別子地域三波川変成帯，五良津緑れん石角閃岩体中のエクロジャイト

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.

In the Besshi district of the Sambagawa metamorphic belt, there are two types of eclogites: one occurring in the Sebadani metagabbro mass and retrograded from high-temperature anhydrous ecologite, and the other in the basic schists and produced by prograde, dehydration of epidote amphibolite. The Sebadani metagabbro mass was originally layered gabbro, which was once equilibrated in the ecologite facies before emplacement into the Sambagawa terrain as a hot eclogite mass. Basic schists surrounding the Sebadani mass, which had suffered the Sambagawa metamorphism of albite epidote amphibolite facies, were contact-metamorphosed at high pressure by the emplacement of the Sebadani mass. As a result, the basic schists were dehydrated to form eclogitic basic schists, i.e. garnet and omphacite porphyroblast-bearing basic schists. Thus, two types of ecologite, retrograde and prograde, converged into the same metamorphic condition, 610–650 °C, 7–17 kb, in a part of the ecologite facies during the Sambagawa metamorphism. Correspondingly, the values of distribution coefficients of Fe and Mg between garnet and omphacite increase from core pairs to rim pairs in the retrograde eclogites and decrease from core pairs to rim pairs in the prograde ecologites. After this stage, both the prograde and retrograde eclogites shared a common metamorphic history; they were retrograded via the epidote amphibolite facies to the greenschist facies. The Sebadani metagabbro mass, as a large tectonic block, had been emplaced into a mélange zone in the Sambagawa metamorphic belt after the peak of the Sambagawa metamorphism, probably following initiation of uplift of the metamorphic rocks from their deep-seated environment.

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.

If the protolith of coesite-bearing eclogite was gabbro, it could undergo ultrahigh-pressure metamorphism under dry condition. In this case, the Hocking temperatures of those minerals could be higher, so that Nd isotope disequilibrium between minerals could be observed. If the protolith of coesite-bearing edogite was metabasalt, amphiboles in the metabasalt were decomposed during ultrahigh-pressure metamorphism and released water. Thus Nd isotope compositions between the minerals were in equilibrium because the blocking temperatures of those minerals could he lower. The secondary alteration and fluid-rock interaction in high-pressure are major problems for Sm-Nd dating of eclogite. The reliable Sm-Nd isotopic ages of coesite-bearing eclogite from the Dabie Mountains and Su-Lu terrane range from 221 to 232 Ma. They are slightly lower, but very close to the peak metamorphic ages of the eclogites. The cold eclogite from the Sujiahe complex could be oceanic subduction origin in the Paleozoic.

Ivozio kyanite-bearing eclogites represent one of the main pre-Alpine mafic complexes of the Sesia Lanzo Zone (Austroalpine Domain) whose protoliths have been dated at Late Devonian to Early Carboniferous. The complex consists of various HP mafic-ultramafic rocks such as amphibole-bearing eclogites, zoisite-bearing eclogites, amphibole-epidote-bearing eclogites, quartz-bearing eclogites, chlorite-bearing amphibolites and ultramafites surrounded by eclogitic micaschists and jadeite-bearing metagranitoids. Multiscale structural analyses, integrated with geochemical investigation, allowed to distinguish heterogeneities of eclogite types consequent to strain partitioning and different degrees of metamorphic re-equilibration during Alpine polyphase deformation history or to pristine magmatic differences. Five groups of Alpine structures (D 1 to D 5 ) have been detected: they consist of folds, foliations and shear zones developed during the Late Cretaceous to Eocene subduction-exhumation path. The metamorphic mineral assemblages related to the deformation stages indicate a polyphase deformation (pre-D 1 to D 3 ) under eclogite-facies conditions followed by a blueschist re-equilibration (during D 4 ), localized shearing and successive folding and discrete shearing (D 5 ) under greenschist-facies conditions. Four veining stages, developed under the eclogite- and blueschist-facies conditions have been documented. Whole rock major and trace element composition of main igneous lithotypes suggest a subduction-related context for the emplaced of the Ivozio mafic Complex. It also suggests that all rocks are not co-genetic and that they likely emplaced in the continental crust. Igneous products with arc and back-arc geochemical affinity (from 380 to 345 Ma) are described in the European Variscan Belt from French Central Massif to Bohemian Massif, supporting the interpretation that the Ivozio mafic Complex protoliths are the witness of such Devonian-Carboniferous arc magmatism in the Alpine chain. TO DOWNLOAD THE GEOLOGICAL MAP SEE THE IN THE MENu SUPPLEMENTARY FILE (ON THE RIGHT COLUMN)

O Gnaisse alcalino de Serra do Matola - São Jõao Del Rei

The inner zone of the Sardinia Variscan segment consists of two metamorphic complexes: I) A polymetamorphic Migmatite Complex, with migmatites showing polyphase anatectic processes, in the presence of kyanite or sillimanite. The Migmatite complex preserved decametric lenses of eclogite relicts (eclogites A) affected by high T, high- to intermediate P recrystallization under granulite facies conditions The decompressional garnet + Ca-clinopyroxene + amphibole ± orthopyroxene-bearing assemblages developed in granoblastic textures generally in no stress conditions. In most cases, only symplectite textures provide evidence for the eclogitic event. II) A medium grade, mostly metapelitic complex consisting of Grt, Ky, Stau-bearing micaschists and paragneisses includes quartzites and garnet-bearing amphibolite boudins with N-MORB chemical affinity. Relicts of eclogite assemblages were locally found in the metabasite (eclogites B). In eclogites A, the geothermobarometric parameters yield temperatures in the range 690°-760°C for minimum pressure A1.3 GPa. Pyroxene compositions accord with temperatures in excess of 700°C. In eclogites B, the thermometric calibrations provide temperatures in the range 610°-700°C for pressures 1.3-1.5 GPa, based on the jadeite content. The temperatures are consistent with the biotite+muscovite+garnet+kyanite+staurolite assemblage in the host paragneisses, and with lack of anatectic processes. The age of 457±2 Ma, obtained by U/Pb dating on one sample of Type A eclogite is interpreted as a minimum estimate for the magmatism of the eclogite protolith. A second zircon population defined an age of 403±4 Ma interpreted as dating the zircon crystallization during the high-grade event. The relationships between Types A and B eclogites, and their bearing on the regional framework (Sardinia, Ligurian Alps) are discussed.

The Pinarbasi ophiolite is located in Central Anatolia and emplaced onto the Tauride platform in Late Cretaceous. It comprises remnants of lower part of oceanic lithosphere, namely mantle tectonites tectonically underlain by high-grade metamorphic sole rocks and ultramafic to mafic cumulates. Number of isolated microgabbro-diabase and pyroxenite dikes cut the mantle tectonites at different structural levels. The mantle tectonites are dominated by harzburgite and dunite, whereas the cumulates consist of wehrlite, clinopyroxenite, olivine gabbro, troctolite and gabbronorite. The metamorphic sole rocks in the Pinarbasi ophiolite crop out as thin slices beneath the sheared serpentinites and display inverted metamorphic gradient from amphibolite to greenschist facies. The rock types in the metamorphic sole are calcschists, epidote + plagioclase + amphibole schists, plagioclase + amphibole schists, amphibole schists, plagioclase amphibolites, amphibolites. The isolated microgabbro-diabase dikes are tholeiitic in character (Nb/Y = 0.03-0.07). The REE patterns, multi-element and tectonomagmatic discrimination diagrams suggest that the isolated dikes formed in a subduction-related environment. The metamorphic sole rocks exhibit two distinct geochemical features. The first group is alkaline (Nb/Y = 1.5-2.6), whereas the second group is tholeiitic (Nb/Y = 0.05-0.22) in nature. The REE patterns, multi-element and tectonomagmatic discrimination diagrams suggest that the protholith of the first group is similar to within-plate alkali basalts, whereas the second group is more akin to island arc tholeiitic basalts. All the evidences suggest that the Pinarbasi ophiolite and the isolated dikes formed in a suprasubduction zone tectonic setting. The alkaline amphibolites were formed as a result of metamorphism of the seamount type basaltic rocks in intraoceanic subduction zone whereas the tholeiitic amphibolites were formed as result of intraoceanic thrusting in a supra-subduction zone (SSZ) basin during the closure of the Inner Tauride Ocean in Late Cretaceous.

New evidence for ultrahigh-pressure metamorphism (UHPM) in the Eastern Alps is reported from garnet peridotites of Pohorje Mts. in Slovenia. In this area, an eo- Alpine UHPM has been recently documented in the eclogites (Janak et al. 2004). These eclogites are closely associated with metaultrabasites - predominantly serpentinised dunite and harzburgite with garnet peridotite remnants. The country rocks of eclogites and metaultrabasites are amphibolites, orthogneisses, paragneisses and micaschists. All these rocks belong to the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriatic fault. Ultramafic rocks have experienced a complex metamorphic history. At least four stages of recrystallization have been identified in the garnet peridotite based on an analysis of reaction textures and mineral compositions. Stage I is a high-temperature protolith assemblage of olivine + orthopyroxene + clinopyroxene + Cr-spinel. Aluminous pyroxenes occur as inclusions in garnet, chromian spinel is preserved in the matrix. Stage II – an ultrahigh-pressure stage is defined by matrix assemblage garnet + olivine + orthopyroxene + clinopyroxene + Cr-spinel. Garnet contains up to 67 mol% of pyrope, olivine has 90 mol% of forsterite, orthopyroxene is low in Al2O3 (~0.8 wt%) and spinel has a Cr* ~ 50. Stage III – a decompression stage is manifested by formation of kelyphitic rims of high-Al orthopyroxene, aluminous spinel and pargasitic hornblende replacing garnet. Due to retrogression, garnet shows a decrease in MgO. Stage IV – is represented by formation of tremolitic amphibole, chlorite, serpentine and talc. P-T estimates based on geothermobarometric calculatios a) Fe-Mg exchange between garnet, olivine and orthopyroxene thermometers, b) the Al-in-orthopyroxene barometer indicate that the peak of metamorphism (stage II) occurred at ~820-900oC and 3-3.5 GPa. This is consistent with previous estimation of very high P-T conditions in metaultrabasites by Hinterlechner-Ravnik et al. (1991) and the associated eclogites (Janak et al. 2004). These results suggest that the mantle fragment (garnet peridotite) and the crustal fragment (eclogite) in the Pohorje Mts. both experienced a common UHPM during the Cretaceous orogeny. We propose that UHPM resulted from deep subduction of a continental slab which incorporated peridotites from an overlying mantle wedge.

The study of late and post-orogenic sedimentary basins is a powerful tool to understand uplift, exhumation and erosion of an orogen. In the Ligurian Alps, high-pressure ophiolitic rocks are directly overlain by the sediments of the Tertiary Piedmontese Basin (TPB); the conglomerates at the bottom of the TPB succession contain clasts of metaophiolites and metasediments which display deformation structures acquired at peak metamorphic conditions ranging from eclogite- to blueschist- facies. The deformation events prevalently recorded by the highpressure rocks of the Ligurian Alps are either related to subduction and peak metamorphism, or to the late-stage greenschist collision. The main structures which accomplish the early exhumation of such high-pressure terrains are only locally recorded and poorly explored. Further information on these early tectonic events can be gathered through the study of the clasts in the conglomerates. In this paper we present a textural and petrologic outline and some thermobarometric estimates of the main types of high-pressure clasts sampled and their comparison with the high pressure equivalents presently exposed in the Ligurian Alps. In particular, some clasts displaying a Na-amphibole + white mica + epidote + sphene blueschist foliation superimposed to an eclogitic garnet + Na-clinopyroxene + rutile tectonitic assemblage have been studied in detail. These kind of rocks record a pressure-temperature path implying cooling during exhumation, whereas the high-pressure bedrocks are characterized by either isothermal decompression, or initial heating and subsequent cooling. We conclude that the blueschist foliation of these clasts most likely developed along shear zones and/or contacts among different slices, formed during tectonic coupling of warm, uprising eclogite units, with cooler blueschist slices during the early stages of exhumation.

The present note summarizes the kinematics of the Voltri Group and the Sestri-Voltaggio Zone (Fig. 1) inferred from new structural data. These data have been collected during fieldworks performed by the authors since 1983 up to now in the Voltri Group and the Sestri-Voltaggio Zone. The Voltri Group is a metaophiolitic massif with metasediments (Chiesa et al., 1975), cropping out in central Liguria (Italy). It encompasses several units, re-equilibrated up to different metamorphic P-T peak conditions, which afterwards suffered common deformation and folding. The units of the Voltri Group suffered eclogite to blueschist facies (HP-LT) peak conditions during a subduction event, followed by decompression down to greenschist facies conditions during the exhumation process (Messiga and Scambelluri, 1991; Capponi and Crispini, 1990; Cabella et al., 1994 and references therein). At present, greenschist facies assemblages prevail at a regional scale. The Sestri-Voltaggio Zone occurs at the eastern margin of the Voltri Group and encompasses three units: the Trias-Lias Unit, the Cravasco-Voltaggio Unit and the Monte Figogna Unit (Cortesogno and Haccard, 1984). Also these units were involved in the Alpine subduction-related tectonic events and underwent metamorphic re-equilibration up to different degrees characterized by blueschist facies (Trias-Lias and Cravasco-Voltaggio Units) and pumpellyite-actinolite facies (Monte Figogna Unit) peak metamorphic conditions, later re-equilibrated in lower metamorphic conditions (albitechlorite- epidote mineralogical associations). The tectonic limit between the Voltri Group and the Sestri- Voltaggio Zone is known as the Sestri-Voltaggio Line. Since the end of the last century it drew the attention of the geologists for its peculiar position among units with different metamorphic and structural characteristics. The Sestri- Voltaggio Line played different geodynamic roles in the models proposed by the authors; it was interpreted as a stratigraphic boundary, for example the limit between the “falda delle Pietre Verdi” and the “falda ligure-toscana” by Rovereto (1939), or it was interpreted as a tectonic boundary, for example as a “trasformante” (= transform) fault by Elter and Perusati (1973), a thrust contact in Cortesogno and Haccard (1984) and, more recently, as an extensional fault by Hoogerduijn Strating (1994).

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.

The Kwoiek Area of British Columbia contains a pendant or screen of metamorphosed sedimentary and volcanic rocks almost entirely surrounded by a portion of the Coast Range Batholith, and intruded by several dozen stocks. The major metamorphic effects were produced by the quartz diorite batholithic rocks, with minor and later effects by the quartz diorite stocks. The sequence of important metamorphic reactions in the metasedimentary and metavolcanic rocks, ranging in grade from chlorite to sillimanite, is: 1. chlorite + carbonate + muscovite → epidote + biotite 2. chlorite + carbonate → actinolite + epidote 3. chlorite + muscovite → garnet + biotite 4. chlorite + epidote → garnet + hornblende 5. chlorite + muscovite → garnet + staurolite + biotite 6. chlorite + muscovite → aluminum silicate + biotite 7. muscovite + staurolite → garnet + aluminum silicate + biotite 8. staurolite → garnet + aluminum silicate Continuous reactions, occurring between reactions 5 and 7, are: A. chlorite + (high Ti) biotite + Al2O3 (from plagioclase?)→ garnet + staurolite + (low Ti) biotite + O2 B. muscovite (phengitic) → garnet + staurolite +muscovite (less phengitic) + O2 (?) Detailed electron microprobe work on garnet, staurolite, biotite, and chlorite shows that: (1) The garnet porphyroblasts are zoned according to a depletion model, called the Rayleigh depletion model, which assumes equilibrium between the edge of a growing garnet and the minerals which are unzoned, notably biotite, chlorite, and muscovite, but which assumes disequilibrium within the garnet. (2) The staurolite porphyroblasts are also zoned, and from their zoning patterns reactions A, B, and 5 are documented. Progressive reduction of iron with increasing grade of metamorphism is also inferred from the staurolite zoning patterns. (3) During a late period of falling temperature garnet continued to grow and the biotite and chlorite reequilibrated. The biotite, chlorite, and garnet edge compositions can vary from point to point in a given thin section, indicating that the volume of equilibrium at the final stage of metamorphism was only a few cubic microns. (4) The horizon within the garnet that grew at maximum temperature can be identified. The Mg/Fe ratio of this horizon, if the garnet composition is a limiting composition in the Al2O3 - K2O - FeO - MgO tetrahedron, increases systematically with increasing metamorphic grade. Biotite and chlorite compositions also show a general increase in Mg/Fe ratio with increasing metamorphic grade, but staurolite appears to show the reverse effect. (5) The Mg/Fe ratio at the maximum temperature horizon of the garnet porphyroblasts is a function of its Mn content as evidenced from the study of five garnet-bearing rocks, collected from one outcrop area, with the same assemblage but with differing proportions of minerals. An important implication of zoned minerals is that the effective composition of a system in a phase lies on the join between the homogeneous minerals (if there are two) and not within three-or- four-phase fields when a zoned mineral, such as garnet or staurolite, is present in the assemblage. Study of the three aluminum silicates found in the Kwoiek Area showed that a constant pressure change in polymorphs from andalusite to kyanite to sillimanite took place with increasing temperature. This transition series is best explained by the metastable formation of andalusite. Photographic materials on pages 15, 121, 160, 162, and 164 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.

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.

Metamorphic zonation and metamorphism of pelitic schists in the higher grade region of the Sambagawa metamorphic belt in central Shikoku, Japan