High-resolution (20-250 Hz) multichannel seismic (MCS) reflection data with record lengths of 4-8 s TWT, totaling approximately 4620 line km on the shelf and slope of the Sandino forearc basin of offshore western Nicaragua, were acquired in November-December 2004 (cruise EW04-12) and subsequently processed at the University of Texas Institute for Geophysics. Seismic sequence interpretation was conducted using these MCS data in conjunction with deeper penetration (16-20. s TWT) MCS profiles from a previous survey (cruise EW00-05). Age estimates were based on cuttings from intersecting industry wells. Structure and isochron maps were created for 16 sequences and used to identify structural and depositional trends within the Sandino basin. The Tectonostratigraphic evolution of the basin varies considerably along-strike and is divided into five general stages from Late Cretaceous to recent. Evidence for multiple episodes of terrane accretion is observed from Late Eocene to Late Oligocene and potentially during Mid- to Late Miocene as well. Stratal stacking patterns suggest the Nicaraguan margin has not been dominated by subduction erosion during its history and extensional features beneath the slope are interpreted to have originated as a result of processes related to collision of allochthonous terrane of the downgoing plate, sediment underplating, and slab roll-back. With more precise age control, the stable northwestern region of the Sandino basin, where sediment is relatively undeformed since Late Oligocene and measures ≥ 16 km thick, offers a unique convergent margin setting for investigations of forcings on sequence development. / text

Topography growth and sediment fluxes in active subduction margin settings are poorly understood. Geological record is often scarce or hardly accessible as a result of intensive deformation. The Hawke Bay forearc basin of the Hikurangi margin in New Zealand is well suited for studying morphstructural evolution. It is well preserved, partly emerged and affected by active tectonic deformation during Pleistocene stage for which we have well dated series and well-known climate and eustasy. The multidisciplinary approach, integrating offshore and onshore seismic interpretations, well and core data, geological mapping and sedimentological sections, results in the establishment of a detailed stratigraphic scheme for the last 1.1 Ma forearc basin fill. The stratigraphy shows a complex stack of 11 eustasy-driven depositional sequences of 20, 40 and 100 ka periodicity. These sequences are preserved in sub-basins that are bounded by active thrust structures. Each sequence is characterized by important changes of the paleoenvironment that evolves between the two extremes of the glacial maximum and the interglacial optimum. Thus, the Hawke Bay forearc domain shows segmentation in sub-basins separated by tectonic ridges during sea level lows that become submerged during sea level highs. Over 100 ka timescale, deformation along active structures together with isostasy are responsible of a progressive migration of sequence depocenters towards the arc within the sub-basins. Calculation of sediment volumes preserved for each of the 11 sequences allows the estimation of the sediment fluxes that transit throughout the forearc domain during the last 1.1 Ma. Fluxes vary from c. 3 to c. 6 Mt.a⁻¹. These long-term variations with 100 ka to 1 Ma timescale ranges are attributed to changes in the forearc domain tectonic configuration (strain rates and active structure distribution). They reflect the ability of sub-basin to retain sediments. Short-term variations of fluxes (<100 ka) observed within the last 150 ka are correlated to drastic Pleistocene climate changes that modified erosion rates in the drainage area. This implies a high sensitiveness and reactivity of the upstream area to environmental changes in terms of erosion and sediment transport. Such behaviour of the drainage basin is also illustrated by the important increase of sediment fluxes since the European settlement during the 18th century and the following deforestation.

The Xigaze forearc basin in southern Tibet, one of the largest and best-preserved forearc basins on Earth, records upper-plate processes active prior to and following the inter-continental collision between India and Asia. However, the understanding of the timing and mechanisms of forearc development and its evolution following collision is spatially and temporally limited. Fundamental questions remain concerning how the basin formed, its paleogeography prior to collision, its subsidence history and the thermal history of the basin following the initial and ongoing continent-continent collision. Answering these questions is important to reconstructing upper plate dynamics during active subduction of oceanic and continental lithosphere. This dissertation addresses the Early Cretaceous to Pliocene history of the Xigaze forearc, using field mapping, sedimentology, sandstone modal petrography, geohistory analysis, U-Pb detrital zircon geochronology, and low-temperature thermochronology (apatite and zircon (U-Th/He)). Appendix A documents the sedimentology and stratigraphy of Lower Cretaceous to Paleocene strata to identify the relationship between the Yarlung-Tsangpo ophiolite and Xigaze forearc basin, reconstruct the sedimentary environments of the southern margin of Asia during the initial to middle stages of forearc deposition, and use the basin history to evaluate the mechanisms controlling forearc subsidence. In Appendix B, analysis of Eocene sedimentary strata, the youngest preserved in the forearc basin, constrains the timing of collision between Asia and the Tethyan Himalaya (India) to be no later than 58-54 Ma based on the similarity of the U-Pb detrital zircon age spectra and sandstone compositions between the Xigaze forearc and strata deposited atop the passive margin of the Tethyan Himalayan at that time. Apatite and zircon (U-Th)/He thermochronologic results in Appendix C constrain the maximum burial temperature of the basin following collision to ~140-200 °C, which corresponds to depths attainable by sedimentation in the forearc and a Paleogene forearc successor basin. This integrated dataset also identifies the initial stage of post-collisional exhumation during the Early Miocene (~ 20-15 Ma), followed by accelerated cooling during the Late Miocene to Early Pliocene (~ 10-4 Ma). These results suggest the presence of a paleo-Yarlung River and/or intensification of the Asian monsoon during the Early to Late Miocene. The Pliocene cooling signal is the youngest reported to date along the IYSZ and likely reflects increased river incision of the Yarlung-Tsangpo driven by accelerated orogen-parallel extension across structures which cross-cut the IYSZ. Robust interpretation of thermochronologic data requires knowledge about the geologic factors and intrinsic properties of the minerals. Appendix D of this dissertation examines intragranular zonation as a source of anomalously young zircon (U-Th)/He ages from leucogranites that intrude Greater Himalayan Sequence rocks at Ronbguk Valley, north of Mt. Everest. Depth profile laser ablation ICP-MS analysis was used to quantify the U-Th concentration profiles of a series of zoned, single, whole zircon grains and to apply a grain specific zonation-dependent age correction. Zircon grains corrected for zonation yield zircon He ages of 15-17 Ma, in agreement with AFT, ZFT and mica ⁴⁰Ar/³⁹Ar ages from the region. This study highlights the importance of characterizing intragranular zonation, especially in complex, zoned zircons that are typical of crustal melts and high-grade metamorphic rocks. Appendix E synthesis the results from Appendices A-C in the context of a global comparison with other ancient and preserved forearc basins. Results from the Xigaze forearc basin are compared to general models for forearc basin formation, subsidence trends, and preservation. The results show similarities between the Xigaze forearc basin and modern forearc basins, such as the Japan forearc off Honshu Island. The mechanisms driving tectonic subsidence are addressed, but remain an area of frontier research in continental dynamics.

Topography growth and sediment fluxes in active subduction margin settings are poorly understood. Geological record is often scarce or hardly accessible as a result of intensive deformation. The Hawke Bay forearc basin of the Hikurangi margin in New Zealand is well suited for studying morphstructural evolution. It is well preserved, partly emerged and affected by active tectonic deformation during Pleistocene stage for which we have well dated series and well-known climate and eustasy. The multidisciplinary approach, integrating offshore and onshore seismic interpretations, well and core data, geological mapping and sedimentological sections, results in the establishment of a detailed stratigraphic scheme for the last 1.1 Ma forearc basin fill. The stratigraphy shows a complex stack of 11 eustasy-driven depositional sequences of 20, 40 and 100 ka periodicity. These sequences are preserved in sub-basins that are bounded by active thrust structures. Each sequence is characterized by important changes of the paleoenvironment that evolves between the two extremes of the glacial maximum and the interglacial optimum. Thus, the Hawke Bay forearc domain shows segmentation in sub-basins separated by tectonic ridges during sea level lows that become submerged during sea level highs. Over 100 ka timescale, deformation along active structures together with isostasy are responsible of a progressive migration of sequence depocenters towards the arc within the sub-basins. Calculation of sediment volumes preserved for each of the 11 sequences allows the estimation of the sediment fluxes that transit throughout the forearc domain during the last 1.1 Ma. Fluxes vary from c. 3 to c. 6 Mt.a⁻¹. These long-term variations with 100 ka to 1 Ma timescale ranges are attributed to changes in the forearc domain tectonic configuration (strain rates and active structure distribution). They reflect the ability of sub-basin to retain sediments. Short-term variations of fluxes (<100 ka) observed within the last 150 ka are correlated to drastic Pleistocene climate changes that modified erosion rates in the drainage area. This implies a high sensitiveness and reactivity of the upstream area to environmental changes in terms of erosion and sediment transport. Such behaviour of the drainage basin is also illustrated by the important increase of sediment fluxes since the European settlement during the 18th century and the following deforestation.

The Scotland Formation onshore Barbados is often called the only example of a successful hydrocarbon producing accretionary prism reservoir. In spite of this, the hydrocarbon system elements of the BAP have nevertheless not been well studied. Seven outcropping locations of the Scotland were examined to document stacking patterns, key surfaces, depositional element geometries, facies occurrences their vertical and lateral extent, and the unit’s gamma response. Six facies were identified in outcrop: silty muds; laminated, centimeter-scale sandstones interbedded with silts and muds; cross-stratified sandstones; massive, medium to coarse-grained sandstones; very coarse grained sands with gravel or pebbles; and rare conglomerates. These facies combine to form architectural elements—channels, levees, and depositional lobes. Observations from petrographic, outcrop and seismic data suggest that the Scotland Formation was never deeply buried within the prism proper and was possibly deposited within the much larger proto-Tobago Basin. / text

Strata in the Cook Inlet forearc basin in south-central Alaska record the effects of tectonic events related to normal subduction and two flat-slab subduction events. Through detrital zircon geochronology we track provenance changes of strata deposited in a forearc basin in conjunction with these different subduction processes. Our data from strata deposited concurrent with normal subduction help to confirm previous provenance models of forearc basins that suggest provenance is sourced primarily from a proximal, coeval arc. However, compared to these models, our data from strata deposited coincident to flat-slab events show markedly different provenance signatures dependent upon: (1) geographic position relative to the flat-slab event; (2) pre-established, or lack thereof, topography; and (3) type of flat-slab event. Detrital zircon signatures of strata deposited in the Cook Inlet after flat-slab subduction of a mid-ocean ridge diversify to include older detritus found in the distal inboard region. This distal signature is then incrementally cut-off in younger strata due to deformation of the upper-plate from progressive insertion of a shallowly subducted oceanic plateau. Detrital zircon signatures for strata associated with each flat-slab event are largely older than depositional age due to the lack of coeval arc activity. Our data may help to improve the ability to recognize other flat-slab events through detrital zircon geochronology. In particular, changes in detrital zircon signatures found in strata deposited during flat-slab subduction of an oceanic plateau correlate well with the exhumation of rocks associated with the propagation of deformation in the over-riding plate due to plate coupling.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22424号 / 工博第4685号 / 新制||工||1731(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 林 為人, 教授 小池 克明, 准教授 村田 澄彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24428号 / 理博第4927号 / 新制||理||1704(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 佐藤 活志, 准教授 堤 昭人, 教授 田上 高広 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

La marge d’Équateur est caractérisée par un bassin avant-arc formé par un socle crétacé et une couverture de sédiments marins d’âge Crétacé à Quaternaire. Le relief de cette zone comprend d’une part la cordillère Côtière proprement dite et la plaine Côtière, située entre la cordillère Côtière et les Andes. Ce travail porte sur l’évolution et le soulèvement de la cordillère Côtière durant le Néogène. Dans un premier temps, nous avons réalisé une étude géologique régionale de la cordillère côtière. À partir de l’analyse stratigraphique et structurale des formations géologiques, nous avons réalisé une carte géologique de la cordillère côtière au 1/500 000 qui nous a permis d’effectuer pour la première fois des corrélations stratigraphique et un schéma structural à l’échelle complète de la cordillère. Dans un deuxième temps nous avons réalisé une étude géomorphologique de la zone. À partir de l’analyse de MNT, d’images satellites et aériennes nous avons défini les principales caractéristiques morphologiques de la zone d’étude. En particulier, le travail a porté principalement sur l’analyse de la géométrie du réseau hydrographique, la mesure de la géométrie des vallées et du profil en long des rivières à l’échelle de la cordillère Côtière. En complément nous avons mesuré le profil longitudinal des terrasses alluviales le long du rio Jama et analysé la morphologie des cônes alluviaux qui se déposent au pied des Andes sur la plaine Côtière. Les résultats ont permis de proposer une évolution du soulèvement de la cordillère Côtière. Les mesures des incisions relatives des rivières suggèrent que le soulèvement de la cordillère Côtière n’est pas homogène et que la cordillère est segmentée en plusieurs blocs dont les taux de soulèvement relatif sont variables: les blocs du Nord présentant les incisions les plus importantes. L’analyse des profils longitudinaux des terrasses alluviales du rio Jama montre une activité néotectonique le long des failles du système de Jama. Le taux de soulèvement estimé à partir de cette analyse est de 0.9 à 1.2 mm/ an pour le segment central de la cordillère Côtière. L’analyse du cône de Santo Domingo, situé aux pieds des Andes, révèle une importante interaction entre le soulèvement de la cordillère Côtière et le remplissage sédimentaire de la plaine côtière dont le résultat est la réorganisation du réseau hydrographique en deux grands bassins hydrographiques: Guayas au Sud et Esmeraldas au Nord. A plus long termes, la géologie et la stratigraphie montrent que la partie du Sud a subis une plus forte érosion (soulèvement ?) qu'au Nord. La mise en évidence de plusieurs discordances à l’échelle régionale montre que la cordillère Côtière s’est soulevée de façon hétérogène depuis le Plio-Pléistocène formant un grand antiforme segmenté et contrôlé par des failles régionales qui présentent une direction proche de la direction du mouvement vers le NE-NNE du bloc Nord-Andin. / The Ecuadorian margin is characterized by a forearc basin composed of a Cretaceous basement covered by marine sediments of the Cretaceous to Quaternary age. The topography of this area displays two main morphological domains: the Coastal cordillera in the west and the Coastal plain in the east at the foothills of Andes cordillera. This work focuses on the genesis of the Coastal cordillera during the Neogene. Firstly, we carried out a geological fieldwork throughout the Coastal cordillera. From stratigraphy and structural studies, we produced a regional geological map of the Coastal cordillera at 1:500000 scale, which have allowed for the first time to realize a regional stratigraphy correlation and determine the structural pattern across the Coastal cordillera. In a second step, we carried out a geomorphologic study of the area. From DEM analysis and satellite and aerial imagery processing, we characterized the main landforms features of the study area. In particular, we focused on the geometry of the drainage network and on the river profiles crossing the Coastal cordillera. In addition, we measured the longitudinal profile of the alluvial terrace treads along the Jama River and analyzed the morphology of alluvial fans that are deposited on the Coastal Plain at the foothills of the Andes cordillera. From the different results obtained, we proposed an evolution scheme of the uplift of the coastal cordillera. The measurements of incisions along river valleys suggest that the uplift of the Costal cordillera is heterogeneous: the cordillera is segmented into several blocks with own uplift rates. The incisions of the northern blocks are the highest. The analysis of the longitudinal profiles along the alluvial terrace treads of the Jama River indicates a recent activity along the faults of the system Jama. The uplift rates estimated from this analysis ranges from 0.9 to 1.2 mm/yr for the central segment of the Coastal cordillera. The analysis of Santo Domingo alluvial fan situated at the foothills of the Andes cordillera reveals a large interaction between the sedimentary filling of the Coastal plain and the contemporaneous uplift of the Andes and the Coastal cordilleras. This interaction results into the reorganization of two major drainage basins: Guayas in the south and Esmeraldas in the north. At long timescales, the geology and stratigraphy of the Neogene formations shows that domains in the southern Coastal cordillera were subject to intense erosion (rising?) with respect to the northern domains. The analysis of the several unconformities evidences that the Coastal cordillera was raised in a heterogeneous way since the Plio-Pleistocene as a large and elongated antiform segmented and controlled by regional faults which have a trend between NE and NNE, which is close to that of the movement to the North Andean block.