Composite Strike-Slip Deformation Belts and Their Control on Oil and Gas Reservoirs: A Case Study of the Northern Part of the Shunbei 5 Strike-Slip Deformation Belt in Tarim Basin, Northwestern China

Strike-slip deformation belts are interesting structures in the crust and are of significance in petroleum exploration. The Shunbei 5 fault belt (SB5), a long strike-slip deformation belt in the Tarim Basin, played an important role in the formation of a recently discovered major oilfield known as the Shunbei oilfield. In this study, models of plan view and vertical profile were established to interpret SB5 with multi-cycled tectonic activities. To this end, its structural framework, tectonic evolution, and associated plate tectonics were investigated using 2D and 3D seismic data. SB5 was formed as a dextral simple shear belt at the end of the Middle Ordovician. In the plan view, R-shears and P-shears with local transpressional and transtensional structures were observed. Along the vertical profiles, various structural styles occurred at various depths and strata in response to various stratigraphy mechanisms. Although these structures show clear boundaries between them, they correspond to the same formation time, indicating that they underwent deformation simultaneously. The second activity of SB5 occurred at the end of the late Ordovician, during which it was a dextral transtensional strike-slip deformation belt consisting of left-stepping en echelon R-shears. The R-shears were transtensional during the progressive deformation. Subsequently, SB5 underwent several strike slips of weak strength. Notably, SB5 cut through a deep Middle Cambrian gypsum salt layer and connected the deep Lower Cambrian source rock with deep Lower and Middle Ordovician carbonates to form the oil and gas reservoirs. The established models are of reference value in the interpretation of other subsurface strike-slip deformation belts.

YIELD POINT AND STRESS RELAXATION BEHAVIOR OF PLY-PLY INTERACTION OF THERMOSET PREPREGS

The forming of continuous-fiber composites is an automated manufacturing process capable of high production rates. Its greatest weakness lies in the tendency to develop wrinkle defects. The formation of wrinkle defects is the effect of a combination of multiple material deformation mechanisms. This paper investigates possible improvements for current manufacturing techniques by studying the interply properties of continuous-fiber thermoset prepreg. In this research, the inter-ply slip deformation behavior is tested via double lap shear tests. The results show that pressure, deformation rate, and moisture have a strong effect on the ply-ply interaction response. The multi-stage nature of the loaddisplacement response suggests the complex nature of the deformation. To better understand each stage of deformation, the total amount of slip deformation of the double lap shear test is measured. The total slip versus displacement profile indicates the presence of a yield point in the ply-ply interface. The yield point indicates both the softening of the ply-ply interface and the initiation of plastic deformation. The plastic deformation past the yield point can be further increased if the preform is held in a deformed state for some time before removing the external load. A new manufacturing process is proposed based on these results. One can take advantage of the yield point of the ply-ply interface and conform a preform onto an intermediate tool before conforming it onto the final tool. As deformation can be preserved once the material deforms past the yield point, this sequential forming approach can reduce the risk of wrinkling by reducing the slip required to complete the forming operation.

Connecting subduction, extension, and shear localization across the Aegean Sea and Anatolia

Summary The Eastern Mediterranean is the most seismically active region in Europe due to the complex interactions of the Arabian, African and Eurasian tectonic plates. Deformation is achieved by faulting in the brittle crust, distributed flow in the viscoelastic lower-crust and mantle, and Hellenic subduction but the long-term partitioning of these mechanisms is still unknown. We exploit an extensive suite of geodetic observations to build a kinematic model connecting strike-slip deformation, extension, subduction, and shear localization across Anatolia and the Aegean Sea by mapping the distribution of slip and strain accumulation on major active geologic structures. We find that tectonic escape is facilitated by a plate-boundary-like, trans-lithospheric shear zone extending from the Gulf of Evia to the Turkish-Iranian Plateau that underlies the surface trace of the North Anatolian Fault. Additional deformation in Anatolia is taken up by a series of smaller-scale conjugate shear zones that reach the upper mantle, the largest of which is located beneath the East Anatolian Fault. Rapid north-south extension in the western part of the system, driven primarily by Hellenic Trench retreat, is accommodated by rotation and broadening of the North Anatolian mantle shear zone from the Sea of Marmara across the north Aegean Sea, and by a system of distributed transform faults and rifts including the rapidly extending Gulf of Corinth in central Greece and the active grabens of western Turkey. Africa-Eurasia convergence along the Hellenic Arc occurs at a median rate of 49.8 mm/yr in a largely trench-normal direction except near eastern Crete where variably-oriented slip on the megathrust coincides with mixed-mode and strike-slip deformation in the overlying accretionary wedge near the Ptolemy-Pliny-Strabo trenches. Our kinematic model illustrates the competing roles the North Anatolian mantle shear zone, Hellenic Trench, overlying mantle wedge, and active crustal faults play in accommodating tectonic indentation, slab rollback, and associated Aegean extension. Viscoelastic flow in the lower crust and upper mantle dominate the surface velocity field across much of Anatolia and a clear transition to megathrust-related slab pull occurs in western Turkey, the Aegean Sea, and Greece. Crustal scale faults and the Hellenic wedge contribute only a minor amount to the large-scale, regional pattern of Eastern Mediterranean interseismic surface deformation.

Experimental Evidence and Characteristic Recognition of the Nanoweakening of Slip Deformation Zones

A central issue in the study of fault evolution is to identify shear weakening and its mechanism; currently, studies of fault weakening in narrow slip deformation zones, including those of various slipping planes such as schistosity, foliation, cleavage, joints and faults in rocks, are ongoing. To verify the nanoweakening in shear slipping, we carried out experiments: triaxial compression experiments on sandstones and uniaxial compression experiments on granites. Furthermore, on the basis of scanning electron microscopy (SEM) observations and experimental data analyses, we suggested three kinds of nanoweakening in terms of the corresponding strain stages: (1) The slip nanoweakening caused by the strain hardening deformation stage of the shear slip, which creates nanograins with dense coatings that may be due to the nanocoating on the shear planes, can result in rolling friction rather than with sliding friction, and the former is a principal mechanism of sliding nanoweakening. (2) The rheological nanoweakening caused by the strain softening deformation stage; in view of developing weakened deformation due to grain boundary migration (GBM), the flow of synkinematic minerals and melt coating phenomena lead to rheological nanoweakening. (3) The dynamic nanoweakening caused by thermal pressurization and fluid pressurization during the strain softening stage and strain degenerating stage. Thus, when these aspects are considered in defining the relationship between the nanoweakening at the slipping planes and the strain stages, the representative mechanism and its behavior rules can be obtained.

Synrift basin inversion: Significant role of synchronous strike-slip motion in a rift basin

In rift basins with superposed strike-slip deformation, the structural style of wrench elements and the roles they play in synrift architecture and evolution are important, poorly understood issues for basin analysis and hydrocarbon exploration. The NE-SW–striking Tan-Lu fault zone, located in eastern China, runs through the Liaodong Bay subbasin within the Cenozoic Bohai Bay Basin and experienced dextral strike-slip motion during the later synrift stage of the basin (ca. 40 Ma to 23 Ma). Investigations of the Liaodong Bay subbasin indicate that rift-fault reactivation and wrench-fault development during strike-slip reactivation were strongly controlled by the distribution and geometry of preexisting rift faults, and local synrift basin inversion, induced by strike-slip reactivation of a preexisting graben during a later synrift stage, was a significant manifestation of synchronous strike-slip motion modifying synrift architecture and evolution. Moreover, synrift basin inversion within the Liaodong Bay subbasin manifested in two ways. First, stronger inversion occurred along the restraining bends of preexisting extensional faults. This induced uplift of the footwalls of graben-controlling faults, leading to deformation characterized by abundant shortcut thrusts and folds. The Liaodong uplift formed via this mechanism, triggered by strike-slip movement along the Tan-Lu fault zone at ca. 40 Ma. Second, weaker inversion induced by newly formed, subvertical, strike-slip faults occurred near the central part of the graben, with the characteristics of positive flower structures. Although inversion was limited to a very local area along a narrow fault zone, it substantially modified the basin’s physiography. In this rift system, coincident with local inversion-induced uplift, large-scale, rift-related subsidence occurred beyond the inversion belt within the flanking graben, leading to complexity and variety in intrabasinal structural deformation and filling, and exerting a complex influence on hydrocarbon prospects. This model of synrift basin inversion has profound implications for the interpretation of inversion structures and basin dynamics in any rift basin with superposed strike-slip deformation.