Paleo-Tethyan Suture Research Articles

Was the Pamir salient built along a Late Paleozoic embayment on the southern Asian margin?

While the northward convex Pamir salient has been interpreted to be a Cenozoic feature, resulting from terranes of the Pamir experiencing ∼300 km of northward translation relative to Tibet and Afghanistan during the India-Asia collision, structural evidence for large magnitudes of translation is generally lacking. We focus on the geology of the Northern Pamir, which forms the outer margin of the salient, to argue that the Pamir salient has not experienced significant northward translation as has been suggested by several recent studies. We then present evidence based on new detrital zircon results that the Pamir salient may be an inherited feature from the Late Paleozoic southern margin of Asia. Kinematic endmember models of northward translation of the Pamir predict either ∼300 km of arc-parallel extension (radial thrusting model) or truncation of geologic terranes at the margins of the salient by strike-slip faults (transfer faulting model). However, both models are inconsistent with the regional geology and structural evolution, which shows minimal extension along outer arc of the Pamir (∼50 km) and no clear truncation or thinning of geologic terranes that make up the Northern Pamir. Regarding the origin of the Pamir salient, a pronounced change in detrital zircon age signature of the Northern Pamir from west to east suggests the regions were not directly connected (i.e. part of a continuous linear belt), and were sourced from distinct cratons. Further, an absence of Triassic arc/forearc flysch deposits and arc plutons along WNW portion of the Northern Pamir suggests the possibility of a transform boundary segment along the Triassic Paleo-Tethys oceanic subduction zone. Based on these observations, we suggest an embayment existed between Tarim and Karakum Cratons after their amalgamation to the southern margin of Asia in the Early Permian. During the Late Triassic, colliding Cimmerian Gondwanan terranes (Central-Southern Pamir) filled in the embayment, resulting in the northward deflection in the trace of the Paleotethyan suture zone and Gondwanan terranes and the current arcuate geometry of the Pamir. Subsequent Cenozoic northward translation of the Pamir is interpreted to be only ∼50 km, no more than ∼80-100 km, and may be coupled with northward translation of northwestern Tibet and northeastern Afghanistan.

Rifting and subduction records of the Paleo–Tethys in North Laos: Constraints from Late Paleozoic mafic and plagiogranitic magmatism along the Song Ma tectonic zone

Abstract In Southeast Asia, the Jinshajiang–Ailaoshan suture in Southwest China and the Song Ma zone in Vietnam were generally accepted as the amalgamation boundary of the South China and Simao/Indochina blocks. However, the tectonic location of the Paleotethyan suture in North Laos and its tectonic affinity remain ambiguous. To address this issue, we present the geochemical and geochronological data of a set of mafic and plagiogranitic rocks along the Song Ma suture zone in North Laos. Three groups of rocks with distinctive petrological, geochronological, and geochemical signatures were identified. The ca. 370 Ma Group 1 plagioclase amphibolite was preserved as xenoliths in the ca. 260 Ma granitoids. It exhibits a normal mid–oceanic–ridge basalt (N–MORB)-like, multi-elemental pattern with highly positive εNd(t) (+3.3 to +10.7) and εHf(t) (+6.68 to +7.41) values and low δ18O values (5.3‰−5.5‰), that are interpreted as products of the Late Devonian − earliest Carboniferous continental rift setting. The ca. 270 Ma Group 2 gabbro/diabase–diorite exhibits arc-like geochemical affinity with the εNd(t), εHf(t), and δ18O values of –5.85 to –3.76, –3.8 to +3.2, and 6.6‰–7.6‰, respectively. It is derived from the metasomatized wedge. The ca. 260 Ma Group 3 plagiogranite shows Nb-Ta and Ti negative anomalies and positive εNd(t) (+3.21 to +4.21), εHf(t) (+8.4 to +13.6), and δ18O (5.9‰−6.8‰) values, which are indicative of its derivation from mafic oceanic crust in a subduction setting. In combination with the published data, these results support the development of the Carboniferous–Permian Paleotethyan branch in North Laos, which represents the tectonic location of the Song Ma suture zone that spatially connects the Jinshajiang–Ailaoshan suture zone in Southwest China and the Chenxing–Bangxi suture zone in Hainan Island, South China.

Rushan-Pshart Paleo-Tethyan suture deduced from geochronological, geochemical, and Sr-Nd-Hf isotopic characteristics of granitoids in Pamir

Correlation of blocks comprising the Pamir plateau with blocks in the Tibetan plateau is debated due to the complex tectonic history of amalgamated orogenic belts, followed by widespread Cenozoic intracontinental deformation within the Pamir plateau. Of particular interest is the Rushan-Pshart suture along the southern edge of the Central Pamir. It is uncertain if the suture zone is a Meso-Tethyan or a Paleo-Tethyan suture and if it is the western extension of the Bangong-Nujiang suture. This study presents new in-situ zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotopes of three granitic plutons (Tahman, Tash, and Mingtie) along the southern edge of the Central Pamir block. Emplacement ages of the three plutons range from ~206 Ma to ~201 Ma. Samples from Tahman and Tash contain 67% to 76% SiO2, and yield A/CNK values between 0.92 and 1.17. They exhibit high LILE/HFSE ratios, negative Eu anomalies (Eu/Eu* = 0.41–0.77), pronounced negative Nb, Ta, P, and Ti anomalies, negative εNd(t) values (between −7.3 and −6.9), and negative zircon εHf(t) values (between −15.5 and −1.4). Geochemical data indicate that the Tahman and Tash samples represent metaluminous or peraluminous, I-type arc-related granitoids. The Tahman granites are inferred to have formed by partial melting of the Precambrian metaigneous and metasedimentary rocks in the lower crust, while the Tash pluton was formed by partial melting of the infracrustal medium-to-high K basaltic compositions within the garnet stability field of the lowermost crust. We suggest that these newly discovered Late Triassic granite plutons are related to the closure of the Rushan-Pshart suture. This is supported by recent geochronological, paleontological, and stratigraphic studies. Thus, the Rushan-Pshart suture is a Paleo-Tethyan suture. We further notice that the Central Pamir block is bounded by the Tanymas and Rushan-Pshart Paleo-Tethyan sutures to the north and south, respectively, which is structurally similar to the North Qiangtang and the Indochina blocks that are also bounded by two Paleo-Tethyan sutures from both sides. This indicates that the Central Pamir block is the western extension of the Tianshuihai-North Qiangtang block, both of which underwent oblique convergence during the closure of the Paleo-Tethys ocean.

Geochemical and geochronological evidence for a Middle Permian oceanic plateau fragment in the Paleo-Tethyan suture zone of NE Iran

The mafic–ultramafic Fariman complex in northeastern Iran has been interpreted as a Paleo-Tethyan ophiolitic fragment with subduction- and plume-related characteristics as well as a basin deposit on an active continental margin. Contributing to this issue, we present geochemical, geochronological, and mineralogical data for transitional and tholeiitic basalts. Thermodynamic modeling suggests picritic parental magmas with 16–21 wt% MgO formed at plume-like mantle potential temperatures of ca. 1460–1600 °C. Rare pyroxene spinifex textures and skeletal to feather-like clinopyroxene attest to crystallization from undercooled magma and high cooling rates. Chromium numbers and TiO2 concentrations in spinel are similar to those in intraplate basalts. 40Ar–39Ar dating of magmatic hornblende yielded a plateau age of 276 ± 4 Ma (2σ). Transitional basalt with OIB-like trace element characteristics is the predominant rock-type; less frequent are tholeiitic basalts with mildly LREE depleted patterns and picrites with intermediate trace element characteristics. All samples show MORB-OIB like Pb/Ce, Th/La, and Th/Nb ratios which preclude subduction-modified mantle sources and felsic crustal material. Tholeiitic basalts and related olivine cumulate rocks show MORB-like initial eNd values of + 9.4 to + 6.2 which define a mixing line with the data for the transitional basalts (eNd ca. + 2.6). Initial 187Os/188Os ratios of 0.124–0.293 support mixed sources with a high proportion of recycled mafic crust in the transitional basalts. High concentrations of highly siderophile elements are in agreement with the high mantle potential temperatures and inferred high-melting degrees. It is argued that the Fariman complex originated by melting of a mantle plume component as represented by the OIB-like transitional basalt and entrained asthenosphere predominant in the MORB-like tholeiites. Two lines of evidence such as association of the Fariman complex with pelagic to neritic sedimentary rocks and the tectonic position at the boundary of two continental blocks defined by ophiolites and accretionary complexes of different ages suggest formation in an oceanic domain. Thus, we interpret it as a fragment of an oceanic plateau, which escaped subduction and was accreted as exotic block in the Paleo-Tethyan suture zone.

Proto- to Paleo-Tethyan evolution of the eastern margin of Simao block

The Simao block, northern extension of Indochina block, was located along the Proto-Tethyan subduction zone in Early Paleozoic and subducted by the Paleo-Tethyan Ailaoshan ocean along its eastern margin in Permo-Triassic. The location of Simao block in the Proto-Tethyan paleogeography and the Permo-Triassic consumption process of the Ailaoshan ocean were unclear. Detrital zircons from Silurian to Triassic strata and the representative Xin'anzhai intrusion in the eastern margin of Simao block are studied to constrain the Proto- to Paleo-Tethyan evolution. The major age peaks of detrital zircons in Early Silurian–Early Devonian strata are ~0.95Ga and ~0.45Ga, which are consistent with those of detrital zircons in the time-equivalent strata in the Simao–Indochina block rather than Yangtze block. This implied that the Paleo-Tethyan suture of the Ailaoshan ocean was located along the Ailaoshan–Tengtiaohe fault. The dominant and diagnostic ~450Ma detrital zircons with large variation of εHf(t) in the above strata were derived from arc igneous rocks associated with the evolution of Proto-Tethyan oceanalong the western margin of Simao block. This feature contrasts with the equivalent strata from Qiangtang and Tethyan Himalaya blocks, located along Gondwana Indian margin, which was dominated by ~0.95Ga detrital zircons that derived from the orogenic belt within Gondwana. This difference indicates that the Simao block located outboard of the Indian margin of Gondwana before the opening of Paleo-Tethyan ocean. During the consumption of Paleo-Tethys, the I-type Xin'anzhai granitic intrusion emplaced at ca. 257Ma. Geochemical compositions of the intrusion can be modeled by the partial melting of Proterozoic gneiss with an addition of 30–45% arc basaltic magma. Age histogram of detrital zircons from Upper Triassic sediments is featured by a peak of 254Ma, similar to the emplacement age of the Xin'anzhai intrusion. This suggests an extensive magmatism occurred at ca. 255Ma, which can be explained by the rollback of the Paleo-Tethyan slab. The subsequent granitoids emplaced in 247–237Ma show different features of high-silica, peraluminous and a derivation from meta-sedimentary rocks, and were suggested to be produced in syn-collision setting. The Early Paleozoic strata in the eastern margin of Simao block generally show a NW–SE foliation and NE–SW striking stretching lineation, reflecting a NE–SW compression resulted from block amalgamation after the Paleo-Tethyan closure. In the angularly-unconformable overlying Upper Triassic strata, these structural traces are absent. It means that the area has evolved into post-collision extensional setting in Late Triassic.

Structure of Masuleh Shear Zone: Evidence for Early–Middle Jurassic Dextral Shear Along Paleo-Tethys Suture Zone in the Western Alborz, NW Iran

The Paleo-Tethys suture zone in northern Iran was formed when the Paleo-Tethys Ocean, (between Gonwana-derived Alborz Microcontinent and the Turan Plate), closed during the Eocimmerian orogeny and after they collided together in the Mid-Late Triassic. The NW-striking Boghrov-Dagh basement Fault Zone that lies in the vicinity of Masuleh village and the southern boundary of Gasht Metamorphic Complex is a part of the Eocimmerian suture zone in the Western Alborz. Along this part of the suture zone, tourmaline leucogranites intruded in metamorphic rocks. We recognize three distinct deformation stages (D1 to D3) in the study area especially in the Masuleh Shear Zone. D1 which was synchronous with formation of the main metamorphic minerals, such as sillimanite and staurolite under medium- to high-grade metamorphic conditions probably during the Hercynian event and a NE-directed shortening. The slaty cleavage in metamorphosed Upper Paleozoic rocks and crenulation cleavage and folds in the older rocks were produced due to D2 deformation during the Eocimmerian event under greenschist facies conditions. The Masuleh Shear Zone formed as a result of a ductile strike-slip shear during the Early-Middle Jurassic Mid-Cimmerian D3 event with a pure dextral to transtension shear sense at low to locally medium-grade conditions. All of the D3 structural features agree with a NNW-directed compression and an ENE-directed extension caused by overall dextral shear parallel to the Masuleh shear zone and the Boghrov-Dagh Fault Zone. Based on the available evidence, especially cross-cutting relationships between structural fabrics and rock units, emplacement of the Gasht-Masuleh leucogranites occurred after the D2 collisional event coeval to the possible slab break-off and before the D3 event, between Eocimmerian and Mid-Cimmerian movements.

Basin classification and tectonic framework of the Nam Pat Group, Uttaradit Province, Thailand: Implications for the Nan Suture Zone

The Nam Pat Group of the Nam Pat Basin, Uttaradit Province, Thailand is situated in the Nan Suture Zone. Two contrasting tectonic framework models of the Nan Suture have previously been proposed: as a main Paleo-Tethyan suture and as a remnant of a closed back-arc basin. The goal of this study is to analyze the tectonic framework of the Nan Suture and reevaluate the existing tectonic models. This research infers the tectonic setting of the basin based on basin-filled lithofacies distributions, provenance, and paleocurrents. Three facies groups are identified. Facies A, B, and C are polymictic conglomerate, interbedded sandstone and mudstone, and mudstone with thin-bedded sandstone, respectively. Generally, the strata strike NE-SW, steeply dip NW, and fine toward the SE. Petrographic results of sandstone samples show that the majority of lithic fragments are volcanic rocks with lesser amount of metamorphic rocks and sedimentary rocks. The modal compositions of sandstones are analyzed on QFL, QmFLt, QmPK, LmLvLs, and QpLvmLsm ternary diagrams. The plots indicate that the sandstones of the Nam Pat Group have high proportions of volcanic-arc detritus. Paleocurrents, determined from the orientation of clast imbrications and cross-stratification, are toward the SE. The results suggest that large quantities of sediment traveled southeastward from a nearby volcanic arc into the basin. The Nam Pat Group stratigraphically overlies the Pak Pat Volcanics. The chemical features of the Pak Pat Volcanics, located to the west of the basin, show that they are andesitic volcanic rocks formed as a magmatic arc. Thus, the nearby Pak Pat Volcanics are the main sediment source of the Nam Pat Group, and the basin is best interpreted as back-arc basin rather than as a forearc basin.

First Discovering of Nanoscale Tectonics in Western of Qiongnan Paleo-Tethyan Suture Zone in North Margin of South China Sea and Its Geotectonic Significance

First Discovering of Nanoscale Tectonics in Western of Qiongnan Paleo-Tethyan Suture Zone in North Margin of South China Sea and Its Geotectonic Significance

An early bird from Gondwana: Paleomagnetism of Lower Permian lavas from northern Qiangtang (Tibet) and the geography of the Paleo-Tethys

The origin of the northern Qiangtang block and its Late Paleozoic–Early Mesozoic drift history remain controversial, largely because paleomagnetic constraints from pre-Mesozoic units are sparse and of poor quality. In this paper, we provide a robust and well-dated paleomagnetic pole from the Lower Permian Kaixinling Group lavas on the northern Qiangtang block. This pole suggests that the northern Qiangtang block had a paleolatitude of 21.9±4.7°S at ca. 296.9±1.9 Ma. These are the first volcanic-based paleomagnetic results from pre-Mesozoic rocks of the Qiangtang block that appear to average secular variation accurately enough to yield a well-determined paleolatitude estimate. This new pole corroborates the hypothesis, first noted on the basis of less rigorous paleomagnetic data, the presence of diamictites, detrital zircon provenance records, and faunal assemblages, that the northern Qiangtang block rifted away from Gondwana prior to the Permian. Previous studies have documented that the northern Qiangtang block accreted to the Tarim-North China continent by Norian time. We calculate a total northward drift of ca. 7000 km over ca. 100 myr, which corresponds to an average south-north plate velocities of ∼7.0 cm/yr. Our results do not support the conclusion that northern Qiangtang has a Laurasian affinity, nor that the central Qiangtang metamorphic belt is an in situ Paleo-Tethys suture. Our analysis, however, does not preclude paleogeographies that interpret the central Qiangtang metamorphic belt as an intra-Qiangtang suture that developed at southernly latitudes outboard of the Gondwanan margin. We emphasize that rigorous paleomagnetic data from Carboniferous units of northern Qiangtang and especially upper Paleozoic units from southern Qiangtang can test and further refine these paleogeographic interpretations.

Development of the Sumdo Suture in the Lhasa Block, Tibet, China

The Qinghai–Tibet plateau is a composite continental fragment formed by collision of multiple terranes and island arcs. The Lhasa terrane, which is located in the central part of the plateau, is bounded by the Yarlung–Zangbo suture to the south and Bangong‐Nujiang suture to the north. An E–W–trending belt of (ultra)‐high pressure eclogite was discovered in the Sumdo region of the Lhasa terrane. Careful field studies combined with petrological, geochemical and isotopic analyses show that the Sumdo eclogites mark a Carboniferous–Permian suture zone, at least 100 km long, containing ophiolite fragments, eclogites and Indosinian post–orogenic granitoids. This suture divides the Lhasa block into a northern and southern segment.Sumdo eclogite occurs about 200 km east of Lhasa city, and extends over 100km in an E–W direction. Sumdo eclogites were accompanied by garnet amphibolite and plagioclase amphibolite formed by retrograde metamorphism of the eclogites. The eclogites were derived from oceanic basalts. LA–ICPMS U–Pb dating of zircon from the Sumdo eclogites indicates a Permian metamorphic age (260–270 Ma) and a Carboniferous protolith age of 303 ±4.8 MaThe ophiolite fragments in the Sumdo suture zone are composed of the ultramafic rocks, MORB–type basalt, OIB–type basalt and island arc basaltic andesite, some of which are intruded by post‐collisional granites. The ultramafic body, a typical tectonic block in the suture zone, is completely serpentinized. Its geochemical features suggest that it is composed of harzburgite, typical of depleted mantle peridotite. The MORB and OIB–type basalts crop out in the Chasagang Formation, and the basaltic andesite crops out in the Leilongku Formation, both of which make up the Sumdo Group.Zircons from the OIB–type basalt with typical magmatic characteristics yield an average U–Pb age of 306 (95%) Ma, suggesting formation in a Paleo–Tethyan basin in the Carboniferous. U–Pb dating of zircon from the basaltic andesites yielded a concordant age of 265±3.1 Ma, similar to the metamorphic age (266–270 Ma) of the eclogites, suggesting formation during subduction of the oceanic crust. Indosinian granodiorite with an age of 194±4.3 Ma crops out north of the Sumdo suture. These granodiorites are similar to the late Indochina granites in the Lhasa block, and most likely formed during continent‐arc collision or during closure of the Paleo‐Tethyan Ocean.A four–stage model for the evolution of the Sumdo Paleo–Tethyan suture is proposed: 1) From the Ordovician to the Devonian Gondwanaland was part of an epicontinental sea; 2) In the Carboniferous, continental rifting produced a local basin, which then evolved into a Paleo‐Tethyan ocean basin, dividing the Lhasa block into two segments; 3) From the Permian to the early Triassic, Paleo‐Tethyan oceanic crust was subducted northward and; 4) In the middle Triassic and early Jurassic, the two fragments collided to form the modern Lhasa block.

Late Triassic granites from Bangka, Indonesia: A continuation of the Main Range granite province of the South-East Asian Tin Belt

The South-East Asian Tin Belt is one of the most tin-productive regions in the world. It comprises three north-south oriented granite provinces, of which the arc-related Eastern granite province and the collision-related Main Range granite province run across Thailand, Singapore, and Indonesia. These tin-producing granite provinces with different mineral assemblages are separated by Paleo-Tethyan sutures exposed in Thailand and Malaysia. The Eastern Province is usually characterised by granites with biotite±hornblende. Main Range granites are sometimes characterised by the presence of biotite±muscovite. However, the physical boundary between the two types of granite is not well-defined on the Indonesian Tin Islands, because the Paleo-Tethyan suture is not exposed on land there. Both hornblende-bearing (previously interpreted as I-type) and hornblende-barren (previously interpreted as S-type) granites are apparently randomly distributed on the Indonesian Tin Islands. Granites exposed on Bangka, the largest and southernmost Tin Island, no matter whether they are hornblende-bearing or hornblende-barren, are geochemically similar to Malaysian Main Range granites. The average ɛNd(t) value obtained from the granites from Bangka (average ɛNd(t)=−8.2) falls within the range of the Main Range Province (−9.6 to −5.4). These granites have SIMS zircon U-Pb ages of ca. 225Ma and ca. 220Ma, respectively that are both within the period of Main Range magmatism (∼226–201Ma) in the Peninsular Malaysia. We suggest that the granites exposed on Bangka represent the continuation of the Main Range Province, and that the Paleo-Tethyan suture lies to the east of the island.

Origin of Permian OIB-like basalts in NW Thailand and implication on the Paleotethyan Ocean

The basaltic rocks in NW Thailand belong to part of giant Southeast Asian igneous zone that delineates the extension of the Paleotethyan Ocean from SW China into NW Thailand. The Chiang Mai basaltic samples from the Chiang Dao, Fang, Lamphun and Ban Sahakorn sections are divisible into two groups of high-iron basalt. Group 1 has SiO2 of 38.30–49.18wt.%, FeOt of 13.09–25.37wt.%, MgO of 8.38–1.60wt.%, TiO2 of 3.92–6.30wt.%, which is rarely observed in nature. Group 2 shows SiO2=44.71–49.21wt.%, FeOt=10.88–14.34wt.%, MgO=5.24–16.11wt.%, TiO2=2.22–3.07wt.% and mg#=44–70. Olivine and pyroxene are responsible for the fractionation of the Group 2 magma whereas low oxygen fugacity during the late-stage differentiation of the Group 1 magma prolonged fractionation of ilmenite and magnetite. The onset of ilmenite and magnetite fractionations controls the distinct differentiation commencing at MgO=~7wt.%. Both groups show similar REE and primitive mantle-normalized patterns with insignificant Eu, Nb-Ta and Zr-Hf anomalies. They have similar Nd isotopic compositions with εNd (t) values ranging from +2.8 to +3.7 and similar Nb/La, Nb/U, Th/La, Zr/Nb, Th/Ta, La/Yb, Nb/Th, Nb/Y and Zr/Y, resembling those of OIB-like rocks. The representative basaltic sample yields the argon plateau age of 282.3±1.4Ma, suggestive of Early Permian origin. Our data argue for Group 1 and Group 2 are coeval in the intra-oceanic seamount setting within the Paleotethyan Ocean, which at least continued till 283Ma. These data, along with other observations, suggest that the Inthanon zone defines the main Paleotethyan suture zone, which northerly links with the Changning-Menglian suture zone in SW China.

Eastern Mediterranean Tectonics

extended to many other colleagues working in the Eastern Mediterranean. The papers of the present issue were written by structural geologists, sedimentologists, petrologists, geochemists, geophysics and seismologists, thus covering a wide range of disciplines. All these contributions are aiming to reveal the tectonic evolution and paleogeography of the Eastern Mediterranean. A first collection sequence of papers is dealing with the pre-Alpine tectonic evolution and paleogeography. A second collection is addressing problems related to the Eoand the Meso-Alpine orogenic phases occurring from Late Jurassic to Oligocene. Finally, there are papers dealing with the Late Miocene to Holocene evolution of the south Aegean and west Anatolian domains. Specifically, the issue starts with two papers (Chatzaras et al., and Zulauf et al.), which are mainly based on detrital zircon U–Pb ages to track the margin of northern Gondwana and the Paleotethys suture in the southern and southwestern part of the External Hellenides. Detrital zircon U– Pb ages are also used by Hinskens et al. to constrain Late Cretaceous maximum sedimentation ages and a Triassic to Neoproterozoic provenance for the metasedimentary rocks of the Cycladic blueschists of Tinos. The following two papers by Ferriere et al. and Michail et al. describe the evolution of the Vardar Ocean and suggest west-directed obduction of the ophiolitic complex to the Pelagonian zone during the Eo-Hellenic orogenic phase. Based on structural and geochronological data, Georgiev et al. suggest Jurassic to Paleogene nappe stacking in the Rhodope metamorphic complex and Middle Eocene extensional overprinting. Okay and Altiner present new constraints on the Cretaceous development of the southern part of the Pontides close to the Izmir–Ankara suture (Haymana and Ankara regions) using mainly biostratigraphical data. The Late Cretaceous to Eocene evolution of the Asterousia Most rocks exposed in the Eastern Mediterranean show evidence for a long-standing and complex tectonic history. Besides the active Hellenic subduction system, this history includes at least four major orogenic episodes, namely the Cadomian, the Variscan, the Cimmerian, and the Alpine Orogeny, accompanied by the destruction and/or formation of large oceans such as the Paleotethys and the Neotethys. Therefore, with the term “Eastern Mediterranean Tectonics” we refer to all tectonic processes that occurred from the Neoproterozoic to present and contributed to the formation of the present geological edifice of the Eastern Mediterranean. This topical issue of the International Journal of Earth Science sheds some more light on the tectonic history of the Eastern Mediterranean presenting a collection of fifteen papers, which cover processes that took place in Aegean and Anatolian domains from the Neoproterozoic to the present (Fig. 1). The idea for this issue was born during the GeoFrankfurt2014 conference, where we convened a session entitled “The Evolution of the Alpine Orogenic System in the Eastern Mediterranean.” Apart from the participants of this session, the invitation to submit papers was

Petrogenesis and tectonic implications of Triassic mafic complexes with MORB/OIB affinities from the western Garzê-Litang ophiolitic mélange, central Tibetan Plateau

Although numerous Paleo-Tethyan ophiolites with mid-oceanic ridge basalts (MORB) and/or oceanic-island basalt (OIB) affinities have been reported in the central Tibetan Plateau (CTP), the origin and tectonic nature of these ophiolites are not well understood. The petrogenesis, mantle sources and geodynamic setting of the mafic rocks from these ophiolites are unclear, which is the main reason for this uncertainty. In this paper, we present new geochronological, mineralogical and Sr-Nd isotopic data for the Chayong and Xiewu mafic complexes in the western Garzê-Litang suture zone (GLS), a typical Paleo-Tethyan suture crossing the CTP. Zircon LA-ICP-MS U–Pb ages of 234±3Ma and 236±2Ma can be interpreted as formation times of the Chayong and Xiewu mafic complexes, respectively. The basalts and gabbros of the Chayong complex exhibit enriched MORB (E-MORB) compositional affinities except for a weak depletion of Nb, Ta and Ti relative to the primitive mantle, whereas the basalts and gabbros of the Xiewu complex display distinct E-MORB and OIB affinities. The geochemical features suggest a probable fractionation of olivine ± clinopyroxene ± plagioclase as well as insignificant crustal contamination. The geochemical and Sr-Nd isotopic data reveal that the Chayong mafic rocks may have been derived from depleted MORB-type mantle metasomatized by crustal components and Xiewu mafic rocks from enriched lithospheric mantle metasomatized by OIB-like components. The ratios of Zn/Fet, La/Yb and Sm/Yb indicate that these mafic melts were produced by the partial melting of garnet + minor spinel-bearing peridotite or spinel ± minor garnet-bearing peridotite. We propose that back-arc basin spreading associated with OIB/seamount recycling had occurred in the western GLS at least since the Middle Triassic times, and the decompression melting of the depleted MORB-type asthenosphere mantle and partial melting of sub-continental lithosphere were metasomatized by plume-related melts, such as OIB s, which led to the generation of the Chayong and Xiewu mafic melts.

U–Pb zircon and biostratigraphic data of high-pressure/low-temperature metamorphic rocks of the Talea Ori: tracking the Paleotethys suture in central Crete, Greece

Inherited deformation microfabrics of detrital quartz grains and U–Pb (Laser ablation (LA)-ICPMS and ID TIMS) ages of detrital zircons separated from the Phyllite–Quartzite Unit s.l. of the Talea Ori, central Crete, suggest strikingly different source rocks. Albite gneiss of the lower Rogdia Beds includes Cambrian and Neoproterozoic rounded zircons with main U–Pb age peaks at 628 and 988 Ma. These and minor Paleoproterozoic and Archean peaks, together with the lack of Variscan-aged and Mesoproterozoic zircons, are similar to the age spectra obtained from the Phyllite–Quartzite Unit s.str. of the Peloponnesus and eastern Crete and from the Taurides. All of these zircons should be derived from the northeastern passive margin of Gondwana (Cimmeria). Metatuffites of the uppermost Rogdia Beds and metasandstone of Bali beach, on the other hand, include euhedral detrital zircons displaying a Variscan U–Pb age spectra at ca. 300 Ma with concordia ages at 291 ± 3, 300 ± 1 Ma (Rogdia) and 286 ± 3, 300 ± 3, 313 ± 2 Ma (Bali). Both types of metasediments and their zircons are similar to those of the pre-Alpine basement and overlying Tyros Beds of eastern Crete, revealing a provenance at the southern active margin of Laurasia. Thus, in central Crete the Paleotethys suture should be situated inside the Rogdia Beds. Magmatic zircons separated from a rhyolite boulder of the lower Achlada Beds yielded a concordant U–Pb zircon age at 242 ± 2 Ma placing a maximum age for the deposition of the (meta)conglomerate from which the boulder was collected. This age is compatible with an Olenekian-early Anisian age of the underlying Vasilikon marble suggested by new findings of the foraminifera Meandrospira aff. pusilla. Both the Achlada Beds and the Vasilikon marble can be attributed to the lower Tyros Beds of eastern Crete. The Alpine deformation led to a pervasive mylonitic foliation, which is affecting most of the studied rocks. This foliation results from D2 top-to-the-north shearing, which post-dates the growth of blue amphiboles (crossite).

Late Triassic paleomagnetic result from the Baoshan Terrane, West Yunnan of China: Implication for orientation of the East Paleotethys suture zone and timing of the Sibumasu-Indochina collision

In order to better understand the paleogeographic position of the Baoshan Terrane in the northernmost part of the Sibumasu Block during formation of the Pangea supercontinent, a paleomagnetic study has been conducted on Late Triassic basaltic lavas from the southern part of the Baoshan Terrane in the West Yunnan region of Southwest China. Following detailed rock magnetic investigations and progressive thermal demagnetization, stable characteristic remanent magnetizations (ChRMs) were successfully isolated from Late Triassic Niuhetang lava flows. The ChRMs are of dual polarity and pass fold and reversal tests with magnetic carriers dominated by magnetite and subordinate oxidation-induced hematite; we thus interpret them as a primary remanence. This new paleomagnetic result indicates that the Baoshan Terrane was located at low paleolatitudes of ∼15°N in the Northern Hemisphere during Late Triassic times. Together with available paleomagnetic data from the Baoshan Terrane and surrounding areas, a wider paleomagnetic comparison supports the view that the East Paleotethys Ocean separated the Sibumasu and Indochina blocks and closed no later than Late Triassic times. We argue that the currently approximately north-to-south directed Changning-Menglian suture zone is very likely to have been oriented nearly east-to-west at the time of the Sibumasu-Indochina collision.

Petrogenesis of Malaysian granitoids in the Southeast Asian tin belt: Part 1. Geochemical and Sr-Nd isotopic characteristics

The Malaysian granitoids of the Southeast Asian tin belt have been traditionally divided into a Permian to Late Triassic “I-type”–dominated arc-related Eastern province (Indochina terrane) and a Late Triassic “S-type”–dominated collision-related Main Range province (Sibumasu terrane), separated by the Bentong-Raub Paleo-Tethyan suture that closed in the Late Triassic. The present study, however, shows that this model is oversimplified and that the direct application of Chappell and White’s (1974) I- and S-type classification cannot account for many of the characteristics shared by Malaysian granitoids. Despite being commonly hornblende bearing, as is typical for I-type granites, the roof zones of the Eastern province granites are hornblende free. In addition, the Main Range province granitoids contain insignificant primary muscovite, and are dominated by biotite granites, mineralogically similar to many of the plutons of the Eastern province. In general, the Malaysian granitoids from both provinces are more enriched in high field strength elements than typical Cordilleran I- and S-type granitoids. The mineralogy and geochemistry of the Eastern province granitoids, and their relationship with contemporaneous volcanics, confirm their I-type nature. The bulk liquid lines of descent of both granitic provinces largely overlap with one another. Sr-Nd isotopic data further demonstrate that the Malaysian granitoids, especially those of the Main Range, were hybridized melts derived from two “end-member” source regions, one of which is isotopically similar to the Kontum orthoamphibolites and the other akin to the Kontum paragneisses of the Indochina block. However, there are differences in the source rocks for the two provinces, and it is suggested in this paper that these are related to differing proportions of igneous and sedimentary protoliths. The incorporation of sedimentary-sourced melts in the Eastern province is insignificant, which allowed the granites in this belt to maintain their I-type nature. The presence of minor primary tin mineralization in the Eastern province compared to the much more significant tin endowment in the Main Range is considered to reflect the incorporation of a smaller proportion of sedimentary protolith in the melt products of the former.

Petrogenesis of Malaysian granitoids in the Southeast Asian tin belt: Part 2. U-Pb zircon geochronology and tectonic model

In our complementary geochemical study (Part 1), the Malaysian granitoids of the Southeast Asian tin belt were divided into a Middle Permian to Late Triassic I-type–dominated Eastern province (Indochina terrane) and a Triassic to Early Jurassic transitional I/S-type Main Range province (Sibumasu terrane), separated by the Bentong-Raub suture zone which closed in the Late Triassic. Previous geochronology has relied on only a few U-Pb zircon ages together with K-Ar and whole rock Rb-Sr ages that may not accurately record true magmatic ages. We present 39 new high-precision U-Pb zircon ion microprobe ages from granitoids and volcanics across the Malay Peninsula. Our results show that ages from the Eastern province granitoids span 289–220 Ma, with those from the Main Range province granitoids being entirely Late Triassic, spanning 227–201 Ma. A general westerly younging magmatic trend across the Malay Peninsula is considered to reflect steepening and roll-back of the Bentong-Raub subduction zone during progressive closure of Paleo-Tethys. The youngest ages of subduction-related granites in the Eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the Paleo-Tethyan suture zone. Our petrogenetic and U-Pb zircon age data support models that relate the Eastern province granites to pre-collisional Andean-type magmatism and the western Main Range province granites to syn- and post-collisional crustal melting of Sibumasu crust during the Late Triassic. Tin mineralization was mainly associated with the latter phase of magmatism. Two alternative tectonic models are discussed to explain the Triassic evolution of the Malay Peninsula. The first involves a second Late Triassic to Jurassic or Early Cretaceous east-dipping subduction zone west of Sibumasu where subduction-related hornblende and biotite–bearing granites along Sibumasu are paired with Main Range crustal-melt tin-bearing granites, analogous to the Bolivia Cordilleran tin-bearing granite belt. The second model involves westward underthrusting of Indochina beneath the West Malaya Main Range province, resulting in crustal thickening and formation of tin-bearing granites of the Main Ranges. Cretaceous granitoids are also present locally in Singapore (Ubin diorite), on Tioman Island, in the Noring pluton, of the Stong complex (Eastern Province), and along the Sibumasu terrane in southwest Thailand and Burma (Myanmar), reflecting localized crustal melting.

Yellow Sea Transform Fault (YSTF) and the developemnt of Korean Peninsula

The Yellow Sea Transform Fault (YSTF), the boundary between the Korean Peninsula and the South China Plate was a repeatedly reactivated ancient fault, extant since 1 Ga or more ago. Similarly polycyclic continental collisions along the Qinling-Dabie-Sulu (QDS) suture dispatched the lateral (vectorial) collisional effects eastwardly toward the Korean Peninsula across YSTF, the east end of the QDS belt. The Korean Peninsula, coexisted with YSTF, has been a promontory of the Sino-Korean Plate (SKP) at least since the Rodinia assembly, ca 1 Ga. The Jarly Paleozoic rift origin of the Okcheon Trough, a major aulacogen developed within the Korean Peninsula of the Sino-Korean Plate is attributed to the transform role of the YSTF. Euring the Middle Paleozoic, the Yangtze Plate, an inherent component of the South China Plate, collided SKP so mildly and enduringly that SKP had to develop the Late Ordovician-Early Carboniferous ‘great hiatus’ over the cratonic SKP. Contemporaneously, the clustered aulacogens were formed over an area near the YSTF. It is envisioned that during the middle Paleozoic, the compressed part of the SKP by the eastward-pushing Yangtze Plate formed an extensional upper crust where the aulacogens formed. The Yangtze sea invaded the aulacogens where the clastic sediments of the mixed environment were dominated by the supply from the Yangtze Plate as witnessed by the clastic zircon grains showing the Yangtze-akin isotope dates. The development of both the middle Paleozoic ‘great hiatus’ and the clustered aulacogens represents the Caledonian tectonic phase though scarcely accompanied deformations or an orogeny. The Carboniferous-Permian metamorphism recorded in the Middle Paleozoic aulacogens represents the Hercynian (Variscan) phase, but without obvious structural deformations. The deepest subduction and the most intensive collision of the Yangtze Plate along the Paleotethyan suture was made in the late Permian-mid-Triassic time, the Indosinian phase. The coeval Songnim Orogeny in Korea was similarly intensive, though it was a derived, secondary, orogeny propagated ultimately from the QDS collision belt. Because of the eastward compression derived then from the QDS collision belt, YSTF was so deformed and considerably pushed eastward that it now occurs as a deformed-dislocated fault zone called the West Marginal Fault of Korean Peninsula (WMF in Fig. 1). The location of the mid-Triassic Korean Peninsula was inserted between the eastwardly compressing marginal Yangtze Plate and the counter balancing Permian-Triassic subduction-metamorphic-accretionary complex of the Japanese Pacific. Such a sandwich tectonics effectively intensified the Indosinian Songnim Orogeny of Korea.

Metallogenic model for the Laochang Pb–Zn–Ag–Cu volcanogenic massive sulfide deposit related to a Paleo-Tethys OIB-like volcanic center, SW China

The Laochang Pb–Zn–Ag–Cu volcanogenic massive sulfide (VMS) deposit, located within the Changning–Menglian Paleotethyan suture, SW China, is an economically significant deposit with explored reserves of 866,000 metric tons (t) Pb at 4.5%, 336,000t Zn at 3.3%, 1700t Ag at 155g/t, 116,000t Cu at 0.5–0.9%, 2.84Mt pyrite and accompany 0.8t Au. The deposit comprises three ore clusters (No. I, II and III), each of which comprises dozens of vertically stacked lenticular and stratiform orebodies. Ore clusters I and II within the Early Carboniferous volcano-sedimentary sequence erupted around 320Ma comprise most of the reserves. The Early Carboniferous sequences, situating beside the Laochang caldera, are mainly composed of basaltic to andesitic lavas and volcaniclastic rocks, and divided into three major volcanic cycles. The massive sulfides mostly accumulated in the waning time of the second and third cycles. The orebodies (e.g., orebodies I1+2 and II1) display stockwork and disseminated sulfide ores in the lower part and the semi-horizontal massive sulfide lenses and laminated carbonaceous-sulfidic chert with delicate exhalative-sedimentary textures in the upper part, and they also show vertical metal zonation transiting from Fe–Cu, Cu–Zn–Pb to Pb–Zn–Ag. The underlying rock of the semi-horizontal orebodies has pervasively sericite–pyrite–quartz alteration; comparatively, the overlying is little altered. Ores are dominantly composed of sulfides, lacking sulfate and Fe-oxides, suggesting a very low SO42− concentration in the hydrothermal solution.The host andesitic tuff and basalt show pattern of fractionated rare earth elements (REE) and the enrichment in large ion lithophile elements (LILE; e.g., Rb, Th, U and light REE) and most high field strength elements (HFSE; e.g., Nb, Ta, Hf and Zr). These features are similar to those of oceanic island basalt. The higher REE fractionation and the greater enrichment of LILE (includes light REE) in the andesitic tuffs compared to those in the basalts comply with a fractionational crystallization process in a shallow magma chamber. The δ34S‰ (CDT) of the sulfides ranges from −2.1 to 3.5‰ with an average of 0.2‰. The limited variation of δ34S‰ near zero implies that the sulfur was derived via leaching of the footwall volcanic rocks and/or degassing directly from a magma chamber. Lead isotopic compositions of sulfides also have a small range. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb are 18.486–18.684, 15.668–15.712 and 38.725–39.024, respectively, indicating an extremely radiogenic feature similar to the host volcanic rocks. Previous fluid inclusion investigations revealed that ore fluid had high salinity, high temperature and the H–O–C isotopic compositions close to the primary magmatic hydrothermal. Our S–Pb isotopic analysis together with the fluid inclusion study, are supportive to the magmatic degassing genesis for this deposit. The vertical zonation of metal species, occurrence of laminated carbonaceous-sulfidic chert and lack of alteration in the hanging wall imply that the orebodies were formed via seafloor sulfide precipitation instead of sub-seafloor replacement. The occurrence of black shale intercalated with sulfide lenses and the carbonaceous-sulfidic chert caps, especially the absence of sulfate and other oxidized facies in the ores indicate a compelling local anoxic environment for mineral precipitation. This anoxic environment was caused by the venting of magmatic fluids characterized by high temperature, high salinity, metal-charged (Fe, Cu, Pb, Zn and Ag) and H2S-rich. The repetitive activity of magma degassing in the waning stage of volcanic eruption corresponded to the stacked structure of massive sulfide lenses within the top layer in a volcanic cyclothem. The enormous base metal enrichment and highly radiogenic lead isotopes at Laochang are explained to reflect the incorporation of a recycled upper continental crust component into the mantle source for the ore-bearing volcanic rocks during the evolution of Tethyan ocean.