The apparent polar wander path (APWP) for the Pacific plate during the Late Cretaceous and Early Cenozoic has been constrained primarily by seamount magnetic anomaly inversions and seafloor magnetic anomaly skewness. The reliability of these data types is uncertain and data are too sparse to provide a consistent or detailed APWP. In an effort to refine the Pacific APWP, we collected a larger, more diverse data set that allowed for the calculation of new mean paleomagnetic poles for the latest Cretaceous and Paleogene. We combined four types of data including sediment core paleocolatitudes, basalt core paleocolatitudes, seamount magnetic anomaly inversion declinations, and effective inclinations from magnetic anomaly skewness calculations. This diverse data set yields paleomagnetic poles that are less affected by bias from any particular data type. We found reasonably good agreement between data types and calculated five mean paleomagnetic poles representing the Oligocene (30 Ma), Late (39 Ma) and Early (49 Ma) Eocene, and Paleocene (61 Ma) epochs and the Maastrichtian (68 Ma) stage. Though a significant percentage of the data are from azimuthallyunoriented cores, which do not provide constraint on paleodeclination, a wide distribution of sites and the use of declination data from seamount anomaly inversions gave relatively good control on pole paleolongitude. The large numbers of data in our calculations allow for reasonably compact uncertainty bounds and the overall agreement among most data implies insignificant systematic errors in the data set. The greatest disagreement among data occurs due to a divergence between poles from anomaly skewness and other data types prior to 55 Ma. As a whole, the new APWP implies northward Pacific plate drift. However, this motion is punctuated with a stillstand from the Late Cretaceous (~80 Ma) until the middle Eocene, (~49 Ma). This stillstand suggests a lack of northward Pacific plate motion during this time, counter to most accepted models. This APWP is consistent with paleomagnetic results from the Emperor Chain that indicate the Hawaiian hotspot moved south during formation of the Emperor Chain, but it implies an amount of motion slightly greater than that previously proposed for hotspot drift.

The Marlborough Fault System is a zone of dextral transpression in continental crust at the southern end of the Hikurangi subduction system between the obliquely convergent Australian and Pacific plates. Detailed mapping of an area of deformed Tertiary cover sequence on the down thrown side of the Kekerengu Fault (the Kekerengu- Washdyke study area) has revealed two phases of deformation, D_e and D_l. In the study area De consists of nine kilometre scale thrust faults cutting sediments derived from extra- and intra-basinal uplift. The timing of this episode is constrained by the age of the first clastic deposits and by a previously unidentified unconformity in this area of Late Miocene age. A clear sequence of D_l events is recognized deforming all earlier structures including Pliocene aged sediments. Although elsewhere in Marlborough a regional post-Pliocene <i>ca.</i> 20° clockwise block rotation has been previously identified, in the Kekerengu-Washdyke study area one site suggested no post-Pliocene rotation and another a large <i>ca.</i> 100° clockwise rotation. This lack of D_l rotation was unexplained and the large rotation attributed to localized Early Miocene deformation. Palaeomagnetic work carried out in this study has identified six more sites which contain this large rotation (average <i>ca.</i> 118+11°). The rotation therefore appears to be a regional event, likely to be a result of the location of Marlborough in the hinge zone at the southern end of the Hikurangi Margin. One site from dykes in basement rocks does not record this large rotation, indicating that the rotation occurred in upper layers detached from unrotating rock below by an unknown structure (such as a thrust fault), or that the rotation did not occur in this area. The large rotation is believed to have been achieved by pinning of the D_e thrusts to the south of the Marlborough region. The data suggests that the D_e thrusts in Marlborough were initially NW-trending and seaward, not landward-directed as was previously supposed. Palaeomagnetic work has also added to the evidence for a lack of D_l regional rotation on the downthrown side of the Kekerengu Fault. A previously unidentified second phase of D_l folding and 'bending' within the study area appears to have accommodated the regional rotation and suggests that the Kekerengu Fault acted as the eastern boundary of the D_l rotating block.

Pliocene to Pleistocene glacial-marine deposits adjacent to the Fairweather Ground basement in the Gulf of Alaska are the focus for seismic interpretation using public domain seismic reflection data. The late Tertiary and early Quaternary sections of the Yakataga Formation record a glacial/ interglacial climate change sequence with increasing rates of sedimentation (175 meters per million years to 4000 meters per million years). The foreland basin sediment load is deposited onto the Yakutat block, a microplate that takes up the strike-slip to convergent movement with respect to North America and Pacific plates. Tectonic activity during the last 5 million years has resulted in Eocene rock exposed at the sea floor. High resolution bathymetry data adjacent to the Yakutat microplate is utilized to 1) observe the results of deformation from Pacific plate loading on the Yakutat microplate and 2) interpret the Transition fault as an active thrust to oblique thrust fault.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24175号 / 理博第4866号 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 成瀬 元, 准教授 河上 哲生, 教授 田上 高広 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM