Caldera is a volcanic structure, generally large, which is principally the result of collapse or subsidence into the top of a magma chamber during or immediately following eruptive activity. Our understanding of how volcanic calderas initiate and evolve structurally during subsidence is speculative,...
Caldera is a volcanic structure, generally large, which is principally the result of collapse or subsidence into the top of a magma chamber during or immediately following eruptive activity. Our understanding of how volcanic calderas initiate and evolve structurally during subsidence is speculative, because caldera formation has not been observed and because most internal structures of calderas are obscured by caldera fills and post-collapse intrusions. Existing ideas arise mainly from inferences from the surficial morphology and geology of young, extant calderas from pyroclastic sequences and from simple theoretical and analogue modeling. The Cretaceous Gyeongsang Basin, located in southeast Korea, formed in a back-arc setting during subduction of the proto-Pacific plate beneath the Eurasian Plate. During Late Cretaceous, a number of calderas formed by active volcanism associated with the subduction of the proto-Pacific plate. The Geumseongsan caldera whose floor is preserved and revealed by erosion has significant implications in terms of caldera researches. The Geumseongsan caldera is elliptical in shape, about 8×12 km, located in middle of the Uiseong sub-basin of the Gyeongsang basin. The caldera floor is consisted of sedimentary rocks, the Hayang Group; Sagok, Chunsan and Shinyang formations. The strata outside of the caldera strike northeast and dip at about 15°to the southeast. Dip angles of the strata in caldera floor range from 20°to 90° and symmetrically dipping toward its center, like a syncline fold. Four structural domains can be divided, based on strikes and dips of strata. The strata in NW-domain and SE-domain are dipping toward southeast and northwest, respectively. In NE-domain and SW-domain, the dip directions of the strata are rotated in a complex, occurred folds whose axis NE-trending and plunging to center. The geometry of caldera reconstructed offset by post-caldera sinistral strike-slip faulting has NNW-trending long axis. The deformation and dip-directions of the strata in caldera floor are symmetric about NE-trend. The NW- and SE-domains and the NE- and SW-domains dominantly occur extensional and contractional deformations, respectively. The tectonic force may control caldera geometry and deformations, resisting collapse in direction of compressive stress (NW-SE direction) and easy to collapse in direction of tensile stress (NE-SW direction). During collapse, horizontal mass movement in the NW-domain and the SE-domain toward caldera center was stronger than those of NE-domain and the SW-domain, but vertical mass movement is vice versa. In addition, the amount of depression in the NE-domain is larger than in the SW-domain. This difference of depression may cause the geometry of caldera elongate to NNW-trend rather than NW-trend.
Caldera is a volcanic structure, generally large, which is principally the result of collapse or subsidence into the top of a magma chamber during or immediately following eruptive activity. Our understanding of how volcanic calderas initiate and evolve structurally during subsidence is speculative, because caldera formation has not been observed and because most internal structures of calderas are obscured by caldera fills and post-collapse intrusions. Existing ideas arise mainly from inferences from the surficial morphology and geology of young, extant calderas from pyroclastic sequences and from simple theoretical and analogue modeling. The Cretaceous Gyeongsang Basin, located in southeast Korea, formed in a back-arc setting during subduction of the proto-Pacific plate beneath the Eurasian Plate. During Late Cretaceous, a number of calderas formed by active volcanism associated with the subduction of the proto-Pacific plate. The Geumseongsan caldera whose floor is preserved and revealed by erosion has significant implications in terms of caldera researches. The Geumseongsan caldera is elliptical in shape, about 8×12 km, located in middle of the Uiseong sub-basin of the Gyeongsang basin. The caldera floor is consisted of sedimentary rocks, the Hayang Group; Sagok, Chunsan and Shinyang formations. The strata outside of the caldera strike northeast and dip at about 15°to the southeast. Dip angles of the strata in caldera floor range from 20°to 90° and symmetrically dipping toward its center, like a syncline fold. Four structural domains can be divided, based on strikes and dips of strata. The strata in NW-domain and SE-domain are dipping toward southeast and northwest, respectively. In NE-domain and SW-domain, the dip directions of the strata are rotated in a complex, occurred folds whose axis NE-trending and plunging to center. The geometry of caldera reconstructed offset by post-caldera sinistral strike-slip faulting has NNW-trending long axis. The deformation and dip-directions of the strata in caldera floor are symmetric about NE-trend. The NW- and SE-domains and the NE- and SW-domains dominantly occur extensional and contractional deformations, respectively. The tectonic force may control caldera geometry and deformations, resisting collapse in direction of compressive stress (NW-SE direction) and easy to collapse in direction of tensile stress (NE-SW direction). During collapse, horizontal mass movement in the NW-domain and the SE-domain toward caldera center was stronger than those of NE-domain and the SW-domain, but vertical mass movement is vice versa. In addition, the amount of depression in the NE-domain is larger than in the SW-domain. This difference of depression may cause the geometry of caldera elongate to NNW-trend rather than NW-trend.
※ AI-Helper는 부적절한 답변을 할 수 있습니다.