Discovery and study of high-pressure basic granulites in Songshugou area of Shangnan, East Qinling

There is a typical assemblage of garnet + kyanite + microperthite + quartz + rutile in high-pressure (HP) felsic granulite of Qinling complex in Songshugou area. East Qinling. The HP granulite was formed at 800 -900℃ and 1.3 -1.6GPa and has experienced two stages of retrograde metamorphism at 600- 650 ℃, 0.8-1.0GPa and 500-600℃, 0.3-0.6GPa, forming two retrograde metamorphic assemblages of margarite + plagiodase (PlI)+quartz and sillimanite + biotite + plagioclase(PlII) + microdine+quartz, respectively. They construct a two-stage clockwise P-T path which shows down-pressure cooling in both early and late stage.

PART I: Phase relationships have been determined for the dehydration-melting of a (powdered and solid) calcic, low-K, olivine tholeiitic amphibolite (hornblende 70%, plagioclase 30%), in runs at 10 kbar, 750 to 1000°C,fO2 ~= Ni-NiO, and for 1 to 21 days. Hornblende is involved in a sliding reaction: hornblende + anorthitic plagioclase -> clinopyroxene + liquid + aluminous hornblende + calcic hornblende + orthopyroxene + garnet. The liquid fraction varies from <1% at 750°C to ~47% at 1000°C, with the big increase occurring above 875°C. Liquids are tonalitic but have very high Al2O3 contents (18-21 wt.%). At high liquid fractions (~0.5), liquids are high-alumina basaltic. Liquids become more sodic with increasing temperature, but the compositional trends reverse direction, and liquids become more calcic above 975°C, where garnet is unstable. The water contents of liquids range from over 7 wt.% at low liquid fractions to 2 wt.% at high liquid fractions. In the solid amphibolite runs, liquid interconnectivity may be attained at 875°C with only 2 vol.% liquid and dihedral angles less than 60°. The removal of water-rich tonalitic liquids from a substantially melted amphibolitic source could help generate a relatively dry mafic granulite terrane, with densities up to 3.5 gm/cm3. Delamination of this dense lower crust is possible. PART II: A cogenetic and coeval tonalitic and mafic dike swarm has been identified within a southern fragment (the Owens Mountain area) of the western Foothills terrane (Sierra Nevada, California). The swarm was mylonitized and transposed during emplacement, from 155 to 148 m.y. (U-Pb zircon data), at an estimated depth of 10 km. Steeply SE-plunging fold axes and S-fold geometries indicate a left-lateral sense of shear. The Late Jurassic Nevadan orogeny is a manifestation of dramatic changes in magnitude and direction of North American motion. The Cordilleran dike swarms record a complex pattern of sinistral-sense transtension-transpression that developed during this period of change, at the J2 (~150 m.y.) apparent polar wander cusp, and during subsequent, rapid northwestward acceleration of North America. EXTENDED ABSTRACT (PART I): Phase relationships and morphologies and reaction kinetics have been determined for the dehydration-melting of a natural amphibolite (mode: hornblende 70%, plagioclase 30%) with no added water, at 10 kbar and 750 to 1000°C, and for durations of l to 21 days, using both finely-powdered and solid starting materials. The amphibolite composition is equivalent to a calcic, low-K, olivine tholeiite. Experimental conditions simulated the dehydration-melting of deep mafic continental crust and hot, subducted oceanic crust. Experiments were conducted in unbuffered Au capsules at oxygen fugacities probably just above the Ni-NiO buffer. Hornblende is involved in the following sliding reaction (the order of the product phases represents the order of appearance with increasing temperature): hornblende + anorthitic plagioclase -> clinopyroxene + liquid + aluminous hornblende + calcic hornblende + orthopyroxene + garnet. The liquid fraction ranges from <1% at 750°C to ~47% at 1000°C, with most of the increase occurring above 875°C. The liquids are generally tonalitic but have very high Al2O3 contents (18-21 wt.%). At high liquid fractions (~0.5), the liquids have a composition of high-alumina basalt. Fractionation of the plagioclase would be necessary to reduce both the CaO and Al2O3 contents of the liquids to calc-alkaline compositions. The liquid compositions become more sodic with increasing temperature, but the compositional trends reverse direction, and the liquid compositions become more calcic above 975°C, as garnet disappears. The water contents of the liquids range from over 7 wt.% at low liquid fractions to 2 wt.% at high liquid fractions. The high-temperature mineral assemblage that coexists with the liquid is clinopyroxene, orthopyroxene and plagioclase ± garnet ± aluminous hornblende. Thus, dehydration-melting of the amphibolite can reproduce natural granulite and garnet pyroxenite mineral assemblages. The removal of the water-rich tonalitic liquids from a substantially melted amphibolitic source would help generate a relatively dry granulite terrane. The stability of garnet plays a major role in determining the REE composition of the liquids. Garnet modes from these runs are consistent with REE patterns of Archean tonalites. Delamination of the garnet clinopyroxenite restite is possible due to the very high densities (up to 3.5 gm/cm3) of these assemblages after liquid segregation. Garnet phenocrysts show syn-growth compositional zoning. The total alumina in hornblende geobarometer appears to work for this mafic mineral assemblage. The solid amphibolite runs indicate that anisotropic crystal structures and rock texture control liquid morphology and distribution during dehydration-melting. The shapes of most liquid pockets are crystallographically-controlled, with many corners having angles greater than 60°. Few crystal/liquid triple-junctions develop the interfacial energy-controlled dihedral angles ([theta]), which form in experiments using finely-ground powders of minerals with poor cleavage. Liquid interconnectivity probably is attained at 875°C with only 2 vol.% liquid, indicating that dihedral angles less than 60° may not be necessary to achieve interconnectivity in partially melted metamorphic rocks. The surfaces between elongated grains in lineated rocks can become pathways for the migration of liquid or the diffusion of components. EXTENDED ABSTRACT (PART II): The geology, petrology and geochronology (U-Pb zircon) of a southern fragment of the western Foothills terrane has been studied (the Owens Mountain area of the western Sierra Nevada foothills, northeast of Fresno, California). A previously unrecognized dike swarm/shear zone is identified within the steeply dipping, Callovian to Kimmeridgian metavolcanic and metasedimentary strata. The dike swarm consists predominantly of cogenetic tonalitic and mafic dikes and tonalitic tabular bodies. Mutually cross-cutting relationships indicate that the tonalitic and mafic dikes also were coeval. Some of the tonalitic dikes range up to ~100 m in thickness, and individual dikes of both tonalitic and basaltic composition can be followed for up to 3 km. The dike swarm is sheeted in places, comprising almost 100% of some outcrops. Textures and fabrics within the dike swarm range from partially recrystallized igneous to strongly deformed S and L metamorphic tectonites, implying that dike emplacement occurred during ductile deformation. Hot subsolidus mylonitization has transposed layering parallel to foliation and has greatly thinned many of the dikes to centimeter to meter thicknesses. Layering and parallel foliation dip subvertically and strike NNW-SSE. Post-tectonic annealing has destroyed most microscopic shear indicators, but macroscopic intrafolial folds are common and have steeply SE-plunging fold axes and S-fold geometries that indicate a left-lateral sense of shear. The geochronological data on the tonalite dikes reveal that emplacement and crystallization of the coeval tonalitic and mafic magmas at Owens Mountain occurred over an 8 m.y. period, from 155 to 148 Ma, at an estimated depth of 10 km. Thus the beginning of intrusion occurred within 5 m.y. of deposition of the metavolcanic and metasedimentary strata into which the dikes were emplaced. A correlation between age and degree of deformation and recrystallization of the tonalites implies syntectonic dike emplacement. Undeformed granitic dikes that cut the strata are younger than 124 Ma. The regional tectonics of the Owens Mountain and other Cordilleran dike swarms can be related in a broad dynamic sense to the absolute motion of North America by using the apparent polar wander (APW) analysis of May and Butler (1986). The Late Jurassic Nevadan orogeny is the manifestation of the drastic changes in magnitude and direction of North American motion (from ~45 km/m.y. to the NNE to ~200 km/m.y. to the NW; May and Butler, 1986). The Late Jurassic dike swarms record a complex pattern of sinistral-sense transtension-transpression that developed at the J2 (~150 Ma) APW cusp and during subsequent, rapid northwestward acceleration of North America.

The Sharyzhalgay block, located in the south-western Baikal region, is an exposure of the Precambrian basement at the margin of the Siberian Platform. It chiefly consists of granitoids (80%) that host relic granulite facies rocks (20%). Metamorphism under granulite facies conditions took place about 2.4-2.5 Ga ago. Petrological and geochemical data on the granulites suggest protoliths of predominantly MORB-like basalt (~70%) and minor sedimentary rocks. Granulites also include ultramafic rocks. Relics of protogranular texture, high XMg in rocks and rock-forming minerals, occurrence of depleted harzburgites, mantle compositional trend of spinels, REE patterns, and thermobarometry data allow us to interpret the provenance of Saramta peridotites as mantle material depleted by partial melting in the stability field of spinel. Peridotites are cut by dikes of layered wehrlite, spinel websterite and garnet websterite. Spinel websterites have a chemistry and mineralogy of Cr-Di series. Their origin inferred to be the result of mineral segregations from percolating melt within the upper mantle. Garnet websterites differ from Al-augite pyroxenites by lower contents of TiO2 and Al2O3, and higher SiO2. Incongruent melting of Cr-Di spinel websterites on the scheme Cpx+ Opx+ Sp ® Mg-richer Ol+ Cr-richer Sp+L produced melts and restite wehrlites. Later on the melt crystallized in situ into garnet websterites with magmatic textures. Regional granulite-facies metamorphism at temperatures of 700-800°C and a pressure of 5-6 kb produced exsolution lamellae of spinel in pyroxene, kelyphite Sp+Opx+Pl rims on garnet, and zoning of orthopyroxene in garnet websterite. Tectonitic restite harzburgites with ultramafic dikes are correlative with the mantle parts of ophiolite sections. All these facts allow us to interpret relic granulite-facies rocks as fragments of Precambrian ophiolites.

This paper deals with the metamorphic evolution of the Bacariza Fm that outcrops in the two uppermost structural units of the Cabo Ortegal Complex (NW Iberian Massif). This formation includes ultramafic and mafic granulites, garnet amphibolites and garnet trondhjemitic gneisses. Although mineral associations characteristic of high pressure granulites predominate in the least retrogressed of these rocks, the presence of relic kyanite along with the fact that plagioclase only appears in symplectitic textures resulting from de-jadeitization of pyroxenes point to an earlier eclogite facies metamorphism. Thermobarometric estimations indicate higher P-T conditions for the rocks in the uppermost structural unit.

The Variegated Formations (VF) of the eastern Rhodope Mountains (SE Bulgaria) form part of the pre-Alpine basement of the region. They are composed of alternating sediments and igneous rocks with a high-grade metamorphic overprint. Numerous ophiolitic slivers are associated with the VF and include metamorphosed peridotites, ultramafic cumulates, and amphibolitized eclogites. The dismembered ophiolites usually form the base of the VF successions. The metasedimentary rock types contain terrigenous materials (metapsammites and quartzites) that frequently alternate with metapelites and marbles. The nature of this sedimentary package, along with the field relations and sedimentary features, reflects its flysch character. The metaigneous rocks of the VF occur either as layers interbedded with the metasediments, or as intrusive bodies that intersect the ultramafic rocks. The principal mineral phases in the metabasites are amphibole + plagioclase + quartz + epidote ± garnet ± chlorite. We calculate temperatures of 630°C to 520°C at 6-2 kbar pressures, indicating moderate amphibolite facies metamorphism. Major rock-forming minerals (amphibole, plagioclase, and garnet) exhibit zoning typical of retrograde P-T conditions. When plotted on tectonic-setting discrimination diagrams, the metabasic rocks of the VF fall mainly in the fields of modern boninites and arc tholeiites. They show low Ti and Zr contents and key elemental ratios of CaO/TiO2, Al2O3/TiO2, Ti/Zr, Ti/Y and Zr/Y, all transitional between island arc tholeiites and boninites. Chondrite-normalized REE patterns reveal the existence of two different trends: U-shaped REE patterns (for the majority of samples) and LREE depleted patterns. Regardless of the existence of these two trends, the [La/Sm]N ratios of the metabasites perfectly coincide with the same ratios for many Cenozoic boninite series. The flysch character of the sedimentary sequences, as well as the clear supra-subduction zone affinities of the igneous rocks, indicates that the VF formed in an oceanic island-arc setting. The boninitic affinities of the meta-igneous rocks indicate possible origin in an immature arc. The character of the VF and its association with the dismembered ophiolite slivers shows the presence of a suture zone. The East Rhodope suture zone distinguishes the VF from the rocks structurally below it, which consist of orthogneisses typical of continental crust. Existing U-Pb zircon data indicate that the orthogneisses are of Variscan age. New U-Pb zircon age data for the VF suggest Late Neoproterozoic ages for some protoliths. Based on regional correlations, the interpretation of the VF as a fossil accretionary prism can be useful for elucidating the structure of the whole Rhodope composite terrane, and for tracing the suture itself to the Central and Western parts of the Massif.

The British Geological Survey is carrying out geological mapping of the northern Emirates on behalf of Department of Mineral Resources of the Ministry of Energy, United Arab Emirates. The mapping of the Hajar Mountains at a scale of 1:25,000, carried out from 2002 – 2005, includes the least well know northernmost part of the Oman-UAE ophiolite and covers around 1000 sq km of mantle and mantle- crust transition zone (MTZ) rocks. The area mapped encompasses three previously recognised tectonic blocks; from the south working northwards they are, Fizh (largely in Oman), Aswad (largely UAE) and Khor Fakkan (entirely UAE). This paper describes the larger scale features and variation within the mantle rocks and a separate paper, Dare et al (this conference) covers the detailed mineralogical and geochemical aspects. The study area is the northern tip of the Oman-UAE ophiolite and is tectonically complex; the exact number of significant tectonic components and the location of the boundary between the Aswad and Khor Fakkan blocks was not clear. Boundaries between the mantle and metamorphic rocks or crustal units of the ophiolite, such as the wadi Ham fault zone and the metamorphic window to the north of Masafi, are easily located, with prominent features in the field consisting of brittle faults, with shattering, carbonate veining and serpentinite fault rocks. Close examination of the area north of Masafi shows that in a few places there are parallel, well-developed, high-temperature fabrics in both the metamorphic and mantle rocks and garnet-pyroxene amphibolites are present close to the contact. Rarely relics of amphibole peridotite mylonites have been found. These few areas appear to preserve ‘original’ high-temperature contacts associated with the ophiolite emplacement, but in most places this has been extensively modified or removed by later faulting. Within the mantle, the area north of Masafi has a welldeveloped banded unit of interbanded dunite and harzburgite, a short distance above the basal contact. The dunite bands are roughly parallel to the contact and range in thickness from a few metres to a maximum of about 30m. In several of these places there are distinct shear zones with localised, but intense, recrystallisation of the harzburgite, which are roughly parallel to the base and are probably detachment related ductile faults. The strong fabric and the close proximity of the banded dunite unit to the basal contact also suggests a tectonic-related origin for these dunites during detachment of the ophiolite. The wadi Ham fault zone, which is generally assumed to be part of the boundary between the Aswad and Khor Fakkan blocks, shows a similar multiphase history with mylonites present at many places but extensive overprinting by later brittle faults. Structural discontinuities within the mantle rocks are more difficult to locate and air photographs and particularly multispectral satellite images are invaluable. Field observations show that distinct linear features relating to alteration, indicate both late faults and ductile shear zones. The results of these studies show that the Khor Fakkan block consists of two main units, separated into a northern and southern part by an extension of the Beni Hamid shear zone. The southern part consists of an upper slice of the ophiolite, predominantly of crust and MTZ but with a thin layer of uppermost mantle, which dips to the east at about 40° giving a good cross section through this block. A lower slice, predominantly the basal part of the mantle, including banded dunite unit, dominates the northern part of Khor Fakkan block. The Aswad block also has a northern lower slice, only composed of deeper mantle, which is the leading edge of the ophiolite thrust slice and is probably relatively thin. The upper, southern slice is mostly crust and MTZ with a thin part of upper mantle in the exposed part. The basal part of the Aswad south unit is never seen, but geophysical surveys show that it extends some 20km to the west where it is covered by the Tertiary foreland basin sequence and modern desert deposits. The small mass of the Fizh block consists of upper mantle with a thin veneer of layered gabbro. The crustal sequence of the ophiolite records two main magmatic phases, an early MORB phase presumably formed at a mid-ocean ridge, with a normal sequence of layered gabbros, high-level gabbros, sheeted dykes and pillow lavas. The second magmatic phase consists of extensive younger gabbros and widespread mafic dykes, as well as composite multiphase intrusive bodies with substantial tonalite. These rocks show chemical affinities to boninite and island arc tholeiite compositions. The boundary between the crust and mantle (MTZ) is complex, consisting largely of ultramafic rocks, dunite, wehrlite and pyroxenite, which shows substantial variation in thickness and composition. This zone has been mapped as two units, of massive dunite, up to 1 km thick, but normally less, in contact with the harzburgite, and a mixed unit, dominated by wehrlites and pyroxenites with variable, subordinate amounts of gabbro screens and xenoliths. These ultramafic rocks often have an intrusive relationship into the MORB-type crust and are largely ascribed to the second magmatic phase, though it is accepted that some probably relate to the earlier MORB phase. The mantle rocks show a range of regional and depth variation and have been studied to see what traces have been recorded of the passage of these two contrasting magma types (Dare et al (this conference)). The mapping shows that mantle rocks exhibit a regional variation in several petrological features. Firstly the nature and abundance of veins cutting harzburgite varies considerably. Narrow dunite veins are present throughout and, apart from the basal banded unit, their abundance varies from sparse to very common. Usually they form part of irregular anastomosing networks, probably largely replacive in origin, formed by reaction of melt with the mantle harzburgite, thus preserving melt pathways (Zhou et al., 1994, Kelemen et al., 1997). However, in a few places planar, parallel-sided bodies appear to be intrusive. In the upper part of the mantle the veins can coalesce to merge into the massive dunite and include xenoliths of harzburgite. Veins of pyroxenite and gabbro pegmatites are abundant in some areas and these loosely correlate with areas where there is a well-developed mixed unit. The proportion of orthopyroxene in harzburgite varies regionally, around 15-20% in the Khor Fakkan block but generally higher, 20-25%, in the Aswad block. However, clinopyroxene-harzburgite and lherzolites have only been found in Aswad north. These appear to be restricted to the basal zone and petrographic studies suggests that they result from infiltration and refertilisation of harzburgite rather than as relics of little depleted mantle. This suggests there has been melt infiltration along the basal zone. The variation and distribution of these features indicates the location of areas which may be the centres of high melt flux, possibly indicating the location of aesthenospheric diapirs.

The Antrona ophiolite (western Central Alps) represents a tectonic fragment of the oceanic lithosphere of the Upper Jurassic - Lower Cretaceous Ligurian- Piedmont basin, a section of the Western Alpine Tethyan Ocean. The Antrona ophiolite occurs at lower structural levels in the Alpine nappe stack and is sandwiched between the overlying continental Monte Rosa Nappe (upper Penninic) and the underlying Camughera-Moncucco continental Unit (middle Penninic). The Monte Rosa Nappe is overlain by the Zermatt Saas ophiolitic Unit. Despite the tectono-metamorphic reworking, the Antrona ophiolite exhibits all typical lithologies of oceanic lithosphere: ultramafic and mafic plutonic rocks, mafic volcanic rocks and deep-sea sediments can be recognized. Several rock types were distinguished among mafic rocks. New findings and inferences are: i) the occurrence of probable relics of magmatic structures in some amphibolites, inferred to be pillow lavas or pillow breccia; ii) the occurrence of lawsonite pseudomorphs-bearing amphibolites, not described so far in the study area as precursor of the origin of epidote-amphibolites the Antrona Valley. A qualitative P-T diagram deduced from the stability conditions of mineral parageneses is presented and compared with published P-T paths for the Antrona and Zermatt-Saas ophiolites. The metamorphic evolution of the studied rocks is characterized by blueschist prograde path followed by high pressure (eclogitic) metamorphic peak. P-T estimates for the metamorphic peak were calculated by the Na-clinopyroxene garnet equilibria and the jadeite content in omphacite. T = 372°C for a nominal pressure of P = 1 GPa and T = 386°C for a nominal pressure of P = 1.5 Gpa were obtained. Jd30 as maximum Jadeite content suggests P > 1 Gpa. Retrograde path, although not well constrained, is dominated by epidote-amphibolite/ amphibolite facies conditions, in accord with published data, differing from those inferred so far for the overlying Zermatt-Saas ophiolite.

پهنه بندی و تعیین منشأ آلودگی منیزیم و فلزات سنگین آهن، روی و مس در آبخوانهای شمال و شمال غرب خوی (زورآباد) با استفاده از GIS

Introduction: The Lapland Granulite Belt is placed on the Kandalaksha region (Kola Peninsula, Russia). The rocks of this Belt are composed mainly of amphibolites and granulites. Materials and methods: The research were focused on the garnets from the amphibolite and granulite rocks of Lapland Granulite Belt. The petrological methods like polarizing microscopy (PM), SEM-EDS, XRD for powdered samples and single crystal diffraction were used together with IR and Mossbauer spectroscopy and REE analysis by ion–microprobe. Results: It was found that the garnets from studied amphibolite and granulite rocks could be classified to pyralspite group without hydrogarnets components, so they were formed in high metamorphic facies. Conclusions: The joint geological observations and results of the performed experiments suggest that the garnets were subject of a blastesy, i.e. there were formed in long lasting metamorphic processes of low dynamics, except of those garnets from tectonic zones, found in the vicinity of mineral veins.

The crust and upper mantle in East Qinling and the adjacent North China and Yangtze blocks exhibit systematic heterogeneity in Pb and Nd isotopic compositions, whereby two tectono-isotopic provinces of North China and Yangtze can be identified. The South Qinling can be assigned to the Yangtze province according to its crustal Pb isotopic composition, crustal growth history and upper mantle evolution. The North Qinling is reasonably considered to be an ancient, independent microcontinent and was formed principally in the Proterozoic over the strongly depicted upper mantle. Some implications of these results for tectonics are discussed.

Discovery of pelitic high-pressure granulite from Manjinggou of the Huai’an Complex, North China Craton: Metamorphic P–T evolution and geological implications

; Recently, garnet pyroxenite enclaves within peridotites occurring near Raobazhai, Huoshan County, have been discovered. The garnet pyroxenite is small pods, decimeters in size, enclosed within intensively serpentinized peridotites. Major mineral components comprise: garnet (Prpas-as), sodium augite (Jd 10-25) with a small amount of ilmenite. There are two stages of retro-metamorphism: the retrogressive granulite facies mineral assemblage is superimposed by that of amphibolite facies. The host rocks of the garnet pyroxenite are spinel peridotites, including spinel harzburgite and Iherzolite. Due to intensive serpentinitization, only 5%-40% of the relic olivine (Fo92-93) are preserved. The orthopyroxenes are Mg-rich (En87-93) with bending of cleavages and granulation at their margins showing intracrystalline plasticity. On the basis of garnet-clinopyroxene Fe-Mg exchange equilibrium geothermometry proposed by Ellis & Green (1979) and Krogh (1988) KD= 4.06 - 5.28; T= 793-919℃, P= 1.5 GPa are estimated for the garnet pyroxenite. It is inferred that the peridotites are mantle rocks about 60 km in depth. During the exhumation of the orogenic belt, it was tectonically emplaced into the lower crust in the solid state and then uplifted to the shallow depth. Obviously, this kind of garnet pyroxenite must be petrogenetically related to its host rock. The REE distribution pattern and the Ni-Co-Sc diagram reveal that they are chemically equivalent to the basaltic melt and ultramafic residua respectively derived from partial melting of mantle rocks.

Introduction The Avan Cu-Fe skarn is located at the southern margin of Qaradagh batholith, about 60 km north of Tabriz. The Skarn-type metasomatic alteration is the result of Qaradagh batholith intrusion into the Upper Cretaceous impure carbonates. The studied area belongs to the Central Iranian structural zone. In regional scale, the studied area is a part of the Zangezour mineralization zone in the Lesser Caucasus. Several studies (Karimzadeh Somarin and Moayed, 2002; Calagari and Hosseinzadeh, 2005; Mokhtari, 2008; Baghban Asgharinezhad, 2012; Mokhtari, 2012) including master’s theses and research programs have been done on some skarns in the Azarbaijan area considering their petrologic and mineralization aspects. However, before this study, the Avan skarn aureole has not been studied in detail. In this paper, various geological aspects of the Avan skarn including mineralogy, bi-metasomatic alteration, metasomatism and mineralization during the progressive and retrograde stages of the skarnification processes have been studied in detail. Research Method This research consists of field and laboratory studies. Field studies include preparation of the geological map, identifying the relationship between the intrusion and the skarn aureole, identifying the relationship between different parts of the skarn zone and also collecting samples for laboratory studies. Laboratory studies include petrography, mineralography and microprobe studies. Cameca SX100 Microprobe belonging to Geological Survey of the Czech Republic was used in order to determine the chemical composition of the calc-silicate minerals such as pyroxene and garnet in garnet skarn and pyroxene- garnet skarn sub-zones. Discussion and conclusion Qaradagh batholith is composed of discrete acid to mafic phases including gabbro, diorite, quartz diorite, quartz monzonite, quartz monzodiorite, tonalite, granodiorite, monzogranite and granite porphyry which is dominated by granodiorite-quartz monzonite. Granitoids of this batholith are metaluminus, high K calc-alkaline I-type granite (Mokhtari, 2008). The Avan Cu-Fe skarn is related to the intrusion of granodioritic-quartz monzonitic part of the Qaradagh batholith into the Upper Cretaceous flysch- type rocks consisting of biomicrite, clay limestone, marl, siltstone and mudstone. The Avan skarn consists of three zones of endoskarn, exoskarn and marble. The main Cu-Fe mineralized zone is related to the exoskarn zone, which has 600 meters of length and 50 meters of thickness, respectively. The Exoskarn zone consists of garnet skarn, pyroxene-garnet skarn and ore skarn sub-zones. Garnet, belonging to ugrandite series (Ad53-89) with more than 50 percentage in volume, is the most important anhydrous calc-silicate mineral in the garnet skarn and the pyroxene-garnet skarn sub-zones. Some of the garnet crystals are zoned and their chemical composition changes toward the rim to almost pure andradite (Ad99). Clinopyroxene which has diopsidic composition (Di75-96), is another anhydrous calc-silicate mineral in the exoskarn zone with an abundance that reaches up to 50 percent in volume in pyroxene-garnet skarn sub-zone. The ore skarn sub-zone is located toward the outer part of the exoskarn zone and close to the border of the marble zone. The abundance of ore minerals in this sub-zone reaches up to 50 percentage in volume and includes magnetite, hematite, pyrite, chalcopyrite, bornite, malachite and goethite among which pyrite is the most abundant. In this sub-zone, anhydrous calc-silicate minerals of garnet and clinopyroxene have undergone intensive alteration and are replaced with hydrous calc-silicate (epidote and tremolite- actinolite), oxide (magnetite and hematite) and sulfide (pyrite, chalcopyrite and bornite) minerals. Based on the textural and mineralogical studies, the skarnification processes in the studied area can be categorized into two main stages: 1) prograde and 2) retrograde. During the prograde stage, the heat flow of the granitoid has caused isochemical metamorphism and changing more pure limestones to marble and marlly limestones to skarnoid (metamorphism and bi-metasomatism). The high temperature magmatic fluids have caused prograde metamorphism during which anhydrous calc-silicate minerals including garnet and pyroxene have appeared. During the early retrograde stage, i.e. the mineralization sub-stage, lower temperature hydrothermal fluids have caused hydrolysis and carbonization because of which anhydrous calc-silicate minerals along with their fractures and microfractures are changed to hydrous calc-silicate (epidote and tremolite-actinolite), oxide (magnetite and hematite), sulfide (pyrite, chalcopyrite and bornite) and carbonate (calcite) minerals. During the late retrograde stage, relatively low temperature fluids have altered anhydrous and hydrous calc-silicate mineral assemblage formed during the previous stages into a very fine grained mineral assemblage including clay minerals, chlorite and iron hydroxides. Presence of replacement textures in ore minerals and anhydrous calc-silicate minerals accompanied with open filling textures in the anhydrous calc-silicate minerals, for example oxide and sulphide veinlets within the garnet crystals, indicate that the mentioned ore minerals have been simultaneously generated with hydrous calc-silicate minerals (epidote and tremolite-actinolite) during the early prograde stage. The presence of minor amounts of wollastonite among the mineral assemblage of the Avan skarn, intergrowth of garnet and pyroxene, absence of reaction rim between garnet and clinopyroxene and absence of replacement textures indicate that these minerals have been simultaneously generated within the temperature ranges of 430–600 ºC and ƒO2 > 10-26, respectively. Acknowledgements The authors are grateful to the Journal of Economic Geology reviewers and editors for their constructive suggestions to the manuscript. Reference Baghban Asgharinezhad, S., 2012. Investigation of genesis, mineralogy and geochemistry of Fe-Cu skarn in Astamal area, NE Kharvana, Eastern Azarbaijan. MSc. Thesis, University of Tabriz, Tabriz, Iran, 185 pp. (in Persian with English abstract) Calagari, A.A. and Hosseinzadeh, G., 2005. The mineralogy of copper-bearing skarn to the east of the Sungun-Chay River, East-Azarbaijan, Iran. Journal of Asian Earth Sciences, 28(4-6): 423-438. Karimzadeh Somarin, A. and Moayed, M., 2002. Granite and gabbro-diorite associated skarn deposits of NW Iran. Ore geology reviews, 20(3-4): 127-138. Mokhtari, M.A.A., 2008. Petrology, geochemistry and petrogenesis of Qaradagh batholith (east of Syahrood, Eastern Azarbaijan) and related skarn with considering mineralization. Ph.D. Thesis, Tarbiat Modares University, Tehran, Iran, 347 pp. (in Persian with English abstract) Mokhtari, M.A.A., 2012. The mineralogy and petrology of the Pahnavar Fe skarn, in the Eastern Azarbaijan, NW Iran. Central European Journal of Geosciences, 4(4): 578-591.

Numerous small ultramafic bodies are exposed in Mesozoic cover units of the central Eastern Alps. The major occurrences are restricted to the tectonic windows of the Penninic zone and their surroundings. In the Lower Engadin window, three different mantle peridotite groups have been investigated. The Idalp ophiolite, situated at the northern rim of the Engadin window, is believed to be of south Penninic origin (Trumpy, 1972), whereas the Ramosch ophiolite at the southwestern margin is assigned to the north Penninic area (Vuichard, 1984). The tectonic position of the ultramafics in the vicinity of Nauders, at the southern margin, is unknown. Ophiolite remnants of south Penninic affinity are also present in the Glockner nappe of the Tauern Window. At the eastern end of the Alpine orogen similar peridotites appear in the small Rechnitz window. Numerous, usually small and highly serpentinized bodies of ultramafic rocks can be traced in the Matrei zone along the southern margin of the Tauern window; the Matrei Zone comprises both, Penninic and Lower Austroalpine elements. The Reckner ophiolite complex, near the NW corner of the Tauern window, is part of the tectonically higher units of the Lower Austroalpine nappe. Geochemical and petrological investigations reveal considerable differences between these mantle slices. The different ultramafic bodies are influenced by a pervasive regional metamorphism locally reaching amphibolite facies. Primary mineral assemblages of the peridotites have been mostly replaced by metamorphic parageneses. The products of metamorphism are dominantly serpentine minerals accompanied by various combinations of diopside, tremolite, chlorite, hydrogarnet and magnetite. In contrast to all other occurences, the samples from Nauders are characterized by a well preserved primary assemblage. Relic clinopyroxene and spinel can be found in peridotites of the Reckner and in the Matrei zone. Olivine and orthopyroxene pseudomorphed by serpentine minerals are present in less deformed areas only. Preserved clinopyroxenes of these mantle peridotites have up to 7 wt% Al2O3 and 1.5-2.0 wt% Na2O, which corresponds to a jadeite component of more than 10 %. The Cr2O3 content is generally high (up to 1 wt%). Clinopyroxene is frequently zoned with progressive depletion of Al, Na, Ti and Cr towards pure diopside. In samples from Nauders the Fo-content of olivine is about 90% and the NiO concentration varies between 0.4-0.5 wt%. The orthopyroxenes range in XMg from 91-92 and Al2O3 reaches up to 5 wt%. Titanian pargasite (XMg 0.88, about 3.5 wt% TiO2) is a secondary phase in Nauders peridotites only. Spinels from Nauders are different in composition to those of the Reckner complex. They are typically poor in Cr2O3 (about 7 wt%), high in Al2O3 (about 60 wt%) and develop rims which usually have lower Cr contents. Relics of spinel with significantly higher Cr values (Cr# 40-50, Cr2O3 35-40 wt%) are preserved in samples of the Reckner complex. The dominant rock types of all Mesozoic ultramafic bodies are residual lherzolites and harzburgites (XMg 87-94). The serpentinized ultramafics of the southern Penninic realm (Idalpe, Tauern and Rechnitz windows) are generally harzburgites with low Al2O3 (<2 wt%) and CaO contents (Fig. 1). The HREE concentrations (0.3-0.5 times chondrite) display patterns of moderately depleted restitic mantle (Fig. 2). Lherzolites and cumulate rocks (XMg = 0.80) are restricted to a few occurrences within the main mass of harzburgites. In contrast, more fertile lherzolites and harzburgites form ultramafic bodies of the Matrei zone, the Reckner complex, the Ramosch ophiolite and Nauders.The high abundances of Al2O3 (up to 4.6 wt%) and TiO2 (up to 0.22 wt%) are consistent with the estimated composition of a primitive upper mantle. All samples display higher HREE concentrations (up to 2.5 times chondrite) and a significant LREE depletion trend (Figs. 1 and 2). The Cr-Yb projection (Pearce and Parkinson, 1993) has been used to investigate the degree of mantle depletion. This diagram provides further evidence that the mantle material of the south Penninic region represents a more depleted source (about 15% melt depletion) than those of the Matrei zone and the Lower Austroalpine region (up to 5% melt depletion). These data support the model of a slow spreading oceanic environment (Hock and Koller, 1992) for the ophiolites of the Idalpe, Tauern and Rechnitz window, whereas the ultramafics of the Reckner, Matrei Zone and Nauders were probably generated in a pre-oceanic stage.

Stretching for > 2000 km between the Sino-Korean craton in the north and the Yangtze craton in the South, the Qinling-Tongbai-Hong’an-Xinxian-Dabie-Sulu-Imjingang orogen is the centrepiece of Chinese geology. From north to south, it comprises the Kuanping, the Erlangping, the Qinling unit Liuling, the Douling and the Wudang, i.e. tectono-metamorphic units with complex evolutions. In Cambrian times, deep subduction of the Qinling microcontinent below an intra-oceanic Erlangping arc created ultra-high pressure metamorphic eclogites and gneisses. The coesite-eclogite facies stage was constrained at 550°C and 3.1 GPa. During uplift, a quartz-eclogite facies recrystallization occured at 2.0-2.3 GPa and ~660 °C. Further uplift was characterized by nearly isothermal decompression and a penetrative overprint at 630-640 °C and 1.1-1.5 GPa. Ar/Ar phengite and U/Pb titanite ages of ~470 Ma highlight exhumation into the crust together with cooling in the Middle Ordovician. The southern margin of the Qinling microcontinent faced a north-trending subduction zone and a magmatic arc set up that was active from the Middle Cambrian till the Early Devonian (~110 Ma). Due to the high heat flow, the central-southern part of the Qinling unit underwent ultra-metamorphism at peak metamorphic conditions of 680-775 °C at 0.5-0.75 GPa. Metamorphics of the Liuling indicate an at least a two-stage burial-exhumation history during Late Carboniferous-Permian. Thermodynamic modelling of zoned garnet reveals a first clockwise Barrovian metamorphism, which took place under medium pressure amphibolite facies conditions (560-590 °C at 0.4-0.6≈GPa) and was followed by a second stage of high pressure amphibolite facies metamorphism (590 °C at 0.9 GPa). Lithology and geochronology classify the Liuling as a Devonian to Early Carboniferous forearc basin, which received its metamorphic overprint at 250-320 Ma. The Douling forms a basement wedge intercalated between the Liuling and the Wudang. Medium to high-grade metamorphic conditions (560-710 °C at 0.8-1.2 GPa) likely reflect a Neoproterozoic event. A thorough LT/HP metamorphic overprint (280-340 °C at 0.5-0.9 GPa) of probable Triassic age affected the Douling Complex as well as its cover units. Similar HP/LT metamorphic conditions (~300 °C at 0.4-0.9 GPa) are recorded in blueschists of the neighbouring northern Wudang Complex. In the centre of the Wudang Complex, HP/MT metamorphic conditions (500-550 °C at 1.0-1.2 GPa) recorded by garnet gneisses and amphibolites are followed by a HP/LT overprint of 300 °C and 0.6-0.7 GPa. Thermobarometry and geochronology indicate that the metamorphism in the Wudang Complex occurred due to subduction of the Yangtze craton underneath the amalgamated Qinling-Erlangping-Sino-Korean continent in the Triassic, which is also true for the Douling complex and its cover. In the western part of the orogen, along a north-south profile, petrological invesigations reveal amphibolite facies PT conditions of 590 °C at 0.6 GPa in the northern part and upper amphibolite facies conditions of 760 °C at ~0.7 GPa along with the migmatisation of felsic gneisses in the centre of the profile. Further south, Theria_g modeling applied to garnet from a garnet-staurolite gneiss point to a rather fast prograde clockwise evolution with pronounced heating along with minor burial and nearly isothermal exhumation. The southermost sample gives evidence for medium to upper greenschist-facies conditions. The age of this metamorphic overprint is constrained by Th/Pb monazite ages of 205.8 ± 2.8 Ma and 194.1 ± 2.1 Ma as well as Ar/Ar ages of 192-207 Ma while Ar/Ar ages from adjacent magmatics give a somewhat larger timespan of 186-227 Ma as the younger ages originate from pegmatites and reflect late magmatic activities. Published and new U/Pb zircon arges highlight Triassic – Early Jurassic magmatism spanning ~50 Ma with a major cluster at ~225-205 Ma. Alltogether, these findings highlight a Triassic tectono-metamorphic event in the middle to lower crust of the western Qinling orogen which was strongly influenced by the intensive syn- and post-tectonic magmatic activity. Triassic-Early Jurassic Ar/Ar ages from the Mianlue mylonite zone reflect a Mesozoic metamorphic overprint. However, new and recently published U/Pb zircon ages from mafic rocks prove a Neoproterozoic origen of ophiolite blocks. Thus, there are no indications for the existence of a Late Palaeozoic Myanlue ocean and the hypothesis of the existence of a “Mianlue suture” stretching all through the northern Yangtze craton is falsified.