Petrology and geochronology of andalusite- and sillimanite-bearing kyanite metapelites from the Gobi Altai Mountains: Evidence for prolonged convergent tectonics in the Central Asian Orogenic Belt

Adsorption of lead(II) as a major heavy metal pollutant onto nano-adsorbents of Andalusite, Kyanite and Sillimanite was studied in a batch system. Nano­-adsorbents were prepared via crushing, using a planetary ball mill and then characterized by different analyses such as: SEM, XRD, XRF and FT-IR. Major factors affecting the adsorption process were studied including pH, adsorbents dosage, initial metal concentration and temperature. Afterward, the adsorption process was studied isothermally, kinetically, and thermodynamically. The results show that aluminum silicates polymorphs are efficient adsorbents for removal of lead(II) and the removal exceeds 90%. The Freundlich isotherm model was best fitted with the experimental data. Chemisorption may control the rate of adsorption due to following the pseudo-second-order kinetic model. Thermodynamic investigation proved low randomness, exothermic and spontaneous nature of the process.

مجموعه گرانیتوئیدی کلاه قاضی در جنوب اصفهان و در پهنه ساختاری سنندج‌- سیرجان واقع شده است. بر اساس شواهد زمین‌شناسی سن احتمالی این مجموعه ژوراسیک بالایی بوده و شامل گروه های سنگی گرانودیوریت، گرانیت و آلکالی فلدسپار گرانیت است. کانی های اصلی تشکیل‌دهنده این مجموعه شامل کوارتز، پلاژیوکلاز و فلدسپار آلکالن بوده و بیوتیت تنها کانی فرومنیزین این مجموعه نفوذی است. حضور کانی های آندالوزیت، سیلیمانیت و گارنت در این مجموعه گرانیتوئیدی نشان‌دهنده منشأ رسوبی توده های مورد بررسی است. بر اساس مطالعات صحرایی، پتروگرافی و ژئوشیمیایی، سنگ‌های مجموعه نفوذی مورد بررسی در گروه گرانیتوئیدهای نوع S قرار می گیرند و دارای ماهیت کالک‌آلکالن پتاسیم بالا و از نوع پرآلومین هستند. از لحاظ ژئوشیمیایی طیف تغییرات SiO2 در نمونه های آنالیزشده از 6/64 تا 4/74 متغیر است. الگوی تغییرات عناصر کمیاب بهنجار شده نسبت به گوشته اولیه و کندریت بیانگر غنی‌شدگی این سنگ‌ها از LILE و LREE و تهی شدگی از HFSE و HREE است. نسبت 85/0-28/0 Eu/Eu*= در نمونه های کلاه قاضی نشان‌دهنده حضور اندکی پلاژیوکلاز در باقی‌مانده ذوب در منبع است. بر اساس شواهد زمین‌شناسی، کانی شناسی و ژئوشیمیایی مجموعه نفوذی کلاه قاضی در ژوراسیک بالایی و در طی نفوذ مذاب‌های گوشته ای به داخل پوسته و ذوب‌بخشی سنگ‌های پوسته ای تشکیل شده است.

Phase relation and Al/Si-disordering of sillimanite at high temperatures

In situ U-Pb geochronology was carried out on amphibolites and siliciclastic metasediments of the Kinzigite Formation exposed in the northernmost sector of the Ivrea-Verbano Zone (Finero area). The aim is to shed light on the tectono-metamorphic evolution of this intermediate-lower crustal section and its bearing with the evolution of the southern and better known sectors of the IVZ. Based on field observation and petrography a metamorphic gradient gently increasing from amphibolite to upper amphibolite facies (from SE to NW) characterizes the whole metamorphic sequence. Metapelites consist mainly of biotite, quartz, plagioclase, garnet, and sillimanite; muscovite progressively disappears as K-feldspar appears and becomes abundant. Amphibolites are made of green-brown hornblende and plagioclase and may contain clinopyroxene defining thin layers together with plagioclase and titanite. Both metapelites and amphibolites show mylonitic deformation which is more intense towards NW, i.e. towards the lower structural levels. The mylonitic deformation strongly affected the lower crustal metabasic rocks of External Gabbro unit (Finero Mafic Complex). Zircon, monazite and titanite U-Pb geochronology was carried out with laser ablation (LA)-ICP-MS on amphibolites, migmatitic paragneiss and mafic granulites occurring as slivers of the Kinzigite Formation in the External Gabbro unit of the Finero Mafic Complex. The multi-chronological approach allowed recognizing three discrete tectono-metamorphic events, at Permian, Triassic and Jurassic. Zircon and monazite yielded Permian ages suggesting (re)crystallization during an high temperature event characterized by both metamorphism and magmatism. Titanite dating provided Triassic and Jurassic ages that were interpreted as U-Pb resetting ages. A Triassic perturbation of the U-Pb system was also recorded by zircon and monazite as rare domains. The tectono-metamorphic reconstruction of the evolution of the northernmost IVZ, as revealed by the new geochronological data, is only partially in agreement with the temperature-time evolutions depicted for the southern sectors of the IVZ. Permian ages indicating magmatism and high temperature metamorphism are common throughout the IVZ, as well as the Jurassic ages related to local thermal pulses and tectonic activity. Conversely, the occurrence of well-constrained Triassic ages is in fact peculiar of the Finero area. Two possible explanations may account for this Triassic event: Triassic ages are possibly related to the thermal effect and fluid circulation during the emplacement of the External Gabbro unit; or alternatively, they are the response to the ductile deformation largely recognized in the whole area. This study is a further evidence of the necessity of approaching crystalline basement with multiple geochronometers in order to unravel the complete tectono-metamorphic evolution.

The present study is focused on the influence of tidal cycle on heavy minerals variation in the beaches at Kottilpaducoast of Kanyakumari district, Tamil Nadu. The study area is enriched with a variety of heavy minerals, mostcommonly with ilmenite, along with monazite, rutile, zircon, garnet etc. These placer deposits often vary indistribution due to the effect of tides as well as waves. 5 sampling stations were selected to represent the beach and daily monitoring was carried out during high and low tide levels. oreover, wave parameters such as wave height, wave period, littoral drift and wave direction are also taken into consideration. Further, the sediment samples were analyzed for size fraction and mineral composition. The beach morphology was assessed based on beach profile data. The results reveal that high percentage of heavy minerals is noticed at high tide and low percentage at low tide. Exceptions are noticed in few samples which may be due to varied hydrodynamic conditions prevails in the study area. In all samples more than 40% constitute opaques followed by sillimanite <25% and other constitute rest of the percentage. From the XRD analysis, the peak positions shown by diffractogram is ilmenite (FeTiO3) pyrope and pseudorutile (Fe2Ti3O9), sillimanite (AlFeO2.SiO5), zircon (ZrSiO4) and rutile (TiO2). X-ray fluorescence analytical results also reflect what was inferred from XRD and point counting data. The heavy mineral assemblage of the beach sediment indicates the possibility of mineral supply from alongshore and offshore sources.

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.

The polymorphic modifications of Al2SiO5, namely kyanite, andalusite, and sillimanite, are the most important indicators of metamorphism in rocks. Having the same chemical composition, they are characterized by different crystal structures stable at different P–T parameters. Based on various trends of the evolution of temperature with depth and the rela� tionships between these trends on the P–T diagram with the stability fields of Al2 SiO 5 polymorphs, differ� ent “baric” types of metamorphism are distinguished. Andalusite is stable at low pressures and temperatures; at a pressure increase it is replaced by kyanite, and at a temperature increase, both of them are replaced by sil� limanite, which results in the formation of zoned metamorphic complexes of low and moderate pres� sures.

Heavy minerals in the Pearl River sediments have excellent correlation with their source rocks.Obvious differences in heavy minerals assemblages and their diagnostic minerals have been studied in different branches of the River.The source of the river deposits can be divided into three provinces from west to east on the basis of heavy minerals assemblage types,mineral index(ATi,ZTi,ZTR) values and their correlation.The western province includes the upper reaches of the Xijiang River,where occurs a magnetite-ilmenite-zircon-leucoxene-apatite assemblage characterized by magnetite,ilmenite,apatite and chromite,indicating a provenance dominated by carbonate,with some metamorphic and basic rocks,and scarce ultrabasic and acid rocks.The middle province is located in the lower reaches of the Xijiang River,which is featured by a zircon-ilmenite-magnetite-tourmaline-leucoxene-epidote assemblage,characterized by pyroxene,leucoxene,zircon and epidote,indicating a provenance of clastic rocks and other sedimentary rocks with some metamorphic,basic and acid igneous rocks,as a mixture of local sources and the heavy minerals from upper reaches.The eastern province is the source area of the Dongjiang and Beijiang Rivers dominated by the assemblage of hornblende-tourmaline-magnetite-ilmenite-epidote-garnet characterized by hornblende,tourmaline,garnet,titanite and sillimanite,indicating a provenance of acid rocks with some metamorphic and small amount of sedimentary rocks.The results demonstrate that the characteristics of heavy minerals assemblages are useful tools to trace the provenance evolution of the Pearl River,and of significance in revealing the erosion-transportation-sedimentation pattern in the Pearl River region for source-sink comparison and analysis.

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 Knoxville 1°x 2° quadrangle spans the Southern Blue Ridge physiographic province at its widest point from eastern Tennessee across western North Carolina to the northwest corner of South Carolina. The quadrangle also contains small parts of the Valley and Ridge province in Tennessee and the Piedmont province in North and South Carolina. Bedrock in the Valley and Ridge consists of unmetamorphosed, folded and thrust-faulted Paleozoic miogeoclinal sedimentary rocks ranging in age from Cambrian to Mississippian. The Blue Ridge is a complex of stacked thrust sheets divided into three parts: (1) a west flank underlain by rocks of the Late Proterozoic and Early Cambrian Chilhowee Group and slightly metamorphosed Late Proterozoic Ocoee Supergroup west of the Greenbrier fault; (2) a central part containing crystalline basement of Middle Proterozoic age (Grenville), Ocoee Supergroup rocks east of the Greenbrier fault, and rocks of the Murphy belt; and (3) an east flank containing the Helen, Tallulah Falls, and Richard Russell thrust sheets and the amphibolitic basement complex. All of the east flank thrust sheets contain polydeformed and metamorphosed sedimentary and igneous rocks of mostly Proterozoic age. The Blue Ridge is separated by the Brevard fault zone from a large area of rocks of the Inner Piedmont to the east, which contains the Six Mile thrust sheet and the ChaugaWalhalla thrust complex. All of these rocks are also polydeformed and metamorphosed sedimentary and igneous rocks. The Inner Piedmont rocks in this area occupy both the Piedmont and part of the Blue Ridge physiographic provinces. The intensity of deformation and metamorphism increases from west to east in the Blue Ridge. The west flank is mostly chlorite grade or relatively unmetamorphosed, and the central part of the Blue Ridge is mostly staurolite, garnet, or biotite grade, although sillimanite grade rocks occur along the eastern part of the central Blue Ridge in the vicinity of the leading edge of the Hayesvil Ie fault. The east flank of the Blue Ridge and much of the Inner Piedmont are at kyanite or silli manite grade of Manuscript approved for publication February 22, 1991. regional metamorphism except for a zone of retrograde rocks in the Brevard fault zone and a small area of biotite-grade rocks in the extreme southwest part of the Grandfather Mountain window in the northeast corner of the quadrangle. The major mineral resources in the Knoxville 1°x2° quadrangle are construction materials and a variety of industrial minerals mostly related to either granite and pegmatite or ultramafic rocks. Past production in the quadrangle of metals, which are of secondary importance relative to construction materials and industrial minerals, include copper in massive sulfides of the Besshi type, gold-bearing quartz veins, and residual iron and manganese deposits. Resources are discussed in relation to the Valley and Ridge, Blue Ridge, and Piedmont provinces. The following resources are the most important: A. Construction materials: Dimension stone of the Tennessee marble district in the Valley and Ridge. Limestone and dolomite of the Valley and Ridge. Sand and gravel and crushed stone, widespread throughout the quadrangle. B. Industrial minerals: Feldspar, flake mica, and quartz produced by flotation methods from the Spruce Pine Alaskite (muscovite granodiorite) in the east flank of the Blue Ridge. The district produces about half of the U.S. feldspar and significant amounts of the U.S. flake mica. Olivine produced from alpine-type dunite bodies in the east flank of the Blue Ridge. Talc and marble from the Murphy belt in the central part of the Blue Ridge, Vermiculite produced from a large deposit near Tigerville, S.C-, in the Inner Piedmont. Deposit worked out and mine backfilled. Smaller deposits associated with ultramafic rocks in the east flank of the Blue Ridge are now uneconomic and have not been worked in the past 20 years. C. Metals: Copper in three deposits, the Fontana and Hazel Creek mines in the Great Smoky Mountains Abstract Figure 1. Location of the Knoxville 1ºx2º quadrangle, with state and county boundaries National Park in the Central Blue Ridge, and the Cullowhee mine in the east flank of the Blue Ridge. D. Organic fuels: The rocks of the quadrangle contain no coal and probably lie outside the maximum range in thermal maturity permitting the survival of oil. The rocks in the Valley and Ridge and for a short distance eastward below the west flank of the Blue Ridge probably lie within a zone of thermal maturity permitting the survival of natural gas. Consequently the western part of the quadrangle is an area of high risk for hydrocarbon exploration. No exploration drilling has been done in this belt.

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.

The PALMEIROPOLIS Cu-Zn (Pb) volcanogenic massive sulfide deposit, Brazil, consists of three ore bodies enclosed by hydrothermal alteration zones. The ore bodies and the alteration zones were metamorphosed under amphibolite fades conditions. The Palmeirdpolis alteration zones are characterized by a great diversity of bulk rock composition that originated a wide variety of low variance mineral assemblages. These assemblages are composed of orthoamphiboles (anthophyllite and gedrite), hornblende, biotite, garnet, staurolite, sillimanite, gahnite and, rarer, cordierite. Based on analyses of mineral chemistry aad mineral assemblages, temperatures are estimated to have been 550 - 625°C and pressures 2 - 5.5 kbar. The temperature of metamorphism that prevailed at the Palmeirdpolis deposit is comparable to other amphibolite fades massive sulfide deposits, such as Geco and Linda, Canada; Falun, Sweden; and Bleikvassli, Norway. The mineralogy of the alteration zones is similar in all these deposits even though they were metamorphosed at different pressure conditions, reflected by the crystallization of one of Al2 SiO5 phase (andalusite, sillimanite or kyanite).

The Limpopo Belt of southern Africa is generally believed to represent the root of a late Archaean continental collision zone, and has been used to demonstrate the validity of the uniformitarian concept in tectonics Large scale tectonic models have been applied in spite of the fact that large portions of the belt yet await the most basic investigations. Here we report the first detailed field and petrographic study of the northernmost part of the Limpopo Belt, the Northern Marginal Zone sensu stricto (NMZ s.s) and conclude, on the basis of relative age relation, nature of PT evolution and deformation, that none of the current models can correctly explain the evolution of the study area. The evolution of NMZ s.s, is complex and includes four metamorphic stages, two major plutonic episodes and at least three deformation events. The oldest rocks, mafic granulites, record all four stages of metamorphic mineral growth. The first two stages predate deposition of sediments and the intrusion of voluminous enderbite and charnockite between 2.72 and 2.62 Ga. The bulk of our observations relate to the late Archaean (stage 3) granulite facies event. Abundant reaction textures are preserved in mafic granulite, metasediments, metamorphosed charnockite and enderbite and allow us to qualitatively reconstruct the PT evolution. Prograde heating occurred in the sillimanite stability held. During peak temperature conditions vapour-absent melting is observed in most felsic lithologies,Temperatures between 800 and 850 degrees C at pressures as low as 0.4-0.5 GPa are indicated by various mineral assemblages. The thermal peak was followed by an increase in pressure. Typical reactions of anti-clockwise PT evolution, like breakdown of cordierite + spinel to sapphirine and orthopyroxene + plagioclase to garnet + quartz, are frequently found. Maximum pressure is constraint to ca. 0.85 GPa by the complete absence of garnet in mafic granulites. Initial cooling was rapid, and is indicated by the back reaction of melt + orthopyroxene to biotite + quartz symplectites preserved in migmatites. This metamorphic event was accompanied by intrusion of porphyritic charnockite and granite, and by coeval compressional deformation. The observed evolution, especially the combination of an anti-clockwise PT loop and compressional tectonics, requires a strong, transient heat-source affecting the base of the crust. Neither the thermal evolution nor the relative timing is correctly predicted by existing collision models. The NMZ s.s. granulites were finally exhumed in a separate event along upper greenschist-facies thrusts, in response to a transpressive orogeny affecting the units further south at 2.0 Ga. In spite of potential ambiguities inherent to a qualitative approach, our observations show that petrography and field work, if used in conjunction with dating of a few key age relations and structural interpretation, are a pre-requisite to the erection of realistic tectonic models. The example of the NMZ s.s. may encourage geoscientists with limited access to analytical facilities to reassess the geological evolution of terrains which lack basic description.

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The paramagnetic resonance spectra of Cr3+ and Fe3+ in natural crystals of the mineral sillimanite have been investigated. The chromium results can be interpreted with a spin Hamiltonian having axial and rhombic terms. Four magnetically inequivalent (directionally) sites (Site I) are observed, with parameters g⊥ = 1.975, g∥ = 1.963, B = 6.91, and B = 3.77 GHz. The iron results have been interpreted on the assumption that Fe3+ occupies the two crystallographically inequivalent Al3+ sites in the sillimanite. Site II having tetrahedral coordination and Site III octahedral coordination. The constants of the conventional orthorhombic spin Hamiltonian are as follows, Site II: B = 1.74 GHz, B = 1.62 GHz, B = 0.0 GHz, B = 0.0 GHz, B = 0.0 GHz, and gx = gy = gz = 2.004; Site III: B = 11.8 GHz, B = 4.04 GHz, B = 0.37 GHz, B = 0.09 GHz, and gx = gy = gz = 2.004. A comparison of the results for the octahedrally coordinated sites in the three polymorphs kyanite, andalusite, and sillimanite is made. Die EPR-Spektren von Cr3+ und Fe3− in naturlichen Kristallen des Minerals Sillimanit wurden untersucht. Die Ergebnisse an Chrom konnen mit einem Spin-Hamiltonian mit axialen und rhombischen Termen interpretiert werden. Vier magnetisch nichtaquivalente (Richtung) Platze (Platz I) werden beobachtet, mit Parametern g⊥ = 1.975, g∥ = 1.963, B = 6,91 und B = 3.77 GHz. Die Ergebnisse an Eisen werden mit der Annahme erklart, das Fe3+ die beiden kristallographisch inaquivalenten Al3+-Platze in Sillimanit — Platz II hat tetraedrische und Platz III oktaedrische Koordination — besetzt. Die Konstanten des konventionellen rhombischen Spin-Hamiltonians sind fur Platz II: B = 1,74 GHz, B = 1.62 GHz, B = 0,0 GHz, B = 0,0 GHz, B = 0,0 GHz und gx = gy = gr = 2,004; fur Platz III: B = 11,8 GHz, B = 4,04 GHz, B = 0.37 GHz, B = 0,09 GHz und gx = gy = gz = 2,004. Ein Vergleich der Ergebnisse fur die oktaedrisch koordinierten Platze wurde fur die drei Polymorphe Cyanit, Andalusit und Sillimanit durchgefuhrt.

The paper describes the results obtained from the x-ray K-band spectra of Al for andalusite, sillimanite and kyanite. The fine structure of the aluminium K-band is correlated with the crystal structure of these minerals. It is considered that the difference between the energies of the K-and .KTjS'-lines depends on the distance between the aluminium and oxygen atoms. The energy differences between the Al and O atoms in andalusite, sillimanite and kyanite have been determined. The energy differences show a linear correlation to the known interatomic distances.

Sillimanite from the Kyakhta deposit