Paleo-Tethyan Suture Research Articles

Late Triassic continental eclogite in the central Tibetan Plateau reveals 2500-km-long Paleo-Tethys continental subduction

Permian−Triassic eclogites exposed on the Tibetan Plateau have traditionally been attributed to Paleo-Tethys oceanic subduction. Here we report new data that indicate a continental-subduction origin of the Pianshishan eclogites along the Longmuco-Shuanghu Paleo-Tethys suture in northern Tibet. Phase equilibrium modeling and zircon U-Pb dating constrain eclogite-facies metamorphism of ∼2.1 GPa/530 °C to have occurred ca. 235 Ma. Xenocrysts of ca. 1850 Ma metamorphic zircons and crustal trace element signatures reveal a continental protolith for the Pianshishan eclogites, demonstrating deep subduction of continental passive margins during the early Late Triassic. The Qianmai eclogites along the Changning-Menglian suture in Southwest China have the same petrogenesis, indicating that these two coeval eclogites resulted from continental subduction that extended over 2500 km along the Paleo-Tethys suture. This collision not only marks the end of the Paleo-Tethys Wilson cycle but also could have formed a high-elevation range, comparable in length to the Himalaya, that amplified Tethyan megamonsoons during the Late Triassic Carnian Pluvial Episode.

Spatio-temporal variations of Late Triassic granitic magmatism in the Lincang batholith and implications for post-collisional process along the Paleo-Tethys suture in SW China

ABSTRACT The most striking Lincang granitic batholith widely distributed in the Sanjiang Paleo-Tethys Orogen provides us a crucial window to understand the subduction, consumption, and associated geodynamic mechanism of the Paleo-Tethys Ocean during the late Paleozoic to early Mesozoic. In this study, we carry out an integrated study of petrology, zircon U-Pb geochronology, whole-rock major and trace elements, and in situ zircon Hf isotope of the Late Triassic granitic rocks from the Lincang granitic batholith, with the aim of investigating their geochronological framework, spatio-temporal variations, genetic mechanism, and tectonic significance. The granitic rocks presented in this study consist of granodiorite and monzogranite, with minor syenogranite. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating of these granitic rocks yield crystallization ages of 237.6–209.0 Ma, indicating multi-stage granitic magmatic activities during the Late Triassic. Geochemical analyses show that these granitic rocks belong to medium-K calc-alkaline and shoshonite series, and have metaluminous to peraluminous characteristics and low whole-rock zircon saturation temperature (726–834°C). The Late Triassic granitic rocks show transitional characteristics and originate from different magma sources, indicative of transitional I-type and S-type granite affinities. The 237.6 Ma gneissic granodiorites belong to I-type granite and have typical continental arc granites of enrichments in large ion lithophile elements (Rb, K, Pb, and Th) and light rare earth elements (LREEs), and depletion in high field strength elements (Nb, Ta, Ba, Ti, and P) and heavy rare earth elements (HREEs), with parental magma derived from garnet amphibolite facies lower crust. Whereas the 222.7–209.0 Ma granitic rocks have S-type granite affinities with psammitic source. The transitional geochemical characteristics led us to favour that syn-collisional stage in response to final closure of the Paleo-Tethys Ocean in Southwestern Yunnan lasted at least until 237.6 Ma. Subsequent extensional mechanism and associated asthenosphere upwelling after final closure of the Paleo-Tethys Ocean induce large-scale partial melting of the middle-lower crust, resulting in voluminous generation of S-type and A-type granitic rocks and associated volcanic rocks in Southwestern Yunnan.

Geochemistry and geochronology of the Neyshabur meta-volcanic rocks, Binalood mountains, NE Iran: witnesses of Paleo-Tethys rifting and closure

Geochemical and geochronologic data are presented for meta-mafic to meta-felsic rocks along the Paleo-Tethys Suture in the Binalood Mountains east of Neyshabur, NE Iran. The rocks have a late Cambrian age (U–Pb zircon, ~ 490 Ma) and were metamorphosed in the Early Jurassic (40Ar/39Ar amphibole and plagioclase, 199–192 Ma). The rocks of this suite are alkaline and sub-alkaline (tholeiitic). The alkaline rocks are enriched in light relative to heavy rare earth elements, and do not show depletion of high-field strength elements on primitive mantle-normalized multi-element diagrams; they are similar to ocean island basalts (OIB). The tholeiitic rocks are depleted in Nb and Ta and have higher MgO and lower TiO2 than the alkaline rocks. Both types have similar, high and variable 87Sr/86Sr(i) isotopic compositions of 0.7044 to 0.7082 and 143Nd/144Nd(i) values of 0.5118 to 0.5122. The alkaline rocks are lower-degree partial melts than the tholeiitic rocks and were generated at greater depths; they likely originated from a garnet pyroxenite-rich source. The spatial, temporal, and geochemical relationships of early Paleozoic meta-mafic to felsic rocks along the Paleo-Tethys Suture (e.g., Shahrud, Jajarm, Binalood, Torbat-e-Jam) substantiate the role of a mantle plume in continental breakup along the northern margin of Gondwana and a late Cambrian-Ordovician onset of rifting that resulted in the opening of the Paleo-Tethys Ocean. The Early Jurassic metamorphism post-dates its closure.Graphical abstract

Melting of Subducted Continental Crust in the Cimmerian Collisional Orogenic Belt, NE Iran

Abstract The subduction of continental crust in orogenic belts that are not associated with high-pressure metamorphism is still poorly understood. The Late Triassic postcollisional granitic rocks of NE Iran are related to the convergence between the Central Iran terrane and the Turan terrane on the southern margin of the Eurasian continent. They intruded into the Paleo-Tethyan suture between the Central Iran and Turan terranes. Granitoids of the Torbat-e-Jam pluton were emplaced at ca. 217 Ma, and their moderately high SiO2 (>64 wt. %), low MgO contents (mostly <2 wt. %), slightly depleted Sr-Nd, and zircon Hf isotopes suggest partial melting of a juvenile crust. Granodiorites from NW and SE Mashhad were emplaced at ca. 217 and 200 Ma, and their geochemical features and enriched Sr-Nd and zircon Hf isotopes suggest melting of continental crust. Inherited zircon cores in both the NW and SE Mashhad intrusions have dominant age peaks of ca. 540 and 770 Ma, similar to the age spectrum of adjacent Paleozoic sediments derived from the Central Iran terrane, but distinct from Triassic sediments sourced from the Turan terrane. The inherited zircon cores cannot be explained by crustal contamination during magma ascent, rather the age pattern of inherited zircon cores coincides with major magmatic events in the Central Iran terrane and fingerprint their source, suggesting partial melting of the subducted Central Iran continental crust. This study suggests that the melting of subducted continental crust can occur in simple collisional belts, rather than being confined to ultrahigh-pressure metamorphic orogenic belts.

The hydrocarbon source potential of Permo-Triassic rocks of the Indochina Block adjacent to the Paleo-Tethys suture in Thailand

The main Thailand petroleum systems are found in the syn-rift and post rift sections of Cenozoic rift basins. The Khorat Plateau area is a separate gas province with Permian limestone reservoirs possibly sourced from Triassic lacustrine, and Permo-Carboniferous marine shales. However, these source rocks and those of equivalent age west of the Khorat Plateau are not well described in the literature. This study investigated the source potential of outcropping Permo-Triassic shales from the western margin of the Khorat Plateau and the Khao Khwang Fold and Thrust Belt (KKFTB). The key formations sampled are: Permian: Alum Shale, Nong Pong, Sap Bon, Khao Khad, and Nam Duk formations; Triassic: Pang Asok and Hua Hin Lat Formation. Most potential Permo-Triassic source rocks sampled exhibited little potential due to the dominance of Type IV, non fluorescent amorphous, vitrinite and intertinite mascerals and low <1 % TOC content. Probably the Type IV kerogens are not original, but the product of subsurface alteration of other kerogen types (most likely Type III). The complex burial histories of the formations indicates such alteration could have occurred post-maturation. Probably maximum burial in the KKFTB was attained during the Triassic Indosinian Orogeny when upper diagenetic to anchizone conditions were attained. Significant burial also occurred when the Jurassic-Cretaceous Khorat Group (>2 km thick) was deposited. This later burial could be responsible for later maturation in areas north of the KKFTB. Simply in terms of TOC content >1, the Hua Hin Lat and Khao Khad formations have the most promising source potential.

Detrital record of sediment influx in the Triassic Chuxiong broken foreland basin in southeastern Tibetan Plateau

The Triassic Chuxiong basin represents a classic example of a foreland system that is thought to be associated with the closure of eastern branches of the Paleo-Tethys and subsequent Indosinian collision, yet how it was filled remains poorly understood. Here, we use paleocurrent measurements, sandstone petrology, and detrital zircon UPb geochronology to examine the patterns of basin fill. Paleocurrent reconstruction indicates that although some evidence exists for axial transport, the basin was mainly filled transversely with abundant sediment input from the Paleo-Tethyan suture to the west and the Kangdian High to the east. Qualitative determination of sandstone petrology shows that the lithic fragments contained within the Late Triassic strata are not of a uniform mode: volcanic lithics and glass grains are contained within nine Carnian and Rhaetian samples from the western part of the basin, but rarely observed in thirteen samples from the eastern basin. Similarly, detrital zircon UPb geochronology of sandstone samples from five sections reveals marked temporal and spatial changes in their age signatures that can be divided into three distinct types. Type-1 age spectra are represented by a narrow unimodal age probability peak at ca. 250 Ma that correlates with the Indosinian-aged arc sources developed along the Jinsha Jiang-Ailao Shan and Changning-Menglian sutures. Type-2 also shows a major zircon age population, but with a diagnostic peak at ∼780 Ma that corresponds to the Neoproterozoic basement outcropped in Kangdian High. Type-3 is generally characterized by multimodal distribution with major populations of ca. 200–350 Ma, ca. 400–500 Ma, ca. 700–900 Ma, ca. 1750–2000 Ma, and ca. 2350–2600 Ma. Comparing our new data with existing age spectra for the Triassic strata across the western Yangtze and the Indochina blocks demonstrates that the Chuxiong basin was primarily filled by a magmatic arc along the Paleo-Tethyan suture zone during the Carnian, and mostly fed by a reorganized drainage system by incorporating the fold-thrust belt and uplifted foreland basement as source area when the basin expanded eastward through the Norian and Rhaetian as the basin-fill onlaps onto the basement of Kangdian High. The patterns of sediment dispersal of the Triassic Chuxiong basin not only provide a new example of the interplay between orogen and craton sediment input in the peripheral setting but also highlight that the local basement-cored uplifts may dominate the provenance of a broken foreland system during underthrusting.

Petrology, geochemistry and Ar-Ar geochronology of eclogites in Jinshajiang orogenic belt, Gonjo area, eastern Tibet and restriction on Paleo-Tethyan evolution

As one of the important Paleo-Tethys suture zones in eastern Tibet, the Jinshajiang orogenic belt is of great significance to study the tectonic evolution of the main suture zone of Paleo-Tethys. In this paper, eclogites developed in the Jinshajiang suture zone in Gonjo area, eastern Tibet, are selected as specific research objects, and petrological, geochemical and Ar-Ar geochronological analyses are carried out. The major element data of the whole rock reveals that the eclogite samples have the characteristics of picritic basalt-basalt and belong to the oceanic low potassium tholeiites. The results of rare earth elements and trace elements of the samples show that the protoliths of eclogites have characteristics similar to oceanic island basalt (OIB) or normal mid ocean ridge basalt (N-MORB). Muscovite (phengite) from two eclogite samples yield the Ar-Ar plateau ages of 247 ± 2 Ma and 248 ± 2 Ma respectively, representing the peak metamorphic age of eclogite facies and the timing of complete closure of the Jinshajiang Paleo-Tethys Ocean. Muscovite and biotite selected from the hosting rocks of eclogite yield the Ar-Ar plateau ages are 238 ± 2 Ma and 225 ± 2 Ma respectively, reflecting the exhumation age of eclogites and their hosting rocks. Combined with the zircon U-Pb dating data (244 Ma) of eclogites obtained in previous work, it can be concluded that the Jinshajiang Paleo-Tethys ocean was completely closed and arc-continent collision was initiated at about 248–244 Ma (T₂¹). Subsequently, due to the large-scale arc (continent)-collision orogeney between Deqin-Weixi continental margin arc and Zhongza block (T₃¹–T₃²), the eclogites were rapidly uplifted to the shallow crust.

Metamorphic Evolution and Orogenic Process Related to the Eastern Paleo-Tethyan Warm Subduction and Indochina–South China Collision

Abstract The eastern Paleo-Tethyan Jinshajiang–Ailaoshan–Song Ma orogenic belt in the Southeast Tibetan Plateau represents the tectonic boundary between the Indochina and South China blocks. Regional Cenozoic lithospheric strike-slip movements caused by the India–Asia collision have modified many of the pristine geological records associated with the Indosinian orogeny. The lack of reliable petrological evidences, particularly of high-pressure (HP) metamorphism, has hindered the tracing of the evolutionary history of the Paleo-Tethyan orogenic belt. We report the mineralogy, geochemistry, geochronology and thermodynamic modelling of eclogite lenses/blocks and their host garnet–phengite schists from the Song Ma Suture Zone of Northwest Vietnam and reveal their protolith origins and metamorphic evolution. The eclogites are geochemically similar to mid-ocean ridge basalt, showing weak depletions in high field-strength elements, positive to slightly negative whole-rock ɛNd(t) ratios (−1.69 to +5.15) and slightly high 87Sr/86Sr(t) ratios (0.70466–0.70834). The igneous protolith of the eclogites formed in the late Silurian (425.4 ± 3.6 Ma; igneous zircon dating, 638–459 Ma TDM dating), which makes them the oldest known mid-ocean ridge mafic rocks in an ancient Paleo-Tethyan Ocean. Various eclogites preserve similar peak mineral assemblages (garnet + omphacite + phengite + rutile + quartz ± epidote/clinozoisite ± kyanite ± winchite) under indistinguishable peak conditions. Their prograde P–T trajectories show a uniform pattern of progressive heating and weak compression along a geothermal gradient of 8°C–10°C/km, indicating a warm subduction setting at a low angle that contrasts with the cold oceanic subduction recorded in the adjacent Paleo-Tethyan suture zones. Combined with detrital U–Pb ages from previous studies, our geochronological data indicate that the host schists originated from continental crust within the South China Block and underwent a pervasive Triassic HP metamorphism related to the Indosinian orogeny. The eclogites and host schists yielded HP metamorphic ages of 239–234 Ma and retrogressive amphibolite-facies metamorphic ages of 231–229 Ma, suggesting rapid cooling (14.0°C–21.6°C/Myr) and exhumation (6.4 km/Myr) from the mantle to the crust. The Song Ma eclogites and their host schists formed when the final ocean closure transitioned to the initial Indochina–South China collision. The Song Ma eclogites and their host schists provide essential information on the opening and closure of the eastern Paleo-Tethys and the subsequent amalgamation of Southeast Asian continental fragments.

The 2022 Twin Earthquakes and Tectonic Environment in Kyaing Tong Basin, Eastern Myanmar

The first earthquake of magnitude 4.8 struck at 57 km south of Kyaing Tong, latitude 21.1141°N longitude 99.850°E, on 21st July 2022, at 16:40:08 UTC ( 11:07 a.m. local time ) at the depth of 10 km. Immediately after 30 minutes on the same day of 21st July 2022, the second earthquake with magnitude 5.9 occurred, 53 km south of Kyaing Tong at latitude 21.150°N 99.863°E, 17:07:26 UTC (11:37 a.m. local time) at 10 km depth. Focal mechanism solution for the first event was left-lateral strike-slip faulting and the second by normal faulting with a component of strike-slip component (United States Geological Survey). Many lesser aftershocks followed the main shocks and continued since July and still ongoing up to date in 2022. Twin earthquakes ruptured along the Wan Ha fault which bounds the southeast side of the Kyaing Tong basin, eastern Myanmar. The rupture propagated southward. The Kyaing Tong basin is one of the tectonic basins in the Paleo-Tethys suture zone in eastern Myanmar. These earthquakes are due to the movement of Wan Ha fault, affected the town Kyaing Tong where it caused some houses and schools collapsed. No casualty was reported. According to data from USGS, and other earthquake agencies, there is a clear increase in detected earthquakes, particularly smaller quakes of magnitude around ≥ 1.0 and ≥ 2.0 at shallower depth of 1000 meter. From the studies of satellite images, aerial photographs, shaded relief map and Digital Elevation Model map, several lineaments are visible and detailed mapping of these lineaments show the strike-slip faults in ENE-WSW direction and normal faults in NE-to NNE-striking direction. NW-SE extension is evident by the occurrence of brittle normal faults and NE-to ENE-oriented sinistral strike-slip fault. Within this zone is the trace of regional compression in a NE-SW direction. This region is presently undergoing active tectonic deformation, as indicated by current seismicity and earthquake focal mechanism solution.

Cimmerian metamorphism and post Mid-Cimmerian exhumation in Central Iran: Insights from in-situ Rb/Sr and U/Pb dating

The pre-Alpine evolution of the Tethyan domains between Gondwana and Laurasia, and in particular that of the Cimmerian continental blocks, remains poorly constrained. Central Iran is a key area to constrain the closure of the Paleotethys and the collision of Laurasia with the Cimmerian blocks drifted from Gondwana. The present study provides a combined metamorphic and geochronologic approach focused on two areas of Central Iran: the Kashmar-Kerman Tectonic Zone (KKTZ) and the Jandaq area, whose tectonometamorphic units are affected low- to middle-pressure high-temperature metamorphism. We performed in-situ texturally constrained U/Pb dating on titanite and Rb/Sr dating on mica to quantify the timing and intensity of burial and exhumation of these metamorphic rocks. Results show that metamorphism in the central and eastern KKTZ (7–9 kbar; ∼700 °C) is synchronous or slightly postdates the Cimmerian orogeny (∼190-180 Ma) and relates to the collision following the Paleotethys closure, whereas metamorphism in the Jandaq complex (12–13 kbar; ∼450 °C) relates to the Paleotethys subduction. Based on paleogeographic reconstructions, the KKTZ lied hundreds of kilometers south of the Paleotethys suture zone. As such, we propose that metamorphism along the KKTZ results from the closure and shortening of a rheologically weak domain located outboard of the main suture. In-situ Rb/Sr dating of biotite yields precise and accurate cooling ages (±2-5 Ma) ranging from 170 to 140 Ma. These cooling ages document the exhumation of these terranes from the Mid-Cimmerian event onward (∼170 Ma), coeval with the widespread extension distributed across Iran and thought to reflect upper plate extension above the Neotethyan subduction system.

Geological Significance of Late Permian Magmatic Rocks in the Middle Section of the Ailaoshan Orogenic Belt, SW China: Constraints from Petrology, Geochemistry and Geochronology

The Ailaoshan orogenic belt, located in the SE margin of the Qinghai–Tibet Plateau, is an important Paleo-Tethys suture zone in the eastern margin of the Sanjiang Tethys tectonic domain. The areas of Mojiang and Zhenyuan, located in the middle part of the Ailaoshan orogenic belt, are the key parts of the Ailaoshan Paleo-Tethys Ocean closure and collision orogeny. The rhyolites outcropped in the Mojiang area, and the granite porphyries outcropped in Zhenyuan area, are systematically studied for petrology, isotope geochemistry and geochronology. The Zircon U-Pb geochronology of rhyolites and granite porphyries give weighted average ages of 253.4 ± 4.2 Ma and 253.3 ± 2.0 Ma, respectively, both of which were formed in the late Permian period. The rhyolites belong to potassic calc-alkaline to subalkaline series. The patterns of the rare earth elements (REE) show a right-inclined seagull-type distribution, and the trace elements plot is right-inclined. The granite porphyries are high potassic calc-alkaline to subalkaline. The REE patterns show a right-inclined distribution, and the trace elements plot is right-inclined, which is consistent with the typical patterns observed in the crust. The peraluminous, highly differentiated and high ASI values suggest that rhyolites and granite porphyries are S-type granites. The zircon εHf(t) of the rhyolites range from −7.22 to −0.72, and two-stage Hf zircon model ages are (TDMC) 1771–2352 Ma, indicating that the magma source area is mainly crust-derived. The zircon εHf(t) of the granite porphyries range from −0.97 to 4.08, and two-stage Hf zircon model ages are (TDMC) 1336–1795 Ma, indicating that the magma is derived from a depleted mantle source and the partial melting of ancient crustal materials. The rhyolites and granite porphyries were possibly formed in the syn-collisional tectonic setting during the late Permian, and their ages limited the time of the final closure of the Ailaoshan Ocean and the initiation of collisional orogeny.

The composite Triassic\u2013Eocene Poshteh pluton, eastern Iran, an Eo-Cimmerian element south of the main Paleotethys suture

The composite Poshteh Pluton, at the northeastern margin of the Central Iranian Microplate near Taybad in eastern Iran, is positioned at a critical tectonic junction, south of the inferred main Paleotethys suture and along the major regional Doruneh Fault system. It consists of two distinct intrusions. Quartz monzonite is dated in this study by zircon U–Pb ID-TIMS to 215.8 ± 0.5 Ma, an age that coincides with the time of closure of the Paleotethys during the late collisional stages of the Eo-Cimmerian Orogeny. It is geochemically very similar to coeval plutons present along and north of the Paleotethys suture, where they intruded Carboniferous-Permian arc sequences, ophiolites and flysch. The Poshteh quartz monzonite is located south of the suture in a position similar to the Anarak and related complexes further west, which previously have been interpreted as reflecting Mesozoic and Cenozoic disruption of the Eo-Cimmerian Orogen by extensional and transtensional processes. The Triassic quartz monzonite was subsequently invaded by granite at 41.23 ± 0.31 Ma. The emplacement was in part structurally controlled by the Doruneh Fault system and associated to hydrothermal alteration and Fe mineralization. The granite is thus a coeval member of a widespread late Eocene to Oligocene plutonic suite in the region, and likely the result of delamination and melting of the subcontinental lithosphere.

Nature and structural heterogeneities of the lithosphere control the continental deformation in the northeastern and eastern Iranian plateau as revealed by shear-wave splitting observations

To investigate the intracontinental deformation during the early stage of Arabia-Eurasia collision, we studied the seismic anisotropy of the northeastern and eastern Iranian plateau via teleseismic shear-wave splitting analysis using a dense array of 65 stations. While the average delay times of ∼0.75 s for most stations suggest a moderate magnitude of anisotropy, small-scale variations in fast polarization directions (FPDs) indicate complex anisotropic features that may be related to the nature and structural heterogeneities of the lithosphere. The variations in FPDs are correlated with tectonic boundaries, including the northeastern plateau around the Paleo-Tethys suture and large-scale strike-slip faults bounding the Lut block in the eastern plateau. This suggests that the weak boundary zones may have significantly impacted the lithospheric deformation and anisotropy in response to the ongoing continental collision. Within the Lut block, the insignificant surface deformation suggests that the upper crust might not be noticeably affected by collision, and the fault-induced deformation mainly occurs at depth. The regional northeastward asthenospheric flow driven by the lithospheric thickness contrast across the collisional front could contribute but to different extents among areas. The asthenosphere-induced anisotropy has a magnitude (delay time) comparable to that from lithospheric deformation in central Lut, consistent with the two-layer model observed there. It dominates the seismic anisotropy in northern Lut where the thin lithosphere may contribute less but probably facilitates melt concentration on the top of the asthenosphere and thus enhances anisotropy through aligned melt-filled pores. The complex deformation pattern of the study region suggests that the intracontinental deformation may be controlled by not only the collisional processes at the plate boundary but also the nature and structural heterogeneities of the continental lithosphere itself, and the Arabia-Eurasia convergence may be more preferentially accommodated along tectonic boundaries and at depth.

Cenozoic Dextral Shearing Along the Arusan Sector of the Great Kavir–Doruneh Fault System (Central Iran)

AbstractThe structural analysis of large intracontinental wrench faults is fundamental for deciphering the long‐term evolution of continental crust in complex areas in terms of their geodynamic evolution and large‐scale crustal block displacements. In this contribution, we demonstrate a pre‐Miocene dextral activity of the present‐day left‐lateral Great Kavir ‐ Doruneh Fault System (GKDFS, Central Iran), one of the major intracontinental active strike‐slip faults extending from the Afghan border to the Nain region between Central Iran and the Sanandaj‐Sirjan Zone. We document important dextral shearing recorded along a segment of the GKDFS, the Arusan Fault System (AFS), located east of Jandaq, close to the present‐day active trace of the GKDFS. The AFS include several ENE‐WSW striking strands exposed for a length of more than 50 km, which couple pre‐Cretaceous ophiolites and metamorphic basement units with the Cretaceous succession of the Khur basin. The fault shows transpressional structures consistent with a dextral shear including thrusts and en échelon folds affecting the Cretaceous carbonate units. Paleostress reconstruction based on mesoscopic fault analysis and related folds geometry allowed to establish vorticity parameters indicating that deformation occurred close to a total simple shear regime with a calculated Wk between 0.9 and 1. The enormous Meso‐Cenozoic dextral displacements occurred along the AFS and along the entire GKDFS are attested by the up to several hundreds of kilometers offset of the Paleotethys suture zone, from NE Iran to the western border of Central Iran.

Bitu ophiolite in eastern Tibet: The last piece of the jigsaw puzzle in the Paleotethyan regime along the eastern Cimmerian continental margin

As part of the eastern Cimmerian continent, the Qiangtang terrane played an important role in the evolution of the Pangea supercontinent. Recent studies suggest the Qiangtang terrane be divided into two parts along the Longmu Co-Shuanghu Paleotethyan suture, which connected with the Changning-Menglian suture as the boundary of the Cimmerian continents from the Laurasia. However, this proposal has been challenged by the absence of ophiolite mélanges in 700-km length in eastern Tibet. To fill this gap, here we investigate an ophiolite mélange suite, named Bitu, in eastern Tibet. The mélange includes blocks of serpentinites, gabbros, basalts, and minor radiolarian-bearing cherts. Zircon UPb dating indicates that the gabbro crystallized at ~265 Ma and one basalt sample has zircon ages that cluster at ~426 Ma. Geochemical analysis shows that the mafic rocks have oceanic island basalt (OIB) or mid-ocean ridge basalt (MORB) characteristics. This indicates an expanded ocean from the Late Silurian to the Middle Triassic in eastern Tibet, comparable to that of other Paleotethyan sutures. Thus, based on regional comparison, we infer that the Longmu Co-Shuanghu, Bitu, and Changning-Menglian sutures represent the vanished Paleotethyan Ocean that spanned over ~4000 km between the eastern Cimmerian and the Laurasia continents. Reconstruction of the Paleozoic plate tectonics provides robust evidence for terrane correlation from Pamir to Southeast Asia. Moreover, the pre-Cenozoic plate configuration proposed by this study questions the suggestions of 400–500 km offset in the Cenozoic along the Karakorum-Jiali-Ailaoshan fault system based on the correlation of the Rushan-Pshart with the Bangong-Nujiang suture and the correlation of the Jinshajiang with the Dien Bien Phu suture.

Paleo-Tethys subduction induced slab-drag opening the Neo-Tethys: Evidence from an Iranian segment of Gondwana

The Iranian plateau has a more straightforward relationship between the Paleo-Tethys and Neo-Tethys, than other regions in the Tethyan realm and is an ideal place to test the genetic connection of how the Paleo-Tethys affected the Neo-Tethys. Moreover, there is no consensus on how Paleo-Tethyan evolution influenced the Neo-Tethyan Wilson cycle. We studied the petrology , geochemistry , and metamorphic age of an eclogite suite at Rasht in northern Iran from the Paleo-Tethyan suture. The eclogitic protolith was a typical mid-ocean-ridge basalt and achieved its peak metamorphic condition of 2.7 GPa and 590 °C at 353 ± 8.9 Ma. Reconstructed pressure-temperature-time path of the eclogite-facies rocks suggests that the eclogitic protolith entered the trench at 356 ± 8.9 Ma. Mid-oceanic ridge rocks formed at ~380 Ma at the Rasht region and other places along the Alborz Mountain strike. A ~ 25 million years (Myr) period from the birth of oceanic crust to subduction at Rasht region implies that the mid-ocean-ridge was close to the trench. We propose that the Paleo-Tethyan mid-ocean-ridge was trench-parallelly subducted beneath the Eurasian boundary in northern Iran. This ridge-subduction propagated from east to west between 380 and 355 Ma. 47–27 Myr after ridge consumption, subduction of the remaining Paleo-Tethyan oceanic crust exerted a continuous extensional stress of ~0.1 GPa on the passive margin of Gondwana since the late Carboniferous. The drag-force eventually detached the Central Iranian Block from Gondwana, and opened the Neo-Tethyan ocean during the middle-late Permian .

Southern extension of the Paleotethyan zone in SE Asia: Evidence from the Permo-Triassic granitoids in Malaysia and West Indonesia

The consumption of the East Paleotethyan Ocean was the final step in creating the united SE Asia continent. However, uncertainties remain as to the significance of Paleotethyan-associated granitoids and when ocean closure finally occurred in west Indonesia and Malaysia. This paper presents new U-Pb geochronological, petrologic, elemental and Sr-Nd-Pb-Hf isotopic results for granitoids from west Kalimantan, West Java, Bangka-Belitung and Peninsular Malaysia. These granitoids are geochemically subdivided into the Eastern and Main Range granites. The Eastern granites include the granitoids from west Kalimantan, West Java and East Peninsular Malaysia and are dated at ~256–207 Ma, ~208–207 Ma and ~289–217 Ma, respectively. They have εNd(t) = +0.2 ~ −9.1, with two-peaks of +0.1 and −5.6, (206Pb/204Pb)i = 18.64–19.49, (207Pb/204Pb)i = 15.61–15.78 and (208Pb/204Pb)i = 38.56–39.47, and originated from a mixed source involving juvenile crust and Indochina basement. The Main Range granites occur in Bangka-Belitung (West Indonesia) and West Peninsular Malaysia, and have crystallization ages of ~226–198 Ma. They share the similar Sr-Nd-Pb-Hf isotopic compositions with those in the South China and Inthanon Triassic granites, with 87Sr/86Sr(t) = 0.70725–0.72652, εNd(t) = −5.6 ~ −10.8, ∆8/4 = 28.1–109 and ∆7/4 = 13.7–23.6, and were derived from a meta-greywacke source. Our data reveals the development of the Paleotethyan-associated Permo-Triassic granitoids in West Java, Belitung and west Kalimantan. The Bentong-Raub suture forms the East Paleotethyan suture boundary in Peninsular Malaysia, and extends southwards into the easternmost Bangka-Belitung Islands (and even West Java). To the north, it links to the Inthanon-Changning-Menglian suture in NW Thailand and SW China. It is concluded that the temporal pattern of the East Paleotethyan Ocean in west Indonesia and Malaysia correlates with that in NW Thailand and SW China. Its evolution switched from subduction to assembly of the Indochina-East Malaysia and Sibumasu at ~230 Ma. The Eastern granites might reflect active margin processes in response to the eastward subduction of the Paleotethyan Ocean, and the Main Range granites represent the post-collisional igneous rocks.

Geochemistry, origin and anatexis temperature of monzogranite formation in Mount Khalaj (Mashhad, Iran)

Geochemistry, origin and anatexis temperature of monzogranite formation in Mount Khalaj (Mashhad, Iran)

Petrology and P–T path of blueschists from central Qiangtang, Tibet: Implications for the East Paleo-Tethyan evolution

The Paleo-Tethys Ocean records the initial geodynamic processes related to the dispersion of Gondwana and the subsequent accretion of Laurasia. However, whether the blueschist-bearing central Qiangtang metamorphic belt (CQMB) within the Qiangtang Block represents an in situ Paleo-Tethys suture remains controversial. Since the starting point of this debate is the subduction type (i.e., warm subduction vs. cold subduction) recorded by the associated central Qiangtang blueschists, here, we approach this debate by investigating their petrogenesis, which records the subduction and exhumation of an oceanic plate. We reconstruct the clockwise pressure–temperature (P–T) paths using phase equilibrium modeling for two types of blueschists from the Rongma and Gangma Co areas, and their peak P–T conditions reveal typical cold subduction with a uniform low geothermal gradient of 5–10 °C/km. Combining this information with published radiometric dating and bulk-rock geochemical data, we find that the central Qiangtang blueschists record almost all of the early Permian-Late Triassic subduction of the LSPTO and subsequent continental subduction, as well as the Late Triassic exhumation of oceanic and continental material. This study confirms that the central Qiangtang blueschist-bearing mélange marks an in situ suture, which formed during the northward subduction and subsequent exhumation of the LSPTO.

Origin of Carboniferous intra-oceanic arc granitoids from the eastern Pamir and implications for the Paleo-Tethyan ocean

The expanding and diminishing of the Paleo-Tethyan ocean recorded in the Pamir, and relationships between different segments of the Paleo-Tethyan suture from Pamir to Tibet are poorly constrained. Here we present new zircon U–Pb ages and geochemical data of the Waqia granitoid pluton from the eastern Pamir. Both the host granitoids and gabbroic to dioritic enclaves have similar zircon U–Pb ages of 323–318 Ma, being contemporaneous in origin. These rocks are metaluminous, calc-alkaline, tholeiitic series. They exhibit low K2O, low Sr/Y ratios, low REE contents with depleted to flat LREE patterns, slight enrichment in Rb, Ba, Zr, Hf, and negative Nb, Ta, P, and Ti anomalies. They have similar initial 87Sr/86Sr ratios of 0.7040 to 0.7045, positive εNd(t) (+4.63 to +5.02) and εHf(t) (+9.9 to +14.7) values. Detailed elemental and isotopic data indicate that these coeval rocks in the Waqia pluton were cognate and formed by hydrous partial melting of a juvenile mafic crust within an intra-oceanic arc setting. This study is the first to report reliable isotopic ages of the early Paleo-Tethyan subduction in the eastern Pamir. Further, the Tanymas-Mazha Paleo-Tethyan suture in the eastern Pamir should be the western extension of the Jinshanjiang Paleo-Tethyan suture in the central to eastern Tibetan plateau. An integration of published results leads us to conclude that closure of the Jinshanjiang Paleo-Tethyan ocean was diachronous along its 3000–4000 km length, with closure times of ca 240 Ma in the Pamir and ca 220 Ma in the Sanjiang region.