abstract: Establishing the timing of impact crater formation is essential to exploring the relationship between bolide impact and biological evolution, and constraining the tempo of planetary surface evolution. Unfortunately, precise and accurate impact geochronology can be challenging. Many of the rock products of impact (impactites) contain relict, pre-impact phases that may have had their isotopic systematics completely reset during the impact event, only partially reset, or not reset at all. Of the many isotopic chronometers that have been used to date impactites, the U/Pb zircon chronometer (ZrnPb) seems least susceptible to post-impact disturbances, and ZrnPb dates are typically much more precise than those obtained using other chronometers. However, the ZrnPb system is so resistant to resetting that relict zircons in impactites often yield dates that reflect the igneous or metamorphic ages of the target rocks rather than the age of the impact itself. The present study was designed to answer a simple question: is there a straightforward sample collection and analysis strategy for high-accuracy ZrnPb dating of an impact structure if the impactites collected from it may contain inherited zircons? To study this, ZrnPb dates were determined for impactites from a single crater with a well-constrained impact age: the West Clearwater Lake impact structure, located at Lake Wiyâshâkimî, Québec, Canada. The amount of ZrnPb resetting and the mechanisms responsible for resetting varied amongst the samples. Each sample characteristically contained either: newly crystallized zircons from the impact melt ("neocrystalline"), relict zircons ~50-100% reset, or, relict zircons ~0-50% reset. The variably reset relict zircons define a discordia line from ~2700 Ma to ~286 Ma – consistent with the ages of the target rock and the impact, respectively (Schmieder et al., 2015a; Simard, 2004). ZrnPb measurements from the neocrystalline zircons provided a new preferred impact age of 286.64 ± 0.35 Ma (2σ), a ~10x improvement in precision. The characteristics of the West Clearwater ZrnPb data vary between samples yet become easily interpretable as a whole, showing that efforts to measure robust, precise impact ages benefit from strategies that prioritize applying multiple analytical techniques to multiple types of impactite from the same crater. / Dissertation/Thesis / Masters Thesis Geological Sciences 2019

Indiana University-Purdue University Indianapolis (IUPUI) / Tills from major ice streams (Institute, Foundation, Academy, Recovery, and Slessor) of the Weddell Sea Embayment contain detrital zircons with distinct U-Pb age populations that can be used as a provenance tool to better understand ice stream dynamics. U-Pb ages of detrital zircons were measured in 21 samples of onshore till, erratics, and bedrock of potential source rocks, and 12 samples of offshore till. Grains were analyzed by LA-ICPMS at the University of Arizona (n=5447). Relative probability U-Pb age density plots of till in moraines along the Institute Ice Stream have dominant Grenville (1070 Ma) and secondary Ross/Pan-African peaks (560 Ma, 630 Ma). The Foundation and Academy show prominent Ross/Pan-African peaks (500-530 Ma and 615-650 Ma). The Recovery transports zircons with prominent 530 Ma and 635 Ma peaks along the southern margin, and 1610 and 1770 Ma along the northern margin. The Slessor carries zircons with prominent populations at 1710 Ma and secondary 2260-2420 Ma. U-Pb ages in zircons from offshore till samples show a general trend of fewer Mesozoic ages from west to east. The western most core, PS 1423, has dominant Jurassic populations while cores 1197 and 1278 have a high proportion of early Ross/Pan-African ages relative to Grenville ages. The similar zircon age distributions between PS 1278 and the Foundation Ice Stream tills suggest that the Foundation switched to an easterly flow path around Berkner Island (BI) at some point during the LGM. In the eastern Weddell Sea (PS 1400), there was a near absence of Proterozoic zircon age populations carried by the Slessor and northern side of the Recovery. Another unexpected find was a lack of Grenville ages in PS 1423 relative to the Institute tills. The U-Pb data in this study provides a basis for two possible LGM ice flow reconstructions. In the first, the Institute flowed west around the unnamed isolated bedrock highs, deposited tills between PS 1423 and PS 1197, providing a westerly flow path around BI for the Foundation. In the second, the Institute flows over the subglacial topography and deposited till closer to PS 1197, forcing the Foundation east around BI.

Indiana University-Purdue University Indianapolis (IUPUI) / A broad range of samples were collected from the Huron-Erie Lobe, Lake Michigan Lobe, Saginaw Lobe, and Tipton Till Plain of northern Indiana to determine the provenance of Laurentide Ice Sheet till in the Midwest U.S. during the Illinoian and Wisconsinan glaciations. U-Pb age distributions from approximately 300 detrital zircons (DZ) were used as provenance indicators for each till sample. Till from the Lake Michigan Lobe and was found to be largely homogenized. The distinct lobe DZ age distributions are the Lake Michigan Lobe till with a dominant ~1465 Ma peak, the northern Huron-Erie Lobe till with a dominant ~1060 Ma and a secondary peak at ~1450 Ma, the southern Huron-Erie Lobe till with nearly equal peaks at ~1435 Ma, ~1175 Ma, and ~1065 Ma, and the southern Saginaw Lobe till with a dominant peak at ~1095 Ma. Those four DZ age distributions were treated as endmembers in a nonlinear least-squares mixing model to calculate the contribution of each lobe to till in the Tipton Till Plain. Huron-Erie and Saginaw lobe tills were found to be the primary components of the Tipton Till Plain, and Lake Michigan Lobe till was only found in the western Tipton Till Plain. Zircons from the Saginaw Lobe till increased 39 % in the eastern Tipton Till Plain between the Illinoisan and Wisconsinan glaciations. The mixing model was also applied to relate the DZ age distributions of the lobes to bedrock within and near their flow paths. When comparing nearby bedrock to each lobe’s till, mixing model results, yield an approximate maximum transport distance between 500 and 630 kilometers for the matrix vii fraction of till in the Lake Michigan, Huron-Erie, and Saginaw lobes. Samples for the southern Huron-Erie Lobe indicate that the most of the zircon ages within the southern Huron-Erie Lobe till in Indiana were specifically entrained between Niagara County, New York and east-central Indiana. Within the model’s error, 93 – 100 % of the detrital zircons in each of the three lobes are relatable to nearby Paleozoic and Precambrian sedimentary and metamorphic bedrock formations.

Published detrital zircon geochronological data was compiled to form the Global Detrital Zircon Database (GDZDb). This database provides a reference block for provenance analysis by future detrital zircon geochronological studies. This project entailed three subprojects: 1. crustal growth/crustal recycling patterns, 2. a provenance study of the Triassic Dry Fork Formation of the Danville-Dan River Rift basin of Virginia and North Carolina, and 3. sample size issues in detrital zircon studies. The global detrital zircon age frequency distribution exhibits six prominent, statistically significant peaks: 3.2-3.0, 2.7-2.5, 2.0-1.7, 1.2-1.0, 0.7-0.5, and 0.3-0.1 Ga. These peaks are also observed when the data is sorted for continent of origin, the tectonic setting of the host sediment and for modern river sediments. Hf isotope model ages were also incorporated into the database where grains were dated with both U-Pb and Hf isotopes. The Hf isotope model ages suggest that the majority of detrital zircons U-Pb ages reflect crustal recycling events that generated granitic magmatism, as most grains exhibited Hf isotope ages that are much older than the corresponding U-Pb age. The Triassic Dry Fork Formation was sampled from a site in southern Virginia in the Danville-Dan River Basin. The detrital zircon age frequency distribution for this formation was strongly unimodal with a peak at 400-450 Ma and a paucity of Grenville-age zircons. Comparison of the Dry Fork sample to published east coast data and to the North American record (from the GDZDb) illustrate the unusual nature of the Dry Fork Formation sample. It is probable that older Grenville zircons were blocked from the rift valley by the rift shoulder. Using the GDZDb a study of sample size was conducted in order to estimate the best sample size to use when trying to constrain the maximum age of sedimentation of the host sediment. Rift basins and active margins exhibited smaller offsets from the youngest zircon grain age to host sediment maximum age than observed in samples from passive margins. This study recommends that at least 50 grains need to be age dated on average in order to best constrain the age of the host sediment. / Ph. D.

The rocks of the Appalachian orogen are world-class examples of collisional and extensional tectonics, where multiple episodes of mountain building and rifting from the pre-Cambrian to the present are preserved in the geologic record. These orogenic events produced plutonic rocks, which can be used as probes of the thermal state of the source region. SIMS (secondary ion mass spectrometry) U/Pb ages of zircons were obtained for ten plutons (Leatherwood, Rich Acres, Melrose, Buckingham, Diana Mills, Columbia, Poore Creek, Green Springs, Lahore and Ellisville) within Virginia. These plutons are distinct chemically, isotopically, and show an age distribution where felsic rocks are approximately 440 Ma, and Mafic rocks are approximately 430 Ma. Initial strontium isotopic ratios and bulk geochemical analyses were also performed. These analyses show the bimodal nature of magmatism within this region. In order to facilitate management of geologic data, including radiometric ages, strontium isotope initial ratios and major element geochemistry, a GIS based approach has been developed. Geospatially references sample locations, and associated attribute data allow for analysis of the data, and an assessment of the accuracy of field locations of plutons at both regional and local scales. The GIS based assessment of plutons also allows for the incorporation of other multidisciplinary databases to enhance analysis of regional and local geologic processes. Extending such coverage to the central Appalachians (distribution of lithotectonic belts, plutons, and their ages and compositions) will enable a rapid assessment of tectonic models. / Master of Science

<p>U-Pb zircon results are presented with a U-Pb zircon Datatables for Bedrock Samples excel data sheet that have information for location (GPS and Geographic) and sample information. In addition, raw data formats of each individual sample is included that have additional information about laser settings per analysis.</p> <p><br></p> <p>Note the raw dataset for sample 062618WA-01 is included with two other analyses that are NOT bedrock samples. Use caution.</p> <p><br></p> <p>All analyses were conduction at the University of Arizona LaserChron Center ( <strong>NSF-EAR 1649254 </strong> )</p>

<p>U-Pb zircon datasets for Plutonic Clasts collected from conglomerate are presented first as a summary that includes sample name, GPS location, and datatables for each sample.</p> <p><br></p> <p>Additionally, raw datasets for each sample are included that includes detailed information on laser settings for each analyses</p> <p><br></p> <p>Note: Sample 062618WA-01 is included in one raw dataset as three igneous samples were analyzed on the same sample mount. This particular sample is a bedrock sample. Use caution</p> <p><br></p> <p>All analyses were completed at the University of Arizona Laserchron Center (NSF-EAR 1649254)</p>

<p>This dataset includes a summary excel file that details all the datatables for each detrital zircon sample and their location relative to each site and depth collected.</p> <p><br></p> <p>In addition to this summary, raw datasets for each individual analyses is included that have detailed information regarding the laser settings used for analyses.</p> <p><br></p> <p>All datasets were analyzed at the University of Arizona LaserChron Center (NSF-EAR 1649254)</p>

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / A estrutura crustal do Orógeno Ribeira pode ser definida, em seu segmento central, por alguns terrenos tectono-estratigráficos distintos entre si, e limitados por empurrões por sobre o Cráton de São Francisco e zonas de cisalhamento oblíquas, resultado de sucessivos eventos de colagem no Brasiliano. Neste contexto, o Terreno Paraíba do Sul se apresenta como uma estrutura sinformal, recobrindo o Terreno Ocidental, margem retrabalhada do Cráton de São Francisco (Heilbron et al., 2004). Ainda que o Orógeno Ribeira seja o mais estudado do Gondwana Oeste, esta tese contribui para o entendimento da constituição, origem e evolução das unidades que compõem o Terreno Paraíba do Sul, neste orógeno. Para tanto foram realizadas investigações geocronológicas sistemáticas subsidiadas por análises litogeoquímicas, tendo em vista o caráter regional do terreno estudado. Este estudo integrado se faz necessário em virtude da poucas e espacialmente restritas idades existentes para os ortognaisses do embasamento (Complexo Quirino) e granitóides, e à ausência de idades de proveniência de sua cobertura metassedimentar (Grupo Paraíba do Sul). Os dados litogeoquímicos de quarenta e uma análises (trinta e duas de Valladares et al., 2002) discriminam duas séries cálcio-alcalinas para o Complexo Quirino: uma de médio-K e composição tonalítica; e outra de alto-K e composição granítica/granodiorítica, relacionadas a ambiente de arco vulcânico. Foram ainda identificados alguns possíveis grupos cogenéticos, para cada uma destas séries (grupos 1 a 8 para a série de alto-K, e 1 a 3 para a série de médio-K), considerando razões entre elementos incompatíveis com variações inferiores a 1,5 vezes (Allégre & Minster, 1978) e outros critérios petrológicos, para orientação da investigação geocronológica. A análise geocronológica U-Pb foi realizada pelo método LA-ICPMS, em zircões selecionados de dez amostras, sendo seis de ortognaisses do Complexo Quirino (quatro da série de alto-K e duas da série de médio-K), duas de quartzitos do Grupo Paraíba do Sul e duas de granitóides neoproterozóicos. Todas as análises foram produzidas pelo autor no Radiogenic Isotope Facility of University of Alberta, Canadá. Os dados obtidos apresentaram, para o Complexo Quirino, idades de cristalização paleoproterozóica relacionadas ao Evento Transamazônico, sendo a série de alto-K mais antiga (2308 9,2 Ma a 2185 8 Ma) do que a série de médio-K (2169 3 Ma a 2136 14 Ma). A integração dos dados geocronológicos obtidos, com as avaliações petrogenéticas, possibilita a interpretação de que quatro ou cinco suítes ocorram na série de alto-K. A série de médio-K seria representada por uma única suíte cogenética, evoluída por assimilação concomitante à cristalização fracionada, consequente de fusão de crosta arqueana pré-existente durante o mesmo evento que gerou crosta juvenil. A expressiva quantidade de grãos herdados e idade TDM (Valladares et al., 2002) corroboram com esta hipótese. Os metassedimentos investigados são provenientes da erosão de rochas paleoproterozóicas (com maior concentração entre 1,9 Ga e 2,1 Ga), em parte oriundas do próprio embasamento, juntamente com contribuições subordinadas de fontes arqueanas. A idade de deposição máxima obtida a 1951 Ma (zircão concordante mais jovem), juntamente com a idade concordante mais antiga de metamorfismo do seu embasamento (645 13 Ma), define a melhor estimativa para a implantação da Bacia Paraíba do Sul em algum intervalo entre o final da Orogenia Transamazônica e o início da Orogenia Brasiliana. Três eventos metamórficos neoproterozóicos também foram identificados com base em registros de bordos de grãos, pontas de prismas e interceptos inferiores de zircões do embasamento e idades de cristalização de granitóides: um precoce, entre 645-605 Ma caracterizado nesta tese como pré-M1; e outros dois subseqüentes, com intervalos de 605-570 Ma e 540-520 Ma correlacionáveis respectivamente aos eventos M1 e M2 de Heilbron (1993) para o Orógeno Ribeira. Dentre as hipóteses para o registro metamórfico pré-M1, é sugerida uma possível influência dos episódios colisionais, de idade cronocorrelata, ao sul do Orógeno Brasília, ou a existência de um fragmento de crosta continental posicionada entre o Arco Rio Negro (Terreno Oriental) e o Cráton de São Francisco. No segundo caso, um evento de acresção deste fragmento de crosta ao arco, anterior à colisão com o Cráton, resultaria nas idades de metamorfismo mais precoce. Por fim, a idade ID-TIMS de 503 2 Ma em titanita do Complexo Quirino (Valladares, 1996) continuaria sendo a mais nova, refletindo a diminuição da atividade metamórfica para este terreno. / The crustal structure of the Ribeira Belt can be defined, in its central segment, by some tectono-estratigraphic terrains which are different, and limited by thrusts over São Francisco Craton and obliquous shear zones, result of successful docking events in the Brasiliano. In this context, the Paraíba do Sul Terrane is presented as a sinformal structure, covering the Occidental Terrane, a reworked margin of São Francisco Craton (Heilbron et al., 2004). Although the Ribeira mobile belt is the most studied in the West Gondwana, this study has contributed to the understanding of the constitution, origin and evolution of the units which compose the Paraíba do Sul Terrane, in this orogen. For that, systematic geochronological investigations were carried out, subsidized by lithogeochemical analysis, considering the regional character of the terrane being analyzed. This integrated study is necessary due to the few and spaciously restricted existing ages for the orthogneisses of the basement (Quirino Complex) and granitoids, and the absence of ages of provenance of its metasedimentary coverage (Paraiba do Sul Group). The litogeochemical data of 41 analyses (32 from Valladares et al., 2002) distinguish two calc-alkaline series for Quirino Complex: one of medium-K and tonalitic composition; other of high-K and granitic/granodioritic composition, related to a volcanic arc environment. Some possible cogenetic groups we identified, for each of these series (groups 1 to 8 for the high-K series, and 1 to 3 for the medium-K series), considering rates between incompatible elements varying below 1.5 times (Allégre & Minster, 1978) and other petrologic criteria, for the orientation of the geochronological investigation. The U-Pb geochronological analysis was performed by LA-ICPMS method, in zircons selected from ten samples, of which six were from orthogneisses from the Quirino Complex (four from the high-K series and two from the medium-K series), two from quartzites from Paraíba do Sul Group and two from neoproterozoic granitoids. All the analyses were produced by the author in the Radiogenic Isotope Facility of University of Alberta, Canada. The data obtained presented, for the Quirino Complex, palaeoproterozoic crystallization ages related to the Transamazonic Event, the high-K series being older (2308 9.2 Ma a 2185 8 Ma) that the medium-K series (2169 3 Ma a 2136 14 Ma). The integration of the geochronological data with the petrogenetic evaluation leads to the conclusion that four or five suites occur in the high-K serie. The medium-K series would be represented by one sole cogenetic suite, evolved by concomitant assimilation during fractioned crystallization, resulting, in part, from the melt of an archean crust during the same event which generated juvenile crust on the Palaeoproterozoic. The expressive quantity of inherited archean grains and TDM archean age (Valladares et al., 2002) support this hypothesis. The metasediments investigated are originated from the erosion of palaeoproterozoic rocks (with higher concentration between 1.9 Ga and 2.1 Ga), partly originated from the basement itself, together with subordinated contributions of archean sources. The maximum deposition age obtained at 1951 Ma (youngest zircon concordant), together with the oldest concordant age of the metamorphism of its basement (645 13 Ma), defines the best estimate for the implementation of the Paraíba do Sul Basin, in some interval between the end of the Transamazonic Orogeny and the beginning of the Brasilian Orogeny. Three neoproterozoic metamorphic events were also identified based on registers of overgrowth grain, prismatic tips and lower intercepts of zircons of the basement and granitoid crystallization ages: one precocious, between 645-605 Ma, characterized in this study as pre-M1; and two subsequent, with intervals of 605-570 Ma and 540-520 Ma respectively correlated to Heilbron (1993) M1 and M2 events for the Ribeira Belt. Among the hypothesis for the metamorphic pre-M1 register, we suggest possible influence of the collision episodes, of chronorrelated age, south of the Brasilia Belt, or the existence of a fragment of continental crust positioned between the Rio Negro Arc (Oriental Terrane) and São Francisco Craton. In the second case, an accretion event of this crust fragment to the arc, from before the collision with the Craton, would result in the earlier metamorphism ages. Finally, the ID-TIMS age of 503 2 Ma in titanite of the Quirino Complex (Valladares, 1996) would still be the youngest, reflecting the decrease of the metamorphic activity for this terrane.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / O Orógeno Ribeira representa um cinturão de dobramentos e empurrões, gerado no Neoproterozóico/Cambriano, durante a Orogênese Brasiliana, na borda sul/sudeste do Cráton do São Francisco e compreende quatro terrenos tectono-estratigráficos: 1) o Terreno Ocidental, interpretado como resultado do retrabalhamento do paleocontinente São Francisco, é constituído de duas escamas de empurrão de escala crustal (Domínios Andrelândia e Juiz de Fora); 2) o Terreno Oriental representa uma outra microplaca e abriga o Arco Magmático Rio Negro; 3) o Terreno Paraíba do Sul, que constitui-se na escama superior deste segmento da faixa; e 4) o Terreno Cabo Frio, cuja docagem foi tardia, ocupa pequena área no litoral norte do estado do Rio de Janeiro. Em todos os diferentes compartimentos do segmento central da Faixa Ribeira podem ser identificadas três unidades tectono-estratigráficas: 1) unidades pré-1,8 Ga. (ortognaisses e ortogranulitos do embasamento); 2) rochas metassedimentares pós-1,8 Ga; e 3) granitóides/charnockitóides brasilianos. O Complexo Mantiqueira é composto por ortognaisses migmatíticos, tonalíticos a graníticos, e anfibolitos associados, constitui o embasamento pré-1,8 Ga das rochas da Megasseqüência Andrelândia no domínio homônimo do Terreno Ocidental. Foram integrados 68 dados litogeoquímicos dentre ortognaisses e metabasitos do Complexo Mantiqueira. As rochas dessa unidade pertencem a duas séries distintas: série calcioalcalina (rochas intermediárias a ácidas); e série transicional (rochas básicas, ora de afinidade toleítica, ora alcalina). Com base em critérios petrológicos, análise quantitativa e em valores [La/Yb]N, verificou-se que o Complexo Mantiqueira é bastante heterogêneo, incluindo diversos grupos petrogeneticamente distintos. Dentre as rochas da série transicional, foram identificados 2 conjuntos: 1) rochas basálticas toleiíticas, com [La/Yb]N entre 2,13 e 4,72 (fontes do tipo E-MORB e/ou intraplaca);e 2) rochas basálticas de afinidade alcalina, com [La/Yb]N entre 11,79 e 22,78. As rochas da série calciolacalina foram agrupadas em cinco diferentes conjuntos: 1) ortognaisses migmatíticos quartzo dioríticos a tonalíticos, com [La/Yb]N entre 11,37 e 38,26; 2) ortognaisses bandados de composição quarzto diorítica a granodiorítica, com [La/Yb]N entre 4,35 e 9,28; 3) ortognaisses homogênos de composição tonalítica a granítica, com [La/Yb]N entre 16,57 e 38,59; 4) leucognaisses brancos de composição tonalítica/trondhjemítica a granítica, com [La/Yb]N entre 46,69 e 65,06; e 5) ortognaisse róseo porfiroclástico de composição tonalítica a granítica, com [La/Yb]N entre 82,70 e 171,36. As análises geocronológicas U-Pb SHRIMP foram realizadas no Research School of Earth Science (ANU/Canberra/Austrália). Foram obtidas idades paleoproterozóicas para as rochas das duas séries identificadas, interpretadas como a idade de cristalização dos protólitos magmáticos desses gnaisses e metabasitos. Os resultados obtidos mostram uma variação de idades de cristalização de 2139 35 a 2143,4 9,4, para as rochas da série transicional, e de 2126,4 8 a 2204,5 6,7, para aquelas da série calcioalcalina. Dentre todas as amostras estudadas, apenas a amostra JF-CM-516IV forneceu dados discordantes de idades arqueanas (292916 Ma), interpretados como dados de herança. Contudo, evidências dessa herança semelhantes a esta são observadas em outras amostras. Ambas as séries também apresentaram idades de metamorfismo neoproterozóico, no intervalo de 548 17 Ma a 590,5 7,7 Ma que é consistente com o metamorfismo M1 (entre 550 e 590 Ma), contemporâneo à colisão entre os Terrenos Ocidental e Oriental do setor central da Faixa Ribeira (Heilbron, 1993 e Heilbron et al., 1995). / The Ribeira Orogen is a complex orogenic belt developed during the Brasiliano Orogeny, along the southern and southeastern borders of the São Francisco Craton, and is subdivided into four tectono-stratigraphic terranes: 1) the Occidental Terrane, taken as the reworked margin of São Francisco paleocontinent, displays an internal tectonic organization with two crustal scale thrust sheets (Andrelândia and Juiz de Fora); 2) the Oriental Terrane, comprises another crotonic block or microplate and includes the Rio Negro magmatic arc; 3) the Paraíba do Sul Terrane, which comprises the uppermost thrust slice of the central segment of the belt; and 4) the Cabo Frio Terrane, which occupies a restrict area at the coast of Rio de Janeiro State, records a late docking event. Within all the forementioned terranes, it can be identified three litho-tectonic units: pre-1.8 Ga basement units (orthognaisses and orthogranulites); 2) post-1.8 Ga supracrustal rocks; and 3) brasiliano granitoids and charnockitoids. Mantiqueira Complex comprises a great variety of tonalitic to granitic orthogneisses and minor orthoamphibolites. This unit comprises the basement rocks of the Andrelândia Megasequence within the Andrelândia tectonic domain. Lithogeochemical data of 68 samples, including orthogneisses and metabasites, indicate that the Mantiqueira Complex comprises two different series: calcalkaline series (intermediate to acid calcalkaline rocks); and transicional series (alkaline to tholeiitic basic rocks). Based on petrological criteria, quantitative analysis and [La/Yb]N values, it was possible to verify that the Mantiqueira Complex is heterogeneous and includes many petrogenetic groups. The transicional series comprises two groups: 1) tholeitic basic rocks, with [La/Yb]N between 2,13 and 4,72 (E-MORB and/or Intraplate type); and 2) alkaline basic rocks, with [La/Yb]N between 11,79 and 22,78. The calcalkaline rocks of the Mantiqueira Complex may be grouped into five different petrogenetic groups: 1) migmatitic quartz dioritic to tonalitic orthogneisses, with [La/Yb]N between 11,37 and 38,26; 2) banded quartz dioritic to granodioritic orthogneisses, with [La/Yb]N between 4,35 and 9,28; 3) tonalitic to granitic homogeneous orthogneisses, with [La/Yb]N between 16,57 and 38,59; 4) white tonalitic/trondhjemitic to granitic leucogneisses, with [La/Yb]N between 46,69 and 65,06; and 5) pinkish orthogneiss of tonalitic to granitic composition and [La/Yb]N between 82,70 and 171,36. U-Pb SHRIMP geocronological analysis were performed at the Research School of Earth Science (ANU/Canberra/Australia). Paleoproterozoic ages, interpreted as protoliths cristalization ages, were obtained for rocks from both the calcalkaline and transitional series. Obtained results display a range of cristalization ages from 2139 35 to 2143,4 9,4, to the rocks of the transitional series, and from 2126,4 8 to 2204,5 6,7, for those of the calcalkaline one. Among all studied rocks, only one (sample JF-CM-516 IV) yielded discordant archean zircons (292916 Ma), interpreted as inherited ones. However, evidences of archean zircons were obtained from zircons of other samples. All studied samples record a neoproterozoic metamorphic event in the interval from 548 17 Ma to 590,5 7,7 Ma, which is consistent with the M1 metamorphic event (from 550 to 590 Ma), contemporaneous to the main collision of the central segment of Ribeira Belt (collision between the Occidental and Oriental Terranes (Heilbron, 1993 e Heilbron et al., 1995).