The formation conditions and time sequences for various types of wrench-related fractures are not clear. Based on a parabola-type failure criterion, this paper has gotten new insights on those questions. In a simple s...The formation conditions and time sequences for various types of wrench-related fractures are not clear. Based on a parabola-type failure criterion, this paper has gotten new insights on those questions. In a simple shear, the occurrence of either tensional fractures or Riedel shears is controlled by the ratio (Rtc) of tensile strength to cohesion. In a pure shear, the occurrence of either second order tensional fractures or second order Riedel shears is controlled by the ratio (Rtci) of tensile strength to cohesion, given a constant inner frictional coefficient. Where the Rtc or the Rtci is less than a certain value, the en echelon tensional fractures will occur first. Where the Rtc or the Rtci is bigger than the certain value, the Riedel shears will occur first. Where the Rtc or the Rtci is equal to the certain value, the en echelon tensional fractures and the Riedel shears will occur simultaneously. The understandings will enhance the research on wrench related fractures and will be of significance in petroleum exploration and development, because fractures are both important accumulation spaces and key migration paths for oil and gas.展开更多
The work is a vivid description of the structural relationship between brittle deformation of the Precambrian basement in the southern continental part of the Cameroon Line and intrusive Paleozoic and Mesozoic basalt ...The work is a vivid description of the structural relationship between brittle deformation of the Precambrian basement in the southern continental part of the Cameroon Line and intrusive Paleozoic and Mesozoic basalt dykes swarms. A multidisciplinary approach that involves a combination of remote sensing techniques and field studies show that the major trend of brittle structures correspond to well-known regional structures: N70°E (Adamawa Shear Zone), N135°E (upper Benue trend) and N30°E (Cameroon Volcanic Line) corresponding to E-W and N-S directions respectively. Basalt dykes are associated to NE-SW, E-W and NW-SE oriented fractures. An integration of the available information on brittle structures and basalt dykes directions suggest an emplacement of the Mesozoic and Paleozoic basalt dykes structurally controlled by Precambrian structures that were originated through Riedel’s fracture kinematic model with dextral strike-slip Adamawa Shear Zone as the main shear zone during late stage of the Pan-African collision. Spatially, the restriction of the basalt dykes to the corridor of the Adamawa Shear Zone indicate that a rejuvenation of Precambrian faults may very well be the origin of the dykes with possibility that they may have been reworked several times during the Phanerozoic eon.展开更多
文摘The formation conditions and time sequences for various types of wrench-related fractures are not clear. Based on a parabola-type failure criterion, this paper has gotten new insights on those questions. In a simple shear, the occurrence of either tensional fractures or Riedel shears is controlled by the ratio (Rtc) of tensile strength to cohesion. In a pure shear, the occurrence of either second order tensional fractures or second order Riedel shears is controlled by the ratio (Rtci) of tensile strength to cohesion, given a constant inner frictional coefficient. Where the Rtc or the Rtci is less than a certain value, the en echelon tensional fractures will occur first. Where the Rtc or the Rtci is bigger than the certain value, the Riedel shears will occur first. Where the Rtc or the Rtci is equal to the certain value, the en echelon tensional fractures and the Riedel shears will occur simultaneously. The understandings will enhance the research on wrench related fractures and will be of significance in petroleum exploration and development, because fractures are both important accumulation spaces and key migration paths for oil and gas.
文摘The work is a vivid description of the structural relationship between brittle deformation of the Precambrian basement in the southern continental part of the Cameroon Line and intrusive Paleozoic and Mesozoic basalt dykes swarms. A multidisciplinary approach that involves a combination of remote sensing techniques and field studies show that the major trend of brittle structures correspond to well-known regional structures: N70°E (Adamawa Shear Zone), N135°E (upper Benue trend) and N30°E (Cameroon Volcanic Line) corresponding to E-W and N-S directions respectively. Basalt dykes are associated to NE-SW, E-W and NW-SE oriented fractures. An integration of the available information on brittle structures and basalt dykes directions suggest an emplacement of the Mesozoic and Paleozoic basalt dykes structurally controlled by Precambrian structures that were originated through Riedel’s fracture kinematic model with dextral strike-slip Adamawa Shear Zone as the main shear zone during late stage of the Pan-African collision. Spatially, the restriction of the basalt dykes to the corridor of the Adamawa Shear Zone indicate that a rejuvenation of Precambrian faults may very well be the origin of the dykes with possibility that they may have been reworked several times during the Phanerozoic eon.
