Rift Flank Uplift Research Articles

Detrital zircon and apatite U-Pb provenance and drainage evolution of the Newark Basin during progressive rifting and continental breakup along the Eastern North American Margin, USA

Abstract Mesozoic rift basins of the Eastern North American Margin (ENAM) span from Florida in the United States to the Grand Banks of Canada and formed during progressive extension prior to continental breakup and the opening of the north-central Atlantic. The syn-rift strata from all the individual basins, lumped along the entire margin into the Newark Supergroup, are dominated by fluvial conglomerate and sandstone, lacustrine siltstone, mudstone, and abundant alluvial conglomerate and sandstone lithofacies. Deposition of these syn-rift sedimentary rocks was accommodated in a series of half grabens and subsidiary full grabens situated within the Permo-Carboniferous Appalachian orogen. The Mesozoic ENAM is commonly depicted as a magma-rich continental rift margin, with magmatism (Central Atlantic magmatic province [CAMP]) driving continental breakup. However, the southern portion of the ENAM shows evidence of magmatic breakup (e.g., seaward-dipping reflectors), and rifting and crustal thinning appeared to start ~30 m.y. prior to CAMP emplacement in the Jurassic. This study provides extensive new detrital zircon and apatite U-Pb provenance data to determine the provenance and reconstruct the paleodrainages of the Newark Basin during progressive rifting and magmatic breakup and the implications for the overall rift configuration and asymmetry during progressive rifting along the ENAM rift margin. Detailed new detrital zircon (N = 21; n = 3093) and apatite (N = 4; n = 559) U-Pb results from sandstone outcrop and core samples from the Newark Basin indicate a distinct provenance shift, with relatively older Carnian syn-rift strata predominately sourced from the hanging wall of the basin bounding fault in the east while relatively younger Norian strata were regionally sourced from both the hanging wall and footwall. The syn-rift strata at the Triassic-Jurassic boundary were sourced from the hanging wall before a transition to local footwall terranes. These results suggest two major provenance changes during progressive rifting—the first occurring during Carnian crustal necking and rift flank uplift as predicted by recent numerical models and the second occurring at the onset of the Jurassic due to regional and local thermal uplift during CAMP magmatism as seen along other magma-rich margins, such as the North Atlantic and the southern portion of the South Atlantic margin.

Tectonic evolution of the Gabal Loman area, North Eastern Desert, Egypt: implications from low-temperature multithermochronometry on the Arabian-Nubian shield

The Neoproterozoic Arabian-Nubian Shield (ANS) in the Eastern Desert of Egypt encloses the regional thermal-tectonic history from its development till the Oligo-Miocene when the Red Sea rift system was initiated. The application of multi-thermochronometry techniques has proven to be a successful approach to revealing the influence and extent of each regional tectonic event and the recreation of the tectono-thermal development of the studied region through time. Therefore, characteristic samples from the ANS different rock suits of the Gabal Loman area at the western flank of the northern Red Sea were collected. The Zircon fission-track data reveals the Carboniferous cooling ages, while the apatite fission-track cooling ages present two differential time spans of Cretaceous and Eocene-Oligocene. The time-temperature history modeling is integrated with fission-track data to reveal three differentiated cooling events developed in response to regional tectonic events: 1) the Hercynian (Variscan) tectonic event that influenced the ANS vicinity with rock uplifts of ca. 4 km through the Devonian-Carboniferous time, 2) the Gondwana disintegration event which influenced the region with differential rock exhumations, and 3) the northern Red Sea rifting through the Oligo-Miocene which caused a regional ca. 1 km of rift flanks exhumation. This modest rift flank uplift suggests a passive rift of the northern Red Sea rifting in the region of study.

A two phase escarpment evolution of the Red Sea margin of southwestern Saudi Arabia. Insights from low-temperature apatite thermochronology

Rifting of the Red Sea resulted in the formation of one of the highest escarpments on our planet: the Great Escarpment of southwestern Saudi Arabia. Published low-temperature geochronology ages are around the Paleogene-Neogene transition, but geomorphic features like the height, the steepness and the preservation of the escarpment may indicate a younger aspect to the exhumation history. Here we use apatite fission track (AFT) and (U-Th-Sm)/He (AHe) cooling ages in combination with a geomorphic analysis of the region from Jeddah to Jizan to test this idea. Pooled AFT ages range from 352.1±17.6 to 13.2±1.7 Ma (1σ). The base of the AFT partial annealing zone prior to rock uplift is at ∼200 m elevation in most of the studied area, but track length data show that the amount of exhumation is insufficient to affect all coastal plain samples. Consistent with earlier estimates in the literature, the total amount of rock uplift is estimated to be ∼4 km. Single grain AHe ages range from 264.5±19.6 to 2.8±0.3 Ma (1σ) and do not have a clear trend with distance from the escarpment. Overall, the distribution of data appears to indicate widespread downwearing of the elevated topography around the rift flank. In contrast, geomorphic analysis that indicates escarpment retreat including a flexural uplift response. We suggest that the conflict between geomorphological and geochronological data can be resolved by invoking a two-stage erosion model. The first stage involved dome-shaped rift flank uplift since initiation of the Afar plume, downwearing of this topography and cooling recorded by the AFT ages. The second stage involved the massive erosion that excavated the present day Saudi escarpment and reset the AHe ages. We suggest that this second stage is related to the formation of oceanic lithosphere since 13 Ma in the Red Sea, associated downwarping of the margin and flexural updoming of the eastern rift flank. The consequential orographic precipitation initiated asymmetric erosion and formation of a retreating escarpment. This model is consistent with the large age difference between Miocene AFT and Pliocene AHe ages and the geomorphic metrics.

A Multi-proxy Provenance Study of Late Carboniferous to Middle Jurassic Sandstones in the Eastern Sverdrup Basin and Its Bearing on Arctic Palaeogeographic Reconstructions

A multi-proxy provenance study of Late Carboniferous to Middle Jurassic sandstones from the eastern Sverdrup Basin was undertaken employing optical petrography and heavy mineral analysis, chemical analysis of apatite, garnet and rutile grains, as well as detrital zircon U–Pb geochronology and Hf isotope analysis. Late Carboniferous to Middle Jurassic strata on the southern basin margin are inferred as being predominantly reworked from Silurian to Devonian strata within the adjacent Franklinian Basin succession. Higher-grade metamorphic detritus appeared during Middle to Late Triassic times and indicates exhumation and erosion of lower (Neoproterozoic to Cambrian) levels within the Franklinian Basin succession and/or a direct detrital input from the Canadian-Greenland Shield. The provenance of northern-derived sediments is more enigmatic owing to the subsequent opening of the Arctic Ocean. Northern-derived Middle Permian to Early Triassic sediments were likely derived from proximal areas of the Chukotkan part of the Arctic Alaska-Chukotka microplate. Late Triassic northern-derived sediments have different detrital zircon U–Pb age spectra from Middle Permian to Early Triassic ones and were likely derived from the Uralian orogenic belt and/or the Arctic Uralides. The loss of this sand input during latest Triassic times is interpreted to reflect drainage reorganisation farther upstream on the Barents Shelf. Middle Jurassic sands in the northern and axial parts of the basin were largely reworked from local northern-derived Late Triassic strata. This may have been facilitated by rift flank uplift of the northern basin margin in response to rifting in the adjacent proto-Amerasia Basin.

Uplift evolution along the Red Sea continental rift margin from stream profile inverse modeling and drainage analysis

Continental rifted margins can have complex uplift histories related to different processes including footwall uplift by mechanical unloading, dynamic uplift and interaction with transfer margins. Deciphering uplift histories along rift flanks is integral to understanding the margin evolution as a whole. Here, a combination of drainage analysis and stream profile inverse modeling is utilized to estimate the rift flank uplift along the north-eastern Red Sea onshore margin. The drainage network was extracted from an ASTER DEM (∼30 x 30 m-horizontal resolution) and the uplift history was calculated using an inverse model, which builds on the relationship between uplift, erosion and stream profile shape. Local relief, minimum erosion volumes and minimum erosion volume:catchment area ratios (Rva) were also calculated and compared to uplift estimates. Within the study area, small catchments represent footwall drainage and larger catchments are mostly associated with pre-rift structures and syn-rift accommodation zones. Uplift initiated in the southern part during early rifting (21-15 Ma) before shifting northward (12-0 Ma). This uplift distribution is reflected in Rva and relief maps. Early-rift uplift is interpreted as a record of early-rift faulting with possible additional mantle support, whereas later uplift was driven by fault linkage and mantle upwelling (12-6 Ma) as well as transform tectonics (6-0 Ma). These modeling results are largely in agreement with other independent data (low-temperature thermochronology and dated carbonate terraces). Our workflow benefits from its utilization of ubiquitous drainage data. The combination of drainage analysis and inverse modeling proves to be more discerning than either one method in isolation, and may have application to analysis of other margins.

Spatially variable syn- and post-Alleghanian exhumation of the central Appalachian Mountains from zircon (U-Th)/He thermochronology

Abstract To assess spatial and temporal patterns of Phanerozoic orogenic burial and subsequent exhumation in the central Appalachian Mountains, we present mid-temperature zircon (U-Th)/He (ZHe; closure temperature [TC] = 140–200 °C) dates for 10 samples along a 225 km, strike-perpendicular transect spanning the Appalachian Plateau, Valley and Ridge, Blue Ridge, and Piedmont physiographic provinces in West Virginia and western Virginia. Ranges of single-grain ZHe dates exhibit an eastward younging trend from 455–358 Ma in the Pennsylvanian Appalachian Plateau to 336–209 Ma in the Valley and Ridge, 298–217 Ma in the Blue Ridge, and 186–121 Ma in the Piedmont. Within the Pennsylvanian Appalachian Plateau, detrital ZHe dates are older than corresponding depositional ages, thus limiting postdepositional burial temperatures to less than 160 °C. These ZHe dates capture predepositional mid-Paleozoic cooling signatures, indicating provenance from either recycled Taconic or Acadian basin strata or mid-Paleozoic Appalachian terranes. Across the Valley and Ridge and western Blue Ridge provinces, reset Permian detrital ZHe dates feature flat date-effective uranium correlations that suggest rapid Alleghanian cooling initiating prior to 270 Ma. ZHe dates within the Valley and Ridge are more than 100 m.y. older than previously reported regional apatite fission-track dates, reflecting a protracted period of stable post-Alleghanian thermal conditions within the foreland. By contrast, post-Triassic single-grain ZHe dates in the interior Piedmont document rapid postrift cooling, likely resulting from both the relaxation of an elevated geothermal gradient and exhumation from rift-flank uplift. The spatial discontinuity between stable synrift thermal conditions in the Valley and Ridge and rapid cooling in the Piedmont suggests that rift-flank uplift and cooling were concentrated outboard of the foreland within the Piedmont province.

Thermal evolution of onshore West Iberia: A better understanding of the ages of breakup and rift-to-drift in the Iberia-Newfoundland Rift

The age of breakup which formed the Central-North Atlantic has been debated for many decades and is still subject to debate: from ca. 150 Ma to 110 Ma. To address this issue, we have carried out a thermochronological study of the eastern margin of the rifted Iberia-Newfoundland sector. New apatite fission-track (AFT) data acquired on samples from the footwall (Variscan basement) and one sample (Triassic of the Lusitanian Basin) from the hanging wall of the principal normal fault bounding the basin. Thermal history of western Iberia can be then reconstructed since ca. 250 Ma. Fission-track ages of Variscan granitoids (whose crystallization age is >275 Ma) range between 191 ± 8 Ma and 75 ± 5 Ma, indicating that significant thermal events affected the study area during that period. Thermal inversion supports two main cooling events that we attribute to a major uplift and denudation of the Variscan basement, consistent with widespread basement-derived siliciclastic rocks of similar ages: Late Jurassic/Early Cretaceous (ca. 150–145 Ma) and late Early Cretaceous (ca. 110 Ma). From the sedimentary record in the Lusitanian Basin and the new AFT data, we deduce that: (1) temperatures >70–110 °C affected west Iberia between ca. 190 and 150 Ma, which can be explained partly by a subsiding basement in both foot and hanging walls; (2) the main cooling event at ca. 150–145 Ma is interpreted as major rift flank uplift; (3) the ca. 110 Ma cooling event may be linked to the final evolution of the margin and onset of oceanic spreading. We infer that the AFT main cooling event at ca. 150–145 Ma reflects the break of the elastic core of the lithosphere (whole lithosphere failure = breakup) with significant rift shoulder uplift (end of Rift 1), which was followed by hyper-extension and mantle exhumation (Rift 2) and finally, by oceanic spreading (rift-to-drift) at ca. 110 Ma (onset of Rift 3).

The evolution of Santa Maria Island in the context of the Azores Triple Junction

Santa Maria is the oldest island in the Azores, formerly belonging to the Eurasia plate and currently the only one sitting on the Nubia Plate, thus sharing a geodynamic evolution with the Azores Triple Junction. It is therefore important to evaluate the effects of active tectonics on the evolution of Santa Maria, for example on its vertical movements. We present new stratigraphic, geomorphologic, structural and geochronological data from Santa Maria which shed further light on how a volcanic ocean island evolves in a tectonically active setting. Santa Maria island started with a first shield volcano (Old Volcanic Complex) that emerged ca. 6.0 Ma ago and was active until ca. 5.3 Ma. The short time span between the first and second shield volcanoes (ca. 0.3 Ma) and the preservation of only the western flank of this first shield volcano indicate an initial flank collapse at ca. 5 Ma. The collapse scar was covered by an eastwards dipping sedimentary complex (Intermediate Sedimentary Complex), with a likely tsunami deposit at the base. A second shield volcano (Young Volcanic Complex) rapidly grew on these sediments from 4.8 to 3.8 Ma, and the island subsided by more than 100 m. At 3.7 Ma, a second flank collapse occurred, as inferred from the missing summit and eastern flank. Volcanism then resumed (3.6 to 2.8 Ma), giving rise to Strombolian cones lying unconformably on the collapse scar and conformable parasitic cones on the unaffected flank. Submarine lavas occurring at up to 200 m altitude with a youngest age of 3.0 Ma indicate major uplift of the island since, at most, that time. Here we interpret uplift as the result of rift flank uplift on the southern shoulder of the nearby Terceira Rift in the last ca. 1.5 Ma.

A minimum Thanetian (Paleocene) age for the African Surface in the Eritrean highlands, Northeast Africa

Supergene alunite from a supergene leached capping zone in the Daero Paulos area near Asmara, Eritrea yields Thanetian (late Paleocene) K–Ar ages of 58.6 ± 2.3 and 59.4 ± 2.3 Ma. The leached capping is exposed in an erosional window through a laterite profile, with the supergene alunite forming by oxidation of pyrite contained in quartz veinlet stockworks hosted by porphyry copper-related, felsic porphyry and adjacent volcano-sedimentary country rocks. Geologic relationships show that the leached capping and contained supergene alunite formed simultaneously with the lateritic weathering event that accompanied regional planation of equatorial and subequatorial Afro-Arabia to form the African Surface. Landscape modification of the central Ethiopian-Eritrean plateau by incision of transverse valleys and canyons commenced in the Oligocene, with a principal exhumation event occurring in the Miocene in response to swell-induced rift-flank uplift during Red Sea opening.

Structure and tectonic setting of the Chingale Igneous Ring Complex, Malawi from aeromagnetic and satellite gravity data: Implication for Precambrian terranes collision and Neogene - Quaternary rifting

This work examines the structure and tectonic setting of the possibly late Neoproterozoic - early Cambrian Pan-African (henceforth Pan-African) Chingale Igneous Ring Complex (CIRC) in southern Malawi to document its internal emplacement structure and solicit implications for Precambrian terranes collision and Neogene – Quaternary rifting. The CIRC is located along the boundary between the Mesoproterozoic – Neoproterozoic Southern Irumide orogenic belt in the northwest (dominantly amphibolite facies metamorphic terrane) and the Unango complex to the southeast (dominantly granulite facies metamorphic terrane). Portion of the Southern Irumide orogenic belt has been recently recognized as the Niassa craton. The CIRC is also dissected by the southeastern border fault of the Malawi rift, which represents a segment of the Neogene – Quaternary Western Branch of the East African Rift System. This work uses reduced to the pole (RTP) aeromagnetic data enhanced through tilt derivative and three-dimensional (3D) magnetic susceptibility modeling to reveal that the CIRC comprises three overlapping 7 km–12 km wide circular to elliptical ring structures that are aligned in a NE-SW direction along the boundary between the Southern Irumide orogenic belt and the Unango complex. This work also uses Bouguer gravity anomalies of the World Gravity model 2012 (WGM 2012) subjected to upward continuation of 2 km and 12 km to show that the CIRC is located along a relatively steep gravity anomaly gradient coinciding with the boundary between the Southern Irumide orogenic belt and the Unango complex. Together with structural, lithological, metamorphic, and lithospheric structure observations, this work proposes that the CIRC mark the location of a Pan-African suture zone resulting from the collision of the Southern Irumide orogenic belt (Niassa craton) and the Unango complex and this is named here the Chingale suture zone. The presence of this Pan-African suture zone facilitated localization of extensional strain during the onset of the Malawi rift allowing it to change its orientation from NNW-trending in its northern part to NE-trending in its southern part. Igneous ring complexes are hypabyssal intrusions. Hence, the exposure of the CIRC within the southern Malawi rift suggests the lack of rift-related subsidence. This makes much of the ~300 m–~500 m high relief of the topographic escarpment of the southeastern border fault of the rift the result of rift flank uplift.

The source of topography across the Cumberland Peninsula, Baffin Island, Arctic Canada: differential exhumation of a North Atlantic rift flank

Elevated topography is evident across the continental margins of the Atlantic. The Cumberland Peninsula, Baffin Island, formed as the result of rifting along the Labrador–Baffin margins in the late Mesozoic and is dominated by low-relief high-elevation topography. Apatite fission-track (AFT) analysis of the landscape previously concluded that the area has experienced a differential protracted cooling regime since the Devonian; however, defined periods of cooling and the direct causes of exhumation were unresolved. This work combines the original AFT data with 98 apatite new (U–Th)/He (AHe) ages from 16 samples and applies the newly developed ‘broken crystals’ technique to provide a greater number of thermal constraints for thermal history modelling to better constrain the topographic evolution. The spatial distribution of AFT and AHe ages implies that exhumation has been significant toward the SE (Labrador) coastline, and results of thermal modelling outline three notable periods of cooling: in the pre-rift stage (460–200 Ma), from synrift stage to present (120–0 Ma) and within the post-rift stage (30–0 Ma). Pre-rift cooling is interpreted as the result of exhumation of Laurentia and synrift cooling as the result of rift-flank uplift to the SE and differential erosion of landscape, whereas the final post-rift period is probably an artefact of the modelling process. These results suggest that the source of the Cumberland Peninsula's modern-day elevated topography is uplift during rifting in the Cretaceous and the isostatic compensation following continuous Mesozoic and Cenozoic differential erosion. This work highlights how interaction of rift tectonics and isostasy can be the principal source for modern elevated continental margins, and also provides insight into the pre-rift exhumational history of central Laurentia. Supplementary material: Thermal histories are available at: https://doi.org/10.6084/m9.figshare.c.4528409

Mechanism of rift flank uplift and escarpment formation evidenced by Western Ghats, India

The Western Ghats is one of the largest escarpments on earth, containing Reunion plume derived Deccan Traps, it is an excellent example to probe epeirogenic uplift, extension and subsidence in volcanic continental margins. The most continuous unbiased stratigraphic section of basalt down to the basement within a 1250 m drill hole of the Continental Scientific Deep Drilling Project is a valuable resource to investigate the above aspects. The flows across the entire drill core are geologically subaerial in character with basement exposed ~300 m below the mean sea level; they clearly display more evolved compositions from primary melts of mantle in terms of petrology, and only a single geomagnetic polarity transition in palaeomagnetic data. These results, combined with existing geological and geophysical data, constitute a multi-method approach that demonstrates (a) igneous underplating caused uplift prior to frequently suggested flexural isostasy (b) plume impact and eruption are near-simultaneous and extension/rifting essentially followed soon after volcanism and (c) lithosphere beneath the continental margin, while returning to normal temperatures following the Seychelles-India breakup, experienced thermal collapse and subsidence causing slumping of basalt basement below sea level.

Early flank uplift along the Suez Rift: Implications for the role of mantle plumes and the onset of the Dead Sea Transform

The Suez Rift is the northern extension of the Red Sea Rift and is an ideal location to study young continental breakup tectonics. Yet, despite much effort to constrain the timing of rift flank uplift and extensional exhumation in this region, the emerging picture remains uncertain. Here we present new thermochronologic constraints including apatite (U–Th)/He and fission track data from a transect across the eastern flank of the Suez Rift in SW Sinai. The use of two different thermochronometers in conjunction with thermal history modeling and well constrained kinetic parameters delineates a pronounced episode of relatively rapid cooling at 25-18 Ma followed by subdued post ∼18 Ma cooling. In contrast to previous estimates, this cooling pattern suggests that the most rapid uplift and exhumation phase along the Gulf of Suez took place during the early stage of rift formation, prior to the middle Miocene, with over 2.4 km of exhumation occurring during this stage. Uplift and exhumation along the Suez Rift flank slowed substantially post ∼18 Ma, as deformation migrated to the newly formed plate boundary along the Dead Sea Transform. This finding complements and strengthens previous indications for the initiation timing of the Dead Sea Transform plate boundary. The inferred late Oligocene–early Miocene timing of rapid exhumation, associated with tectonic extension and rift flank uplift coincides with the onset of regional alkali-basalt magmatism, suggesting lithospheric heating prior to the rift formation. This observation, along with the elevated topography around the Sinai triple junction and indications for some pre-rifting uplift, supports a more active mantle plume role in the rifting process.

An upper bound on Pluto's heat flux from a lack of flexural response of its normal faults

The topography of rifts on icy bodies can be used to probe their internal properties. Uplifted and curved rift flanks occur when the elastic thickness (te) of the crust is low, indicative of high heat flow out of the body. Stereo topography of Pluto shows no evidence of rift-flank uplift associated with large extensional graben to the west of Sputnik Planitia. Modeling the amount of topographic deflection expected from varying elastic thicknesses yields a conservative lower bound on te of 8 km at the time of deformation; the maximum implied heat flux since graben formation is 66–85 mWm−2. This upper bound is consistent with the predicted paleo-heat fluxes from radioactive decay (~6 mWm−2), but likely only marginally consistent with nearby apparently viscously-relaxed impact craters. Additionally, we also analyze the shear stresses on these faults and find that Pluto's faults only need to support low stresses in the range of 100–300 kPa to explain their dimensions.

Lithospheric flexure and rheology determined by climate cycle markers in the Corinth Rift

Geomorphic strain markers accumulating the effects of many earthquake cycles help to constrain the mechanical behaviour of continental rift systems as well as the related seismic hazards. In the Corinth Rift (Greece), the unique record of onshore and offshore markers of Pleistocene ~100-ka climate cycles provides an outstanding possibility to constrain rift mechanics over a range of timescales. Here we use high-resolution topography to analyse the 3D geometry of a sequence of Pleistocene emerged marine terraces associated with flexural rift-flank uplift. We integrate this onshore dataset with offshore seismic data to provide a synoptic view of the flexural deformation across the rift. This allows us to derive an average slip rate of 4.5–9.0 mm·yr−1 on the master fault over the past ~610 ka and an uplift/subsidence ratio of 1:1.1–2.4. We reproduce the observed flexure patterns, using 3 and 5-layered lithospheric scale finite element models. Modelling results imply that the observed elastic flexure is produced by coseismic slip along 40–60° planar normal faults in the elastic upper crust, followed by postseismic viscous relaxation occurring within the basal lower crust or upper mantle. We suggest that such a mechanism may typify rapid localised extension of continental lithosphere.

Modelling reservoir deliverability within the Northern Beagle Sub-basin, Western Australia

Reservoir deliverability is a critical component affecting the viability of petroleum systems within a sedimentary basin. Deliverability can be described as the ability of a given rock to flow hydrocarbons to the surface. Calculating deliverability relies on estimates of reservoir pressure, permeability and thickness as well as fluid viscosity, all of which are difficult to predict in a frontier basin. Burial and erosional processes exert a fundamental control on these rock and fluid properties. If this erosion is not uniformly distributed across an area then complex variations in deliverability may result. This paper presents a novel approach to quantifying predictions of reservoir deliverability within the Northern Beagle Sub-basin of Western Australia, via the use of a 3D basin-scale model that provides spatial and temporal estimates of variations in rock and fluid properties.Active extension began in the Northern Beagle Sub-basin during the Early Jurassic and resulted in deposition of proposed source and reservoir intervals. A thick (>5km) succession of progradational Middle Jurassic deltaics overlies the early Jurassic petroleum system. During the Late Jurassic, the basin underwent a complex phase of erosion (attributed to rift flank uplift), which resulted in upwards of 3km of sediment being locally removed on footwall blocks of active faults, as well as over structural highs. In other areas, however, such as contemporaneous structural lows, amounts of erosion are minimal. This complex spatial pattern of erosion has implications for both the thermal history (affecting fluid viscosity), as well as reservoir quality (permeability).The final product generated from this workflow was an integrated, basin-scale 3D model of reservoir deliverability for the Northern Beagle Sub-basin.

Age constraints on intra-formational unconformities in Upper Jurassic-Lower Cretaceous carbonates in northeast Turkey; geodynamic and hydrocarbon implications

Upper Jurassic-lowermost Cretaceous carbonate build-ups are imaged on seismic data in the Black Sea. They form important, untested, hydrocarbon reservoirs that are the focus of active exploration. Outcrop analogues to these build-ups around the Black Sea contain a series of subaerial exposure surfaces. The hiatuses associated with a number of these subaerial exposure surfaces have been dated in a well exposed Callovian or Upper Oxfordian to Barremian shallow-water inner platform carbonate succession (the Berdiga Formation) in the Eastern Pontides using strontium isotope stratigraphy and foraminiferal biostratigraphy. They span the latest Kimmeridgian to Tithonian or Berriasian, and the Hauterivian to Barremian. Less well constrained, but broadly contemporaneous stratigraphic gaps in multiple successions around the Black Sea provide additional insights and point to a regional driving mechanism. The timing of hiatus formation does not correspond to periods of eustatic lowstand. It does coincide, however, with Late Tithonian to Berriasian and Hauterivian to Early Aptian episodes of rifting in the Greater Caucasus Basin, located farther to the north. Thus, it is possible that subaerial exposure was caused by rift flank uplift during periods of regional extension. Uplift due to slab break off is discounted as a control because it post-dates (rather than pre-dates) locally developed Kimmeridgian magmatism. Rift-flank uplift is likely to have also affected carbonate build-ups on the intervening rift shoulders of the eastern Black Sea, the Shatskiy Ridge and the Mid Black Sea High. At outcrop, subaerial exposure is often associated with karstification and secondary porosity development. Similar processes may have occurred in the offshore helping to enhance the reservoir quality of these exploration targets.

Crustal-scale subsidence and uplift caused by metamorphic phase changes in the lower crust: a model for the evolution of the Loppa High area, SW Barents Sea from late Paleozoic to Present

The Loppa High area has been subject to several events of uplift and subsidence from the Late Paleozoic to Present. The driving mechanisms behind the vertical movements, however, are not fully understood. We propose that uplift and subsidence were influenced by the combination of density changes caused by metamorphic phase changes in a 90 × 140 km wide mafic lower crustal body below the Loppa High and local (rift-related) and far-field stress. Through a numerical modelling approach we analyse the tectonically induced variations in pressure and temperature in the lower crust, their influence on phase changes in the mafic body and the affiliated vertical movements. Results show that (1) densification of the mafic body caused by far-field compression associated with the late Triassic westward translation of Novaya Zemlya could cause surface subsidence, (2) heat and fluid influx provided by early Cretaceous rifting could trigger density reduction and surface uplift and (3) the present-day geometry of the Loppa High as observed in seismic data can be reproduced by combining the modelled effect of rift flank uplift and phase changes in the mafic body. Phase change-driven vertical movements may also have affected other structural highs in the western Barents Sea, including the Stappen High.

The influence of extension rate and crustal rheology on the evolution of passive margins from rifting to break-up

Extension rate and crustal strength are two important factors that influence the shape of initial rift basins and final passive margin architecture. The extension rate will also affect crustal strength as the passive margin evolves, therefore adding more complexity to the system. We used thermomechanical numerical experiments to systematically explore the relationship of extension rate and initial crustal strength on final passive margin structure. Varying the initial amount of ductile crust from 33% to 70% and extension rates from 2 to 50mmyr−1 results in passive margins of different widths, shapes, and evolution histories. We find four distinct margin types: Type I–narrow symmetric margins, Type II–wide symmetric margins, Type III–asymmetric margins, and Type IV–rift jumping. Experiments with strong initial crust (33% ductile crust) have crust-mantle coupling of strain and produce narrow, symmetric margins with high rift flank uplift (Type I margins). Ultraslow extension experiments (2mmyr−1) undergo thermal cooling and produce wide, symmetric margins with hyperextended crust (Type II margins). Experiments with intermediate to fast extension rates (10–50mmyr−1) and thick layers of ductile crust will produce initial rift basins that are symmetric, but later rifting stages yield asymmetric conjugate margins with hyperextended domains 100–250km wide (Type III margins). In special cases with intermediate extension rates and thick ductile crustal layers, we observe a jump in rift location over 50km and abandoned rifts with isolated crustal blocks (Type IV margins). These results highlight how ductile crustal layers and extension rates influence passive margin formation during different stages of rifting.

Initiation, evolution and extinction of pull-apart basins: Implications for opening of the Gulf of California

We present a model for the origin, crustal architecture, and evolution of pull-apart basins. The model is based on results of three-dimensional upper crustal elastic models of deformation, field observations, and fault theory, and is generally applicable to basin-scale features, but predicts some intra-basin structural features. Geometric differences between pull-apart basins are inherited from the initial geometry of the strike-slip fault step-over, which results from the forming phase of the strike-slip fault system. As strike-slip motion accumulates, pull-apart basins are stationary with respect to underlying basement, and the fault tips propagate beyond the rift basin, increasing the distance between the fault tips and pull-apart basin center. Because uplift is concentrated near the fault tips, the sediment source areas may rejuvenate and migrate over time. Rift flank uplift results from compression along the flank of the basin. With increasing strike-slip movement the basins deepen and lengthen. Field studies predict that pull-apart basins become extinct when an active basin-crossing fault forms; this is the most likely fate of pull-apart basins, because basin-bounding strike-slip systems tend to straighten and connect as they evolve. The models show that larger length-to-width ratios with overlapping faults are least likely to form basin-crossing faults, and pull-apart basins with this geometry are thus most likely to progress to continental rupture. In the Gulf of California, larger length-to-width ratios are found in the southern Gulf, which is the region where continental breakup occurred rapidly. The initial geometry in the northern Gulf of California and Salton Trough at ~6Ma may have been one of widely-spaced master strike-slip faults (lower length-to-width ratios), which our models suggest inhibits continental breakup and favors straightening of the strike-slip system by formation of basin-crossing faults within the step-over, as began ~1.2Ma when the San Jacinto and Elsinore - Cerro Prieto fault systems formed.