the Chonide Event of central Patagonia. The onset of deformation in the Antarctic Peninsula is linked to tectonic events in central Patagonia and is associated with non-collisional slab dynamic processes during flat slab subduction in the Late Triassic. No consistent tectonic regime is evident during the mid-to Late Triassic episodes of deformation and metamorphism, but an initial period of extension/transtension (mid-Triassic) and a compressional regime in the Late Triassic is favoured in the Antarctic Peninsula and Patagonia. The newly acquired metamorphic ages provide no clear evidence for a segmented terrane model for the Antarctic Peninsula, as Late Triassic metamorphic ages are identified from across the central and eastern domains. New U–Pb zircon ages are also presented from a suite of strongly foliated granitoids that cross-cut the Triassic orthogneisses. They are dated in the interval 140–136 Ma and represent an episode of Early Cretaceous magmatism, transtensional deformation and widespread metamorphism across northwest and central Palmer Land.

Carboniferous to Early Triassic magmatism and accretion in Alxa (NW China): implications for accretionary orogenesis of the southern Altaids

Alxa occupies a crucial position between the Tianshan–Beishan orogen to the west and the Solonker suture to the east and is important in our understanding of the accretionary orogenesis of the southern Altaids. To unravel the tectonic history of the Alxa region, we undertook an integrated study of the field geology, geochemistry and geochronology of magmatic rocks and an accretionary complex. Six granites and one rhyolite from the Zhusileng–Hangwula arc show a peraluminous, high-K calc-alkaline composition and one gabbro is tholeiitic. They show patterns rich in incompatible elements and negative Nb–Ta anomalies on primitive mantle-normalized trace element spider diagrams. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating reveals 348–329 and 267–250 Ma magmatic events. These data indicate that the Zhusileng–Hangwula arc was a Japan-type island arc from the late Paleozoic to Early Triassic. The Engger Us mélange comprises pillow basalts with a normal-type mid-ocean ridge basalt composition, tuffs, cherts, siliceous mudstones, limestones and turbidites, which are tectonically juxtaposed by a block-in-matrix structure. This mélange is interpreted as a Carboniferous–Permian accretionary complex. These new data, combined with previous studies, confirm that the Palaeo-Asian Ocean subducted bidirectionally in the Alxa region in the Carboniferous–Early Triassic. A consistent divergent subduction system existed from Alxa to Solonker before the terminal closure of the Palaeo-Asian Ocean in the Mid- to Late Triassic. Supplementary material: Major and trace element data and zircon U-Pb age results of all the samples are available at: https://doi.org/10.6084/m9.figshare.c.4962230

A tectonic transition from closure of the Paleo-Asian Οcean to subduction of the Paleo-Pacific Plate: Insights from early Mesozoic igneous rocks in eastern Jilin Province, NE China

The timing of tectonic transition from the Paleo-Asian oceanic regime to the Paleo-Pacific regime in the easternmost Central Asian Orogenic Belt remains controversial. To constrain the event, we present new zircon U-Pb ages, Hf isotopic compositions, and whole-rock major- and trace-element data for early Mesozoic igneous rocks from eastern Jilin Province, NE China. These new ages, together with existing age data, indicate that early Mesozoic magmatism in the Kaiyuan–Yanji area can be subdivided into four stages: Early Triassic (ca 250 Ma), Early–Middle Triassic (249–235 Ma), Late Triassic (229–208 Ma) and latest Triassic to Early Jurassic (207–175 Ma). The Early Triassic igneous rocks constitute a bimodal igneous rock association that formed in an extensional environment caused by break-off of the subducting slab during final closure of the Paleo-Asian Ocean. The Early–Middle Triassic magmatism is dominated by adakitic granitoids whose primary magmas were derived from partial melting of thickened mafic lower crust, suggesting that the North China Craton and Songliao–Xilinhot Block were still undergoing collisional orogenesis at 249–235 Ma. The Late Triassic igneous rocks comprise a typical bimodal association of rocks in an E–W-trending belt, formed in a post-orogenic extensional environment related to final closure of the Paleo-Asian Ocean. The latest Triassic to Early Jurassic igneous rocks have calc-alkaline characteristics, were emplaced as a NE–SW-trending belt parallel to the eastern margin of Eurasia, and formed in an active continental margin setting associated with initial subduction of the Paleo-Pacific Plate. We conclude that the tectonic transition between the Paleo-Asian and the Paleo-Pacific regimes took place during the latest Triassic.

Triassic magmatism in the European Southern Alps as an early phase of Pangea break-up

AbstractMagmatic rocks from the Dolomites, Carnic and Julian Alps, Italy, have been sampled to investigate the origin and geodynamic setting of Triassic magmatism in the Southern Alps. Basaltic, gabbroic and lamprophyric samples have been characterized for their petrography, mineral chemistry, whole-rock major and trace elements, and Sr, Nd and Pb isotopic compositions. Geothermobarometric estimates suggest that the basaltic magmas crystallized mostly at depths of 14–20 km. Isotopic data show variable degrees of crustal contamination decreasing westwards, probably reflecting a progressively more restitic nature of the crust, which has been variably affected by melting during the Permian period. Geochemical and isotopic data suggest that the mantle source was metasomatized by slab-derived fluids. In agreement with previous studies and based on geological evidence, we argue that this metasomatism was not contemporaneous with the Ladinian–Carnian magmatism but was related to previous subduction episodes. The lamprophyres, which likely originated some 20 Ma later by lower degrees of melting and at higher pressures with respect to the basaltic suite, suggest that the mantle source regions of Triassic magmatism in the Dolomites was both laterally and vertically heterogeneous. We conclude that the orogenic signatures of the magmas do not imply any coeval subduction in the surrounding of Adria. We rather suggest that this magmatism is related to the Triassic rifting episodes that affected the western Mediterranean region and that were ultimately connected to the rifting events that caused the break-up of Pangea during the Late Triassic – Early Jurassic period.

Anisian granodiorites and mafic microgranular enclaves in the eastern Kunlun Orogen, NW China: Insights into closure of the eastern Paleo–Tethys

Granitoids and their mafic microgranular enclaves (MMEs) provide important insights into magmatic activity and tectonic evolution associated with accretionary orogens. Here we investigate the origin of Middle Triassic granodiorites and MMEs in the central segment of the eastern Kunlun Orogen (EKLO) in NW China, which is an important region to evaluate the history of closure of the Paleo–Tethys, through zircon U–Pb geochronology, major and trace element geochemistry, and Sr–Nd–Hf isotopes. Zircon U–Pb ages indicate the coeval formation of granodiorites and their MMEs during the Anisian (ca. 245 Ma). The granodiorites are calc‐alkaline and metaluminous with high SiO2 contents and Mg# values. They are characterized by enrichment of LREEs and LILEs, and depletion of Nb, Ta, and Ti. Their Sr–Nd –Hf isotopic compositions indicate that the magmas were derived from enriched mantle and Paleoproterozoic basement. The monzodioritic‐dioritic MMEs exhibit low SiO2 contents and high Al2O3 and MgO with high Mg# values, enrichment in LREEs and LILEs, and depletion in HFSEs with negative Nb, Ta, Ti, and P. In contrast, the gabbroic MMEs show higher Mg# values and Cr contents. Both types of MMEs have Sr–Nd–Hf isotopic compositions similar to the host granodiorites, and originated from mixing of lower crust‐ and enriched mantle‐derived magmas. The mantle‐derived sources were metasomatized by slab‐derived melts. The Middle Permian to Middle Triassic magmatism, metamorphism, sedimentation, and tectonics in the EKLO suggest northward subduction of the Paleo–Tethys Ocean as represented by the A'nyemaqen Ocean. The magma mixing that generated the Anisian granodiorites and MMEs was likely associated with slab break‐off of the Paleo–Tethys Ocean. The formation of the Anisian magmatic rocks in the EKLO suggest that the cessation of subduction of the Paleo–Tethys Ocean and onset of collision took place during the late stage of Middle Triassic.

Permian–Triassic magmatism in response to Palaeotethys subduction and pre-Late Triassic arrival of northeast Gondwana-derived continental fragments at the southern Eurasian margin: Detrital zircon evidence from Triassic sandstones of Central Iran

The closure of Palaeotethys that led to the collision of the Cimmerian blocks with the southern Eurasian margin causing the Eo-Cimmerian orogeny during the Early Mesozoic is still controversially discussed. The Triassic Nakhlak Group in Central Iran is a key sedimentary succession for better understanding the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East. The Nakhlak Group is composed of the Alam (Olenekian to Middle Anisian), Baqoroq (?Upper Anisian to Middle Ladinian) and Ashin (Upper Ladinian to ?Carnian) formations, which consist mainly of volcaniclastic sandstones, mixed siliciclastic conglomerates, and marine carbonates. Here we present for the first time detrital zircon UPb ages from the Nakhlak Group to unravel its provenance and constrain its palaeotectonic position within the Palaeotethyan realm. Most detrital zircons from the Nakhlak Group are euhedral and subhedral with Permian–Triassic ages (ca. 280–240 Ma) suggesting sediment supply from Permian–Triassic magmatic rocks of the Silk Road Arc. Minor zircon populations show pre-Permian Palaeozoic ages, with age peaks at ca. 320 Ma and 480 Ma, which are probably derived from the basement on which the magmatic arc developed. Neoproterozoic–latest Mesoproterozoic (ca. 550–1100 Ma) and Palaeoproterozoic (ca. 1800–2200 Ma) zircon grains are anhedral (rounded). The latter are prominent in the upper Baqoroq Formation (Middle Ladinian) suggesting recycling of older sedimentary rocks. Sandstone petrography points toward an additional metamorphic provenance for this formation. This short-lived provenance change can be explained by tectonic uplift in the source area that led to erosion of metamorphosed rocks with a northeast Gondwanan affinity. It clearly indicates that northeast Gondwana-derived continental fragments likely belonging to the Cimmerian blocks already arrived at the southern Eurasian margin in pre-Late Triassic time. Current palaeotectonic models of the closure of Palaeotethys and the Eo-Cimmerian orogeny in the Middle East during the Triassic may need to be revised.

Geochemical characteristics of the adakite-like Dodurga Pluton (Central Pontides, N Turkey): implications for Middle Triassic continental arc magmatism in southern Black Sea region

The tracing of Triassic arc magmatism is much-debated for a long time along the Sakarya Composite Terrane in Turkey and the southern Black Sea region. The Dodurga Pluton is located in the Central Pontides (N Turkey), one of the most complicated regions around the Black Sea region, and represents the first documented middle Triassic continental arc in the region. This pluton comprises of dacite porphyry and granodiorite, and displays calc-alkaline signatures, which is in agreement with arc-related and I-type magmas. The PM-normalized multi element and CN-normalized REE patterns are akin to volcanic arc granites, and characterized by LILEs and LREEs enrichments relative to HFSEs and HREEs coupled with negative Nb anomalies, which confirm derivation in a subduction-related tectonic setting. Moreover, the major and trace element systematics of the samples including higher Sr/Y ratios (22.93–101.36) and lower Yb contents (0.31–1.30 ppm) are consistent with those from adakitic melts compared to classical arc magmas. Therefore, this pluton also represents the first middle Triassic adakite-like magmatic occurrence in Turkey. Overall petrographic and geochemical signatures reported here indicate that the Dodurga Pluton might have been derived from a heterogeneous source, mixed by melts from subducted oceanic slab and lower continental crust in an active continental margin. Based on the Tethyan evolution in the Anatolian realm, three geodynamic scenarios are possible for its formation, and it could have been formed as a result of northward or southward-subduction of the Paleotethys Ocean or northward-subduction of the northern branch of Neotethys Ocean during the middle Triassic.

The giant Zaozigou Au-Sb deposit in West Qinling, China: magmatic- or metamorphic-hydrothermal origin?

Understanding the relationship between mineral occurrences and host granitic rocks can be controversial. The Zaozigou Au-Sb deposit (118 t Au, 0.12 Mt Sb), hosted in metasedimentary rocks and dacitic to granodioritic sills and dikes, is one such example of a large gold deposit argued to have formed from either magmatic or metamorphic hydrothermal processes. Two populations of monazite are identified within a mineralized dacite located along a major shear zone. Magmatic monazite commonly occurs within magmatic biotite and quartz phenocrysts and is characterized by uniform and high Th concentrations. It has a crystallization age of 238.3 ± 2.6 Ma, consistent with the zircon U-Pb age of 238.0 ± 1.8 Ma from the same dacite. Hydrothermal monazite is associated with sulfides and sericite, and has a 207Pb-corrected 206Pb/238U age of 211.1 ± 3.0 Ma. The amount of Th in hydrothermal monazite is widely variable. The low Th content of some monazite grains reflects direct precipitation from a metamorphic hydrothermal fluid. Furthermore, the elevated Th content in other hydrothermal monazite grains is likely due to the release of Th (and U) into hydrothermal fluids by dissolution of pre-existing Th-rich minerals in the country rock during ore-related alteration events. The magmatism, which overlaps Middle-Late Triassic terrane subduction-accretion in the West Qinling orogen, thus pre-dates the ore-forming event by about 30 m.y. The δ34S values of pyrite, arsenopyrite, stibnite, marcasite, and chalcopyrite from disseminated- and vein-type ores range from − 12.0 to − 5.5‰. Such negative values are distinct from those measured for other deposits in the northwestern part of the orogen that are genetically related to Triassic magmatism, including the Xiekeng-Jiangligou-Shuangpengxi Cu-Au-Fe-Mo skarn, Laodou reduced intrusion-related Au, and Gangcha epithermal Au ores. The Zaozigou deposit is best classified as an epizonal orogenic Au-Sb deposit. Our results demonstrate the usefulness of high-precision in situ geochronology on monazite for deciphering age relationships in ore deposits that have spatial associations with granitic rocks, thus aiding in the testing of the veracity of ore formation models.

The Late Triassic basic magmatism and tectonic implication in Leiwuqi area, eastern Tibet

羌塘地体东部类乌齐地区是龙木措-双湖古特提斯洋和班公湖-怒江特提斯洋的叠加控制区域，该地区三叠纪的岩浆活动同时受两个大洋演化的影响，导致该地区岩浆岩的构造属性尚不明确。本文对类乌齐地区吉塘岩群内出露的变辉长岩的岩石学、锆石U-Pb年代学和Lu-Hf同位素以及岩石地球化学进行了研究。LA-ICP-MS锆石U-Pb测年结果显示变辉长岩结晶年龄为212~206Ma（晚三叠世）。岩石富集LREEs、Th，亏损Nb、Ta、Zr、Hf和Ti，表现出典型的岛弧火山岩的地球化学特征，较低的ε_Hf（t）值（-10.6~-3.2）表明岩浆来自中元古代岩石圈地幔部分熔融或富集地幔，较高的Th和LREEs含量以及Th/Yb和Th/Nb比值表明岩浆源区有不同程度俯冲沉积物的加入。结合区域上前人的研究成果，本文认为类乌齐地区变辉长岩是形成在班公湖-怒江特提斯洋向北俯冲在羌塘地体下的大陆弧背景下。;The Leiwuqi area in the eastern Qiangtang terrane is a tectonic superposition region, of which the tectonic evolution was controlled by both the Longmu Tso-Shuanghu Paleo-Tethyan Ocean and the Bangong-Nujiang Tethyan Ocean. The Triassic magmatism occurred in this area has been suggested to be related to the evolution of these two ancient oceans, which leads to controversy about the tectonic settings of the Triassic magmatic rocks. In this paper, we investigated the metagabbro of Jitang Group in the Leiwuqi area with petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotope. The zircon U-Pb dating result indicates that the metagabbro crystallized at the Late Triassic (c. 212~206Ma). The metagabbro displays enrichment in LREEs and Th, and depletion of Nb, Ta, Zr, Hf and Ti, consistent with those of arc-related magmatic rocks. The negative zircon ε_Hf(t) values (-10.6~-3.2) of the metagabbro indicates it was probably derived from the partial melting of the Meso-proterozoic continental lithospheric mantle or enriched mantle. The high LREEs and Th contents and Th/Yb and Th/Nb ratios suggest the involvement of subducted sediments to the magma source. Combined with previous published data, it is concluded that the metagabbro formed in an arc-related setting related to the northward subduction of the Bangong-Nujiang Tethyan Ocean beneath the Qiangtang terrane.

Late Triassic extensional deformation and magmatism in the eastern part of the Central Asian Orogenic Belt: Constraint from <sup>40</sup>Ar/<sup>39</sup>Ar and zircon U-Pb geochronology

通过对中亚造山带东段南缘发育的解放营子韧性剪切带的构造学研究，揭示出该地区岩石圈减薄后发生了一期强烈的伸展变形事件。野外观测和岩相学分析显示该韧性剪切带呈北东-南西走向，变形带内发育有大量的A型褶皱，矿物和砾石拉伸线理以及同构造花岗质岩墙。S-C组构、σ型角闪石残斑、压力影构造、斜长石书斜构造以及云母鱼等显微构造，指示该韧性剪切带为右旋剪切。多晶石英的波状消光、晶粒边界迁移重结晶、多晶石英条带等显微变形组构表现出中温（300~500℃）的变形条件。动态重结晶颗粒的粒径统计分析和岩石有限应变分析显示该韧性剪切带形成于一个地壳中等层次的伸展变形环境。剪切带内同构造白云母40Ar/39Ar阶段加热同位素年代学分析以及同构造花岗岩的锆石U-Pb同位素年代学测试显示，该韧性剪切带的伸展变形时代为晚三叠世（219~227Ma）。该期伸展变形事件在华北板块北缘和中亚造山带形成了低硅型和高硅型两种花岗质岩浆的侵入。其中中亚造山带内发育的低硅型岩石的岩浆源区为亏损型地幔岩石圈，并进一步演化出高硅型岩石；而华北板块北缘发育的低硅型岩浆起源于富集型岩石圈地幔，同时混入了亏损的软流圈地幔组分。

The Gondwanan margin in West Antarctica: Insights from Late Triassic magmatism of the Antarctic Peninsula

Triassic orthogneisses of the Antarctic Peninsula provide evidence for the Palaeozoic and Mesozoic geological evolution of southern Gondwana within Pangaea. These rocks are sporadically exposed in southeastern Graham Land and northwestern Palmer Land, although reliable geochronological, geochemical and isotopic data are sparse. We combine new geochronological (LA-ICP-MS zircon UPb), geochemical, and zircon (Hf, O) and whole rock isotopic (Nd, Sr and Pb) data to constrain the age and Triassic – Palaeozoic tectonic setting of these rocks. Zircon cores record Palaeozoic arc magmatism between 253 ± 2 and 528 ± 6 Ma, which was mainly located to the west of the Eastern Palmer Land Shear Zone (Central Domain; Vaughan and Storey, 2000). The arc is considered to be an extension of contemporaneous Palaeozoic arcs that have been identified along the Pacific margin of South America and the Thurston Island Block. Regions to the east of the Palmer Land Shear Zone (Eastern Domain, Vaughan and Storey, 2000) were located distal from the Terra Australis Margin, and possibly resided within Sunsas-aged belts within Pangaea. Triassic continental arc, calc-alkaline magmatism during 223–203 Ma modified the crust of the Antarctic Peninsula on both sides of the Eastern Palmer Land Shear Zone. Magmatic sources included igneous and sedimentary crustal material, which formed by crustal reworking during Sunsas- and Braziliano-aged orogenesis, and Palaeozoic arc magmatism. Arc magmatism accompanied sinistral extension which brought both domains into the arc and resulted in steady oceanward migration of the Triassic arc during the Middle – Late Triassic. We propose that sinistral displacement occurred along the Eastern Palmer Land Shear Zone, and this structure was active as early as the Triassic. Finally, we conclude that both the Eastern and Central Domains are autochthonous to Gondwana.

Recognition of Late Triassic Cu-Mo Mineralization in the Northern Yidun Arc (S.E. Tibetan Plateau): Implications for Regional Exploration

The Yidun arc, located in the southeastern Tibetan Plateau, was formed by the westward subduction of the Ganze-Litang Paleo-Tethys ocean in Late Triassic. It is well-known for the formation of numerous Mesozoic porphyry-skarn Cu-Mo-(Au) deposits in the arc. To date, more than 20 Cu-Mo-(Au) deposits (>10 million tonnes Cu resources) have been discovered in the southern Eastern Yidun arc. However, few Cu-Mo deposits have been discovered in the northern Eastern Yidun arc. In recent years, some Cu-Mo deposits or occurrence are successively discovered in the northern Eastern Yidun arc, but their ore-forming ages are not well constrained. It remains unclear whether such Cu-Mo mineralization formed by similar metallogenic event and geodynamic setting as the Cu-Mo-(Au) mineralization in the south. In order to determine the metallogenic age and shed light on potential links between Cu-Mo mineralization and regional magmatic events, we present molybdenite Re-Os and zircon U-Pb ages to constrain the timing of two types of Cu-Mo mineralization in the northern Eastern Yidun arc (type I and type II). Molybdenite ICP-MS Re-Os dating results show that type I mineralization was formed at 217.7 ± 3.6 Ma, which is highly consistent with the formation ages of the host granite (218.1 ± 1.5 Ma, 2σ, n = 15, MSWD = 0.92) and aplite dyke (217.3 ± 1.3 Ma, 2σ, n = 16, MSWD = 0.50) within error. While the type II mineralization has a relatively younger formation age of 211.8 ± 4.7 Ma than the host granite (217.1 ± 1.5 Ma, 2σ, n = 14, MSWD = 0.96) and type I Cu-Mo mineralization. These data indicate that the Cu-Mo mineralization in the northern Eastern Yidun arc was temporally and spatially related to the Late Triassic magmatism in the region. Rhenium (Re) concentrations in the molybdenite from type I mineralization, ranging from 12.77 to 111.1 ppm (typically > 100 ppm), indicate that the ore-forming metals were derived mainly from a mantle source. However, Re contents in molybdenite from the type II mineralization, ranging from 7.983 to 10.40 ppm, indicate that the ore-forming metals were derived from a mixed mantle and crustal source with a predominantly crustal component. This study confirms that the northern Eastern Yidun arc exists Late Triassic Cu-Mo metallogenesis, and thus much attention should be paid on this region to find more Late Triassic Cu-Mo resources.

Paleo-tethys late triassic orogenic gold mineralization recorded by the Yidi’nan gold deposit, West Qinling, China

The Tongren-Xiahe-Hezuo polymetallic district in the West Qinling Orogen of central China has emerged as a promising new gold belt. However, significant debate exists as to whether the numerous Triassic intrusion-hosted lode gold deposits in the district represent intrusion-related or orogenic mineral systems. The Yidi’nan gold deposit is an example of a Triassic intrusion-hosted gold deposit endowed with an estimated resource of over 20 tonnes gold. The gold mineralization at Yidi’nan is fault-controlled and hosted by granite breccias associated with cataclastic zones. Its large size and intrusive host rocks make Yidi’nan an ideal site for attempting to resolve the origin of the intrusion-hosted gold systems in the West Qinling. Zircon U-Pb ages obtained as part of this study indicate that the ore-hosting quartz diorite pluton and a later dacite dike formed at 240.3 ± 2.5 and 239.3 ± 2.4 Ma. Hydrothermal sericite from fault gouge from main gold orebody returned much younger 40Ar/39Ar plateau and normal isochron ages of 220.21 ± 0.44 and 220.42 ± 7.69 Ma. Optical microscopy investigation revealed that the sericite coexists with gold-bearing sulfides, indicating that the sericite is coeval with gold mineralization. Our new age data reveal that gold mineralization at Yidi’nan postdated the Triassic magmatism by ca. 20 million years. Such a temporal framework is consistent with the observed geologic relationships, namely mineralized breccia ore crosscutting the quartz diorite host. Such evidence also suggests that the orogenic gold mineralization in West Qinling was not genetically linked to the Triassic magmatism associated with the subduction of the Paleo-Tethys Ocean. Instead, the formation of the Yidi’nan gold deposit appears to have been part of a mineralization event associated with a Late Triassic collisional event with the release of gold-bearing fluids possibly related to crustal thickening processes. High-angle reverse shear zones produced during ongoing continental collision probably facilitated the movement of hydrothermal fluids along major structures, eventually leading to the formation of plentiful orogenic gold deposits in West Qinling.

Late Paleozoic–Early Mesozoic southward subduction-closure of the Paleo-Asian Ocean: Proof from geochemistry and geochronology of Early Permian–Late Triassic felsic intrusive rocks from North Liaoning, NE China

Many studies have confirmed the existence of Late Paleozoic–Early Mesozoic accretionary arc and subduction complex belt to the south of the Solonker-Xar Moron-Changchun-Yanji Suture (SXCYS) zone. Nevertheless, since the suture from the east is covered by the Songliao Basin, until now there have been no completed reports focused on the Late Paleozoic–Early Mesozoic intrusive rocks of this area. Recently, a sequence of granitoid intrusions was identified in the Faku area, northern Liaoning. Zircon (SHRIMP) U-Pb dating results show that there are eight groups of felsic intrusions in the study area, and the intrusions formed at 283–227 Ma (Early Permian to Late Triassic). Together with study of regional events, A four-stage tectonic evolution scenario was recommended during Permian-Triassic in the Faku area: Early Permian magmatism in an activity continental margin setting (293–274 Ma); Middle-Late Permian magmatism in a setting where subduction is translated into collision (270–255 Ma); Early-Middle Triassic magmatism in a setting where collision is translated into detachment of the oceanic slab (255–242 Ma); and Middle to Late Triassic magmatism recorded procedure of post-collision orogeny transformed into extensional environment (241–215 Ma). The Early Permian–Late Triassic felsic intrusions documented the extension-collision of the convergent continental margin and the subduction-extinction of the Paleo-Asian Ocean. Zircon Hf isotopic analyses yield εHf(t) values of −2.03–15.80, almost all of which are positive (with two points being negative), indicating the depleted characteristics of the source area. According to emplacement time and occurrence location, the plutons are interpreted to have been generated by the subduction-collision of the Paleo-Asian oceanic crust beneath the North China Craton (NCC). This study provides strong evidence for Late Paleozoic–Early Mesozoic tectonic evolution and the characterization of the eventual closure of the Paleo-Asian Ocean in the Songliao Basin overlying the northern margin of the NCC.

Tectonic evolution of the southwestern margin of Pangea and its global implications: Evidence from the mid Permian–Triassic magmatism along the Chilean-Argentine border

The tectonic evolution of the southwestern margin of Pangea supercontinent is represented by the extensive late Paleozoic–Triassic magmatism along the southwestern margin of South America, including the Chilean Frontal Andes batholiths as part of the Choiyoi province. Several models have proposed cessation of subduction as the reason behind the vast amounts of felsic magmatism and apparent lack of typical arc magmas. Here, new U-Pb in zircon ages, and geochemical and isotope analyses (Rb-Sr, Sm-Nd, Re-Os) indicate that mid Permian–Triassic granitic magmatism originated in a subduction-related extensional setting (slab rollback). Subduction and anatexis of lower continental crust were the main magma-generation mechanisms, the latter caused by asthenospheric upwelling, decompression and subsequent accumulation of underplated basalts. A comparison with coeval igneous units along the Chilean-Argentine border allows extension of this model from at least 21° to 40°S. The key elements triggering slab rollback are low subduction plate velocities and convergence rates, which can be attributed to the assembly of Pangea supercontinent (mid Permian–Triassic). Therefore, subduction of the oceanic plate beneath South America has been a continuous process from early Paleozoic times onwards—rather than having a period without subduction before the onset of the Andean cycle as previous models have invoked. New geochronological constraints indicate that the peak of the voluminous crustal-derived magmatism and related explosive volcanism (Choiyoi province) was contemporaneous with the emplacement of the Emeishan and Siberian Traps LIPs, potentially conditioning the Earth system for the environmental collapse and biotic crises related to those LIPs. The observed tectonic changes, magmatism and related environmental implications could potentially be linked to the assembly of Pangea supercontinent.

Genesis of the giant Shizhuyuan W–Sn–Mo–Bi–Pb–Zn polymetallic deposit, South China: Constraints from zircon geochronology and geochemistry in skarns

The giant Shizhuyuan W–Sn–Mo–Bi–Pb–Zn polymetallic skarn-type deposit, which lies in the world-famous Nanling W–Sn metallogenic belt, has a close affinity with the Qianlishan granite complex. Previous studies focused on the Qianlishan granitoids rather than relevant skarns, where the evolutionary processes of skarn-forming fluids, mineralized fluids and sources of metals are debated. This study carried out systematic EPMA and LA-ICPMS zircon U–Pb dating, major- and trace-element and Lu–Hf isotopic analyses for three types of skarns: ore-free, greisen stockwork and sulfide-bearing skarns at Shizhuyuan. The whole skarn zircons were classified into six age clusters (125–187 Ma, ∼235 Ma, 345–509 Ma, 677–772 Ma 811–921 Ma and >1000 Ma) and three genetic types (detrital, magmatic and hydrothermally-altered). Among them, the majority of the skarn zircons are of detrital origin (345 to 2225 Ma, peaking at ∼410 Ma, ∼710 Ma and ∼905 Ma) and showing a wide range of Th/U ratios (0.05–7.09). They share similar characteristics of zircons hosted by Devonian strata in South China, suggesting the inheritance from wall-rock. The magmatic zircons in skarns can be further subdivided into two clusters: Triassic (∼235 Ma) and Jurassic (∼150 Ma), which are derived from the corresponding granite. Ore-free skarn contains only detrital zircons that have experienced the weakest alteration, indicating the minor participation of granitic fluid. The greisen stockwork skarn consists of both detrital zircons and Jurassic magmatic–hydrothermal zircons, implying that granitic and stratigraphic materials may both contribute greatly to the W–Sn polymetallic mineralization. Sulfide-bearing skarn includes abundant detrital zircon, a few of Triassic zircons but no Jurassic zircons, indicating that the latest sulfide mineralization was dominated by sediments rather than granitic rocks. The two mineralized skarn zircons display elevated concentrations of most trace elements (e.g., U, REE, Ti, Y, P, Nb and Ta) coupled with decreased Si and Zr, which reflects strong fluid-rock reaction. The lowest ratios of Ce/Ce* (1.22–89.78, mean = 24.13) in greisen stockwork skarn zircons reveal the most reducing environment for the main W–Sn mineralizing event. Jurassic zircons are homogeneous in 176Hf/177Hf (0.282352–0.282454) and εHf (t) (−11.58 to −7.27), in well accord with local granitic rocks. Triassic zircons have variable εHf (t) (−9.5 to −1.6) values, suggesting more mantle input of precursor pluton before the Jurassic main mineralization event. Based on the zircon geochronology in skarns, we speculate that concealed Triassic magmatism exists in the deep Shizhuyuan area. Consequently, a three-stage ore-forming model was established for the giant Shizhuyuan deposit. This study further illustrates that zircon can be used as an important indicator for ore genesis in complex metallogenic systems.

Geochronology, geochemistry and petrogenesis of Late Triassic dolerites associated with the Nibao gold deposit, Youjiang Basin, southwestern China: Implications for post-collisional magmatism and its relationships with Carlin-like gold mineralization

The relationship between gold mineralization and magmatism within the Youjiang Basin of SW China remains poorly constrained as a result of the lack of outcropping igneous units in this region. This study presents new geological, geochronological, and geochemical data for recently discovered dolerite dykes associated with the Nibao gold deposit, which is located within the NW Youjiang Basin of SW China. Zircon laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) U-Pb dating of these dykes yielded an age of 213.6 ± 2.5 Ma, indicating that these dykes were emplaced during the Late Triassic and providing new evidence for Late Triassic magmatism within the study area. The dykes also represent an opportunity to investigate the petrogenesis of mafic rocks and the tectonic setting of the Late Triassic magmatism in the Youjiang Basin. These Nibao dolerite dykes contain relatively low concentrations of SiO2 (46.03–47.66 wt%), have moderate total alkali contents (K2O + Na2O = 2.71–3.15 wt%) and high total Fe as Fe2O3 (TFe2O3) contents (13.49–14.96 wt%). Their trace element compositions are indicative of an OIB-like geochemical affinity barring depletion in the high field strength elements (HFSE) such as Nb, Ta and Th. The Nibao dolerites have homogeneous Lu-Hf and Sr-Nd isotopic compositions with (87Sr/86Sr)i and (143Nd/144Nd)i values of 0.70562–0.70677 and 0.51233–0.51239, respectively. These dykes have a narrow range in associated εNd(t) and εHf(t) values from –0.70 to +0.51 and from +0.04 to +3.24, respectively. These geochemical data indicate that the dolerites associated with the Nibao gold deposit were derived from an enriched region of the asthenopheric mantle (>90 km depth) and the magmas that formed these dykes were generated by 5–10% partial melting of ∼75% garnet peridotite and ∼25% spinel peridotite material. The ascending magmas underwent both crustal contamination and the fractional crystallization of olivine, clinopyroxene and Fe oxides (e.g., magnetite or ilmenite) prior to emplacement. The Nibao dolerites are geochemically distinct from mafic rocks related to the Emeishan large igneous province, suggesting that they are not linked to this mantle plume event. Instead, they formed in an extensional setting generated by the subduction of the Song Ma oceanic plate beneath South China Block and the subsequent collision between the Indochina and South China blocks. The breakoff of the Song Ma oceanic slab caused the partial melting of the mantle source region for the Nibao dolerite dykes. These relationships suggest that the post-collision extensional environment associated with this breakoff contributed to the deeply sourced, mantle-derived Late Triassic magmatism in this area and, perhaps as well, the gold mineralization in the Youjiang Basin. Most importantly, combining the new geochronological data presented in this study with the timing of extension in this region and the results of previous research suggest that the Carlin-like gold deposits in the Youjiang Basin formed at around 213 Ma (i.e., the Late Triassic).

Origin of Triassic magmatism of the Southern Alps (Italy): Constraints from geochemistry and Sr-Nd-Pb isotopic ratios

During Middle-early Late Triassic (∼243–235?Ma) a diffuse igneous activity developed in the Southern Alps (Italy). Sparse lava flow and pyroclastic succession remnants of such Southern Alps Triassic Igneous Rocks (SATIR) crop out in the Brescian Prealps, the Vicentinian Alps (Recoaro-Schio-Posina), Non Valley, Dolomites and Julian Alps. Plutonic rocks are found in two main plutonic complexes (Monzoni and Predazzo) and a small stock (Cima di Pape). Coeval igneous products can be traced eastward to Austria and Dinarides, for a total length of ∼450?km.The coeval formation of major late Anisian-late Ladinian carbonate platforms in the subsiding eastern Dolomites, and significant uplift and subaerial erosion in the western Dolomites suggest, for these areas, the occurrence of large-scale strike-slip and extensional tectonics with the development of horst-and-graben structures.This study reports the first complete review of the SATIR activity, including new mineral chemical data on 14 samples, 61 major and trace element whole rock analyses and 7 Sr-Nd-Pb isotopic ratios for volcanic and plutonic samples from Dolomites (lavas plus Monzoni and Predazzo plutonic rocks) and Vicentinian Alps lavas. Despite the variable post-magmatic modifications, the large areal distribution of the products and their wide spectrum of chemical compositions, these samples show rather common geochemical and mineralogical characteristics and define major and trace element trends that can be associated with nearly close-system magmatic evolution. Minor upper crustal contaminations can be observed in specific cases, mostly in the most differentiated products (SiO2 >70?wt%).A specific characteristic of SATIR is their calcalkaline to shoshonitic affinity, resembling the derivation from subduction-modified mantle sources, a feature at odds with the coeval strike-slip and extensional tectonics. Geochemical modelling, petrological considerations and geological constraints allow us to propose a model in which the SATIR mantle sources reflect previous subduction metasomatism (likely occurred during Variscan times). These metasomatised mantle sources were reactivated ∼90–100 Myr after the end of the subduction, when continental rifting caused a raise of the geotherms and passive upwelling of asthenospheric mantle.

Copper Mineralization Potential of Late Triassic Granitoids in Northern Yidun Arc, SW China

Yidun arc is an important constituent of the Sanjiang Tethyan Domain in SW China. The Changdagou pluton, located in the northern part of the Yidun Arc, mainly consists of granodiorite. In this study, we conducted in-situ LA-ICP-MS zircon U-Pb dating, and trace element and Hf isotope analyses on the Changdagou granites. Age dating results yielded a weighted mean U-Pb age of 214.97 ± 0.98 Ma (MSWD = 1.2, 2σ), broadly coeval with extensive late Triassic magmatism across the Yidun Arc. All zircon grains analyzed showed high concentrations of Th, U, and HREE, with positive Ce and negative Eu anomalies. Logfo2 and CeN/CeN* values vary from FMQ −3.14 to FMQ +7.44 (average FMQ +3.98), and 14 to 172 (avg. 98), respectively. The zircon EuN/EuN* (avg. 0.22) ratios have no clear correlation with the CeN/CeN* ratios, suggesting that the former were mainly affected by the magma water content. In addition, zircon εHf(t) values vary in a narrow range (–2.9 to −4.9, avg. −3.4) that clusters around zero, indicating a greater component of mantle-derived magma. Hence, we propose that the Changdagou granodiorite was derived from a highly oxidized, “wet”, Cu-rich source, of the type likely to generate porphyry Cu mineralization. However, these parameters (logfO2, EuN/EuN*, (Ce/Nd)/Y, and εHf(t)) are all lower than those of intrusions associated with Cu ores at Pulang and Lannitang, which may explain why the Cu deposit discovered at Changdagou is small by comparison. Furthermore, on the basis of the decreasing trends of εHf, logfO2, and H2O content from south to north along the Yiduan arc, we infer that the northern segment of the Yidun arc (including Changdagou) was located further away from the subduction front.