Block Rotation Model Research Articles

Late Mesozoic-Cenozoic strike-slip and block rotation in the inner belt of southwest Japan

The inner belt of Southwest Japan is located in the region north of the Median Tectonic Line (MTL), which is the largest strike-slip fault in the Japanese Islands belonging to an island-arc system. The inner belt is divided into ten or more small blocks bounded by active faults and geological tectonic lines. The blocks are 20 to 80 km in width and approximately 200 km in length. The width and the length have remained nearly constant during the long history since the Late Cretaceous. Significant igneous activity has occurred along boundaries of the blocks from the Late Cretaceous to the present. With the use of a geometrical strike-slip and block rotation model, the small blocks were rotated in such a way that they are to be rearranged in parallel with each other at the time of the block formation. The inner belt of Southwest Japan was then placed north of its present location to the position occupied in mid-Cretaceous time. With this configuration the inner belt is found to be situated between two major strike-slip faults; the MTL and the Sikhote-Alin fault. Faulting and igneous activity that occurred from the Late Cretaceous to the present can be geometrically interpreted by the strike-slip and block rotation model which induces left-lateral slip movement of the two major bounding faults. Main plutonic activity occurs at triangle gaps generated by the block rotation. Other igneous activity occurred along block terminations block boundary faults and Riedel shear fractures inside the block. Bending of Southwest Japan occurred along three block boundaries: the Itoigawa-Shizuoka Tectonic Line, the Tsurugawan-Isewan Tectonic Line and the Hanaore-Kongo fault line, during the opening of the Sea of Japan Blocks raised by underthrusting during the rotation of the inner belt due to the opening of the Sea of Japan at about 15 Ma have continued to tilt, even at present. Most earthquake faults were generated along block boundary faults, while a few earthquake faults also appearing along Riedel shear fractures that originated from the block boundary faults.

3-D Block Rotation in the West Transverse Ranges: the Key to Structure History and Basin Development: ABSTRACT

Block rotation is widespread in regions of distributed shear. As rigid block-faulted domains rotate, gaps open up along their boundaries and sedimentary basins may develop. The evolution and the geometry of these basins is controlled by the slip history of the faults that bound them. To unravel their history, a three-dimensional (3-D) model was developed that combines the kinematics of block rotation with the mechanics of faulting. As an example, the authors present a 3-D computer simulation for the history of rotation of the west Transverse Ragges domain, southern California. A set of preexisting faults, striking north-northeast, is allowed to slip and rotate in accordance with known friction criteria. Rotation is assumed to occur in the strike-slip stress regime. The principal stress axes are assumed fixed in the present-day orientation throughout the deformation. Therefore, as faults slip and blocks rotate, the sense of motion along the faults changes. This simulation predicts, in agreement with the observations, an initial period of normal motion along the reactivated faults. Upon fault slip and block rotation the same faults go through a phase of strike slip. With further slip and rotation they eventually become the east-west-striking oblique reverse faults that characterize the present-day tectonicsmore » of this domain. The model shows that a single set of faults can experience both dipslip and strike-slip motion throughout its deformation history within a strike-slip stress regime. It is not necessary to appeal to complex and arbitrary changes in the orientation of the stress field. Only by combining a 3-D block rotation model with structural and paleomagnetic data may it be possible to unravel the complex tectonics of distributed deformation and basin evolution.« less