Search

The Whitehorse Trough formed during early Mesozoic accretion of the Intermontane terranes to northwestern North America. Here we investigate its thermal history using detrital mineral thermochronology, including 171 single-crystal (U–Th)/He zircon (ZHe) ages from 35 samples, 158 single-crystal (U–Th)/He apatite (AHe) ages from 33 samples, and apatite fission track (AFT) ages from 12 samples. ZHe single crystal ages range from 222 to 42 Ma and define Triassic–Early Jurassic, Late Jurassic, and Cretaceous–Paleogene age groups. AFT central ages range from 95 to 30 Ma with a dominant age peak at ∼50 Ma, and AHe single crystal ages range from 228 to 13 Ma with a dominant age peak between 50 and 40 Ma. Forward and inverse models of thermochronological data are compatible with two regional burial/heating stages that variably reset He in zircon. Maximum temperatures of the Whitehorse Trough strata locally exceeded 150 °C during Early Jurassic burial and shortening into a fold and thrust belt. Following Middle to Late Jurassic exhumation-related cooling and development of a prominent unconformity, Whitehorse Trough strata were buried again. Temperatures locally exceeded 150 °C during the Cretaceous, suggesting maximum burial of between ∼4 and 7.5 km. Heating and cooling rates during the Early–Middle Jurassic were ∼10 °C/myr, coinciding with deposition, fold and thrust belt development, and regional crustal thickening during the final stages of Intermontane terrane accretion. Maximum heating rates during the Cretaceous were ∼4–7 °C/myr and likely correspond to regional crustal thickening of the northern Cordillera hinterland and establishment of an outboard, Andean-type continental arc system. [ABSTRACT FROM AUTHOR]

Continental arc is characterized by alternant magmatic flare-ups and lulls. From the Permian to the Middle Jurassic period, two flare-ups with a lull developed in NE China, but the tectonic controls that caused the flare-ups remain unclear. Sedimentary rocks of the Heilongjiang Complex were derived from these magmatic rocks; thus, we employed detrital zircon U-Pb dating and trace elements analyses to unravel the regional tectono-magmatic evolution. Eu anomaly, (Dy/Yb)N and Th/U ratios of the detrital zircons and Sr/Y and (La/Yb)N of the regional granitoids together indicate the occurrence of two episodes of crustal thickening during the two flare-ups, accompanied with a westward migration of magmatism. We propose that the Permian flare-up was caused by the shallowing subduction from the east, which thickened the upper plate and enhanced the deep crustal melting. During the Middle Triassic period, the mantle wedge was expelled by the flat slab and thickened crust, leading to the magmatic lull. However, the westward subduction of the back-arc oceanic plate occurred before the lull, gradually producing the Jurassic magmatic flare-up and crustal thickening. Closure of the back-arc ocean caused by the outboard Paleo-Pacific oceanic plate subduction was important in the formation of the episodic magmatic flare-ups and crustal thickening in NE China. [ABSTRACT FROM AUTHOR]

[Display omitted] • Widespread felsic volcanic rocks are sourced from the juvenile crust. • Sedimentary rocks consist mainly of pyroclastic materials. • Local extensional setting was induced by the slab-rollback during Early Devonian. • High grades of ores were inhibited by low metallic abundance and heat flow. • Long-lived arc volcanism leads to abundant metals and continued heat sources. Questions about the role of volcanism in the formation of VMS deposits and the origin of metals in pre-ore volcanic rocks in accretionary orogen generally puzzle scholars. The volcanic-sedimentary sequence of Lower Devonian Kangbutiebao Formation (KBTB Fm) associated with VMS deposits in the Altai Mountains is studied to attempt to solve these issues. The KBTB Fm is predominantly composed of felsic volcanic rocks with subordinate sedimentary rocks. Zircon U-Pb dating of rhyolite and rhyodacite suggests that felsic volcanism occurred in the Early Devonian (400.1 ± 0.8 Ma to 395.3 ± 0.9 Ma). Partial melting of juvenile crust under the environment of lower temperature (662 to 728 °C) and pressure (<∼15 km) resulted in volcanic rocks with arc-like trace elements and depleted Hf isotopes. Both compositional heterogeneity of source rocks and contrasting melting temperatures are responsible for the variety of petrochemistry. Sedimentary rocks exhibit low CIA values (51–66) and varied ICV values (0.76–1.78), implying that the provenance was affected by weak weathering. As suggested by detrital zircon geochronology, detrital materials from sedimentary rocks are dominated by pyroclastic materials that erupted from the volcano, together with minor eroded detrital materials from adjacent intrusions. It is proposed that the KBTB Fm was formed under continental rifted arc or back-arc condition, and local extensional setting was induced by slab-rollback of the Paleo-Asian Ocean, which produced bimodal volcanic rocks and VMS deposits. Large volumes of sequences with low metallic abundance were produced and protracted hydrothermal circulation was sustained under the condition of long-lived arc volcanism, leading to most VMS deposits with low to moderate grade, and rarely, high grade. All these parameters are grouped together (i.e., abundant but low contents of metals, long-lived heat source, and syn -volcanic faults), leading to most VMS deposits hosted by the KBTB Fm in the southern Chinese Altai. [ABSTRACT FROM AUTHOR]

The Gamburtsev Subglacial Mountains (GSMs) in the interior East Antarctic Craton are entirely buried under the massive East Antarctic ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is modelled to underlie the GSMs, which may have formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs are underlain by part of a Pan-African age advancing accretionary orogen superimposed on Precambrian basement. [ABSTRACT FROM AUTHOR]

• Baluntai Complex contains rocks of different ages and metamorphic grades. • Metamorphic protoliths of the Baluntai complex were formed in the Paleozoic. • The Baluntai Complex was formed in the Japan-type arc setting. The Central Tianshan, in the southern Altaids, is characterized by abundant gneiss–schist complexes. The origins and tectonic affinities of these complexes have been controversial in the past two decades. This systematic detrital zircon study used geological mapping of the Baluntai Complex (BC) in the middle section of the Central Tianshan to address these issues. Geological mapping revealed that the BC is a thrust stack that formed by a series of top-to-north thrust faults. Our 1135 concordant U-Pb detrital zircon dating results suggest that the gneisses, schists, and metasandstones of the BC were formed during the Middle Silurian to Early Carboniferous (ca. 433–346 Ma), rather than the Precambrian, as previously assumed. Detrital zircon age provenance of these samples suggests that they are sourced from a continental arc. Combining our new data, we concluded that the BC was generated in the arc-related basins by the northward subduction of the South Tianshan Ocean and that the Central Tianshan was a typical Japan-type arc in the middle and late Paleozoic. [ABSTRACT FROM AUTHOR]

Earth's continental crust has grown and been recycled throughout geologic history along convergent plate margins. The main locus of continental crustal growth is in intra-oceanic and continental-margin arc systems in Archean time. In arc systems, oceanic lithosphere is subducted to the deeper mantle, and together with its overlying sedimentary sequence is in some cases off-scraped to form accretionary prisms. Fluids are released from the subducting slab to chemically react with the mantle wedge, forming mafic-ultramafic metasomatites, whose partial melting generates mafic melts that rise up to form arcs. In intra-oceanic arcs, they produce dominantly basaltic lavas, with a mid-crust that includes variably-developed vertically-walled intermediate plutons and higher-level dikes and sills. In continental-margin arcs, different petrogenetic processes cause assimilation and fractionation of basaltic magmas, partial melting/reworking of juvenile basaltic rocks, and mixing of mantle- and crust-derived melts, so they produce andesitic calc-alkaline melts but still have a mid-crust dominated by vertically-walled felsic plutons, which form 3-D dome-and-basin structures, akin to those in some Archean terranes such as parts of the Pilbara and Zimbabwe cratons. Notably, the continental crust of Archean times is dominated by tonalite-trondhjemite-granodiorite (TTG) plutons, similar to that of the mid-crust of these arc systems, suggesting that early continental crust may have formed largely by the amalgamation of multiple arc systems. The patterns of magmatism, in terms of petrogenesis, rock types, duration of magmatic and accretionary events, and the spatial scales of deformation and magmatism have remained essentially the same throughout geological history, demonstrating that plate tectonic processes characterized by subduction and arc magmatism have been in operation at least as long as recorded by the preserved geologic record, since the Eoarchean. However, the early Earth was dominated by accretionary orogens and oceanic arcs, that gradually grew thicker through multiple accretion events to form early continental-margin arcs by 3.5–3.2 Ga, and accretionary orogens. Slab melting and warmer metamorphism was more common in Archean arc systems due to higher mantle temperatures. These early arcs were further amalgamated into large emergent continents by ∼3.2–3.0 Ga, allowing large-scale processes such as lithospheric rifting and continental collisions, and the start of the supercontinent cycle. Further work should apply the null hypothesis, that plate tectonics explains the geologic record, to test for differences in the style of plate tectonics and magmatism through time, based on the fundamental difference in planetary heat production and the evolution of rotational dynamics of the Earth-Sun-Moon system. [ABSTRACT FROM AUTHOR]

Porphyry Cu deposits (PCDs) are major global exploration targets for Cu, Mo, and Au, and mainly formed in accretionary orogens. This study integrates the whole-rock geochemical and Nd isotopic mapping based on ca. 5000 intermediate to felsic magmatic rocks to characterize the crustal structure and metallogeny of PCDs in the Central Asian Orogenic Belt (CAOB), the world's largest Phanerozoic accretionary orogen. The Nd isotopic maps image clearly the extent of cratons, microcontinents, and juvenile crustal blocks, with the PCDs intimately associated with juvenile crust that is consistent with the conclusions drawn by study in other orogens such as Himalayan–Tibetan. More importantly, PCDs are mainly distributed in the juvenile crust's margin adjacent to cratons or microcontinents, indicating that the external magmatic arcs are favorable sites for PCDs. The ore-forming intrusions of Cu-Au deposits are isotopically more depleted than those of Cu-Mo deposits, implying more input of mantle or juvenile crust materials into magmatic sources of Cu-Au deposits. Crustal thickness proxy mapping shows that Cu-Au deposits formed in thinner crust than Cu-Mo deposits, which could be used to target favorable sites for mineral exploration. The crustal thickness proxy and εNd(t) define a negative linear relationship, which quantifies the contributions of juvenile materials to PCDs in response to the changing crustal thickness, from which a newly proposed crustal maturity index was derived to distinguish the Cu-Au and Cu-Mo PCDs. The structure of the crust plays an important role in localizing PCDs; therefore, the integrated mapping of Nd isotopes and crustal thickness proxy could provide mappable exploration targets of PCDs at the orogen scale. [ABSTRACT FROM AUTHOR]

In Central Asia, the Carboniferous is a crucial period in the formation of the Tianshan Belt and associated bending of the Kazakhstan tectonic collage. In order to reveal Carboniferous magmatic events of the region and their tectonic implications, we conducted field investigations, zircon U–Pb dating, whole-rock geochemical and Sr–Nd isotopic studies on the Early Carboniferous Dahalajunshan Formation and Late Carboniferous Yishijilike Formation volcanic rocks of the Wusun Mountain Range (southern Yili-Central Tianshan Block). Volcanic rocks of the Dahalajunshan Formation consist of calc-alkaline basalt, andesite and dacite, yielding new zircon U–Pb ages of ~ 350 Ma. They have positive whole-rock εNd(t) values (+ 0.5 to + 1.6). In contrast, the Yishijilike Formation volcanic rocks dominantly comprise alkaline and calc-alkaline bimodal suites that erupted at ~ 337 Ma to 313 Ma and have higher whole-rock εNd(t) values (+ 2.3 to + 4.3). These two episodes of Carboniferous magmatism were correlated with partial melting of depleted mantle that metasomatized by slab-derived fluids. The late Carboniferous Wusun Mountain magmatic belt shows characteristics of a back-arc system that evolved due to trench retreat relative to the southern margin of the Yili-Central Tianshan Block. This mechanism induced an extensional regime with gradually depleting magma sources. The asymmetric retreat of the paleo-subduction zones of the South Tianshan Ocean and Junggar Ocean relative to the Yili-Central Tianshan Block was hence a vital driving force for the bending of the Kazakhstan Orocline. [ABSTRACT FROM AUTHOR]

End‐on arc collision and onset of the northern Cordilleran orogen is recorded in Late Triassic to Jurassic plutons in the Intermontane terranes of Yukon, and in development of the synorogenic Whitehorse trough (WT). A synthesis of the extensive data set for these plutons supports interpretation of the magmatic and tectonic evolution of the northern Intermontane terranes. Late Triassic juvenile plutons that locally intrude the Yukon‐Tanana terrane represent the northern extension of arc magmatism within Stikinia. Early Jurassic plutons that intrude Stikinia and Yukon‐Tanana terranes were emplaced during crustal thickening (200–195 Ma) and subsequent exhumation (190–178 Ma). The syn‐collisional magmatism migrated to the south and shows increasing crustal contributions with time. This style of magmatism in Yukon contrasts with coeval, juvenile arc magmatism in British Columbia (Hazelton Group), that records southward arc migration in the Early Jurassic. Exhumation and subsidence of the WT in the north were probably linked to the retreating Hazelton arc by a sinistral transform. East of WT, Early Jurassic plutons intruded into Yukon‐Tanana record continued arc magmatism in Quesnellia. Middle Jurassic plutons were intruded after final enclosure of the Cache Creek terrane and imbrication of the Intermontane terranes. The post‐collisional plutons have juvenile isotopic compositions that, together with stratigraphic evidence of surface uplift, are interpreted to record asthenospheric upwelling and lithospheric delamination. A revised tectonic model proposes that entrapment of the Cache Creek terrane was the result of Hazelton slab rollback and development of a sinistral transform fault system linked to the collision zone to the north. Key Points: End‐on latest Triassic to Early Jurassic arc‐continent collision in the northern CordilleraCrustal thickening and syn‐collisional magmatism north of Stikine arch linked by transform faults to retreating Hazelton slab to the southSouthward slab retreat and transform faults result in entrapment of the Cache Creek terrane [ABSTRACT FROM AUTHOR]

The Gamburtsev Subglacial Mountains (GSMs) in the interior East Antarctic Craton are entirely buried under the massive East Antarctic ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is modelled to underlie the GSMs, which may have formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs are underlain by part of a Pan-African age advancing accretionary orogen superimposed on Precambrian basement.

40Ar/39Ar and U–Pb data from five structural domains constrain the late Neoproterozoic – early Palaeozoic tectonothermal history of the eastern part of the East African–Antarctic Orogen in Sør Rondane. A total of 27 new Ar/Ar ages span 570–474 Ma, roughly corresponding to the age range of three generations of syn- to post-tectonic granitoids. The ages are distinct for the five structural domains. The oldest cooling ages come from the weakly deformed southern part of the SW Terrane of Sør Rondane (SW Terrane S), a sliver of a Tonian island arc, which escaped much of the late Neoproterozoic accretionary deformation. This terrane was intruded by the oldest and largest granitoid complex at c. 640–620 Ma. The oldest Ar/Ar amphibole and biotite ages of 570–524 Ma are from the Main Shear Zone, along the northern margin of the SW Terrane S sliver. It hosts granites of age c. 584–570 Ma strung out along the shear zone. Two younger granitoid phases are recorded in the adjacent four terranes to the west, north and east of the SW Terrane S, and correlate with the younger group of Ar/Ar biotite ages spanning 513–474 Ma. We interpret the magmatic and cooling history of duration > 150 Ma to reflect repeated phases of accretion, magmatism and reactivation, that is, collage-style tectonism, partly pre-dating the incorporation of Sør Rondane into Gondwana. The study area first accreted to the cryptic Valkyrie Craton in Tonian times, was then 'sandwiched' between the Kalahari and Indo-Antarctica cratons, and experienced extensional tectonics and elevated heat flux due to lithospheric delamination, which resulted in slow cooling during the Pan-African Orogeny. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive tectonic evolution of Proterozoic to Cambrian rocks that integrate the crystalline basement of Rio de Janeiro State, based on the new geological map, is presented. The map combines detailed geological data integrated to a 1:400.000 scale and new geochemical and geochronology data to characterize the distinct terranes amalgamated during three pulses of the Brasiliano orogeny. The Occidental terrane comprises the Tonian to Late Cryogenean passive margin of the São Francisco paleocontinent, including reworked cratonic basement. At the same period, two magmatic arc systems were developed outboard: The Continental Inner arc system represented by the dismembered terranes (Paraíba do Sul, Embú, and Cambuci domain) integrated now in the Central Superterrane: and the Intra-oceanic Outer Arc System, the Oriental Terrane, developed from 860 to 620 Ma. Related active basins were detected in association with the two arc systems that collided at ca. 620 - 595 and 605 - 550 Ma against the São Francisco passive margin. A later collision episode at ca. 535 to 510 Ma brought the Cabo Frio Terrane (Angola tip) and closed the Búzios back-arc basin. Finally, the collapse of the orogenic belt, probably related to slab detachment and asthenosphere upwelling marks transition to Gondwana stabilization.

Accretionary orogens are hallmarks of subduction tectonics along convergent plate margins. Here we report a sequence of low-grade metasediments carrying exhumed blocks of ultramafic, mafic and felsic rocks from Sargur in the Western Dharwar Craton in India. These rocks occur along the southern domain of the Chitradurga Suture Zone, which marks the boundary between the Western and Central Dharwar Cratons and thus provide a window to explore Archean convergent margin processes. We present zircon U-Pb and Lu-Hf data from Sargur metasediments including quartz mica schist, fine-grained quartzite, and pelitic schist, as well as from blocks/layers of trondhjemite, garnet amphibolite, and chromite-bearing serpentinite occurring within the metasedimentary accretionary belt. The detrital zircon grains from the metasediments show multiple age groups, with the oldest age as 3482 Ma and an age peak at 2862 Ma. Magmatic zircons in trondhjemite show 207Pb/206Pb weighted mean age of ca. 2972 Ma, whereas those in the chromite-bearing serpentinite display multiple age populations of ca. 2896, 2750, 2648, 2566 and 2463 Ma, tracing zircon crystallization in an evolving mantle wedge adjacent to a subducting oceanic plate. Metamorphism is dated as ca. 2444 Ma from zircon grains in the garnet amphibolite. Zircon εHf(t) in the mafic-ultramafic rocks and trondhjemite are mostly positive, suggesting a juvenile (depleted mantle) source. The detrital zircon Lu-Hf data suggest that the sediment source involved Paleoarchean juvenile and reworked components. Based on our findings, we propose that the Sargur sequence represents an accretionary mélange which forms part of a major Mesoarchean accretionary orogen that witnessed multiple stages of tectonic erosion at least during three periods at ca. 3200–3000 Ma, 3000–2800 Ma and 2800–2500 Ma removing a large part of the accretionary prism along the convergent margin. We correlate the processes with prolonged subduction-accretion cycle culminating in the final collision between the Western and Central Dharwar cratonic blocks. Unlabelled Image • Detrital zircon in low grade metasediments trace Paleoarchean crust in Dharwar • Multiple stages of subduction erosion associated with convergent margin tectonics • Identification of Mesoarchean accretionary mélange formed through wedge extrusion [ABSTRACT FROM AUTHOR]

Copyright of Tectonics is the property of Wiley-Blackwell 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.)

When plate tectonics emerged and how it has evolved over Earth history are two of the most fundamental challenges in Earth Sciences. These questions are tackled using a holistic approach to analyze tectonic styles in the history of Earth, giving rise to the interpretation of two styles of plate tectonics since the Archean. In these interpretations, there are different styles of deformation and metamorphism between early times dominated by warm subduction, and later times preferring cold subduction. The two styles of plate tectonics are recorded by different properties of regional metamorphism at convergent plate boundaries, which are linked to the differences in mantle temperature between the Archean and Phanerozoic. A transition to modern plate tectonics is recorded by the signature of blueschist facies metamorphism developed in the Neoproterozoic. This is consistent with geological evidence for the operation of ancient plate tectonics since the early Archean. The temporal cooling of the mantle explains the geochemical trends of mantle-derived melts, the likely change from numerous small plates to fewer but larger plates, changes in thickness and preservation of oceanic crust and lithosphere in accretionary and collisional orogens, and led to the oxygenation of the surface environment providing the environments needed to foster life. [ABSTRACT FROM AUTHOR]

A comprehensive tectonic evolution of Proterozoic to Cambrian rocks that integrate the crystalline basement of Rio de Janeiro State, based on the new geological map, is presented. The map combines detailed geological data integrated to a 1:400.000 scale and new geochemical and geochronology data to characterize the distinct terranes amalgamated during three pulses of the Brasiliano orogeny. The Occidental terrane comprises the Tonian to Late Cryogenean passive margin of the São Francisco paleocontinent, including reworked cratonic basement. At the same period, two magmatic arc systems were developed outboard: The Continental Inner arc system represented by the dismembered terranes (Paraíba do Sul, Embú, and Cambuci domain) integrated now in the Central Superterrane: and the Intra-oceanic Outer Arc System, the Oriental Terrane, developed from 860 to 620 Ma. Related active basins were detected in association with the two arc systems that collided at ca. 620 - 595 and 605 - 550 Ma against the São Francisco passive margin. A later collision episode at ca. 535 to 510 Ma brought the Cabo Frio Terrane (Angola tip) and closed the Búzios back-arc basin. Finally, the collapse of the orogenic belt, probably related to slab detachment and asthenosphere upwelling marks transition to Gondwana stabilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Early Paleozoic granitoids are widely distributed in the North Qinling Orogen. • Granitoid geochemical compositions reveal changes in the source and tectonic setting during the early Paleozoic. • Partial melting of enriched oceanic arc crust and the addition of evolved crustal material caused crustal maturation. Accretionary orogens are sites of extensive continental crustal growth and modification. The mechanism by which mafic crust is transformed into silicic melts (i.e., maturation of continental crust) is important for understanding the formation of the continental crust. The North Qinling Orogen (NQO) is a composite orogenic belt and contains an early Paleozoic accretion-dominated orogenic system, which is ideal for investigating continental crustal maturation. We obtained zircon and monazite U–Pb age and O isotope data, zircon Lu–Hf isotope data, and whole-rock major- and trace-element and Sr–Nd isotope data for early Paleozoic granitoids of the NQO. The granitoids are divided into three groups. Group 1 includes the Taiping tonalite (445 ± 3 Ma), the Manziying syenogranite (445 ± 2 Ma), and the Huoshenmiao granodiorite (436 ± 2 Ma). The Taiping and Huoshenmiao plutons have relatively high SiO 2 contents (68.64–71.67 wt.%) and Na 2 O/K 2 O ratios (1.15–4.19), with enrichments in Rb, Ba, Th, and U and depletions in Nb, Ta, P, and Ti, and they are geochemically similar to sodic arc magmas. The Manziying syenogranite is a peraluminous potassic granite with high K 2 O contents (4.59–5.27 wt.%). Grantioids from Group 1 have similarly depleted Sr–Nd–Hf–O isotopic features (ε Hf [ t ] = +5.9 to +8.8; δ 18O = 3.98‰–5.41‰), indicative of derivation via partial melting of oceanic arc crust, which suggests that partial melting of oceanic arc crust in a subduction system contributes to the generation of continental crust and causes its maturation. Group 2 consists of the Wuduoshan monzogranite (418 ± 2 Ma) and the Sikeshu granodiorite (423 ± 3 Ma). These plutons have relatively high SiO 2 (65.59–72.06 wt.%), K 2 O (3.26–4.79 wt.%), and Al 2 O 3 (14.65–16.12 wt.%) contents and Sr/Y (33–87) and (La/Yb) N (23–48) ratios. The Wuduoshan monzogranite has positive zircon ε Hf (t) (+0.4 to +3.1) and uniform δ 18O (6.38‰–8.07‰) values, but the Sikeshu granodiorite has more variable isotopic compositions (ε Hf [ t ] = −1.9 to +5.0; δ 18O = 6.37‰–10.60‰). The Wuduoshan monzogranite and Sikeshu granodiorite have similar whole-rock Sr–Nd isotopic compositions to basement rocks of the NQO. These features indicate that the two plutons formed by partial melting of basement rocks (i.e., subducted into the lower crust) of the North Qinling unit, along with juvenile crustal material. Group 3 is represented by the Xiaguan monzogranite, which formed at 434–430 Ma, and can be subdivided into heavy rare earth element (REE)-depleted and -enriched units. The former has high Sr/Y (56–98) and (La/Yb) N (34–73) ratios and low MgO (0.13–0.24 wt.%), Cr (0.37–1.69 ppm), and Ni (0.32–1.09 ppm) contents, similar to adakites derived from metabasaltic sources. The heavy REE-enriched nature of the Xiaguan monzogranite may reflect modification of its source by melt or fluid. Our results show that partial melting of enriched oceanic arc crust contributed to crustal maturation in an accretionary orogen. The addition of evolved crustal material also facilitated this process; therefore, the basement rocks and crustal thickness should be considered when assessing crustal dynamics in an accretionary orogen. [ABSTRACT FROM AUTHOR]

The Arabian-Nubian Shield (ANS) is a rapidly emerging world-class province for gold resources mainly in structurally-controlled quartz ± carbonate veins that are best classified as late Neoproterozoic orogenic gold deposits. Gold has been mined in the Eastern Desert of Egypt, in the northwestern part of the ANS, for >6000 years, that is since the times of the Pharaohs, but production prior to the 1900s was likely only about 25 t and mainly from alluvial workings. In the first half of the 1900s, about 7 t Au was recovered from the El Sid orogenic gold deposit. Today, Sukari is the single major producing mine in the Eastern Desert but many other significant gold occurrences are being actively explored. Formation of the ANS took place during closure of the Mozambique Ocean between the East and West Gondwana continental blocks. Ocean closure led to amalgamation of numerous ca. 870–625 Ma juvenile arc and back-arc igneous and sedimentary rock sequences, with many resulting terrane sutures marked by mafic-ultramafic ophiolitic assemblages and fragments. The 100 m.y. of orogeny beginning at ca. 650 Ma included crustal shortening, lithospheric reworking, escape tectonics, and eventual orogenic collapse. Peak metamorphism was reached in different parts and depths of the orogen diachronously between 620 and 585 Ma, magmatism was widespread during 650–580 Ma, and rapid exhumation of the metamorphosed rocks and mid-crustal intrusions took place from ca. 600 to 580 Ma. Regional fault sets that controlled much of the gold occurrences were related to initial transpression by oblique convergence between the arcs and associated with subsequent sinistral shearing reported as overlapping the exhumation. Because existing geological data are not adequate to fully evaluate the overall terrane history, we have subdivided the Eastern Desert into nine structural blocks, rather than arc terranes, based commonly on bounding shear zones and major faults. The greatest abundance of gold deposits is associated with the NW-trending Najd Fault System that comprises many splays throughout the blocks in the Central Eastern Desert that underwent episodes of shearing at ca. 640–570 Ma. Important deposits are also notably widespread along reactivated east-west thrust faults in the Allaqi-Sol Hamed block of the South Eastern Desert, with significant shearing at 610–580 Ma. Sulfide mineralogy of the Eastern Desert gold-bearing veins is dominated by pyrite, arsenopyrite, and (or) pyrrhotite, in addition to subordinate chalcopyrite, sphalerite, galena and tetrahedrite as well as alteration minerals that include white mica, chlorite, and carbonate, are those typical of orogenic gold deposits. Many gold occurrences are located along sheared margins to granitic intrusions or along contacts between different lithologies; sheared silica- and carbonate-altered ultramafic rocks along many fault zones are particularly widely associated with many of the gold occurrences. Ore-forming fluids were generally low-salinity aqueous-carbonic with most measured δ18O of mineralized quartz ranging from 8‰ to 15‰, δ13C for associated carbonate from −10‰ to −1‰, and δ34S for ore-related sulfides varying between −5 and +10‰, but much more consistent for individual occurrences or deposits. Gold was deposited at temperatures of generally between 250° and 370 °C, depending on location, and largely variable pressures. The few obtained absolute dates on ore formation, from the Fawakhir and Atalla deposits in the Central Eastern Desert, indicate that at least some of the mineralization was formed at ca. 600 Ma. Orogenic gold formed after the cessation of arc-terrane accretion in the ANS and during a period in which most of the shield became established with a 30–40 km-thick continental crust and underwent a transition from compressional/transpressional terrane accretion to post-amalgamation transtensional shearing. This also was marked by a petrogenetic transition from pre- to syn-accretionary, arc-related calc-alkaline I-type magmatism to late- or post-tectonic A-type magmatism within the newly formed shield. Concurrently, the Eastern Desert was affected by widespread crustal flow of aqueous-carbonic fluids, particularly on the through-going, extensive strike-slip shears of the Najd Fault System. Gold and sulfide minerals were deposited in the Eastern Desert shallow and middle crust coevally with rapid terrane exhumation, during changes in fluid chemistry associated with pressure cycling and multiple vein quartz precipitation. Unlabelled Image • Available information on gold occurrences in the Eastern Desert of Egypt is reviewed, assessed and thoroughly discussed. • New ideas of the genesis and controls of the scattered gold occurrences in the shield are herein presented and detailed. • Orogenic gold in the Eastern Desert formed after the cessation of arc-terrane accretion and post-peak metamorphism. • Transition from subduction-related to within-plate magmatism was concomitant with widespread aqueous-carbonic fluid flow. • Significant orogenic gold mineralization formed at ca. 600 Ma, concurrent with crustal exhumation and extensive shearing. [ABSTRACT FROM AUTHOR]

The Altai‐Junggar‐Tianshan collage in southern Altaids is an important metallogenic domain in Central Asia that contain world‐class copper‐iron‐nickel deposits. As an accretionary‐type metallogenic system, the metallogenic processes of the Altai‐Junggar‐Tianshan collage is essential in understanding the genetic mechanism of ore deposits in general. Here in this paper we present a brief introduction to the project on the western part of the Southern Altaids, entitled "The deep structure and metallegenic processes of the North China accretionary metallogenic systems". This project mainly focuses on the deep structure and metallogenic background of the Altai‐Junggar‐Tianshan collage by integrated studies from field geology, structural mapping, geochemistry and geophysical exploration. Multiple new geological and geophysical methods will be applied to make transparency of the Kalatongke and Kalatage ore clusters. This will update our understanding of the geodynamic processes of metallogenesis and lead to the development and foundation of new metallogenic theories in accretionary orogens. [ABSTRACT FROM AUTHOR]

Under oblique convergence, the intraoceanic subduction zones tend to have a tectonically-escaped accretionary prism, incorporates exotic materials from different sources and oceanic crust fragments. The western part of the Allaqi-Heiani suture (AHS) is the type locality for a significant accretionary prism extends for ⁓ 200 km; this prism is mainly metavolcanic, and metasedimentary rocks have interwoven serpentinite, marble blocks and intruded with different phases of plutonism. Geologic studies of the western part of the AHS have suggested the allochthonous origin for this complex, and terrane accretion happened earlier than ⁓ 700 Ma and subsequently thrusted over Gabgaba terrane to the south. Magnetic data was applied to follow the deep-seated structures and the connectivity between ophiolite belts in the AHS. Magnetic data unravelled the presence of a deep-seated strike-slip faults aligned along N–S and NNE trends underneath the northern belt, and this fault zone was erased at the surface by a major zone of the post-accretionary left-lateral strike-slip faults. In the southern part, E-W and WNW-ESE faults are dominant at the edge of the autochthon Gabgaba terrane. At greater depths, thrusts related to the emplacement of the northern belt disappeared, while those to the south aligned with the suture zone becomes significant. In conclusion, there are two ophiolite belts are located in the western part of the AHS; the southern belt is extended along the edge of the Gabgaba terrane to the south and the Eastern Desert (ED) to the north. This south belt is the western extension of a major arc-arc suture zone that extends to the east into the Arabian shield. The northern ophiolite belt was emplaced onto the southern part of the ED ⁓ 70 km away from the arc-arc to the south. Image 1 • Unpaired ophiolite belts in the western part of the Allaqi-Heiani suture. • The southern ophiolite belt is the western extension of the Allaqi-Heiani suture. • The northern belt is an accretionary complex which emplaced onto the southern Eastern Desert. • The accretionary prism was emplaced along deep-seated fault zone perpendicular to the suture zone. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The most important crustal differentiation in the Chinese Altai occurred in the middle Paleozoic. • The middle Paleozoic mafic rocks were derived from magmas that were evolved mainly within the amphibole stability field. • The middle Paleozoic granites were formed without the involvement of garnet. • The crustal differentiation at the shallow depth was not related to a thickened crust. Abstract The Chinese Altai underwent intensive mafic and felsic magmatism in the middle Paleozoic, which was the most important magmatic event in the region. It is still unclear for the role of the event in formation of the crust that is thick (∼56 km) and has structure of three-layer stratification. In this study, the data for the middle Paleozoic mafic rocks and granites are comprehensively compiled and integrated with new geochronological, petrological, geochemical and Sr-Nd-Pb isotopic data for gabbroic rocks from Keketuohai area and tonalite and biotite granites from Habahe area. The middle Paleozoic mafic rocks exhibit two evolutionary trends, which can be defined as high-Al and low-Al types because of their evolution at different crustal levels but mainly at amphibole stability field. The middle Paleozoic I-type granites are mainly metaluminous to weakly peraluminous and were possibly generated by dehydration melting of those mafic rocks evidenced by similar Nd isotopic compositions (ε Nd (t) = −2.7 to +3.8 for granites; ε Nd (t) = −2.5 to +8.5 for the middle Paleozoic mafic rocks). The strongly peraluminous granites show large range in MgO (0.41–3.85 wt%), Cr (5.32–153 ppm) and Ni (3.69–104 ppm), suggesting that they might be produced by dehydration melting of a mixed source composed of materials from the Habahe Group and the middle Paleozoic igneous rocks. The middle Paleozoic I-type and strongly peraluminous granites mostly have high contents of Y and Yb and show low Sr/Y and La/Yb ratios, indicating insignificant residual garnet in the source. The Habahe tonalites (372 ± 3 Ma) are characterized by positive ε Nd (t) values (+4.7–+4.8) and high (207Pb/204Pb) t and (208Pb/204Pb) t ratios, similar to those of the middle Paleozoic mafic rocks. These granites have low contents of MgO (0.50–0.88 wt%), flat rare earth elements (REE) patterns ([La/Yb] N = 1.1–1.6) and strongly positive Eu anomaly (1.6–2.5), indicating that they were possibly evolved from the high-Al mafic magma through fractionation of Mg-rich minerals. The Habahe biotite granites (359 ± 4 to 381 ± 4 Ma) are strongly peraluminous (A/CNK = 1.12–1.23), show concaved REE patterns ([Dy/Yb] N = 0.90–1.24), and have low (87Sr/86Sr) i ratios, positive ε Nd (t) values (+1.9 to +5.5) and high (207Pb/204Pb) t and (208Pb/204Pb) t ratios. These geochemical features suggest that they were possibly derived from hydrous melting of the middle Paleozoic mafic rocks with residual amphibole at middle crustal level. The middle Paleozoic magmatism recorded the most important period for the crustal differentiation in the Chinese Altai. The evolution of mafic magma and formation of granites mainly occurred within amphibole stability field, illustrating a relatively shallow crustal differentiation process (<30 km) although the crust may have been thickened. [ABSTRACT FROM AUTHOR]

Abstract Hydrothermal ore deposits at convergent plate boundaries represent extraordinary metal enrichment in the continental crust. They are generally associated with felsic magmatism in extensional settings at high thermal gradients. Although their formation is common during accretionary orogeny, more and more ore deposits have been discovered recently in the collisional orogens of China. Because collisional orogeny was operated in a compressional regime at low thermal gradients, it is not favorable for mobilization of ore-forming elements and thus for the production of hydrothermal ore deposits. Nevertheless, continental collision is generally preceded by oceanic subduction, which enables the preliminary enrichment of ore-forming elements in the mantle wedge due to chemical metasomatism by subducting slab-derived fluids. This gave rise to metal pre-enriched domains in the overriding lithosphere, which may be reactivated by extensional tectonism for hydrothermal mineralization either immediately during accretionary orogeny or at a later time during and after collisional orogeny. It is these tectonic processes that have resulted in the progressive enrichment of ore-forming elements through the geochemical differentiation of the subducting oceanic crust, the metasomatic mantle domains and the mafic juvenile crust, respectively, at different depths. Finally, the reactivation of metal pre-enriched domains by continental rifting in the orogenic lithosphere is the key to the metallogenesis of collisional orogens. [ABSTRACT FROM AUTHOR]

Identifcation of subduction to back-arc tectonic transitions is critical to the study of accretionary orogens. Some new geochronological and geochemical data for the Late Devonian (380–361 Ma) Kezier mafic–felsic complex and Tuwu granitic pluton in this study have well recorded such transition feature in the Chinese Eastern Tianshan orogen. The Kezier gabbro is classified as high-Al basalt given their high Al contents (A1 2 O 3 > 17 wt%). They were originated from a depleted mantle fluxed by fertile mantle components at shallow depths under hydrous condition. Both the Kezier and Tuwu granites show geochemical characteristics of high total alkali, Ga/Al, HFSE, low CaO, and strongly negative Ba, Sr, and Eu anomalies, demonstrating a close affinity with A-type granites. The granites were probably generated by high temperature melting (zircon saturation temperature up to 916 °C) of crustal rocks under a low-pressure (<0.8–1.0 GPa) condition. These rocks can help identify the Late Devonian back-arc extensional event in the Eastern Tianshan. This extensional event contemporaneous with the onset of the earliest arc magmatic records southward rejuvenating. The back-arc extensional with crustal high-temperature melting event can be reconciled with the Kangguer Ocean rollback, which forced the arc rifting occur on the Dananhu fore-arc side during the Late Devonian. • Late Devonian gabbros and granites were identified in the Chinese Eastern Tianshan; • The high-Al gabbros were formed by hydrous pressure-release partial melting; • The A-type granites were derived from high-T and low-P melting of juvenile crust; • The Eastern Tianshan orogen was back-arc extension during the Late Devonian. [ABSTRACT FROM AUTHOR]

Abstract The accretion of the Avalon and Meguma terranes to the Laurentian margin was a major event in the development of the Appalachian orogen. The Minas Fault Zone delineates the boundary between these terranes. A strongly lineated and foliated granite intrusion (Kelly Brook pluton) exposed along the West River St. Mary's Fault intruded into Meguma Supergroup metasedimentary rocks. Well-developed C-S fabrics characterize the pluton with muscovite aligned in the S fabric, and a shallow (~10°) westerly plunging quartz stretching lineation. New U-Pb (zircon, LA-ICP-MS) geochronological data yield a crystallization age of 375.0 ± 4.6 Ma for the Kelly Brook pluton that is indistinguishable from other Late-Devonian intrusive rocks in the Meguma terrane. Petrographic data for muscovite indicate that it grew prior to deformation. A 100% plateau 40Ar/39Ar age of 369.0 ± 1.2 Ma on a single muscovite grain constrains the time of cooling of the granite to approximately 450 to 420 °C. Apatite grains also demonstrate pre- to syn -deformational fabrics and yield a U-Pb (LA-ICP-MS) age of 361.2 ± 5.6 Ma indicating the temperature of the granite was still above 350 °C at this time. Earliest Tournaisian fossils in the unconformably overlying Horton Group strata indicate that the granite was exposed by ca. 359 Ma. Exhumation rates of the Kelly Brook pluton and the Meguma terrane from approximately 9.5–13.3 km depth from ca. 375 Ma to surface exposure at ca. 359 Ma are 0.06 to 0.08 cm yr−1. Estimates for the Upper Devonian regional geothermal gradient in the northern Meguma terrane are high between 39.5 °C km−1 and 67.8 °C km−1, gradients that are common in extensional tectonic environments such as the Basin and Range province. An apatite fission-track age of 215 ± 14 Ma indicates Mesozoic reburial and reheating of the granite prior to opening of the Atlantic Ocean. Highlights • Geochronological and microstructural data record the Late-Devonian relationship between the Avalon and Meguma terranes • The Late-Devonian (ca. 375–359 Ma) geothermal gradient in the northern Meguma terrane was high • Age data coupled with a fabric analysis can elucidate the geothermal gradient and exhumation rates along terrane boundaries [ABSTRACT FROM AUTHOR]

Abstract Combined zircon geochronology and Hf isotopes of plutonic rocks from eastern Marie Byrd Land and Thurston Island, Antarctica, provide a detailed record of Phanerzoic arc magmatism along the paleo-Pacific margin of Gondwana. Magmatism along the Antarctic margin initiated in a dominantly contractional arc setting with an isotopically enriched lithospheric mantle source during the Ross Orogeny (c. 540–485 Ma). After termination of the Ross Orogeny through the Cretaceous, detrital zircon and zircon from igneous rocks record relative increases in zircon εHf i inferred to represent episodes of lithospheric-scale extension and relative decreases during inferred contractional episodes along the Antarctic margin. Comparison of this secular isotopic evolutionary trend with similar data from along the paleo-Pacific margin of Gondwana demonstrates a shared history among Marie Byrd Land, Australia, and Zealandia that contrasts with the shared record of Thurston Island, Antarctic Peninsula, and South America. These two contrasting histories highlight an early Permian along arc geochemical and inferred geodynamic switch from an isotopically enriched contractional arc system in South America, Antarctic Peninsula, and Thurston Island to an isotopically depleted extensional arc system in Marie Byrd Land, Zealandia, and Australia. Despite differences in timing, all segments of the paleo-Pacific margin underwent a similar secular isotopic evolution with dramatic shifts from enriched to juvenile isotopic compositions during extensional collapse. Graphical abstract Unlabelled Image Highlights • New and compiled zircon U-Pb and Hf isotopes track Gondwana margin evolution. • Marie Byrd Land and Transantarctic Mountains share history with Australia and Zealandia. • Thurston Island and Antarctic Peninsula correlate to South America. • Accretionary orogens undergo lithosphere rejuvenation during major extensional collapse. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Detrital zircon ages constrain transition from Cadomian orogen to passive margin. • This transition spanned about 50 M.y. • Curved geometry of the West African margin and subduction zone played a key role. • The transition was driven by oblique ridge–trench interaction. • Slab pull of the Iapetus Ocean followed. Abstract The Avalonian–Cadomian belt formed as a collage of accretionary complexes, island arcs, and sedimentary basins along the northern margin of Gondwana during the Neoproterozoic times. One of the enigmatic issues is how and when this active margin evolved to a passive margin in the southern realms of the Rheic Ocean during late Cambrian to early Ordovician. This issue is addressed here using U–Pb detrital zircon dating of key stratigraphic sections in the Teplá–Barrandian unit, Bohemian Massif. The new ages constrain the base of the Davle volcanic arc to 608 ± 6 Ma, 591 ± 6 Ma, and 590 ± 4 Ma and its termination to 563 ± 7 Ma. The lower part of the overlying Příbram–Jince continental basin was deposited between 512 ± 5 and 511 ± 3 Ma. These brackets define a time span of about 50 M.y. for the geodynamic transition from Cadomian subduction, accretion, and arc magmatism to a passive margin and lithospheric extension. In our model, a major role is assigned to a presumably curved geometry of the adjacent West African continental margin, which consisted of the outboard Armorican–Saxothuringian portion at an angle to the inboard Iberian–Barrandian portion. We suggest that during oblique subduction, ridge–trench collision and slab break-off occurred in the former at ca. 540 Ma, while subduction/accretion continued in the latter and was terminated by a major pulse of sediment accretion at around 527 Ma and ridge subduction at ca. 524–520 Ma. Finally, the tectonic regime in the Cadomian arc and accreted upper crust switched to extension associated with crustal remelting to produce intraplate magmatism and development of continental basins with short-lived marine transgressions between ca. 512 Ma and ca. 488 Ma. The continued extension led to rifting and basaltic volcanism, directly linked to the diachronous opening of the Rheic Ocean. We conclude that the prolonged transition from active to passive margin in the Cadomian belt was driven two principal geodynamic causes: first by oblique oceanic subduction and ridge–trench interactions, bearing many similarities to modern Cordilleran-type active margins, and then by the far-field slab-pull force of the subducting Iapetus Ocean. [ABSTRACT FROM AUTHOR]

Abstract: Accretionary orogens generally involve trench advance and retreat, recognition of which is critical to understand the thermal evolution and geodynamics of the lithosphere. A systematic study has been conducted on the Silurian to Carboniferous volcanic rocks from the Dananhu‐Harlik arc in the Chinese eastern Tianshan. Three distinct episodes of volcanism have been recognized: Late Silurian normal andesite, high Sr/Y andesite and sanukitoid, Late Devonian bimodal high‐alumina basalt and dacite, and Early Carboniferous high‐alumina basalt. These magmatism experienced variable degrees of interaction between a depleted mantle wedge and subducting slab‐/sediment‐derived fluid/melt. Combining with previous geological data, we propose that the Dananhu‐Harlik arc was formed by the northward subduction of the North Tianshan Ocean (NTO), different from the traditional southward subduction of the Junggar Ocean, which was likely subducted northward to account for the East Junggar arc system. Temporal changes in Ce/Y of basalts and Ho/Yb of felsic rocks in the Dananhu‐Harlik arc imply that the arc crust underwent episodic thickening and thinning, which probably reflect the trench advance/retreat processes. The high Ce/Y and Ho/Yb ratios in the Late Ordovician to Devonian and Late Carboniferous correspond to two phases of trench advance. Conversely, the low Ce/Y and Ho/Yb ratios in the Early Carboniferous record a period of trench retreat, which caused the splitting of the Dananhu‐Harlik arc and formation of the Bogda back‐arc basin. Meanwhile, a southward subduction initiated along the south margin of the NTO, producing the Yamansu arc. Late Carboniferous bipolar subduction of the NTO led to its final closure. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens on Earth and is characterized by the occurrence of tight oroclines (Kazakhstan and Tuva-Mongolian oroclines). The origin of these large-scale orogenic curvatures is not quite understood, but is fundamentally important for understanding crustal growth and tectonic evolution of the CAOB. Here we provide an outline of available geological and paleomagnetic data around the Kazakhstan Orocline, with an aim of clarifying the geometry, kinematics and geodynamic origin of the orocline. The Kazakhstan Orocline is evident in a total magmatic image, and can be traced by the continuation of high magnetic anomalies associated with the Devonian Volcanic Belt and the Late Devonian to Carboniferous Balkhash-Yili arc. Paleomagnetic data show ∼112–126° clockwise rotation of the northern limb relative to the southern limb in the Late Devonian to Early Carboniferous, as well as ∼15–28° clockwise rotation of the northern limb and ∼39–40° anticlockwise rotation of the southern limb relative to the hinge of the orocline during the Late Carboniferous to Permian. We argue that the Kazakhstan Orocline experienced two-stage bending with the early stage of bending (Late Devonian to Early Carboniferous; ∼112–126°) driven by slab rollback, and the later stage (Late Carboniferous to Permian; 54–68°) possibly associated with the amalgamation of the Siberian, Tarim and Baltic cratons. This new tectonic model is compatible with the occurrence of rift basins, the spatial migration of magmatic arc, and the development of large-scale strike-slip fault systems during oroclinal bending. [ABSTRACT FROM AUTHOR]

The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80–57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87 Sr/ 86 Sr ratios range from 0.7048 to 0.7114, and ε Nd (t) values vary from +1.7 to −3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The generation of this belt was ascribed to subduction of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

Accretionary orogens are major sites of modern continental growth, yet their role in the development of Archean continental crust remains enigmatic. Diverse granitoid suites from tonalite-trondhjemite-granodiorite (TTG) to potassic granitoids appeared during late Archean, representing a period of major continental formation and stabilization. In this study, whole-rock geochemical and zircon U-Pb and Lu-Hf isotopic data are reported for Neoarchean granitoid gneisses from the Northern Liaoning Terrane, northeastern North China Craton (NCC). Older granitoid gneisses (~2592-2537 Ma) define three magmatic zones migrating from southeast to northwest, each showing a common magmatic evolution from high-pressure TTGs to medium-/low-pressure TTGs and potassic granitoids. They have depleted zircon ƐHf( t) of +0.5 to +8.7. Younger ~2529-2503 Ma potassic granitoids and TTGs occur throughout the terrane, which are marked by variable zircon ƐHf( t) of −4.7 to +8.1, and are coeval with regional high-grade metamorphism. Petrogenetic modeling and changing Sr/Y and (La/Yb)N of the granitoids suggest that the crust experienced episodic thickening and thinning and became progressively evolved through development of potassic granitoids and sedimentary successions. The metavolcanic basement to the granitoids display tholeiitic to calc-alkaline affinities, together with the top-to-the-northwest thrusting and associated volcanogenic massive sulfide-type Cu-Zn deposits, suggesting cyclic crustal formation of Northern Liaoning within an accretionary orogen with a SE-dipping subduction polarity. Cyclic crustal thickening and thinning is related to tectonic switching from advancing to retreating relations between the downgoing and overriding plate. After ~2530 Ma, this accretionary system accreted to the ancient continental nucleus of NCC (Anshan-Benxi Terrane), signifying final lithosphere stabilization. [ABSTRACT FROM AUTHOR]

The mechanisms that drove Permian-Triassic orogenesis in Australia and throughout the Cordilleran-type Gondwanan margin is a subject of debate. Here we present field-based results on the structural evolution of the Gympie Terrane (eastern Australia), with the aim of evaluating its possible role in triggering widespread orogenesis. We document several deformation events (D1-D3) in the Gympie Terrane and show that the earliest deformation, D1, occurred only during the final pulse of orogenesis (235-230 Ma) within the broader Gondwanide Orogeny. In addition, we found no evidence for a crustal suture, suggesting that terrane accretion was not the main mechanism behind deformation. Rather, the similar spatiotemporal evolution of Permian-Triassic orogenic belts in Australia, Antarctica, South Africa, and South America suggest that the Gondwanide Orogeny was more likely linked to large-scale tectonic processes such as plate reorganization. In the context of previous work, our results highlight a number of spatial and temporal variations in pulses of deformation in eastern Australia, suggesting that shorter cycles of deformation occurred at a regional scale within the broader episode of the Gondwanide Orogeny. Similarly to the Cenozoic evolution of the central and southern Andes, we suggest that plate coupling and orogenic cycles in the Late Paleozoic to Early Mesozoic Gondwanide Orogeny have resulted from the superposition of mechanisms acting at a range of scales, perhaps contributing to the observed variations in the intensity, timing, and duration of deformation phases within the orogenic belt. [ABSTRACT FROM AUTHOR]

Accretionary orogens are major sites of generation of continental crust but the spatial and temporal distribution of crust generation within individual orogens remains poorly constrained. Paleozoic (∼540–270 Ma) granitic rocks from the Alati, Junggar and Chinese Tianshan segments of the Central Asian Orogenic Belt (CAOB) have markedly bimodal age frequency distributions with peaks of ages at ∼400 Ma and 280 Ma for the Altai segment, and ∼430 Ma and 300 Ma for the Junggar and Chinese Tianshan segments. Most of the magma was generated in short time intervals (∼20–40 Ma), and variations in magma volumes and in Nd–Hf isotope ratios are taken to reflect variable rates of new crust generation within a long-lived convergent plate setting. The Junggar segment is characterized by high and uniform Nd–Hf isotope ratios ( ε Nd ( t ) = + 5 to + 8 ; zircon ε Hf ( t ) = + 10 to + 16 ) and it appears to have formed in an intra-oceanic arc system. In the Altai and Chinese Tianshan segments, the Nd–Hf isotope ratios ( ε Nd ( t ) = − 7 to + 8 ; zircon ε Hf ( t ) = − 16 to + 16 ) are lower, although they increase with decreasing age of the rock units. The introduction of a juvenile component into the Chinese Tianshan and Altai granitic rocks appears to have occurred in continental arc settings and it reflects a progressive reduction in the contributions from old continental lower crust and lithospheric mantle. Within the long-lived convergent margin setting (over ∼200 Ma), higher volumes of magma, and greater contributions of juvenile material, were typically emplaced over short time intervals of ∼20–40 Ma. These intervals were associated with higher Nb/La ratios, coupled with lower La/Yb ratios, in both the mafic and granitic rocks, and these episodes of increased magmatism from intraplate-like sources are therefore thought to have been in response to lithospheric extension. The trace element and Nd–Hf isotope data, in combination with estimates of granitic magma volumes, highlight that crust generation rates are strongly non-uniform within long-lived accretionary orogens. The estimated crust generation rates range from ∼0.1 to ∼40 km 3 /km/Ma for the Paleozoic record of the CAOB, and only comparatively short (20–40 Ma) periods of elevated magmatic activity had rates similar to those for modern intra-oceanic and continental arcs. [ABSTRACT FROM AUTHOR]

• We present detrital zircon U-Pb/Lu-Hf and monazite U-Pb data from the SW Grenville Province. • The complete Great Proterozoic Accretionary Orogen period is represented. • The margin was established on Archean crust, followed by juvenile additions and outward growth. • The data record periodic basin formation followed by inversion during collisional events. The Great Proterozoic Accretionary Orogeny along the southern and southeastern margin of Laurentia is arguably the first long-lived, modern-style active plate margin on Earth, representing significant crustal growth and reworking. Here, we present new detrital zircon U–Pb and Hf data, along with zircon and monazite metamorphic ages, from tectonic domains in the southwestern Grenville Province that represent depositional basins formed and reworked during a series of events between 2.2 and 1.2 Ga. As such, the data allow a glimpse into the evolution and assembly of this extensive margin. The Nepewassi domain contains Archean basement overlain by mature sandstone characterized by near-unimodal, ca. 2.7–2.6 Ga detrital zircon peaks and likely correlative with Superior Province basement and its Huronian cover. The Nepewassi domain underwent both Archean (ca. 2.65 Ga) and Killarnean (ca. 1.76 Ga) metamorphism. In addition, all units preserve evidence of Grenvillian high-grade metamorphism between ca. 1.05 and 0.99 Ga. The structurally highest parts of the Nepewassi domain also contain younger sedimentary rocks that received detritus from Killarnean sources, with evolved Hf isotopic compositions indicative of reworked Archean crust. Sedimentary rocks in the Tomiko domain preserve detrital zircon of Penokean and Killarnean age (1.9–1.7 Ga) with evolved Hf compositions, along with Labradorian (1.7–1.6 Ga) grains of more juvenile composition. Detrital zircon from the Kiosk domain yield Penokean through Labradorian ages, with Hf compositions ranging from evolved to juvenile. In contrast to the sedimentary rocks found in these Laurentia-derived parautochthonous domains, similar rocks from younger, more allochthonous units, including the Shawanaga and basal Parry Sound domain, dominantly contain zircon ranging from Pinwarian (ca. 1.45 Ga) through ca. 1.20 Ga that show exclusively juvenile isotopic compositions. The data show that sedimentary basins received detritus from nearby active sources as well as from the nearby Superior continent, and that successively younger sources and basins became increasingly less influenced by continental input as the margin grew wider. The data add to a growing database of similar data from other parts of this several thousand-kilometer-long margin that seemingly displayed little along-strike variation in overall evolution, implying the existence of a vast, Pacific-scale ocean. [ABSTRACT FROM AUTHOR]

Field geological mapping of tropical West Africa is hampered by the variable development of deep regolith and tropical rainforest and this has impeded the progress of geological research. Nevertheless, there are areas in which field geological mapping can be effective. A 1:100,000 scale map of the Paleoproterozoic geology of the West African Craton in the Toumodi area of central Ivory Coast was developed on the basis of five months of independent field geological mapping carried out on foot, and with the aid of a motorised vehicle (Main Map). The field mapping was carried out in 1987 and 1988 using traditional field geological techniques and 1950s 1:50,000 and 1:200,000 topographic base maps published by the Institut Géographique National (Paris). Original field observations and the interpreted geological map were recently compiled using a geographic information system software, which was also used to confirm the positional accuracy of the field mapping using satellite imagery. The field geological mapping presented here provided the basis for recognition of discrete lithostratigraphic terranes exposing different crustal levels within the Paleoproterozoic Birimian domain of the West African Craton which are interpreted to have originated as juvenile crustal additions in a Paleoproterozoic accretionary orogen at an obliquely convergent plate boundary. [ABSTRACT FROM AUTHOR]

We studied high-grade metamorphic rocks of the El Cristo hill area of the Tandilia belt. Mineral analyses and thermodynamic calculations were carried out for two adjacent rock samples: an amphibole–biotite gneiss and a garnet–biotite-bearing migmatite. Peritectic garnets in the migmatite show core compositions of pyr 4.5 (gro + andr) 10 spes 6 alm 79.5 changing to pyr 3.5 (gro + andr) 17 spes 6 alm 73.5 at their thin rims. Garnet compositions in the gneiss are pyr 6.5 (gro + andr) 26 spes 12 alm 55.5 and pyr 4.5 (gro + andr) 34 spes 12 alm 49.5 for core and rim, respectively. A P–T path was constructed by calculating pseudosections in the 11-component system Si–Ti–Al–Fe–Mn–Mg–Ca–Na–K–O–H and contouring them by isopleths for garnet components using the PERPLE_X software package. Supra-solidus crystallization of garnet cores in the migmatite began at 5.8 kbar and 660 °C. Garnet rims equilibrated at 7.0 kbar and 640 °C compatible with garnet cores in the amphibole–biotite gneiss (7.6 kbar and 660 °C). The further chemical development of garnet in this rock points to P–T conditions of 11.6 kbar and 620 °C and 12.2 kbar and 595 °C (outermost garnet rim). At this high-pressure stage Ca-amphibole was not stable. Most biotite formed during exhumation whereas the high-pressure accessory minerals, titanite and epidote, persisted. According to the obtained anti-clockwise P–T path the originally partly melted material was tectonically transported from ∼22 km (middle crust) to ∼40 km (lower crust) depths reaching a geothermal gradient as low as 15 °C km −1 . This transport probably occurred along a major suture zone, which was active during the Paleoproterozoic (2.25–2.10 Ga), before a terminating collision of terranes near the SW boundary of the Rio de la Plata craton. [ABSTRACT FROM AUTHOR]

• Linking the Amazonia, Rio Apa and Paraguá terranes with zircon U-Pb-Hf evolution. • New zircon U-Pb-Hf data from the Rio Apa and Paraguá terranes spanning 3.0–1.25 Ga. • Rio Apa and Paraguá terranes share similar geodynamic setting along SW Amazonia. • Secular zircon εHfT evolution switches from advancing to retreating accretionary orogen. Despite a general consensus of a petrogenetic link in Paleo- to Mesoproterozoic times between the Rio Apa Terrane (RAT) and the Ventuari-Tapajós and Rio Negro-Juruena provinces of the SW Amazonian Craton, their connection with the adjoining Paraguá Terrane is still tentative. Here, we test the connection between SW Amazonia, Rio Apa and Paraguá terranes by comparing an extensive dataset of new and published zircon U–Pb–Hf isotopic data. A locally weighted scatterplot smoothing (LOWESS) curve based on a near continuous zircon εHf T time series (∼1400 data) indicates that the Western domain of the RAT, the San Diablo domain (southern Paraguá Terrane), and the Ventuari-Tapajós Province are characterized by a crustal reworking array associated with the recycling of the Amazonian Archean crust. Change-point statistical analysis indicates the time of a switch from this reworking array to an episode of juvenile input into the magmatic sources at 1809–1805 Ma (95 % confidence), giving rise to the juvenile Eastern domain of the RAT, the Paraguá Terrane and the Rio Negro-Juruena Province. This secular zircon εHf T evolution is interpreted to represent a switch from advancing (crustal reworking) to retreating (juvenile input and crustal growth) episodes in the Paleo- to Mesoproterozoic accretionary orogen of SW Amazonia. Similar temporal isotopic patterns are recorded in modern accretionary orogens such as the Andes. This data supports a petrogenetic link between the RAT, the Paraguá Terrane, and the SW Amazonian Craton. We postulate that the Mesoproterozoic Alto Guaporé orogeny (ca. 1470–1430 Ma, accretionary phase) eventually juxtaposed the high-pressure/medium-temperature (amphibolite facies) RAT and the high-temperature (granulite facies) Paraguá Terrane along the SW margin of Amazonia, establishing a paired metamorphic belt during Rodinia assembly. The newly formed RAT-Paraguá-Amazonia connection lasted until at least ca. 1110 Ma based on the expression of the Rincon del Tigre-Huanchaca large igneous province that crosscut the Amazonia-Paraguá and RAT. The timing of fragmentation and drift of the RAT and the Paraguá Terrane from the SW Amazonia is still unknown. [ABSTRACT FROM AUTHOR]

A compilation of magmatic ages from the Mesozoic South China Block suggests a number of “magmatic quiescence” periods at ca. 205–195 Ma, ca. 150–140 Ma and ca. 125–115 Ma, casting doubt on tectonic models that suggest ongoing Andean-type subduction along the South China continental margin. However, SIMS U-Pb analyses on two detrital zircon samples from the Cretaceous Lumuwan Formation on Hainan Island, southeast China, reveal three major age peaks at ca. 120 Ma, ca. 155 Ma and ca. 235 Ma. Zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning, suggesting short-distance transport from nearby magmatic sources. The extremely rare occurrence of ca. 120 Ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to Hainan Island but presently missing. Therefore, our data provide new evidence for ongoing magmatic activity in late Mesozoic South China. In situ Hf and O isotope analyses of the Mesozoic detrital zircons reveal large variations in both ε Hf ( t ) (− 21.2 to 10.5) and δ 18 O (4.4‰ to 13.6‰) values. A general negative correlation between them suggests the reworking of old supracrustal materials (average crustal residence age of ca. 2.0 Ga) by juvenile mantle-derived magmas. The progression of increasing ε Hf ( t ) and decreasing δ 18 O values of zircons from the Triassic to the Cretaceous suggests progressive crustal growth during the Mesozoic. The results are consistent with hybridization at an active continental margin. We briefly review tectonic models for the Indosinian orogeny and suggest that the petrologic evidence indicates that Mesozoic magmatism was part of the circum-Pacific accretionary orogens that formed along the continental margin of East Asia no later than ca. 250 Ma and continued at least to the late Cretaceous. [ABSTRACT FROM AUTHOR]

The NW–SE Irtysh Shear Zone is a major tectonic boundary in the Central Asian Orogenic Belt (CAOB), which supposedly records the amalgamation history between the peri-Siberian orogenic system and the Kazakhstan/south Mongolia orogenic system. However, the tectonic evolution of the Irtysh Shear Zone is not fully understood. Here we present new structural and geochronological data, which together with other constraints on the timing of deformation suggests that the Irtysh Shear Zone was subjected to three phases of deformation in the late Paleozoic. D 1 is locally recognized as folded foliations in low strain areas and as an internal fabric within garnet porphyroblasts. D 2 is represented by a shallowly dipping fabric and related ∼ NW–SE stretching lineations oriented sub-parallel to the strike of the orogen. D 2 foliations are folded by ∼ NW–SE folds (F 3 ) that are bounded by a series of mylonite zones with evidence for sinistral/reverse kinematics. These fold and shear structures are kinematically compatible, and thus interpreted to result from a transpressional deformation phase (D 3 ). Two samples of mica schists yielded youngest detrital zircon peaks at ∼322 Ma, placing a maximum constraint on the timing of D 1 –D 3 deformation. A ∼ NE–SW granitic dyke swarm (∼252 Ma) crosscuts D 3 fold structures and mylonitic fabrics in the central part of the shear zone, but is displaced by a mylonite zone that represents the southern boundary of the Irtysh Shear Zone. This observation indicates that the major phase of D 3 transpressional deformation took place prior to ∼252 Ma, although later phases of reactivation in the Mesozoic and Cenozoic are likely. The late Paleozoic deformation (D 1 –D 3 at ∼322–252 Ma) overlaps in time with the collision between the Chinese Altai and the intra-oceanic arc system of the East Junggar. We therefore interpret that three episodes of late Paleozoic deformation represent orogenic thickening (D 1 ), collapse (D 2 ), and transpressional deformation (D 3 ) during the convergence between the Chinese Altai and the East Junggar. On a larger scale, late Paleozoic sinistral shearing (D 3 ), together with dextral shearing farther south, accommodated the eastward migration of internal segments of the western CAOB, possibly associated with the amalgamation of multiple arc systems and continental blocks during the late Paleozoic. [ABSTRACT FROM AUTHOR]

The Sikhote-Alin Range of the Russian Far East is an important accretionary orogen of the Western Pacific Orogenic Belt. In order to study the formation and tectonic evolution of the orogen, we performed zircon U–Pb dating, as well as geochemical and Sr–Nd–Hf isotopic analyses on 24 granitoid samples from various massifs in the Primorye and Khabarovsk regions. The zircon dating revealed that the granitoids were emplaced from 131 to 56 Ma (Cretaceous to Paleogene). In the Primorye Region, granitoids in the coastal Sikhote-Alin intruded the Cretaceous Taukha Accretionary Terrane from ca. 90 to 56 Ma, whereas those along the Central Sikhote-Alin Fault zone intruded the Jurassic Samarka Accretionary Terrane during ca. 110–75 Ma. The “oldest” monzogranite (131 Ma) was emplaced in the Lermontovka area of the NW Primorye Region. Granitoid massifs along the Central Sikhote-Alin Fault zone in the Khabarovsk Region formed from 109 to 58 Ma. Thus, the most important tectonothermal events in the Sikhote-Alin orogen took place in the Cretaceous. Geochemical analysis indicates that most samples are I-type granitoids. They have initial 87 Sr/ 86 Sr ratios ranging from 0.7040 to 0.7083, and initial Nd isotopic ratios, expressed as ε Nd ( t ) values, from +3.0 to −6.0 (mostly 0 to −5). The data suggest that the granitoid magmas were generated by partial melting of sources with mixed lithologies, including the subducted accretionary complex ± hidden Paleozoic-Proterozoic basement rocks. Based on whole-rock Nd isotopic data, we estimated variable proportions (36–77%) of juvenile component (=mantle-derived basaltic rocks) in the generation of the granitic magmas. Furthermore, zircon Hf isotopic data ( ε Hf ( t ) = 0 to +15) indicate that the zircon grains crystallized from melts of mixed sources and that crustal assimilation occurred during magmatic differentiation. The quasi-continuous magmatism in the Sikhote-Alin orogen suggests that the Paleo-Pacific plate subduction was very active in the Late Cretaceous. The apparently regular progression of granitic intrusion ages from 80 to 56 Ma in the Taukha Terrane may reflect oblique underflow of the Paleo-Pacific plate beneath the Eurasian continental margin. Subduction was not only manifested by granitic intrusion, but also by abundant silicic volcanism. The Late Cretaceous Paleo-Pacific plate motion probably changed from parallel or sub-parallel to oblique relative to the continental margin of the Sikhote-Alin, leading to the change of magmatic source region and geochemical characteristics of the derived igneous rocks. Late Cretaceous rapid sea-floor spreading at ca. 100 Ma induced highly active subduction and led to voluminous magmatism in the entire Circum-Pacific realm. Finally, the present age and isotopic study lends support to the hypothesis of geologic and tectonic correlation between Sikhote-Alin and SW Japan. [ABSTRACT FROM AUTHOR]

The growth of continental crust in accretionary orogenic belts takes place through repeated cycles of subduction–accretion of rock units from continental and oceanic magmatic arcs, supra-subduction zone backarcs and forearcs loaded with continent-derived materials. An ancient example relevant to magmatic arc accretion models is represented by the remnants of the Cambrian–Ordovician Ross Orogen in the Morozumi Range, Victoria Land (Antarctica). There, late Neoproterozoic phyllites host an intrusive complex which preserves a remarkably uncommon record of genetically unrelated magma pulses emplaced under a variable stress regime in a short time span: (1) a dominant K-feldspar–phyric granite, (2) fine-grained dioritic stocks and dykes, (3) a peraluminous granite; and (4) a tonalitic–granodioritic dyke swarm. Laserprobe U–Pb zircon dates cluster at late Cambrian times for all these units, yet they carry differential cargoes of relict cores. Unique geochemical–isotopic signatures for both the less evolved magmas (diorite and dyke tonalite) and the most acidic ones (granite and peraluminous granite) indicate that each one of them originated from distinct sources at depth. Additionally, field relationships and chemical evolutionary trends testify for a variety of shallow level open-system processes, such as magma mingling/mixing between diorite and main granite magmas, as well as progressive incorporation of the host schists by the dyke tonalite magma. In summary, crustal growth in the Morozumi intrusive complex was contributed by fresh mantle magma issuing from the metasomatised mantle wedge, while the production of other melts did recycle different crustal portions/layers: the main granite derived from Grenville-age granulitic lower crust; the peraluminous granite from late Proterozoic upper crust, and the tonalite magmas derived from subduction erosion-enriched subarc mantle and evolved by ingestion of local metasedimentary rocks. Overall, the Morozumi intrusive complex yields evidence for emplacement in the same site at the same time of magmas issuing from different sources that are usually found at a different depth in the arc lithospheric section. A likely scenario to activate this specific mechanism of melt production is a subduction zone affected by subduction erosion. [ABSTRACT FROM AUTHOR]

Absolute ages of migmatization and protolith formation, and constraints on the timing of ductile deformation in two major lithotectonic units in the south-western part of a 2.0–1.8 Ga orogenic belt in the Fennoscandian Shield, south-eastern Sweden, have been determined using U–Pb ion probe analysis of different generations of zircon in veined gneisses and leucocratic granite. Detrital and xenocrystic zircon in paragneiss and garnet-bearing leucogranite, respectively, in the Bergslagen lithotectonic unit show ages of 2.1–2.0 Ga and 1.9 Ga. Deposition of the sedimentary material occurred during or after a subduction-related magmatic event at 1.91–1.87 Ga. Two orthogneiss protoliths formed during this magmatic event around 1.88 Ga while most zircon in the leucosome in a third migmatitic orthogneiss was inherited from a 1.85 Ga igneous protolith. A polyphase tectonothermal evolution with anatexis under low-P metamorphic conditions around 1.86 Ga (M 1 ) and 1.84–1.81 Ga (M 2 ) is inferred for the migmatitic gneisses in the Bergslagen unit; garnet-bearing leucogranite crystallised around 1.84–1.83 Ga, close in time to major folding of the M 1 gneissic fabric. A previously unrecognised 1.86–1.85 Ga ductile deformational event under medium-grade metamorphic conditions has been identified in the adjacent lithotectonic unit to the south (Småland lithotectonic unit), close in time to the M 1 event in the Bergslagen unit to the north. By constraining the timing of anatexis and comparing with information bearing on crustal thickness, excess mass at depth and the character and age of magmatic activity, it is inferred that anatexis in the Bergslagen lithotectonic unit is related to pulses of mafic underplating, during the early stages of two separate, subduction-related magmatic episodes after the 1.91–1.87 Ga magmatic event. It is suggested that each pulse was related to intra- or back-arc spreading above a subduction boundary, which had entered a retreating mode with separate, long periods (20–50 Ma) of extension or transtension. This study challenges the need to invoke crustal thickening related to plate collision at 1.9–1.8 Ga as a mechanism to explain high-grade metamorphism in the southern part of the 2.0–1.8 Ga orogen. Instead, a solely accretionary tectonic model involving an overriding plate along an active continental margin with significant extensional or transtensional crustal deformation is preferred. [ABSTRACT FROM AUTHOR]

[Display omitted] • Transpressional collision of the Eburnean accretionary orogen and its flanking craton. • Collision absorbed through a multi-scale anastomosed shear zone network. • Oblique shearing of the cratonic margin and indentation of the accretionary orogen. • Lithospheric delamination at craton edge enabling HP-HT collisional orogeny. • Enhanced syn -collisional juvenile magmatic accretion at the expense of the craton. In order to decipher the collision processes between the Eburnean (Paleoproterozoic) accretionary orogen and its flanking Archean craton, photointerpretation was combined with the extraction of structural data from geological quadrangle maps to draw the structural pattern of the southern West African craton. This pattern reveals multi-scale transpressive anastomosing shear zone networks affecting both the Eburnean orogen and its Archean buttress that absorbed protracted E-W convergence as juvenile crust was still being accreted. Collision involved oblique transcurrent shearing of the craton margin that led to the asymmetrical indentation and escape of the accretionary orogen. As part of the collisional deformation pattern, the craton margin developed a narrow orogenic system recording intense transpressional strain and high pressure-high temperature metamorphism. Lithospheric mantle delamination at the craton margin explains focused heat advection and extreme thermal softening of the crust, enabling steep narrow transpressional collisional orogeny at the rear of accretionary orogens. Delamination also provides a mechanism for the growth of accretionary orogens at the expense of their flanking cratons. [ABSTRACT FROM AUTHOR]

Oceanic arcs are known as the critical sites to generate new continental crust. However, additional processes are needed to transform mafic oceanic crust to mature continental crust. Ascertaining the petrogenesis of granitoids therein is vital to understand such a maturation process. In this study, we carried out a combined study of in-situ zircon U-Pb dating and Hf-O isotopic analyses, as well as whole-rock geochemical and Sr-Nd isotopic compositions for the Changwan granitoids in the Erlangping oceanic arc unit of the Tongbai orogen. This intrusion mainly consists of biotite granite with subordinate trondhjemite. LA-ICPMS and SIMS zircon U-Pb dating yielded identical U-Pb ages of ca. 460 Ma, representing the intrusion ages. Whole-rock analyses demonstrated that the Changwan granitoids have relatively high SiO 2 (72.71–77.14 wt%) and Al 2 O 3 (12.61–14.24 wt%), but low MgO (0.31–0.74 wt%) contents and Mg# (32.0–40.2). The relatively high K 2 O (2.81–3.63 wt%) contents and K 2 O/Na 2 O values (0.76–1.03) of the granitic samples suggest they belong to middle-K weakly peraluminous I-type granite, while the trondhjemitic samples with low K 2 O (1.06–1.96 wt%) and K 2 O/Na 2 O values (0.23–0.42) are tholeiitic to middle-K series. In both cases, the samples show arc-type trace element distribution patterns. They are characterized by depleted Sr-Nd-Hf isotopic compositions with (87Sr/86Sr) i of 0.7038–0.7050, ε Nd (t) of +0.52 ~ +2.85, zircon ε Hf (t) of +3.4 ~ +9.6, and relatively low zircon δ18O values of 4.71 ± 0.17–4.97 ± 0.18‰. These isotopic fingerprints suggest the Changwan granitoids were derived from a relatively depleted source that had been hydrothermally altered under high temperature conditions. The most likely candidate is the accreted Erlangping lower oceanic crust which might have been heterogeneously modified in a supra-subduction zone. This is further verified by the trace element modeling on potential mafic source rocks enriched in incompatible elements in the Erlangping unit. We suggest that the high K 2 O/Na 2 O granitic samples were derived from K-rich segment of the Erlangping lower oceanic crust whilst the low K 2 O/Na 2 O trondhjemites from K-poor part. Therefore, our results show that partial melting of enriched oceanic crust in supra-subduction zone plays an important role for crust maturation in accretionary orogens. • The Changwan granitoids were formed at ca. 460 Ma. • They were derived from an incompatible-element-enriched lower oceanic crust source. • Remelting of enriched oceanic crust holds a key for continental crustal maturation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Granitoid magmatism changed in composition with evolution of Kadiri greenstone belt. [•] Initial sanukitoid magmatism was followed by transitional TTG, leucogranite and A-type granite. [•] A convergent setting characterized by repeated slab break-off and crustal reworking. [•] Finally post-subduction anorogenic granite magmatism. [•] Reworking of Mesoarchaean crust in eastern Dharwar craton identified. [Copyright &y& Elsevier]

Abstract: Accretionary orogenic belts are considered the most important sites for the generation of continental crust. However, it is still not very clear whether in such settings the continental crust has been significantly transported back to the mantle accompanied with its lateral growth. Continental UHP rocks, the best indicators of the recycling of the continental crust, have rarely been discovered in accretionary orogenic belts, which hinder the exploration of this essential process. The possible occurrence of early Paleozoic UHP metamorphism in the Qinling orogen provides an excellent opportunity to address this question. This article reports an integrated study of U–Pb age, trace element and mineral inclusion of zircon from an amphibolite sample in the Qinling orogen. The zircon crystals show typical metamorphic growth zoning, low Th/U ratios, flat HREE patterns, and insignificant Eu anomalies. They give a weighted mean U–Pb age of 490.4±5.8Ma. Most importantly, an in situ diamond inclusion was identified from one of the zircon crystals. Therefore, the obtained 490.4±5.8Ma age was taken as registering the peak UHP metamorphism. The discovery of in situ diamond inclusion provides important evidence for the UHP metamorphism of the Qinling orogen and indicates that the North Qinling microcontinent was subducted to mantle depths of >120km when it collided with the Erlangping arc attached to the southern margin of the North China Block. Combining with previous results, we suggested that the North Qinling UHP terrane underwent fast exhumation from >120km to ca. 30km within 10Myr intervals. As a few examples of UHP metamorphism have been discovered in some accretionary orogens, more attention needs to be paid to the occurrence of continental UHP metamorphism during accretionary orogenic process. Furthermore, evident crustal growth has been documented in the North Qinling orogen during the early Paleozoic. It is inferred that the accretionary orogenic belts may play important roles in recycling of continental crust into the mantle besides generation of continental crust. [Copyright &y& Elsevier]

The island of Hokkaido is a young accretionary terrane, basically built with a Jurassic accretionary complex and Cretaceous arc in the west (= NE Japan arc terrane), a Cretaceous-Paleogene forearc basin and accretionary complex with the Hidaka metamorphic belt in the center, and a Cenozoic island arc with Cretaceous basement in the east (= Chishima or Kuril arc terrane). Though volumetrically small, Paleogene and Neogene granitoids are widespread in central Hokkaido (Hidaka Belt). Granitoids are the most representative component of the continental crust, so in this work we aimed to study the mode of generation and source characteristics of these granitoids in order to assess the crustal composition of Hokkaido and examine the general problem of continental growth. New zircon geochronology on nine granitic and one gabbroic rocks from the Hidaka Belt reveals three distinct magmatic episodes, two in the Eocene at 45-46 Ma (3 granites), and 37.0 ± 0.5 Ma (1 granite), and one in the Miocene at 18 to 19 Ma (5 granites and 1 gabbro). The Miocene episode represents the most important granitic emplacement in Hokkaido. The early Eocene zircon ages of 45 to 46 Ma are identified for the first time for granitoids that occur in the northern part of the Hidaka Belt. The zircon age of 37 Ma for a granite from Shirataki is rather rare in Hokkaido, but similar ages had been reported for a tonalite and a granite from the Hidaka metamorphic belt. Geochemically, all granites are slightly peraluminous but not S-type, and they possess volcanic arc granitoid characteristics. Their REE distribution patterns are typically "granitic," showing fractionated patterns with LREE enrichment and distinct negative Eu anomaly. The whole-rock isotopic signatures [ISr = 0.7044 to 0.7061;ε Nd(t) = +1.0 to +4.7; TDM-1 = 400-1000 Ma] reveal their largelyjuvenile characteristics. This is corroborated by the zircon Hf isotopic compositions [εHf(t) 11, in = +8 to +19]. The Eocene granites were most probably generated by melting of subducted accretionary complex in a prolonged period from 46 to 37 Ma in supra-subduction zone; whereas the Miocene granites were also generated by melting of accretionary complex in a back-arc rifting setting. In both cases, the involved accretionary complex was probably dominated by the mantle-derived lithological component with little Paleozoic or older crustal material. Hokkaido provides an excellent example of juvenile crust addition to the continental crust. [ABSTRACT FROM AUTHOR]

Eduard Suess recognized the unusual size and internal tectonic configuration of the mountainous terranes of Central Asia that he termed Altaids and which differ considerably from curvi-linear foldbelts such as the Alps and Urals. However, he did not realize that this orogenic domain or province evolved over a period of some 750 Ma from the late Mesoproterozoic (ca. 1000 Ma) to the late Permian (ca. 260 Ma), contains large volumes of pre-orogenic crust as well as many synorgenic metamorphic complexes, and exhibits many structures similar to modern thrust-and-fold belts. We therefore do not favour the name Altaids for this large orogenic domain because it is associated with the concept of an essentially Palaeozoic evolution and certain features that have since been shown to be incorrect. The non-genetic term Central Asian Orogenic Belt (CAOB) seems to be more appropriate and characterizes one of the largest accretionary terranes on Earth whose evolution has many similarities with the tectonics of the Indonesian Archipelago. In contrast to popular thinking, crustal growth in the CAOB during accretion was not anomalously high but was similar to that in the Palaeozoic Tasmanides of Australia and the Jurassic to Present evolution in southeastern Asia. [ABSTRACT FROM AUTHOR]