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Early Miocene limestones from the Wairarapa region of New Zealand were deposited on thrust-bounded margins of trench-slope basins, and consist of two superposed stratal units, namely units A and B, interpreted as forced regressive and forced transgressive foralgal and rhodolith-bearing deposits, respectively. Unit A is floored by a regressive surface of marine erosion cut into shelfal to bathyal siliciclastic successions, and is overlain across a transgressive surface of erosion by Unit B. A drowning surface abruptly places the latter deposits in contact with deeper hemipelagites and turbidites. The succession is explainable within a tectono-eustatic based framework as follows: (1) Structurally controlled rapid relative sea-level fall, (i.e. sea-bed rise), from upper bathyal to shelfal depths promoted development of regressive ('lowstand') mixed carbonate–siliciclastic deposits. Continuation of seabed rise resulted in deposition of pure carbonate sediments, which are represented by channel-fill rhodolithic rudstones; (2) early stage of relative sea-level rise (i.e. seabed drowning) caused emplacement of transgressive glauconitic limestones, consisting of either foralgal deposits, or incised rhodolithic limestones; (3) continued relative sea-level rise terminated carbonate production. The present study documents carbonate production and termination in a tectonically active and confined intra-slope setting, reflected in the development and distribution of unusual forced regressive, and transgressive rhodolithic-heterozoan carbonates. [ABSTRACT FROM AUTHOR]

Continental shelves generally supply large-scale mass-wasting events. Yet, the origin and significance of shelf-derived mass-transport deposits (MTDs) for the tectonostratigraphic evolution of subduction complexes and their trench-slope basins have not been extensively studied. Here, we present high-resolution, outcrop-scale insights on both the nature of the reworked sediments, and their mechanisms of development and emplacement along tectonically active margins, by examining the Middle Miocene shelf-derived MTDs outcropping in the exhumed southern portion of the Hikurangi subduction margin. Results show that periods of repeated tectonic activity (thrust propagation, uplift) in such compressional settings not only affect and control the development of shelfal environments but also drive the recurrent generation and destruction of oversteepened slopes, which in turn, favour the destabilisation and collapses of the shelves and their substratum. Here, these events produced both large-scale, shelf-derived sediment mass-failures and local debris flows, which eventually broke down into a series of coalescing, erosive, genetically linked surging flows downslope. The associated MTDs have a regional footprint, being deposited across several trench-slope basins. Recognition of tectonic activity as another causal mechanism for large-scale shelf failure (in addition to sea-level changes, high-sedimentation fluxes) has implications for both stratigraphic predictions and understanding the tectonostratigraphic evolution of deep-marine fold-and-thrust belts. [ABSTRACT FROM AUTHOR]

In the 60s, the Hellenic belt was taken as the "Geosyncline model". Here we take a modern look at this Hellenic/Aegean region which as a concentrate encompasses all the main geodynamic processes known in orogens. This region documents the fundamental characteristics of the geodynamic processes related to mountain building, namely continental rifting, oceanic spreading, oceanic then continental subduction, collision i.e., closure of oceanic basins. In particular, the Mesozoic obduction events in northern Hellenides, and the effects of a still ongoing major extension linked to the active subduction under the Aegean domain. [ABSTRACT FROM AUTHOR]

Deformation across the active Hikurangi subduction margin, New Zealand, including shortening, extension, vertical-axis rotations, and strike-slip faulting in the upper plate, has been estimated for the last ∼24 Myr using margin-normal seismic reflection lines and cross sections, strike-slip fault displacements, paleomagnetic declinations, bending of Mesozoic terranes, and seafloor spreading information. Post-Oligocene shortening in the upper plate increased southward, reaching a maximum rate of 3-8 mm/year in the southern North Island. Upper plate shortening is a small proportion of the rate of plate convergence, most of which (>80%) accrued on the subduction thrust. The uniformity of these shortening rates is consistent with the near-constant rate of displacement transfer (averaged over ≥5 Myr) from the subduction thrust into the upper plate. In contrast, the rates of clockwise vertical-axis rotations of the eastern Hikurangi Margin were temporally variable, with ∼3°/Myr since 10 Ma and ∼0°-1°/Myr prior to 10 Ma. Post 10 Ma, the rates of rotation decreased westward from the subduction thrust, which resulted in the bending of the North Island about an axis at the southern termination of subduction. With rotation of the margin and southward migration of the Pacific Plate Euler poles, the component of the margin-parallel relative plate motion increased to the present. Plate convergence dominated the Hikurangi Margin before ca. 15 Ma, with the rate of margin-parallel motion increasing markedly since 10 Ma. Vertical-axis rotations could accommodate all margin-parallel motion before 1-2 Ma, eliminating the requirement for large strike-slip displacements (for example, >50 km) in the upper plate since the Oligocene. [ABSTRACT FROM AUTHOR]

In the Hikurangi subduction wedge (New Zealand), a strong relationship exists between tectonic structures and fluid migrations. In the study area, outcropping tubular carbonate concretions, corresponding to the shallow subsurface plumbing systems of paleo-cold seeps, are hosted by Miocene syn-subduction mudstones. New observations demonstrate the presence of migrated solid bitumen within the tubular concretions and in the fault gouge of a major fault zone. A multi-proxy approach was performed to determine the organic matter thermal maturity in the study area (organic matter petrography and solid bitumen reflectance (BR) R r % (R r : random reflectance)). We also used Rock-Eval pyrolysis, vitrinite reflectance (VR) R r %, and clay mineral reaction progress (illite Kübler-Index and clay mineral paragenesis) to determine the diagenesis grade of the rocks. Low T max values and clay minerals indicate a thermally immature sedimentary cover. The main source rock of the region, the Waipawa Formation is locally thermally mature (VR = 0.86 R r %) suggesting that tectonic thrust-sheet stacking isresponsible for a structural thickening causing local organic maturation. The seaward propagation of out-of-sequence thrusts at base of intra-slope basins could be responsible for the inititation of biogenic fluid flows sourced in the shallow sedimentary cover that is subjected to deformation above the blind thrusts, leading to the earlier generation of the first carbonate tubular concretions. With the continuation of blind thrusting, deep thermogenic fluids then migrated laterally through fault planes (primary migration) and finally vertically through the intrabasinal pre-existing tubular concretions (secondary migration). In this paper, solid bitumen is used for the identification of a fossil thermogenic fluid migration from the source rock, along faults and through tubular carbonate conduits within a subduction thrust-wedge. The study evidences a multi-genetic tubular concretion formation, related with the timing and style of the deformation, being therefore a potential reliable indicator for the evolution of tectonic activity. • Integrated analysis of a plumbing system of paleo-cold seeps on an active margin. • Samples from SR, faults and tubular concretions to determine thermal maturity, bitumen migration, clay mineral reactions. • Circulation of thermogenic fluids in cold seep systems, which correspond initially to migration of shallow biogenic gas. • Role of the shallow plumbing system of biogenic cold seeps as vertical paths for subsequent thermogenic fluid circulations. • Structural thickening due to thrust sheet stacking favor maturation, thrust faults then acting as lateral migration pathway. [ABSTRACT FROM AUTHOR]

The forearc of the North-Central Peruvian Andes (FNCPA, 6–10°S) provides an exceptional opportunity to study the long-term processes that affect a convergent plate boundary. First, it shows long-term subsidence, depocenter superimposition and individualization. Second, although being mostly extensional and characterized as a typical erosive margin, the FNCPA shows complex uplifted regions. Older deformation is expressed by basement horst and grabens disposed in a complex geometry which onset may have resulted from strike-slip tectonics. A long-lived episode of regional subsidence affected the forearc and led to the relatively thick and regional deposition of the lower Miocene series coeval with a significant increase of the convergence velocity. This period was followed by an episodic uplift of trench-parallel corridors along the so-called Main Deformation Zone. Uplift ceased through the late Miocene and restarted during Pliocene and Quaternary, generating accommodation space by basin flank uplift for a forearc depocenter characterized by landward tilted strata. Significant along-strike differences in the degree of uplift resulted in either uplifting series producing sharp seaward dipping erosional surfaces or less uplifted areas covered by seawards prograding clinoforms. As a consequence of the shallow-water marine setting, the seismic strata geometry, lateral extent and thickness of the deposits for the Neogene successions in the FNCPA have been also tightly controlled by accommodation changes. Uplift is uneven along-strike independently of fault direction and closely followed the increase of the subsidence of the continental slope produced by subduction-erosion. Therefore, sediment underplating seems the most appropriate mechanism at the origin of uplift; as observed in other parts of the Peruvian and Chilean margins. Although the erosive character of the margin, the effects on basin geometry of the raised zone resemble that of typical outer forearc highs in accretionary margins such as in the Kumano basin in Japan. • Transtensional depocenters resulted from high obliquity convergence during the Paleogene. • A trench-parallel uplift affected unevenly and episodically the transtensional depocenters since middle Miocene. • Formation of an outer forearc high, similar to those of accretionary settings, individualized a depocenter during Neogene. • Formation of the outer forearc high may have been induced by sediment underplating. [ABSTRACT FROM AUTHOR]