Ridge Subduction Research Articles

Three‐Dimensional Variation of the Slab Geometry Within the South American Subduction System

AbstractSubduction of the Nazca plate results in the uneven distributions of earthquakes and arc volcanoes along the South America's western margin. Here, we construct a high‐resolution shear‐wave velocity model from immediately offshore to the backarc in South America, using advanced full‐wave ambient noise tomography. Our new model confirms and provides further constraints on three major features, including (a) extensive low‐velocity anomalies within the continental crust, (b) two high‐velocity flat slab segments located beneath southern Peru and central Chile, and (c) complex slab geometry at flat‐to‐normal transitional subduction. The flat slab segments roughly correlate with the volcanic gaps but not with the seismicity gaps. We suggest that variations of slab geometry along strike and down dip have significantly modified the flow patterns within the mantle wedge. Subduction of oceanic ridges has altered the slab dehydration processes, which can influence the distribution of arc volcanism and the occurrence of intermediate‐depth earthquakes.

Melting of mafic slab and mantle peridotite during ridge subduction of the Proto-Tethys Ocean (Qilian Orogen, NW China)

Ocean-ridge subduction and the induced slab windows are important to understand the generation of arc magmatism and growth of juvenile crust both in present and ancient subduction zones. The physical conditions of oceanic ridges control the compositions of magmas during ridge subduction, and therefore magmatic composition can act as a marker of ridge subduction in ancient orogenic belts. Here we present the petrological, geochemical and geochronological studies for sodic rhyodacites and a concurrent ophiolite complex (basalt/dolerite-gabbro and harzburgite) within the North Qilian orogen, NW China. The sodic rhyodacites are low Sr/Y tonalite-trondhjemite with depleted SrNd isotopic compositions, suggesting derivation from melting of normal mid-ocean-ridge basalts (N-MORB) at 449 ± 2.9 Ma. Phase equilibrium and geochemical modeling confirm that the sodic rhyodacites formed via the partial melting of N-MORB sources at 3–5 kbar/780–840 °C. The basalts/dolerites exhibit similar geochemical characteristics to typical N-MORB rocks, and the gabbro gives zircon UPb age of 450 ± 2.5 Ma. The petrogenesis of the basalts/dolerites is similar to the “blow-torch” effect often seen during ocean-ridge subduction. The harzburgites are similar to abyssal peridotites in mineral compositions and have equilibrium temperatures of 1230–1460 °C, suggesting the obduction of a hot asthenospheric mantle on the continental margin. Our results show the integrated melting processes of the upwelling mantle peridotite and the subducted oceanic crust within the slab window during ridge subduction of the Proto-Tethys Ocean. These results are also significant in understanding the petrogenesis of low Sr/Y tonalite-trondhjemites, which are widely preserved in Archean to modern terranes.

Ridge Subduction as a Mechanism for Strike-Slip System Formation: Examples from the Chugach Metamorphic Complex, Alaska, and the Norumbega Fault System, Maine

Ridge Subduction as a Mechanism for Strike-Slip System Formation: Examples from the Chugach Metamorphic Complex, Alaska, and the Norumbega Fault System, Maine

The Influence of Ridge Subduction on the Geochemistry of Vanuatu Arc Magmas

AbstractThe effects of buoyant ridge subduction have been researched for decades. However, it remains unclear how this process influences magma chemistry. Here we use a compilation of geochemical data, well‐established geochemical proxies (i.e., Ba/Nb, Th/Nb) and mantle redox modeling (i.e., V/Sc, Cu) to propose that the subduction of a ridge underneath the central portion of the Vanuatu arc causes shallow‐angle subduction and the development of a slab tear. We suggest that the shallow slab pinches out the asthenospheric mantle and bulldozes ancient metasomatized lithospheric mantle from the forearc toward the main‐arc. Slab‐fluxed melting of this bulldozed material could account for the along‐arc 87Sr/86Sr‐143Nd/144Nd variations of the Vanuatu magmas. The influx of hot sub‐slab material into the Vanuatu arc mantle wedge through a slab tear produces magmatism within the forearc. Modeling of V/Sc and Cu systematics suggest that the mantle source of the forearc magmas has a higher fO2 and Cu content than the source of the main‐arc and rear‐arc samples. The main‐arc and rear‐arc mantles were metasomatized by both slab‐derived fluids and melts. Whereas release of high Cu‐SO2 slab‐derived fluids caused oxidation and Cu enrichment of the forearc mantle. These systematics indicate a decrease in the fO2 of slab fluxes with increasing depth‐to‐slab and distance‐from‐trench. Our findings highlight the role of ridge subduction in controlling the along‐arc and across‐arc variations in the chemistry of Vanuatu arc magmas. This updated geodynamic model, based on geochemistry, is consistent with recent geophysical constraints and 3D numerical modeling.

Lateral variation in slab window viscosity inferred from global navigation satellite system (GNSS)–observed uplift due to recent mass loss at Patagonia ice fields

AbstractThe geographic coincidence of the Chile Ridge slab window and the Patagonia ice fields offers a unique opportunity for assessing the effects of slab window rheology on glacial isostatic adjustment (GIA). Mass loss of these ice fields since the Little Ice Age causes rapid but variable crustal uplift, 12–24 mm/yr around the North Patagonia ice field, increasing to a maximum of 41 mm/yr around the South Patagonia ice field, as determined from newly collected or processed geodetic data. We used these observational constraints in a three-dimensional Maxwell viscoelastic finite element model of GIA response above both the subducting slab and slab window in which the upper-mantle viscosity was parameterized to be uniform with depth. We found that the viscosity of the northern part of the slab window, ~2 × 1018 Pa·s, is lower than that of the southern part by approximately an order of magnitude. We propose that this along-strike viscosity contrast is due to late Cenozoic ridge subduction beneath the northern part of the slab window, which increases asthenospheric temperature and reduces viscosity.

Late Carboniferous gabbro-granite suite from West Ujimqin of central Inner Mongolia: Petrogenesis and geodynamic implication

辉长岩和花岗岩组成的双峰式火成岩系列通常产出于威尔逊板块构造旋回的诸多伸展周期。基于其岩石地球化学特征示踪伸展地球动力学过程与相关壳幔相互作用的独特视角，本文报道了中亚造山带东段内蒙古中部西乌旗地区新近识别的晚石炭世猴头庙辉长岩-花岗岩系列。SIMS锆石U-Pb定年揭示辉长岩和花岗岩的侵位年龄分别为~307Ma和~305Ma。辉长岩主要由斜长石、辉石和角闪石组成；SiO₂含量介于50.4%~53.4%之间，呈现镁质、准铝质和钙碱性特征；富集大离子亲石元素，亏损高场强元素；并具有OIB型全岩Sr-Nd （I_Sr（t）=0.704249~0.704330，ε_Nd（t）=+1.73~+3.81）和锆石Hf （ε_Hf（t）=+4.58~+15.16）同位素组成，其锆石δ¹⁸O介于5.75‰~6.61‰之间。这些特征指示辉长岩可能源于俯冲板片流体交代的亏损地幔楔部分熔融。同期花岗岩主要由斜长石、钾长石、石英和黑云母组成；其SiO₂含量变化于76.3%~77.6%，高硅碱、贫铁镁、弱过铝、富钍铀、亏锶钡、Eu负异常，契合典型高分异I型花岗岩的元素地球化学特征；花岗岩具有中等放射性成因的全岩I_Sr（t）（0.704923~0.704981）、ε_Nd（t）值（-0.15~+0.57）和锆石ε_Hf（t）值（-2.63~+7.40），以及高的锆石δ¹⁸O （6.44‰~8.06‰）。鉴于元素和同位素特征指示的高分异特征和高演化源区，猴头庙高硅花岗岩可能衍生自中元古代和古生代多期增生物质所组成的复合中基性地壳的部分熔融及其后的结晶分异作用。综合区域石炭纪-早二叠世蛇绿混杂岩和岛弧岩浆岩时空展布格局，晚石炭世猴头庙辉长岩-花岗岩系列记录了内蒙古中部其时因洋脊俯冲引发的弥散性区域伸展事件。一方面，该事件既有别于建造西乌旗早-中石炭世弧-盆体系的板片回退阶段，又迥异于早二叠世大规模后碰撞伸展过程；另一方面，这些周期性伸展事件共同见证了中亚造山带东段晚古生代威尔逊造山旋回的完整历程。;Coeval bimodal igneous suites of gabbro and granite commonly typify frequent extensional episodes in the Wilson cycle of plate tectonics. With a unique view to tracing extensional geodynamic processes and related crust-mantle interactions through the petro-geochemical characteristics of such suites, this paper reports the newly identified Late Carboniferous Houtoumiao gabbro-granite suite from West Ujimqin of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB). SIMS zircon U-Pb dating unravels the emplacement age of gabbro at ca. 307Ma and that of granite at ca. 305Ma. The gabbros mainly consist of plagioclase, pyroxene and amphibole. They range in SiO₂ from 50.4% to 53.4%, exhibiting magnesian, metaluminous and calc-alkalic affinities, with enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs). They possess OIB-type whole-rock Sr-Nd (I_Sr(t)=0.704249~0.704330, ε_Nd(t)=+1.73~+3.81) and zircon Hf (ε_Hf(t)=+4.58~+15.16) isotope compositions, and zircon δ¹⁸O values from 5.75‰ to 6.61‰. These features suggest that the gabbros might be derived from the partial melting of a depleted metasomatised mantle wedge from subduction-derived fluids. The coeval granites mainly comprise plagioclase, K- feldspar, quartz and biotite. They span in SiO₂ from 76.3% to 77.6%, with high alkalis, thorium and uranium but low iron, magnesium, strontium and barium. They are weakly peraluminous with negative Eu anomalies. These features are typical of highly fractionated I-type felsic magmas. With respect to isotopic compositions, the granites are characterized with medium radiogenic whole-rock I_Sr(t) (0.704923~0.704981), ε_Nd(t) (-0.15~+0.57) and zircon ε_Hf(t) (-2.63~+7.40), and high zircon δ¹⁸O (6.44‰~8.06‰). Given their highly fractionated character and highly evolved sources, the Houtoumiao granites tend to have been derived from the partial melts of the composite mafic to intermediate lower crust composed of multi-stage accretionary materials in the Mesoproterozoic and Paleozoic times, with subsequent fractional crystallization yielding the high-silica granites. Combined with the spatial and temporal distribution patterns of regional Carboniferous-Early Permian ophiolitic mélange and island arc magmatic complexes, the Late Carboniferous Houtoumiao gabbro-granite suite seems to record diffuse regional extension event due to ridge subduction in central Inner Mongolia. On one hand, this event is not only distinct from slab rollback episode of the Early-Middle Carboniferous arc-basin system in West Ujimqin, but also in contrast with large-scale post-collisional extension during Early Permian time. On the other hand, when taken together, these episodic extensional events tend to witness the complete course of the Late Paleozoic Wilson cycle in the eastern CAOB.

A Late Cretaceous Adakitic intrusion from Northern Haiti: additional evidence for slab melting and implications for migration of ridge-trench-trench triple junction during the Cretaceous in the Greater Antilles

ABSTRACT We present a new U-Pb zircon age and geochemical data from an intermediate calc-alkaline pluton with adakitic affinity from NW Hispaniola (Haiti). The data provide important constraints and offer new insight on the Late Cretaceous (~90 Ma) development and geological evolution of the Greater Antilles Arc (GAA). The pluton intrudes Cretaceous basalts and mafic basic tuffs of the volcanic arc domain in the Massif du Nord (northern Haiti), equivalent to the Tireo Fm (Cordillera Central) in the Dominican Republic. The calc-alkaline, low-K tonalite shows LREE enrichment, and HREE depletion and have geochemical features similar to adakites, including 67.11 wt.% SiO2, high Na2O contents (3.69 wt.%), and high Sr/Y (38.6). U-Pb SHRIMP zircon dating yielded a concordant 206Pb/238U emplacement age of 88.9 ± 1.1 Ma, similar to other calc-alkaline intrusions in Hispaniola and Cuba related to the Cretaceous GAA. We link the presence of rocks with adakitic affinities in Eastern Cuba (La Corea and Sierra del Convento Mélanges), Haiti (Massif du Nord; present study), and Dominican Republic (Cordillera Central) with subduction of the Proto-Caribbean ridge and eastward (present coordinates) migration of the corresponding ridge-trench-trench triple junction since at least ~120 Ma in eastern Cuba to the mid-Cretaceous (~90 Ma) in Hispaniola. Here we show that this migration is not consistent with left-lateral oblique subduction and propose that it was not characterized by steady motion but by sudden jumps resulting from the segmentation of the proto-Caribbean ridge by transform faults. Ridge subduction and jumping triple point migration should have been active during the Late Cretaceous to early Tertiary, when the activity of the Proto-Caribbean ridge vanished.

The Mode of Trench-Parallel Subduction of the Middle Ocean Ridge

Trench-parallel subduction of mid-ocean ridges occurs frequently in plate motion history, such as along the western boundary of the Pacific plate in the early Cenozoic and along the eastern boundary of the Pacific plate at present. Such subduction may strongly alter the surface topography, volcanic activity and slab morphology in the mantle, whereas few studies have been conducted to investigate its evolutionary process. Here, we construct a 2-D viscoelastoplastic numerical model to study the modes and key parameters controlling trench-parallel subduction of mid-ocean ridges. Our model results show that the subduction modes of mid-ocean ridges can be primarily categorized into three types: the fast spreading mode, the slow spreading mode, and the extinction mode. The key factor controlling these subduction modes is the relative motion between the foregoing and the following oceanic plates, which are separated by the mid-ocean ridge. Different subduction modes exert different surface geological expressions, which may explain specific evolutionary processes related to mid-ocean ridge subduction, such as topographic deformation and the eruption gap of volcanic rocks in East Asia within 55–45 Ma and in the western North American plate during the late Cenozoic.

A cold seep triggered by a hot ridge subduction

The Chile Triple Junction, where the hot active spreading centre of the Chile Rise system subducts beneath the South American plate, offers a unique opportunity to understand the influence of the anomalous thermal regime on an otherwise cold continental margin. Integrated analysis of various geophysical and geological datasets, such as bathymetry, heat flow measured directly by thermal probes and calculated from gas hydrate distribution limits, thermal conductivities, and piston cores, have improved the knowledge about the hydrogeological system. In addition, rock dredging has evidenced the volcanism associated with ridge subduction. Here, we argue that the localized high heat flow over the toe of the accretionary prism results from fluid advection promoted by pressure-driven discharge (i.e., dewatering/discharge caused by horizontal compression of accreted sediments) as reported previously. However, by computing the new heat flow values with legacy data in the study area, we raise the assumption that these anomalous heat flow values are also promoted by the eastern flank of the currently subducting Chile Rise. Part of the rift axis is located just below the toe of the wedge, where active deformation and vigorous fluid advection are most intense, enhanced by the proximity of the young volcanic chain. Our results provide valuable information to current and future studies related to hydrothermal circulation, seismicity, volcanism, gas hydrate stability, and fluid venting in this natural laboratory.

The Mesozoic magmatic, metamorphic, and tectonic evolution of the eastern Gangdese magmatic arc, southern Tibet

ABSTRACTMagmatic arcs are natural laboratories for studying the growth of continental crusts. The Gangdese arc, southern Tibet, is an archetypal continental magmatic arc that formed due to Mesozoic subduction of the Neo-Tethyan oceanic lithosphere; however, its formation and evolution remain controversial. In this contribution, we combine newly reported and previously published geochemical and geochronological data for Mesozoic magmatic rocks in the eastern Gangdese arc to reveal its magmatic and metamorphic histories and review its growth, thickening, and fractionation and mineralization processes. Our results show that: (1) the Gangdese arc consists of multiple Mesozoic arc-type magmatic rocks and records voluminous juvenile crustal growth. (2) The Mesozoic magmatic rocks experienced Late Cretaceous granulite-facies metamorphism and partial melting, thus producing hydrous and metallogenic element-rich migmatites that form a major component of the lower arc crust and are a potential source for the Miocene ore-hosting porphyries. (3) The Gangdese arc witnessed crustal thickening and reworking during the Middle to Late Jurassic and Late Cretaceous. (4) Crystallization-fractionation of mantle-derived magmas and partial melting of thickened juvenile lower crust induced intracrustal chemical differentiation during subduction. We suggest that the Gangdese arc underwent the following main tectonic, magmatic, and metamorphic evolution processes: normal subduction and associated mantle-derived magmatism during the Late Triassic to Jurassic; shallow subduction during the Early Cretaceous and an associated magmatic lull; and mid-oceanic ridge subduction, high-temperature metamorphism and an associated magmatic flare-up during the early Late Cretaceous, and flat subduction, high-temperature and high-pressure metamorphism, partial melting, and associated crust-derived magmatism during the late Late Cretaceous. Key issues for further research include the temporal and spatial distributions of Mesozoic magmatic rocks, the evolution of the components and compositions of arc crust over time, and the metallogenic processes that occur in such environments during subduction.

Late Triassic granites (ca. 230 Ma) from Cairi area in eastern Qiangtang subterrane, central Tibet: Product of a mid‐oceanic ridge subduction

Although a large number of Triassic magmatism were found in the Qiangtang terrane, central Tibet, the tectonic evolution of the Shuanghu Palaeo‐Tethys Ocean remains controversial. In this study, we present the zircon U–Pb age and major‐ and trace‐element data for the Late Triassic pluton from the Cairi area in the eastern Qiangtang terrane. Zircon U–Pb dating indicates that the samples were emplaced at ca. 230 Ma. The magmatism from the Cairi area primarily consists of granites (SiO2 = 67.28–77.74), with the characteristics of medium‐K calc‐alkaline, metaluminous, and peraluminous. The Cairi granites are enriched light rare earth elements ([La/Yb]N = 5.01–10.56), with obvious Eu anomaly (Eu/Eu* = 0.32–0.47). The Cairi granites are characterized by low 1,000 × Ga/Al (2.10–2.64), FeO*/MgO (3.41–5.03), Ce (57.95–114.36 ppm), Y (27.30–45.19 ppm), and negative correlation between P2O5 and SiO2. These geochemical features reveal that the Cairi granites are calc‐alkaline, I‐type granites. The four samples show relatively restricted (87Sr/86Sr)i ratios (0.70598–0.70724), 143Nd/144Nd ratios (0.51192–0.51196), and εNd(t) of −8.19 to −7.54. Based on the variations of Rb–Sr–Ba and Th–La–Nb and the zircon saturation of temperatures (806–868°C), we suggest that the primary magmas of the Cairi granites were generated through various degrees of mixing between sediments and mantle‐derived components. Petrological and geochemical characteristics, as well as regional geological characteristics indicate that the Cairi granites formed in a continental volcanic arc setting. Our results, in combination with the coeval granites and elcogite, indicate that the generation of Late Triassic (ca. 230 Ma) Cairi granites is related to ocean ridge subduction and subsequent development of a slab window.

Late Paleozoic subduction-related magmatism in NE China and its implication: Insights from intrusions in the Handagai Fe[sbnd]Cu deposit

North East (NE) China forms the easternmost part of the Central Asian Orogenic Belt. However, its Paleozoic geological evolution process remains controversial, especially the complex subduction-accretion-orogeny processes of the Paleo-Asian Ocean plate, as well as the linking magmatism-metallogenic with tectonic evolution during that time. This paper reports the results of geochemical, geochronological, and isotopic analyses of igneous rocks at the Handagai skarn Fe–Cu deposit to elucidate the late Paleozoic tectonic framework and evolution of NE China and the setting of ore formation. New zircon LA–ICP–MS U–Pb data for monzogranite, quartz diorite, and quartz monzodiorite record Carboniferous ages of 350 ± 2 Ma, 321 ± 3 Ma, and 319 ± 2 Ma, respectively. The monzogranites have high SiO2 (69.57–71.97 wt%) and total-alkali (6.68–7.56 wt%) contents and relatively low MgO contents (0.60–1.03 wt%) and Mg numbers (33–41). They have arc-type trace-element signatures, with enrichment in large-ion lithophile elements and light rare earth elements, together with depletion in Nb, Ta, P, and Ti. Their whole-rock Sr–Nd–Pb and zircon in-situ LuHf isotopic compositions ((87Sr/86Sr)i = 0.7008–0.7062; εNd(t) = −1.9 to +1.9; (206Pb/204Pb)t = 17.900–19.006; εHf(t) = 5.04–15.28) and young two–stage Nd–Hf model ages (TDM2 = 1105–749 Ma and 899–574 Ma, respectively) indicate that their precursor magma was derived from partial melting of Mesoproterozoic to Neoproterozoic juvenile lower crust that had been metasomatized by fluids/melts from an enriched mantle wedge. The quartz diorites and quartz monzodiorites are characterized by intermediate SiO2 (58.21–61.47 wt%), high MgO (3.62–5.42 wt%), and low CaO (3.15–4.96 wt%) contents, and high Cr (151–222 ppm) and Ni (97–131 ppm) contents, as well as elevated Sr and Ba. They have strong Nb and Ta depletion and highly fractionated rare earth elements, indicating a geochemical affinity to typical high-Mg andesites. These rocks exhibit mid-ocean ridge basalt (MORB)-like whole-rock Nd–Sr–Pb–Hf isotopic characteristics, with high εNd (t) and εHf (t) values of +1.60 to +3.20 and + 10.21 to +13.61, respectively, and relatively low (87Sr/86Sr)i and (206Pb/204Pb)i ratios of 0.7028–0.7045 and 16.768–17.856, respectively. They also have low Sr/Y (30–59), Ba/Th (75–213), and Ba/La (26.05–38.24), but elevated Th/Yb (4.51–7.36), Th/Nb (0.78–1.17), and Rb/Y (2.79–6.29) ratios. We conclude that they were generated by partial melting of depleted lithospheric mantle previously metasomatized by subduction-related fluids and sediment melts. These results, integrated with regional geological, geochronological, and geochemical data, constrain the tectonic evolution of NE China during the late Paleozoic. This involved normal subduction at 400–335 Ma, ridge subduction at 333–319 Ma, and slab break–off at 315–272 Ma. The high-Mg andesitic/dioritic magmas had high oxygen fugacities and high water and volatile (e.g., Cl, S) contents, and sufficient ore resources (e.g., Cu, Au, Fe) from the mantle wedge to be favorable for Cu (–Au–Fe) mineralization.

Variscan intracrustal recycling by melting of Carboniferous arc-like igneous protoliths (Évora Massif, Iberian Variscan belt)

Abstract Bulk rock geochemistry and sensitive high-resolution ion microprobe zircon geochronology of igneous and metaigneous rocks of the Évora gneiss dome, located to the north of the reworked Rheic Ocean suture zone in the southwest Iberian Variscan belt, reveal a succession of magmatic and melting events lasting ~30 m.y. between ca. 341–314 Ma. The study of detailed field relationships of orthomigmatites (i.e., migmatites from igneous protoliths) and host granitic rocks proved to be crucial to reconstruct the complex sequence of tectono-thermal events of the Évora gneiss dome. The older igneous protoliths, with marked geochemical arc-like signatures, are represented by 338 ± 3 Ma tonalites and 336 ± 3 Ma diorites. These tonalites and diorites appear as mesosomes of igneous orthomigmatites containing new melts (leucosomes) of monzogranite composition and silica-poor trondhjemites formed in a melting episode at 329 ± 4/6 to 327 ± 3 Ma. The absence of peritectic phases (e.g., pyroxene), together with shearing associated with migmatization, imply the existence of water-rich fluids during melting of the older igneous rocks of the Évora gneiss dome. This melting event is coeval with the second magmatic event of the Évora gneiss dome represented by the neighboring Pavia pluton. A porphyritic monzogranite dated at 314 ± 4 Ma defines a later magmatic event. The porphyritic monzogranite encloses large blocks of the orthomigmatites and contains magmatic mafic enclaves (autoliths) dated at 337 ± 4 Ma that are ~23 m.y. older than the host rock. All studied rocks of the Évora gneiss dome show arc-like, calc-alkaline geochemical signatures. Our results support recycling of intermediate-mafic plutonic rocks, representing the root of an early magmatic arc that formed at the time of Gondwana-Laurussia convergence (after the closure of the Rheic Ocean) and coeval subduction of the Paleotethys. A geodynamic model involving ridge subduction is proposed to explain the Early Carboniferous intra-orogenic crustal extension, dome formation, exhumation of high-grade rocks, compositional variations of magmatism and formation of new granitic magmatism in which, arc-like signatures were inherited from the crustal source.

Porphyry CU deposits in the Central Andes of Argentina: An overview

Porphyry Cu deposits are the world's most important source of Cu and the Central Andes of South America hold some of the largest Cu resources worldwide. In Argentina many porphyry-type deposits and prospects with different degrees of exploration straddle along ~1500 km of the Central Andes. The review and analysis of the tectono-magmatic, metallogenic and economic data of the better-known deposits and prospects allow to define the controls of porphyry-type mineralization and the metallogenic epochs and belts which in turn indicate the potential for porphyry-type mineralization in some relatively poorly explored segments of the Central Andes.Slab shallowing (particularly linked to the subduction of aseismic ridges) and associated eastward arc migration/expansion appears to be a favorable geodynamic scenario for Paleozoic and Cenozoic mineralizing magmatism which show variable adakitic signatures probably as a result of a progressive crustal thickening. In this context the V/Sc and especially the Sr/Y ratios are a useful tools for assessing magma fertility. Major WNW-trending deep crustal pre-Andean structures controlled the inland migration of the magmatism and are a first order control on porphyry emplacement during these epochs of magmatic activity.There are five favorable metallogenic epochs linked to the arc magmatism in Argentina: Permian, Upper Cretaceous-Eocene, late Eocene-early Oligocene, late Oligocene-early Miocene and Miocene-Pliocene. The Permian and Upper Cretaceous-Eocene metallogenic epochs are represented by a small number of deposits with low metal (Cu–Mo–Au) content; however, the extension of the magmatism of both epochs suggests they are favorable for further exploration. The late Eocene–early Oligocene magmatism involves few deposits but formed the second largest known copper resource in Argentina. The Miocene-Pliocene magmatism, particularly between ~11 and 6 Ma, generated the largest porphyry-type deposits with the greatest metal resources. Based on the available information ten metallogenic belts are outlined: 1) Permian Puna-Frontal Cordillera/Neuquén basement, 2) Upper Cretaceous–Eocene Neuquén, 3) late Eocene-early Oligocene, 4) late Oligocene-early Miocene, 5) middle Miocene Puna-Frontal Cordillera, 6) middle Miocene Precordillera, 7) late Miocene Cordillera, 8) late Miocene-Pliocene Cordillera, 9) late Miocene-Pliocene Northern Sierras Pampeanas, 10) late Miocene-Pliocene Famatina. These ten metallogenic belts accumulate 74.21 Mt Cu, 1.70 Mt Mo, 2160.66 t Au and 23,876.71 t Ag of known resources and approximately 239 Mt Cu, 6.4 Mt Mo, 4240 t Au and 77,900 t Ag contained in undiscovered deposits. The Miocene belts are the most endowed, confirming their economic importance as well as their prospectivity for exploration. The largest total known resources are hosted by the late Miocene belt in the Frontal Cordillera, followed by the late Eocene-Early Oligocene one and the Miocene-Pliocene belt in the Sierras Pampeanas. The continuation of the late Miocene-Pliocene Cordillera belt that extends from Los Bronces and El Teniente in Chile, further south into Argentina, is here considered the most prospective underexplored belt.

Geochemistry and genesis of the Nadun Nb-enriched arc basalt in the Duolong mineral district, western Tibet: Indication of ridge subduction

The Duolong mineral district in western Tibet is one of the largest porphyry Cu–Au deposit fields with significant metallogenic potential in China. Its tectonic environment relevant to Early Cretaceous Cu–Au mineralization remains controversial. Here we report new whole-rock major and trace element, and Sr-Nd-Hf-Pb isotopic data for the newly discovered basalt in the Nadun area, Duolong mineral district, to decipher their genesis and further constrain the tectonic environment. A contemporaneous rhyolite sample interbedded with the basalt in the lower part of the volcanic section in the Nadun area yields an LA-ICP-MS zircon U–Pb age of 122.5 ± 1.2 Ma. The basalt samples exhibit high-K calc-alkaline/shoshonite properties and are enriched in high field strength elements, e.g., high TiO2 (1.43–1.79 wt.%) and Nb (14.6–19.5 ppm) contents, with high Nb/La ratios (0.4–0.6), which are compositionally comparable to those of Nb-enriched arc basalts (NEABs). The (87Sr/86Sr)i ratios of 0.7052 to 0.7056, negative εNd(t) (− 0.7 to − 0.2) and εHf(t) values (+ 6.0 to + 6.5), and high (206Pb/204Pb)i, (207Pb/204Pb)i, (208Pb/204Pb)i and ratios (18.522 to 18.561, 15.641 to 15.645 and 38.679 to 38.730, respectively) suggest that the Nadun NEABs are more enriched than those of the island arc basalts (IABs) in the area. The slightly enriched radiogenic isotopes for the Nadun NEABs indicate that the subducting sediments play an important role in the source. Furthermore, their high Nb, Ti, and Cu contents indicate that the source mantle wedge was metasomatized by slab melts. The Nadun NEAB and other coeval magmatic rocks in the Duolong mineral district, including adakite, OIB-like basalt, MORB-type basalt, A-type rhyolite, and common IAB, are typical rock assemblages of ridge subduction. We infer that the Duolong mineral district were formed by ridge subduction in the Early Cretaceous.

Geochemistry and Sr–Nd–Hf–Pb isotope systematics of late Carboniferous sanukitoids in northern West Junggar, NW China: Implications for initiation of ridge-subduction

The study of Carboniferous magmatism in northern West Junggar plays an important role in understanding the tectonic evolution of that part of the Central Asian Orogenic Belt. In this study, we present petrology, zircon U–Pb geochronology, mineral and whole-rock geochemistry, and the Sr–Nd–Hf–Pb isotope compositions of volcanic rocks from the Hamutusi area of northern West Junggar. LA–ICP–MS zircon U–Pb analysis of a representative andesite yielded an early to late Carboniferous age of 324.4 ± 6.9 Ma. The volcanic rocks are calc-alkaline, with high SiO2 (54.2–57.8 wt%), MgO (5.97–8.33 wt%), Mg# (60–69), Cr (147–448 ppm), and Ni (29.1–120 ppm) contents, and are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), but depleted in high field strength elements (HFSE), these characteristics are similar to those of typical sanukitoids within the Setouchi volcanic belt in Japan. All samples have radiogenic initial Sr and Pb isotopic compositions, and low εNd(t) and εHf(t) values, indicating the sanukitoids were generated by partial melting of subducting sediments in which the melts interacted with the mantle. Geochemical modeling calculations indicate a proportion of 3–10% sediment melt and slab-derived fluids were mixed with the depleted mantle to produce the bulk of the Hamutusi rocks. We conclude that the studied rocks from north West Junggar record the initiation of ridge subduction related to a transition from normal subduction to subduction of young and hot oceanic lithosphere between the early and late Carboniferous.

Petrology and geochronology of andalusite- and sillimanite-bearing kyanite metapelites from the Gobi Altai Mountains: Evidence for prolonged convergent tectonics in the Central Asian Orogenic Belt

To further constrain the tectonic evolution of the convergent margin of the West Mongolian segment in the Paleo–Asian Ocean, we have investigated coarse-grained kyanite metapelites associated with quartz veins in the Gobi Altai Mountains, Mongolia, where the metamorphic belt is in a thrust contact with a Paleozoic accretionary complex. The metapelites contain coarse-grained granoblastic kyanite grains that are surrounded by sillimanite (Sil-II) with moat-like andalusite (And-II). The garnet grains in the garnet-bearing kyanite metapelites contain inclusions of andalusite (And-I) in their cores and sillimanite (Sil-I) in their mantles. Detailed textural characterization of the aluminosilicate phases indicates five distinct generations in the sequence andalusite (And-I), sillimanite (Sil-I), kyanite (Ky), sillimanite (Sil-II), and andalusite (And-II). Thermobarometric calculations and thermodynamic modeling suggest a hairpin-shaped P–T evolution with prograde conditions starting from ~530 °C at 3.5 kbar, reaching a peak of 600 °C at 6 kbar, and then a retrogression to ~550 °C at 4 kbar. U-Pb zircon and U–Th–Pb monazite ages indicate that the multistage aluminosilicate formation has occurred during c. 260–245 Ma. The detrital zircon age distribution is essentially similar to those in the accretionary sedimentary rocks from the entire Altai Range (a sharp peak at 550–490 Ma and a broad peak at 900–700 Ma), but is characterized by more abundant Proterozoic zircon grains and an older maximum deposition age (Early Ordovician) compared with Devonian pelitic gneisses in the Mongolian Altai. These petrological and geochronological results indicate the following development of the orogen: (1) Subduction of an oceanic plate beneath a microcontinental block as early as 550 Ma, evidenced by the youngest peak of detrital zircon ages. (2) Development of the accretionary wedge and volcanic front due to maturation of the arc until c. 360 Ma. The development of the volcanic front due to the magmatism has provided abundant Paleozoic detritus to the accretionary wedge and has stemmed supply of Proterozoic detritus from the inland at the same time. (3) Burial of the youngest accretionary wedge at c. 360–350 Ma, which is not observed in the current samples. Ridge subduction has also been suggested to have occurred in this period. (4) Arc magmatism in the upper (older) part of the accretionary wedge during the late Permian that resulted in prograde high-T and low-P metamorphism (formation of And-I). (5) Burial of the heated accretionary wedge to a depth of ~20 km due to subsequent collision (formation of Sil-I and Ky) at c. 260 Ma. (6) Rapid exhumation of the buried accretionary wedge to a shallow depth by thrusting (formation of Sil-II and And-II) at c. 245 Ma. In summary, the metapelites in the Altai Range clearly preserve the evolution of both the accretion and collision events as well as their transformation processes, which are likely to be a good natural example of the Wilson cycle for a period of ~300 Myr.

A Biogeochemical Imprint of the Panama Basin in the North Andean Arc

AbstractOceans and continents mingle at convergent margins. However, the effects of this interaction in the construction and evolution of the continental crust remain poorly understood. Here we use geochemical data from the Panama Basin and the Northern Volcanic Province of Colombia to reveal that the oceanological and biogeochemical processes of a subducted ocean basin are imprinted in the compositions of continental arc volcanoes. The Panama Basin is a biologically highly productive area of the Eastern Equatorial Pacific in which the strongly biogenic sedimentation is reclassified and preserved differently depending on tectonically controlled depositional environments. Due to a shallow lysocline, sediments deposited on newly formed spreading centers are carbonate‐rich, whereas those accumulated on older subsiding seafloor become gradually richer in terrigenous components, organic carbon and authigenic U. Volcanoes of the North Volcanic Province of Colombia erupt high‐Mg# andesites that are common in some arcs, but display unusually high U contents and a symmetrical or “parabolic‐shaped” along‐arc trace element and isotopic variations that appear unrelated to differentiation or the pre‐existent crustal architecture. Instead, the parabolic‐shaped elemental trends mirror the reconstructed compositional variations of sediments deposited across axis on the currently subducted Sandra and Buenaventura ocean ridges. We interpret that subduction of these ocean ridges delivered a compositionally variable sediment influx that influenced the compositions of arc magmas. These findings demonstrate a strong connectivity between oceans and continents, and further imply that arc volcanoes can be reliable records of the oceanological and biogeochemical conditions of long subducted ocean basins.

The timeline of prolonged accretionary processes in eastern Central Asian Orogenic Belt: Insights from episodic Paleozoic intrusions in central Inner Mongolia, North China

Abstract Updating magmatic profile in crucial constituent terranes across the Central Asian Orogenic Belt presents a key to chronicling the timeline of prolonged accretionary processes and termination of the Paleo-Asian Ocean in the northern China–southern Mongolia tract. Here we performed a systematic geochronological and geochemical study on a spectrum of Paleozoic intrusions from the Erenhot region in central Inner Mongolia, North China, within the hinterland of the tract, with four distinct magmatic episodes unraveled. Combining these episodes with the previously documented events from contiguous regions defines two major tectono-magmatic cycles. The early Paleozoic cycle (500–450 Ma) evolved from initial fluid-fluxed tholeiitic and calc-alkaline granitoids to melt-fertilized mafic-intermediate magmatism. It appears to experience the initiation and maturation of a Western Pacific-type intra-oceanic arc system that culminated in ridge subduction. The late Paleozoic cycle expanded in magmatic expression from sporadic Late Devonian (373–365 Ma) calc-alkaline intermediate-felsic pulses through Early-Middle Carboniferous (356–320 Ma) medium to high-K calc-alkaline flare-up to a Late Carboniferous–Early Permian (310–277 Ma) province of diverse lithologies. These magmatic episodes seem to encompass a complete active continental arc–back-arc system that spanned from resuming oceanic plate subduction through slab rollback and backarc rifting to ridge-trench collision and backarc basin closure. Featuring a Rodinia-aged terrane affinity and a representative Paleozoic magmatic profile, the Erenhot region provides an optimal site for correlating the evolution of mosaic terranes in southern Mongolia and northern China, and for evaluating the coupled evolution of shifting tectonic regimes and plural crustal generation mechanisms within a retreating accretionary orogen.

Opening of the West Paleo-Tethys Ocean: New insights from earliest Devonian meta-mafic rocks in the Saualpe crystalline basement, Eastern Alps

The timing of the opening of the West Paleo-Tethys Ocean in Eastern Alps remains unclear. To constrain this event, we present new zircon U-Pb ages, Hf isotopic compositions, and whole-rock major- and trace-element data for the meta-mafic rocks (amphibolites) in the southern and western Saualpe crystalline basement, Eastern Alps. Zircon U-Pb dating of three samples yield crystallization ages of 418 ± 6 Ma, 417 ± 3 Ma and 415 ± 3 Ma, indicating that they formed during the earliest Devonian. Geochemically, these meta-mafic rocks have relatively low SiO2 and MgO contents and high TiO2 contents. They are enriched in light rare earth elements (LREE), particularly in Nb and Ta, and show relatively flat heavy rare-earth elements (HREE) patterns, suggesting that they have affinities with the alkaline oceanic island basalts (OIB). The geochemical characteristics, together with the positive εHf(t) values of 0.7–11.1, imply that the OIB-like meta-mafic rocks originated from partial melting of a lherzolite source including spinel and garnet. The primary magma shows complex sources involving asthenospheric, lithospheric mantle and subducted slab components, which was subsequently modified by crustal contamination. This reveals that the magma formed in a slab window environment associated with mid-ocean ridge subduction. The contemporaneous OIB-like alkaline amphibolites were also found in the Central Austroalpine basement and in Northwestern Turkey. We suggest that the Late Silurian–earliest Devonian OIB-like magmatism is related to a back-arc extension setting along the northern margin of Gondwana leading to the separation of the European Hunic terranes and hence placing age constraints on the opening of the West Paleo-Tethys Ocean.