TECTONIC SIGNIFICANCE OF STRATIGRAPHIC AND STRU ~ CT URAL CONTRASTS BETWEEN THE PURCELL ANTICLINORIUM ANC THE KOOTENAY ARC , EAST OF DUNCAN LAKE
The main goal of this study is to elucidate the wture and tectonic significance of the profound stratigraphic and struttural changes that occur between the crest of the Purcell anticlinorium and the Kootenay Arc. Reconnaissance (12.50 000) mapping by Reesor (1973) outlined conspicuous contrasts between the thick hasal Paleozoic (Hamill-Badshot) succession that overlies the Windermere Supergroup in the western Purcell Range and the thin, condensed early Paleozoic succession with overlapping Upper Devonian strata that occurs in the eastern Purcell Range. Reesor also described the abrupt contrast between the tight upright fold structures in this area and the refolded, west-verging, recumbent isoclinal folds that occur immediately to the west in the Kootcney Arc. He also showed that several small granitic plutons in the area probably were emplaced while the folding was still underway. The rocks exposed in this area (Figure 1-l-l ) record both the Late Proterozoic early Paleozoic birth and development of the Cordilleran miogeoclinal passive margin of North America (Bond and Kominz, 1984; Bond of a/., 1983, and the late Mesozoic -early Cenozoic deformation, regional metamorphism and granitic plutonism resulting from “collisions” between North America and a series of allochthonous terranes that have been accreted to it (Monger et al., 1982). Detailed geological mapping (I:50 000 and greater) was completed during July and August of 199 I and 1992 within an area of about 900 square kilometres in the western Purcell Mountains, between Duncan Lake and the headwaters of Tohy and Jumbo creeks (Figure I-I-2). This work will link the detailed mapping along the Kootcnay Arc by Fyles (I 964) to the detailed mapping by Root (I 987) and Pope (1990) in the central and eastern Purcell anticlinorium. The main objectives of this study are: (I) to establish the nature and tectonic significance of the stratigraphic rclationships within the thick sequence of Windermere, Hamill and Badshot strata in the study area; (2) to investigate the stratigraphic and tectonic relationships between these strata and the condensed onlapping early Paleozoic succession that occurs on “the Windermere high” to the east. below the Mount Forster thrust fault in the central and eastern Purcell Mountains (Root, 19X5: Reesor, 1973); (3) to establish the nature, evolution and regional tectonic significance of the change in structural style between the study area and the adjacent areas in the Kootenay Arc and in the central Purcell Mountains; and (4) to invest&ate the relation ship hetaeeo the initial structural configuration of the rifts d margin and the major structures that develc#ped during Me iozoic tenam: accretion and deformation of the margin.
Structure and Metamorphism
The Brioverian formations of the Armorican Massif have been involved in orogenic events generated by the plate tectonic regime during latest Proterozoic-Early Cambrian times; these gave rise to the Cadomian fold-belt which is contemporaneous with the Pan-African (sensu lato) and Avalonian progenies.
Archaeological Survey of Dangoyama Kofun by 3DGPR
We presented a three-dimensional ground penetrating radar (3DGPR) system for the archeological investigation in a harsh site, where we have to deal with many trees and/or great topographic variations. This system consists of a commercial GPR system with a laser positioning system. With this system, we can move the GPR antenna freely, on which a positioning detector can record accurate position for each GPR data trace. We applied our 3DGPR system at Dangoyama Kofun, a burial mound, in Fukushima prefecture, Japan. A lot of trees and bushes covered the survey area and cannot be cut. We acquired six datasets in two days in this area. We successfully imaged the boundary between the original surface of the burial mound and the covering soil clearly at about 0.3 m depth around the mound. Furthermore, we found some strong reflections appeared at 0.8 m depth in the top area of the mound, which can be from the artificial parts of the burial mound. The results would greatly aid the following archaeological excavation. In addition, we compared the non-interpolated depth slice with interpolated depth slice at same position and demonstrated that the interpolation process on threedimensional GPR data may introduce some artifacts which might mislead our interpretation.