AN UNUSUAL ASSEMBLAGE OF TALC-PHENGITE-CHLORITE-K-FELDSPAR IN QUARTZ SCHISTS FROM THE NAHAVAND AREA, SANANDAJ-SIRJAN ZONE, IRAN

The studied metaultramafic rocks occur in the supracrustal sequences on the south of Sao Francisco Craton, at Sao Paulo State portion of the Itapira/Amparo Metamorphic Belt, between the parallels 22o 25’ e 22o 45’ S and the meridians 46o 55’ e 46o 35’ W, preciselly at Serra das Aguas Claras (SAC), situated to the WNW of Aguas de Lindoia city, and at the District of Arcadas (ARC), Amparo city. In the Arcadas/Aguas de Lindoia metamafic/ultramafic belt, the bodies occur like tabular to lenticular intercalations, parallel to the main structure, inside or between metasedimentary rocks of Itapira Complex and orthogneisses or neoproterozoic granitoid rocks. These lithotypes are not enclosed by basement rocks (Amparo Complex), only between these and metasediments and neoproterozoic granitoids. The rocks are represented by metaperidotites, olivine pyroxenites, anthophyllite schists/fels, tremolite/actinolite schists/fels, clinopyroxene-amphibole banded schists, hornblende schists, cummingtonite/grunerite schists, glimmerites, chlorite schists, talc schists, amphibolites and banded diopside amphibolites. Between these two concentration areas of metaultramafic rocks, there are several lenticular bodies, parallel to the general structure, which it suggests that both concentrations were linked and they were disrupted because of tangential and directional tectonics. Syn to tard granitic mobilizations, can be observed the formation of phlogopite and/or biotite schists in the edges of metaultramafic bodies or tectonic discontinuites. Post granitic magma mobilization, i.e., when temperatures were lower than 650 oC, we can analyse processes of amphibole chloritization and talcification (anthophyllite, tremolite and cummingtonite), formation of talc-phlogopite schists, chlorite schists, talc-chlorite schists, talc schists or fels and anthophyllite or tremolite/actinolite amianthus, making metasomatism evident (Fig. 1, 2). At SAC the glimmerites are generally at the edges and along shear zones internal to the lenses; the amphibole-talc schists are in the inner portions and can form preserved cores among biotite schists and talc schists (Fig.3). The hornblende/actinolite schists constitute smaller lenses, even at the edge of metaultramafic bodies or isolated in the granitoid rocks around. Mineralogical transformation noticed in the metamafic and metaultramafic rocks, in association with infiltration features of granitic material and quartz, makes it evident that metamorphic evolution happened at opened chemical system. The variation diagrams suggest SiO2 entry in the system, which is compatible with the talcification process of these rocks. The distribution patterns of rare earth elements and incompatibles, normalized to chondrite C1, show Ce negative anomaly, suggesting oceanic environment for these rocks or metasomatic modification caused by fluid passage. The mobility of major elements (Si, Al, Mg, Fe, Ca, K, Na), can be seen at field and at laboratory observing the processes of phlogopitization, talcification, chloritization, etc., however the quantification is too dificult due to the absence of a rock with preserved former composition. The zirconium, minor elements and, probably, the rare earth elements, mobility can be exemplified with the presence of diminute zircon crystals in quartzvenulation, suggesting in situ crystallization and the entrance of these elementes across fluid solution. Petrography showed that in SAC metaultramafic bodies, retrometamorphic transformations do not allowed preservation of olivine and pyroxene. Bodies with olivine and pyroxenes vestiges occur just at neighbourhood of SAC. Minerals forming the rocks of SAC exhibit minor compositional variance, insinuating better re-equilibrium during retrometamorphism, compared to ARC rocks. This can be due to a major fluid passage, what facilitated generalized phlogopitization, chloritization and talcification and the amianthus formation. The metamafic and metaultramafic lithotypes of ARC region are similar to those of SAC, although the first ones have better preserved mineral assemblage of metamorphic peak. Isotopic Sm/Nd analyses did not permit accurate calculus in relation to eNd. They make evident a strong contamination, which could have happened during magma emplacement or during the evolution of tectonic-metamorphic processes. Rb/Sr method demonstrated that the region was intensively affected by a neoproterozoic event, which was responsible for isotopic changes of palaeoproterozoic and archaean rocks, anatexy and amphibolite facies metamorphism. The ARC occurrences were less affected by greenschist transformation and by metasomatism, which are associated to the final phase of solidification of evolved granites and late anatetic material (Late Proterozoic, possibly with age around 600 Ma). Although, mineralogical evolution is similar to that of SAC, insinuating the same origin and evolution. The metamafic and metaultramafic rocks that appear between the both concentration areas (SAC and ARC) make evident a physical connection of these bodies, before tangential and directional tectonics. Zanardo (1987) and Lazarini (2000) suggested that the rocks treated here were ophiolites disrupted by the tectonics mentioned, but, in face of chemical changes that affected these rocks, it isn´t possible to certify their origin. The authors are grateful to Fapesp, by research assistance (Process 2001/10034-2), and to CNPq (fellowship).

Introduction The Bornaward area is located in the Northeastern Iran (in the Khorasan Razavi province) 28 km northwest of the city of Bardaskan at 57˚ 46΄ to 57˚ 52΄ N latitude and 35˚ 21΄ to 35˚ 24΄E longitude. The Taknar structural zone, situated in the North central Iranian micro continent, is part of the Lut block (Forster, 1978). The Taknar zone is an allochthonous block bounded by the Darouneh and Taknar major faults. Much of this zone consists of metarhyolite-rhyodacite volcanic rocks, and rhyolitic tuff with interlayers of sandstone and dolomite (Taknar Formation). Analytical Results ICP-MS analysis of REE and minor elements of samples of the Bornaward metarhyolites was carried out at the ACME Laboratory in Vancouver, Canada. U-Pb dating of the metarhyolites was performed on isolated zircons in Crohn's Laser Lab, in Arizona (Gehrels et al., 2008). Measurement of Rb, Sr, Sm and Nd isotopes and (143Nd/144Nd)i and (87Sr/86Sr)i ratios took place in the radioisotope laboratory of the University of Aveiro in Portugal. Petrography The volcanic rocks are porphyritic, commonly containing phenocrysts of orthoclase and rarely sanidine, quartz and intermediate plagioclase in a groundmass of fine-grained quartz and feldspar. An alteration has produced oriented needles of sericite and clay minerals, clusters of fine-grained green biotite and clots of epidote and chlorite. Geochemistry The compositions of the volcanic rocks are calc alkaline and high K- calc alkaline. The obtained Shand index (Al2O3/( CaO+Na2O+K2O) is above 1.1, in the peraluminous S-type granite field (Chappell and White, 2001). Plotted on the TAS diagram (Middlemost, 1994), all the metarhyolite-rhyodacite samples are located in the sub-alkaline field and the majority fall into the rhyolite group. The metarhyolite-rhyodacites show enrichment of LREE with a moderately ascending pattern ((La/Yb)N=2.51-10.11 and La=46.45-145.48). Europium shows a negative anomaly (Eu/Eu*=0.23-0.71). U-Pb zircon geochronology Measurement of U-Pb isotopes of the Bornaward metarhyolite zircons of sample BKCh-103, indicates an age of 552.23+4.73,-6.62 Ma (Upper Precambrian). Sr-Nd isotopes The Sr ratios of the metarhyolites (87Sr/86Sr) were found to fall in the range of 0.688949 to 0.723435 and the Nd ratios (143Nd/144Nd)i were in the range of 0.511701 to 0.511855. These values indicate that the metarhyolites of samples BKCh-12, BKCh-103 and BKCh-177 were affected by hydrothermal alteration since their (87Sr/86Sr)I ratios are high. The Sr ratios suggest that the more negative Nd anomaly and the more negative ɛNd(552) of the samples BKCh-12, BKCh-103 and BKCh-177 indicate that these lavas originated in an enriched upper mantle source and/or lower continental crust. In contrast, two recent examples (Xua et al., 2005) can be related to sialic continental crust with significant contamination. Petrogenesis The Bornaward metarhyolite- rhyodacites show an enriched pattern for Rb, Th, U, K, Pb, Nd and Y relative to the primitive mantle, while Ba, P, Ti, Sr, Zr and Nb show a reduction as a result of fractional crystallization. Based on isotopic correlations of207Pb/204Pb vs 206Pb/204Pb, the primitive source of the Bornaward metarhyolite- rhyodacites is the lower continental crust. This part of the continental crust is only slightly depleted in Pb. Consequently, it has a low 87Sr/86Sr ratio (Samples BKCh-138 and BKCh-198). In contrast, the samples of BKCh-12, BKCh-103 and BKCh-177 have high 87Sr/86Sr ratios that could be the result of significant contamination to parts of the continental crust with very high 87Sr/86Sr (Karimpour et al., 2011). Results and Conclusions The calc-alkaline compositions of samples BKCh-12, BKCh-103 and BKCh-177, the high K- calc alkaline of samples BKCh-138 and BKCh-198 of the Bornaward metarhyolites and the higher temperature overgrowth of plagioclase on lower temperature microcline phenocrysts can be a reason for entrance lavas with different generations. The distinct isotopic characteristics of the two groups of rhyolitic samples are the reasons for two different sources for the production of these lavas: 1) partial melting of an enriched mantle reservoir or lower continental crust, and 2) sialic continental crust with high contamination. With respect to the Bornaward metarhyolite- rhyodacites with (143Nd/144Nd)i ratios from 0.511701 to 0.511855, geochemical characteristics and the high volume of volcanic rocks in the area, their formation can be attributed to a continental rift environment. This rift system can be formed by initiation of a plume in the upper mantle beneath East Iran during Neoproterozoic time. References Chappell, B.W. and White, A.J.R., 2001. Two contrasting granite types. Australian Journal of Earth Sciences, 48(4): 489-499. Forster, H., 1978. Mesozoic – cenozoic metallogenesis in Iran. Journal of the Geological Society, 135(4): 443-455. Gehrels, G.E., Valencia, V.A. and Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U–Pb ages by laser ablation–multicollector–inductively coupled plasma-mass spectrometry. Geochemistry, Geophysics, Geosystems, 9(3): 1-13. Karimpour, M.H., Farmer, G.L., Stern, C.R. and Salati, E., 2011. U-Pb zircon geochronology and Sr-Nd isotopic characteristic of Late Neoproterozoic Bornaward granitoids (Taknar zone exotic block), Iran. Iranian Society of Crystallography and Mineralogy, 19(1): 1-18. Middlemost, E.A.K., 1994.Naming materials in the magma igneous rock system. Earth Science Reviews, 37(3- 4): 215-224. Xua, B., Jianb, P., Zhenga, H., Zouc, H., Zhanga, L. and Liub, D., 2005. U–Pb zircon geochronology and geochemistry of Neoproterozoic volcanic rocks in the Tarim Block of northwest China: implications for the breakup of Rodinia supercontinent and Neoproterozoic glaciations. Precambrian Research, 136(2): 107–123.

Introduction Lamprophyres are mesocratic to melanocratic igneous rocks, usually hypabyssal, with a panidiomorphic texture and abundant mafic phenocrysts of dark mica or amphibole (or both) with or without pyroxene, with or without olivine, set in a matrix of the same minerals, and with alkali-feldspar restricted to the groundmass (Woolley et al., 1996). Lamprophyres are frequently associated with orogenic settings and a mantle modified by dehydration of subducted slab (Gibson et al., 1995). Small outcrops of lamprophyres with Paleozoic to Oligocene age are reported from the central parts of Iran (Torabi 2009 and 2010). The primary magmas of these lamprophyres were derived from decompression melting of the mantle induced by a tensional regime of continental crust (Torabi, 2010). Bayat and Torabi (2011) called the western part of the CEIM (Central-East Iranian Microcontinent) (Anarak to Bayazeh) a “Paleozoic lamprophyric province” and suggested that the lamprophyre magmas were formed by subduction of Paleo-Tethys oceanic crust from the Early to late Paleozoic which resulted in the mantle metasomatism and enrichment. Lamprophyric dykes and stocks of the Kal-e-kafi area (Central Iran, Northern part of Yazd Block) cross-cut the Eocene volcanic rocks and other older rock units such as Cretaceous limestone. These lamprophyres are mainly composed of hornblende (magnesio-hastingsite), clinopyroxene (diopside) and plagioclase (labradorite to bytownite) as phenocryst, in a matrix of fine to medium grained of the same minerals and orthoclase, apatite, magnetite, chlorite and epidote. In this paper that is a report on the first study on the calc-alkaline lamprophyres of Central Iran, the petrography and mineral chemistry of calc-alkaline lamprophyric dykes of the Kal-e-kafi area are discussed. Materials and methods Chemical composition of minerals were conducted at Kanazawa University (Kanazawa, Japan) using the wavelength-dispersive electron probe microanalyzer (EPMA) (JEOL JXA-8800R), with 20kV accelerating potential, 20 nA beam current and a counting time of 40 seconds. Natural minerals and synthetic materials were used as standards. The ZAF program was used for data correction. The Fe3+ content of minerals was estimated by stoichiometry. The Mg# and Fe# were calculated as [Mg/(Mg+Fe2+)], and [Fe2+/(Fe2++Mg)] atomic ratio of minerals, respectively. Trace element values of phenocrystic clinopyroxene, amphibole and plagioclase were analyzed by LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) using an ArF 193 nm Excimer Laser coupled to an Agilent 7500S at the Earth Science Department of the Kanazawa University (Japan). The diameter of the analyzed points was 60 micrometers for clinopyroxene and 120 micrometers for amphibole and plagioclase. Mineral abbreviations are adopted from Whitney and Evans (2010). Results and Discussion Lamprophyres of the Kal-e-kafi area (Central Iran, West of Yazd Block) are exposed as dykes and stocks which cross-cut the Eocene volcanic rocks and other older rock units such as Cretaceous limestone. Field studies indicate that calc-alkaline lamprophyric dykes of the Kal-e-kafi (east of Anarak) are younger than the other igneous rocks. According to the results of petrography and mineral chemistry, the mesocratic lamprophyres of Kal-e-kafi area are calc-alkaline spessartite. Unique values of Al2O3 and TiO2 associated with oscillatory zoning of clinopyroxenes reveal the crystallization of clinopyroxenes during ascending of magma. Plagioclase phenocrysts are labradorite to bytownite in composition and the plagioclases of matrix are labradorite. Chemical composition diversity of plagioclase indicates the fractional crystallization of these lamprophyres. Amphibole thermometry estimate average temperature of 860°C and barometry by Anderson and Smith (1995) shows 1.5 to 3 kbars pressure. Clinopyroxene thermobarometry calculate 1150 °C temperature and pressure between 2 to 5 kbars. The geochemical features and thermobarometry of the Kal-e-kafi spessartite minerals suggest that the primary lamprophyric magma was derived from partial melting of a lithospheric mantle spinel lherzolite. Changes in values of pressure, water content, and Oxygen fugacity during magma ascending lead to oscillatory zoning minerals. Based on the mineral chemistry, it can be concluded that the Kal-e-kafi lamprophyres were formed in a subduction-related environment by a calc-alkaline magmatism. References Anderson, J.L. and Smith, D.R., 1995. The effects of temperature and Oxygen fugacity on the Al-in-hornblende barometer, American Mineralogist, 80 (5-6): 549-559. Bayat, F. and Torabi, G., 2011. Alkaline lamprophyric province of Central Iran. Island Arc, 20(3): 386 – 400. Gibson, A.S., Thompson, R.N., Dickin, A.P. and Leonardos, O.H., 1995. High-Ti and low-Ti mafic potassic magmas: key to plume-lithosphereinteractions and continental flood-basalt genesis. Earth Planetary Science Letters, 136(3): 149–165. Torabi, G.H., 2009. Late Permian lamprophyric magmatism in North-East of Isfahan Province, Iran: A mark of rifting in the Gondwanaland. Comptes Rendus Geoscience, 341(1): 85–94. Torabi, G.H., 2010. Early Oligocene alkaline lamprophyric dykes from the Jandaq area (Isfahan Province, Central Iran): Evidence of Central–East Iranian microcontinent confining oceanic crust subduction. Island Arc, 19(2): 277-291. Whitney, D.L. and Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist, 95(1): 185-187. Woolley, A.R., Bergman, S.C., Edgar, A.D., Le Bas, M.J., Mitchell, R.H., Rock, N.M.S. and Scott-Smith, B.H., 1996. Classification of lamprophyres, lamproites, kimberlites and the kalsilite mellitic and leucitic rocks. The Canadian Mineralogist, 34(2): 175-186.

سنگهای ولکانیک ائوسن جنوب‌غرب جندق (کوه گدارسیاه، خردقاره شرق ایران مرکزی) ترکیب بازالت آندزیتی و آندزیت دارند. این سنگها دارای زینولیت‌هایی با کانی‌شناسی گرانولیت می‌باشند. مجموعه کانیایی این زینولیت‌ها در شرایط اوج دگرگونی شامل پلاژیوکلاز+ فلوگوپیت+ کروندوم+ سلیمانیت+ اسپینل+ کلریت+ فنژیت با بافتهای گرانوبلاستیک، پوئیکلیوبلاستیک و جهت‌یافته است. میانگین نتایج دماسنجی فلوگوپیت موجود در این زینولیت‌ها دمای oC 782 را نشان می‌دهد. ویژگیهای این سنگها با دگرگونی رسوبات پوسته‌ای غنی از Al و فقیر از Ca و Si در شرایط پوسته تحتانی در رخساره گرانولیت سازگار است. افزایش درجه دگرگونی و ذوب این گرانولیت‌ها، مذابی را تشکیل داده که گرانیتوئید تیپ S متبلور نموده است. تداوم تفریق و تبلور این مذاب می‌تواند به تشکیل گرانیت‌های تیپ S منجر گردد. از اینرو احتمال می‌رود گرانیت‌های تیپ S موجود در منطقه مورد بررسی، حاصل ذوب گرانولیت‌هایی باشد که بخشهایی از آن به‌صورت زینولیت توسط ماگماتیسم ائوسن جنوب جندق (کوه گدار سیاه) حمل و به سطح زمین رسیده‌اند. گرانیت‌های پرآلومین تیپ S در محدوده مورد بررسی در امتداد گسلهای درونه، چوپانان و آیرکان در مناطق آیرکان و افیولیت جندق رخنمون دارند. این گرانیت‌ها منشأ عناصر رادیواکتیو اورانیم و توریم و کانه‌زایی اورانیم در جنوب‌غرب کوه آیرکان می‌باشند.

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

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Experimental petrology suggested that phlogopite has a peculiar mineral chemistry at high pressure: excess of Si coupled with a decrease in IVAl and deficiency in K+Na. This K-edenite exchange, □XIISi(K+Na)-1Al-1, where □XII is a vacancy in the interlayer, should imply that phlogopites incorporate significant amount of talc component. At high pressure conditions, however, in a fluid saturated system, a talc component might translate into a 10 Å phase component, being the latter phase the product of the reaction talc + H2O = 10 Å phase occurring at P = 4-5 GPa and at T = 600-700 °C. We aim to study the structure of natural and synthetic phlogopites showing this peculiar mineral chemistry. Samples were analysed by single-crystal X-ray diffraction, powder X-ray diffraction with full profile fitting, EMP, SIMS, TEM and Mössbauer spectroscopy. The natural samples were recovered from spinel and garnet wedge peridotites of the Ulten Zone Eastern Italian Alps, (Italy), whereas synthetic ones were obtained from high pressure synthesis in a K-doped lherzolite system. The single crystal X-ray refinements of natural phlogopites, together with the EMP analysis, showed two coupled substitutions: Tschermak (Si + Mg = IVAl + VIAl) and talc exchanges (□ + Si = K + Al), with no octahedral vacancies. The Rietveld refinement of the synthetic samples confirmed the ipersilicic character and K deficiency found with EMPA and SIMS analysis. The c lattice parameter of both synthetic and natural phlogopites positively correlates with the increase of vacancies at the interlayer site, pointing toward the c lattice parameter of the 10Å phase. The tetrahedral α rotation angle of natural phlogopites was about 9°, lower than that expected by Tschermak substitution. The present data indicate that the 10 Å phase component, instead of the talc component, stabilizes the phlogopite structure by reducing the α rotation under high pressure condition. This increases the pressure conditions needed to reach the upper limit value for the tetrahedral rotation.

The ophiolitic Voltri Group in the eastern part of the Ligurian Alps (NW Italy) is made up of a number of thrust sheets emplaced during Alpine collision. These thrust sheets include (1) the Voltri-Rossiglione calcschist unit of Mesozoic high-pressure calcareous micaschists, metavolcanics and slices of serpentinite, overlain by (2) the Beigua serpentinite unit, of mainly antigorite serpentinite and eclogitic metagabbro, in turn overlain by (3) the Erro-Tobbio peridotites. In the northern part of the Voltri Massif, a conspicuous melange-type lithology occurs along the contact of the Beigua serpentinite unit and the Voltri-Rossiglione calcschist unit. In the vicinity of the contact, the structure in the hanging-wall serpentinites is dominated by kink-type crenulations. Towards the base of the serpentinite nappe these crenulations become intense, and veins and patches of talc + chlorite + tremolite + carbonate replace the original antigorite-dominated assemblage. The thrust itself is marked by a layer, at least several tens of metres thick, of intensely deformed and foliated antigorite-bearing talc-chlorite-tremolite schist, enclosing rounded and lense-shaped (phacoid) blocks, up to 25 metres across, of retrogressed eclogitic metagabbro, antigorite serpentinite, metabasic rock, calcschist and schistose micaceous marble. The main features of this chaotic lithology meet the descriptive criteria of a tectonic melange. The structures and assemblages in the wall rock units and those in the melange indicate that the melange lithology developed at a relatively late stage of greenschist facies ductile thrusting, emplacing the Beigua unit onto the rocks of the Voltri-Rossiglione unit. The structures indicate that the blocks and lenses were formed during localized deformation in a relatively narrow zone along the thrust plane via intense stretching and boudinage of the various lithologies in the foot- and hanging wall. The development of talc-chlorite-tremolite-carbonate assemblages at the expense of the overriding antigorite serpentinites require significant calciummetasomatism, hence extensive fluid activity, whilst the microstructures in the melange matrix suggest that the talc-chlorite-tremolite-carbonate assemblage was mechanically weak. It is suggested that both fluid activity and the associated metamorphic reactions strongly facilitated ductile to semi-brittle deformation along the thrust, leading to progressive fragmentation and mixing of the different lithologies and development of a tectonic melange.

In the last decades, helicopter-borne electromagnetic (HEM) method became a focus of interest in the fields of mineral exploration, geological mapping, groundwater resource investigation and environmental monitoring. As a standard approach, researchers use 1-D inversion of the acquired HEM data to recover the conductivity/resistivity-depth models. Since the relation between HEM data and model parameters is strongly nonlinear, in the case of dealing with simple 1-D models which the number of model parameters is less than the number of measured data, i.e. overdetermined system, implementation of regularized nonlinear least square methods is a common approach to recover the model parameters. Among the least square methods, Marquardt-Levenberg acts as an integrated optimization algorithm which comprises both the gradient-descent and Gauss-Newton strategies. This algorithm resolves the deficiencies of the slow convergence of gradient-descent and the singularity of the sparse matrix in the Gauss-Newton. Furthermore, involving the line search strategy improves the objective function to ensure that the algorithm converges to the global optimum point. In this research work, we implemented the Marquardt-Levenberg including the backtracking-Armijo line search for HEM data inverse modeling. Moreover, we used a linear filter of the Fast Hankel Transform (FHT) to figure out the forward operator for data simulation. Developing our algorithm via programming using MATLAB, we successfully obtained a resistivity model of layered earth. We employed the algorithm to recover a resistivity model from the HEM data acquired above the Alut region located at the northwest of Iran where is characterized by shear zone structure consisting of chlorite schist, Phyllite/Phyllonite, metamorphosed limestone and dolomite, mylonite and ultra-mylonite rock units. As a result, in accordance with the geological map the study area, we have successfully derived a resistivity-depth section of the subsurface along the HEM flight line and detected plausible shear zone and mylonitic granite as the favorite targets for the orogenic gold mineralization.

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 reviews the occurrence and significance of talc- and amphibole-rich fault rocks developed in mafic-ultramafic sequences and evaluates their role in deformation and alteration of the oceanic lithosphere from different tectonic settings (from spreading mid-ocean ridges up to orogenic belts). Recently, talc and amphibole-rich fault rocks have been sampled and studied from detachment fault surfaces along slow and ultra-slow spreading mid-ocean ridges, and constraining the conditions of deformation and strain localization during the evolution of oceanic core complexes. These rocks are documented not only in oceanic core complexes, but also in other oceanic fracture zones where ultramafic rocks are exposed on the seafloor, while only few occurrences have been reported in ophiolite sequences. Samples recovered in situ in oceanic settings record heterogeneous deformation (crystal-plastic to cataclastic) under greenschist- facies conditions and are commonly restricted to localized shear zones (< 200 m) and are associated with intense talc-amphibole metasomatism. The presence of mechanically weak minerals, such as talc, serpentine and chlorite, may be critical to the development of such fault zones and may enhance unroofing of upper mantle peridotites and lower crustal gabbroic rocks during seafloor spreading. Talc in particular may be influential in lubricating and softening mylonitic shear zones and can lead to strain localization and focused hydrothermal circulation along such faults. The rheology of these rocks, and its evolution during dehydration reactions could play an important role also in subduction-zone processes and during the formation of ultramafic orogenic belts. Here, we review the occurrence and significance of talc- and amphibole-rich fault rocks in different tectonic settings on the seafloor and evaluate their role in deformation and alteration of the oceanic lithosphere.

The surface properties of minerals have important implications in geology, environment, industry and biotechnology and for certain aspects in the research on the origin of life. This research project aims to widen the knowledge on the nanoscale surface properties of chlorite and phlogopite by means of advanced methodologies, and also to investigate the interaction of fundamental biomolecules, such as nucleotides, RNA, DNA and amino acid glycine with the surface of the selected phyllosilicates. Multiple advanced and complex experimental approaches based on scanning probe microscopy and spatially resolved spectroscopy were used and in some cases specifically developed. The results demonstrate that chlorite exposes at the surface atomically flat terraces with 0.5 nm steps typically generated by the fragmentation of the octahedral sheet of the interlayer (brucitic-type). This fragmentation at the nanoscale generates a high anisotropy and inhomogeneity with surface type and isomorphous cationic substitutions determining variations of the effective surface potential difference, ranging between 50-100 mV and 400-500 mV, when measured in air, between the TOT surface and the interlayer brucitic sheet. The surface potential was ascribed to be the driving force of the observed high affinity of the surface with the fundamental biomolecules, like single molecules of nucleotides, DNA, RNA and amino acids. Phlogopite was also observed to present an extended atomically flat surface, featuring negative surface potential values of some hundreds of millivolts and no significant local variations. Phlogopite surface was sometimes observed to present curvature features that may be ascribed to local substitutions of the interlayer cations or the presence of a crystal lattice mismatch or structural defects, such as stacking faults or dislocation loops. Surface chemistry was found similar to the bulk. The study of the interaction with nucleotides and glycine revealed a lower affinity with respect to the brucite-like surface of chlorite.

The Mount Fitton talc deposit and associated alteration, located in the northern Adelaide Geosyncline, has been observed to have characteristic spectral signatures in the short-wave infrared and thermal infrared wavelength regions. In particular, reflectance and emissivity spectral measurements of field samples collected in the area have been shown to contain spectral absorption features diagnostic of talc, muscovite/white mica, chlorite, and amphibole minerals. Such minerals are products of the hydrothermal alteration associated with the formation of talc mineralisation. Spectral measurements of field samples also identified other minerals related to the host-rock composition, such as quartz, dolomite, calcite, magnesite and mica/illite. The distinct, and often unique, nature of these spectral signatures indicates the potential for mapping alteration and lithological units at Mount Fitton. Several airborne sensors and recently launched satellite-borne systems have acquired data in the Mount Fitton area, and these data have been processed to evaluate their ability to map the outcropping geology. In particular, the Mount Fitton test site has been used to test various remote-sensing systems with different spectral and spatial resolutions, wavelength ranges and viewing platforms, for their ability to provide useful exploration information, including the location and nature of hydrothermal alteration. Although airborne and satellite-borne multi-spectral systems successfully discriminated geological units and mineral groups, identification of talc and other alteration minerals without a priori information required hyperspectral sensors. It was also found that higher signal-to-noise, spectral resolution and access to different wavelength regions improved the mapping of talc and associated alteration. Spectrally derived mineral maps were found to provide useful supplementary information, which complements traditional airborne geophysical datasets, such as radiometrics or magnetics.

반암동 광화작용이 수반된 관입암체로 이루어진 촉트체치 지역은 몽골 남부 중앙아시아 조산대의 구르반사이한 호상열도 지형에 위치한다. 이러한 촉트체치 지역에서 예비조사를 수행하였다. 촉트체치 지역의 동 광화작용은 페름기에 관입한 알칼리 화강암과 관련된 반암동 광상이다. 공작석이 산출되는 알칼리 화강암 지역에서 프로필리틱 변질대가 넓게 분포한다. 편광현미경에서 확인된 광석광물은 자철석, 황철석, 반동석이다. 프로필리틱 변질대 시료에서는 석영, 견운모, 녹니석, 녹렴석 등이 관찰되었다. XRD와 SEM-EDS 분석 결과 동 광물은 주로 공작석과 적동석으로 이루어진다. 공작석 산출지에서 채취한 시료의 평균 동 함량은 759 ppm이고 최대 동 함량은 6190 ppm이다. 촉트체치 지역의 광화작용 특성은 촉트체치 지역으로부터 남쪽으로 56 km 떨어진 오유 톨고이 동-금(-몰리브덴) 광상 및 북동쪽으로 120 km 떨어진 차간 수바르가 동-몰리브덴 광상과 유사하다. 조사지역의 지질, 지구조 환경, 암상, 광물, 변질 등이 다른 반암동 광상과 유사한 특성을 갖는다. 따라서 촉트체치동 광화 지역에 대해 지하 광체 확인을 위한 IP 탐사를 포함한 추가 광물자원 탐사가 필요하다.

The meta-ultramafic rocks that are part of the Paleoproterozoic unit termed the Nyong Series in SE Cameroon were investigated in this study. The lithologic assemblage mapped is exposed on a cliff face and consists of distinguishable horizons that include least, moderately to intensely altered pyroxenite to amphibolite units. The rocks are partially to completely serpenitinized and foliated. The main mineral phases identified under the microscope include pyroxenes (clinopyroxene and orthopyroxene), olivine, hornblende, plagioclase, garnet and sulphides. The rocks depict variable alteration of the pyroxenes and other primary minerals such as olivine to actinolite, chlorite, serpentine, talc, epidote and tremolite. Electron microprobe analysis on chlorite show that the principal chlorite type ranges from talc-chlorite to penninite. Using the chlorite geothermometer it is observed that the hydrothermal alteration temperatures vary between 160-180°C. This has been overprinted by surface temperatures (20 - 40°C) during the process of weathering.