Geochronology and origin of Paleoproterozoic charnockites with old crustal signature in the Haisyn block of the Ukrainian shield

Results of a geochemical and geochronological study of the Paleoproterozoic rock assemblage in the Haisyn block of the Ros-Tikych Domain of the Ukrainian Shield are reported.Within the block,the Haisyn Complex comprises granitoids,including pyroxene-bearing diorites,quartz diorites,granodiorites,amphibole-biotite and biotite granites,and aplite and pegmatite granites.Monazite U-Pb isotope age of charnockitic syenite belonging to the Haisyn Complex was defined at 2027±6 Ma.This age coeval with the time of granulite facies metamorphism and emplacement of numerous granitic intrusions in the area.The Sm–Nd apatite isochron yielded an age of 2100±150 Ma.TheεNd isochron value of-5 indicates a long crustal residence time of the crustal protolith.Geochemical data do not indicate any enrichment of the studied rocks in relation to the Eoarchean and Neoarchean charnockites developed in the same area.So,if the model of partial melting of the older crustal protolith is involved then the degree of melting must be quite high.However,deep negative anomalies of Sr,Eu,Zr,and Ti indicate that plagioclase,zircon,and Fe–Ti oxides probably remained unmelted in the source.The Haisyn block was buried in the lower crust at high temperature and pressure conditions in the Paleoproterozoic time.Such a situation resulted in partial melting of the existing crust and formation of melts,containing undigested zircon and bearing ancient Nd isotope signature.

Proterozoic Granitization of the Archaean Gneisses in the Central Zone of the Precambrian Limpopo High-grade Terrain

Our research covers the granitization and charnockitization processes that affected the metapelitic gneisses in the Central Zone of the Precambrian Limpopo high-grade terrain,South Africa.Precambrian granulite facies terrains underwent two regional high-grade events,of which the first one occurred

The potential role of fluids during regional granulitefacies dehydration in the lower crust

High-grade dehydration of amphibolite-facies rocks to granulite-facies is a process that can involve partial melting, fluid-aided solid-state dehydration, or varying degrees of both. On the localized meter scale, solid-state dehydration, due to CO：-rich fluids traveling along some fissure or crack and subsequently outwards along the mineral grain boundaries of the surrounding rock, normally is the means by which the breakdown of biotite and amphibole to orthopyroxene and clinopyroxene occur. Various mineral textures and changes in mineral chemistry seen in these rocks are also seen in more regional orthopyroxene-clinopyroxene-bearing rocks which, along with accompanying amphibolite-facies rocks, form traverses of lower crust. This suggests that solid-state dehydration during high-grade metamorphism could occur on a more regional scale. The more prominent of these fluid-induced textures in the granulite- facies portion of the traverse take the form of micro-veins of K-feldspar along quartz grain boundaries and the formation of monazite inclusions in fluorapatite. The fluids believed responsible take the form of concentrated NaCl- and KCl- brines from a basement ultramafic magma heat source traveling upwards along grain boundaries. Additional experimental work involving CaSO4 dissolution in NaCl-brines, coupled with natural observation of oxide and sulfide mineral associations in granulite-facies rocks, have demonstrated the possibility that NaCl-brines, with a CaSO4 component, could impose the oxygen fugacity on these rocks as opposed to the oxygen fugacity being inherent in their protoliths. These results, taken together, lend credence to the idea that regional chemical modification of the lower crust is an evolutionary process controlled by fluids migrating upwards from the lithospheric mantle along grain boundaries into and through the lower crust where they both modify the rock and are modified by it.Their presence allows for rapid mass and heat transport and subsequent mineral genesis and mineral re- equilibration in the rocks through which they pass.

Phase equilibrium modeling of incipient charnockite formation in NCKFMASHTO and MnNCKFMASHTO systems:A case study from Rajapalaiyam,Madurai Block,southern India

Incipient charnockites represent granulite formation on a mesoscopic scale and have received considerable attention in understanding fluid processes in the deep crust. Here we report new petrological data from an incipient charuockite locality at Rajapalaiyam in the Madurai Block, southern India, and discuss the petrogenesis based on mineral phase equilibrium modeling and pseudosection analysis. Rajapalaiyam is a key locality in southern India from where diagnostic mineral assemblages for ultrahigh-temperature （UHT） metamorphism have been reported. Proximal to the UHT rocks are patches and lenses of charnockite （Kfs＋Qtz ＋Pl＋ Bt ＋ Opx＋ Grt ＋Ilm） occurring within Opx-free Grt-Bt gneiss （Kfs ＋Pl ＋ Qtz ＋ Bt ＋ Grt ＋ Ilm ＋ Mt） which we report in this study. The application of mineral equilibrium modeling on the charnockitic assemblage in NCKFMASHTO system yields a p-T range of 820 ℃ and -9 kbar. Modeling of the charnockite assemblage in the MnNCKFMASHTO system indicates a slight shift of the equilibrium condition toward lower p and T （- 760 ℃ and - 7.5 kbar）, which is consistent with the results obtained fiom geothermobarometry （710--760 ℃, 6.7-7.5 kbar）, but significantly lower than the peak temperatures （〉1000 ℃） recorded from the UHT rocks in this locality, suggesting that charnockitization is a post-peak event. The modeling of 7 versus molar H2O content in the rock （M（H2O）） demonstrates that the Opx-bearing assemblage in charnockite and Opx- free assemblage in Grt-Bt gneiss are both stable at M（H2O） = 0.3 mol%--0.6 mol%, and there is no significant difference in water activity between the two domains. Our finding is in contrast to the previous petrogenetic model of incipient charnockite formation which envisages lowering of water activity and stabilization of orthopyroxene through breakdown of biotite by dehydration caused by the infiltration of CO2-rich fluid. T-XFe3＋ （= Fe2O3/（FeO ＋ Fe2O3） in mole） pseudosections suggest that the oxidation condition of the rocks played a major role on the stability of orthopyroxene; Opx is stable at XFe3＋〈0.03 in charnockite, while Opx-free assemblage in Grt-Bt gneiss is stabilized at XFe3＋ 〉0.12. Such low oxygen fugacity conditions of XFe3＋ 〈0.03 in the charnockite compared to Ort-Bt gneiss might be related to the infiltration of a reduced fluid （e.g., H2O ＋ CH4） during the retrograde stage.

A geochemical perspective on charnockite magmatism in Peninsular India

Large charnockite massifs occur in the high-grade Southern Granulite Terrain （SGT） and Eastern Ghats Belt （EGB） crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is episodic, associated with distinct orogenic cycles in the different crustal domains. The geochemical data also indicate a change in composition from trondhjemitic at - 3.0-2.9 Ga to domi- nantly tonalitic at - 2.6-2.5 Ga to tonalitic-granodiorite-granitic at - 2.0--1.9 Ga to dominantly tonalitic at 1.7--1.6 Ga to quartz monzonitic or tonalitic at - 1.0-0.9 Ga to granodiorite-granitic at - 0.8-0.7 Ga. The trondhjemitic and tonalitic end members are metaluminous, magnesian and calcic to calc-alkalic, characteristic of magnesian group charnockites. The granodioritic to granitic end members are metalumi- nous to slightly peraluminous, ferroan and calc-alkalic to alkali-calcic, characteristic of ferroan group charnockites. The quartz monzonitic end members are metaluminous to peraluminous, magnesian to ferro- an and calcic to calc-alkalic, neither characteristic of the magnesian group nor of the ferroan group of char- nockites. Based on the occurrence and difference in composition of the charnockite massifs, it is suggested that the charnockite magmatism registers the crustal growth of the Indian plate on its southern （SGT） and eastern （EGB） sides, along active continental margins by accretion of arcs.

Charnockite microstructures:From magmatic to metamorphic

Charnockites sensu lato （charnockite-enderbite series） are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. They either represent dry （H2O-poor） felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. In the first case, post- magmatic high-temperature recrystallisation may result in widespread metamorphic granulite microstruc- tures, superimposed or replacing the magmatic microstructures. Despite recrystallisation, magmatic remnants may still be found, notably in the form of melt-related microstructures such as melt inclusions. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at inter- grain boundaries during retrogradation are documented by microstructures including K-feldspar micro- veins and myrmekites. They indicate that a large quantity of low-H2O activity salt-rich brines, were present （together with CO2 under immiscible conditions） in the lower crust.

Experimental and petrological constraints on local-scale interaction of biotite-amphibole gneiss with H_2O-CO_2-(K,Na) Cl fluids at middle-crustal conditions:Example from the Limpopo Complex,South Africa

Reaction textures and fluid inclusions in the -2.0 Ga pyroxene-bearing dehydration zones within the Sand River biotite-hornblende orthogneisses （Central Zone of the Limpopo Complex） suggest that the formation of these zones is a result of close interplay between dehydration process along ductile shear zones triggered by H2O-CO2-salt fluids at 750--800 ℃ and 5.5--6.2 kbar, partial melting, and later exsolution of residual brine and H2O-CO2 fluids during melt crystallization at 650--700 ℃. These processes caused local variations of water and alkali activity in the fluids, resulting in various mineral assemblages within the dehydration zone. The petrological observations are substantiated by experiments on the interaction of the Sand River gneiss with the H2O-CO2-（K, Na）Cl fluids at 750 and 800 ℃ and 5.5 kbar. It follows that the interaction of biotite-amphibole gneiss with H2O-CO2-（K, Na）CI fluids is accompanied by partial melting at 750--800 ℃. Orthopyroxene-bearing assemblages are characteristic for temperature 800 ℃ and are stable in equilibrium with fluids with low salt concentrations, while salt-rich fluids produce clinopyroxene-bearing assemblages. These observations are in good agreement with the petrological data on the dehydration zones within the Sand River olthogneisses.

Multiple origins of charnockite in the Mesoproterozoic Natal belt,Kwazulu-Natal,South Africa

Four different varieties of charnockitic rocks, with different modes of formation, from the Mesoproterozoic Natal belt are described and new C isotope data presented. Excellent coastal exposures in a number of quarries and river sections make this part of the Natal belt a good location for observing charnockitic field relationships. Whereas there has been much debate on genesis of charnockites and the use of the term charnockite, it is generally recognized that the stabilization of orthopyroxene relative to biotite in granitoid rocks is a function of low aH2O （-- high CO2）, high temperature, and composition （especially Fe/（Fe ＋Mg））. From the Natal belt exposures, it is evident that syn-emplacement, magmatic crystallization of charnockite can arise from mantle-derived differentiated melts that are inherently hot and dry （as in the Oribi Gorge granites and Munster enderbite）, as well as from wet granitic melts that have been affected through interaction with dry country rock to produce localized charnockitic marginal facies in plutons （as in the Portobello Granite）. Two varieties of post-emplacement sub-solidus charnock- ites are also evident. These include charnockitic aureoles developed in leucocratic, biotite, garnet granite adjacent to cross-cutting enderbitic veins that are attributed to metamorphic-metasomatic processes （as in the Nicholson＇s Point granite, a part of the Margate Granite Suite）, as well as nebulous, patchy charnocki- tic veins in the Margate Granite that are attributed to anatectic metamorphic processes under low-aH2O fluid conditions during a metamorphic event. These varieties of charnockite show that the required physical conditions of their genesis can be achieved through a number of geological processes, providing some important implications for the classification of charnockites, and for the interpretation of charnock- ite genesis in areas where poor exposure obscures field relationships.

High Ba-Sr adakitic charnockite suite from the Nagercoil Block,southern India:Vestiges of Paleoproterozoic arc and implications for Columbia to Gondwana

The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane(SGT)in India and is mainly composed of charnockitic rocks and felsic gneisses(charnockite suite).In this study,we present petrologic,geochemical,zircon U-Pb,REE,and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block.Based on field investigations and petrologic studies,the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene.The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks,with enrichment in LREEs(light rare earth elements)and LILEs(large ion lithophile elements),and depletion in HREEs(heavy rare earth elements)and HFSEs(high field strength elements).Some of the charnockites and the leucogneiss show typical HSA(high silica adakite)characters,(high SiO_(2),Al_(2)O_(3),Ba-Sr,La/Yb,and Sr/Y).The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge.The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian.The magmas were underplated and subjected to fractional crystallization.Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims.Magmatic zircon grains from the charnockites show ages ranging from 1983±8.8 Ma to 2046±14 Ma,and the metamorphic domains show an age range of 502±14 Ma to 547±8.7 Ma.Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860±20 Ma and 575.6±8.8 Ma.Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma.The REE data of the zircon grains show LREE depletion and HREE enrichment,with the metamorphic grains showing more depletion in HREE.Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yieldedε_(Hf)(t)values from-1.17 to 0.46 with T_(DM)and T_(DM)~C and age peaks at 2392 Ma and 2638 Ma,suggesting Neoarchean to Paleoproterozoic juvenile sources.We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent,and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian.Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.

Charnockites and charnockites

1. Introduction The continental crust, covering nearly a third of the Earth＇s surface, is dominantly made up of granites and granodiorites （Rudnick and Gao, 2003）. Although the vast majority of these granitoids are amphibole- and/or biotite-bearing, orthopyroxene-bearing granitoids form a minor but important component of the lower continental crust in many high-grade terrains （e.g., Bohlender et al., 1992; Kilpatrick and Ellis, 1992; Sheraton et al., 1992; Berger et al., 1995; Zhou et al.,

Incipient charnockites from southern India:The role of brines

Southern India and Sri-Lanka are the places where “incipient charnockites”,i.e.the local transformation of amphibolite-facies gneisses into orthopyroxene-bearing,igneous looking charnockites,have been discovered in the early sixties.The fact that some incipient charnockites occur along a network of brittle fractures,together with CO2 remnants preserved in mineral inclusions,had called for the role of fluids during charnockite alteration.The present work presents new observations on fluid inclusions and microtextures of incipient charnockites from type localities in southern India.In addition to CO2-rich fluid inclusions in quartz and feldspar,all of the occurrences have disrupted remnants of concentrated aqueous alkali chloride solutions.CO2 inclusions are more abundant in paragneiss (Kerala) than in orthogneiss (Karnataka/Tamil Nadu).The finding of disrupted brine inclusions in the Kabbal charnockite is a key link between closely associated massive charnockites and Closepet Granite,both of which also share the brine remnants.All of the occurrences studied here have feldspar or feldspar-quartz microvein networks along grain boundaries of recrystallized quartz,feldspar and orthopyroxene.These metasomatic veins again indicate the action of alkali-exchanging fluids (i.e.,saline solutions).Feldspar microveins,which have been found in most “massive” charnockites,along with the CO2-rich fluid inclusions,suggest a commonality of incipient charnockite and massive charnockite,both types differing in intensity of interaction with metasomatizing pore fluids.

Petrology and SHRIMP zircon geochronology of granulites from Vesleknausen, Lützow-Holm Complex, East Antarctica: Neoarchean magmatism and Neoproterozoic high-grade metamorphism

We report new petrological data and geochronological measurements of granulites from Vesleknausen in the highest-grade section of the L＆#252;tzow-Holm Complex, part of the Gondwana-assembling collisional orogen in East Antarctica. The locality is dominated by felsic to intermediate orthogneiss （charnockite and minor biotite gneiss）, mafic orthogneiss, and hornblende-pyroxene granulite, with deformed and undeformed dykes of metagranite and felsic pegmatite. Pseudosection analysis of charnockite in the system NCKFMASHTO, supported by geothermometry of mafic orthogneiss, was used to infer peak metamorphic temperatures of 750e850 ？C, approximately 150 ？C lower than those estimated for met-asedimentary gneisses from Rundv？gshetta, 6 km to the northeast. SHRIMP U-Pb analysis of zircons from feldspar-pyroxene gneiss, which corresponds to a partially molten patch around mafic orthogneiss, yielded a Concordia upper intercept ages of 2507.9 ？ 7.4 Ma, corresponding to the time of formation of the magmatic protolith to the orthogneiss. Partial melting during peak metamorphism probably took place between 591 and 548 Ma, as recorded in rims overgrew around magmatic zircon. Our results suggest that Rundv？gshetta-Vesleknausen-Strandnibba region in southwestern L＆#252;tzow-Holm Bay, where orthogneisses are dominant, consists of a single crustal block, possibly formed by ca. 2.5 Ga arc mag-matism. The Neoarchean magmatic terrane was tectonically mingled with other fragments （such as metasedimentary units in northern L＆#252;tzow-Holm Bay） by subduction/collision events during the as-sembly of Gondwana supercontinent, and subsequently underwent w850 ？C granulite-facies meta-morphosed during Neoproterozoic to Cambrian final collisional event.

Review: the charnockite problem, a twenty first century perspective

Beginning of the twentieth century was marked by coinage of a new rock name, Charnockite, first described as a hypersthene-bearing granite from Southern India. Since then charnockites have been described from most of the conti-nents and mostly restricted to high-grade belts. Later half of the last century saw a lively debate over an igneous versus metamorphic origin. However, two factors acted as deterrents for the resolution of the debate. First, charnockites and associated rocks occur in a variety of different structural setting and display diverse field rela-tions, attesting to possible different mode of origin. Second and possibly more important is the lack of consensus on the nomenclature of charnockites and associated rocks and this is commonly linked with the metamorphic versus magmatic perspective. Scanning the literature of this period makes one believe that both metamorphic and magmatic hypotheses are valid, but applicable to different field setting only. Before critically evaluating individual cases, it is imperative that a uniform approach in nomenclature should be agreed upon. It is proposed that name charnockite be adopted for any quartzofeldspathic rock with orthopyroxene, irrespective of its mode of occurrence, struc-tural setting and mode of origin. The associated more mafic varieties, be better described as mafic granulite, rather than basic charnockite. For the patchy charnockites of east Gondwana (including parts of Peninsular India, Sri Lanka and Antarctica), metamorphic transformation from amphibolite facies gneiss, by two different mechanisms: CO2 ingress from deep level, and drop in fluid pressure, has been proposed. However, all such patchy occurrence is not amenable to explanation by metamorphic trans- formation. In some instances, migmatisation of older charnockitic rocks is evident. Also pro- gressive charnockitisation relating patchy char-nockite to banded variety could be argued against on two counts: grain-size relation and time-relation. Larger bodies or bands have been explained as magmatic, but in many instances, from geochemical consideration alone. The compositional variation, commonly encoun-tered in many high-grade belts, if not described in terms of field relation, may lead to wrong no-tions of magmatic differentiation of mantle-de- rived melts. Crustal melting of dry granulite fa-cies source rocks has been proposed from geochemical and isotopic data of charnockitic intrusions. This model proposes high-tempera-ture melting of previously dehydrated and dry granulite source rocks. However, tectonic per-turbation subsequent to granulite facies meta-morphism that might have been responsible for such high temperatures, is not well constrained in this model. Finally, with advent of high- pressure dehydration-melting experiments in the nineties, dehydration-melting of mafic to intermediate composition, syn-kinematic with granulite facies metamorphism has been pro-posed.

New experimental constraints: implications for pe-trogenesis of charnockite of dioritic composition

Hornblende-dehydration melting experiments at high temperatures (> 950oC) indicate change of melt composition from tonalite/granodiorite to quartz-diorite;clinopyroxene instead of hornbl- ende as the residual phase and change in melting reaction from peritectic hornblende-dehydr- ation to eutectic clinopyroxene-orthopyroxene- plagioclase. In the light of these experimental results, petrogenesis of a charnockite pluton of homogeneous dioritic composition in the Eastern Ghats Belt, India, can be explained as melting at high-temperatures (> 950oC). Negative Sr and Eu anomalies further indicate plagioclase as a major residual phase, consistent with melt- ing at high-temperatures (> 950oC).

Geochemical Characteristic of Charnockites in North Margin of North China Craton: Indicating the Significiant of the Neoarchean Tecnotic Event

The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian-charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu-enrichment and Eu-depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian-charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian-charnockite is closely connected with the subduction of the NCC oceanic crust(About ~2.5 Ga). However, Ferroan-charnockite may be the formed by the crystallization differentiation of the upwelling of mantle-derived shoshonitic magma(About ~2.45 Ga), with the lower crust material addition.

Charnockite Formation and Early Precambrian Crust Evolution in Yishui Area, Shandong Province, China

Charnockite and granulite in Yishui area, Shandong Province are located in the middle part of the Tancheng Lujiang fault zone, eastern China. Field studies have shown that the charnockites, derived from the adjacent granulites, are classified as three types: enderbite, garnet enderbite and hypersthene trondhjemite. In addition, two generations of minerals are present in the charnockites: the relic minerals such as garnet, hypersthene and clinopyroxene, and the neocrystallized minerals such as plagioclase and K feldspar. The relic minerals occurring in the granulite facies stage were affected by the later partial melting. The relic minerals, irregular and usually ragged in shape, occupy the interstitial positions in the neocrystalline minerals. The neocrystalline minerals are usually euhedral subhedral crystals. The study of petrology, mineralogy and geochemistry of charnokites concludes that the enderbite was formed by the anatexis of the two pyroxene plagioclase granulite, that the garnet enderbite was formed by the anatexis of sillimanite garnet gneiss, and that the hypersthene trondhjemite was formed by the anatexis of the leucocratic two pyroxene plagioclase granulite. The U Pb dating of the zircon indicates that the formation of the charnockite and granulite was related to the Archean Proterozoic upwelling of a mantle plume (hot spot) around 2 500 Ma, in Yishui area, Shandong Province.

Geochemistry of Major Oxides in Host Rocks in Vizianagarm Manganese Ores Belt (A.P.), India

The abundance, distribution trends and significance of the major oxides in the host rocks in Vizianagarm Manganese Ores Belt (A.P.) (between N latitude 18°12' and 18°30' and E longitudes 83°20' and 83°45'), 15 samples of host rocks from different localities of the area under study were collected and analyzed for major oxides. We describe here in major oxides geochemistry of host rocks and manganese ore deposits associated with Precambrian Khondalite and Charnockite in Vizianagarm Manganese Ores Belt (A.P.): 1) Preponderance of SiO2 over Al2O3;2) Dominance of K2O and CaO over Na2O;3) Abnormally high concentration of phosphorus and a positive relationship of P2O5 with CaO and Ti contents;4) Manganese increases with increases of iron, lime and soda and vice versa, 5) CaO increases with the increases of Al2O3, Ti, K2O and vice versa.?High P2O5content in these manganese ores appears to be the result of precipitation from secondary manganese rich solutions containing dissolved phosphorus from the P2O5 enriched host rocks.?Another source of P2O5 may be the associated granitic and pegmatitic intrusions. Elements like K, Na, Ca, Mg, Co, Ni, Pb and Zn etc. appear to be mostly concentrated in the Mn-minerals viz. psilomelane, cryptomelane, hollandite and pyrolusite and related secondary phases [1] and [2]. Stratigraphically, the study area includes within a thick succession of Precambrian Group belonging to the Khondalite and Charnockite Groups of Dharwar Supergroup, that form a part of Eastern Ghat Complex of India. The manganiferous rocks that have been encountered in the Vizianagarm Manganese Ores Belt (A.P.) India are known as Kodurites.

Mineral Chemistry and Geochemistry as Proxy for Petrogenetic Evaluation of Charnockites: Evidences from Marandahalli, Salem Block of Southern India

The charnockites of Marandahalli, Dharmapuri District, Tamil Nadu India, form a part of the southern granulitic terrain in the Salem Block (SB). The charnockites are medium to coarse grained, inequigranular, with porphyroblastic and granophyric textures. They are composed of plagioclase feldspars (49 - 66 vol.%), K-feldspar (1 - 5 vol.%) and quartz (21 - 34 vol.%). The mafic minerals include pyroxene (2 - 7 vol.%) and biotite (1 - 12 vol.%). The accessory minerals include magnetite and apatite. Orthopyroxene compositions (MgO 16 - 22 wt.%) fall within the hypersthene series (En55.03Fs43.57Wo1.4) and yield peak metamorphic temperatures of 800˚C - 1000˚C. Biotites show K2O, MgO, FeO, TiO2, and Al2O3 concentrations consistent with magmatic formation, and Ti-in-biotite thermometry suggests temperatures of ~740˚C - 800˚C. Plagioclase compositions (An26-33) plot in the oligoclase field, while K-feldspar (Or93-99) plots in the orthoclase/microcline field. A ternary feldspar geothermometer indicates a retrograde temperature of 2 (65 - 68 wt.%), Na2O > K2O, high CaO (3 - 5 wt.%), MgO (2.5 - 4 wt.%) and Fe2O3 (2 - 6 wt.%). The concentration of V, Rb and Ni, and LREE-rich and HREE-depleted patterns of the rocks indicate low degree of partial melting.