Magnetic fabric (anisotropy of magnetic susceptibility) constraints on emplacement mechanism of clastic dikes

초록

Clastic dikes are generally classified into neptunian and injected dikes. Using the magnetic fabrics (AMS: anisotropy of magnetic susceptibility), we attempt to classify the clastic dikes in the Late Cretaceous Dadaepo Basin, SE Korea, and interpret their emplacement mechanisms. The neptunian dikes exhibit a typical oblate sedimentary fabric which makes a sharp contrast with the injected dikes. The fabrics of the injected dikes are greatly influenced by current conditions and transportation types of filling materials. Based on the AMS fabrics, they are classified into four types. (1) VP (vertical flow-parallel) type is formed by imbrication of long axis of grains in low- to moderate-energy vertical flow of a Newtonian fluid and characterized by a bilateral symmetry of fabrics across the dike. (2) VT (vertical flow-transverse fabric) type results from grain rolling in vertical high-energy flow and is characterized by subvertical k(2) and subhorizontal k(1) axes on the dike plane. (3) HP (horizontal flow-parallel) type is formed by imbrication of long axis of grains in horizontal low- to moderate-energy flow, resulting in subvertical k(3) and subhorizontal k(1) and k(2) axes. (4) HT (horizontal flow-transverse) type is formed by grain rolling in horizontal high-energy flow, resulting in streaked k(2)-k(3) on the dike plane and horizontally clustered k(1) axes. The AMS fabrics of each type can be a significant indicator for flow direction. Based on abundant AMS fabrics formed by high-energy current, coexistence of paleoseismic structures, and tectonic setting of the basin, earthquake-induced liquefaction is the most plausible trigger for the dike formation.

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