Serpentinization is a complex set of hydration reactions, where olivine and pyroxene are replaced by serpentine, magnetite, brucite, talc and carbonate minerals. Serpentinization reactions alter chemical, mechanical, magnetic, seismic, and hydraulic properties of the crust. To understand the complicated nature of serpentinization and the linkages between physical and chemical changes during the reactions, I performed flow-through laboratory experiments on cylindrically cored samples of ultramafic rocks. Each core had a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at an effective pressure of 30 MPa, and temperature of 260°C, simulating a depth of 2 km under hydrostatic conditions. Fracture permeability decreased by one to two orders of magnitude during the 200 to 340 hour experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferro-magnesian minerals. The rate of transformation of olivine to serpentine in a tensile fracture is calculated using the data on evolution of fracture permeability assuming the fracture permeability could be represented by parallel plates. Assuming the dissolution and precipitation reactions occur simultaneously; the rate of transformation at the beginning of the experiments was ~ 10-8-10-9 (mol/m2s) and decreased monotonically by about an order of magnitude towards the end of the experiment. Results show that dissolution and precipitation is the main mechanism contributing to the reduction in fracture aperture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems may be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of tectonic and crystallization-induced stresses may be required to maintain fluid circulation. Another set of flow through experiments were performed on intact samples of ultramafic rocks at room temperature and effective pressures of 10, 20 and 30 MPa to estimate the pressure dependency of intact permeability. Porosity and density measurements were also performed with the purpose of characterizing these properties of ultramafic rocks. The pressure dependency of the coefficient of matrix permeability of the ultramafic rock samples fell in the range of 0.05-0.14 MPa-1. Using porosity and permeability measurements, the ratio of interconnected porosity to total porosity was estimated to be small and the permeability of the samples was dominantly controlled by microcracks. Using the density and porosity measurements, the degree of alteration of samples was estimated. Samples with high density and pressure dependent permeability had a smaller degree of alteration than those with lower density and pressure dependency. / Ph. D.

A Nappe Lima Duarte, localizada na porção oriental do sistema orogênico Tocantins Meridional, sudoeste do estado de Minas Gerais, é constituída por rochas supracrustais de alto grau (gnaisses e micaxistos com e sillimanita e quartzitos) com lascas de ortognaisses arqueanos tonalíticos - granodioríticos (antigos terrenos TTG) tectônicamente intercaladas. É nesta Nappe de Lima Duarte que ocorrem os dois corpos metaultramáficos tema deste estudo. O corpo ultra máfico de Lima Duarte, bandado - estratificado, sem foliação evidente, encontra-se encaixado em uma zona de cisalhamento entre hornblendabiotita gnaisses e migmatitos, e sillimanita - muscovita - biotita - quartzo xistos/gnaisses. Trata-se de um corpo lenticular alongado em direção NW - SE, com 700 metros de comprimento e aproximadamente 300 metros de largura. Já o corpo ultramáfico de Olaria aflora como um conjunto de blocos anguloso de alguns metros de tamanho, e ocorre como corpo lenticular pequeno encravado em hornblenda - biotita ortognaisses. Em ambos corpos o grau de intemperismo impossibilita estabelecer as relações de contato com as rochas encaixantes. O corpo de Lima Duarte apresenta bandamento composicional como relíquia ígnea, indicando que se trata do fragmento de um corpo bandado - estratificado desmembrado. Seus litotipos, que ocorrem alternados em bandas centimétricas, são constituídos por proporções variáveis de olivina, ortopiroxênio, magnésio-hornblenda, espinélio / magnetita, Mg-clorita e serpentina e, considerando a Mg-hornblenda como substituta do clinopiroxênio ígneo, representam metadunitos, metaharzburgitos, meta-olivina- ortopiroxenitos e metalherzolitos, serpentinizados com intensidade variável. O corpo de Olaria apresenta texturas grano-nematoblásticas poligonizadas a lobadas, e é constituído de ortopiroxênio e hornblenda - espinélio + Mg-clorita + olivina, com serpentinização apenas incipiente em olivina. Os minerais do corpo de Lima Duarte são mais magnesianos (Mg/Mg+Fe2+mais altos, hornblenda e ortopiroxênio sem pleocroísmo), enquanto os de Olaria são mais ricos em ferro (Mg/Mg+Fe2+mais baixo, ortopiroxênio e hornblenda pleocróicos), sugerindo protólitos mais magnesianos para Lima Duarte. As texturas e paragêneses metamórficas (ortopiroxênio - olivina - Mg-hornblenda - Mg-Al-espinélio, + Mg-clorita) sugerem condições de limiar fácies anfibolito-fácies granulito. A evolução metamórfica é modelada com base nas variações composicionais que ocorrem no anfibólio cálcico e na Mg-clorita. A quebra final da Mg-clorita, definida pela reação: Mg-Clorita forsterita + enstatita + espinélio + H20, representa as condições de pico alcançadas, com reconstituição parcial retrometamórfica da clorita. . Estimativas termobarométricas com o programa Thermocalc para a paragênese olivina - ortopiroxênio - espinélio - hornblenda forneceram temperaturas de 810ºC para o corpo de Lima Duarte e 840ºC para o de Olaria, compatíveis com as estimativas citadas na literatura para as rochas encaixantes e com as condições de quebra da Mg-clorita. No corpo de Lima Duarte, a intensa serpentinização ocorreu inicialmente através e substituições por domínios composicionais, resultando em texturas pseudomórficas de olivina (mesh) e ortopiroxênio (bastita), tornando-se mais pervasiva a seguir, com serpentinização da hornblenda e clorita, implicando mobilidade de Ca e Al no sistema. / The ultramafic rocks of this study occur in the Lima Duarte nappe, which is constituted of high-grade metassedimentary rocks such as sillimanite schists and gneisses as well as quartzites, with intercalated tectonic slices of tonalitic-granodioritic gneisses and migmatites from the archean TTG basement. This nappe belongs to the eastern part of the southern Tocantins Orogenic system, in southwestern Minas Gerais State, Brazil. The ultramafic rocks make up two bodies in the Lima Duarte nappe. The Lima Duarte body is stratified, without foliation, included in a shear zone between sillimanite-garnet schists and gneisses and hornblende-biotite gneisses and migmatites as a lenticular body approximately 700 m long and 300 m thick. The Olaria body outcrops as a few meter-size boulders, possibly as a lenticular body intercalated in hornblende-biotite orthogneisses. Neither body exhibits its contacts with the country rocks due to the intense weathering. The Lima Duarte body exhibits layering inherited from stratified igneous rocks, and thus represents a fragment of a dismembered stratified igneous complex. It´s rock types, constituted by varying proportions of olivine, orthopyroxene, magnesian hornblende, green spinel, magnetite, Mg-chlorite and serpentine, occur alternated in centimetric bands and, if hornblende is taken as correspondent to clinopyroxene, can be identified as metadunites, meta-olivine orthopyroxenites, metaharzburgites and metalherzolites, all serpentinized in various degrees. The Olaria body exhibits grano-nematoblastic, polygonized to lobate textures, and is constituted by orthopyroxene - hornblende - green spinel + olivine + Mg-chlorite, with incipient serpentinization in olivine grains. The Lima Duarte rocks are more magnesian (higher Mg/Mg+Fe2+ in minerals, non-pleochroic orthopyroxene and hornblende) than the ones from Olaria (lower Mg/Mg+Fe2+ in minerals, pleochroic hornblende and orthopyroxene). The metamorphic textures and parageneses (olivine - orthopyroxene - hornblende - Mg-Al-spinel + Mg-chlorite) suggest metamorphic conditions transitional from amphibolites to granulite facies, with late low-grade serpentinization in the Lima Duarte body. The metamorphic evolution is modeled through continuous compositional changes in calcic amphibole and Mg-chlorite. The final breakdown of chlorite, through the reaction: Mg-chlorite olivine + orthopyroxene + spinel + H2O represents peak conditions, with later partial retrometamorphic reconstitution of chlorite. Thermobarometric estimates for the paragenesis orthopyroxene - hornblende - olivine - spinel with the help of Thermocalc yielded 810oC for Lima Duarte rocks and 840oC for Olaria rocks, in good agreement with previous results for the high-grade country rocks from literature and for the chlorite breakdown conditions. In the Lima Duarte body, the intensive serpentinization started with compositional domain substitutions, mainly in olivine and orthopyroxene, resulting in pseudomorphic textures (mesh and bastite, respectively). In later stages, calcic amphibole as well as chlorite suffered serpentinization, thus indicating Ca and Al mobility in the system.

A Nappe Lima Duarte, localizada na porção oriental do sistema orogênico Tocantins Meridional, sudoeste do estado de Minas Gerais, é constituída por rochas supracrustais de alto grau (gnaisses e micaxistos com e sillimanita e quartzitos) com lascas de ortognaisses arqueanos tonalíticos - granodioríticos (antigos terrenos TTG) tectônicamente intercaladas. É nesta Nappe de Lima Duarte que ocorrem os dois corpos metaultramáficos tema deste estudo. O corpo ultra máfico de Lima Duarte, bandado - estratificado, sem foliação evidente, encontra-se encaixado em uma zona de cisalhamento entre hornblendabiotita gnaisses e migmatitos, e sillimanita - muscovita - biotita - quartzo xistos/gnaisses. Trata-se de um corpo lenticular alongado em direção NW - SE, com 700 metros de comprimento e aproximadamente 300 metros de largura. Já o corpo ultramáfico de Olaria aflora como um conjunto de blocos anguloso de alguns metros de tamanho, e ocorre como corpo lenticular pequeno encravado em hornblenda - biotita ortognaisses. Em ambos corpos o grau de intemperismo impossibilita estabelecer as relações de contato com as rochas encaixantes. O corpo de Lima Duarte apresenta bandamento composicional como relíquia ígnea, indicando que se trata do fragmento de um corpo bandado - estratificado desmembrado. Seus litotipos, que ocorrem alternados em bandas centimétricas, são constituídos por proporções variáveis de olivina, ortopiroxênio, magnésio-hornblenda, espinélio / magnetita, Mg-clorita e serpentina e, considerando a Mg-hornblenda como substituta do clinopiroxênio ígneo, representam metadunitos, metaharzburgitos, meta-olivina- ortopiroxenitos e metalherzolitos, serpentinizados com intensidade variável. O corpo de Olaria apresenta texturas grano-nematoblásticas poligonizadas a lobadas, e é constituído de ortopiroxênio e hornblenda - espinélio + Mg-clorita + olivina, com serpentinização apenas incipiente em olivina. Os minerais do corpo de Lima Duarte são mais magnesianos (Mg/Mg+Fe2+mais altos, hornblenda e ortopiroxênio sem pleocroísmo), enquanto os de Olaria são mais ricos em ferro (Mg/Mg+Fe2+mais baixo, ortopiroxênio e hornblenda pleocróicos), sugerindo protólitos mais magnesianos para Lima Duarte. As texturas e paragêneses metamórficas (ortopiroxênio - olivina - Mg-hornblenda - Mg-Al-espinélio, + Mg-clorita) sugerem condições de limiar fácies anfibolito-fácies granulito. A evolução metamórfica é modelada com base nas variações composicionais que ocorrem no anfibólio cálcico e na Mg-clorita. A quebra final da Mg-clorita, definida pela reação: Mg-Clorita forsterita + enstatita + espinélio + H20, representa as condições de pico alcançadas, com reconstituição parcial retrometamórfica da clorita. . Estimativas termobarométricas com o programa Thermocalc para a paragênese olivina - ortopiroxênio - espinélio - hornblenda forneceram temperaturas de 810ºC para o corpo de Lima Duarte e 840ºC para o de Olaria, compatíveis com as estimativas citadas na literatura para as rochas encaixantes e com as condições de quebra da Mg-clorita. No corpo de Lima Duarte, a intensa serpentinização ocorreu inicialmente através e substituições por domínios composicionais, resultando em texturas pseudomórficas de olivina (mesh) e ortopiroxênio (bastita), tornando-se mais pervasiva a seguir, com serpentinização da hornblenda e clorita, implicando mobilidade de Ca e Al no sistema. / The ultramafic rocks of this study occur in the Lima Duarte nappe, which is constituted of high-grade metassedimentary rocks such as sillimanite schists and gneisses as well as quartzites, with intercalated tectonic slices of tonalitic-granodioritic gneisses and migmatites from the archean TTG basement. This nappe belongs to the eastern part of the southern Tocantins Orogenic system, in southwestern Minas Gerais State, Brazil. The ultramafic rocks make up two bodies in the Lima Duarte nappe. The Lima Duarte body is stratified, without foliation, included in a shear zone between sillimanite-garnet schists and gneisses and hornblende-biotite gneisses and migmatites as a lenticular body approximately 700 m long and 300 m thick. The Olaria body outcrops as a few meter-size boulders, possibly as a lenticular body intercalated in hornblende-biotite orthogneisses. Neither body exhibits its contacts with the country rocks due to the intense weathering. The Lima Duarte body exhibits layering inherited from stratified igneous rocks, and thus represents a fragment of a dismembered stratified igneous complex. It´s rock types, constituted by varying proportions of olivine, orthopyroxene, magnesian hornblende, green spinel, magnetite, Mg-chlorite and serpentine, occur alternated in centimetric bands and, if hornblende is taken as correspondent to clinopyroxene, can be identified as metadunites, meta-olivine orthopyroxenites, metaharzburgites and metalherzolites, all serpentinized in various degrees. The Olaria body exhibits grano-nematoblastic, polygonized to lobate textures, and is constituted by orthopyroxene - hornblende - green spinel + olivine + Mg-chlorite, with incipient serpentinization in olivine grains. The Lima Duarte rocks are more magnesian (higher Mg/Mg+Fe2+ in minerals, non-pleochroic orthopyroxene and hornblende) than the ones from Olaria (lower Mg/Mg+Fe2+ in minerals, pleochroic hornblende and orthopyroxene). The metamorphic textures and parageneses (olivine - orthopyroxene - hornblende - Mg-Al-spinel + Mg-chlorite) suggest metamorphic conditions transitional from amphibolites to granulite facies, with late low-grade serpentinization in the Lima Duarte body. The metamorphic evolution is modeled through continuous compositional changes in calcic amphibole and Mg-chlorite. The final breakdown of chlorite, through the reaction: Mg-chlorite olivine + orthopyroxene + spinel + H2O represents peak conditions, with later partial retrometamorphic reconstitution of chlorite. Thermobarometric estimates for the paragenesis orthopyroxene - hornblende - olivine - spinel with the help of Thermocalc yielded 810oC for Lima Duarte rocks and 840oC for Olaria rocks, in good agreement with previous results for the high-grade country rocks from literature and for the chlorite breakdown conditions. In the Lima Duarte body, the intensive serpentinization started with compositional domain substitutions, mainly in olivine and orthopyroxene, resulting in pseudomorphic textures (mesh and bastite, respectively). In later stages, calcic amphibole as well as chlorite suffered serpentinization, thus indicating Ca and Al mobility in the system.

Submitted by Igor Matos (igoryure.rm@gmail.com) on 2017-01-31T14:38:14Z No. of bitstreams: 1 DISS_2015_Jennifer Cardoso Farias Almada.pdf: 5724861 bytes, checksum: 75d76d597050375391c29d0a04f80995 (MD5) / Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2017-01-31T15:18:18Z (GMT) No. of bitstreams: 1 DISS_2015_Jennifer Cardoso Farias Almada.pdf: 5724861 bytes, checksum: 75d76d597050375391c29d0a04f80995 (MD5) / Made available in DSpace on 2017-01-31T15:18:18Z (GMT). No. of bitstreams: 1 DISS_2015_Jennifer Cardoso Farias Almada.pdf: 5724861 bytes, checksum: 75d76d597050375391c29d0a04f80995 (MD5) Previous issue date: 2015-08-28 / CAPES / Os estágios do período pós-cosilisional do Ciclo Brasialiano/Panafricano na região de Cocalinho, porção leste do estado de Mato Grosso, divisa com o estado de Goiás, é marcado por corpos graníticos intrusivos associados a rochas máficas e ultramáficas. O Plutão Itacaiu é um corpo extenso e alongado segundo um trend regional, na direção NE/SW. É caracterizado por um magmatismo expressivo de natureza alcalina e composição que varia de monzo a álcali-feldspato-granitos. Este extenso corpo é definido por três fácies petrográficas denominadas de Fácies Biotita-Granito, Fácies RiebeckitaBiotita-Granito e Fácies Biotita-Granito Porfirítico. Os granitóides imprimem evidências de processos deformacionais decorrentes de duas fases de deformação, representada principalmente pelo desenvolvimento da foliação penetrativa marcada pela orientação preferencial dos minerais placóides, com direção NE e mergulho para SE, variando de baixo a alto ângulo, e foliação milonítica decorrente do cisalhamento de característica transcorrente. A composição química permitiu classificar essas rochas como granitos do tipo-A, gerados em ambiente de arco magmático e intra-placa pós-colisional. Dados geocronológicos U/Pb extraídas de cristais de zircão indicaram idade de cristalização variando de 806.6±4.0 a 582.9±6.3 Ma, consistentes com aquelas registradas para o Arco Magmático de Goiás. Idades modelo TDM= 0.97 a 1.08 Ga, mostram valores positivo εNd(T) = +4.39, +4.31,+3.69. Os valores positivos de εNd sugerem um empobrecimento do magma que deu origem aos granitóides em ETR leves. O valor negativo de εNd indica origem a partir de fusão parcial de crosta continental Paleoproterozóica. As rochas máficas-ultramáficas ocorrem alinhadas aproximadamente a leste-oeste, com variáveis níveis de alteração. Definem um magmatismo toleítico a cálcio-alcalino, metaluminoso, de caráter intermediário a ultrabásico. Os estudos isotópicos sugerem caráter juvenil do magma parental, devido aos valores positivos de εNd(T). As idades modelo variam de TDM = 0,71 a 1,44Ga e estão relacionadas a outras unidades de rochas juvenis do Arco Magmático de Goiás / Post-collisional stages of the Brasiliano/Pan-African Cycle in the region of Cocalinho on eastern Mato Grosso, bordering the State of Goiás, are represented by granitic intrusive bodies associated with mafic and ultramafic rocks. The Itacaiu Pluto is an NE-SWelongated body conform to the regional trend. It is characterized by a expressive magmatism of alkaline nature and composition ranging from monzo the alkali-feldspargranites. This extensive body is defined by three petrographic facies termed biotitegranite Facies, riebeckite-biotite-granite Facies and biotite-granite porphyry Facies. The granitoids show evidence of deformational processes resulting two-phase of deformation, represented mainly by development of penetrative foliation marked by the preferred orientation of minerals placoid, with direction NE and dip to SE, ranging from low to high angle, and mylonitic foliation resultant by strike-slip shear. The chemical composition allowed to classify the rocks as granite type-A, generated in magmatic arc environment and intra-plate post-collisional. Geochronological data U / Pb extracted in zircon crystals indicated crystallization age ranging from 806.6 ± 4.0 to 582.9 ± 6.3 Ma, consistent with those recorded for the Goiás Magmatic Arc. model ages TDM= 0.97 to 1.8 Ga, show positive values of εNd(T) = +4.39, +4.31,+3.69. Positive values of εNd suggest impoverishment of the magma that gave rise to the granitoids in LREE. The negative value of εNd indicates origin from partial melting of continental crust Paleoproterozoic. The rocks mafic-ultramafic occur aligned approximately east-west, with varying degrees of alteration. Define a tholeiitic to calcium-alkaline magmatism, metaluminous, of character intermediate to ultrabasic. The Isotopic studies suggest juvenile character of the parental, magma due to positive values εNd(T). The model ages ranging from TDM = 0.71 to 1,44 Ga and are related to other units of juvenile rocks of the Goiás Magmatic Arc.

Submitted by Simone Souza (simonecgsouza@hotmail.com) on 2017-11-06T16:06:43Z No. of bitstreams: 1 DISS_2014_ Regiane Ferreira de Oliveira.pdf: 6027017 bytes, checksum: f165c49fb24857b10d67f0c0b49ba85f (MD5) / Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2018-02-02T15:10:33Z (GMT) No. of bitstreams: 1 DISS_2014_ Regiane Ferreira de Oliveira.pdf: 6027017 bytes, checksum: f165c49fb24857b10d67f0c0b49ba85f (MD5) / Made available in DSpace on 2018-02-02T15:10:33Z (GMT). No. of bitstreams: 1 DISS_2014_ Regiane Ferreira de Oliveira.pdf: 6027017 bytes, checksum: f165c49fb24857b10d67f0c0b49ba85f (MD5) Previous issue date: 2014-03-21 / Este trabalho apresenta os resultados de estudos geológicos e petrográficos realizados na região do Distrito de Noroagro – município de Comodoro no Estado de Mato Grosso com enfoque na geoquímica e geocronologia Sm e Nd de diques e “plugs máficos”, intrudidos nas rochas do Granito Rio Piolho e do Complexo Rio Galera. Os diques estudados situam-se no sudoeste do Cráton Amazônico na província Rondoniana San – Ignacio, especificamente nos domínios da Faixa Alto Guaporé. Petrograficamente, as rochas apresentam como aspectos macroscópicos feições estruturais características de rochas maciças de granulação fina a media variando de máficas a ultramáficas e cor cinza- esverdeada a preta. Apresentam texturas inequigranulares e composição gabroica ou peridotítica, constituídas, essencialmente, por minerais máficas (piroxênios e anfibólios) e plagioclásio por vezes alterados por processos de saussuritização. Opticamente, são rochas holocristalinas, textura ofítica a cumulática (peridotitos) onde os piroxênios representam à fase cumulus e os plagioclásios a fase inter-cumulus. Dados geoquímicos enfatizam que o magmatismo é do tipo toleítico, de natureza subalcalina, estando a totalidade das rochas no campo dos Basaltos de Fundo Oceânico – OFB (Ocean Floor Basalts), sendo que duas amostras apresentam assinatura de arco de ilhas. Datações de Sm- Nd indicaram idades de 1,24 , 1,27 e 1,57 (Ga) e apresentam ɛ Nd (t)a entre +6,27e + 6,50 para os gabros +5,80 para metapiroxênito. Os valores positivos de ɛ Nd (t)a juntamente com a razão 87Sr/86Sr de 0,704 para litotipo metagabro confirma que as rochas máficas –ultramáficas da região da Fazendas Maringá e Imaculada são derivadas de manto empobrecido / This works presents the results of Geological studies and petrographics realized in the Noroagro District, Comodoro municipality of Mato Grosso State focused on Geochemistry and Sm/Nd geochronology of dykes and maphic plugs emplaced in Rio Piolho Granite and Rio Galera Complex. The studied dykes is located in southwest of Amazonian Craton, Rondonian-San Ignácio Province, specifically in the Alto Guaporé Belt. Petrographically the rocks exhibit macroscopic strutural feature characteristics of massiveslightelly oriented rocks, fine to médium grain ranging of mafic to utramafic composition and greenhish – gray to black color. They presets inequigranular textures and gabbroic or peridotite composition, consisting essentially of mafic minerals (pyroxene and amphibole) and sometimes altered plagioclase and its partial saussuritization process. Optically Show holocrystalline granular rocks, with cumulate and ophitic texture ( peridotites) where pyroxene representes the cumulus crystal phase and the plagioclase inter-cumulus phase. Geochemical data emphasize that the magmatism is tholeiitic with sub-alkaline nature, being all of the rocks in the field of Ocean Floor Basalts (OFB) and two samples representes signatures island arc. Geochoronological Sm-Nd data indicated ages of 1,24 ,1,27 and 1,57 (Ga) and Show ɛ Nd (t)a between + 6,27 and +6,50 for gabbro and +5,80 for pyroxenite. The positive ɛ Nd (t)a values together with razão 87Sr/86Sr ratio of 0,704 for metagabbro suggests for the mafic- ultramafic rocks of region of Maringa and Imaculada Farm are derived of depleted mantle.

The Madurai Block is the largest granulite block in Southern Granulite Terrain which lies between Palghat-Cauvary shear zone in the North and Achankovil shear zone in the South. This terrain underwent extreme crustal metamorphism under ultrahigh-temperature metamorphic conditions which provides vital information about the tectonic process of the lower crust. Ultrahigh temperature metamorphism was defined by Harley (1998b) as a subclass of granulite facies metamorphism of crustal rocks in which peak temperature exceeds 900°C at moderate pressures (7-13 kbar) in the deep crust. However, considering the lacunae about the present understanding of ultrahigh temperature metamorphism, the study attempts to identify the heat source and role of lower crustal fluids in high temperature metamorphism. To understand the role of lower crustal fluids, a case study on migmatised metapelites from the Kodaikanal region was done where the metapelites have undergone UHT metamorphism. In-situ electron microprobe Th-U-Pb isochron (CHIME) dating of monazites in a leucosome and surrounding silica saturated and silica under saturated restite from the same outcrop indicate three principal ages which can be linked in with the evolutionary history of these rocks. The monazite grains in leucosome sample show alteration along the rims. These altered rims are experimentally replicated in a monazite-leucosome experiment at 800°C and 200MPa. This experiment, coupled with earlier published monazite-fluid experiments involving high pH alkali-bearing fluids at high P-T, helps to confirm the idea that alkali-bearing fluids, in the melt and along grain boundaries during crystallization, were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution-reprecipitation. Lower crustal fluids during migmatization and high temperature metamorphism from leucosome monazites signify the need for a more precise texturally-controlled geochronological determination. Considering the possible heat source of high temperature metamorphism, the role of associated rocks of charnockites/granites and ultramafics was studied from Kodaikanal and Ganguvarrpatti. The results indicate that both charnockites and granites are not the heat source of high temperature metamorphism. However, to recognize the ultramafic as the potential heat source the sapphirine-bearing high Mg-Opx bearing rock was studied from Kambam town. The sapphirine–cordierite intergrowth pods are characterized by unique texture and peraluminous sapphirine composition suggesting that these domains could represent cryptic pathways through which aluminous melts migrated. The mineral phase equilibria considerations suggest that such peraluminous melts interacted with Mg-rich orthopyroxene in the host granulite at 1025°C and 8 kbar, with subsequent isobaric cooling. The underplated mafic magma (T>1000°C) is suggested as a possible mechanism that provided the heat source for partial melting of lower crust and the UHT metamorphism. Moreover, field evidence of metapelite in direct contact with an ultramafic body was observed resulting into granulite grade metamorphism. The other evidence of ultramafic magma as heat source is though the mineral chemistry and geochemical modeling of the studied ultramafic rocks.