Using case studies discuss the extent to which regional tectonic activity may be deduced from meso-scale landforms - Essay Example

Using case studies discuss the extent to which regional tectonic activity may be deduced from meso-scale landforms Studies on geological structures,such as mountains, generally reflect the effect of deformation and tectonic activities. However, the geological history may involve other and possibly more moderate regional activities that are not evident in large-scale structures. Mesoscale structures, or structures in the order several meters, provide a more comprehensive geological history, particularly for moderate strain fields, than large scale structures.

Feinstein et al. (1999) studied the implications of mesoscale structures for deformational history in Moose Mountain of the Canadian Rockies. In their work, they measured the attitudes of meso-faults, striations of fault planes, veins and fold-axes, which comprise most of the mesostructures in the area. In addition, the sites studied provide a good three-dimensional cover of the Moose Mountain structure since they were located at various stratigraphic levels. Kinematic analysis of the mesostructures showed three different shortening directions changes during the evolution of Moose Mountain.

One of these directions is compatible with the large-scale geometry thrust-fault orientation of the study region. However, the remaining two directions are less obvious. This suggests that the mesoscopic strike-slip faults and veins developed later compared to small-scale reverse faults which formed earlier in association with the development of macro-scale thrust faults. Thus they were able to show that mesoscale structures can "discriminate modifications in regional strain directions and identify moderate episodes of deformation within deformed terrains".

Another case where mesoscale structures can deduce tectonic activity involves those in actual fault lines. In the study of Schulz and Evans (2000), they were able to determine the geophysical structure of Punchbowl Fault, an exhumed ancient trace of the San Andreas Fault, based on mesoscopic structures. The structures examined were fractures, small faults and veins, inventoried along three strike-perpendicular traverses along the fault. Based on their measurements, they were able to show that the fault-zone thickness is a function of the structure being measured.

Fractures and faults in the damaged zone are mainly at high angles to the main fault zone, despite having various orientations. Combining the results with geophysical imaging, the data suggests the existence of trapped headwaves traveling in the damaged zone. In addition, aftershock events produce slips and structures, which have orientations very different from the principal slip surface. Fractures associated with fault zones can also provide vital formation on its propagation, evolution and termination.

Young-Seog et al. (2003) mapped the well-exposed strike-slip faults in the northwestern part of Gozo Island, Malta, and were able to see three fracture, or damage, zones. These zones, namely the distributed damage, tip damage and, linking damage zones, describe a particular characteristic and region in the fault zone. By analyzing the characteristics of each damage zone, they managed to characterize local tectonic activities. In addition, they proposed three models for fault propagation and from these models, they were able to deduce the general direction of fault propagation.

Based on these studies, it was shown that despite the evident large-scale structures from tectonic activities, analysis of mesoscale structures can provide vital information on minor to moderate activities in a particular region. In addition, due to their size, mesoscale structures are more representative of regional tectonic activities than large-scale structures. Variations in regional tectonic activities may also provide crucial data on the general behavior and evolution of large-scale structures tectonic activities.

BIBLIOGRAPHY Feinstein, S., Eyal, Y. and Bell, J.S. (1999) Implications of meso-structures for deformational history of Moose Mountain structure, Canadian Rocky Mountain foothills. Journal of Structural Geology, 21, p.55-66. Schulz, Steven E. and Evans, James P. (2000) Mesoscopic structure of the Punchbowl Fault, Southern California and the geologic and geophysical structure of active strike-slip faults. Journal of Structural Geology, 22, p. 913-930. Young-Seog, Kim, Peacock, D.CP. and Sanderson, David J. (2003) Mesoscale strike-slip faults and damage zones at Marsalforn, Gozo Island, Malta, Journal of Structural Geology, 25, p. 793-812.