Numerosos terrenos pré-cambrianos de origem enigmática são individualizados nas regiões do vale e serrania do Rio Ribeira e Planalto Alto Turvo (SP, PR), com base em histórias evolutivas contrastantes e diferentes padrões litotectônicos, metamórficos e estruturais. Esses terrenos suspeitos formam três grandes terrenos compostos justapostos no final do Ciclo Brasiliano: Terreno Apiaí, Terreno Curitiba e Terreno Luís Alves. A evolução geotectônica de uma área que abrange estes três terrenos compostos foi investigada por meio da integração de análises petrológicas, microestruturais e estruturais, apoiadas com trabalhos de mapeamento geológico e compilação e integração de dados geocronológicos disponíveis. Os estudos foram concentrados em unidades geológicas representativas de cada um dos três terrenos compostos. Análises petrológicas, estimativas geotermobarométricas e quantificações de trajetórias PT mostram que os terrenos estudados apresentam assinaturas metamórficas contrastantes, refletindo ambientes geotectônicos distintos. O Grupo Votuverava e a Seqüência Serra das Andorinhas (Terreno Apiaí) passaram por metamorfismo barroviano com caminhamento P-T horário sob pressões e temperaturas máximas ao redor de 8 kbar e 550-650ºC. Parte do Complexo Turvo-Cajati (Terreno Curitiba) apresenta gradiente metamórfico acima do barroviano, com pico metamórfico (650-800ºC) sob pressões relativamente altas (9-12 kbar). Parte desta unidade passou por uma trajetória horária com aquecimento isobárico até atingir o pico térmico, enquanto algumas rochas passaram por descompressão praticamente isotérmica. Datações químicas em monazita indicam que o pico metamórfico do Complexo Turvo-Cajati ocorreu entre 590 e 575 Ma, sendo consideravelmente posterior ao clímax metamórfico das unidades do Terreno Apiaí (>= 600-620 Ma). Trajetórias P-T estimadas para o Complexo Atuba (Terreno Curitiba) sugerem um caminhamento retrógrado com resfriamento praticamente isobárico de 750ºC até um reequilíbrio ao redor de 650-700ºC e 6-7 kbar; a união dos dados petrológicos, microestruturais e geocronológicos sugere que o pico metamórfico teria ocorrido no Paleoproterozóico e o reequilíbrio no Ediacarano. A Suíte Alto Turvo (Terreno Luís Alves) compreende granulitos máficos a intermediários formados no Paleoproterozóico sob temperaturas mínimas ao redor de 850ºC, parcialmente reequilibrados em condições de fácies xisto verde ainda neste período e marginalmente re-metamorfizados em condições de fácies xisto verde a anfibolito no Ediacarano, seguindo uma trajetória horária com pico metamórfico ao redor de 650ºC e 6 kbar. Os padrões estruturais do Terreno Curitiba na área estudada estão associados a uma tectônica de cavalgamentos para oeste e nappismo tardios em relação ao Ciclo Brasiliano e concomitantes com a atuação do sistema transcorrente destral regional na Faixa Ribeira. Os dados multidisciplinares disponíveis indicam que as relações espaciais atualmente observadas para os terrenos estudados não decorrem de relações genéticas e geográficas pretéritas. Os dados convergem para uma evolução geotectônica onde a acresção de diferentes terrenos suspeitos e, em alguns casos, exóticos teria ocorrido em posições diferentes das atualmente observadas, sendo que a justaposição final teria sido controlada por dispersão lateral ao longo das grandes zonas de cisalhamento transcorrentes em períodos tardi- a pós-metamórficos. / Numerous Precambrian terranes of enigmatic origin are recognized in the Ribeira Valley and Alto Turvo Plateau regions (Southeastern Brazil), based on contrasting evolutive histories and distinct lithotectonic, metamorphic and structural patterns. These suspect terranes form three major composite terranes juxtaposed during the late Brasiliano Cycle: Apiaí Terrane, Curitiba Terrane and Luís Alves Terrane. The geotectonic evolution of an area that covers these three composite units was investigated by the integration of petrological, microstructural and structural analysis supported by geological mapping and compilation and integration of available geochronological data. The studies were concentrated on representative geological units from the three composite terranes. Petrological analysis, geothermobarometric estimatives and P-T path quantifications show that the studied terranes exhibit contrasting metamorphic signatures, refleting distinct geotectonic environments. The Votuverava Group and the Serra das Andorinhas Sequence (Apiaí Terrane) underwent barrovian metamorphism with clockwise P-T paths under maximum pressures and temperatures at around of 8 kbar and 550-650ºC. A part of the Turvo-Cajati Complex (Curitiba Terrane) shows a metamorphic field gradient above the barrovian type, with metamorphic peak (650-800ºC) under relatively high pressures (9-12 kbar). A part of this unit underwent a clockwise path with isobaric heating until to reach the thermal peak, while some rocks underwent a near isothermal descompression. Chemical dating of monazite indicate that the metamorphic peak of the Turvo-Cajati Complex occurred between 590 and 575 Ma, a period significantly younger than the metamorphic climax of the Apiaí Terrane units (>= 600-620 Ma). P-T paths from rocks of the Atuba Complex (Curitiba Terrane) suggest a retrograde path following near isobaric cooling from 750ºC to a reequilibration at around of 650-700ºC and 6-7 kbar; the integration of petrological, microstructural and geochronological data suggests that the metamorphic peak would have occurred during the Paleoproterozoic and the metamorphic reequilibration during the Ediacaran. The Alto Turvo Suite (Luís Alves Terrane) comprises mafic and intermediate granulites formed in the Paleoproterozoic under minimum temperatures at about 850ºC, partially reequilibrated under greenschist facies conditions yet in the same period and marginally remetamorphosed from greenschist to amphibolite facies conditions during the Ediacaran, following a clockwise path with metamorphic peak at around of 650ºC and 6 kbar. The structural patterns of the Curitiba Terrane in the studied area are related to a thrust nappe tectonics with westward movement late in relation to the Brasiliano Cycle and concomitant with the activation of the regional dextral transcurrent system in the Ribeira Belt. The available multidisciplinary data indicates that the present spatial relationships between the studied terranes do not imply in previous genetic and geographic relations. The data suggest a geotectonic evolution where the accretion of distinct suspect terranes, and in some cases exotic terranes, would have occurred in different positions in relation to the present array, and the final terrane juxtaposition would have been controlled by lateral dispersion along the major transcurrent shear zones during late- to post-metamorphic periods.

The stratigraphy of the late Precarnbrian upper Brachina Subgroup has been studied in detail throughout the southern and central Flinders Ranges of South Australia. Ten stratigraphically significant facies associations are readily recognisable within which 18 separate and distinct lithotypes have been defined and described. The complex regional strati - graphic arrangement has been simplified by using a Markov Chain technique of analysis. The resultant lithotype stratigraphy is used as the base upon which the palaeogeographic history of the upper Brachina Subgroup is reconstructed. A detailed sedimentologic analysis of each lithotype was undertaken in order to ascertain their individual palaeoenvironments of deposition. This involved a petrologic analysis of the arenaceous component of each lithotype, the analysis of the suite of sedimentary structures contained within each lithotype, and the analysis of all directional structures for palaeocurrent directions. For this latter analysis a new computer technique was developed whereby up to 3 individual populations can be separately analysed from any one distribution. Deposition of the upper Brachina Subgroup succession was due to a phase of uplift tectonism and minor accompanying basic volcanism. Within this succession two distinct depositional episodes are readily discernable. During the first episode a massive sand influx flowed from a westerly source region ( the Gawler Craton ) into a shallow submerged, though possibly tidally influenced mudflat as a prograding deltaic succession ( the " Alligator River Delta " ). This initial delta developed in the western region of the Adelaide ' Geosyncline ' as a fluvial and tide modified, wave dominated system which was fed by stable outlet channels, protected by barrier - bars and surrounded by a low intertidal aerobic mudflat. Preserved wi - bhin this mudflat deposit are the probable body fossils of primitive cup - shaped coelenterates ( ? ), which were possibly the ancestral organisms of the Ediacara assemblage. With, continued sediment influx and basin shallowing, this initial delta system evolved to an unbarred fluvial modified, tide - dominated delta which was fed by migrating channels and surrounded by an intertidal mudflat. This mudflat was anaerobic, possibly due to the activity of abundant microscopic organisms. The second depositional episode of the upper Brachina Subgroup developed when tectonic instability affected a portion of the basin's western margin ( Uplift I ). As a result, part of the previously deposited deltaic succession was eroded and reworked into a vast, thin intertidal sandflat which extended through the central region, and into the northern region of the Adelaide ' Geosyncline '. A second phase of tectonic instability ( Uplift II ) caused renewed activity along the basin ' s western margin, and also induced the emergence of at least two islands within the basin. Around these islands a thin, dominantly fluvial deposit was generated. The final phase of tectonic instability ( Uplift III ) affected only the western margin of the basin, and produced a narrow sand deposit of probable beach origin. Meanwhile, within the basin gradual subsidence induced the development of a shallow, possibly tidal aerobic mudflat and marked the end of the upper Brachina Subgroup phase of sedimentation. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1978.

During deposition of the mixed carbonate - clastic sequence of the Mundallio Subgroup, the " Adelaide Geosyncline " was a very shallow, elongate sedimentary basin, flanked to the west and east by older Precambrian basement. In much of the southern and northern Flinders Ranges, clastic deposition predominated in the lower Mundallio Subgroup. In the north, alternating development of shallow mudflats and sandflats ( Nankabunyana Formation ) depended on the interplay between the sediment supply and winnowing processes, while dolomite mudstones were locally deposited in the shallowest areas. In the eastern half of the Willouran Ranges, massive shales were deposited as the environment remained persistently below wave base ( Camel Flat Shale ), but a renewed sand influx led to deposition of the Tilterana Sandstone. In the southern Flinders Ranges, terrigenous clay and silt were deposited on submergent mudflats which shallowed into intermittently exposed dolomite mudflats ( Nathaltee Formation ). Dolomite mudflats were a more persistent feature in areas more distal from the terrigenous source, and sometimes contained isolated, ephemeral lakes which were sites of magnesite deposition ( Yadlamalka Formation ). Dolomite and magnesite mudstone deposition of the Yadlamalka Formation became wide spread in the northern and southern Flinders Ranges in the upper Mundallio Subgroup, as shallowing and retreat of the basin margin led to the formation of semi - isolated lakes, separated and enclosed by exposed carbonate mudflats. The elastics deposited in association with these carbonate mudstones consisted largely of sand sized detritus, probably derived from the reworking of aeolian deposits. In the eastern Willouran Ranges, the greater influx of sand and the slightly deeper, largely submergent environments, led to the deposition of the sandstones, dolomites and siltstones of the Mirra Formation. Because of little clastic influx into the northern Mt. Lofty Ranges, shallow to occasionally exposed environments were largely sites of dolomite deposition ( Skillogalee Dolomite ). To the south, shales were deposited in slightly deeper environments ( Woolshed Flat Shale ), although local dolomite deposition occurred in the Adelaide region ( Castambul Formation, Montacute Dolomite ). In the uppermost part of the subgroup, the area of shale deposition extended northward, encroaching over the dolomite mudflats of the upper Skillogalee Dolomite. Dolomite, occurring largely as mudstones, is the major carbonate mineral present in the Mundallio Subgroup, but magnesite is also widespread. Limestones are not present. The carbonates experienced minor replacement by early diagenetic chert, initially precipitated as both crystalline and amorphous phases. Within the upper Mundallio Subgroup, the preservation of fine details of the detrital texture of dolomite mudstones and peloidal dolomites, and the high Sr contents of dolomites ( largely in the range of 400 - 650 ppm ), suggest that these sediments consisted of Ca - Mg carbonates ( protodolomite, Mg - calcite ) at the time of deposition. Slightly greater recrystallisation of dolomites in the lower Mundallio Subgroup resulted in their lower Sr and higher Mn and Fe contents. Magnesite mudstones may have initially precipitated as hydrated Mg - carbonates. Lithification of surface sediments as a result of subaerial exposure, led to the formation of micritic magnesite. Much of this magnesite was subsequently reworked into intraclastic beds. The carbonate mineralogy of this sequence, and the evidence of only rare sulphates, indicate that the carbonates were precipitated from alkaline, Mg - Ca - C03 waters, with a higher carbonate and lower sulphate content than seawater. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1980.

8 fold. maps in end pocket of v.2 Includes bibliographical references (p. 227-234)

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Oracle granite, probably emplaced in older Precambrian time contains the relic pattern imposed on the Pinal schist by the Mazatzal orogeny. The "granite" of that time was a granodiorite. It is now a porphyritic quartz monzonite that varies unsystematically toward granodiarite and biotite granite. The trend of its principal Precambrian foliation is northeast-southwest and this is crossed by northwesterly-trending Precambrian foliation. After the Mazatzal orogeny, peneplanation, and deposition of the younger Precambrian Apache group, a series of dikes was emplaced in the Oracle granite, beginning with coarse and medium grained diabase and ending with andesite and rhyolite. The earlier members of the sequence, including diabase, aplite, pegmatite, quartz and latite were emplaced when tensional stresses opened a series of northwest trending fractures. The tension seems to have been related to right lateral strike-slip along the Mogul fault zone, which forms the southern border of the granite. In Jurassic or Cretaceous time the strike-slip on the Mogul fault was reversed; northeast-trending Pinal schist south of the fault was rotated counter-clockwise into partial parallelism with the fault, a transition zone north of the fault was likewise dragged and andesite and rhyolite dikes were emplaced in northeast-trending "feather fractures." The structural and petrographic evidence suggests that metasomatism was important in the origin of the Precambrian granodiorite, but the existence of some magma cannot be precluded. Likewise the evidence suggests that the potash metasomatism that changed the granodiorite to quartz monzonite may have taken place at the time of the later intense movements, that is, during Jurassic or Cretaceous time. However, an earlier age of potash introduction is not unlikely.

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