• 한국해양공학회지
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• 제4권1호
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• pp.35-42
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• 1990

The area where age dating of the seafloor and interpretation of geomagnetic basic structure are conducted is also important in the aspect of geophysics. Near the sea mount (water depth to the top is 3900m and 6500m to the bottom), there are Mesozoic magnetic lineations at the sea-side flank along the trench axis. A two dimensional model analysis of Talwani and Heirtzler(1964) and a three dimensional model analysis of Talwani are performed by using data obtained from the marine proton magnetometer. Distribution, direction of the lineation, amplitude and period of magnetic anomaly are correlated and analysed with speed of the plate movement and lineation of the sea mount. In the west and north-west Pacific there are lots of huge sea mounts retaining the history of oceanic crust. This indicates that geomagnetic basis subsided into the oceanic crust and has interest in the aspects of the isostasy theory of the gravity.

• 자원환경지질
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• 제40권2호
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• pp.171-189
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• 2007

경상분지 남동부에 위치한 양산단층 동편의 화강암질암, 화산암류, 퇴적암류를 대상으로 총 77개 지점으로부터 독립적으로 정향된 542개의 코어시료를 채취하여 대자율 이방성(AMS) 연구를 실시하였다. 총 대자율 측정, 고온대자율 실험 및 등온잔류자기 획득실험을 통하여 연구대상 암석들의 주 자성광물이 자철석 위주의 티탄자철석계열의 것임이 밝혀졌다. 연구의 주 대상암체인 화강암질암에는 자기적 엽리구조와 자기적 선구조 모두가 존재하고 있으며, 자기적 엽리구조의 주향은 북동-남서가 지배적이다. 이 자기적 엽리구조는 화강암질암의 변형에 대한 강한 저항의 물성, 주변 모암의 자기적 엽리구조와의 불일치, 고화 이후 취성변형으로 만들어진 소단층이나 절리 등의 지질구조와의 모순점, 현미경에서 관찰되는 조직 등의 증거로부터 마그마가 관입정치하여 완전히 고화되기 전에 응력을 받아 생성된 일차 미세구조(primary fabric)로 판단된다. 이 북동-남서 주향의 자기적 엽리구조는 북서-남동의 압축력으로 만들어질 수 있는데 이러한 응력은 양산단층의 좌수향 주향운동의 산물로 해석된다. 연구지역 화강암질암의 연령이 약 $60\sim70Ma$로 알려져 있음을 감안하면 양산단층은 이 시기(백악기 말에서 신생대 초)에 걸쳐서 좌수향 주향이동 운동을 하였음을 알 수 있다.

• 자원환경지질
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• 제23권1호
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• pp.59-71
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• 1990

Magnetic anisotropy of a total of 213 independently oriented Tertiary rock samples from Pohang-Ulsan area has been studied. The sampled strata comprise basalts, tuffs and black shale, and range in age from Eocene to Miocene. The previous palaeomagnetic studies indicate that their magnetic carrier minerals are titanomagnetites. Among 23 sampled sites, 11 sites were found to preserve magnetic load foliation parallel to the bedding plane caused by the Iithostatic load of the overlying strata. Other 4 sites showed magnetic lineation indicating the flow direction of lava and tuffs. The remaining 8 sites revealed the magnetic tectonic foliation nearly vertical to the bedding plane. This magnetic foliation is interpreted to be generated by tectonic compression which acted nearly horizontally during the solidification stage of the strata. The compression directions deduced from the tectonic foliation of the 8 sites can be grouped into internally very consistent two group: a N-S trending one and the other WNW-ESE trending one. It is interpreted that the former N-S compression was associated with the N-S spreading of the East Sea(Sea of Japan) and the dextral strike-slip movement of the Yangsan-Ulsan fault system. The latter WNW-ESE compression is interpreted to represent the folding and reverse faulting activity in the Korean and Tsushima straits during middle/late Miocene times.

• 자원환경지질
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• 제54권6호
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• pp.629-647
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• 2021

Located in the eastern part of the Anti-Atlas, the Tafilalet region shows numerous dykes and sills that crosscut the Paleozoic terrains. The magmatic structures (dykes and sills) of the Tadaout-Tizi n'Rsas (TTR) anticline is studied here, it located neighboring the main branch of the Anti-Atlas Major Fault (AAMF), known in this location as the Oumejrane-Taouz Fault (OJTF). The N20° to N60° trending dykes crosscut the Paleozoic formations (Ordovician to Devonian), whereas sills are injected into the Silurian and Devonian ones. The dyke swarms of TTR have been studied using the Anisotropy of Magnetic Susceptibility (AMS), petrographic study and structural analyses. The petrographic study of the TTR doleritic dykes shows a dominance of plagioclase feldspars, alkali feldspars, amphiboles, pyroxenes and biotite. The dykes contain also mesotype (natrolite), sphene (titanite), apatite, actinolite and pegmatitic enclaves of biotite, orthoclase feldspars and pelites. Concerning field works, they show the deformation of TTR dykes by the Variscan tectonics events, it is marked by the presence of displacements (strike-slip faults) and cleavages. The Magnetic Susceptibility (MS) measured on magmatic specimens show the dominance of ferromagnetic and paramagnetic minerals. The high values of MS in the dykes are due to the presence of hematite, amphibole, pyroxene and biotite. In addition their magnetic fabric, determined by our AMS study, allows us to reconstitute the tectonic event which affected the magmatic bodies. This one is characterized by a magnetic foliation and a NNW-trending lineation that reflect the Variscan shortening orientation.

• 자원환경지질
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• 제29권3호
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• pp.357-367
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• 1996

A total of 113 samples (basalts, tuffs, and siltstones from coal-bearing sediments) was collected from 14 sites of the Tertiary Changgi basin in southeastern Korea, and studied palaeomagnetically. Site-mean declination of the ChRM from 5 sites was found to be deflected clockwise about $30^{\circ}$. Other 5 sites showed no vertical-axis deflection of ChRM direction. In consideration of previous palaeomagnetic data from other Tertiary basins in the vicinity, it is interpreted that the deflection of ChRM directions has been caused by NNW-SSE simple shear associated with the opening of the East Sea, and the time of rotation should be about 16 Ma. Other 2 sites showed counterclockwise deflection of site-mean ChRM. These sites might be located among lager tectonic blocks which were rotating clockwise. AMS (anisotropy of magnetic susceptibility) study revealed $NE{\rightarrow}SW$ directed magnetic lineation at two tuffaceous sites. This might indicate flow direction of tuffs during the time of deposition. Most of the other sites showed load-foliation lying subparallel to the bedding plane. This must have been caused by gravitational loading acted vertically to the strata.

• 자원환경지질
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• 제30권6호
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• pp.613-624
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• 1997

A study of anisotropy of magnetic susceptibility (AMS) was conducted on the Ordovician-Eocene strata in the Taebaek area. The study area is a northeastern part of the Okchon belt, sometimes called as Paegunsan Synclinal Area. A total of 600 independently oriented samples were collected from 60 sites covering the whole area. With a few exception of late Cretaceous-Eocene volcanic rocks, all the sampled strata are nonmetamorphosed sedimentary rocks, mainly sandstones. Among the 60 sites, 5 sites showed flow lineation lying on the bedding plane, 11 sites showed load foliation parallel to the bedding plane, and 21 sites showed tectonic foliation unrelated to the bedding plane. The tectonic foliations are defined by $k_1-k_2$ ($k_{max}-k_{int}$) anisotropy plane, and are considered as a result of tectonic forces acted perpendicularly to the foliation plane in the geologic past. Regardless of sample-site locations, tectonic force directions defined by $k_3$ ($k_{min}$) axis perpendicular to the tectonic foliation are consistent among the strata of the same geologic age. In the course of geologic time, however, the tectonic force directions showed a clockwise rotation: approximately E-W in the Ordovician sites, NW-SE in the Permian sites, N-S in the Triassic sites, and lastly NE-SW in the late Cretaceous-Eocene sites. The pre-Permian directions showed better clustering in the in-situ (geographic) coordinates, while the younger directions become better clustered after the bedding-tilt correction. It is interpreted that the major tectonic structures of the Taebaek area were controlled by the above-mentioned tectonic forces: The Paegunsan Syncline and the Hambaeksan Fault must have been generated by the NW-SE force of late Permian-early Triassic time. It was then reactivated in the reverse (dextral) sense by the N-S force of Triassic time. The Osipchon Fault in the eastern part of the study area was either generated or reactivated by the NE-SW force of late Cretaceous-Eocene time. The Permo-Triassic NW-SE force should be an expression of the Songnim Disturbance in the Korean peninsula, which is in turn related with the SCB/NCB collision in China.

• 자원환경지질
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• 제43권6호
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• pp.625-636
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• 2010

본 연구에서는 울릉분지 북동부지역에서 획득한 중력, 자력, 수심자료 등 지구물리자료를 이용하여 이 지역의 지구물리학적 특성 및 지구조를 고찰하고자 하였다. 각각의 자료는 조사기간 및 사용 장비의 차이로 인하여 자료간의 오차가 나타나는데 상대적인 보정을 실시한 후 통합하였다. 울릉분지 북동부에 위치한 연구지역은 울릉도와 독도해산들, 그리고 한국해저간극으로 이루어져 있으며 최대수섬은 약 -2500 m를 보인다. 후리에어이상는 지형의 영향을 잘 반영하며 전체적으로는 울릉도와 독도 및 해산들에서 높은 값을 보인다. 부게이상은 해산들에 의한 국지적인 이상치를 보이지만 한국해저간극 및 울릉분지를 중심으로 고이상을 보이는데 이는 맨틀상승에 의한 영향이라 판단된다. 자기이상도를 살펴보면 화산체(섬과 해산들)들을 중심으로 복잡한 자기이상대를 나탄낸다. 연구지역 부게중력이상의 파워스펙트럼 분석으로부터 계산된 연구지역 모호면의 평균 깊이는 -16.1 km로 나타났다. 이 파워스펙트럼 분석을 이용하여 모호면 심도 역산을 수행하였다. 이 역산법으로 계산된 모호면의 심도는 한국해저간극지역에서 -16~17 km 정도이며 오끼뱅크 및 울릉도의 북서부쪽으로 갈수록 심도가 깊어지는 결과가 나타났다. 이 역산결과는 울릉분지의 해양지 각이 일반적인 해양지각에 비해 두껍다는 기존 결과와 일치한다. 2차원 중력 모델링 결과에서도 모호면의 심도가 해저면지진계 탐사측선이 지나가는 안용복해산과 독도 사이의 한국해저간극지역에서 얕은 것을 볼 수 있으며 오끼뱅크쪽으로 갈수록 깊어진다. 자화분포도에서는 울릉도와 독도 등 화산체에 의한 강한 자기이상대에 의해 나타나는 자화 분포대를 제외하면 주로 북동-남서방향의 선형배열이 나타난다. 섬도역산 결과, 2차원 중력모델링 및 자화분포 결과를 종합해보면 동해의 생성사 울릉분지의 가능성 있는 spreading center(해저면 확장중심) 위치가 한국해저간극에서부터 울릉분지까지 북동-남서 방향일 것이라는 기존 논문들의 주장과 부합된다고 판단된다.