243 research outputs found
Rock magnetic analysis for samples of the Napier Complex in the Mt. Riiser-Larsen area, East Antarctica
No full textP(論文)Samples collected at eight sites from granulites of the Archean Napier Complex and dolente dikes intruding the complex in the Mt. Riiser-Larsen area, East Antarctica, were analyzed rock-magnetically in order to assess the stability of their natural remanent magnetizations (NRMs). Results of isothermal remanence acquisition experiments and hysteresis measurements indicate the presence of magnetite in the pseudo-single to multi domain size, which is consistent with N. ISHIKAWA and M. FUNAKI (Proc. NIPR Symp. Antarct. Geosci., 10, 79, 1997). Stable magnetic components carried by fine-grained magnetites were isolated from some sites. Samples with such components may have a mixture of magnetites with different grain sizes although the effect of the mixing was not clearly observed. Heavily-deformed samples were found to be magnetically amsotropic, while magnetic fabrics of less-deformed samples indicate the possibility that the fabrics are of primary origin. The high-stability magnetic components from the less-deformed dolente samples of one site with primary magnetic fabrics may be of primary remanence acquired in the emplacement of the dike at 0.8-1.0Ga.departmental bulletin pape
Paleomagnetic study of the Mount Riiser-Larsen area in Enderby Land, East Antarctica
No full textP(論文)Paleomagnetic analyses were performed on samples of two sites from felsic gneiss of the Archaean Napier Complex and two sites from a dolerite dike (Amundsen dikes) in the Mt Rnser-Larsen area in Enderby Land, East Antarctica As a result of progressive demagnetization experiments, directions of the high-stability (H) components, carried probably by fine-grained magnetite, were determined for one dolerite and two gneiss sites Among the three sites, gneiss samples at the two sites were found to be magnetically amsotropic, while magnetic fabrics at the dolerite site indicated the possibility that the fabrics are of primary origin Based on the results of demagnetization experiments and magnetic amsotropy measurements, the H component direction of one dolerite site was regarded as a primary one Virtual geomagnetic poles of two sites form the dolerite dikes in this study and Ishikawa and Funaki (1998) appeared to be situated near the segment of the apparent polar wander path between 1 0 and 1 2 Ga for Australia in the East Gondwanaland frame It might be implied that East Antarctica and Australia formed East Gondwanaland at the time of igneous activity of the Amundsen dikesdepartmental bulletin pape
A report of rock sampling for paleomagnetic investigations by participating in the Australian National Antarctic Research Expedition (1987)
No full textThe author participated in voyage 6 of the Australian National Antarctic Research Expedition (ANARE) in the 1986/1987 season in order to collect rock samples for the study of paleomagnetism. A total of 501 samples were obtained from Heard Island, Larsemann Hills, Vestfold Hills, Scullin Monolith and Davis Station areas. The samples were collected mainly with an engine core drill and partially with a hammer. The directions of the samples were determined by the sun and the magnetic compasses. The author was impressed by the efficient field operations of ANARE using small helicopters and portable field huts called Apple Hut
A preliminary study of secondary magnetization during successive heating of rocks from the Napier Complex
No full textP(論文)Secondary magnetization produced during a thermal experiment in Thelliers' method was studied on 12 samples from the Mt. Riiser-Larsen area for that paleomagnetic data already been reported (N. ISHIKAWA and M. FUNAKI: Proc. NIPR Symp. Antarct. Geosci., 10, 79, 1997), and considered suitable for paleomagnetic study from the rock magnetic characteristics of samples. A remeasurement test of NRM on the same temperature step (NRM-check) as well as PTRM (PTRM-check) in air and in vacuum revealed secondary magnetization concerned with NRM and TRM which appeared at the same temperature, around 350℃, that would be explained by the oxidation of sulfide observed under a microscope. Secondary magnetization around 550℃ which appeared in air might also be caused by magneto-mineralogical change. These results are supported by the large variation of initial susceptibility around 300℃ and 550℃. Both the secondary magnetization of NRM and that of PTRM produced in vacuum were comparable to in air.departmental bulletin pape
ACQUISITION OF NATURAL REMANENT MAGNETIZATION IN SNOW AND ICE CONTAINING ROCK DUST
No full textP(論文)Paleomagnetic study of the dirt-ice collected at the Allan Hills in Antarctica showed stable remanent magnetization in the dirt-ice (FUNAKI and NAGATA, Mem. Natl Inst. Polar Res., Spec. Issue, 39,209,1985). However, the magnetization mechanism has not been investigated at all. We performed the experiments to make clear the magnetization mechanisms of the dirt-snow and dirt-ice. Two types of artificial samples were prepared for this purpose. One was the dirt-ice frozen from the wet-snow and the other was the dry-snow containing rock dust. The former samples acquired the stable remanent magnetization parallel to the geomagnetic field. This natural remanent magnetization (NRM) was acquired immediately during the freezing process from the wet-snow. The latter samples preserved under the low temperature conditions of both -10 and -20℃, acquired gradually the NRM in the direction of the geomagnetic field. The NRM's moment in the latter samples was not saturated during the 22-day preservation in the low temperature conditions. The acquisition of NRM advanced more effectively under the temperature of -10 than -20℃. The experimental data obtained indicate that the NRM of the dirt-ice and dirt-snow may become a useful means for paleomanetic and glaciological studies.departmental bulletin pape
The Paleomagnetic Investigation of Antarctica. 1. Paleomagnetism of Hut Point Peninsula Valcanic Sequence
No full textP(論文)Paleomagnetic studies of 10 basaltic rock masses collected from the Hut Point Peninsula of Ross Island, Antarctica, gave the following main results. (a) The positions of virtual paleomagnetic pole (VGP) (8 normals and 2 reverses) are within a polar cap area of about 30° in radius. (b) A synthetic summary of paleomagnetic, geological and geochronological data gives a time sequence of geologic history in this area, from the younger to the older, as Twin Crater Sequence (Brunhes epoch), Half Moon Crater (Jaramillo event), Observation Hill and Cape Armitage Sequence (Matuyama epoch), and Crater Hill and Castle Rock Sequence (older than Gilsa event).departmental bulletin pape
Paleomagnetic investigation of the Beacon Group in the McMurdo Sound region, Antarctica
No full textA total of 216 paleomagnetic samples of the Beacon Group (sandstone) were collected from Mt. Circe, Mt. Knobhead, Allan Hills and Mt. Fleming. The respective sedimentary sequences are Pre- or Early-Devonian, Devonian, Permo-Triassic and Triassic. The representative samples were tested for NRM stability against AF and thermal demagnetization, ARM and TRM acquisition, and AF demagnetization of ARM. The following results were obtained. The samples from Mt. Circe and Mt. Knobhead have stable NRM of parallel direction to that of the Ferrar dolerite. From this we conclude that these samples were remagnetized in the Jurassic Age and the primary magnetization disappeared. The samples from Mt. Fleming were also remagnetized by the dyke of the Ferrar dolerite or do not have stable NRM. However, parts of the samples from the Allan Hills have stable depositional remanent magnetization (DRM) of the Permo-Triassic Age. The direction of NRM for these samples is parallel to that of the Ferrar dolerite in the Jurassic Age. This suggests that East Antarctica had no shift of VGP. This conclusion is consistent with the results on the Mesozoic Age in Australia. Thus Australia must have been linked to Antarctica at least up to the Jurassic Age
Investigation of the paleomagnetism of the basement complex of Wright Valley, southern Victoria Land, Antarctica.
No full textPaleomagnetic investigation of McMurdo volcanics, Antarctica
No full textA total of 212 paleomagnetic samples were collected from the Hut Point Peninsula, the Cape Royds and the Taylor Valley in the McMurdo Sound, Antarctica. These samples have stable natural remanent magnetization. The results of paleomagnetic studies are as follows : (1) The position of Antarctica has been almost the same from the Late Pliocene Age up to the present. The position of the virtual geomagnetic pole (VGP) (11 normals and 3 reverses) from the Pliocene Age to the present is within a polar cap area of about 30°latitude, whose center is located almost exactly at the south geographical pole. (2) The sequence of lava eruption was determined by synthetic evidence from paleomagnetic, geological and geochronological data. The result revealed, from the latest to the earliest, Twin Crater Sequence and Cape Royds Sequence (Brunhes Epoch), Half Moon Crater Sequence (Jaramillo Event), Observation Hill Sequence, Cape Armitage Sequence (Matuyama Epoch), Crater Hill and Castle Rock (Olduvai or Reunion Events) and Taylor Valley Sequence (Kaena Event)
Temperature dependence of coercivity for chondrites: Allende, Allan Hills-769, and Nuevo Mercurio
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