Neotethyan Ophiolites and Their Geodynamic Evolution During the Mesozoic: A Global Overview

Neotethyan ophiolites evolved in multiple seaways separated by Gondwana–derived ribbon continents within an eastward widening, latitudinal oceanic realm(Neotethys) throughout the Mesozoic. Opening and closure of these seaways were diachronous events, resulting in E–W variations in the timing of oceanic crust production and ophiolite emplacement. The Neotethyan ophiolites are highly diverse in their crustal–mantle structures and compositions, isotopic fingerprints, and sedimentary cover types, pointing to major differences in their mantle melt sources and tectonic and paleogeographic settings of magmatic construction(Dilek and Furnes, 2019). The Jurassic Western Alpine and Ligurian ophiolites in Europe and their counterparts in southern and northern Iberia formed in a narrow basin(Western Tethys) that developed between Europe and North Africa–Adria–Iberia. Their peridotites represent exhumed, continental lithospheric mantle, and the ophiolites display a Hess–type oceanic crustal architecture with MORB geochemical signatures(Dilek and Furnes, 2011). All these ophiolites were incorporated into continental margins from the downgoing oceanic lithosphere of the Western Tethys. Triassic, Jurassic and Cretaceous ophiolites east of Adria formed in different Neotethyan seaways(Dilek et al., 1990), and their rift–drift, seafloor spreading and suprasubduction zone(SSZ) magmatic construction involved multiple episodes of melting, depletion and refertilization of previously or actively subduction metasomatized mantle sources. Deep mantle recycling processes through subduction zone tectonics and/or plume activities played a major role in their melt evolution, and in the incorporation of mantle transition zone(MTZ) materials into their peridotites(Fig. 1;Dilek and Yang, 2018;Xiong et al., 2019). Tectonic mélanges structurally beneath these ophiolites include Permo–Triassic, OIB–type extrusive rocks, indicating that the initial dismantling of the Pangea supercontinent that led to the opening of the Triassic and Jurassic ocean basins within the Neotethyan realm was associated with plume magmatism(Dilek, 2003 a;Yang and Dilek, 2015). This plume signature is absent in the Permo–Triassic magmatic record of the Western Tethys to the west. The Cretaceous ophiolites around the Arabia(Dilek et al., 1990;Dilek and Delaloye, 1992;Dilek and Eddy,1992) and India sub-continents(Fareeduddin and Dilek, 2015) occur discontinuously along a ~9000-km-long belt from SW Anatolia to SE Tibet and Indo-China. The majority of these ophiolites have a Penrose–type oceanic crustal architecture(Dilek, 2003 b) and display SSZ geochemical affinities, complete with a MORB–IAT–BON progression of their chemo-stratigraphy(Fig. 1;Dilek and Thy, 1998;Dilek et al., 1999;Dilek and Furnes, 2014;Saccani et al., 2018). They evolved above a N–dipping, Trans–Tethyan subduction–accretion system that was situated in sub-tropical latitudes within the Neotethyan realm. The Trans–Tethyan subduction–accretion system was segmented into two major domains(Western and Eastern domains) by the NNE–SSW–oriented, sinistral Chaman–Omach–Nal transform fault plate boundary. This Cretaceous intraoceanic arc–trench system was analogous to the modern Izu–Bonin–Mariana(IBM) and Tonga arc–trench systems in the western Pacific in terms of its size. Diachronous collisions of the Arabia and India sub-continents with this segmented Trans-Tethyan arc–trench system resulted in the southward emplacement of the SSZ Neotethyan ophiolites onto their passive margins in the latest Mesozoic(Dilek and Furnes, 2019). A separate N–dipping subduction system, dipping beneath Eurasia to the north during much of the Jurassic and Cretaceous, was consuming the Neotethyan oceanic lithosphere and was responsible for the construction of a composite magmatic arc belt extending discontinuously from Southern Tibet to Northern Iran. Slab rollback along this northern subduction system produced locally developed forearc–backarc oceanic lithosphere that was subsequently collapsed into the southern margin of Eurasia. The existence of these two contemporaneous, Ndipping subduction systems within Neotethys led to its rapid contraction and the fast convergence of India towards Eurasia during the late Mesozoic–early Cenozoic(Dilek and Furnes, 2019). It was the collision with Eurasia of the India sub-continent with the accreted ophiolites around its periphery in the Late Paleogene that produced the Himalayan orogeny.

Late Triassic sedimentary records in the northern Tethyan Himalaya:Tectonic link with Greater India

The Upper Triassic flysch sediments(Nieru Formation and Langjiexue Group)exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalayan orogen.This work reports new detrital zircon U-Pb ages and whole-rock geochemical data for clastic rocks from flysch strata in the Shannan area.The mineral modal composition data suggest that these units were mainly sourced from recycled orogen provenances.The chemical compositions of the sandstones in the strata are similar to the chemical composition of upper continental crust.These rocks have relatively low Chemical Index of Alteration values(with an average of 62)and Index of Compositional Variability values(0.69),indicating that they experienced weak weathering and were mainly derived from a mature source.The geochemical compositions of the Upper Triassic strata are similar to those of graywackes from continental island arcs and are indicative of an acidicintermediate igneous source.Furthermore,hornblende and feldspar experienced decomposition in the provenance,and the sediment became enriched in zircon and monazite during sediment transport.The detrital zircons in the strata feature two main age peaks at 225-275 Ma and 500-600 Ma,nearly continuous Paleoproterozoic to Neoproterozoic ages,and a broad inconspicuous cluster in the Tonian-Stenian(800-1200 Ma).The detrital zircons from the Upper Triassic sandstones in the study area lack peaks at 300-325 Ma(characteristic of the Lhasa block)and 1150-1200 Ma(characteristic of the Lhasa and West Australia blocks).Therefore,neither the Lhasa block nor the West Australia blocks likely acted as the main provenance of the Upper Triassic strata.Newly discovered Permian-Triassic basalt and mafic dikes in the Himalayas could have provided the 225-275 Ma detrital zircons.Therefore,Indian and Himalayan units were the main provenances of the flysch strata.The Tethyan Himalaya was part of the northern passive margin and was not an exotic terrane separated from India during the Permian to Early Cretaceous.This evidence suggests that the Neo-Tethyan ocean opened prior to the Late Triassic and that the Upper Triassic deposits were derived from continental crustal fragments adjacent to the northern passive continental margin of Greater India.

Basement of the South China Sea Area:Tracing the Tethyan Realm

The basement of the South China Sea（SCS）and adjacent areas can be divided into six divisions（regions）-Paleozoic Erathem graben-faulted basement division in Beibu Gulf,Paleozoic Erathem strike-slip pull-apart in Yinggehai waters,Paleozoic Erathem faulted-depression in eastern Hainan,Paleozoic Erathem rifted in northern Xisha（Paracel）,Paleozoic Erathem strike-slip extending in southern Xisha,and Paleozoic-Mesozoic Erathem extending in Nansha Islands（Spratly）waters.The Pre-Cenozoic basement in the SCS and Yunkai continental area are coeval within the Tethyan tectonic domain in the Pre-Cenozoic Period.They are formed on the background of the Paleo-Tethyan tectonic domain,and are important components of the Eastern Tethyan multi-island-ocean system.Three branches of the Eastern Paleo-Tethys tectonic domain,North Yunkai,North Hainan,and South Hainan sea basins,have evolved into the North Yunkai,North Hainan,and South Hainan suture zones, respectively.This shows a distinctive feature of localization for the Pre-Cenozoic basement.The Qiongnan（i.e.South Hainan）Suture Zone on the northern margin of the South China Sea can be considered the vestige of the principal ocean basin of Paleo-Tethys,and connected with the suture zone of the Longmucuo-Shuanghu belt-Bitu belt-Changning-Menglian-Bentong-Raub belt,the south extension of Bitu-Changning-Menglian-Ching Mai belt-Chanthaburi-Raub-Bentong belt on the west of South China Sea,and with the Lianhua-Taidong suture zone（a fault along the east side of Longitudinal Valley in Taiwan）-Hida LP/HT（low pressure-high temperature）metamorphic belt-Hida -marginal HP/LT metamorphic belt in southwestern Honshu of Japan,on the east of the South China Sea.The Qiongbei（North Hainan）suture zone may eastwards extended along the Wangwu-Wenjiao fault zone,and connects with the Lufeng-Dapu-Zhenghe-Shangyu（Lianhuashan）deep fault zone through the Pearl River Mouth Basin.The Meso-Tethys developed on the south of the South China Sea.The Nansha Trough may be considered the vestige of the northern shelf of the Meso-Tethys. The oceanic crust of the Meso-Tethys has southwards subducted along the subduction-collision-thrust southern margin of the Nansha Trough with a subduction-pole opposite to those of the Yarlung Zangbo-Mytkyina-Bago zone on the west of the South China Sea,and the Meso-Tethyan（e.g.Northern Chichibu Ocean of the Meso-Tethys）suture zone＂Butsozo tectonic line＂in the outer belt of the Jurassic-Early Cretaceous terrene group in southwest Japan,on the east of the South China Sea.

Geological Features of the Eastern Sector of the Bangong Co-Nujiang River Suture Zone:Tethyan Evolution

According to an analysis of the geological features in the eastern sector of the Bangong Co-Nujiang River suture zone, the Tethyan evolution can be divided into three stages. (1) The Embryo-Tethyan stage (Pz1): An immature volcanic arc developed in Taniantaweng (Tanen Taunggyi) Range, indicating the existence of an Embryo-Tethyan ocean. (2) The Palaeo-Tethyan stage (C-T2: During the Carboniferous the northern side of the Taniantaweng Range was the main domain of the Palaeo-Tethyan ocean, in which developed flysch sediments intercalated with bimodal volcanic rocks and oceanic tholeiite, and Pemian-Early Triassic are granites were superimposed on the Taniantaweng magmatic are; on the southern side the Dêngqên-Nujiang zone started secondary extension during the Carboniferous, in which the Nujiang ophiolite developed, and the Palaeo-Tethyan ocean closed before the Middle Triassic. (3) The Neo-Tethyan stage (T3-E): During the Late Triassic the Dêngqên zone developed into a relatively matural ocean basin, in which the Dêngqên ophiolite was formed. By the end of the Triassic intraocean subduction occurred, and the ocean domain was reduced gradually, and collided and closed by the end of the Early Jurassic, forming the Yazong mélange; then the Tethyan ocean was completely closed.

Evolution of the Madrean-Tethyan disjunctions and the North and South American amphitropical disjunctions in plants

The present paper reviews advances in the study of two major intercontinental disjunct biogeographic patterns： （i） between Eurasian and western North American deserts with the Mediterranean climate （the Madrean- Tethyan disjunctions）; and （ii） between the temperate regions of North and South America （the amphitropical disjunctions）. Both disjunct patterns have multiple times of origin. The amphitropical disjunctions have largely resulted from long-distance dispersal, primarily from the Miocene to the Holocene, with available data indicating that most lineages dispersed from North to South America. Results of recent studies on the Mediterranean disjuncts between the deserts of Eurasia and western North America support the multiple modes of origin and are mostly consistent with hypotheses of long-distance dispersal and the North Atlantic migration. Axelrod＇s Madrean-Tethyan hypothesis, which implies vicariance between the two regions in the early Tertiary, has been favored by a few studies. The Beringian migration corridor for semiarid taxa is also supported in some cases.

Zircon SHRIMP U–Pb age of Late Jurassic OIB-type volcanic rocks from the Tethyan Himalaya: constraints on the initial activity time of the Kerguelen mantle plume

This work presents zircon U–Pb age and wholerock geochemical data for the volcanic rocks from the Lakang Formation in the southeastern Tethyan Himalaya and represents the initial activity of the Kerguelen mantle plume. SHRIMP U–Pb dating of zircons from the volcanic rocks yielded a ^(206) Pb/^(238) U age of 147 ± 2 Ma that reflects the time of Late Jurassic magmatism. Whole rock analyses of major and trace elements show that the volcanic rocks are characterized by high content of Ti O_2(2.62 wt%–4.25 wt%) and P_2O_5(0.38 wt%–0.68 wt%), highly fractionated in LREE/HREE [(La/Yb)N= 5.35–8.31] with no obvious anomaly of Eu, and HFSE enrichment with no obvious anomaly of Nb and Ta, which are similar to those of ocean island basalts and tholeiitic basaltic andesites indicating a mantle plume origin. The Kerguelen mantle plume produced a massive amount of magmatic rocks from Early Cretaceous to the present, which widely dispersed from their original localities of emplacement due to the changing motions of the Antarctic, Australian, and Indian plates. However, our new geochronological and geochemical results indicate that the Kerguelen mantle plume started from the Late Jurassic. Furthermore, we suggest that the Kerguelen mantle plume may played a significant role in the breakup of eastern Gondwanaland according to the available geochronological, geochemical and paleomagnetic data.

TECTONIC SETTING AND METALLOGENESIS OF THE PRINCIPAL SECTORS OF THE TETHYAN EURASIAN METALLOGENIC BELT

Three global metallogenic belts were formed in the world during Mesozoic and post Mesozoic times. Two of them are situated along the western and eastern Pacific margins, and the third one——the Tethyan Eurasian metallogenic belt (TEMB) is related to the domain of Eurasian plate and flanked on the south by the Afro Arabian and Indian plates.The general tectonic evolution of the realm where the TEMB was formed is closely connected with the history of Tethys. The emplacement of ore deposits and the development of regional metallogenic units are related to a definitive time interval and to specific tectonic settings such as: (1) Intracontinental rifting along the northern margin of Gondwana and/or fragments already separated; (2) Oceanic environments (i.e. ophiolite complexes and ocean floor sediments) host podiform chromite deposits, volcano sedimentary cupriferous pyrite deposits (Cyprus type), stratiform manganese deposits, and sporadically PGE deposits; (3) Subduction related settings involve mainly porphyry copper deposits, hydrothermal massive sulphide polymetallic deposits, and epithermal deposits. So far identified mineralization of porphyry copper exceeds in the TEMB over 100 million tons of copper metal; and (4) Collision and post collision continent continent setting includes deposits of lead zinc, antimony, gold, in some sectors tin deposits, as well. The giant deposits of Li pegmatite occur sporadically. The TEMB is almost a continuously mineralized belt, but within it, some sectors display specific features of tectonic settings, association of elements, minerals and morphogenetic types of mineralization.

Late Cretaceous Adakitic Granites of the Southeastern Tibetan Plateau: Garnet Fractional Crystallization of Arc-Like Magmas at the Thickened Neo-Tethyan Continental Margin

The tectonic setting of Cretaceous granitoids in the southeastern Tibet Plateau,east of the Eastern Himalaya Syntax,is debated.Exploration and mining of the Laba Mo–Cu porphyry-type deposit in the area has revealed Late Cretaceous granites.New and previously published zircon U–Pb dating indicate that the Laba granite crystallized at 89–85 Ma.Bulk-rock geochemistry,Sr–Nd isotopic data and in situ zircon Hf isotopic data indicate that the granite is adakitic and was formed by partial melting of thickened lower crust.The Ca,Fe,and Al contents decrease with increasing SiO2 content.These and other geochemical characteristics indicate that fractional crystallization of garnet under high-pressure conditions resulted in the adakitic nature of the Laba granite.Cretaceous granitoids are widespread throughout the Tibetan Plateau including its southeastern area,forming an intact curved belt along the southern margin of Eurasia.This belt is curved due to indenting by the Indian continent during Cenozoic,but strikes parallel to both the Indus–Yarlung suture zone and the Main Frontal Thrust belt.It is therefore likely that Cretaceous granitoids in both the Gangdese and southeastern Tibetan Plateau areas resulted from subduction of Neo-Tethyan lithosphere.

Multiple Phases of Mafic Magmatism in Gyangze-Kangma Area: Implications for the Tectonic Evolution of Eastern Tethyan Himalaya

A number of E-W trending subparallel mafic dikes of diabase composition occurred in Gyangze-Kangma area,eastern Tethyan Himalaya,southern Tibet.They intruded into the Tethyan Himalaya sedimentary sequence.Whether they belong to the;32 Ma Comei LIP（Zhu et al.,2009）or

Elusive Cenozoic Metamorphism in Mafic Dike Swarms within the Tethyan Himalaya, Southern Tibet

Mafic dike swarms are well-developed within the Tethyan Himalaya,southern Tibet,in response to the breakup of Gondwana supercontinent,seafloor spreading of the Tethyan Ocean,and forearc hyperextension during the

TERTIARY BLOCK ROTATIONS AND PYRRHOTITE/ MAGNETITE GEOTHERMOMETRY IN THE TETHYAN HIMALAYA(SHIAR KHOLA,CENTRAL NEPAL)

In Mesozoic carbonates of the Tethyan Himalayas two characteristic remanent magnetisations(ChRM\-1 and ChRM\-2)were identified by their unblocking spectra.The ChRM\-1 is carried by pyrrhotite(unblocking spectra:270～340℃),acquired as a secondary thermoremanent magnetisation (TRM) during exhumation and cooling.The ChRM\-2 is carried by magnetite (unblocking spectra:430～580℃).A primary origin is indicated by calcite twin geothermometry and remanences consistent with the expected direction.Along an E—W profile of 10km length the ratio of remanence intensity of pyrrhotite to magnetite ( R PYR/MAG )changes systematically (from 0 38 to 1 00,Fig.1).It is known that pyrrhotite is formed in marly carbonates during low\|grade metamorphism (Rochette 1987).This occurs at the expense of magnetite.Thus the ratio R PYR/MAG is related to metamorphic temperatures and can be used as a geothermometer for temperatures≤300℃ in low\|grade metamorphic carbonates where other methods are rare.Stable remanence directions were used to estimate the amount of block rotation around vertical and horizontal axes(i.e.Klootwijk et al.1985,Appel et al.1991 & 1995).In the Shiar area the pyrrhotite remanence directions follow a small\|circle distribution with a best fit parallel to the N—S direction(Fig.2).

RECORD OF BLOCK ROTATION AND MAGNETIC FIELD REVERSALS IN THE TETHYAN HIMALAYA(HIDDEN VALLEY,CENTRAL NEPAL)

Metasediments from the Tethyan Himalaya (TH) were sampled for paleomagnetic studies in several areas. In this paper, we will present the first results from Carboniferous and Early Triassic marly limestones from Hidden Valley (Central Nepal).. The paleomagnetic directions reflect a Tertiary overprint probably synchronous with the metamorphism. In this area, the metamorphic conditions reached during Tertiary are poorly constrained. Temperatures are probably in between 300 and 400℃. The age of the thermal event is still debated. No geochronological data is available in this area. Previously published geochronological data from the northern part of TH metasediments in India ranges from 47 to 42Ma (Ar/Ar Illite) after Weissman et al. (1999) and Bonhomme and Garzanti (1991). While in the southern part (close to HHC), biotite Ar/Ar data ranges from 30 to 26Ma in Marsyandi Valley (Coleman and Hodges, 1998) and muscovite Ar/Ar ranges from 18 to 12Ma in the upper Kali Gandaki Valley (Godin et al., 1998).. In this context, the age of the magnetization can′t be defined with precision.

Fingerprints of the Kerguelen Mantle Plume in Southern Tibet: Evidence from Early Cretaceous Magmatism in the Tethyan Himalaya

Early Cretaceous magmatism suggested to be related with the Kerguelen mantle plume has been reported in both the eastern and western Tethyan Himalayan terrane.Coeval magmatism(133-138 Ma)recorded by hypabyssal intrusive rocks have been recently discovered in the central Tethyan Himalaya(TH).The hypabyssal intrusions are dominated by OIB-like basaltic rocks intruded by later porphyritic/ophitic intermediate rocks and are characterized by strongly light rare earth element enrichment and prominent Na-Ta depletion and Pb enrichment.The basaltic rocks have low 143Nd/144Nd ratios ranging from 0.512365 to 0.512476 but relatively high 87Sr/86Sr ratios ranging from 0.708185 to 0.708966.TheεNd(t)ratios of the basaltic rocks are between-4.33 and-2.20 and initial 87Sr/86Sr ratios are 0.707807 to 0.708557.Geochemical data demonstrate that these rocks have experienced combined crustal assimilation and fractional crystallization processes.Magmatic zircons from the hypabyssal rocks exclusively have negativeεHf(t)values ranging from-0.7 to-12.7,suggestive of assimilation of crustal material.Zircons from these hypabyssal rocks have UPb ages ranging from 130 to 147 Ma.Inherited zircons have UPb ages from 397 to 2495 Ma.All the zircons are characterized by negativeεHf(t)values.The Jiding ocean island basalt(OIB)-like magmatism is geochemically and geochronologically comparable with that in the western and eastern Tethyan Himalaya,indicating widespread OIB-like magmatism in the northern margin of Greater India during the Cretaceous.Collectively,these rocks can be correlated with other early Cretaceous magmatism in western Australia and northern Antarctica.Considering the similarities,we suggest that the Jiding hypabyssal rocks are also genetically related to Kerguelen plume.Within the Yarlung Zangbo Suture Zone(YZSZ),there are also numerous occurrences of OIB-like rocks derived from mantle sources different from those of N-MORB-like magmas.The OIB-like magmatism in the YZSZ is nearly coeval with that in the TH,and the two are geochemically similar.We suggest that the OIB-like magmatism in the Neo-Tethyan ocean and the northern margin of Greater India may represent the dispersed fingerprints of the Kerguelen plume preserved in southern Tibet,China.

Tectono-magmatic evolution of Tethyan oceanic lithosphere in supra subduction zone fore arc regime:Geochemical fingerprints from crust-mantle sections of Naga Hills Ophiolite

The Naga Hills Ophiolite(NHO)belt in the Indo-Myanmar range(IMR)represents a segment of Tethyan oceanic crust and upper mantle that was involved in an eastward convergence and collision of the Indian Plate with the Burmese Plate during the Late Cretaceous-Eocene.Here,we present a detailed petrological and geochemical account for the mantle and crustal sections of NHO,northeastern India to address(i)the mantle processes and tectonic regimes involved in their genesis and(ii)their coherence in terms of the thermo-tectonic evolution of Tethyan oceanic crust and upper mantle.The NHO suite comprises well preserved crustal and mantle sections discretely exposed at Moki,Ziphu,Molen,Washelo and Lacham areas.The ultramafic-mafic lithologies of NHO are mineralogically composed of variable proportions of olivine,orthopyroxene,clinopyroxene and plagioclase.The primary igneous textures for the mantle peridotites have been overprinted by extensive serpentinisation whereas the crustal section rocks reflect crystal cumulation in a magma chamber.Chondrite normalised REE profiles for the cumulate peridotite-olivine gabbro-gabbro assemblage constituting the crustal section of NHO show flat to depleted LREE patterns consistent with their generation from depleted MORB-type precursor melt in an extensional tectonic setting,while the mantle peridotites depict U-shaped REE patterns marked by relative enrichment of LREE and HREE over MREE.These features collectively imply a dual role of depleted MORB-type and enriched arc-type mantle components for their genesis with imprints of melt-rock and fluid-rock interactions.Tectonically,studied lithologies from NHO correspond to a boninitic to slab-proximal Island Arc Tholeiite affinity thereby conforming to an intraoceanic supra subduction zone(SSZ)fore-arc regime coherent with the subduction initiation process.The geochemical attributes for the crustal and mantle sections of NHO as mirrored by Zr/Hf,Zr/Sm,Nb/Ta,Zr/Nb,Nb/U,Ba/Nb,Ba/Th,Ba/La and Nd/Hf ratios propound a two-stage petrogenetic process:(i)a depleted fore arc basalt(FAB)type tholeiitic melt parental to the crustal lithologies was extracted from the upwelling asthenospheric mantle at SSZ fore-arc extensional regime thereby rendering a refractory residual upper mantle;(ii)the crust and upper mantle of the SSZ fore arc were progressively refertilised by boninitic melts generated in response to subduction initiation and slab-dehydration.The vestiges of Tethyan oceanic lithosphere preserved in NHO represent an accreted intra-oceanic fore arc crust and upper mantle section which records a transitional geodynamic evolution in a SSZ regime marked by subduction initiation,fore arc extension and arc-continent accretion.

Permo–Triassic and Liassic Tethyan Oceanic Tracts within the Pontide Belt Along the Southern Margin of Eurasia, Northern Anatolia

The Pontide belt in northern Turkey includes three major tectonic terranes,the Strandja Massif（Sj M）,and the Istanbul（ISZ）and Sakarya Zones（SZ）(Fig.1).We present new age and geochemical data from ophiolites and ophiolitic mélanges within the Sakarya Zone and show that these mafic–ultramafic rocks are the remnants of Tethyan oceanic lithosphere formed in different tectonic settings.The main ophiolite occurrences investigated in this study along the Karakaya Suture（KS）are associated with the latest Triassic Cimmeride orogeny,and in the Küre–Yusufeli ophiolite belt are part of the Alpide orogeny.The Karakaya Suture Zone ophiolites in northern west Turkey are comprised mainly of the Denizgoren（?anakkale）ophiolite,Bo?azk?y（Bursa）,Geyve（Sakarya）,Almac?k（Düzce）and?ele（Bolu）metaophiolites.The Denizg?ren ophiolite largely contains upper mantle peridotites,which are equivalents of the Permo–Triassic Lesvos peridotites and mélange units farther SW in the northern Aegean Sea.The Bo?azk?y ophiolite includes serpentinite and metagabbro,and the Almac?k and Geyve ophiolites display an almost complete Penrose–type sequence consisting of serpentinizeduppermantleperidotites,cumulate ultramafic–mafic rocks,isotropic gabbros,dolerite and plagiogranite dikes,and extrusive rocks.U–Pb zircon dating of plagiogranite dikes from?ele has revealed an igneous age of 260 Ma,and 255,235,227 Ma from Almac?k（Bozkurt et al.,2012a,b）.Consistent with the previouslypublished Permo–Triassic age,we obtained a 268.4±6.3 Ma U–Pb zircon age from a plagiogranite dike within the Almacik ophiolite to the west.This KS ophiolite belt containing the?ele,Almac?k,Geyve ophiolites within the SZ extends westward into the Armutlu Peninsula and then into the Biga Peninsula（i.e.Denizg?ren ophiolite）and most likely connects with the remnants of the Triassic Meliata–Meliac ocean basin（Stampfli and Borel,2002）in the Balkan Peninsula.The KS ophiolites also continue eastward within the Pontide Belt into the Elekda?ophiolite（eastern Kastamonu）and then to the Refahiye ophiolite in NE Anatolia.Triassic granites in the SZ represent a magmatic arc that formed as a result of the northward subduction of the Izmir–Ankara–Erzincan oceanic lithosphere existing during the late Paleozoic through Cretaceous（Sarifakioglu et al.,2014）beneath the Pontides.We obtained a U–Pb zircon age of 231±2 Ma from a metagranitic intrusion into the Variscan basement of the SZ in the Kastamonu region of the central Pontides.This metagranite is enriched in LILE（Rb:63 ppm;Ba:65 ppm;Sr:200 ppm）and depleted in HFSE（Y:12.58 ppm;Yb:1.26 ppm;Ti O2:0.2 wt.%;Nb:7.6 ppm;Hf:3.9 ppm）,characterizing it as subduction–related calc-alkaline pluton.Lead（3.9 ppm）,U（1.6 ppm）and Ce（59 ppm）contents are interpreted as evidence for contamination by continental crust.The Küre basin to the north opened during the late Triassic to Liassic,following a backarc rifting episode in the central Pontides.Metabasic dike intrusions in the Devrekani metamorphic massif represent the first magmatic stage of this backarc rifting event.Whole-rock 40Ar-39Ar dating ofthe metabasic dikes has yielded cooling ages of 160.5±1.2 Ma. We infer that this age was reset due to thermal heating during the emplacement of the Middle Jurassic granitoids as the Küre oceanic basin was closing. The Küre ophiolite contains upper mantle peridotites and oceanic crustal rocks composed mainly of pillow–massive–breccia basalts, dacitic and rhyolitic lavas–tuffs, diabase dyke swarms, massive gabbros and a limited extent mafic cumulates. We obtained 182.6±1.9 Ma as a whole-rock 40Ar-39 Ar age from a pillow basalt and a U–Pb zircon age of 171±1 Ma from the granitic intrusion cross-cutting the peridotites. The easternmost representatives of the Küre ophiolite occur in the Yusufeli（Artvin） area in the eastern part of the Pontide belt. Here, oceanic crustal rocks are tectonically related to metamorphic rocks of the Variscan basement of the SZ. The ophiolitic crustal rocks contain isotropic gabbro and mafic and felsic dikes. Serpentinized upper mantle peridotites are scarce. Pillow lava basalts are overlain by a thick metasandstone–metashale association with locally foliated meta–lava and some manganiferous chert and mudstone interlayers. We obtained a U–Pb zircon age of 172.5±1.4 Ma from the granitic intrusion cross-cutting the Yusufeli ophiolite and of 181.9±0.9 Ma from a felsic dike（plagiogranite） in the Yusufeli ophiolite. The Middle Jurassic granites are related to the closure of the Küre-Yusufeli marginal ocean basin. The Küre and Yusufeli ophiolites have been previously interpreted as the remnants of the Paleotethys or the Intra-Pontide Ocean. However, we posit that these ophiolites represent amarginal, short-lived（;0 Ma） ocean basin, which opened during the late Triassic through Liassic, and then closed in Dogger. This oceanic lithosphere is similar to the Evros ophiolite in the northeastern Greece in terms of its ages and geochemical characteristics.

Compositions & Melt Evolution of Upper Mantle Peridotites in the Tethyan Ophiolites

The Jurassic–Cretaceous ophiolites in the Alpine–Himalayan orogenic belt represent fragments of oceanic lithosphere,developed in different seaways separated by Gondwana–derived ribbon continents within a broad

Origin of the DUPAL anomaly in the Tethyan mantle domain and its geodynamic significance

Mantle heterogeneity has revealed systematic differences in Pb isotopic compositions between the Indian OceanSouth Atlantic mantle in the Southern Hemisphere and the Pacific Ocean-North Atlantic mantle in the Northern Hemisphere.This large-scale difference in mantle isotopes in the Southern Hemisphere is known as the DUPAL anomaly,but its origin remains controversial.Based on a systematic review of the Nd-Pb isotopic evolution of the Tethyan mantle domain,this study identified the long-term presence of the DUPAL anomaly in this domain since the early Paleozoic,characterized by long-term and high mantle thorium/uranium(Th/U)ratios.By comparing the Nd-Pb isotopic compositions of the Tethyan mantle domain with the Panthalassic-Pacific mantle domain(the Paleo-Asian,Paleo-Pacific,and modern Pacific oceans),it is shown that the mantle initially had low Th/U features due to early Earth crust-mantle differentiation,with the crust having high Th/U ratios.As such,the mantle initially had uniformly low Th/U ratios that were inherited throughout the Panthalassic-Pacific mantle domain.However,the plate tectonics and continental collisions in the Tethyan domain affected its characteristics,leading to the long-term and large-scale DUPAL anomaly.During the opening of and subduction in the Tethys Ocean,Gondwanaland fragmentation and frequent continent-continent collisions led to long-term and extensive crust-mantle interactions and the continuous input of highTh/U mantle sources,which thus modified the mantle.This process formed not only the unique DUPAL anomaly in the Tethyan mantle domain,but also the Tethyan tectonic domain dominated by continental collisions.Moreover,the high DUPAL anomaly in the Proto-and Paleo-Tethyan mantle domains records the effects of mantle plumes,which might have occurred primarily during the formation of the Proto-and Paleo-Tethys oceans during the early evolution of the Tethyan domain.Therefore,the inherent coupling of mantle domain properties and plate tectonic mechanisms provides important insights for understanding plate tectonics and geodynamic processes in the Tethyan domain.

The influence of Tethyan evolution on changes of the Earth's past environment

Understanding changes in Earth's past can provide valuable insights into prediction of its future.An example is the interactions between the internal and external spheres of Earth.The cyclical northward breakup-drift of Gondwana,driven by the opening and closure of Proto-,Paleo-,and Neo-Tethyan oceans,facilitated the transfer of landmasses from the southern to the northern hemisphere,traversing the tropic region.We have observed a compelling correlation between episodic increases in landmass area within the tropic regions(those lying at less than 20°latitude)and a subsequent temperature decrease during the three major glacial periods in the last 500 million years.This phenomenon can be attributed to low latitude regions receiving more solar energy influx on Earth's surface than high latitude areas.In addition,an increase of landmass in tropic regions(low latitude)attenuates the net energy absorption by the Earth's surface,consequently impeding the conduction and convection of absorbed energy toward the poles.The result is a decrease in global surface temperature.The tropic regions,benefiting from abundant sunlight,create an ideal environment for the proliferation of marine plankton species.These species are important in the generation of organic-rich sediment.Massive biological debris is therefore deposited on continental margins when a continent drifts across the tropic region.This creates favorable conditions for future hydrocarbon and reservoir formation.Northward subduction of organic-rich sediments during the closure of the Tethyan oceans results in the generation of mafic arc magmas with low oxygen fugacity.This chemical environment helps the mineralization of reduced-type ore deposits such as tungsten,tin,and lithium.Subducted-driven plate tectonics in the Tethys realm changes the distribution of oceans and landmass,subsequently affecting the balance and distribution of solar energy across Earth's surface.These changes trigger consequential environmental shifts which in turn,impact the composition of rock and mineral along the Eurasian margin due to subduction.Consequently,the Tethyan realm and its history is an ideal natural laboratory for comprehending the processes and changes of the entire Earth's system.

Enrichment of Mississippi Valley-type(MVT) deposits in the Tethyan domain linked to organic matter-rich sediments

The Tethyan domain hosts the world's most abundant hydrocarbon and Mississippi Valley-type(MVT) Pb-Zn resources. The relations among organic matter-rich sediments, MVT Pb-Zn mineralization, and the Tethyan tectonic evolution history are an important scientific issue. The data of paleogeographic reconstruction indicate that the Proto-, Paleo-, and NeoTethys oceans mainly lay in low latitude areas between 30°N and 45°S. The high temperature and precipitation and the lack of sea water overturning in stagnant basins resulted in high marine biological productivity and good preservation conditions for organic matter-rich sediments. Consequently, abundant organic matter-rich sediments were developed and preserved in the Tethyan domain and thus created abundant hydrocarbon resources. Mineralization age data demonstrate that MVT deposits mainly formed during the continent-continent convergence in the late stage of the Tethyan tectonic evolution. Deposits are located in the fold-and-thrust belts and forelands of the continent-continent convergence orogen, and spatially associated with hydrocarbon basins. Organic matter-rich sediments are well developed in MVT ore districts, where hydrocarbon activity appeared earlier than or nearly simultaneous with the Pb-Zn mineralization event. Hydrocarbon activity generally began earlier than the Pb-Zn mineralization in individual deposits. Organic matter-rich sediments and hydrocarbons mainly play the role of reducing agents in the MVT Pb-Zn mineralization process. Through bacterial or thermal reduction, dissolved sulfates from sedimentary strata were reduced to generate reduced sulfur for Pb-Zn sulfide mineralization. In summary, the Tethyan oceans have long been in low latitude areas near the equator, making the Tethyan domain develop abundant organic matterrich sediments and associated hydrocarbon resources which reduce sulfates to provide sufficient reduced sulfur for MVT PbZn mineralization in the region.

Global seismic tomography reveals remnants of subducted Tethyan oceanic slabs in the deep mantle

The Tethyan evolution depicts the continuous process of landmasses separating from the Gondwana continent in the south,drifting northwards,and subsequently colliding with the continents in the north over the past 500 million years.In this process,the Tethyan oceans that formed between the landmass and the southern or northern continents underwent growth,evolution,and eventual closure with the early Cenozoic India-Eurasia collision.However,the Tethyan lithosphere did not disappear but rather continued to evolve after entering into the deep Earth.The current position,morphology,and volume of the subducted Tethyan oceanic slabs in the deep mantle record the latest moment of this continuous evolution,providing critical constraints for Tethyan studies.This paper summarizes and analyzes the results of global-scale whole-mantle seismic tomography in the past nearly two decades,revealing a northwest-southeast seismically high-velocity anomaly,which is linearly distributed at depths of 1000–2000 km beneath the Tethyan realm and referred to as the Tethyan anomaly.By searching for an optimal linear combination of previous global seismic tomographic models to best match the known subducted slabs in the upper mantle,we observe that the Tethyan anomaly extends approximately 8700 km in length and 2600 km in width,exhibiting a parallel structure with northern and southern branches.Combining geological records of oceanic subduction initiation and previous geodynamic studies,this study suggests that the main body of the Tethyan anomaly represents the remnants of the subducted Neo-Tethyan oceanic slabs,which subducted from the Late Jurassic to the early Cenozoic.The northern branch consists of subducted slabs from the Neo-Tethys beneath the southern margin of Eurasia,while the southern branch likely reflects the intra-oceanic subducted slabs of Neo-Tethys during the Cretaceous.The western portion of the Tethyan anomaly may reflect remnants of Paleo-Tethys,while the eastern portion,towards India and the Bay of Bengal,shows signs of subduction towards the core-mantle boundary.Finally,this study discusses the future prospects of whole-mantle seismic tomographic studies focusing on the Tethyan realm.