Subduction-related Magmatic Arc Research Articles

Superhydrous Arc Magmas in the Alpine Context

Magmatic rocks in the Alps are scarce. What little arc magmatism there was pre-dates the Eurasia–Adria collision at 43–34 Ma but ends at 30–29 Ma. Conversely, geochemical data for magmatic rocks from the Alps resemble that of subduction-related magmatic arcs. A characteristic of Alpine magmatism is the occurrence of relatively deep (80–100 km) super-hydrous (>8 wt% H2O) low-K primary magmas in the east and shoshonitic K-rich magmas in the west. These features are likely related to the absence of vigorous mantle wedge convection. Superhydrous primary magmas undergo extensive crystallization and fluid saturation at depth, producing high ratios of plutonic to volcanic rocks. We speculate that superhydrous primary arc magmas are a consequence of slow convergence and the initial architecture of subducting crust.

Geochronology and geochemistry of low-grade metamorphic rocks from the Erdaowa Group and its significance on the tectonic evolution of the Paleoproterozoic Khondalite Belt, North China Craton

Khondalite Belt is located in the northwestern part of North China Craton, and is a typical continent-to-continent collisional orogen, along which the Yinshan Block collided with the Ordos Block at 1.95–1.85 Ga. However, this model was mainly relied on high-grade metamorphic records in the Khondalite Belt, whether the extensively exposed low-grade rocks were also involved in such collision remains poorly constrained. Erdaowa Group is an important lithological unit of the belt and consists of extensive low-grade metamorphic rock assemblages (i.e. greenschist to amphibolite facies), and provide crucial insights into understanding the issue. Based on petrological and geochemical characteristics, low-grade metamorphic rocks of Erdaowa Group show a large affinity to bimodal volcanic sequence characterized by basaltic and acidic endmembers. Meta-mafic rocks were derived from partial melting of lithospheric mantle with minor contamination of crustal materials, whereas meta-acidic rocks were generated from the middle-to-lower crust. Geochemical data of both rock assemblages show depletion of HFSE and enrichment of LILE, indicative of a subduction-related magmatic arc environment. U-Pb zircon dating results indicated that these rocks erupted at 2465 ± 42 Ma, and experienced metamorphism at 1940–1861 Ma. In combination with available petrological, geochemical and geochronological data, we infer that arc magmatism was developed at a back-arc basin area of a ~2.45 Ga active continental margin along southern Yinshan Block. Together with those high-grade metamorphic rocks, these low-grade rocks were also incorporated into the final collisional event at ~1.95–1.90 Ga.

Possible imprints of late Paleoproterozoic orogeny in the Dunhuang terrane, NW China: Constraints from igneous and metapelitic rocks

The Dunhuang terrane is a NEE trending tectonic belt confined by the Tarim Craton, Beishan Orogen, Alxa Block and Altyn Tagh Fault. To constrain the late Paleoproterozoic geotectonic background of this terrane, a synthetic research on petrology, geochemistry, zircon and monazite geochronology, and zircon Lu-Hf and whole-rock Nd isotopes of late Paleoproterozoic (ca. 1.9–1.8 Ga) igneous rocks and metapelites was conducted. The Sanweishan-Dongshuigou Na-rich rhyolite and granite formed at ca. 1.84–1.82 Ga exhibit enriched light rare earth elements (LREEs), depleted heavy rare earth elements (HREEs) and insignificant Eu anomalies, with low Y (3.44–6.39 ppm) and Yb (0.29–0.53 ppm) but relatively high Mg# (54.5–58.5) and Sr (368–643 ppm), and variable Cr (5.58–29.7 ppm) and Ni (2.82–15.6 ppm) contents, as well as negative to positive εHf(t) (−6.1 to +6.4) values, indicating subduction-related arc magmatism accompanied by crustal-mantle interaction. The Shuwozi granitic gneiss crystallized at ca. 1.81 Ga displays S-type granite affinity (A/CNK > 1.1) and has low Sr/Y (1.0–1.3) and (Gd/Yb)N (1.50–1.98) ratios, and negative εHf(t) (−20.3 to −5.1) and εNd(t) (−4.3) values, suggesting partial melting of crustal rocks at shallow crustal depth. The Hanxia amphibolite with protolith age of ca. 1.86–1.84 Ga is featured by depleted LREE and flat HREE patterns, insignificant Eu anomalies, low Nb/Ta (11.0–12.0), Ta/Yb (0.02–0.04), Th/Yb (0.01–0.04) and Th/Ta (0.7–1.3) but high Ti/V (22.9–26.7) ratios, and positive εNd(t) (2.7–4.0) values, resembling depleted mantle-derived N-MORB- or BABB (back-arc-basin basalt) geochemical affinities. The metapelite, characterized by mineral assemblage of garnet, biotite, sillimanite, plagioclase, K-feldspar, quartz and rutile, documented ca. 1.81 Ga upper amphibolite-facies metamorphism with peak metamorphic P-T conditions being restricted to 690–810 °C and 5.3–6.4 kbar based on conventional geothermobarometry. These magmatic and metamorphic rocks were variously altered and deformed during Paleozoic (ca. 430–360 Ma) tectonothermal event. Integrated with published data, it can be inferred that the Dunhuang terrane underwent ca. 1.89–1.81 Ga subduction-collisional orogeny related to late Paleoproterozoic (ca. 2.0–1.8 Ga) global assembly of the Columbia supercontinent, similar as those recorded in the northern Tarim Craton, Alxa Block and Quanji massif, and then overprinted Paleozoic (ca. 440–360 Ma) orogenic process, corresponding to the previously proposed composite orogeny in the Dunhuang terrane.

Southward subduction of the Bangong-Nujiang Tethys Ocean: insights from ca. 161–129 Ma arc volcanic rocks in the north of Lhasa terrane, Tibet

The Meso-Tethys Ocean was mainly represented by the Bangong-Nujiang suture zone between the South Qiangtang and Lhasa terranes in the Tibetan plateau. The subduction polarity of this Tethys Ocean during the Mesozoic is still being debated and it has been suggested to be northward or bidirectional subduction. A series of volcanic rocks, including andesite, dacite, rhyolite and volcaniclastic rocks, are documented in the Xinji area, north of Lhasa terrane, Tibet. These samples yielded zircon U–Pb ages between 161 and 129 Ma, which represent the emplacement age of the volcanic rocks. The volcanic rocks show typical arc calc-alkaline signatures, with strong depletion in Nb, Ta and Ti, enrichment in Rb, Th, U and Pb. These features are indicative of subduction-related arc magmatism. The Jurassic andesite shows high Mg# values, and high Th but low Sr contents, and it is interpreted as a result of interaction of subduction sediment-derived melting with mantle wedge peridotite. The Early Cretaceous andesite, dacite and rhyolite show similar geochemical features and are suggested to be formed by melting of ancient crustal materials with contribution of mantle-derived magma, following by varying degrees of fractional crystallization and assimilation. Finally, we suggest that the Xinji volcanic rocks represent an Andean-type magmatic arc along the north of Lhasa terrane. They were produced by southward subduction of the Bangong-Nujiang Tethys Ocean. Consequently, a bidirectional subduction model was suggested for the evolution of the Bangong-Nujiang Tethys Ocean during the Middle Jurassic to Early Cretaceous.

Paleoproterozoic Mafic-Ultramafic Magmatism in the Northern Borborema Province, Northeast Brazil: Tectonic Setting and Potential for Deposits

Mafic-ultramafic intrusions form a 32-km-long NE-SW-trending array within Paleoproterozoic arc-related calc-alkaline plutonic rocks of the Rio Piranhas terrane in the Borborema Province, Northeast Brazil. The mafic-ultramafic intrusions consist of wehrlite, clinopyroxenite, and troctolite. They outcrop as small elongated bodies hosted by orthogneiss and migmatites associated with minor amphibolite and supracrustal rocks. Primary magmatic features predominate in the core of the intrusions, whereas metamorphic minerals and textures characterize their outer zones. The composition of cumulus olivine from different intrusions ranges from Fo80.6 to Fo67.6 (forsterite), indicating moderately primitive parental magmas. The compositional range of cumulus plagioclase coexisting with cumulus olivine in troctolites is characterized by high anorthite content (An79.9–An89.0). This feature, together with interstitial magmatic amphibole in troctolites, is characteristic of gabbroic intrusions in subduction-related magmatic arcs. U-Pb zircon ages indicate that mafic-ultramafic intrusions crystallized at ca. 2190 ± 5 Ma. U-Pb zircon ages of host orthogneiss indicate that they crystallized from calc-alkaline felsic magmas at ca. 2220–2223 Ma, thus providing only ∼30 My for the reported events of felsic and mafic plutonism. U-Pb zircon ages of host rocks include older ages (2.47 and 2.69 Ga) indicating that older crustal components are associated with the 2.23 Ga calc-alkaline magmatism. The presence of older crustal components is consistent with arc-related features, indicated by geochemical data and variable εNd(t) values in the mafic-ultramafic intrusions. The tholeiitic and calc-alkaline magmatism is correlated with the ca. 2.15–2.25 Ga magmatic arc reported in previous studies of the Rio Piranhas terrane. The mafic-ultramafic magmatism is interpreted as having originated in a magmatic arc, possibly resulting from partial melting of a mantle wedge above the subduction zone in late stages of the orogeny and suggests a new window of opportunity for exploration of Ni-Cu–platinum group element deposits.

Building the Wutai arc: Insights into the Archean – Paleoproterozoic crustal evolution of the North China Craton

The Wutai complex is located within the Trans–North China Orogen (TNCO) which marks the collision zone between the Eastern and Western Blocks of the North China Craton (NCC). Here we investigate the timings and mechanisms of Precambrian arc building in Wutai from a suite of newly identified greenstone – felsic tuff – Banded Iron Formation (BIF) – phyllite sequence. Zircon grains from the felsic tuff layer intercalated within the greenstones provide robust constraints on the timing of BIF deposition. Geochemical features of the greenstones and felsic tuff suggest E - MORB and volcanic arc affinity, whereas the BIFs are of submarine hydrothermal origin. Zircon grains in the greenstones define an upper intercept age of 2951 ± 41 Ma and a lower intercept age of 1845 ± 190 Ma. Those from the felsic tuff show 207Pb/206Pb weighted mean age of 2557 ± 10 Ma, whereas those from the BIF intercalated with felsic tuff shows an age of 2585 ± 14 Ma. Metamorphic zircon grains in the BIF define two age populations of ca. 2471 and 1906 Ma. Zircon grains in the phyllite yield an age of 2594 ± 14 Ma. Kernel density plots define age peaks at 2873 and 2578 Ma marking the major phase of arc building in Wutai. Zircon εHf (t) values are mostly positive, in the range of 3.15–7.72, suggesting new crustal growth from juvenile/depleted mantle components. Our study provides insights into the Mesoarchean to Neoarchean crust building through subduction-related arc magmatism, followed by Paleoproterozoic metamorphism in the North China Craton.

Pb isotope geochemistry of the late Miocene–Pliocene volcanic rocks from Todeshk, the central part of the Urumieh–Dokhtar magmatic arc, Iran: Evidence of an enriched mantle source

The late Miocene–Pliocene volcanic rocks from Todeshk, south-east of Isfahan, are located in the middle of the Urumieh–Dokhtar magmatic belt. The belt is considered the subduction-related magmatic arc. The late Miocene–Pliocene calc-alkaline volcanic rocks are mainly andesite and dacite. The rocks have been formed during the post-collisional stage of the Zagros orogen. Geochemical data show the enrichment of light rare-earth elements and large ion lithophile elements such as Cs, Rb, K, Pb, Ba and Th as well as the depletion of elements with high field strength such as Nb, Ta and Ti. The Pb–Sr–Nd isotopic ratios of the studied rocks are characterised by \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb} =18.41\)–18.72; \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb} =15.64\)–15.67; \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb} = 38.49\)–38.83; \({}^{207}\hbox {Pb}/{}^{206}\hbox {Pb} = 0.8372\)–0.8496; \({}^{208}\hbox {Pb}/{}^{206}\hbox {Pb} = 2.0743\)–2.0905; \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr} = 0.7051\)–0.7068 and \({}^{143}\hbox {Nd}{/}{}^{144}\hbox {Nd} = 0.5125\). The rocks have \({\Delta }7/4\hbox {Pb} = 15.44\)–15.82 and \({\Delta }8/4\hbox {Pb} = 57.26\)–60.44. Based on petrological studies and the whole rock Pb, Sr and Nd isotopes data, the late Miocene–Pliocene calc-alkaline volcanic rocks have been generated from the partial melting of the subduction-related metasomatised mantle. Additionally, the slab-derived melts and fluids were recycled into the mantle source. The data demonstrate that terrigenous sediments accompanied by a subducted slab play an important role in the formation of the enriched mantle as the source of volcanic rocks.

Early Paleozoic magmatism and metallogeny related to Proto-Tethys subduction: Insights from volcanic rocks in the northeastern Altyn Mountains, NW China

Remnants of the Proto-Tethys are mainly preserved in the region between south of the North China-Tarim Block and north of Qiangtang-Sibumasu/Baoshan Blocks. Magmatic-metallogenic events related to the Proto-Tethyan subductions were rarely reported, and the subduction history and polarity of the Proto-Tethyan are still under debate. Here, we presented new data of zircon UPb ages, whole-rock Sr–Nd–Pb isotopes, major and trace elements and zircon Hf isotopes for the volcanic rocks in the northeastern Altyn Mountains. Information of over 14 volcanic-hosted deposits/prospects in the region has been compiled. These volcanic ore hosts consist mainly of basaltic andesite, andesite, dacite and rhyolite rocks. The andesite and rhyolite rocks are newly zircon UPb dated to be Late Cambrian-Early Ordovician (andesite: 490.5 ± 5.2 Ma; rhyolite: 492.6 ± 2.9 Ma and 491.6 ± 5.6 Ma), representing the timing of volcanism and VMS (Volcanogenic Massive Sulfide) mineralization. All the volcanic rocks belong to the high-K calc-alkaline and shoshonite series: the andesite rocks from the Kaladawan area in north of the region display arc geochemical affinities and contain (87Sr/86Sr)i (0.7082–0.7083) and εNd(t) (−9.7 to −7.6), indicating that they were likely formed by partial melting of the mantle wedge with subducted sediment inputs. The rhyolite rocks from the Kaladaban area in south of the region are characterized by high SiO2 (64.46–78.55 wt%), low alkali (Na2O + K2O, 3.46–7.17 wt%), and contain (87Sr/86Sr)i (0.7063–0.7095), εNd(t) (−6.6 to −1.5), and zircon εHf(t) (−5.5 to 5.4), indicating that they were likely derived from partial melting of the lower crust with depleted mantle inputs. Rock assemblage and geochemistry suggest that volcanic rocks in the northeastern Altyn Mountains may have formed in a continental arc setting. Their spatial distributions with respect to the ophiolites in the region suggest that the subduction was likely south-dipping. This subduction-related arc magmatism may have formed the many important VMS and porphyry–skarn deposits in the region.

Early Cambrian Muli arc–ophiolite complex: a relic of the Proto-Tethys oceanic lithosphere in the Qilian Orogen, NW China

The Qilian Orogen in the northern margin of the Tibetan Plateau is the northernmost of the Tethyan domain. Abundant ophiolites record the closure of an early Tethyan ocean and amalgamations between micro-continents of North China, Qaidam, and Tarim. The Muli arc–ophiolite complex in the western segment of the South Qilian belt represents remnants of the Proto-Tethyan oceanic lithosphere. It comprises serpentinite, dunite, cumulate gabbro, basalt, plagiogranite, and chert, which are in tectonic contact with Upper Ordovician turbidites. Basalts have typical subduction-related calc-alkaline geochemical affinity, representing portions of an island arc. Geochemical results for plagiogranites and spinels from serpentinite indicate that the Muli arc–ophiolite complex represents a super-subduction zone (SSZ)-type ophiolite. U–Pb zircon data indicate formation associated with southward subduction of the Proto-Tethys Ocean during a short interval between 539 and 522 Ma. Results of petrology, geochemistry, and zircon U–Pb dating demonstrate that granitoids intruded into this complex are Middle to Late Ordovician (470–450 Ma) products of subduction-related arc magmatism. Voluminous Late Ordovician–Early Silurian rocks include deep-water marine siliciclastic and volcaniclastic turbidites and abundant volcanic arc rocks located to the south of the Muli arc–ophiolite complex, whereas fluvial coarse-grained sandstones and conglomerates unconformably overlie the Cambrian–Middle Ordovician ophiolite–arc systems in the eastern South Qilian belt. This indicates that closure of the Proto-Tethys Ocean was diachronous during the early Paleozoic.

Newly discovered early Neoproterozoic (ca. 900 Ma) andesitic rocks in the northwestern Tarim Craton: Implications for the reconstruction of the Rodinia supercontinent

The Tarim Craton, one of the largest continental blocks in China, has been considered as a constituent block of the Rodinia supercontinent. However, the early Neoproterozoic tectonic evolution and the role of the Tarim Craton in the reconstruction of Rodinia remain controversial. Here, we present zircon U-Pb and Lu-Hf isotopic and whole-rock geochemical data for the newly discovered andesitic rocks in the Aksu area of northwestern Tarim Craton. LA-ICP-MS zircon dating results show that they were formed at ca. 908–903 Ma. These andesites have arc-type geochemical features such as enrichment in LREEs with (La/Yb)N ratio of 4.4–6.9 and obviously negative Nb, Ta, Ti anomalies. The high positive zircon εHf (t) (+7.5 to +11.9) values, integrated with trace element signatures, indicate that the magma source of the andesitic rocks were derived from partial melting of mantle wedge that was metasomatized by the sediment/slab-derived fluids through subduction, with possibly insignificant contributions from crustal materials. These geochronological and geochemical data suggest that subduction-related arc magmatism occurred in the northwestern Tarim Craton as early as ca. 900 Ma. Combined with a compilation of previous published data, these results therefore indicate that active continental margin probably widely occurred along the northwestern and southeastern margins of the Tarim Craton and adjacent microcontinents during the early Neoproterozoic, which may be linked to the Neoproterozoic circum-Rodinia subduction-accretion system.

Critical-wedge theory and the Mesozoic accretionary wedge of New Zealand

We apply principles of critical-wedge theory to explain the Jurassic and Early Cretaceous tectonic development of the Mesozoic accretionary wedge of New Zealand, one of the best-exposed subduction complexes on Earth, by summarizing factors that can lead to drastic changes in wedge balance. The wedge has a Carboniferous to Cretaceous (∼330-110 Ma) stratigraphic record, with an early Cretaceous (∼145-130 Ma) hiatus in clastic deposition across the Esk Head Melange near the front of the wedge. In the rear of the wedge, the age of moderately high-pressure metamorphism of the Otago Schist, which represents the forearc-high of the wedge, occurred near the end of this stratigraphic hiatus. The Otago Schist has a subhorizontal foliation indicative of underplating as the mode of accretion. The outer (frontal) part of the wedge has a subvertical foliation indicative of frontal accretion. We propose that in the Jurassic and earliest Cretaceous the wedge grew by frontal accretion. By ∼135 Ma the wedge became too long and was subcritical. This resulted in tectonic erosion of the front of the wedge. The tectonically eroded material was underthrust/underplated beneath the rear of the wedge to form the subhorizontally foliated Otago Schist. Colliding seamounts and/or oceanic plateaux (preserved in the Esk Head Melange) may have aided wedge instability. The proposed wedge instability and increased horizontal shortening was largely coeval with major changes in the chemistry of subduction-related arc magmatism and a phase of shortening and high-pressure metamorphism in the arc. Our model provides a holistic and coherent interpretation explaining the major tectonic features of the long-lived New Zealand part of the east Gondwana subduction zone.

Postglacial faulting near Crater Lake, Oregon, and its possible association with the Mazama caldera-forming eruption

Abstract Volcanoes of subduction-related magmatic arcs occur in a variety of crustal tectonic regimes, including where active faults indicate arc-normal extension. The Cascades arc volcano Mount Mazama overlaps on its west an ∼10-km-wide zone of ∼north-south–trending normal faults. A lidar (light detection and ranging) survey of Crater Lake National Park, reveals several previously unrecognized faults west of the caldera. Postglacial vertical separations measured from profiles across scarps range from ∼2 m to as much as 12 m. Scarp profiles commonly suggest two or more postglacial surface-rupturing events. Ignimbrite of the ca. 7.6 ka climactic eruption of Mount Mazama, during which Crater Lake caldera formed, appears to bury fault strands where they project into thick, valley-filling ignimbrite. Lack of lateral offset of linear features suggests principally normal displacement, although predominant left stepping of scarp strands implies a component of dextral slip. West-northwest–east-southeast and north-northwest–south-southeast linear topographic elements, such as low scarps or ridges, shallow troughs, and straight reaches of streams, suggest that erosion was influenced by distributed shear, consistent with GPS vectors and clockwise rotation of the Oregon forearc block. Surface rupture lengths (SRL) of faults suggest earthquakes of (moment magnitude) Mw6.5 from empirical scaling relationships. If several faults slipped in one event, a combined SRL of 44 km suggests an earthquake of Mw7.0. Postglacial scarps as high as 12 m imply maximum vertical slip rates of 1.5 mm/yr for the zone west of Crater Lake, considerably higher than the ∼0.3 mm/yr long-term rate for the nearby West Klamath Lake fault zone. An unanswered question is the timing of surface-rupturing earthquakes relative to the Mazama climactic eruption. The eruption may have been preceded by a large earthquake. Alternatively, large surface-rupturing earthquakes may have occurred during the eruption, a result of decrease in east-west compressive stress during ejection of ∼50 km3 of magma and concurrent caldera collapse.

Age and petrogenesis of the Andagul granodiorite and its implications on gold mineralization of the Kassan region, western Kyrgyzstan Tian Shan

A number of significant gold deposits in the Kassan region in west Kyrgyzstan are associated with the Andagul granitic intrusion. These gold deposits share similarities with the class of “intrusion-related gold deposits”, implying that the gold mineralization may be genetically related to the intrusion. In order to evaluate this potential relationship, it is important to study the petrogenesis of the intrusion. This paper examines the sources and physiochemical conditions of magma generation and crystallization of the Andagul intrusion and their implications for gold mineralization, through an integrated study involving zircon geochronology, mineral chemistry, whole-rock chemistry and isotopic geochemistry. The Andagul intrusion consists mainly of granodiorite, which is characterized by metaluminous and median-K calc-alkaline compositions, high LREE and LILE, low HFSE, right-inclined REE pattern with a flat HREE pattern, and insignificant Eu anomalies ((Eu/Eu∗)N = 0.79–0.85). These geochemical characteristics, together with relatively low positive εNd(t) values (+2.1–+4.3), moderately low (87Sr/86Sr)i ratios (0.7049–0.7059), relatively low initial Pb isotopic ratios ((206Pb/204Pb)t = 17.76–18.51, (207Pb/204Pb)t = 15.56–15.62, and (208Pb/204Pb)t = 37.89–38.33), juvenile εHf(t) (+2.29–+4.80) but relatively old model ages (T2DM(Hf) = 1026–1175 Ma, T2DM(Nd) = 728–907 Ma) indicate that the magma was mainly sourced from partial melting of juvenile basaltic lower crust with the involvement of a small proportion (ca. 5%–10%) of Precambrian basement rocks. The high Zr saturation temperatures (807 °C to 825 °C), relatively high Mg# values (43–52) and presence of mafic enclaves, and development of acicular apatite and oscillatory plagioclase and titanite, suggest that the magmatism was related to injection of hot mantle material. The magma generation and intrusion took place during 299–310 Ma based on LA-ICPMS zircon U-Pb dating, suggesting a post-collisional setting. Remelting of sulfide accumulate residual with high Au/Cu ratios in the juvenile lower crust, formed in the pre-collisional plate subduction-related magmatic arc stage, is proposed to account for the Au mineralization in the Kassan region. The high water contents (4.0–5.2 wt% H2O) and weakly oxidized or slightly reduced redox state (ΔFMQ = −0.33 ∼ +0.49) deduced from mineral composition and zircon Ce anomaly are favorable for the transport and enrichment of gold in the magmatic fluids. These geochemical characteristics suggest that the Andagul granodiorite and related granitic rocks in the Kassan region have the potential to provide ore-forming materials and fluids for gold mineralization.

Middle Permian–early Triassic magmatism in the Western Pontides, NW Turkey: Geodynamic significance for the evolution of the Paleo-Tethys

Permian-Triassic magmatic rocks are widely exposed in different tectonic terranes and continental blocks in the Aegean region. This study is focussed on the İstanbul Zone and the Istranca (Strandja) Massif, which are located in the Western Pontides of NW Turkey. The Kırklareli and the Tepecik plutons intruded into the metamorphic basement rocks of the Istranca Massif, and the Sancaktepe pluton is emplaced into the İstanbul Paleozoic sedimentary sequences. We present new geochemical data for these plutons, in order to interpret their petrogenesis and time of emplacement and use this information for geodynamic interpretation. The zircon U–Pb crystallization ages are 268.3 ± 2.1 Ma for the Kırklareli pluton, 249.4 ± 1.5 Ma for the Tepecik pluton and 257.3 ± 1.5 Ma and 253.7 ± 1.75 Ma for the the Sancaktepe pluton. They are high-K, calc-alkaline to shoshonitic granitoids with aluminum saturation index (ASI) values between 0.9 and 1.3, which define them as peraluminous and slightly metaluminous. 87Sr/86Sr(i) values for the studied plutons range between 0.701123 and 0.707704. 143Nd/144Nd(i) ratios calculated for crystallization ages are between 0.512052 and 0.512431, and εNd(i) values vary from −4.71 to 2.22. TDM model ages range between 0.83 and 1.41 Ga. These plutons are enriched in LILEs and LREE and depleted in HFSEs with negative Eu anomalies, indicating that the melts were derived from mafic crustal sources. Our new data suggest that the Kırklareli pluton was generated in a subduction-related magmatic arc, and the highly fractionated Sancaktepe and Tepecik plutons were formed in a back-arc setting in response to the northward subduction of the Paleo-Tethys Ocean during the Mid Permian–Early Triassic.

Precambrian Hongqiyingzi Complex at the northern margin of the North China Craton: Its zircon U-Pb-Hf systematics, geochemistry and constraints on crustal evolution

The Precambrian Hongqiyingzi Complex (HQC) in the middle segment of the northern margin of the North China Craton (NCC) is a crucial magmatic intrusive complex offering insights into the early evolutionary history of the northern margin of the NCC. The HQC, exposed from Congli to Longhua towns in the northern Hebei Province, is mainly composed of Neoarchean quartz dioritic-tonalitic-granodioritic (DTG) gneisses and Paleoproterozoic granodiorite-monzogranite-syenogranite (GMS) intrusions. SHRIMP and LA-ICP-MS zircon dating results show that the DTG gneisses formed at 2546–2532 Ma, while the GMS intrusions were emplaced between 1870 and 1819 Ma. LA-MC-ICP-MS zircon Lu-Hf isotope analyses indicate that the Neoarchean DTG magmas were mainly derived from partial melting of juvenile crust, but the Paleoproterozoic GMS magmas originated from partial melting of the metamorphic basalts and greywackes from Neoarchean to Paleoproterozoic volcanic or related sedimentary materials.Lithological assemblages, chronological and geochemical data, petrogensis and geodynamic settings of the Neoarchean DTG and Paleoproterozoic GMS magmatism show that the HQC is most likely at the northernmost part of the Trans-North China orogen of the NCC. The Precambrian HQC thus recorded Neoarchean subduction-related arc magmatism and Paleoproterozoic post-collisional magmatism that were associated with subduction and collision at the northern margin of the NCC. These Precambrian geological units were intensively overprinted by Late Paleozoic calc-alkaline magmatism, which may be caused by southward subduction and collision of the Central Asian Orogenic Belt (CAOB) with the NCC.

Geochronology and facies analysis of subaqueous volcanism of lower ordovician, Famatinian arc, Argentina

The Chuschín formation is a sedimentary-volcanic succession of the Famatina System subduction-related arc magmatism. This formation developed along the western margin of Gondwana during the early and middle Ordovician. The interpretation of the Chuschín formation is significant for the understanding of the Famatinian arc. This study provides a detailed facies analysis, which allows characterizing the deposits as well as defining some of the characteristics of the volcanism and sedimentation. Coherent, autoclastic, peperitic, pyroclastic and volcaniclastic facies were recognized between the different volcanic facies. The characteristics and relationships between these facies indicate events of effusive subaqueous volcanism as well as explosive volcanism showing predominantly high temperature features. Both types of volcanism are interbedded with volcanogenic deposits and epiclastic sediment that are associated mainly with turbidity currents. The magmatic and volcanic rocks are dominantly subalkaline, weakly peraluminous and silicic. Two new U-Pb zircon crystallization ages on volcanic rocks from the Chuschín Formation show that this section of the Famatinian arc formed between 463 and 469 Ma (Middle Ordovician).

Geochemistry of Sandstones from the Silurian Hanxia Formation, North Qilian Belt, China: Implication for Provenance, Weathering and Tectonic Setting

The North Qilian orogenic belt is the key to figure out the evolution and assembly of Asia. The Upper Silurian Hanxia Formation which is deposited in the north area of North Qilian Orogenic Belt is of utmost important to reveal the architecture and orogenic process of the North Qilian belt. So provenance analysis of the Hanxia Formation is of significance to reveal not only that the tectonic evolution of the central orogenic belt China, but also that Paleozoic Asia plate reconstruction. The ratios of elements and some discrimination diagrams based on geochemistry indicate that felsic rocks constitute their main source rocks. The chemical index of alteration is less than 80, indicating that the source rocks are relatively fresh and of low maturity. On the Th/Sc versus Zr/Sc scatter plot, samples from Hanxia Formation occur along the magmatic compositional variation trend of rocks, indicating that the rocks did not undergo obvious sedimentary sorting and recycling. The major and trace elements discrimination diagrams imply that Hanxia Formation rocks were derived from continental island arc. Recent studies show that the North China plate subducted southwards and produced subduction-related arc magmatism along the southern margin of the North Qilian Terrane during the Silurian. Therefore, we infer that in the late Silurian period the subduction-related arc became accreted to the Central Qilian terrane to the south, forming a composite continental arc, and the North Qilian belt accumulated in a fore-arc basin.

Potential role of lithospheric mantle composition in the Wilson cycle: a North Atlantic perspective

Abstract Although the Wilson cycle is usually considered in terms of wide oceans floored with normal oceanic crust, numerous orogens result from the closure of embryonic oceans. We discuss how orogenic and post-orogenic processes may be controlled by the size/maturity of the inverted basin. We focus on the role of lithospheric mantle in controlling deformation and the magmatic budget. We describe the physical properties (composition, density, rheology) of three types of mantle: inherited, fertilized and depleted oceanic mantle. By comparing these, we highlight that fertilized mantle underlying embryonic oceans is mechanically weaker, less dense and more fertile than other types of mantle. We suggest that orogens resulting from the closure of a narrow, immature extensional system are essentially controlled by mechanical processes without significant thermal and lithological modification. The underlying mantle is fertile and thus has a high potential for magma generation during subsequent tectonic events. Conversely, the thermal state and lithology of orogens resulting from the closure of a wide, mature ocean are largely modified by subduction-related arc magmatism. The underlying mantle wedge is depleted, which may inhibit magma generation during post-orogenic extension. These end-member considerations are supported by observations derived from the Western Europe–North Atlantic region.

Petrochemistry, Mineral Chemistry, and Pressure–Temperature Model of Corundum-Bearing Amphibolite from Montepuez, Mozambique

Montepuez corundum deposits in the northeastern Mozambique are geologically linked to parts of Neoproterozoic Mozambique Belt collectively described as the Montepuez Complex, containing high-grade metamorphic rocks, belonging to amphibolite facies and including corundum-bearing and corundum-barren amphibolites. Corundum-bearing amphibolites contain pargasite, spinel, and anorthite with minor amounts of corundum and secondary altered rock types containing significant mica and clay minerals. The corundum-barren amphibolites are dominated by pargasite, anorthite, and spinel. Geochemical analyses indicate that the amphibolites probably originated from basaltic protoliths associated with subduction-related arc magmatism. Phase equilibrium modeling in the system $$\hbox {Na}_{2}\hbox {O}{-}\hbox {MgO}{-}\hbox {MnO}{-}\hbox {Al}_{2}\hbox {O}_{3}{-}\hbox {SiO}_{2}{-}\hbox {CaO}{-} \hbox {FeO}{-}\hbox {H}_{2}\hbox {O}$$ in combination with mineral isopleths indicate pressure–temperature (P–T) conditions of about 10–11.5 kbar and 450– $$600\,^{\circ }\hbox {C}$$ , lower than those recorded for the Eastern Granulite of the Mozambique Belt that extends northward to Kenya and Tanzania as part of the Pan-African orogen. Therefore, metamorphic P–T condition increased northward, suggesting different levels of crustal thickening of NE Mozambique compared with Tanzania and Kenya.

Crustal Evolution of NW Iran: Cadomian Arcs, Archean Fragments and the Cenozoic Magmatic Flare-Up

The Cadomian orogen of NW Iran includes a series of metamorphic rocks with zircon U-Pb ages between ca 562 and 505 Ma (Ediacaran to middle Cambrian). The Ediacaran-Cambrian basement is intruded by a series of Late Eocene-Late Oligocene I-type granitic rocks. U-Pb geochronology, integrated with geochemical and isotopic data for the basement rocks in NW Iran, provides further evidence of a Cadomian (562-505 Ma) arc-related magmatic event lasting ∼ 60 Myr. Cadomian magmatism in Iran was a part of a ∼ 100 Myr long episode of subduction-related arc magmatism at the northern margin of Gondwana. Zircon Hf-isotope compositions show that during Cadomian magmatic arc activity, juvenile arc magmas interacted with reworked Archean crust to generate the Ediacaran-Cambrian igneous rocks. Our results document both inheritance of old zircons and the presence of zircons with juvenile signatures in NW Iran, suggesting that the geotectonic setting for the Cadomian rocks was an Ediacaran continental magmatic arc and probably a neighboring back-arc basin. The occurrence of Ediacaran ophiolitic slices in NW Iran may provide evidence of back-arc basin opening at that time. Cenozoic plutonism in NW Iran is part of an Eocene-Oligocene magmatic ‘flare-up’ along the Urumieh-Dokhtar Magmatic Belt in central Iran, which lasted for ca 30 Myr. The melts responsible for the formation of these rocks had an essentially juvenile signature with minor contamination by Archean to Cadomian middle-lower continental crust. Continuous convergence between Arabia and Iran was accompanied by the transition of SW Eurasia from a compressional to an extensional convergent plate margin in Eocene-Oligocene times, leading to orogenic collapse, core-complex formation, exhumation of Cadomian crust and a major increase in arc magmatism.