Kinematic Restoration Research Articles

Nonlinear flame response dependencies of a V-flame subjected to harmonic forcing and turbulence

We study the dependence of the flame sheet response of an open V-flame when subjected to simultaneous but independently controlled – (1) narrowband, coherent disturbances, (2) mean flow velocity, and (3) turbulent broadband disturbances. We re-examine the data presented in Humphrey et al. (2018). Flame edge and flow field were obtained from Mie scattering images and PIV vector fields, respectively. We determine the flame sheet response, which allows us to understand the effects of kinematic restoration on the local and global flame dynamics. We find some highly nonlinear behaviors in the flame sheet response, which have not been reported previously. In particular, we observe (1) oscillations in the rise and peak region of the flame response, and (2) early onset of the nonlinear coupling between narrowband and broadband disturbances, resulting in oscillatory decay immediately downstream of the flame holder region. The spatial oscillations seen in the flame response arise only when unalike disturbances such as vortical and flame wrinkle disturbances have a comparable wavelength and, thus, interfere. We then find that higher nominal velocity and turbulent intensities increase asymmetry in the flame response, and subsequently affect the local and global heat release response (HRR). We analytically calculate HRR from flame sheet response. We find that there is a monotonic increase in the response with increasing flame length for lower nominal velocities, possibly due to higher flame symmetry. Moreover, the HRR calculated from flame sheet response captures the effect of kinematic restoration very well. Notably, there is a decrease in HRR with increasing turbulence intensity due to enhanced smoothing from kinematic restoration at higher turbulence levels. We further find that the flame response dependence on harmonic forcing manifest in the low-pass filter characteristics of the global HRR response.

Emplacement mechanisms of a dyke swarm across the brittle-ductile transition and the geodynamic implications for magma-rich margins

Igneous dykes are the main magma transport pathways through the Earth's crust, and they are considered to contribute to tectonic extension in volcanic rifts. Dykes are typically considered to result from brittle fracturing, even in the ductile crust. A common assumption is that dyke orientation is controlled by tectonic stresses, such that dykes in rifts are expected to be vertical and perpendicular to extension. Here we report on detailed field observations of a spectacularly well-exposed dyke swarm to show that dykes were not systematically emplaced by purely brittle processes and that dyke orientation may differ from the dominant tectonic stress orientations. The dyke complex formed near the brittle-ductile transition during opening of the Iapetus Ocean and is now exposed in the Scandinavian Caledonides. Distinct dyke morphologies related to different emplacement mechanisms has been recognized: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, en-echelon segments with bridges exhibiting angular fragments; 2) Brittle-ductile dykes that exhibit undulating contacts, rounded tips, ductile folding in the host rock and contemporaneous brittle and ductile features; 3) Ductile “dykes” that exhibit rounded shapes and mingling between the soft ductile host rock and the intruding mafic magma. The brittle dykes exhibit two distinct orientations separated by c. 30° that are mutually cross-cutting, suggesting that the dyke swam did not consist of only vertical sheets perpendicular to regional extension, as expected in rifts. We were able to use the well-exposed host rock layers as markers to perform a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex: it accommodated for >100% extension, but counter-intuitively it also accommodated for 27% crustal thickening. We infer that the magma influx rate was higher than the tectonic stretching rate, implying that magma was emplaced forcefully, as supported by field observations. Finally, our observations suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle-ductile transition, and lead to a considerable weakening of the crust. The interpretations presented here could potentially have large implications for surface topography and seismicity in active rifts and volcanic areas around the world.

Integrated deterministic and predictive discrete fracture network modeling for an Eocene carbonate reservoir, Bengal Basin, India

Prediction of fracture porosity and permeability remains a challenge for fractured carbonate reservoirs. As natural fractures are heterogeneous and subseismic in scale, core data and image logs only provide partially sampled data, leading to sparse information on fracture length, height, orientation, spacing, and aperture. In the present study, an integrated discrete fracture network was generated that is capable of predicting fracture porosity in Eocene carbonates of the Bengal Basin in northeastern India. The predictive fracture modeling method used 3D kinematic and geomechanical restoration of interpreted seismic horizons to estimate infinitesimal stress and strain values and to characterize associated fracture sets. Seismic attribute analysis was used to extract faults and fractures from an ant-track cube, which provided sharper definition of discontinuities seen in conventional curvature attribute data. An integrated discrete fracture model was created using information from seismic attributes, seismic inversion, and strain distribution to determine fracture intensity. Faults and fractures that are seismically resolved were statistically analyzed, which indicated that spatial distribution of fracture length follows a power law. Based on theoretical concepts of fracture mechanics, linear aperture-to-length scaling was used to characterize aperture population. A present-day geomechanical earth model was used to identify open fracture sets. This model shows that northeast–southwest-oriented fracture sets are critically stressed and will contribute to porosity and permeability. Criticality of fractures to shear failure was analyzed by computing geomechanical parameters — slip stability and dilation tendency, based on the direction and magnitude of far-field stresses. Fractures with slip and dilation tendencies greater than 0.6 in the modeled discrete fracture network were taken as inputs for porosity and permeability estimation.

Constraining erosion rates in thrust belts: Insights from kinematic modeling of the Argentine Precordillera, Jachal section

Kinematic restorations in fold and thrust belts, which are a valuable tool for studying the deformational history of fold and thrust belts, have been poorly used to understand erosion rates. In this contribution, we estimated the amount of eroded material in thrust-belts via kinematic reconstructions. We combined kinematic restitutions with the classic critically-tapered Coulomb wedge model, following the assumption that at times when thrusting is triggered, the surface slope was less than the angle required to reach self-similar growth, i.e. critical. Following conservative geometrical considerations, we were able to compute a time-varying Coulomb wedge. Such unsteady wedge is used to calculate first-order, time dependent erosion rates, which are compared to denudation and provenance results derived from other techniques. We applied our model to the Argentine Precordillera at the Jáchal river section, whose extensively studied outcrop data have let establish a well-constrained episodic deformation of the thrust-belt; even though no kinematic model of the area had been presented so far. Our results show two contrasting erosion rates, one prior to the movement along the last-in-sequence fault (Niquivil) and one after, 0.1 and 1.34 Km/Myr, respectively. Our findings indicate that the amount of eroded material might not always be directly proportional to cumulative slip in the thrust system, as slip along Niquivil thrust is only 22% of the total horizontal displacement, though it produced most of the uplift and erosion. Our results are in striking accordance to long-term erosion estimation proxies, like U-Th/He, 10Be and sedimentological studies, which highlights the validity of the economical methodology herein proposed. Furthermore, our kinematic model of the evolution of the Argentine Precordillera allows us to perform 2D flexural numerical modeling, which suggests that tectonic loading seems to not be enough to reproduce basin geometry and that additional mechanisms, such as dynamic subsidence or lithospheric mantle thickening (among others), would be required.

Integrating kinematic restoration and forward finite element simulations to constrain the evolution of salt diapirism and overburden deformation in evaporite basins

In evaporite basins, salt deformation including inflation, diapirism, and salt canopy emplacement is inherently non-coaxial and ductile and thus it presents challenges for two-dimensional kinematic restorations that rely on line-length and area-balancing assumptions. Also, because salt flow and the resulting deformation of adjacent cover units can be driven by temporally and spatially transient salt pressure gradients, kinematic restorations are generally unable to predict the magnitude and distribution of subseismic deformation that results from a particular structural scenario. Here, we use a case study from the Atwater fold belt, Gulf of Mexico, to test a new workflow that involves comparison of kinematic restoration models with forward numerical (finite-element) models of structural evolution to examine the physical validity of solutions derived from the kinematic restorations and to determine the nature and spatial distribution of the resultant subseismic deformation. In the Atwater fold belt, which represents the downdip portion of a linked updip (landward) extensional-downdip (seaward) contractional system, our kinematic restorations indicated that major anticlines likely result from early short wavelength folding followed by (1) inflation of the autochthonous salt to drive failure of the overburden, (2) collapse of the updip limb of the major salt-cored anticline as the salt evacuates updip, and (3) rapid emplacement of the allochthonous salt canopy. In margin scale finite element models of the same system, progradation of the sedimentary wedge above the weak salt substrate leads to basinward migration of the salt and produces inflation of the major downdip salt-cored folds, as predicted by the kinematic model. However, in relatively strong overburden materials (equivalent friction angle = 32°), such salt flow only sustains inflation of the anticlines and is unable to reproduce the interpreted collapse of the anticlinal backlimb or emplacement of the salt canopy. Alternate model runs that include a significant reduction in material strength (equivalent friction angle = 18°) allow salt in the anticlinal crest to drive both reactive and active diapirism and ultimately lead to rapid emplacement of allochthonous canopies. In all of these models, diapirism drives substantial seismically-resolvable and subseismic deformation of wall rocks. Additionally, these models clearly show that the stress field, and particularly the K value (horizontal-vertical stress ratio) of the sediments adjacent to salt structures used for estimating stress magnitudes for drilling predictions, is fundamentally dependent on what point along the evolutionary path from autochthonous salt, to diapir, to salt sheet, that each structure resides. These results highlight the need to test complex kinematic restorations with physics-based techniques. Additionally, they demonstrate that integrating kinematic restorations with these finite element solutions can substantially increase our ability to predict both subseismic reservoir damage in sediments adjacent to salt structures and the K values used for forecasting drilling conditions, particularly in young basins filled with poorly consolidated sediments.

Southwest Pacific Absolute Plate Kinematic Reconstruction Reveals Major Cenozoic Tonga-Kermadec Slab Dragging.

Tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench‐parallel slab motion through the mantle, recently defined as a form of “slab dragging.” We investigate here long‐term slab‐dragging components of the Tonga‐Kermadec subduction system driven by absolute Pacific plate motion. To this end we develop a kinematic restoration of Tonga‐Kermadec Trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle. Estimating Tonga‐Kermadec subduction initiation is challenging because another (New Caledonia) subduction zone existed during the Paleogene between the Australia and Pacific plates. We test partitioning of plate convergence across the Paleogene New Caledonia and Tonga‐Kermadec subduction zones against resulting mantle structure and show that most, if not all, Tonga‐Kermadec subduction occurred after ca. 30 Ma. Since then, Tonga‐Kermadec subduction has accommodated 1,700 to 3,500 km of subduction along the southern and northern ends of the trench, respectively. When placed in a mantle reference frame, the predominantly westward directed subduction evolved while the Tonga‐Kermadec Trench underwent ~1,200 km of northward absolute motion. We infer that the entire Tonga‐Kermadec slab was laterally transported through the mantle over 1,200 km. Such slab dragging by the Pacific plate may explain observed deep‐slab deformation and may also have significant effects on surface tectonics, both resulting from the resistance to slab dragging by the viscous mantle.

Western Caribbean intraplate deformation: Defining a continuous and active microplate boundary along the San Andres rift and Hess Escarpment fault zone, Colombian Caribbean Sea

The San Andres rift (SAR), located on the lower Nicaraguan Rise, is a previously poorly studied, active, 015°-trending, bathymetric, and structural rift basin that is 11–27 km (7–17 mi) wide and extends for 346 km (215 mi) across the western flank of the Caribbean plate. In this study, we integrate bathymetric maps, potential field data, and high-resolution, two-dimensional (2-D) seismic lines to understand the crustal structure, tectonic history, and tectonic origin of the SAR, which is one of the active areas within the otherwise stable Caribbean plate. We compiled regional gravity and magnetic data that revealed a negative gravity anomaly and positive magnetic anomaly that we interpret as a result of crustal thinning and an elevated Moho along the main rift axis of the SAR. Forward models of gravity data show four possible interpretations for the origin of the crust underlying and surrounding the SAR. Interpretations of 2-D seismic reflection data show structural features within the upper crust and sedimentary sections typical of other active rift systems including a SAR-parallel, north–south alignment of earthquakes with the larger events showing normal and strike-slip focal mechanisms. Sequential kinematic restorations based on 2-D seismic profiles reveal three major phases of SAR opening: (1) the initial early Eocene rifting stage; (2) middle Eocene extension; and (3) a rapid middle Miocene to early Pliocene extension accompanied by emergence of the San Andres Island as a rift shoulder. We propose slab rollback and intraplate extension as main tectonic mechanisms to explain all rift phases and Neogene volcanism found in the western Caribbean region.

Cenozoic Rotation History of Borneo and Sundaland, SE Asia Revealed by Paleomagnetism, Seismic Tomography, and Kinematic Reconstruction.

SE Asia comprises a heterogeneous assemblage of fragments derived from Cathaysia (Eurasia) in the north and Gondwana in the south, separated by suture zones representing closed former ocean basins. The western part of the region comprises Sundaland, which was formed by Late Permian‐Triassic amalgamation of continental and arc fragments now found in Indochina, the Thai Penisula, Peninsular Malaysia, and Sumatra. On Borneo, the Kuching Zone formed the eastern margin of Sundaland since the Triassic. To the SE of the Kuching Zone, the Gondwana‐derived continental fragments of SW Borneo and East Kalimantan accreted in the Cretaceous. South China‐derived fragments accreted to north of the Kuching Zone in the Miocene. Deciphering this complex geodynamic history of SE Asia requires restoration of its deformation history, but quantitative constraints are often sparse. Paleomagnetism may provide such constraints. Previous paleomagnetic studies demonstrated that Sundaland and fragments in Borneo underwent vertical axis rotations since the Cretaceous. We provide new paleomagnetic data from Eocene‐Miocene sedimentary rocks in the Kutai Basin, east Borneo, and critically reevaluate the published database, omitting sites that do not pass widely used, up‐to‐date reliability criteria. We use the resulting database to develop an updated kinematic restoration. We test the regional or local nature of paleomagnetic rotations against fits between the restored orientation of the Sunda Trench and seismic tomography images of the associated slabs. Paleomagnetic data and mantle tomography of the Sunda slab indicate that Sundaland did not experience significant vertical axis rotations since the Late Jurassic. Paleomagnetic data show that Borneo underwent a ~35° counterclockwise rotation constrained to the Late Eocene and an additional ~10° counterclockwise rotation since the Early Miocene. How this rotation was accommodated relative to Sundaland is enigmatic but likely involved distributed extension in the West Java Sea between Borneo and Sumatra. This Late Eocene‐Early Oligocene rotation is contemporaneous with and may have been driven by a marked change in motion of Australia relative to Eurasia, from eastward to northward, which also has led to the initiation of subduction along the eastern Sunda trench and the proto‐South China Sea to the south and north of Borneo, respectively.

3-D kinematic restoration of the eastern Sudbury Igneous Complex, Canada, and its importance for Cu-Ni-PGE sulphide exploration

Kinematic restorations of deformed igneous terranes have rarely been attempted due to the general absence of (1) planar primary lithological contacts, (2) tightly constrained deformation kinematics, and (3) geometric constraints on lithologies and structures at depth. Because of the vast number of exploration drill holes, the deformed and layered 1.85 Ga Sudbury Igneous Complex (SIC) in Ontario, Canada, is reasonably well understood with respect to (1) and (3). We therefore explored the kinematics of folding and faulting in the eastern SIC and use the subsurface geometry of faults extracted from a model integrating surface mapping and drill core logs in an attempt to restore the geometry of part of the SIC. Specifically, we identified rotation magnitudes and the tilt axis of a kilometer-scale plunging fold, the West Bay Anticline, which appears to have folded the eastern part of the SIC. We combined a 3-D model of the faults and lithological contacts of the SIC, fault kinematics calculated from the inversion of brittle shear faults at surface, and limb rotations of the West Bay Anticline to kinematically restore the eastern part of the SIC. Results of restorations using simple shear and flexural-slip algorithms highlight the importance of slip on prominent, curved faults that displaced the SIC and facilitated its folding. Flexural slip appears to be the more plausible mechanism of the two, as it removed the curvature of, and displacement on, prominent faults. Flexural-slip restoration helps to estimate primary thickness variations of the SIC and the results show that thickened parts of the Main Mass of the SIC correspond spatially with known Cu-Ni-PGE sulfide deposits. This result demonstrates that 3-D restoration can be an important tool for mineral exploration in igneous terranes.

Reconstructing Greater India: Paleogeographic, kinematic, and geodynamic perspectives

Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of ‘Greater India’, the Indian plate lithosphere that subducted since Tethyan Himalayan continental collision with Asia. Here, we discuss this reconstruction from paleogeographic, kinematic, and geodynamic perspectives and isolate the evolution scenario that is consistent with all three. We follow recent constraints advocating a ~58 Ma initial collision and update a previous kinematic restoration of intra-Asian shortening with a recently proposed model that reconciles long-debated large and small estimates of Indochina extrusion. Our new reconstruction is tested against paleomagnetic data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows ~1000–1200 km of post-collisional intra-Asian shortening, leaving a 2600–3400 km wide Greater India. From a paleogeographic, sediment provenance perspective, Eocene sediments in the Lesser Himalaya and on undeformed India may be derived from Tibet, suggesting that all Greater Indian lithosphere was continental, but may alternatively be sourced from the contemporaneous western Indian orogen unrelated to India-Asia collision. A quantitative kinematic, paleomagnetic perspective prefers major Cretaceous extension and a ‘Greater India Basin’ opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that subduction rates close to 20 cm/yr was driven by a down-going lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. We conclude that the Greater India Basin scenario is the only sustainable one from all three perspectives. We infer that old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post-collisional continental and young Greater India basin lithosphere did not, inciting the rapid India-Asia convergence deceleration ~8 Myr after collision. Subsequent absolute northward slab migration and overturning caused flat slab subduction, Tibetan shortening, arc migration and arc volume decrease.

Paleomagnetic constraints on the timing and distribution of Cenozoic rotations in Central and Eastern Anatolia

Abstract. To quantitatively reconstruct the kinematic evolution of Central and Eastern Anatolia within the framework of Neotethyan subduction accommodating Africa–Eurasia convergence, we paleomagnetically assess the timing and amount of vertical axis rotations across the Ulukışla and Sivas regions. We show paleomagnetic results from ∼ 30 localities identifying a coherent rotation of a SE Anatolian rotating block comprised of the southern Kırşehir Block, the Ulukışla Basin, the Central and Eastern Taurides, and the southern part of the Sivas Basin. Using our new and published results, we compute an apparent polar wander path (APWP) for this block since the Late Cretaceous, showing that it experienced a ∼ 30–35° counterclockwise vertical axis rotation since the Oligocene time relative to Eurasia. Sediments in the northern Sivas region show clockwise rotations. We use the rotation patterns together with known fault zones to argue that the counterclockwise-rotating domain of south-central Anatolia was bounded by the Savcılı Thrust Zone and Deliler–Tecer Fault Zone in the north and by the African–Arabian trench in the south, the western boundary of which is poorly constrained and requires future study. Our new paleomagnetic constraints provide a key ingredient for future kinematic restorations of the Anatolian tectonic collage.

Tectonic inversion of salt-detached ramp-syncline basins as illustrated by analog modeling and kinematic restoration

Salt-detached ramp-syncline basins are developed in extensional settings and are characterized by wide synclinal sedimentary basins detached on salt and formed above the hanging wall of active ramp-flat-ramp extensional faults. They are rarely fault bounded; instead, they are bounded by salt structures that are in general parallel to the major subsalt structures. As such, the formation of these extensional systems requires the presence of (1) a subsalt extensional fault with significant dip changes and (2) an evaporitic unit above the extensional fault, which partially or completely decouples the basin from a subsalt extensional fault. Salt-detached ramp-syncline basins have a significant exploration potential when their extensional geometry is preserved and when they have undergone positive tectonic inversion and consequent uplift and fold amplification. However, in some cases, their subsalt geometry may not be fully recognizable, especially when subsalt seismic imaging is poor. To obtain a deeper understanding of the geometry and kinematic evolution of these salt-detached ramp-syncline basins, we performed a series of analog modeling experiments, in which the models’ cross sections had been sequentially restored. Analog models and restoration results reveal that the kinematic evolution of the salt-detached ramp-syncline basins during extension and inversion depends on the interaction of different factors that may function simultaneously. Our results are used to improve the interpretation of seismic sections in inverted Mesozoic salt-detached ramp-syncline basins on the Atlantic margins, where subsalt faults are not well-imaged, and thus the suprasalt geometries must be used to infer the subsalt structure.

Quantifying Arabia–Eurasia convergence accommodated in the Greater Caucasus by paleomagnetic reconstruction

Since the late Eocene, convergence and subsequent collision between Arabia and Eurasia was accommodated both in the overriding Eurasian plate forming the Greater Caucasus orogen and the Iranian plateau, and by subduction and accretion of the Neotethys and Arabian margin forming the East Anatolian plateau and the Zagros. To quantify how much Arabia–Eurasia convergence was accommodated in the Greater Caucasus region, we here provide new paleomagnetic results from 97 volcanic sites (∼500 samples) in the Talysh Mountains of NW Iran, that show ∼15° net clockwise rotation relative to Eurasia since the Eocene. We apply a first-order kinematic restoration of the northward convex orocline that formed to the south of the Greater Caucasus, integrating our new data with previously published constraints on rotations of the Eastern Pontides and Lesser Caucasus. This suggests that north of the Talysh ∼120 km of convergence must have been accommodated. North of the Eastern Pontides and Lesser Caucasus this is significantly more: 200–280 km. Our reconstruction independently confirms previous Caucasus convergence estimates. Moreover, we show for the first time a sharp contrast of convergence between the Lesser Caucasus and the Talysh. This implies that the ancient Paleozoic–Mesozoic transform plate boundary, preserved between the Iranian and East-Anatolian plateaus, was likely reactivated as a right-lateral transform fault since late Eocene time.

Structural style, formation of low angle normal fault and its controls on the evolution of Baiyun Rift, northern margin of the South China Sea

Recent studies of high-resolution seismic reflection profiles in the northern rifted margin of the South China Sea revealed that low angle normal faults dominated the structural evolution of deepwater basins rather than high angle normal faults solely as was previously assumed; however, none of the studies proposed kinematic restorations of the fault system and the relationship to continental margin formation. The Baiyun Rift is located in the slope of the northern margin of the South China Sea underlain by extremely thinned continental crust. It is filled with a relatively complete sequence of Cenozoic sediments up to 10 km and has been considered the best-documented deepwater basin. Basin-wide 3D seismic data together with the available deepwater well data have allowed the structural framework to be built and tectono-stratigraphic history of the Baiyun Rift to be traced in detailed from the rift stage; a quantitative study of the primary geometry and kinematics of the major faults can be performed consequently. Results show the inception of the rift is characterized by faults slipped at high angles; the later stage (mid-Eocene) of intensive extension is dominated by a fault system with large horizontal displacements (>10 km) and initial low dips (<30°). The observations can be best explained by a low angle normal faulting (faults started out at shallow angles during mid-Eocene or being rotated from high angles) following a scattered high angle normal faulting. As a consequence, the polyphase faulting created a large accommodation space vertically and horizontally and formed a deep and wide shape of the Baiyun Rift. Besides, the phenomenon that the cessation of the rift in the Baiyun Rift predated the final breakup of the continental margin suggests the timing of the rifting events along the northern margin of the South China Sea is non-instantaneous. This study implies the progressive deformation dominated by low angle normal faulting causes an uneven distribution of the continental crustal thickness and may favor the breakup location in the northern South China Sea.

Initiation and growth of salt diapirs in tectonically stable settings: Upbuilding and megaflaps

We use finite element modeling to show that upbuilding can be a significant component of salt diapir growth in tectonically stable systems when basin sediments are elastoplastic mudrocks. The ability of such sediments to deform plastically and the dependence of their strength on confining pressure enable structural thinning, which allows salt to pierce through a relatively thick roof. Once pierced, the originally continuous roof uplifts to form a megaflap. We show that the evolution to an upturned megaflap adjacent to a salt stock causes shortening of the bedding layers in the radial and vertical directions and extension in the hoop (circumferential) direction. These deformations lead to significant shear strains within the sediments; as a result, in some areas within the upturned megaflap, mudrocks have reached their maximum level of shear resistance and are failing. Thinning and shear failure of sediments are also significant near salt walls, despite the absence of out-of-plane deformation. We illustrate that cross-sectional area and bedding line lengths are not necessarily preserved. Based on our results, we re-evaluate traditional assumptions of kinematic restoration and show that established workflows may not properly restore salt systems that interact with shallow plastic sediments. Finally, we show that when wall rocks are deformable, salt diapir shapes are not necessarily a simple function of sedimentation and salt flux rates (qfx/A) and that the diapir hourglass shape might result from lateral deformation of the megaflap.

Restoration of the Cretaceous uplift of the Harz Mountains, North Germany: evidence for the geometry of a thick-skinned thrust

Reverse movement on the Harz Northern Boundary Fault was responsible for the Late Cretaceous uplift of the Harz Mountains in northern Germany. Using the known geometry of the surface position and dip of the fault, and a published cross section of the Base Permian horizon, we show that it is possible to predict the probable shape of the fault at depth, down to a detachment level. We use the ‘inclined-shear’ method with constant heave and argue that a shear angle of 30° was most likely. In this case, the detachment level is at a depth of ca. 25 km. Kinematic restoration of the Harz Mountains using this fault geometry does not produce a flat horizon, rather it results in a ca. 4 km depression. Airy–Heiskanen isostatic equilibrium adjustment of the Harz Mountains restores the Base Permian horizon to the horizontal, as well as raising the Moho to a depth of 32 km, a typical value for northern Germany. Restoration also causes a rotation of tectonic fabrics within the Harz Mountains of about 11° clockwise. We show that this model geometry is very good fit to the interpreted DEKORP BASIN 9601 deep seismic profile.

Along-strike continuity of structure, stratigraphy, and kinematic history in the Himalayan thrust belt: The view from Northeastern India

The Himalaya consists of thrust sheets tectonically shingled together since ~58 Ma as India collided with and slid beneath Asia. Major Himalayan structures, including the South Tibetan detachment (STD), Main Central thrust (MCT), Lesser Himalayan duplex (LHD), Main Boundary thrust (MBT), and Main Frontal thrust (MFT), persist along-strike from northwestern India to Arunachal Pradesh near the eastern end of the orogenic belt. Previous work suggests significant basement involvement and a kinematic history unique to the Arunachal Himalaya. We present new geologic and geochronologic data to support a regional structural cross-section and kinematic restoration of the Arunachal Himalaya. Large Paleoproterozoic orthogneiss bodies (Bomdila Gneiss) previously interpreted as Indian basement have ages of ~1774-1810 Ma, approximately 50 Ma younger than Lesser Himalayan strata into which their granitic protoliths intruded. Bomdila Gneiss is therefore part of the Lesser Himalayan cover sequence, and no evidence exists for basement involvement in the Arunachal Himalaya. Minimum shortening in rocks structurally beneath the STD is ~421 km. The MCT was active during the early Miocene; STD extension overlapped MCT shortening and continued until ca. 15-12 Ma; growth of the LHD began ~11 Ma; followed by slip along the MBT (post-7.5 Ma) and MFT (post-1 Ma) systems. Earlier thrusting events involved long-distance transport of strong, low-taper thrust sheets, whereas events after 12-10 Ma stacked smaller, weaker thrust sheets into a steeply tapered orogenic wedge dominated by duplexing. A coeval kinematic transition is observed in other Himalayan regions, suggesting orogenic wedge behavior was controlled by rock strength and erodibility.

Biomechanical comparison of graft structures in anterior cruciate ligament reconstruction

PurposeDouble-bundle (DB) anterior cruciate ligament (ACL) reconstruction may offer kinematic restoration superior to anatomic single bundle (SB), but it remains technically challenging. The femoral attachment site has the most effect on ACL graft isometry, so a simplified three-socket (3S) construct which still uses two sockets to cover the femoral ACL attachment is attractive. It was hypothesised that ACL reconstruction using three- and four-socket techniques would more closely restore native knee kinematics compared to anatomic two-socket (SB) surgery.MethodsNine cadaveric knees were used to evaluate the kinematics of ACL-intact, ACL-deficient, anatomic SB, three-socket, and DB arthroscopic ACL reconstructions. Suspensory fixation was used, and grafts were tensioned to match the anterior draw of the intact knee at 20°. A six-degree-of-freedom robotic system measured knee laxity under 90 N anterior tibial force and rotational laxity under 5 N-m torque. Combined moments were applied to simulate the pivot-shift subluxation: 4 N-m internal rotation and 8 N-m valgus.ResultsSignificant differences between reconstructions were not found during anterior tibial loading, apart from SB being more lax than DB at 60° flexion. All reconstructions produced comparable laxity to the intact state, apart from SB at 60°. Significant differences between reconstructions were not found at any flexion angle during tibial internal/external applied torques. Under combined loading, DB produced significantly less laxity than SB constructs apart from anterior tibial translation at 0° and internal rotation at 45°. 3S and DB were comparable to the native knee throughout.ConclusionAlthough 3S restored laxities to a similar extent to DB, significant superiority over SB surgery was not observed. Although statistically significant differences were found between SB and DB surgery during anterior tibial and simulated pivot-shift loading, both remained similar to the native knee. The clinical relevance is that this study did not support an ACL graft construct more complex than an anatomic single bundle.

On colliding spherical flames: Morphology, corner dynamics, and flame-generated vorticity

The collision of two identical spherical flames was studied for its relevance in flame interactions in various practical situations including those within turbulent flames. Experimentally, premixtures of fuel (H2, C3H8) and oxidizer were ignited by two synchronized sparks in a closed chamber under atmospheric pressure, with the subsequent flame-front evolution tracked by a Schlieren system with high-speed camera, as well as computationally simulated. Results show that development of the morphology of flame collision can be distinguished in three stages: independent propagation, strong interaction with flattened interfaces, and corner dynamics after merging of the interfaces. It is further demonstrated that propagation of the flame corner is controlled by the interacting mechanisms of preferential diffusion and kinematic restoration, that vorticity of considerable strength is generated downstream of the corner flame segment, and that the kinetic energy of the flame-generated vorticity is substantial as compared to those of the Kolmogorov eddies such that it could have strong influence on the turbulence energy spectrum and flame burning rate.

Movement vectors and deformation mechanisms in kinematic restorations: A case study from the Colombian Eastern Cordillera

We have developed a new method to assess the movement of particles in different steps of a well-calibrated sequential kinematic restoration. Calibration included correct assessment of amounts of overburden, sedimentation, erosion, and thermal behavior through time. Our method allowed a better understanding of the mechanisms of deformation and uplift in different geologic provinces. In our pilot case study in the Colombian Eastern Cordillera, we have used movement vectors in balanced cross sections to document an initial phase of dominant vertical uplift and a final phase of dominant tangential horizontal shortening. Our findings challenged the common assumptions related to folding and deformation mechanisms in fold-and-thrust belts used for cross-section balancing and palinspastic reconstructions. Thus, we found that the movement vectors in cross sections can be used to test and validate a complete procedure to obtain calibrated sequential kinematic restorations and represent a powerful tool to better understand deformation mechanisms in different settings.