Cretaceous continental extension was accommodated by the development of the Paparoa Metamorphic Core Complex, resulting in the separation of New Zealand from Gondwana. High grade (Lower Plate) and low grade (Upper Plate) rocks are separated by the Ohika and Pike Detachment Faults. The two detachment faults have distinctly different histories, with greater exhumation along the Pike Detachment Fault. The onset of crustal extension is proposed to have commenced along the Pike Detachment Fault at 116.2 ± 5.9 Ma (Rb/Sr dating). Both geochemical and geochronological approaches are adopted for this thesis, through the in situ analysis of oxygen and hafnium isotope ratios, trace metals and U-Pb content. Chemical changes are tracked during the petrogenesis of the Buckland Granite, with mafic replenishment observed in the later stages of crystallisation. Crystallisation temperatures of the Buckland Granite are calculated using zircon saturation thermometry, with an average Ti-in-zircon temperature of 697℃ (upper-amphibolite facies). Inherited zircons in Lower Plate rocks show distinct age peaks at c. 1000, 600 and 300 Ma, illustrating the incorporation of heterogeneous local crust (Greenland Group and Karamea Batholith). Model ages (TDM) are calculated for inherited zircons of the Lower Plate rocks, which record the time at which magma bodies (zircon host rocks) were extracted from the mantle. Maximum and minimum model ages for the Buckland Granite average at 3410 Ma and 2969 Ma, with the maximum TDM value of 3410 Ma coinciding with the proposed major crustal formation event of the Gondwana supercontinent at c. 3.4-3.5 Ga. Two distinct U-Pb zircon age peaks are observed in the Buckland Granite at 102.4 ± 0.7 and 110.3 ± 0.9 Ma. The 110.3 ± 0.9 Ma age is interpreted as the crystallisation age of the pluton, while the 102.4 ± 0.7 is proposed to represent a younger thermal (magmatic?) event associated with the 101-102 Ma Stitts Tuff.

Passive margins along the eastern seaboard of North America formed during early Mesozoic continental rifting and seafloor spreading, tectonic processes that are not fully understood. Seismic refraction and reflection data at the northeastern and north-central Gulf of Mexico and the Grand Banks of Newfoundland, Canada, are used to interpret the deep seismic velocity structure of sediments, crust, and mantle. These interpretations allow for a better understanding of continental rifting, mantle upwelling, magmatism, and seafloor spreading. Magma-poor rifting of the Newfoundland-Iberian margin developed a wide continent-ocean transition zone (COT). I present an analysis of 2-D marine seismic refraction and reflection data from the SCREECH project, including a shear velocity model to constrain the composition of the Newfoundland COT. Comparing SCREECH Line 2 Vp/Vs ratios with depth to potential lithologies supports a COT comprised of hyperextended continental crust and serpentinized mantle. Reconstructions of the opening of the Gulf of Mexico basin are impeded by a lack of seafloor magnetic anomalies and an abundance of sediments that obscure acquisition of seismic refraction datasets. Accordingly, the roles of mantle upwelling, magmatism, and lithospheric extension in this small ocean basin are poorly known. I present new 2-D marine seismic refraction data from the U.S. Gulf of Mexico collected during the 2010 GUMBO project. Rifting in the eastern Gulf of Mexico developed above a zone of anomalously high mantle potential temperatures that led to abundant magmatism. Syn-rift basins in continental crust, high velocity lower crust, a narrow zone of crustal thinning, and seaward-dipping reflectors support this interpretation. Oceanic crust here is thick despite slow seafloor-spreading rates, implying continuation of a thermal anomaly after rifting. In the north-central Gulf of Mexico, transitional crust is consistently thin (~10 km) across a wide zone. Velocity-depth comparisons, asymmetry of the north-central Gulf with the Yucatán margin, and dating of onshore xenoliths support either stretched and magmatically intruded continental crust or a multi-stage episode of seafloor spreading with ridge jumps. I contend that although tectonic inheritance may ultimately influence the location of a passive margin, the rifting process is largely controlled by mantle potential temperature and upwelling rate. / text

Cretaceous continental extension was accommodated by the development of the Paparoa Metamorphic Core Complex, resulting in the separation of New Zealand from Gondwana. High grade (Lower Plate) and low grade (Upper Plate) rocks are separated by the Ohika and Pike Detachment Faults. The two detachment faults have distinctly different histories, with greater exhumation along the Pike Detachment Fault. The onset of crustal extension is proposed to have commenced along the Pike Detachment Fault at 116.2 ± 5.9 Ma (Rb/Sr dating). Both geochemical and geochronological approaches are adopted for this thesis, through the in situ analysis of oxygen and hafnium isotope ratios, trace metals and U-Pb content. Chemical changes are tracked during the petrogenesis of the Buckland Granite, with mafic replenishment observed in the later stages of crystallisation. Crystallisation temperatures of the Buckland Granite are calculated using zircon saturation thermometry, with an average Ti-in-zircon temperature of 697℃ (upper-amphibolite facies). Inherited zircons in Lower Plate rocks show distinct age peaks at c. 1000, 600 and 300 Ma, illustrating the incorporation of heterogeneous local crust (Greenland Group and Karamea Batholith). Model ages (TDM) are calculated for inherited zircons of the Lower Plate rocks, which record the time at which magma bodies (zircon host rocks) were extracted from the mantle. Maximum and minimum model ages for the Buckland Granite average at 3410 Ma and 2969 Ma, with the maximum TDM value of 3410 Ma coinciding with the proposed major crustal formation event of the Gondwana supercontinent at c. 3.4-3.5 Ga. Two distinct U-Pb zircon age peaks are observed in the Buckland Granite at 102.4 ± 0.7 and 110.3 ± 0.9 Ma. The 110.3 ± 0.9 Ma age is interpreted as the crystallisation age of the pluton, while the 102.4 ± 0.7 is proposed to represent a younger thermal (magmatic?) event associated with the 101-102 Ma Stitts Tuff.

Abstract Three dimensional finite strain and kinematic data from the Resolution Island Shear Zone, Fiordland, New Zealand record the progressive evolution of a lower crustal metamorphic core complex. The Resolution Island Shear Zone is a mid-Cretaceous (~114-90 Ma) extensional shear zone that juxtaposes high-pressure (P~17-19 kbar) garnet-granulite and eclogite facies orthogneiss from the lower crust against mid-crustal (P~6-8 kbar) orthogneiss and paragneiss along a low-angle upper amphibolite facies ductile normal fault. In the lower plate of the Resolution Island Shear Zone the high-pressure garnetgranulite and eclogite facies gneissic foliations (S1) are attenuated by granulite facies extensional shear zone foliations (S2). Retrograde metamorphism marked by the breakdown of omphacite and garnet to amphibole and feldspar in S2 foliation records the unloading of the lower plate during extension. Continued extension localized strain into weaker amphibole and feldspar-bearing lithologies. Upper amphibolite facies shear zones anastomose around rigid lenses that preserve the S1 and S2 fabric. Upper amphibolite facies shear zone fabrics (S3/L3) that envelop these pods display a regional-scale domeand- basin pattern. These shear zones coalesce and form the Resolution Island Shear Zone. Coeval with the formation of the Resolution Island Shear Zone, a conjugate, southwest dipping, and lesser magnitude shear zone termed the Wet Jacket Shear Zone developed in the upper plate of the Resolution Island Shear Zone. Three-dimensional strain analyses from S3/L3 fabric in the Resolution Island Shear Zone show prolate-shaped strain ellipsoids. Stretching axes (X) from measured finite strain ellipsoids trend northeast and southwest and are subparallel to L3 mineral stretching lineations. Shortening axes (Y, Z) are subhorizontal and subvertical, respectively, and rotate through the YZ plane of the finite strain ellipsoid. This pattern reflects the dome-and-basin geometry displayed by anastomosing S3 foliations and indicates the Resolution Island Shear Zone developed in the field of constriction. Threedimensional kinematic results indicate a coaxial-dominated rotation of stretching lineations toward the X-axis in both the XZ and XY planes of the finite strain ellipsoid. Results suggest that a lower crustal metamorphic core complex developed in a constrictional strain field with components of coaxial-dominated subvertical and subhorizontal shortening. Mid-Cretaceous (~114-90 Ma) extensional structures exposed in Fiordland, including the Resolution Island, Wet Jacket, Mount Irene and Doubtful Sound shear zones and the Paparoa metamorphic core complex allows the reconstruction of a crustal column that describes the geometry of mid-Cretaceous continental rifting of Gondwana. The overall symmetry of crustal-scale structures during continental extension suggests kinematic links between flow in the lower crust and the geometry and mode of continental extension. This result is consistent with numerical models of lithospheric rifting that predict the lower crust has a primary control on the style of continental extension.

La lithosphère continentale peut s’étirer selon trois modes (rift large, rift étroit et Core Complex). En Asie de l’Est, une extension continentale a eu lieu de la fin du Mésozoïque au Cénozoïque et ne semble correspondre à aucun des trois modes actuellement définis. Cette période est caractérisée par un amincissement lithosphérique exceptionnel (>100 km), la présence de MCC, de bassins sédimentaires et une importante activité magmatique. Basé sur une approche multi-échelles, ce travail vise à mieux comprendre les mécanismes à l’origine de cette déformation lithosphérique (jamais abordés) ainsi que du moteur de l’extension (encore vivement discuté). Pluridisciplinaire, cette étude apporte de nouvelles contraintes à partir de l’analyse de la déformation finie (ductile ou fragile), du magnétisme des roches (ASM, paléomagnétisme), de la géochronologie (U/Pb sur zircon et 40Ar/39Ar sur monograins) et de la gravimétrie. Différents objets reconnus, révélant des quantités d’extension différentes (MCC vs. pluton cisaillé), montrent que la croûte continentale se déforme de manière très localisée, par la mise en place de larges dômes extensifs séparant des domaines de « radeaux » ou « boudins » présentant une déformation faible à nulle. Par comparaison des données crustales et mantelliques (tomographie sismique, géochimie) disponibles, cette étude met en évidence que l’amincissement lithosphérique reconnu pour le Mésozoïque est principalement lié à un important flux thermique du manteau, l’extension n’ayant qu’un rôle limité dans cet amincissement (<20%). En outre, eu égard au gradient géothermique exceptionnellement élevé de la région, à la fin du Mésozoïque, il semble très probable que des MCC puissent s’être développés sans épaississement préalable de la croûte. L’analyse comparée des directions d’étirement dans la croûte et dans le manteau met en évidence le rôle majeur de la subduction des panneaux plongeants le long de la marge est-asiatique. Un modèle géodynamique a été proposé montrant le rôle du retrait successif des panneaux plongeants couplé à un phénomène d’érosion thermique de la lithosphère. / Continental lithosphere can be stretched according to three modes (wide rift, narrow rift, Core Complex). In East Asia, a continental extension occurred during the Late Mesozoic to Cenozoic times and seems to do not correspond to any of three modes currently defined. This period is characterised by an exceptional lithospheric thinning (> 100 km) with the presence of MCC, sedimentary basins and a huge magmatic activity. Based on a multi-scale approach, this work aims to better understand the mechanisms of this lithospheric deformation (never addressed) and the engine of the extension (yet highly debated). This study provides new multidisciplinary constraints from the analysis of finite strain (ductile or brittle), rock magnetism (AMS, palaeomagnetism), geochronology (U/Pb on zircon and 40Ar/39Ar on single crystals) and gravity. Different objects have been recognised, revealing different amounts of extension (MCC vs. sheared pluton), and show that the continental crust is locally highly deformed, with emplacements of large MCCs between "rafts" or "boudins" domains which are weakly strained to unstrained. By comparison of available crustal and mantle data (seismic tomography, geochemistry), this study shows that the lithospheric thinning recognised for the Mesozoic is mainly related to a major mantle heat flux, the extension plays a limited role in this thinning (<20%). In addition, given the exceptional high geothermal gradient in the region at the end of the Mesozoic, it seems very likely that MCC may have developed without pre-thickened crust. Comparative analysis of stretching directions within the crust and mantle highlights that the subduction of the (palaeo) Pacific plate along the East Asian margin may play an initial and major role during Late Mesozoic extensional event. A geodynamic model has been proposed to show the role of the successive retreat of subducting slabs coupled to a thermal erosion of the lithosphere.

Gediz Graben is a continental extensional basin filled with Neogene sediments. Its margins are controlled by active ~E&amp / #8211 / W-trending fault systems with major system, in terms of total offset and duration of activity, located along the southern margin. The graben evolved as a half graben by the activity of the southern margin during the entire Miocene. Then, the northern margin-bounding structure initiated by Plio&amp / #8211 / Quaternary to form the current configuration of the graben with an inherited asymmetry. The southern margin-bounding fault system forms a graben-facing step-like pattern from the horst block (~2000 m) down to the graben floor (~200 m). The faults become younger towards the graben and the structural maturity decreases in the same direction. Fault plane data suggest ~N&amp / #8211 / S-oriented regional crustal extension through the entire graben history with no evidence of temporal change in the regional extension direction. Minor spatial variations are attributed to poorly defined s3-axis or local stress field anomalies caused by fault interactions. Evolution of the Gediz Graben is a dynamic process as indicated by pronounced changes in the geometry and lateral extend of the southern margin-bounding structures along strike and dip directions. This also influenced the lithofacies, depositional pattern and thickness of the graben fill units. The western Anatolian extension is episodic with earlier (Miocene) and later (Plio&amp / #8211 / Quaternary) phases of extension and intervening short phase of contraction (Late Miocene&amp / #8211 / Early Pliocene). Despite of this fact, evidence for the short-term intervening contractional phase throughout the Gediz Graben is scarce and there is local observation of folds and thrust/reverse faults affecting the AlaSehir formation. These structures suggest that the short-term phase of contraction might have existed but most probably been absorbed by the high rates of extension. This data may further imply that graben evolution from half-graben phase (Miocene configuration) to full graben phase (present day configuration) might be a discontinuous process accompanied by a short-time break in-between.

The D'Entrecasteaux Island (DEI) gneiss domes are fault-bounded domes with ~2.5 km of relief exposing ultrahigh-pressure (UHP) and high-pressure (HP) metamorphic gneisses and migmatites exhumed in an Oligocene-Miocene arc-continent collision and subduction zone subject to Late Miocene to Recent continental extension. To study the style of continental extension accompanying exhumation of the DEI gneiss domes, a grid of 1,518 km of 2-D multi-channel seismic (MCS) reflection data and well data is interpreted from the offshore areas surrounding the DEI, including the Trobriand basin and the Goodenough basin. The offshore study is combined with onshore geologic information to constrain the area's Oligocene to Recent basinal and tectonic evolution. MCS and well data show the Trobriand basin formed as a forearc basin caused by southward Miocene subduction at the Trobriand trench. Late Miocene basin inversion uplifted the southern and northern basin margins. Subduction slowed at ~8 Ma as the margin transitioned to an extensional tectonic environment. Since then, the Trobriand basin has subsided 1-2.5 km as a broad sag basin with few normal faults deforming the basin fill. South of the DEI, the Goodenough rift basin developed after extension began (~8 Ma) as the hanging-wall of the north-dipping Owen-Stanley normal fault bounding the southern margin of the basin. Rapid uplift of the adjacent footwall of the Owen-Stanley fault zone in the Papuan Peninsula accompanied the formation of the Goodenough submarine rift basin. The lack of upper crustal extension accompanying subsidence in the Trobriand and Goodenough basins suggests depth-dependent lithospheric extension from 8-0 Ma has accompanied uplift of the DEI gneiss domes. Structural reconstructions of seismic profiles show 2.3 to 13.4 km of basin extension in the upper crust, while syn-rift basin subsidence values indicate at least 20.7 to 23.6 km of extension occurred in the lower crust since ~8 Ma. Results indicating thinning is preferentially accommodated in the lower crust surrounding the DEI are used to constrain a schematic model of uplift of the DEI domes involving vertical exhumation of buoyant, post-orogenic lower crust, far-field extension from slab rollback, and an inverted two-layer crustal density structure. / text