Accretionary Orogen Research Articles

Counterclockwise P-T-t path, cyclic crustal anatexis and magmatic tempo in accretionary orogens: A case study in the Devonian arc of Central Patagonia, Argentina

Counterclockwise P-T-t path, cyclic crustal anatexis and magmatic tempo in accretionary orogens: A case study in the Devonian arc of Central Patagonia, Argentina

Research on the Closure Polarity of the Paleo‐Asian Ocean: Evidence From the Three‐Dimensional Lithospheric Resistivity Structure of Central Asian Orogenic Belt

AbstractThe Central Asian Orogenic Belt (CAOB) is a Phanerozoic accretionary orogen with a complex formation process. This study imaged the three‐dimensional electrical structure of the lithosphere using the magnetotelluric data collected covering the southern margin of the CAOB. The resistivity model shows alternating high and low resistivities along the southern margin of the CAOB in the north, with the low resistivities in the middle and lower crust interpreted as remnants of the subducted crust of the Paleo‐Asian Ocean (PAO). The belt‐like low‐resistivity body encased by high‐resistivity bodies on both sides is interpreted as residual back‐arc oceanic crust. The Alxa Block (AB) in the south exhibits overall high‐resistivity characteristics, but a large low‐resistivity area exists near the southeastern connection to the Ordos block. Based on the characteristics of the resistivity model, we propose that the final closure position of the PAO in the southern margin of the CAOB is the Enger Us fault zone, with a north‐south bidirectional subduction mode. The widespread low‐resistivity anomaly near the Badain Jaran fault zone is interpreted as residual subduction of the back‐arc oceanic crust. The subduction of the PAO is a typical “trench‐arc‐basin” model. The variation in the subduction angle of the PAO along the strike may indicate that the later stage of the southern margin of the CAOB was subjected to the convergence effect of northeast‐directed stress from the northeast margin of the Tibetan Plateau and the associated tectonic activities.

The Hf and O isotope record of long-lasting accretionary orogens: The example of the Proterozoic and Paleozoic-Triassic central South America

The Hf and O isotope record of long-lasting accretionary orogens: The example of the Proterozoic and Paleozoic-Triassic central South America

Evolution of the subcontinental lithospheric mantle beneath accretionary orogens: Implications for the stabilization of cratons

Evolution of the subcontinental lithospheric mantle beneath accretionary orogens: Implications for the stabilization of cratons

The geology of the Shyok suture zone: evidence for Cretaceous extension of the southern Eurasian margin and Eocene India–Eurasia collision

This study discusses whether the Eurasian margin, before the onset of the India–Eurasia collision, was a Cordillera-style accretionary orogen or a more complex Japan–Mariana-style margin with extended back-arc basins and oceanic crust between the volcanic arc(s) and continental lithosphere. This distinction is critical to understanding the development of the India–Eurasia orogenic system because each of these scenarios has very different implications for the timing of the continental collision between India and Eurasia. We present new field mapping, U/Pb zircon dates and whole-rock geochemical results that constrain the tectonostratigraphic and structural development of the Shyok suture zone, which separates the Kohistan–Ladakh arc from the Karakoram terrane in northwestern India and Pakistan. Our results suggest that the Shyok suture comprises a Jurassic forearc ophiolite overlain by Eurasia-derived sedimentary strata interlayered with andesites, which accumulated throughout the Cretaceous in a back-arc basin that was under extension between 115 and 72 Myr ago. Closure of this back-arc basin post-dates the formation of the Indus suture zone between the Kohistan–Ladakh arc and India.

Early Devonian Ferroan Granites Document Tectonic Switching from Advancing to Retreating Accretionary Orogen, Southern Central Asian Orogenic Belt

Early Devonian Ferroan Granites Document Tectonic Switching from Advancing to Retreating Accretionary Orogen, Southern Central Asian Orogenic Belt

Tectonic evolution of the Alxa, NW China: From a Precambrian continental ribbon to a Paleozoic–Early Triassic accretionary orogen

The Alxa is a key region for understanding the architecture and accretionary history of the southern Central Asian Orogenic Belt (CAOB) during the late Paleozoic–Triassic assembly of Pangea. However, its origin and tectonic evolution have been debated for decades. Here we use integrated geological, geochronological and isotopic data to uncover the complex history of Alxa from Neoarchean to Triassic. The Precambrian proto-Alxa is a continental ribbon consisting of Archean–Paleoproterozoic amphibolite to granulite facies rocks and Meso-Neoproterozoic gneiss-schist complexes, which underwent multiple tectonic cycles associated with assembly of Nuna, Rodinia, and Gondwana. Since Ordovician, subduction of the Paleo-Asian Ocean (PAO) generated calc-alkaline magmatic rocks with enriched Nd-Hf isotopic compositions in Andean-type continental arcs. Rollback of the subducting PAO in Devonian induced regional extension, followed by opening of the Quagan Qulu back-arc basin in late Carboniferous–early Permian, as supported by mantle-derived magmatism, shelf-type carbonate rocks, and rifting-related volcanic-sedimentary sequences. The Permian archipelago scenario with multiple subduction zones was terminated by Middle-Late Triassic when the amalgamated intra-oceanic arcs collided with the Alxa continental arc. The accretion of Alxa illustrates the importance of continental ribbon in the construction of CAOB and shed lights on understanding the architecture of accretionary orogens.

A New Geological Map of the Marginal Basins of Eastern Papua New Guinea: Implications for Crustal Accretion and Mineral Endowment at Arc–Continent Collisions

Abstract Accretion of island arc terranes is a fundamental process of crustal growth and the formation of new continents. Convergent margin tectonics, both compressional and extensional, in accretionary orogens also control the origin and distribution of their contained mineral resources, including many of the world’s important Cu and Au deposits. However, the details of crustal growth and accretion are often lost because of deformation and selective preservation during subduction. The Melanesian Borderland, which includes the offshore regions of eastern Papua New Guinea and the Solomon Islands, contains several active and relict arc and backarc systems that have formed in response to more than 50 Ma of subduction and complex plate tectonic adjustments. The composite terrane is a region of some of the fastest growing crust on Earth and also spectacular mineral endowment, including three of the top ten porphyry Cu and epithermal Au deposits in the world. However, more than 80% of the belt is submerged, and so little is known about its geological evolution and makeup. Here, we present the first detailed geological map of the region in one map sheet, including the marginal deep ocean basins. The map identifies and groups the key lithostratigraphic formations and correlates associated tectonic events across the belt. The final compilation is presented at 1:1,000,000 scale, which is sufficient to allow quantitative analysis of crustal growth and accretion during ocean–continent collision throughout the region. The map shows the diversity of assemblages in accreting terranes that may eventually become part of a growing continent and highlights their complex formation and structural relationships. Because so much of that history has occurred offshore, the new map presents the first complete picture of the geology of the region in the critical period leading up to its eventual incorporation in the Australian continent.

Recycling of subducted continent slab in an accretionary orogen: Insight from the Liangwan potassic granitoids in the Tongbai orogen, Central China

Recycling of subducted continent slab in an accretionary orogen: Insight from the Liangwan potassic granitoids in the Tongbai orogen, Central China

Early Neoproterozoic (Tonian) subduction-related magmatism and tectonothermal activity in Shetland and northern mainland Scotland: implications for the tectonic evolution of NE Laurentia and Rodinia reconstructions

The tectonic setting of Tonian orogenic events recorded in the present-day circum-North Atlantic region is uncertain. U–Pb zircon geochronology shows that the Yell Sound and Westings groups (Shetland) and metasedimentary rocks of the Naver Nappe (northern mainland Scotland) were deposited between c. 1050 and 960 Ma and intruded by mafic, intermediate and felsic igneous rocks at c. 965–950 Ma. Chemical discrimination diagrams and Hf and Nd isotope data together suggest that the protoliths of the mafic meta-igneous rocks were emplaced as relatively juvenile crustal contributions in an active plate margin. Zircon growth at c. 920 Ma within the Yell Sound Group correlates with high-grade metamorphism documented previously in Shetland. Further zircon growth and Pb loss at c. 470–460 Ma indicates overprinting during the Ordovician Grampian orogenic event. Similar age successions of Ellesmere Island, Svalbard and East Greenland also contain evidence for Tonian magmatism (some calc-alkaline), deformation and metamorphism. The new data favour Rodinia reconstructions that incorporate subduction-related magmatism and associated tectonism along the margin of NE Laurentia during the Tonian. The Yell Sound Group and correlative peri-Laurentian successions were intruded by subduction-related magmas and deformed and metamorphosed during development of the Valhalla exterior accretionary orogen, part of a more extensive peri-Rodinian subduction system.

How does a soft collision orogen uplift and collapse? Insight from the eastern Central Asian Orogenic Belt

Abstract The mechanism of uplift and collapse is critical for understanding orogenic evolution within the Wilson cycle. The Central Asian Orogenic Belt (CAOB) represents one of the largest Phanerozoic accretionary orogens on Earth, experiencing terminal soft collision following the closure of the Paleo-Asian Ocean. However, the timing and mechanism of crustal thickening and thinning in the eastern CAOB remain unclear. Here, we present geochronological, mineralogical, geochemical, and Sr-Nd-Hf isotopic data of the newly identified Late Triassic bimodal dike associations in the easternmost CAOB. The ca. 236–230 Ma mafic dikes can be divided into two groups based on petrographic and geochemical characteristics. Major element modeling using the MELTS software indicates that they evolved via independent differentiation paths. Trace element and isotope simulations reveal that the ca. 236–230 Ma mafic dikes originated from the 4%–10% partial melting of spinel- to garnet-lherzolite lithospheric mantle sources over a range of depths, with varying inputs of asthenospheric mantle materials. Coeval ca. 233 Ma felsic dikes exhibit adakitic geochemical characteristics and strong imprints of crust-mantle interaction, suggesting derivation from melting of a heated juvenile mafic lower crust as a result of the upwelling of asthenospheric mantle. The formation of bimodal dike associations records the transition from lithospheric mantle thinning to delamination. Integrating a large dataset and employing multiple geochemical proxies, our results reveal that the crust of the easternmost CAOB reached a thickness of 54 ± 3 km at ca. 280–255 Ma, likely resulting from magmatic underplating due to rollback of the subducting Paleo-Asian Oceanic slab. This region underwent a further slight increase in crustal thickness to 61 ± 2 km at ca. 254–237 Ma in response to limited tectonic shortening associated with soft collision orogeny before it thinned to 45 ± 13 km at ca. 236–210 Ma due to lithospheric delamination during post-collisional extension. Our findings reveal that the uplift of the eastern CAOB was primarily driven by magmatic underplating, with minimal contribution from tectonic shortening. Lithospheric delamination emerged as an important factor leading to the eventual collapse of the eastern CAOB. Compared to typical hard collisional orogens (e.g., the Himalaya-Tibet orogen), the CAOB experienced significantly weaker tectonic shortening followed by similar lithospheric delamination during post-collisional extension. This study highlights the importance of integrating geochemical and isotopic data in quantifying the complex evolutionary histories of ancient collisional orogenic belts.

Cuartel Ophiolite: Structure, timing and exhumation mechanisms for a Cadomian suture zone in the peri-Gondwanan Realm (SW Iberia)

Cuartel Ophiolite: Structure, timing and exhumation mechanisms for a Cadomian suture zone in the peri-Gondwanan Realm (SW Iberia)

Late Paleozoic tectonic switching and metallogenic evolution of the southern Yili arc terrane, NW China

Late Paleozoic tectonic switching and metallogenic evolution of the southern Yili arc terrane, NW China

Chemical and isotopic investigation of the I-type Bega Batholith, southeastern Australia: Implications for batholith compositional zoning and crustal evolution in accretionary orogens

Cordilleran granitic batholiths represent significant episodes of crustal growth and differentiation, and commonly display lateral isotopic and chemical variations. Establishing the tectono-magmatic processes responsible for generating this compositional asymmetry is important for understanding crustal evolutionary processes throughout the Phanerozoic. The Bega Batholith, an example of a ‘Cordilleran style’ granite batholith, is the largest I-type Siluro-Devonian granite complex in the Lachlan Fold Belt (LFB) of southeastern Australia and comprises seven granite supersuites that display systematic lateral isotopic and chemical asymmetry. From west to east towards the present-day continental margin, an increase in the content of Na2O, Sr, Al2O3, and P2O5, with concomitant decreases in CaO, Sc, Rb, and V are observed. In the same direction, whole-rock initial 87Sr/86Sr decreases from 0.7098 to 0.7039, εNd values increase from −8.3 to +4.4, and δ18O decreases from 10.2 ‰ to 7.9 ‰. Depleted-mantle model ages also decrease from ca. 1800 Ma in the west to 600 Ma in the east. Here, we address whether these chemical and isotopic variations were generated by interaction between two distinct components (mantle-derived magmas and supracrustal sources) or were alternatively produced by partial melting of infracrustal source rocks formed sequentially by much earlier episodes of crustal underplating. Combined whole-rock Nd-Sr-O isotopic and geochemical analyses indicate that several I-type supersuites exhibit chemical and isotopic correlations consistent with two-component magma mixing. This new evidence challenges the long-held view that I-type granites derive exclusively from the melting of infracrustal sources, and that granite terranes represent wholesale crustal reworking rather than new crustal growth. Our results show that the compositional zoning within the Bega Batholith is multifaceted. Firstly, the presence of two discrete mantle sources endows chemically and isotopically distinct eastern and western segments in the batholith. Secondly, within these compositionally distinct regions the lateral compositional changes across supersuites derives from mixing between mantle-derived and supracrustal sources. Finally, progressive extension within a developing back-arc environment regulates the ratio of crust-mantle contributions and compositional architecture of each I-type supersuite.

Geochemistry and geochronology of 1.7-1.8 Ga peraluminous A-type granites and granite-gneiss from the Mahakoshal Basin, Central Indian Tectonic Zone (CITZ): implications for an accretionary orogen for the evolution of CITZ

ABSTRACT Here, we report petrography, whole-rock geochemistry, and zircon U-Pb geochronology to understand the origin, source, geodynamic setting, and evolution of A-type granite and granite gneiss as well as establish their emplacement age from Mahakoshal Basin. Mineralogically, Sidhi granite gneiss and Madanmahal granite of the Mahakoshal Basin dominantly consist of quartz, K-feldspar, and plagioclase. Geochemically, Sidhi granite gneiss and Madanmahal granite are ferroan in nature. The studied rocks are akin to peraluminous A-type granites and have average zircon saturation temperatures of 955°C and 977°C, respectively. The studied rock types are derived from partial melting of pre-existing crust indicated by (Y/Nb)N >0.18, (Th/Nb)N >2, (Ce/Pb)N <1, and (La/Nb)N >2 accompanied by the Eu, Ba, Sr, Ti, and Nb negative anomalies. The zircon U-Pb geochronology yielded emplacement ages of 1723 ± 16 Ma for the Sidhi granite gneiss and 1801 ± 64 Ma for the Madanmahal granite. Based on similar geochemical characteristics such as rare earth element patterns, Eu anomalies, and Ce/Pb, La/Nb, and Th/Nb ratios, we propose that the Sidhi granite gneiss and Madanmahal granite are derived from the same source i.e. Bundelkhand gneisses and granites, and formed in a post-orogenic rift environment of the accretionary orogen setting.

Geographic bias effects on interpretations of secular trends of Hf isotope times series in zircons

Geographic bias effects on interpretations of secular trends of Hf isotope times series in zircons

From an accretionary margin to a sediment-rich collision: Spatiotemporal evolution of the magmatism during the closure of the Mongol-Okhotsk Ocean

From an accretionary margin to a sediment-rich collision: Spatiotemporal evolution of the magmatism during the closure of the Mongol-Okhotsk Ocean

Carboniferous Barrovian to Permian Buchan‐type metamorphic cycles in the Mongolian Altai Zone: Implication for pressure cycles in accretionary orogens

AbstractIn the Altai Accretionary Wedge, several periods of Barrovian‐ and Buchan‐type metamorphic cycles were dated from Ordovician to Permian. However, the timing and link between these cycles are not clear, and their causes are debated. In order to contribute to the understanding of Barrovian‐ to Buchan‐type evolution of the accretionary wedges, we studied an area composed of three parallel belts in the easternmost extremity of the Hovd domain located in Mongolian Altai Zone: garnet gneiss in the north, garnet–staurolite–kyanite schist overprinted by ±sillimanite±cordierite±andalusite‐bearing assemblages in the centre and garnet–sillimanite gneiss in the south. Petrography, garnet zoning and thermodynamic modelling indicate that the garnet gneiss from the northern belt records burial from ~510°C and ~3–4 kbar to ~600°C and ~5 kbar, followed by heating to ~660°C and decompression to ~4.5 kbar. The garnet–staurolite–kyanite schist from the central belt records burial from ~550°C and ~3–4.5 kbar to ~640–680°C and ~7 kbar, followed by decompression to the sillimanite stability field at ~650°C and ~6 kbar. Crystallization of cordierite, andalusite, late muscovite and chlorite in some samples indicates cooling on decompression to ~540°C and ~3.5 kbar. In the southern gneiss belt, the garnet–sillimanite gneiss with almost unzoned garnet suggests re‐equilibration at ~6 kbar and ~710°C. In situ U–Pb monazite and xenotime dating carried out inclusions in porphyroblasts and matrix grains revealed Carboniferous and Permian ages. The monazite and xenotime from gneisses of the northern and southern belts record Carboniferous and Permian ages, which are interpreted as Carboniferous crystallization at c. 347 Ma associated with metamorphic peak, followed by Permian (re)crystallization at c. 300 and 283 Ma. In the central belt, rare Carboniferous xenotime grains in a garnet–staurolite–kyanite–andalusite–muscovite schist indicate a possible Carboniferous age of the prograde metamorphism. Predominant ages between c. 280 and 260 Ma recorded by monazite are interpreted as a result of complete recrystallization during an LP metamorphic overprint. The Carboniferous ages from the gneisses can be interpreted as constraining the timing of the exhumation of deep crustal rocks to shallow crustal levels. This event corresponds to the formation of crustal‐scale migmatite‐magmatite domes in the Mongolian Altai Zone. The prograde Barrovian assemblages in the central schist belt are interpreted as having formed contemporaneously during burial in a synform between the migmatite‐magmatite domes. The Permian ages reflect LP–HT metamorphism, best recorded by the Buchan‐type assemblages in the central schist belt, and are related to massive heat flux from tectonically mobile deep partially molten crust. Correlation with similar Barrovian‐ and Buchan‐type episodes from the Chinese Altai Zone indicates multiple compressional and extensional events in the upper plate accretionary wedge, probably related to retreating and advancing modes of the subduction zone.

Geochronology and Sr-Nd-Pb-Hf-O isotopes of Neoproterozoic orthogneisses in the Jiamusi Block, NE China: Implications for tectonic origin and secular crustal evolution

Geochronology and Sr-Nd-Pb-Hf-O isotopes of Neoproterozoic orthogneisses in the Jiamusi Block, NE China: Implications for tectonic origin and secular crustal evolution

Shortening and extrusion in the East Anatolian Plateau: How was Neogene Arabia-Eurasia convergence tectonically accommodated?

Deformation in orogenic belts is typically widely distributed but may be localized to form discrete, fast-moving fault zones enclosing semi-rigid microplates. An example is the Anatolian microplate, which is extruding westwards from the East Anatolian Plateau in the Arabia-Eurasia collision zone along the North and East Anatolian Faults that cause devastating earthquakes, including those of February 6, 2023 in Southeast Anatolia. Here, we summarize the orogenic architecture of the East Anatolian Plateau and its underlying kinematic history since the Cretaceous, and use this to reconstruct the tectonic situation that existed at the onset of and during the development of the Neogene East Anatolian Plateau and the Anatolian microplate. The orogen first formed in the late Cretaceous by subduction-accretion of microcontinental lithosphere below Neotethys oceanic lithosphere. Then, in Paleogene time, the accretionary orogen underwent regional upper plate extension, causing crystalline crust exhumation and deep-marine basin formation. From early Miocene time onwards, the extended orogen shortened again and must have accommodated ∼350 km of convergence, making crust up to 45 km thick, and causing >2 km of uplift. Since the ∼13 Ma onset of North Anatolian Fault formation, microplate extrusion absorbed no more than 25 % (∼65 km) of Arabia-Eurasia convergence and even during this time alone, >200 km of convergence must have been accommodated by continued ∼N-S shortening. We highlight the need for field studies of the East Anatolian Plateau to identify where and how this major shortening was accommodated, what role it played in plateau rise and the onset and dynamics of microplate extrusion, and to better assess seismic hazards.