The origin of the Cantabrian orocline of the Variscan orogen in NW Iberia remains a topic of debate. We present a structural study of the Ponga Unit, a Cambrian to Carboniferous tectonostratigraphic package within the Variscan foreland fold and thrust belt that lies within the core region of the Cantabrian orocline. Our primary goal is to determine if the structure of the Ponga Unit is attributable to secondary orocline formation or if west-plunging regional folds in the area reflect lateral ramps in underlying Variscan thrust sheets. Our mapping and structural analysis within the Ponga Unit focuses on the Laviana, Rioseco and Campo de Caso thrust sheets, and associated bounding thrusts. More than 800 structural orientation measurements were collected across the study area during a four-week field campaign. These data, coupled with data compiled from regional geological maps, allow for analysis of the crustal structure. West-plunging folds of the Laviana, Rioseco and Campo de Caso thrust sheets form km-scale anticline-syncline pairs, producing a complex fold interference pattern that is characteristic of the Ponga Unit. Our analysis shows that: 1) the geometry of the west-plunging folds is inconsistent with a lateral-ramp related interpretation; 2) the map pattern resembles a mushroom fold interference pattern that is the result of two deformation phases including secondary, orocline-related N-S shortening immediately after the cessation of E-W Variscan shortening; and 3) paleomagnetic data, notably a ‘B’ remanence magnetism, in the Ponga Unit likely overlaps in time with the cessation of Variscan deformation and records post-Variscan deformation associated with the onset of oroclinal buckling. Our results indicate that early N-S trending folds, which resulted from Variscan orogenesis, were refolded by a N-S oriented compressive stress that is attributable to the secondary buckling of the Cantabrian orocline. / Graduate

Most researchers contend that the destruction of the Rheic Ocean culminated in the formation of the supercontinent Pangea. However, despite the importance of this ocean, there are major uncertainties in the identification of its margins, mechanisms and timing of its formation, and the geodynamics of its closure. Rocks recording the evolution of the Rheic are excellently preserved in the southern Iberian peninsula of Western Europe. Here, the Ossa Morena (OMZ) is separated from the South Portuguese (SPZ) zone by a sequence of polydeformed rocks know as the Pulo do lobo Zone (PDLZ). The PDLZ isinterpreted as a late Paleozoic accretionary prism, which contains potential vestiges of the ancient Rheic Ocean (ophiolites). The objective of this study is to better understand the processes associated with the formation of Pangea by determining the lithotectonic histories of both the PDLZ and SPZ. New field, geochronological and geochemical data are used to test and further constrain current models for the evolution of Pangea as recorded in the Variscan orogen. Fieldwork and geochronological data indicate that the PDLZ was derived from neither the OMZ (Gondwana) nor the SPZ suggesting that if the PDLZ is an accretionary prism it was not derived from the upper or lower plate. This apparent conundrum can be reconciled by a model involving excision of a crustal fragment during collision between an Iberian indenter (Gondwana) with Laurussia during the formation of Pangea. Geochronological and Geochemical data from the SPZ indicate that the lower crust isnot compositionally similar to the overlying Devonian-Carboniferous continental detritus. This unusual relationship is similar to the relationship between the relatively juvenile basement and ancient upper crust documented in the exposed portion of the Meguma terrane in the northern Appalachians, which paleogeographic reconstructions show was immediately outboard of southern Iberia in the Late Devonian. Taken together with the suggested complex tectonic history of the PDLZ the results of this thesis provide important insight into the geometry and timing of the formation of Pangea and indicate that re-interpretation may be required for what is known concerning the tectonic evolution of both the Variscan and Appalachian orogens.

The Central Atlantic Magmatic Province (CAMP) is the large igneous province (LIP) that coincides with the breakup of the supercontinent Pangea. Major and trace element data, Sr-Nd-Pb radiogenic isotopes, and high-precision olivine chemistry were collected on primitive CAMP dikes from Virginia (VA). These new samples were used in conjunction with a global CAMP data set to elucidate different mechanisms for supercontinent breakup and LIP formation. On the Eastern North American Margin, CAMP flows are found primarily in rift basins that can be divided into northern or southern groups based on differences in tectonic evolution, rifting history, and supercontinental inheritance. Geochemical signatures of CAMP suggest an upper mantle source modified by subduction processes. We propose that the greater number of accretionary events, or metasomatism by sediment melts as opposed to fluids on the northern versus the southern Laurentian margin during the formation of Pangea led to different subduction-related signatures in the mantle source of the northern versus southern CAMP lavas. CAMP samples have elevated Ni and low Ca in olivine phenocrysts indicating a significant pyroxenite component in the source, interpreted here as a result of subduction metasomatism. Different collisional styles during the Alleghanian orogeny in the North and South may have led to the diachroneity of the rifting of Pangea. Furthermore, due to a low angle of subduction, the Rheic Plate may have underplated the lithosphere then delaminated, triggering both the breakup of Pangea and the formation of CAMP. / Master of Science

Submitted by Cássio da Cruz Nogueira (cassionogueirakk@gmail.com) on 2017-08-31T16:39:13Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_PermoTriassicoBacia.pdf: 19484036 bytes, checksum: 8d3b997bc500a9599e4b55947421d615 (MD5) / Approved for entry into archive by Irvana Coutinho (irvana@ufpa.br) on 2017-09-12T12:10:17Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_PermoTriassicoBacia.pdf: 19484036 bytes, checksum: 8d3b997bc500a9599e4b55947421d615 (MD5) / Made available in DSpace on 2017-09-12T12:10:18Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Tese_PermoTriassicoBacia.pdf: 19484036 bytes, checksum: 8d3b997bc500a9599e4b55947421d615 (MD5) Previous issue date: 2016-06-03 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico / O Permo-Triássico foi marcado pelo maior evento de extinção em massa da história geológica da Terra, com a perda de 90-95% das espécies marinhas e terrestres, estando relacionado a mudanças paleogeográficas e paleoclimáticas, em parte atribuídas a eventos catastróficos. No final do Permiano, condições áridas prevaleceram em todo o globo como consequência da queda eustática do nível do mar, do desaparecimento das áreas glaciais e da multiplicação de bacias fechadas. Estas condições somadas à intensa continentalização do Pangea propiciaram a desertificação do supercontinente com o desenvolvimento de extensos desertos e complexos de sabkha. Os registros desses eventos no norte do Brasil são encontrados nas bacias intracratônicas, particularmente na Bacia do Parnaíba, representados pela sucessão siliciclástica-evaporítica do Grupo Balsas, que inclui as formações Pedra de Fogo, Motuca e Sambaíba. Sete associações de fácies foram reconhecidas: (1) Lacustre dominado por planícies de lama, representado pela intercalação de pelitos cinza esverdeados/avermelhados e arenitos finos com expressivo conteúdo de sílex; (2) Campo de dunas marginal constituído por estratos cruzados de arenitos finos a médios; (3) Lagos de playa perenes, consistindo dominantemente de pelitos vermelhos laminados com descontínuas camadas de arenitos sigmoidais; (4) Planície de lama salina / Panela salina, representadas por camadas de pelitos intercaladas a lentes de gipsita, calcário e marga; (5) Lençol de areia, constituído por estratos planos lateralmente contínuos de arenitos finos a médios com laminação convoluta, falhas/microfalhas sinsedimentares e estruturas de adesão; (6) Campo de dunas, formado por arenitos finos a médios com estratificações cruzadas de grande porte; e (7) Planície vulcânica, consistindo de basaltos e arenitos intercalados. Durante o Permiano Médio, amplas planícies marcadas pela alternância de fases lacustres rasas a profundas e planícies de lama em sabkhas continentais (AF1) se estendiam na zona tropical das porções oeste e central do Pangea. Esta ciclicidade refletia a sazonalidade de fases úmidas e secas, condicionadas por variações no nível freático, baixa taxa de subsidência e limitado espaço de acomodação. As fases secas mais prolongadas eram caracterizadas pelo avanço dos campos de dunas marginais (AF2) e o estabelecimento de amplas planícies de lama secas. O contínuo processo de amalgamação do Pangea durante o Permiano Superior propiciou o soerguimento das regiões equatoriais e centrais do supercontinente, ocasionando a retração dos mares epicontinentais, o surgimento de extensas bacias fechadas (AF3) e a formação de lagos salinos efêmeros extremamente ácidos, planícies de lama salinas e panelas salinas (AF4). Petrograficamente, os evaporitos das panelas salinas exibem feições de precipitação primária a eodiagenética de gipsita e anidrita, posteriormente afetados por processos telodiagenéticos. A extrema aridez favoreceu a retração destes grandes lagos e a implantação definitiva de um Erg triássico. Lençóis de areia ocorriam na porção marginal do Erg, contendo lagoas efêmeras e abundantes regiões úmidas (AF5). Extensos campos de dunas avançavam conforme aumentava a disponibilidade de sedimentos, enquanto superfícies de deflação eram formadas pela supressão parcial do suprimento sedimentar (AF6). A supressão total de sedimentos para o Erg no Triássico Superior proporcionou uma deflação extrema e regional que ocasionou na formação de uma superfície extremamente plana que assentou rochas vulcânicas eojurássicas (AF7). A análise deformacional da sucessão estudada identificou pelo menos três diferentes níveis de deformação sinsedimentar: (I) feições híbridas rúptil-dúuctil na zona de contato entre as formações Motuca e Sambaíba; (II) dobras e convoluções de médio porte na porção intermediária dos estratos eólicos da Formação Sambaíba; (III) injetitos nos arenitos intertraps da Formação Mosquito. Estes três níveis de camadas deformadas são separados por intervalos de estratos não deformados ou ligeiramente deformados, podendo mostrar lateralmente um aumento gradual da intensidade da deformação. O nível de deformação I ocorre na zona de contato entre as formações Motuca e Sambaíba e é representado por um conjunto de feições híbridas (rúptil-dúctil). A continuidade lateral deste intervalo por centenas de quilômetros, somada ao aumento do grau de deformação na região de Riachão e a concentração anômala de elementos traços (Cr, Co, Cu, Mn, Au, Pd e Pt), são compatíveis com abalos sísmicos de alta magnitude, provavelmente induzidos por impacto meteorítico (astroblema de Riachão). O nível de deformação II é formado por um conjunto de dobras desarmônicas na parte intermediária da Formação Sambaíba. Originou-se por processos autocíclicos relacionados a deformação hidroplástica de sedimentos pela migração e sobrepeso de dunas/draas. O terceiro intervalo consiste em diques de arenito nas rochas vulcânicas eojurássicas da Formação Mosquito. Estes diques foram formados pela injeção hidráulica de areia durante o aumento de gradiente térmico induzido pelo magmatismo básico durante a fase pré-rifte do Pangea Ocidental. / The Permo-Triassic was marked by the great mass extinction of geological Earth history with losses of 90-95% of marine and terrestrial species. These were related to paleogeographic and paleoclimatic changes in part assigned to catastrophic events. In the end of Permian, arid conditions prevailed around the world as a consequence of eustatic sea level fall added to disappearance of glacial areas and large-scale closed basins multiplication. These conditions combined with the intense continentalization of Pangea supercontinent led to desertification with the development of large desert and sabka complexes. In the northern of Brazil the records of these events are found in intracratonic basins, particularly in the Parnaíba Basin. This is represented by siliciclastic-evaporitic succession from Balsas Group compound by Pedra de Fogo, Motuca and Sambaíba formations. It was recognized seven facies associations: (1) Lacustrine mudflat dominated, represented by greenish/reddish gray laminated mudstones interbedded with fine-grained sandstones and great chert content; (2) Marginal dune fields consisting of planar cross-stratified beds of fine- to medium-grained sandstones; (3) Perennial playa lake consisting dominantly of red laminated mudstones with discontinuous layers of sigmoidal sandstones; (4) Saline mudflat / Saline pan represented by reddish laminated mudstones interbedded with lenses of gypsum, limestone, and marl; (5) Sand sheet laterally consisting of continuous fine- to medium-grained sandstones with convoluted lamination, synsedimentary faults/microfaults and adhesion structures; (6) Dune fields formed by fine- to medium-grained sandstones with large-scale cross-bed sets; and (7) Volcanic plain, consisting of basalts interbedded with sandstones. During Middle Permian, the alternating between continental sabkha mudflats and shallow to deep lacustrine phases occurred in large plains in the tropical zone of western to central Pangea (AF1). This cyclicality reflected the seasonal wet and dry phases triggered by changes in the water level, low subsidence rate and narrow accommodation space. The prolonged dry stages were characterized by the advance of the marginal dune fields (AF2) as well as by establishment of large dry mudflats. In the Upper Permian, the continuous amalgamation process of supercontinent Pangea led to the uplift of central and equatorial regions resulting in the retreat of epicontinental seas. However, there were the appearance of large-scale closed basins (AF3) and extremely acid saline ephemeral lakes with saline mudflats and pans (AF4). Petrographically, the evaporate from saline pans display primary features of precipitation to eodiagenetic of gypsum and anidrite posteriorly affected by telodiagenetic processes. The extreme aridity conditions favored the decline of these great lakes and the definitive implementation of Triassic Erg. Sand sheets occurred in the marginal portion of this Erg, containing abundant ephemeral ponds and humid regions (AF5). Large dune fields advancing as consequence of the sediment availability increase, while deflation surfaces were produced by partial removal of sediment supply (AF6). The total interruption of sediment supply to the Erg in the Late Triassic provided an extreme and regional deflation surface overlapping by eojurassics volcanic rocks (AF7). The deformational analysis of the studied succession identified three different synsedimentary deformational levels at least: (I) brittle-ductile hybrid features in the contact zone between the Motuca and Sambaíba formations; (II) folds and medium-sized convolution in the middle portion of the eolic strata of Sambaíba Formation; (III) Injectites in the intertraps sandstones from Mosquito Formation. These three levels of deformed layers are separated by non- or slightly-deformed strata intervals, laterally may show a gradual increase of deformation intensity. The deformation level I occurs in the contact zone between Motuca and Sambaíba formations represented by a set of hybrid (brittleductile) features. Lateral continuity of this interval for hundreds of kilometers added to the increase in the deformation degree in the Riachão area. Furthermore, the anomalous concentration of trace elements (Cr, Co, Cu, Mn, Au, Pd, and Pt) are consistent with earthquakes of high magnitude probably product of meteoritic impact (Riachão structure). The level of strain II is marked by a set of inharmonious folds in the middle part of Sambaiba Formation. These are originated by autociclic processes related to hidroplastic deformation of sediments of sediments by dunen/draas migration and overweight. The third interval it is composed by sandstone dikes in an eojurassic volcanic rocks of Mosquito Formation. These dams were formed by hydraulic injections of sand leading to a thermal gradient increase induced by basic magmatic activities during the pre-rift phase in the Western Pangea.

The two end-member concept of mantle plume-driven versus far field stress-driven continental rifting anticipates high volumes of magma emplaced close to the rift-initiating plume, whereas relatively low magmatic volumes are predicted at large distances from the plume where the rifting is thought to be driven by far field stresses. We test this concept at the Guinea Plateau, which represents the last area of separation between Africa and South America, by investigating for rift-related volumes of magmatism using borehole, 3D seismic, and gravity data to run structural 3D inversions in two different data areas. Despite our interpretation of igneous rocks spanning large areas of continental shelf covered by the available seismic surveys, the calculated volumes in the Guinea Plateau barely match the magmatic volumes of other magma-poor margins and thus endorse the aforementioned concept. While the volcanic units on the shelf seem to be characterized more dominantly by horizontally deposited extrusive volcanic flows distributed over larger areas, numerous paleo-seamounts pierce complexly deformed pre and syn-rift sedimentary units on the slope. As non-uniqueness is an omnipresent issue when using potential field data to model geologic features, our method faced some challenges in the areas exhibiting complicated geology. In this situation less rigid constraints were applied in the modeling process. The misfit issues were successfully addressed by filtering the frequency content of the gravity data according to the depth of the investigated geology. In this work, we classify and compare our volume estimates for rift-related magmatism between the Guinea Fracture Zone (FZ) and the Saint Paul's FZ while presenting the refinements applied to our modeling technique.

The Western European Variscan orogenic belt is thought to represent the final in a series of Paleozoic continental collisions that culminated with the amalgamation of the supercontinent Pangea. The Iberian segment of the Variscan belt is characterized by Cantabrian orocline, which is 180º and convex toward the west. Several lines of evidence are at odds with classical interpretation of the Cantabrian orocline as the core of the much larger ‘Ibero-Armorican’ arc, suggesting instead that it is structurally continuous with a second more southerly and complimentary orocline. Paleocurrent data collected from the Lower Ordovician Armorican Quartzite of the deformed Iberian Paleozoic passive margin sequence confirm the existence of the so-called Central Iberian orocline. Structural continuity between the Cantabrian and Central Iberian oroclines suggests that they formed contemporaneously and in the same fashion. Mesoscale vertical-axis folds deforming slaty cleavage and shear fabric within the Ediacaran Narcea Slates have a dominant vergence toward the hinge of the Cantabrian orocline, suggesting that its formation was in part accommodated by a mechanism of flexural shear during buckling of a linear belt in response to an orogen parallel principle compressive stress. The Cantabrian-Central Iberian coupled oroclines therefore palinspastically restore to an originally linear belt 2300 km in length. Provenance analysis of detrital zircons sampled from the Armorican Quartzite along a 1500-km-long segment of the palinplastically restored Iberian passive margin indicate that it originated in a paleogeographic position stretching east-west along the northern limits of north African Gondwana, from the Arabian-Nubian Shield to the Saharan hinterland. Paleomagnetic data and the distribution of Variscan ophiolites support a model of mid-Paleozoic separation of the Variscan autochthon (Armorican continental ribbon) from north Gondwana preceding or in conjunction with a 90º rotation required to reorient the ribbon to a Late Carboniferous north-south trend. Formation of the Iberian coupled oroclines accommodated 1100 km of orogen parallel shortening. The Western European Variscan belt, North American Cordillera, and Eastern European Alpine system are orogens similarly characterized by both coupled oroclines and paleomagnetic inclinations that are significantly shallower than cratonic reference values. Palinspastic restoration of the Alaskan and Carpathian–Balkan coupled oroclines fully resolves inclination anomalies within the Cordillera and Eastern Alpine system, respectively. Inclination anomalies within the Iberian Variscan belt are only partially resolved through palinspastic restoration of the Iberian coupled oroclines, but the sinuous geometry of the belt is not yet fully deciphered. Oroclines within the Western European Variscan belt, not the orogen itself, provide the true record of Pangean amalgamation. / Graduate

Une marge passive est une zone de transition non-active entre lithosphère continentale et lithosphère océanique. De nombreuses marges passives présentent un fort développement magmatique (>50%). Ces marges passives volcaniques (MPVs) marquent la rupture lithosphérique au-dessus d’un manteau en fusion (partielle) et sont typiquement caractérisées par l’intrusion et l’extrusion d’un volume significatif de produits magmatiques dans la croûte lors des périodes ante-rift, syn-rift et post-rift. A partir d’une compilation bibliographique, de données sismiques (profils de sismique réflexion ION-GXT, sismique 3D) et d’observations réalisées sur le terrain à l’Est et à l’Ouest du Groenland, les objectifs de cette thèse étaient : (1) de mieux caractériser les modes tectoniques d’accommodation des flexures de la croûte supérieure sous les SDRs (seaward dipping reflectors) et l’interprétation des SDRs externes et, (2), de placer la rupture magmatique à l’échelle de la fragmentation d’un supercontinent. Les principaux résultats obtenus sont: 1) La rupture d’un supercontinent est toujours synmagmatique. Cette rupture se propage ensuite de manière non-magmatique (article en préparation); 2) Les SDRs externes sont découplés tectoniquement d’une croûte inférieure d’origine continentale exhumée. Du matériel d’origine continental pourrait exister en profondeur de manière continue au niveau de rides asismiques transverses (comme GIFR) (article soumis); 3) La flexure crustale est aussi accommodée par du magma qui circule dans les failles de détachement sous SDRs. Un découplage existe à l’extrados des flexures accommodé par des injections de magma syn-tectoniques sous forme de laccolithes à la base des SDRs internes. / A passive margin is a non-active transition zone between the continental lithosphere and the oceanic lithosphere. Most of passive margins (>50%) show a strong magmatic development. These volcanic passive margins (VPMs) mark the lithospheric breakup over a melted mantle and they are typically characterized by a huge volume of intrusive and extrusive magmatism into the crust during ante-rift, syn-rift, and post-rift periods.Based on bibliographies, seismic data (IONGXT seismic reflection profiles, 3D seismic) and observations and results gained from fieldtrips on East and West Greenland coast, the objectives of this thesis were: (1) to better characterize the tectonic accommodation of the flexure of the upper crust which beneath inner SDRs and the signification of outer SDRs, and (3) to place the magmatic breakup on the scale of the fragmentation of a supercontinent.The main results obtained are: 1) the breakup of a supercontinent is always syn-magmatic. This breakup then propagates in a non-magmatic way (paper in preparation); 2) the outer SDRs are tectonically decoupled from an exhumed continental lower crust.The material of continental origin could exist deeply continuously across a transverse aseismic ridge such as the GIFR (paper submitted); 3) The crustal flexure is also accommodated by the magma that circulate in detachment faults beneath the inner SDRs. There is a decoupling at the extrados zone of the flexure which is accommodated by syn-tectonic magma injections in the form of laccoliths between inner SDRs and upper crust.

Mid-Late Triassic-age alkali-basalt dikes were emplaced along the coast of New England between 240-200 Ma. Known as the Coastal New England (CNE) magmatic province, this dike swarm is the immediate magmatic predecessor to the formation of the Central Atlantic Magmatic Province large igneous province at 201 Ma and the breakup of Pangea. The intent of this study is to determine the melt source and mechanisms for melting which produced the Triassic coastal dikes. To achieve this goal, major and trace element compositions were analyzed for 53 CNE dikes from Maine and Nova Scotia. Radiogenic Nd-Sr-Pb-Hf ratios, representing some of the first 176Hf/177Hf data for CNE, are reported for 12 of the dikes. Taken together, the compositional data implicate melting of a deep mantle source that is relatively enriched in incompatible elements, such as a mantle-plume similar to those hypothesized as the source of melting in modern ocean-island basalts (i.e. Hawaii). Dike compositions are inconsistent with melts generated at typical spreading-center ridges (i.e. MORB). Modeling suggests that CNE melts ascended through thick continental crust, consistent with the incipient stages of rifting of Pangea, as evidenced by a heterogeneous mix of melting and crystallization depths, between 0-70km, with no clear geographic pattern. Radiogenic isotope data are relatively consistent and represent a mixture between HIMU, EMI and DMM mantle reservoirs, implying component consisting of relict subducted oceanic crust (or other similarly evolved material). CNE magmatism may have contributed to the breakup of Pangea by destabilizing the lower crust in the limited local area where it erupted, but its true relationship with the breakup of Pangea and later CAMP event requires more study. / Master of Science / Approximately 200-250 million years ago, hundreds of sheets of lava, called dikes, erupted along what is today the coast of New England. As these volcanic dikes rose up from the Earth’s mantle, they traveled along cracks and weak areas of the Earth’s crust. Today, these dikes are found along the New England coast as far south as Rhode Island and as far north as Nova Scotia, Canada. Based on the similarity of their geochemistry and petrology, as well as their geologic age and geography of their eruption, geologists group these dikes and similar volcanics together as a single, related magmatic event. This magmatic event produced the Coastal New England (CNE) magmatic province. 250 million years ago, the coast of New England was actually an interior part of the supercontinent known as Pangea. Around 250 m.yr. ago, Pangea slowly began rifting apart, which is when CNE volcanism began. By 200 m.yr. ago, Pangea had broken up, and CNE volcanism had ended. Further complicating the story, a large-igneous province (LIP) also erupted 200 m.yr. ago. Known as the Central Atlantic Magmatic Province (CAMP), this volcanism consisted of enormous volumes of lava that flooded over the entire east coast of the United States. The intent of this study is to determine what geological conditions led to the CNE volcanism. By learning which part of the Earth melted and why, CNE volcanism’s role in the breakup of Pangea, and the much larger CAMP eruptions that coincided with it, will become clearer. For instance, did the geologic events that resulted in CNE volcanism contribute to the breakup of Pangea, or did the breakup of Pangea cause CNE volcanism followed by CAMP volcanism? To achieve this goal, the geochemical compositions of 53 CNE dikes from Maine and Nova Scotia were analyzed. Radiogenic Nd-Sr-Pb-Hf ratios for a subset of the dikes (12) were also analyzed. This study presents some of the first radiogenic hafnium data for rocks from CNE. The data indicate that the melting which produced the CNE dikes began in the deep mantle, similar to the melting of mantle plumes beneath modern ocean-islands such as Hawaii. In contrast, shallow mantle melting, like the melting at mid-ocean ridges where oceanic crust is produced, is not consistent with the geochemical evidence presented for CNE in this study. Modeling suggests that CNE magmas rose through thick continental crust, which caused them to begin forming crystals at relatively high depths. Radiogenic isotope data suggests that part of the mantle that melted was old, recycled oceanic crust or similar mantle material. CNE magmatism may have contributed to the breakup of Pangea by destabilizing the lower crust in the limited local area where it erupted, but its true relationship with the breakup of Pangea and later CAMP event requires more study.