The purpose of the investigation was to map the geology of the north end of Craters of the Moon National Monument and surrounding area. A stratigraphic sequence of Late Paleozoic sedimentary and Tertiary volcanic rocks was compiles and the structures of these rocks and contact relationships with intrusions were delineated. Grade and facies of contact metamorphism were defined. The Snake River Plain basalts were also mapped. The sources of these flows were determined where possible. Preexisting structures and relationships of vents to earlier faulting were explored in ascertaining extensions of the Great Rift Zone into the Pioneer Mountains. Petrographic descriptions of the rock units were completed. Study of the economic geology was not undertaken. The interested reader is referred to Nelson (1969) for descriptions of the mineral deposits in the Lava Creek Mining District.

<p> A series of shallow intrusive and extrusive silicic volcanic rocks near Mamainse Point, Ontario, were sampled and analyzed for major and trace elements. The rocks are mainly fine grained, silicified rhyolites grading to dacites containing phenocrysts of quartz and feldspar. The analyses performed (XRF, AAS) indicate that many of these rocks have been altered from the normal igneous spectrum of rocks to potassic keratophyres. An enrichment in potash from potash metasomatism has accompanied low grade, burial metamorphism to produce a secondary mineral assemblage including chlorite, carbonate, and sericite. Local intense alteration of some rocks involved the depletion of mobile alkalis and addition of water and co2 to form calcite and kaolin. The overall field and chemical evidence suggest a single magmatic source for these rocks. </p> / Thesis / Bachelor of Arts (BA)

<p> Freegold Mountain is part of a northwesterly trending volcanoplutonic arc comprising the eastern portion of the Yukon Crystalline Terrane. Plutonic rocks in the area intrude Paleozoic metasediments and consist of a Late Triassic to Early Cretaceous granodiorite intruded by the Big Creek Syenite dated at 138 ± 10 Ma. A suite of K-rich intrusive volcanic rocks comprise an early period of basalt-andesite-dacite volcanism and a later rhyolitic volcanism dated at 78 ± 6 Ma. Volcanic rocks at Freegold Mountain can be correlated with Mt. Nansen Volcanics.</p> <p> Two sets of fracture planes, oriented at 165/70E and 18/80W, show dextral and sinistral displacement, respectively. Rhyolite dykes and gold-quartz veins predominantly oriented NNE have been emplaced along the 18/80W extensional fracture systems. These fractures may be modelled as high-angle Reidel shears, although evidence indicates that fracture orientations and fault movement have been complicated by changing stress fields from middle Cretaceous to Tertiary time.</p> <p> The gold-bearing quartz veins at Freegold Mountain are high grade, low-tonnage deposits with grades ranging from 0.4 to 1.0 oz/t. Fluid inclusions from the lower portions of the Laforma mine homogenize at 185° C with salinity ranging between 2 and 4.5 wt. % NaCl equivalent. A boiling zone has been detected above the deeper ore where fluid inclusions show extreme ranges in homogenization temperatures (165-430° C) and salinity (4 - 43 wt. % NaCl). Fluid inclusion waters have stable isotopic signatures indicative of meteoric water with 𝛿D = -138 and 𝛿^18O = -18.4. Boiling of the Laforma fluid has caused a shift towards heavier hydrogen and oxygen isotopic values, mineral deposition and appears to enhance gold precipitation over non-boiling zones. Stable isotopic evidence indicates that the paleolatitude of Freegold Mountain during late Cretaceous time was south of the present day Yukon-B.C. border.</p> <p> The Emmons Hill (Dart) prospect is a gold-bearing vein-breccia with a mineral assemblages of barite, stibnite, marcasite, cinnabar, orpiment, Fe and Mn carbonates and chalcedonic silica. Fluid inclusions from these deposits homogenize between 140-185° with salinities of 0-0.5 wt. % NaCl. This property shows marked similarities to acid-sulphate type precious metal deposits in New Zealand and western United States.</p> <p> Large (x to xx Mt) northwesterly trending diatremes appear to be structurally controlled by small transcurrent faults parallel to and coeval with displacement along the Tintina fault. The Antoniuk diatreme (3.7 Mt @ 1.14 g/t Au) consists of heterolithic and monolithic breccias intruded by dacite and rhyolite dykes. Diamond drilling indicates that a large body of fine to medium grained alaskite is present beneath the auriferous breccia. The deposit formed by the explosive escape of volatile components evolved from the retrograde boiling of a silicic magma chamber. Gold mineralization in the breccia is associated with pyrite and arsenopyrite formed at temperatures around 300°C and salinities of about 4.5 wt. % NaCl.</p> / Thesis / Master of Science (MSc)

The principal goal of the thesis is to constrain nature of magmatic and alteration processes, character of mantle source(s), geotectonic setting and palaeogeographic implications of the Silurian and Devonian volcanism in Prague Basin (Teplá-Barrandian Unit, Bohemian Massif). The thesis is based on extensive geochemical study covering major- and trace-element geochemistry, neodymium isotope geochemistry and mineral chemistry supported by petrographic and field observations. The most important conclusions of the thesis are as follows: 1. The Silurian volcanic rocks of the Prague Basin represent within-plate, transitional alkali to tholeiitic basalts, which erupted in continental rift setting through thick Cadomian crust. The basalts originated by low degrees of partial melting of garnet peridotite mantle source. Older Wenlock basalts are similar to alkaline ocean island basalts (OIB) derived from subcontinental lithospheric mantle (SCLM), enriched most probably by frozen pods of Ordovician magmas. Younger Ludlow basalts resemble tholeiitic enriched mid-oceanic ridge basalts (EMORB) derived from subduction-modified SCLM depleted by Late Cambrian melting. The Wenlock-Ludlow melting is characterized by contemporaneous mixing of melts derived from both enriched and depleted SCLM mantle domains. 2....

The main rock unit exposed in the southern part of the Tucson Mountains, Pima County, Arizona, is the Cat Mountain rhyolite. It forms the eastward dipping slope and the western escarpment of the mountain range, capping the large fault blocks which make up the range. Petrographic and radiometric data combine to show that the Cat Mountain rhyolite, as originally defined, consists of two major ash flow eruption sequences. The lower sequence is less uniform and continuous than the highly welded characteristically jointed upper unit. A basal non welded unit is found along the western escarpment, a partly welded transition zone is found between the welded units, and a capping partly-to-non-welded unit is exposed in protected parts of the eastern slope. The volcanic history of the area began with the emplacement of a nuee ardente deposit forming the “chaos” unit. This was followed by two ash flow pulses through the same vents, and the sequence was terminated by the intrusion of spherulitic rhyolite sealing up the vents.

Este estudo se propôs a avaliar a influência da cristalinidade e da deformação do quartzo na ocorrência da reação álcali-agregado. A influência da cristalinidade do quartzo foi analisada através da mesóstase, material intersticial que constitui as rochas vulcânicas, que é um material composto por grãos sub-microscópicos de quartzo e feldspatos. Para tanto foram selecionadas duas rochas vulcânicas, constituídas por quartzo em diferentes quantidades e com diferentes graus de cristalinidade: um basalto, com pouca quantidade de sílica, sem quartzo livre e cuja mesóstase apresenta grãos pobremente cristalizados; e um riolito, com grande quantidade de sílica e de quartzo livre, além de uma mesóstase com grãos melhor cristalizados. A caracterização da cristalinidade do quartzo mostrou que a mesóstase, que tem aparência de material amorfo em microscopia ótica, apresenta diferentes feições quando observada através de microscopia eletrônica de varredura: mesóstase com grãos criptocristalinos de quartzo e K-feldspatos (Mm); mesóstase com grãos de quartzo e feldspato microcristalinos (Mq); mesóstase constituída predominantemente por argilominerais (Ma). Relacionando-se essas características com a reatividade das rochas verificou-se que o quartzo presente nas mesóstases Mm e Mq reage rápida e intensamente, sobressaindo-se à dissolução da mesóstase Mm, enquanto os grãos da mesóstase Ma são preservados. Através da compração dessas constatações, obtidas com o basalto e o riolito, com as características do material intersticial de um basalto inócuo, em ensaios acelerados e em campo, verificou-se que seu material intersticial da rocha inócua possui pouca quantidade de sílica livre (quartzo). Isso evidencia que a reatividade das rochas vulcânicas está relacionada à quantidade de sílica livre presente (quartzo) e a velocidade de ocorrência da reação com a cristalinidade do quartzo constituinte da mesóstase (Mm). A influência da deformação do quartzo no desencadeamento da reação álcali-agregado foi avaliada através do estudo de rochas graníticas com diferentes graus de deformação: uma rocha pouco deformada (granito), uma rocha com deformação intermediária (proto-milonito) e uma rocha muito deformada (orto-milonito). Os graus de deformação do quartzo foram caracterizados, através de microscopia ótica, como: grau 0= ausência de deformação; grau 1= grãos pouco deformados, com extinção ondulante leve; grau 2= quartzo muito deformado, com forte extinção ondulante, chegando a formar bandas de deformação; grau 3= forte deformação, com formação de subgrãos; grau 4= grãos recristalizados. O estudo mostrou que a presença preponderante de quartzo com grau 2 nas rochas denota uma maior velocidade de desencadeamento da reação álcali-agregado. A partir dessa constatação efetuou-se a avaliação das características texturais dos grãos de quartzo de rochas reativas em campo, verificando-se que quanto maior a quantidade de grãos com grau 2 mais rápida a ocorrência da reação em campo. / This research aims to study the influence of crystallinity and deformation of quartz to the occurrence of alkali-aggregate reaction. The influence of the cristallinitiy of quartz was analyzed through the interstitial material (volcanic glass/mesostase) into volcanic rocks. This material is composing by sub-microscopic grains of quartz and feldspars, thus it was selected a basaltic rock, with poor crystallized interstitial material and low silica content; and a rhyolitic rock, with better crystallized interstitial material and high silica content. The characterization of the crystallinity of the quartz showed that interstitial mesostase has appearance of amorphous material on the optical microscopy, but, at scanning electron microscopy it was observe the following features: mesostase with microcrystalline grains of quartz and K-feldspar (Mm); mesostase with better crystallized grains of quartz and K-feldspar (Mq); mesostase with clay predominantly (Ma). Reactivity potential tests showed that quartz in Mm and Mq react quickly and intensely, especially Mm, while quartz in Ma was preserved. Comparing these evidences, obtained with basalt and rhyolite, with interstitial material into innocuous basalt, it was found that interstitial material in innocuous rock has smaller amount of free silica (quartz). It proof that reactivity of volcanic rocks is related to the amount of free silica present into the rocks and poor cristalinity of quartz into mesostase make alkali-aggregate reaction quickness (Mm). The influence of the deformation of quartz on alkali-aggregate reaction was analyzed through granitic rocks with different degrees of deformation: a rock with very little deformation (granite), a medium deformed rock (proto-mylonite), a very deformed rock (orto-mylonite). Deformation degree of quartz was characterized through optical microscopy as follows: order 0= absence of the deformation; order 1= slightly deformed grain (weak ondulatory extinction); order 2= very deformed quartz, with strong ondulatory extinction and forming deformation bands; order 3= very deformed quartz, with formation of sub-grains, order 4= recrystallized quartz. The study showed that rocks with most quartz „order 2‟ denotes the development of alkali-aggregate reaction faster than rocks with other „orders‟ deformation of the quartz. From this conclusion it was obseve the textural characteristics of quartz grains in reative rocks on the field, confirming that quartz with deformation bands cause alkali-aggregate reaction quickly.

Este estudo se propôs a avaliar a influência da cristalinidade e da deformação do quartzo na ocorrência da reação álcali-agregado. A influência da cristalinidade do quartzo foi analisada através da mesóstase, material intersticial que constitui as rochas vulcânicas, que é um material composto por grãos sub-microscópicos de quartzo e feldspatos. Para tanto foram selecionadas duas rochas vulcânicas, constituídas por quartzo em diferentes quantidades e com diferentes graus de cristalinidade: um basalto, com pouca quantidade de sílica, sem quartzo livre e cuja mesóstase apresenta grãos pobremente cristalizados; e um riolito, com grande quantidade de sílica e de quartzo livre, além de uma mesóstase com grãos melhor cristalizados. A caracterização da cristalinidade do quartzo mostrou que a mesóstase, que tem aparência de material amorfo em microscopia ótica, apresenta diferentes feições quando observada através de microscopia eletrônica de varredura: mesóstase com grãos criptocristalinos de quartzo e K-feldspatos (Mm); mesóstase com grãos de quartzo e feldspato microcristalinos (Mq); mesóstase constituída predominantemente por argilominerais (Ma). Relacionando-se essas características com a reatividade das rochas verificou-se que o quartzo presente nas mesóstases Mm e Mq reage rápida e intensamente, sobressaindo-se à dissolução da mesóstase Mm, enquanto os grãos da mesóstase Ma são preservados. Através da compração dessas constatações, obtidas com o basalto e o riolito, com as características do material intersticial de um basalto inócuo, em ensaios acelerados e em campo, verificou-se que seu material intersticial da rocha inócua possui pouca quantidade de sílica livre (quartzo). Isso evidencia que a reatividade das rochas vulcânicas está relacionada à quantidade de sílica livre presente (quartzo) e a velocidade de ocorrência da reação com a cristalinidade do quartzo constituinte da mesóstase (Mm). A influência da deformação do quartzo no desencadeamento da reação álcali-agregado foi avaliada através do estudo de rochas graníticas com diferentes graus de deformação: uma rocha pouco deformada (granito), uma rocha com deformação intermediária (proto-milonito) e uma rocha muito deformada (orto-milonito). Os graus de deformação do quartzo foram caracterizados, através de microscopia ótica, como: grau 0= ausência de deformação; grau 1= grãos pouco deformados, com extinção ondulante leve; grau 2= quartzo muito deformado, com forte extinção ondulante, chegando a formar bandas de deformação; grau 3= forte deformação, com formação de subgrãos; grau 4= grãos recristalizados. O estudo mostrou que a presença preponderante de quartzo com grau 2 nas rochas denota uma maior velocidade de desencadeamento da reação álcali-agregado. A partir dessa constatação efetuou-se a avaliação das características texturais dos grãos de quartzo de rochas reativas em campo, verificando-se que quanto maior a quantidade de grãos com grau 2 mais rápida a ocorrência da reação em campo. / This research aims to study the influence of crystallinity and deformation of quartz to the occurrence of alkali-aggregate reaction. The influence of the cristallinitiy of quartz was analyzed through the interstitial material (volcanic glass/mesostase) into volcanic rocks. This material is composing by sub-microscopic grains of quartz and feldspars, thus it was selected a basaltic rock, with poor crystallized interstitial material and low silica content; and a rhyolitic rock, with better crystallized interstitial material and high silica content. The characterization of the crystallinity of the quartz showed that interstitial mesostase has appearance of amorphous material on the optical microscopy, but, at scanning electron microscopy it was observe the following features: mesostase with microcrystalline grains of quartz and K-feldspar (Mm); mesostase with better crystallized grains of quartz and K-feldspar (Mq); mesostase with clay predominantly (Ma). Reactivity potential tests showed that quartz in Mm and Mq react quickly and intensely, especially Mm, while quartz in Ma was preserved. Comparing these evidences, obtained with basalt and rhyolite, with interstitial material into innocuous basalt, it was found that interstitial material in innocuous rock has smaller amount of free silica (quartz). It proof that reactivity of volcanic rocks is related to the amount of free silica present into the rocks and poor cristalinity of quartz into mesostase make alkali-aggregate reaction quickness (Mm). The influence of the deformation of quartz on alkali-aggregate reaction was analyzed through granitic rocks with different degrees of deformation: a rock with very little deformation (granite), a medium deformed rock (proto-mylonite), a very deformed rock (orto-mylonite). Deformation degree of quartz was characterized through optical microscopy as follows: order 0= absence of the deformation; order 1= slightly deformed grain (weak ondulatory extinction); order 2= very deformed quartz, with strong ondulatory extinction and forming deformation bands; order 3= very deformed quartz, with formation of sub-grains, order 4= recrystallized quartz. The study showed that rocks with most quartz „order 2‟ denotes the development of alkali-aggregate reaction faster than rocks with other „orders‟ deformation of the quartz. From this conclusion it was obseve the textural characteristics of quartz grains in reative rocks on the field, confirming that quartz with deformation bands cause alkali-aggregate reaction quickly.

Este estudo se propôs a avaliar a influência da cristalinidade e da deformação do quartzo na ocorrência da reação álcali-agregado. A influência da cristalinidade do quartzo foi analisada através da mesóstase, material intersticial que constitui as rochas vulcânicas, que é um material composto por grãos sub-microscópicos de quartzo e feldspatos. Para tanto foram selecionadas duas rochas vulcânicas, constituídas por quartzo em diferentes quantidades e com diferentes graus de cristalinidade: um basalto, com pouca quantidade de sílica, sem quartzo livre e cuja mesóstase apresenta grãos pobremente cristalizados; e um riolito, com grande quantidade de sílica e de quartzo livre, além de uma mesóstase com grãos melhor cristalizados. A caracterização da cristalinidade do quartzo mostrou que a mesóstase, que tem aparência de material amorfo em microscopia ótica, apresenta diferentes feições quando observada através de microscopia eletrônica de varredura: mesóstase com grãos criptocristalinos de quartzo e K-feldspatos (Mm); mesóstase com grãos de quartzo e feldspato microcristalinos (Mq); mesóstase constituída predominantemente por argilominerais (Ma). Relacionando-se essas características com a reatividade das rochas verificou-se que o quartzo presente nas mesóstases Mm e Mq reage rápida e intensamente, sobressaindo-se à dissolução da mesóstase Mm, enquanto os grãos da mesóstase Ma são preservados. Através da compração dessas constatações, obtidas com o basalto e o riolito, com as características do material intersticial de um basalto inócuo, em ensaios acelerados e em campo, verificou-se que seu material intersticial da rocha inócua possui pouca quantidade de sílica livre (quartzo). Isso evidencia que a reatividade das rochas vulcânicas está relacionada à quantidade de sílica livre presente (quartzo) e a velocidade de ocorrência da reação com a cristalinidade do quartzo constituinte da mesóstase (Mm). A influência da deformação do quartzo no desencadeamento da reação álcali-agregado foi avaliada através do estudo de rochas graníticas com diferentes graus de deformação: uma rocha pouco deformada (granito), uma rocha com deformação intermediária (proto-milonito) e uma rocha muito deformada (orto-milonito). Os graus de deformação do quartzo foram caracterizados, através de microscopia ótica, como: grau 0= ausência de deformação; grau 1= grãos pouco deformados, com extinção ondulante leve; grau 2= quartzo muito deformado, com forte extinção ondulante, chegando a formar bandas de deformação; grau 3= forte deformação, com formação de subgrãos; grau 4= grãos recristalizados. O estudo mostrou que a presença preponderante de quartzo com grau 2 nas rochas denota uma maior velocidade de desencadeamento da reação álcali-agregado. A partir dessa constatação efetuou-se a avaliação das características texturais dos grãos de quartzo de rochas reativas em campo, verificando-se que quanto maior a quantidade de grãos com grau 2 mais rápida a ocorrência da reação em campo. / This research aims to study the influence of crystallinity and deformation of quartz to the occurrence of alkali-aggregate reaction. The influence of the cristallinitiy of quartz was analyzed through the interstitial material (volcanic glass/mesostase) into volcanic rocks. This material is composing by sub-microscopic grains of quartz and feldspars, thus it was selected a basaltic rock, with poor crystallized interstitial material and low silica content; and a rhyolitic rock, with better crystallized interstitial material and high silica content. The characterization of the crystallinity of the quartz showed that interstitial mesostase has appearance of amorphous material on the optical microscopy, but, at scanning electron microscopy it was observe the following features: mesostase with microcrystalline grains of quartz and K-feldspar (Mm); mesostase with better crystallized grains of quartz and K-feldspar (Mq); mesostase with clay predominantly (Ma). Reactivity potential tests showed that quartz in Mm and Mq react quickly and intensely, especially Mm, while quartz in Ma was preserved. Comparing these evidences, obtained with basalt and rhyolite, with interstitial material into innocuous basalt, it was found that interstitial material in innocuous rock has smaller amount of free silica (quartz). It proof that reactivity of volcanic rocks is related to the amount of free silica present into the rocks and poor cristalinity of quartz into mesostase make alkali-aggregate reaction quickness (Mm). The influence of the deformation of quartz on alkali-aggregate reaction was analyzed through granitic rocks with different degrees of deformation: a rock with very little deformation (granite), a medium deformed rock (proto-mylonite), a very deformed rock (orto-mylonite). Deformation degree of quartz was characterized through optical microscopy as follows: order 0= absence of the deformation; order 1= slightly deformed grain (weak ondulatory extinction); order 2= very deformed quartz, with strong ondulatory extinction and forming deformation bands; order 3= very deformed quartz, with formation of sub-grains, order 4= recrystallized quartz. The study showed that rocks with most quartz „order 2‟ denotes the development of alkali-aggregate reaction faster than rocks with other „orders‟ deformation of the quartz. From this conclusion it was obseve the textural characteristics of quartz grains in reative rocks on the field, confirming that quartz with deformation bands cause alkali-aggregate reaction quickly.

Diploma thesis deals with geological, petrological and geochemical studies of neovolcanic rocks of the SW part of the Most Basin in the area of Tušimice power plant open pit. There are two lava flows affected by coal mining in northern part of the mine. Petrological and geochemical studies with K-Ar dating relatively recent rocks in mostly weatherworn volcanic rocks showed, that they can be classified as Ti-rich basaltic rocks without olivine (tephrites), which belong to the main volcanic phase in the evolution of the Eger graben. It was evidenced geologicaly and with K-Ar dating, that studied rocks were seperated from underlying beda by hiatus which caused erosion of volcanic rocks as well as crystalline bedrock. Mmajor and trace elements composition of co-magmactic volcanics showed that rock were derived from two slightly different sources of upper mantle. Composition of two samples indicates the formation from low degree of partial melting strongly metasomatic asthenospheric mantle. Chemical features of volcanic rocks show that mantle source was comparamble to recent OIB basalts. Last sample arose from less metasomatized and depth distincted mantle which was affected by higher level of partial melting. Melts from which crystallized both rocks were minimaly affected by asimilation or...

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Karst features are more common in relief formed by carbonate rocks, but can occur in silica-rich rocks such as volcanic acid, a fact not yet explored. Thus, this Master's thesis aims to understand the mechanisms responsible for the development of these landforms associated volcanic rocks through the identification and mapping of karst features, analyzing its relationship with the slope, hypsometry, lithology and morpho-structural lineaments. Furthermore, we tried to relate the distribution of features with use and land cover and check the fragility of the Serra Geral Aquifer. The study area comprises the city of São Martinho da Serra - RS, basic and acidic volcanic rocks of the Serra Geral formation. For this, the karst features were identified and mapped using satellite imagery, and morpho-structural lineaments were extracted from SRTM. We generated various cartographic products, which combined with field observations, allowed to classify the karst features that occur in the study area into three types of depressions that correspond to different stages of morphological evolution: a) Depression Surface Planed Top b) Headwater drainages suspended; c) Depression in the Valley bottom. It was found that karst features are controlled by the morpho-structural lineaments, and tend to develop in portions of volcanic flows that are more easily affected by weathering. It was observed that the depressions in the surface Planed Top occur more frequently in the municipality where the land use is predominantly agricultural, denotes the fact that risk of contamination of the aquifer Serra Geral, since its recharge also occurs through these features. / Feições cársticas são mais comuns em relevos formados por rochas carbonáticas, mas podem ocorrer em rochas ricas em sílica como as vulcânicas ácidas, fato ainda pouco explorado. Neste sentido, esta Dissertação de Mestrado tem como objetivo compreender os mecanismos responsáveis pelo desenvolvimento destas formas de relevo associadas as rochas vulcânicas, através da identificação e mapeamento das feições cársticas, averiguando sua relação com a declividade, hipsometria, litologia e lineamentos morfo-estruturais. Além disso, procurou-se relacionar a distribuição das feições com o uso e ocupação do solo e verificar a fragilidade do Aquífero Serra Geral. A área de estudo compreende o Município de São Martinho da Serra - RS, em rochas vulcânicas básicas e ácidas da formação Serra Geral. Para tanto, as feições cársticas foram identificadas e mapeadas através de imagens de satélite, e os lineamentos morfo-estruturais foram extraídos de SRTM. Foram gerados diversos produtos cartográficos, que combinados com as observações em campo, permitiram classificar as feições cársticas que ocorrem na área de estudo em três tipos de depressões que correspondem a diferentes estágios de evolução morfológica: a) Depressão em Superfície Aplainada de Topo; b) Cabeceiras de Drenagens Suspensas e; c) Depressão em Fundo de Vale. Foi constatado que as feições cársticas são controladas pelos lineamentos morfo-estruturais, e tendem a se desenvolverem nas porções dos derrames vulcânicos que são mais facilmente afetadas pelo intemperismo. Também verificou-se que as Depressões em Superfície Aplainada de Topo ocorrem com maior frequência na parte do município onde o uso do solo é predominantemente agrícola, fato que denota risco de contaminação do aquífero Serra Geral, já que sua recarga também ocorre através destas feições. Palavras-Chave: Feições cársticas. Lineamentos morfo-estruturais. Rochas vulcânicas. Aqüífero Serra Geral.