Department of Geosciences

Late Quaternary faulting in the Kaikoura region, southeastern Marlborough, New Zealand

2013-06-12T16:05:41Z

Late Quaternary faulting in the Kaikoura region, southeastern Marlborough, New Zealand Van Dissen, Russell J. Active faults in the Kaikoura region include the Hope, Kekerengu, and Fidget Faults, and the newly discovered Jordan Thrust, Fyffe, and Kowhai Faults. Ages of faulted alluvial terraces along the Hope Fault and the Jordan Thrust were estimated using radiocarbon-calibrated weathering-rind measurements on graywacke clasts. Within the study area, the Hope Fault is divided, from west to east, into the Kahutara, Mt. Fyffe, and Seaward segments. The Kahutara segment has a relatively constant Holocene right-lateral slip rate of 20-32 mm/yr, and an earthquake recurrence interval of 86 to 600 yrs: based on single-event displacements of 3 to 12 m. The western portion of the Mt. Fyffe segment has a minimum Holocene lateral slip rate of 16 ± 5 mm/yr .(southeast side up); the eastern portion has horizontal and vertical slip rates of 4.8 ± 2.7 mm/yr and 1.7 ± 0.2 mm/yr, respectively (northwest side up). There is no dated evidence for late Quaternary movement on the Seaward segment, and its topographic expression is much more subdued than that of the two western segments. The Jordan Thrust extends northeast from the Hope Fault, west of the Seaward segment. The thrust has horizontal and vertical slip rates of 2.2 ± 1.3 mm/yr and 2.1 ± 0.5 mm/yr, respectively (northwest side up), and a maximum recurrence interval of 1200 yrs: based on 3 events within the last 3.5 ka. Drainage-divide elevation and mountain-front morphology of the Seaward Kaikoura Range, abundant evidence for recent activity on the Jordan Thrust, and lack of activity on the Seaward segment indicate that the late Quaternary displacement on the Hope Fault is transferred northward, west of the Seaward segment. The low slip rates for the thrust, compared to the higher lateral slip rates along the Kahutara and Mt. Fyffe segments, suggest that displacement on the Jordan Thrust does not accommodate all the displacement transferred from the Hope Fault. The remaining displacement is accommodated by distributed shear within the Torlesse rocks behind the thrust, and folds in front of and behind the thrust, although the latter was not documented for the Holocene. Graduation date: 1989

The Egan Range volcanic complex : implications for the evolution of a mid-tertiary synextensional volcanic system

2013-06-10T21:34:57Z

The Egan Range volcanic complex : implications for the evolution of a mid-tertiary synextensional volcanic system Feeley, Todd C. Graduation date: 1990

Stratigraphy and depositional environments of the Upper Devonian Fenstermaker Limestone, Eureka County, Nevada

2013-06-10T21:24:03Z

Stratigraphy and depositional environments of the Upper Devonian Fenstermaker Limestone, Eureka County, Nevada Waldman, Jeff L. The Upper Devonian Fenstermaker Limestone is a thickening-upward sequence of interbedded sandy intrapelsparite and subordinate calcareous siltstone and mudstone which averages 190 ft (58 m) thick in the northern Antelope Range. The Fenstermaker Limestone is revised and restricted herein to include only those rocks above a basinal shale sequence of the upper Denay Limestone and below the Mississippian Davis Spring Formation, and replaces the names "Devonian sandstone" of Trojan (1978) and the "Fenstermaker Wash Formation" of Hose and others (1982). Sandy limestone of the Fenstermaker Limestone was deposited rapidly, above upper Denay basinal shales, as resedimented beds in Frasnian Montagne Noir conodont zone 13 and the Lower Famennian Middle triangularis Zone. Reworked conodonts are present at numerous stratigraphic levels in the Fenstermaker, indicating erosion on the inner or middle carbonate platform during two Upper Devonian eustatic regressions (in lower and upper T-R cycle Ild; western U. S. events 7 and 8). Deposition of the Fenstermaker Limestone was by allodapic sediment gravity flows on an outer-shelf-basin ramp or at the toe of a low-angle (<4°) carbonate slope during incipient outer-shelf- basin filling, i.e. as reciprocal sedimentation. Detrital quartz sand averages 11% but ranges much higher in sand-rich laminae preserved in strata along the western range front. Sorting characteristics of the sand were attained in a siliciclastic beach environment prior to deposition in the carbonate lithotope. Pitting and frosting of grain surfaces are at least partially diagenetic in origin and not necessarily a product of eolian transport. Two allochthonous limestone blocks in the southern Fish Creek Range, northern Nye County (blocks A and C of Sans, 1986), are assigned to the Fenstermaker Limestone and are considered to have been derived from the west. Beds the age of the Fenstermaker Limestone are absent at an unconformity in the Cortez Mountains, west-central Eureka County. Detrital quartz sand concentrated along stylolites in the Upper Devonian part of the Popovich Formation, southern Tuscarora Mountains, northern Eureka County, were point-counted as an aid in determining formational thickness loss due to pressure-solution. Thickness reductions are estimated at 12-13%. Graduation date: 1990

I. Direction of maximum horizontal compression in western Oregon determined by borehole breakouts. II. Structure and tectonics of the northern Willamette Valley, Oregon

2013-06-10T20:37:20Z

I. Direction of maximum horizontal compression in western Oregon determined by borehole breakouts. II. Structure and tectonics of the northern Willamette Valley, Oregon Werner, Kenneth Stefan Elliptical borehole enlargements or "breakouts" caused by systematic spalling of a borehole wall due to regional maximum horizontal stresses were identified in 18 wells drilled in the Coast Range and Willamette Valley of western Oregon. The breakouts generally indicate a NNW to NNE orientation of maximum horizontal compression (oH[subscript max]) that agrees with the predominant direction of Gllmax determined from earthquake focal mechanisms, from post-middle Miocene structural features, and from alignments of Holocene volcanic centers in the Pacific Northwest. However, this orientation is inconsistent with the N50°E convergence between the Juan de Fuca and North American plates determined by Riddihough [1984] from Juan de Fuca plate magnetic lineations as young as 730 ka (the Brunhes-Matuyama boundary). The predominant NNW to NNE orientation of Gllmax may be due to the complex interaction of a northwestward-moving Pacific plate driving into the Gorda and Juan de Fuca plates and indirectly transmitting N-S compression across the strongly coupled Cascadia subduction zone into the overriding North American plate [Spence, 1989]. Alternatively, the predominant NNW to NNE orientation of cillmax may be due to a landward counterclockwise rotation of the direction of oHmax from N50°E compression offshore to N-S compression in the Coast Range. The northern Willamette Valley lies on the eastern flank of the broad northnortheast- trending Oregon Coast Range structural arch. Eocene to Oligocene marine sedimentary rocks crop out along the western side of the northern Willamette Valley and form a gently eastward dipping homocline. However, beneath the center of the Willamette Valley, Eocene to Oligocene strata are structurally warped up. During the Eocene several major volcanic centers subdivided the Coast Range forearc region into shallow to deep marine basins. Several such volcanic centers occur adjacent to the northern Willamette Valley and are associated with residual gravity anomaly highs and lineations. The top of basalt in the northern Willamette Valley (middle Miocene Columbia River basalt except near the valley margins) is contoured based on petroleum exploration wells, water wells, and seismic-reflection data. It is structurally downwarped to an altitude of less than -500 m just north of Woodburn. The downwarp is bounded to the south by the NE-trending Waldo Hills range-front fault and in part to the north by the NE-trending Yamhill River-Sherwood fault zone. The NW-trending Mt. Angel fault extends across the northern Willamette Valley between Mt. Angel and Woodburn and deforms middle Miocene Columbia River basalt and overlying Pliocene and Miocene fluvial and lacustrine deposits. The top of Columbia River basalt is vertically separated, NE side up, roughly 100 m based on seismic-reflection data near Woodburn, and 250+ m based on water-well data near Mt. Angel. The Mt. Angel fault is part of a NW-trending structural zone that includes the Gales Creek fault west of the Tualatin basin; however, a connection between the Gales Creek and Mt. Angel faults does not occur through Willamette River alluvial deposits. A series of small earthquakes (6 events with me = 2.0, 2.5, 2.4, 2.2, 2.4, 1.4) occurred on August 14, 22, and 23, 1990 with epicenters near the northwest end of the Mt. Angel fault. Routine locations indicate a depth of about 30 km. The preferred composite focal mechanism is a right-lateral strike-slip fault with a small normal component on a plane striking north and dipping steeply to the west. Both recent mapping of the Mt. Angel fault and the recent seismicity suggest that the Gales Creek-Mt. Angel lineament is similar to the Portland Hills-Clackamas River lineament found to the north. Together, these two lineaments may take up right-lateral strike-slip motions imposed on the upper plate by oblique subduction. Boring Lava appears to occur extensively in the subsurface of the northeastern portion of the northern Willamette Valley based on seismic data. Many of the faults in the area are interpreted to be largely caused by doming from influx of Boring magma or subsidence associated with evacuation of Boring magma. Such faults occur at Petes Mountain, at Parrett Mountain, along the Molalla River, and possibly near Curtis. The fault along the Molalla River appears to offset the Pleistocene (?) Rowland Formation 1 m (Glenn, 1965). Graduation date: 1991