Baikal rift zone: Structure and geodynamics
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Rift zone
Doming
geodynamics
Half-graben
Doming
Syncline
Anticline
Extensional fault
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In the region near Kulyab, Tadjikistan, hundreds of shallow earthquakes with magnitudes greater than 2½ have been reported in Soviet yearly catalogs since 1964. This area appears as a well‐defined cluster of activity, distant from the line of epicenters that defines the Gissar‐Kokshal seismic zone, to the north of the Pamir ranges. The geology of this region is dominated by the presence of numerous salt domes, surrounded by Neogene and Quaternary continental deposits. The spatial relationship between these earthquakes and the salt domes suggests that the two phenomena may be related. Moderate earthquakes (M > 5) occurred in 1972 and 1973, and intensities of surface shaking greater than MM=6 were reported from earthquakes in 1937, 1952, 1969, 1972, 1973 and 1978. The earthquake on 2 April 1973 and its aftershocks were located in a region where no salt domes have been mapped at the surface. However, a buried salt diapir has been mapped at depth by geophysical means. These earthquakes may result from active salt diapirism at depth. The mechanism for producing this seismicity could be either the active fracturing of the cap rock by the rising diapir, or the concentration of tectonic stresses in the thinned section above and adjacent to the diapir. The salt‐related earthquakes may produce lower frequency radiation than other events of the same size.
Salt dome
Doming
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Rift zone
Doming
geodynamics
Half-graben
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Salt tectonics
Overburden
Doming
Salt dome
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Doming
Dome (geology)
Escarpment
Seafloor Spreading
Growth fault
Anticline
Salt dome
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Overburden
Basement
Doming
Growth fault
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Rift zone
Doming
Half-graben
East African Rift
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Abstract. We used physical models to investigate the structural evolution of segmented extensional rifts containing syn-rift evaporites and their subsequent inversion. An early stage of extension generated structural topography consisting of a series of en-échelon graben. Our salt analog filled these graben and the surroundings before continued extension and, finally, inversion. During post-salt extension, deformation in the subsalt section remained focused on the graben-bounding fault systems whereas deformation in suprasalt sediments was mostly detached, forming a sigmoidal extensional minibasin system across the original segmented graben array. Little brittle deformation was observed in the post-salt section. Sedimentary loading from the minibasins drove salt up onto the footwalls of the subsalt faults, forming diapirs and salt-ridge networks on the intra-rift high blocks. Salt remobilization and expulsion from beneath the extensional minibasins was enhanced along and up the major relay/transfer zones that separated the original sub-salt grabens, forming major diapirs in these locations. Inversion of this salt-bearing rift system produced strongly decoupled shortening belts in basement and suprasalt sequences. Suprasalt deformation geometries and orientations are strongly controlled by the salt diapir and ridge network produced during extension and subsequent downbuilding. Thrusts are typically localized at minibasin margins where the overburden was thinnest and salt had risen diapirically on the horst blocks. In the subsalt section, shortening strongly inverted sub-salt grabens, which uplifted the suprasalt minibasins. New popup structures also formed in the subsalt section. Primary welds formed as suprasalt minibasins touched down onto inverted graben. Model geometries compare favorably to natural examples such as those in the Moroccan High Atlas.
Salt tectonics
Horst and graben
Monocline
Doming
Half-graben
Echelon formation
Salt dome
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Rift zone
Half-graben
East African Rift
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