Fe Isotope Geochemistry of Hydrothermal Fe Exhalites

The sediments atop the sequence of ophiolite usually contain Fe(-Mn-Si)exhalites,chemical sediments that aremainlycomposedofamorphousFe-Mn oxy-hydroxides and chert/jasper.They were precipitated from hydrothermal fluids produced by deep leaching of basalt particularly during volcano activity or seafloor spreading.These hydrothermal Fe exhalites provide a good record for the depositional environment and the ocean environment as well.A well-preserved Phanerozoic Fe deposit,Motuosala Fe-Mn deposit,resulted from hydrothermal exhalation,was investigated for its trace element and Fe isotope geochemistry.The deposit is located in Xinjiang province,China and is hosted in a suit of Carboniferous volcano-sedimentary clastic rocks.The Fe deposit is mainly composed of massive hematite Fe oreand banded hematite-jasper ore.The hematite ore/band and jasper band were subjected to be analyzed.They are both composed mainly of Fe2O3 and Si O2,with very low contents of Al2O3 and Ti O2(<1%),indicating they werechemical precipitates with little detrital contamination.They both show slightly LREE depleted or near flat PAAS-normalised REE patterns,with positive Eu anomalies and Y anomolies,indicating that they were sourced from a mixture of high-temperature fluids and seawater.Compared to the hematite Fe ore/band,the jasper band shows higher EuSN/EuSN*but lower Y/Ho values.δ56Fe values for the hematite Fe ores are clustered around-0.3‰,similar to those for high-temperature fluids.The jasper samples show heavier Fe isotope compositions varying from-0.1‰to0.5‰,indicating that they were resulted from partial Fe precipitation.For all samples,δ56Fe values are related to Y/Ho and EuSN/EuSN*values.The results indicate that the hematite Fe ore and jasper were deposited in different environments.The jasper was deposited in a more anoxic condition with higher hydrothermal fluids/seawater ratio,probably when the hydrothermal activity was more intense;while the hematite Fe ore was deposited in a more oxic condition with lower hydrothermal fluids/seawater ratio,probably when the hydrothermal activity was weaker.

Rare earth elements(REE)and isotope composition(δ^(13)C andδ^(18)O)of manganese ores of Chiatura deposit(Georgia):features of ore formation and genesis

The rare earth elements(REE)geochemistry and the isotope(δ^(13)C,δ^(18)O)composition of manganese ores of the Chiatura(Georgia)deposit were studied.One of the major features of all types of manganese ores is negative cerium(Ce/Ce*_(PAAS))anomaly and the absence of europium(Eu/Eu*_(PAAS))anomaly.Oxide oolitic manganese ores were formed in oxic shallow marine environments.The content and distribution of REEs(in particular Ce and Eu)in these ores are connected mainly with ferrous oxides.The performed C-and O-isotope research in Mn-carbonates(oolitic and massive)has indicated that carbonate ores were formed by the participation of isotopic ally light CO_(2)which is a result of the oxidation of organic matter in the sediment strata by reducing environments of early diagenesis(and,partially,catagenesis)zone.Obtained negative cerium anomalies in the studied carbonate ores reflect the specific REE patterns in pore waters of sediments of earlier isdiagenesis zone of the Oligocene Chiatura's basin.The deficiency of cerium in this zone remains debatable and requires further study.Formation of manganese carbonates took place multistage by the input of incisional solutions of different chemistry into sea bottom waters and sediments.The absence of europium anomaly indicates about lack of hydrothermal solution input.

A Study of Sr, Nd and O Isotopes of the K-rich Melanocratic Dykes in the Late Mesozoic Gold Field in the Jiaodong Peninsula

Geologic, petrographic and petrochemical studies of the lateMesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr)i-0.70895-0.71140) and low (143Nd/144Nd)i ratios (varying from 0.51135 to 0.51231); and its δ18OsMow. whole rock values vary from +5.8‰ to +10.6‰ with a mean of +7.1‰. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced me tasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enriched mantle in its mature stage in the back-arc spreading environment. The evolution of magmas is associated with two trends, i.e., fractional crystallization and mixing with or intensive contamination by palaeo-crust materials or metamorphic rocks. The former process is evident in the gold field system of quartz-vein type, whereas the latter is dominated in the gold field system of the altered-rock type. This conclusion is very important for more detailed study of petrogenesis and mineralization through the crust-mantle interaction (exchange) in the Mesozoic in this region.

Metallogenesis and ore-forming time of the Changtuxili Mn-Ag-Pb-Zn deposit in Inner Mongolia:Evidence from C-O-S isotopes and U-Pb geochronology

This paper reports new geochronological(U-Pb) and isotope(C,O,and S) data to investigate the timing of mineralization and mode of ore genesis for the recently discovered Changtuxili Mn-Ag-Pb-Zn deposit,located on the western slopes of the southern Great Hinggan Range in NE China.The mineralization is hosted by intermediate-acidic lavas and pyroclastic rocks of the Baiyingaolao Formation.Three stages of mineralization are identified:quartz-pyrite(Stage I),galena-sphalerite-tetrahedrite-rhodochrosite(Stage II),and quartz-pyrite(Stage Ⅲ).δ13C and δ18O values for carbonate from the ore vary from-8.51‰ to-4.96‰ and 3.97‰ to 15.90‰,respectively,which are indicative of a low-temperature alteration environment.δ34SV-CDT values of sulfides range from-1.77‰ to 4.16‰ and show a trend of equilibrium fractionation(δ34SPy>δ34SSp>δ34SGn).These features indicate that pyrite,sphalerite,and galena precipitated during the period of mineralization.The alteration mineral assemblage and isotope data indicate that the weakly acidic to weakly alkaline ore-forming fluid was derived largely from meteoric water and the ore-forming elements C and S originated from magma.During the mineralization,a geochemical barrier was formed by changes in the pH of the ore-forming fluid,leading to the precipitation of rhodochrosite.On the basis of the mineralization characteristics,new isotope data,and comparison with adjacent deposits,we propose that the Changtuxili Mn-Ag-Pb-Zn deposit is an intermediate-to lowsulfidation epithermal deposit whose formation was controlled by fractures and variability in the pH of the oreforming fluid.The surrounding volcanic rocks yield zircon U-Pb ages of 160-146 Ma(Late Jurassic),indicating that the mineralization is younger than 146 Ma.

Stable isotope(δ^(13)C_(ker),δ^(13)C_(carb),δ^(18)O_(carb)) distribution along a Cambrian outcrop section in the eastern Tarim Basin,NW China and its geochemical significance

This study investigated the geochemical features of the lower Paleozoic strata of Yaerdang Mountain outcrop along with the core samples from well TD2∈ in the eastern Tarim Basin,NW China.The total organic carbon abundance,hydrocarbon-generating precursor biospecies,and stable isotope ratios of organics and carbonate(δ^(13)C_(ker),δ^(13)C_(carb) and δ^(18)O_(carb)) were comprehensively studied for their possible correlative constraints during sedimentary evolution.The results revealed that the δ^(13)C_(ker)(VPDB) of Cambrian kerogens along the outcrop section varied from-34.6‰ to-28.4‰,indicating an increasing tendency from the lower Cambrian to the upper Cambrian.This was on the whole accompanied by the variation in the δ^(13)C_(carb) and δ^(18)O_(carb) along the profile,which might be associated with the changes in the sea level and also in the compositional variation of benthic and planktonic biomass.The large variation in the stable carbon isotope ratios up to 6‰ along the outcrop section reflected the heterogeneity of the Cambrian source rocks from the eastern Tarim Basin.Hence,the ^(13)C-enriched crude oils from well TD2∈might have been derived from a localized stratum of Cambrian source rocks.The results from this study showed the possibility of multiple source kitchens in the Cambrian-lower Ordovician portion of Tarim Basin.

GEOCHEMISTRY STUDY OF GOLD SILVER DEPOSITS IN THE MIDDLE UPPER PROTEROZOIC SUBERATHEM IN SOUTHERN QINLING METALLOGENETIC ZONE

According to Ihe combinations of mctallogcnetic elements and minerals assemblages,the Au-Ag deposits in the Middle-Upper Proterozoic Suberathcm of the middle of northern margin of Yangtze Platform could be classified into four types,(l)Au-Ag-Pb-Zn type,(2)Au-Ag-Te type,(3)Au-quartz vein type,(4)Au-Ag-Pb-Zn-Ba type.The Yangpin formation and the upper Dangyuhe subformation,which belong to Wudangshan group,are regarded as favorable strata for Au-Ag mineralization by systematic assessments for Au-Ag bearing ability of the strata,as well as the felsic rocks of Bikou group.The mctallogcnetic physicochemical conditions and the stable isotopic compositions(S.Pb,H.O,C)have been studied in this paper.The sources of metallogenetic materials,origins of fluids and genesis of various deposits have also been studied.

Geochronology and petrogenesis of the mafic dykes from the Purang ophiolite:Implications for evolution of the western Yarlung-Tsangpo suture zone,southwestern Tibet

The>2000 km Indus-Yarlung Tsangpo suture zone(IYSZ)is composed of the Neo-tethys oceanic remnants,flysch units and related continental rocks,which has been regarded as the boundary between the Eurasian and Indian terranes.Among the ophiolitic complexes,the Purang ophiolite is the biggest massif in the IYSZ,and many studies have been conducted on this ophiolite.However,previous studies have mainly focused on harzburgite,clinopyroxenite and dunite.Field observations show that mafic dykes were emplaced within the Purang ophiolite.However,petrogenetic evolutions of those mafic dykes are poorly understood.In this study,we present new LA-ICP-MS zircon U-Pb dating results,whole-rock geochemistry and Sr-Nd-Hf isotope analyses for microgabbro,gabbro and dolerite dykes from the Purang ophiolite of the southwestern IYSZ,respectively.Three samples yielded zircon U-Pb ages of144.2±2.1 Ma.127.9±2.3 Ma and 126.5±0.42 Ma,suggesting two different phases of magmatic activities distinctly.Whole-rock geochemical results suggest that the gabbro samples show alkaline features marked by enrichments of light rare earth elements(LREE)and large-ion lithophile elements(LILE),as well as Nb-Ta elements,suggesting an oceanic island basalt-like(OIB-like)geochemical affinity.However,the dolerite and microgabbro samples demonstrate sub-alkaline characteristics with normal mid-oceanic ridge basalt-like(N-MORB-like)geochemical features.Three distinct mafic dykes show significant Rb element depletion.The geochemical data and Sr-Nd-Hf isotopic features suggest that the microgabbro and gabbro rocks were derived from a depleted mantle that had been metasomatized by partial melts of sediments and enriched slab-derived fluids.The dolerite was also originated from a depleted mantle marked by significantly depleted Sr-Nd-Hf compositions,which was not influenced by enriched slab-derived fluids and sediments contamination during subsequent evolution.The isotope and geochemical data and tectonic diagrams suggest a tectonic transition from a within-plate to a midoceanic ridge basalt-like(MORB-like)setting during the period from ca.144 Ma to 127 Ma.Combined with regional background and this study,we propose that these mafic dykes were formed in an oceanic back-arc basin setting.Additionally,integrated with previous studies,we suggest that the geodynamic evolution of the southwestern and central parts of the Neo-Tethys oceanic basin is comparable in Early Cretaceous.

Genesis of the Maoling gold deposit in the Liaodong Peninsula:Constraints from a combined fluid inclusion,C-H-O-S-Pb-He-Ar isotopic and geochronological studies

The large tonnage Maoling gold deposit(25 t@3.2 g/t)is located in the southwest Liaodong Peninsula,North China Craton.The deposit is hosted in the Paleoproterozoic metamorphic rocks.Four stages of mineralization were identified in the deposit:(stageⅠ)quartz-arsenopyrite±pyrite,(stageⅡ)quartz-goldarsenopyrite-pyrrhotite,(stageⅢ)quartz-gold-polymetallic sulfide,and(stageⅣ)quartz-calcitepyrrhotite.In this paper,we present fluid inclusion,C-H-O-S-Pb-He-Ar isotope data,zircon U-Pb,and gold-bearing sulfide(i.e.arsenopyrite and pyrrhotite)Rb-Sr age of the Maoling gold deposit to constrain its genesis and ore-forming mechanism.Three types of fluid inclusions were distinguished in quartzbearing veins,including liquid-rich two-phase(WL type),gas-rich two-phase(GL type),and daughter mineral-bearing fluid inclusions(S type).Fluid inclusions data show that the homogenization at temperatures 197 to 372°C for stageⅠ,126 to 319°C for stageⅡ,119 to 189°C for stageⅢ,and 115 to 183°C for stageⅣ,with corresponding salinities of 3.7 to 22.6 wt.%,4.7 to 23.2 wt.%,5.3 to 23.2 wt.%,and 1.7 to14.9 wt.%Na Cl equiv.,respectively.Fluid boiling was the critical factor controlling the gold and associated sulfide precipitation at Maoling.Hydrogen and oxygen stable isotopic analyses for quartz yielded δ^(18)O=-5.0‰ to 9.8‰ and δD=-133.5‰ to-77.0‰.Carbon stable isotopic analyses for calcite and ankerite yielded δ^(13)C=-2.3‰to-1.2‰ and O=7.9‰ to 14.1‰.The C-H-O isotope data show that the oreforming fluids were originated from magmatic water with meteoric water input during mineralization.Hydrothermal inclusions in arsenopyrite have ^(3)He/^(4)He ratios of 0.002 Ra to 0.054 Ra,and ^(40)Ar/^(36)Ar rations of 1225 to 3930,indicating that the ore-forming fluids were dominantly derived from crustal sources almost no mantle input.Sulfur isotopic values of Maoling fine-grained granite range from6.‰1 to 9.8‰,with a mean of 7.7‰,δ^(34)S values of arsenopyrite from the mineralized phyllite(host rock)range from 8.9‰ to 10.6‰,with a mean of 10.0‰,by contrast,δ^(34)S values of sulfides from ore vary between 4.3‰and 10.6‰,with a mean of 6.8‰,suggesting that sulfur was mainly originated from both the host rock and magma.Lead radioactive isotopic analyses for sulfides yielded^(206)Pb/^(204)Pb=15.830–17.103,^(207)Pb/^(204)Pb=13.397–15.548,^(208)Pb/^(204)Pb=35.478–36.683,and for Maoling fine-grained granite yielded ^(206)Pb/^(204)Pb=18.757–19.053,^(207)Pb/^(204)Pb=15.596–15.612,and ^(208)Pb/^(204)Pb=38.184–39.309,also suggesting that the ore-forming materials were mainly originated from the host rocks and magma.Zircon U-Pb dating demonstrates that the Maoling fine-grained granite was emplaced at 192.7±1.8 Ma,and the host rock(mineralized phyllite)was emplaced at some time after2065.0±27.0 Ma.Arsenopyrite and pyrrhotite give Rb–Sr isochron age of 188.7±4.5 Ma,indicating that both magmatism and mineralization occurred during the Early Jurassic.Geochronological and geochemical data,together with the regional geological history,indicate that Early Jurassic magmatism and mineralization of the Maoling gold deposit occurred during the subducting Paleo-Pacific Plate beneath Eurasia,and the Maoling gold deposit is of the intrusion-related gold deposit type.

Depositional age and tectonic environment of the Gouap banded iron formations from the Nyong group,SW Cameroon:Insights from isotopic,geochemical and geochronological studies of drillcore samples

The discovery of the Gouap banded iron formations(BIFs)-hosted iron mineralization in the northwestern of the Nyong Group(Ntem Complex)in southwestern Cameroon provides unique insights into the geology of this region.In this contribution,we firstly report detailed study of geochemistry,isotopic and geochronology of well preserved samples of the Gouap BIFs collected from diamond drillcores.The Gouap BIFs consist mainly of amphibole BIFs and amphibole-pyrite BIFs characterized by dominant Fe_(2)O_(3)+SiO_(2)contents and variable contents of CaO,MgO and SO_(3),consistent with the presence of amphibole,chlorite,epidote and pyrite,formed during amphibolite facies metamorphism and overprinted hydrothermal event.The amphibole–pyrite BIFs are typically enriched in trace and rare earth elements(REE)compared to the amphibole BIFs,suggesting the influence of detrital materials as well as secondary hydrothermal alteration.The Post Archean Australian Shale(PAAS)-normalized REE–Y profiles of the Gouap BIFs display positive La,Eu anomalies,weak negative Ce anomalies,indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow seawater.We present here the first isotopic data of BIFs within the Ntem Complex.Theδ^(30)Si_(NBS28)values of the quartz from the Gouap BIFs vary from-1.5‰to-0.3‰and from-0.8‰to-0.9‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.The quartz hasδ^(18)OV-SMOW values of 6.8‰–9.5‰(amphibole BIFs)and 9.2‰–10.6‰(amphibole–pyrite BIFs).The magnetite from the Gouap BIFs showsδ^(18)O values ranging from-3.5‰to-1.8‰and from-3‰to-1.7‰for the amphibole BIFs and amphibole–pyrite BIFs,respectively.Moreover,the pyrite grains in the amphibole–pyrite BIFs displayδ34S values of 1.1‰–1.8‰.All isotopic data of the Gouap BIFs confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic activity.According to their geochemical and isotopic characteristics,we propose that the Gouap BIFs belong to the Superior type.In situ U–Pb zircon dating of BIFs was conducted to assess the BIF depositional age based on strong evidence of zircon in thin section.The Gouap BIFs were probably deposited at 2422±50 Ma in a region where sediments extended from continental shelf to deep-water environments along craton margins like the Caue Formation of the Minas Supergroup,Brazil.The studied BIFs have experienced regional hydrothermal activity and metamorphism at 2089±8.3 Ma during the Eburnean–Transamazonian orogeny.These findings suggest a physical continuity between the protocratonic masses of both Sao Francisco and Congo continents in the Rhyacian Period.

Evolution of the 3.65-2.58 Ga Mairi Gneiss Complex,Brazil:Implications for growth of the continental crust in the São Francisco Craton

The composition and formation of the Earth’s primitive continental crust and mantle differentiation are key issues to understand and reconstruct the geodynamic terrestrial evolution,especially during the Archean.However,the scarcity of exposure to these rocks,the complexity of lithological relationships,and the high degree of superimposed deformation,especially with long-lived magmatism,make it difficult to study ancient rocks.Despite this complexity,exposures of the Archean Mairi Gneiss Complex basement unit in the São Francisco Craton offer important information about the evolution of South America’s primitive crust.Therefore,here we present field relationships,LA-ICP-SFMS zircon U-Pb ages,and LA-ICP-MCMS Lu-Hf isotope data for the recently identified Eoarchean to Neoarchean gneisses of the Mairi Complex.The Complex is composed of massive and banded gneisses with mafic members ranging from dioritic to tonalitic,and felsic members ranging from TTG(Tonalite-Trondhjemite-Granodiorite)to granitic composition.Our new data point to several magmatic episodes in the formation of the Mairi Gneiss Complex:Eoarchean(ca.3.65–3.60 Ga),early Paleoarchean(ca.3.55–3.52 Ga),middle-late Paleoarchean(ca.3.49–3.33 Ga)and Neoarchean(ca.2.74–2.58 Ga),with no records of Mesoarchean rocks.Lu-Hf data unveiled a progressive evolution of mantle differentiation and crustal recycling over time.In the Eoarchean,rocks are probably formed by the interaction between the pre-existing crust and juvenile contribution from chondritic to weakly depleted mantle sources,whereas mantle depletion played a role in the Paleoarchean,followed by greater differentiation of the crust with thickening and recycling in the middle–late Paleoarchean.A different stage of crustal growth and recycling dominated the Neoarchean,probably owing to the thickening of the continental crust by collision,continental arc growth,and mantle differentiation.

Sulfur Isotopes Geochemistry of the Nage Cu-Pb Polymetallic Deposit,Southeast Guizhou Province,China

The Nage Cu-Pb polymetallic deposit is located in the transitional zone of the Yangtze craton and cathaysia,that is the southwest of Jiangnan orogenic belt. The mainly strata are Wentong formation of Mesoproterozoic Sibo group and the Jialu formation(Qbj) ,Wuye formation(Qbw) ,Fanzhao formation(Qbf) and Gongdong formation(Qbg) of the Neoproterozoic Qingbaikou System Xiajiang group.

Lead Isotope and Rock Geochemistry of Zaibian Mafic-Ultramafic Rock,Southeast Guizhou Province,China

The Zaibian mafic-ultramafic rock is located in the transitional zone of the Yangtze craton and south China fold system,where is the southwest of Jiangnan orogenic belt(Zeng et al.,2003;Wang et al.,in press).

Zircon U–Pb dating,geochemical,and Sr–Nd–Pb–Hf isotopic constraints on the age and origin of intermediate to felsic igneous rocks at South Altyn,Xinjiang,China

As a part of a giant trending fault system in the Asian continent and one where a strong zone of left strikeslip fault is present,the Altyn Orogenic belt(AOB)has become an important focus for research.Magmatic rocks are widely distributed across the AOB.However,many investigations have focused primarily on Paleozoic igneous rocks;discussion of Mesozoic related igneous activity is often ignored.Here we present the result of studies of representative diorite and granite rocks outcropping in the AOB,within the Xinjiang Uygur Autonomous Region,South Altyn,China.We present new zircon LA-ICP-MS U-Pb age,geochemical,and Sr-Nd-Pb-Hf isotopic data for these sample suites,identifying them as typical igneous rocks formed between 238±1.5 and 238.8±1.1 Ma.The rocks that we studied fall into the alkaline series,also enriched in light rare earth elements(LREE),some large ion lithophile elements(LILE;e.g.,Rb,Ba,Sr,and K),Pb,Th and U,and depleted in heavy rare earth elements(HREE),Nb,Ta,Hf,and Ti.The granite and diorite have high initial 87Sr/86Sr ratios(0.7062-0.7114),negativeεNd(t)values(-8.8 to-11.3),εHf(t)values(-8.7 to-18.7),and relatively constant Pb isotopic ratios((206-Pb/204Pb)i=6.74-17.884,(207Pb/204Pb)i=15.51-15.58,and(208Pb/204Pb)i=35.36-38.04),respectively.This suggests that the magmas parental to these rocks were generated from the partial melting of the ancient crust.The parental magmas to these rocks experienced a degree of fractionation of plagioclase,K-feldspar,and hornblende,possibly during rapid magma ascent.Based on these studies,we propose a reasonable model for the origin of the investigated rocks from the Xinjiang Uygur Autonomous Region of South Altyn,which involves crustal thickening,lithospheric extension,and asthenosphere upwelling,that induced crustal melting.

Geochemical and Nd-Sr Isotopic Compositions of Hypabyssal Adakites in the Torud-Ahmad Abad Magmatic Belt,Northern Central Iran Zone:Analysis of Petrogenesis and Geodynamic Implications

Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt(TAMB),in the northern part of the Central Iran zone,are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood.These igneous rocks include hypabyssal dacite,trachyte,andesite,trachy-andesite,and basaltic andesite;they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene,amphibole,and plagioclase,with minor biotite and titanomagnetite;they form domal structures(plugs and stocks),dikes,and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences.Based on isotopic analysis of these intermediate to acidic rocks,initial ratios of^(143)Nd/^(144)Nd range from 0.512775 to 0.512893 and initial ratios of^(87)Sr/^(86)Sr range from 0.703746 to 0.705314,with quite positiveε_(Nd(i))values of+3.69 to+6.00.They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high-field strength elements,the SiO_(2) content is(52-62)wt.%,and Na_(2)O content>3 wt.%,Al_(2)O_(3) content>16 wt.%,Yb<1.8 ppm,and Y<18 ppm.These geological,geochemical,and Sr and Nd isotopic data are consistent with adakitic signatures originating by partial melting of the subducted Neo-Tethys oceanic slab(Sabzevar branch)and lithospheric suprasubduction zone mantle.The mantle signatures typifying the rapidly emplaced adakitic rocks(slab(high-silica adakite)and suprasubduction zone(low-silica adakite)melts)together with their locally voluminous extent are evidences that support a locally extensional geodynamic setting;and the evidence is consistent with an evolution to local transpression in the Late Eocene in this convergent margin are environment to rifting(basalts to adakites)towards submarine conditions in the Neogene.