Lake Fault Research Articles

U-Pb geochronology of detrital zircons from the Snow Lake pendant, central Sierra Nevada—Implications for Late Jurassic– Early Cretaceous dextral strike-slip faulting

The Snow Lake pendant is underlain by a thick (>1500 m) sequence of predominantly quartzite, marble, and schist that has previously been correlated with miogeoclinal strata of the western Mojave Desert. In this study, U-Pb analyses of detrital zircons from the Snow Lake pendant have been conducted to test for possible correlations with strata of the Cordilleran miogeocline, as well as nearby rocks of the Roberts Mountains allochthon and the Shoo Fly Complex. Zircons from Snow Lake strata yield dominant age groups that strongly support correlation of Snow Lake strata with miogeoclinal strata in the Mojave Desert. This correlation provides additional support for previous suggestions that the Snow Lake pendant was displaced ∼400 km northward along the Mojave–Snow Lake fault.

Tectonic implications of a petrographic and geochemical characterization of the Lower to Middle Jurassic Sailor Canyon Formation, northern Sierra Nevada, California

The Lower to Middle Jurassic Sailor Canyon Formation in the northern Sierra Nevada of California consists of basinal volcaniclastic and tuffaceous sedimentary rocks. Petrographic and geochemical data from the formation provide an opportunity to assess a proposed ∼400 km of pre–Late Cretaceous dextral strike- slip displacement on the cryptic Mojave–Snow Lake fault. A corollary to the proposed displacement is that Triassic-Jurassic volcanic complexes exposed in eastern California were the source for Sailor Canyon Formation sediments. However, geochemical data derived from volcanic rocks from this area are unlike those of the volcanic provenance characterized for the Sailor Canyon Formation. Comparisons of geochemical data suggest that contemporaneous volcanic centers exposed in western Nevada north of ∼38°N may be better candidates for the source of the volcanic material in the Sailor Canyon Formation. This interpretation implies that dextral strike-slip displacement on the Mojave–Snow Lake fault may be less than ∼200 km, a value that agrees with some interpretations of Mesozoic intrabatholithic displacements in the Sierra Nevada.

Transient strain accumulation and fault interaction in the Eastern California shear zone

Satellite synthetic aperture radar interferometry reveals transient strain accumulation along the Blackwater-Little Lake fault system within the Eastern California shear zone.

Determination of the origin of the Helvadere drinking springs by means of hydrochemical and isotopic techniques, Aksaray, Central Anatolia, Turkey

The main aquifer of the Helvadere springs that emerges on the strike-slip of the Hasandagi fault set alongside the Tuzgolu (salt lake) fault zone, and trends in a NW–SE direction of Aksaray city, in the western part of Central Anatolia, is the exposed rocks of Hasandagi which are volcanics that have distinct hydrogeological properties. The meteoric origin of the spring waters is deduced from hydrochemical and environmental isotope (18O, 2H, 3H) studies. The springs have high discharge (Q>100 l/s) and low ion concentrations because of fast circulation along the groundwater flow path in the aquifer. Furthermore, because it has Ca-Na-Mg-HCO3 hydrochemical facies, it conforms to high standards of drinking and irrigation water.

The coseismic geodetic signature of the 1999 Hector Mine earthquake

The M = 7.1 Hector Mine earthquake ruptured the Lavic Lake fault near Twentynine Palms, CA at 09:46 UTC October 16, 1999. Because it occurred near the eastern edge of the Southern California Integrated GPS Network (SCIGN), a network of permanent, continuously recording GPS receivers for measuring the crustal deformation field around Los Angeles, CA, it was possible to determine the deformation associated with the earthquake with unprecedented speed and reliability. Thirty‐four stations recorded displacements over the 3‐sigma level. The displacements measured with GPS can be modeled by a fault 46.2±2.6 km long, 8.2±1.0 km wide, striking 330°, dipping 84° east, with 301±36 cm right lateral strike‐slip, and 145±36 cm of east‐up dip‐slip, yielding a potency of 1.3 km³ and geodetic moment of 3.8 × 1026 dyne‐cm. The trace and dip of the model fault is consistent with the observed ground rupture and seismic focal mechanisms.

Structural history of the Manitouwadge greenstone belt and its volcanogenic Cu-Zn massive sulphide deposits, Wawa subprovince, south-central Superior Province

Structural analysis of the Manitouwadge greenstone belt, integrated with detailed mapping and geochronological and petrographic studies, reveals a complex early deformation history that significantly modified the primary distribution of base-metal deposits and alteration zones. The (D3) Manitouwadge synform dominates the map pattern; however, penetrative fabric development and establishment of the tectono-stratigraphy of base-metal deposits mostly predated D3. The D1 Garnet Lake fault, which repeats mineralized horizons within a distinctive lithological sequence, is delineated locally by annealed mylonite. D1 planar fabrics are preserved locally in outcrop and thin section. D2 folding accompanied peak regional metamorphism at upper amphibolite facies. The F2 Agam Lake syncline repeats the volcanic sequence across the southern limb of the Manitouwadge synform. A map-scale F2 sheath fold deforms the Garnet Lake fault. Minor D2 structures include prevalent outcrop-scale folds, locally with sheath geometry, the dominant S2 foliation, and mineral lineations (parallel to fold axes). Northwest-southeast-directed D3 shortening produced the Manitouwadge synform and related regional folds without extensive penetrative fabric development. Flexural slip folding is evident in the inner hinge of the synform where rocks of differing competency are interlayered. Higher strain, stronger fabric development, and a component of simple shear were preferentially partitioned to fold limbs. Relative pre-D3 structural geometries in the inner hinge region of the Manitouwadge synform are not significantly complicated by D3 and younger deformation. Retrodeformation of the mineralized sequence shows systematic stratigraphic patterns in iron formation types, stacked massive sulphide orebodies, and alteration types that can be applied to exploration models.

Influence of tectonism and climate on lithofacies distribution and sandstone and conglomerate composition in the Archean Beaulieu Rapids Formation, Northwest Territories, Canada

The 0.2–1 km thick Archean Beaulieu Rapids Formation is a late-orogenic, tectonically-controlled sedimentary sequence overlying the Beaulieu River volcanic belt unconformably on the west and bordering the major, N-trending Beniah Lake fault on the east. Local porphyry stocks, characteristic of late-orogenic successions, were emplaced along strike of the fault. Four lithofacies comprise the Beaulieu Rapids Formation: (1) the 20–320 m thick conglomerate I; (2) the 10–305 m thick siltstone–sandstone; (3) the 20–120 m thick conglomerate II; and (4) the 40–320 m thick quartz-rich sandstone. Lithofacies stacking displays two distinct, large-scale, fining-upward sequences represented by the 300–375 m thick conglomerate I and sandstone–siltstone (sequence A), and the 300–400 m thick conglomerate II and quartz-rich sandstone (sequence B). Fining-upward sequences, a bounding unconformity, and the Beniah Lake fault are compelling indicators of tectonic influence on sedimentation. Conglomerate I was deposited by debris flows, traction currents, and sheetfloods on the proximal, medial, and distal portions of alluvial fans or fan deltas, respectively. The overlying siltstone–sandstone contains two distinct lithological units. A sandstone-dominated unit formed from fluvial dune migration and overbank deposition in a sandy braidplain setting with scattered ponds, whereas sedimentary structures in the siltstone-dominated unit are consistent with lacustrine deposition. A second phase of tectonic uplift produced sequence B. Conglomerate II was deposited in a proximal braided stream setting characterized by abundant longitudinal gravel bars. The quartz-rich sandstone developed from dune migration on a sandy braidplain. Mineralogy and textures reflect high sediment influx, limited transport distance, local sources, and climatic influence. Clast populations in conglomerate indicate a prevalent mafic volcanic source, whereas sandstones contain prominent quartz (av. 76%) with subordinate feldspar (13%) and lithic fragments (11%). The disparity between clast and sandstone composition is a function of chemical weathering, typical of a humid climate. Source areas are restricted to the mafic-dominated Beaulieu River volcanic belt, the >2.8 Ga gneisso-plutonic Sleepy Dragon Complex, and fault-related porphyry stocks. The humid, weathering-aggressive Archean climate was responsible for destroying labile minerals and lithic fragments in proximal source rocks rich in plagioclase, accounting for the high quartz component in the sandstones. The Beaulieu Rapids Formation is similar to modern strike–slip basins that form along major fault zones in terms of basin geometry, faulted and unconformable contacts, lithological units, and sedimentary facies stacking and organization. Fault-controlled basins of this nature commonly develop during the last stage of terrane accretion on Archean cratons.

Abstract: The Age, Geometry, Kinematic, and Regional Tectonic Setting of the Glacier Lakes and Gemini Fault Zones, Central Sierra Nevada, California 

Abstract: The Age, Geometry, Kinematic, and Regional Tectonic Setting of the Glacier Lakes and Gemini Fault Zones, Central Sierra Nevada, California 

Late Quaternary slip rate and seismic hazards of the West Klamath Lake fault zone near Crater Lake, Oregon Cascades

Crater Lake caldera is at the north end of the Klamath graben, where this N10°W-trending major Basin and Range structure impinges upon the north-south–trending High Cascades volcanic arc. East-facing normal faults, typically 10–15 km long, form the West Klamath Lake fault zone, which bounds the graben on its west side. The fault zone terminates on the south near the epicentral area of the September 1993 Klamath Falls earthquakes. It continues north past Crater Lake as the Annie Spring fault, which is within ∼1 km of the west caldera rim, and Red Cone Spring fault. We have determined a long-term vertical slip rate of 0.3 mm/yr for these two faults using high-precision K-Ar and 40 Ar/ 39 Ar age measurements on offset lava flows ranging in age from ca. 35 to 300 ka. Holocene offset reported by Hawkins et al. and epicenters of eight M W 2 earthquakes in 1994 and 1995 indicate that the West Klamath Lake fault zone is active. Empirical relations between earthquake magnitudes and scarp heights or fault lengths suggest that the fault zone is capable of producing earthquakes as large as M W 7¼. Earthquakes on these or other faults of the zone could trigger landslides and rockfalls from the walls of the caldera, possibly resulting in large waves on Crater Lake.

Ages of prehistoric earthquakes revealed by cosmogenic chlorine-36 in a bedrock fault scarp at hebgen lake

Cosmogenic chlorine-36 reveals dates of the multiple prehistoric earthquakes that have produced a scarp on the Hebgen Lake fault. Apparent chlorine-36 ages are stratigraphically correct, follow a predicted theoretical pattern, and produce geologically reasonable model ages of 24, 20, 7.0, 2.6, 1.7, and 0.4 thousand years ago. This result demonstrates the feasibility of using cosmogenic chlorine-36 to extract paleoearthquake records from bedrock fault scarps.

Climatic and tectonic influences on fan deltas and wave- to tide-controlled shoreface deposits: evidence from the Archaean Keskarrah Formation, Slave Province, Canada

The 2.6 Ga Keskarrah Formation, located in the central Slave Province, Northwest Territories, Canada, is a late-orogenic, tectonically controlled sedimentary sequence that developed under unusual climatic and depositional conditions. The formation is adjacent to the crustal-scale, north-trending Beniah Lake Fault and overlies the 3.15 Ga Augustus Granite, the 2.69–2.7 Ga mafic volcanic Peltier Formation and the turbiditic Contwoyto Formation unconformably. Principal lithofacies in the Keskarrah Formation include conglomerate, sandstone and siltstone–sandstone. The conglomerate lithofacies represents coalescing gravelly streamflow-dominated fan deltas adjacent to topographic highs. Up-section quartz-rich arenites and quartz arenites of the sandstone lithofacies are interpreted to be shallow-water shoreface deposits influenced by wave action and tides. The overlying feldspathic litharenites of the siltstone–sandstone lithofacies are consistent with a lower shoreface to proximal offshore environment dominated by wave and tide interaction. Tidal influence in both sandstone-dominated lithofacies is inferred from the presence of mudstone laminae between bedforms and on foresets of cross-beds, as well as from abundant reactivation surfaces with local mudstone drapes. Intense chemical weathering during the Archaean, resulting from elevated atmospheric CO 2 levels, higher temperatures and moist climatic conditions, played an important role in the development of quartz-rich arenites that appear to be first-cycle deposits. Few lithic fragments and feldspar grains are preserved due to in-situ host rock weathering, chemical weathering during transport and wave and tide action. Hydraulic sorting and abrasion in the shoreface environment contributed to the continued breakdown and transport of labile minerals. Increased proportions of lithic fragments in sandstone beds of the conglomerate lithofacies are the result of shorter transport distances from source areas to the depositional environment. Abundant conglomerate with up to 4-m large granitic boulders derived from the adjacent Augustus Granite and mafic clasts from the Peltier Formation indicate high relief and fault-related uplift and subsidence. The intimate association of fan deltas and wave- and tide-influenced shallow-marine deposits in association with quartz-rich sandstones forming in a high-relief area make the Keskarrah Formation remarkable in the rock record.

The McEwan Lake fault: gravity evidence for a new structural element of the Kapuskasing zone

The Chapleau block, the largest uplifted crustal block within the Kapuskasing zone, continues, after sinistral offset of about 20 km, for a further 60 km to the southwest of Chapleau. This newly discovered extension, referred to as the Pineal Lake block, terminates to the west in a north-south-trending, west-verging thrust, named the McEwan Lake fault. New gravity data suggest that the fault has a vertical displacement of at least 5 km, a dip of about 25°E, and a length of at least 30 km. It is not known whether the fault crosscuts the Kapuskasing structure, in which case it may represent a younger thrusting event, or represents a southerly extension of the Saganash Lake fault that bounds the northwestern side of the Kapuskasing zone in the Chapleau area.

The McEwan Lake fault: gravity evidence for a new structural element of the Kapuskasing zone

The McEwan Lake fault: gravity evidence for a new structural element of the Kapuskasing zone

Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen‐parallel shear zone in the Cordillera of western North America

Results of an investigation of the petrology and structure of the Skymo complex and adjacent terranes constrain the amount, timing, and sense of motion on a segment of the > 600‐km‐long Late Cretaceous ‐ early Tertiary Ross Lake fault zone (RLFZ), a major orogen‐parallel shear zone in the Cordillera of western North America. In the study area in the North Cascades, Washington state, the RLFZ accommodated significant pre‐middle Eocene vertical displacement, and it juxtaposes the Skymo complex with upper amphibolite facies (650°–690°C and 6–7 kbar) Skagit Gneiss of the North Cascades crystalline core to the SW and andalusite‐bearing phyllite of the Little Jack terrane (Intermontane superterrane) to the NE. The two main lithologic units of the Skymo complex, a primitive mafic intrusion and a fault‐bounded block of granulite facies metasedimentary rocks, are unique in the North Cascades. Granulite facies conditions were attained during high‐temperature (> 800°C), low pressure (≤ 4 kbar) contact metamorphism associated with intrusion of the mafic magma. P‐T estimates and reaction textures in garnet‐orthopyroxene gneiss suggest that contact metamorphism followed earlier, higher pressure regional metamorphism. There is no evidence that the Skagit Gneiss experienced high‐T ‐ low‐P contact metamorphism. In the Little Jack terrane, however, texturally late cordierite ± spinel and partial replacement of andalusite by sillimanite near the terrane's fault contact with Skymo gabbro suggest that the Little Jack terrane experienced high‐T (∼ 600°C) ‐ low‐P (≤ 4 kbar) contact metamorphism following earlier low‐grade regional metamorphism. Similarities in the protoliths of metasedimentary rocks in the Skymo and Little Jack indicate that they may be part of the same terrane. Differences in pressure estimates for the Little Jack versus Skymo for regional metamorphism that preceded contact metamorphism indicate vertical displacement of ∼ 10 km (west side up) on the strand of the RLFZ that now separates the two structural blocks. High‐angle faults in the study area are dextral‐reverse mylonitic shear zones that experienced later brittle normal slip. Vertical motion on these shear zones before intrusion of Skymo gabbro can account for metamorphic discontinuities indicated by P‐T results. The terranes have also been internally deformed by nonintersecting but coeval dextral and sinistral shear zones that formed after the terranes were brought together in the RLFZ and intruded by Eocene dikes, These results show that the RLFZ has accommodated significant vertical displacement but perhaps no more than tens of kilometers of early Tertiary lateral movement. Structural evidence for earlier, large‐magnitude strike‐slip displacement is not preserved.

Tectonic Deformation of a Supersonic Naval Ordnance Research Track, Indian Wells Valley, California

The Supersonic Naval Ordnance Research Track (SNORT) located in Indian Wells Valley, California, is being used as a 6.55 km-long tiltmeter and geodetic alignment array. Our scientific usage is a direct result of the track profile and alignment requirements of the rocket powered test sleds used on the track. Data from six surveys during 1952 through 1986 have shown reversible elevation changes of 135 mm and cyclic horizontal changes of 30 mm between subsequent surveys. We attribute the changes to tectonic stress buildup and release associated with earthquakes of about magnitude M = 5, in 1961 and 1982, and to pulsations within a shallow magma body that underlies the SNORT area. Track deformations that occurred between 1984 and 1986 suggest that stress is again building along the nearby and highly active Little Lake fault, which has had three earthquakes of about magnitude 5 since 1938, with recurrence intervals of 21 years. These deformations may be precursors to a moderate-size earthquake that could occur within the next decade, or so.

Proterozoic reactivation of the southern Superior Province and its role in the evolution of the Midcontinent rift

Major reverse faults associated with the late compressional phase of the 1.1 Ga Midcontinent rift in the western Lake Superior region appear to cut across the rift at the eastern end of the lake and join with reverse faults on the eastern shoreline, defined on the basis of geological and potential field data. The continuation of the faults across eastern Lake Superior is inferred on evidence drawn from nearshore shipborne magnetic surveys together with new interpretations of published bathymetric and GLIMPCE aeromagnetic data. In the Archean Superior Province about 100 km east of Lake Superior, paleomagnetic and petrographic data from the 2.45 Ga Matachewan dyke swarm show that the Kapuskasing Zone, a narrow belt of uplifted crust, can be extended to within 50 km of the Lake Superior shoreline and has bounding reverse faults that are almost continuous with two faults of similar dip and sense of displacement that define the inversion of the Midcontinent rift in the central and western parts of the lake. Since the Kapuskasing Zone is dominantly a Paleoproterozoic (about 1.9 Ga) structure, the continuity suggests that the Lake Superior faults, whose last major activity was during the Grenville Orogen, may represent reactivation of much older faults that were part of an extended Kapuskasing structure. Within the Superior Province to the north and east of Lake Superior, published radiometric data on biotites suggest a series of alternating crustal blocks of varying tectonic stability, separated by northeast-trending faults. The Lake Superior segment of the Midcontinent rift developed within the most unstable block, bounded by the Gravel River fault to the northwest and the Ivanhoe Lake fault (the eastern margin of the Kapuskasing Zone) to the southeast.

Early Paleozoic (Cambrian to Early Devonian) Tectonic Framework, Canadian Cordillera

Uppermost Proterozoic to Lower Devonian rocks in the Cordillera of western Canada accumulated within two ancestral continental margin systems--the Canadian Cordilleran and southwestern Franklinian miogeoclines. These miogeoclines are separated by the Ogilvie Arch. Prominent features of the southwestern Franklinian Miogeocline are the Richardson Trough, a failed arm or aulacogen opening northward into the outer Franklinian Miogeocline, and, west and east of it, the Porcupine and Lac des Bois platforms. The Canadian Cordilleran Miogeocline formed in Late Proterozoic as the result of rifting, and although the newly formed margin was Atlantic-type, it continued to have distinct periods of rifting and extension with volcanism, throughout its history. The Canadian Cordilleran Miogeocline is divided by numerous northeast-trending linear features interpreted to reflect the position of ancestral strike-slip or transfer faults. More than six major block segments are recognized. From south to north they are: the Montana Block, bordered north by the Moyie-Dibble Creek fault systems; the Alberta Block, bordered north by the Hay River and Great Slave Lake fault systems, and divided into the Peace and Southern Prairies sub-blocks along the Rimbey Magnetic-Snowbird Tectonic zones; the Macdonald Block bordered north by the Liard Line; the Blackwater Block, bordered north by the Fort Norman Line; and the Mackenzie Block, bordered north by the southwestern Franklinian Miogeocline. Many facies changes occur across these blocks and their bounding ancestral transfer or strike-slip fault zones, and these or associated faults are likely keys to independent tectonic histories, such as that demonstrated by the Peace River Arch. The most prominent and well known northeast-trending lineament is the Liard Line. Apparent on geological maps of Canada, or the Canadian Cordillera, is a northeastward swing of structural trends north of this feature. The Canadian Cordilleran Miogeocline to the north shows extensive preservation of lower Paleozoic (to Lower Devonian) strata northeastward to the Canadian Shield, whereas to the south the same rocks are generally preserved in only the Cordilleran deformed belt. Although Lower Paleozoic rocks in the south have been substantially cut by younger erosional events, facies and thickness patterns, in fringing Lower Paleozoic strata, indicate that the pattern of erosion and nondeposition is as much due to Lower Paleozoic tectonics and paleogeography as it is due to younger exposure or erosion. This profound change, and the connection to the Franklinian, divides the Canadian Cordilleran Miogeocline into three fundamental parts. The Liard Line is interpreted to have been an ancient transfer fault zone across which there was a reversal in the direction of asymmetry within the master separation fault system that formed the ancestral continental margin in Late Proterozoic time. The wide area north of the Liard line has a large outer miogeoclinal basin (Selwyn Basin), discrete rift systems (Misty Creek Embayment, Mackenzie Trough, Root Basin), a peculiar zone of high crustal attenuation and sediment accumulation (Liard Depression). In addition, it is complicated by several different arches or highs (Mackenzie, Redstone, McConnell, Keele, Bulmer Lake, Niddery, etc.). This northern half of the Canadian Cordilleran Miogeocline has the characteristics of a lower plate margin and is here defined as the Northern Cordilleran Lower Plate Zone, comprising the Blackwater and Mackenzie blocks. The Canadian Cordilleran Miogeocline south of the Liard Line is narrowly preserved in the Cordillera and consists of the White River, Robson and Kechika troughs, and their marginal Macdonald and Bow platforms. The eastern miogeocline is dominated by Lower Paleozoic paleotopographic highs (Montania, West Alberta Ridge, Peace River Arch and Macdonald High). This southern zone has the characteristics of an upper plate margin and is here defined as the Southern Cordilleran Upper Plate Zone, comprising the Montana, Alberta and Macdonald blocks. A previous upper-lower plate model of the Canadian Cordilleran Miogeocline is reviewed and its criteria of width, structural complexity and uplift-subsidence are found to be useful as plate-type indicators. However, the use of gneisses to indicate lower crust, transitional gradients base on isopleths, and Cambrian zero edges are found to be equivocal. The Canadian Cordilleran Miogeocline non passive character is compared to that of Mesozoic-Tertiary continental margins, which are also fundamentally non passive, suggesting that models for plate tectonic drifting phases need to be revised.

The Slide Mountain Terrane and the structural evolution of the Finlayson Lake Fault Zone, southeastern Yukon

The Finlayson Lake Fault Zone forms a fundamental, but little studied, tectonic boundary between strata of autochthonous North America and the accreted Slide Mountain and Yukon–Tanana terranes in southeastern Yukon. A structural and petrologic study was undertaken to examine the depositional environment of the Slide Mountain Terrane, its tectono-thermal evolution in the fault zone, and its relationship with the Yukon–Tanana Terrane. The Slide Mountain and Yukon–Tanana terranes are divisible into units dominated by metavolcanic and metasedimentary rocks. Field observations and whole-rock geochemistry indicate that Slide Mountain greenstone is ocean-floor basalt deposited in a deep submarine basin with a proximal terrigenous sediment influx. Either a marginal- or ocean-basin setting is supported by the data. Slide Mountain greenstone is thrust northeastward over metasedimentary rocks of Slide Mountain Terrane and southwestward over rocks of the Yukon–Tanana Terrane. Regional metamorphic grade ranges from subgreenschist to greenschist facies. Pressure–temperature estimates for the subgreenschist–greenschist facies transition are 270–310 °C and 2.1–3.6 kbar (1 kbar = 100 MPa), based on assumed geothermal gradients and the reaction isograd Pmp + Chl = Act + Ep + H2O. Metamorphic peak postdates motion along the westernmost reverse fault that juxtaposes the Slide Mountain and Yukon–Tanana terranes. We interpret the Finlayson Lake Fault Zone as a northeasterly directed thrust sequence disrupted by synmetamorphic back thrusts. The back thrusting may be the consequence of shortening in the upper crust, or larger scale processes such as "tectonic wedging" of Yukon–Tanana Terrane under Slide Mountain Terrane.

Documentation of a 1450 Ma contractional orogeny preserved between the 1850 Ma Sudbury impact structure and the 1 Ga Grenville orogenic front, Ontario, Canada

A 1453–1445 Ma contractional deformation event is documented in rocks of the Early Proterozoic Huron Supergroup at the southeastern boundary between the Hudsonian craton to the northwest and an Early to Middle Proterozoic granitoid suite that forms the northeasternmost recognized extension of the Transcontinental Proterozoic Provinces. Detailed structural mapping, quartz c-axis fabrics, and grain-shape analysis indicate that four major orogenic phases have affected the area: (1) the Penokean orogeny, which predated the 1850 Ma Sudbury impact event, (2) ca. 1750 Ma granite plutonism, (3) ca. 1450 Ma orogenic events, and (4) the ca. 1000 Ma Grenvillian orogeny. The Murray fault zone, which likely accommodated considerable ductile displacement during the Penokean orogeny, underwent only brittle deformation during the younger orogenies. The previously undocumented Long Lake fault represents the northern limit of significant ductile south-over-north reverse thrusting during 1453–1445 Ma deformation. The effect of the Grenvillian orogeny in this area appears to have been minor. No deformation features could be linked to the intrusion of the ca. 1750 Ma granitoid suite.

Flow of Formation Waters, Aquifer Characteristics, and Their Relation to Hydrocarbon Accumulations, Northern Alberta Basin

Based on the wealth of data generated by the oil industry, the regional-scale characteristics of rocks, the flow of formation waters, and their relation to hydrocarbon accumulations were analyzed for the northern Alberta basin. The flow of formation waters in several aquifers and aquifer systems separated by intervening aquitards is at steady state and is driven by the present-day topography both on a regional and a local scale. The flow is generally from a recharge area in the southwest at the fold belt and Bovie Lake fault, to discharge in the northeast at the Great Slave Lake, the lowest point in the basin. The flow in Devonian aquifers is in open systems from recharge to discharge areas, whereas the flow in Carboniferous and Cretaceous aquifers is in semi-open systems, discharging into adjacent aquitards. Very high porosity and permeability in places in the Devonian Elk Point aquifer system are due to reefs, fracturing, dolomitization, and karst processes. Very high permeability probably leads to relatively high flow rates along the Presqu'ile barrier reef, resulting in local advective effects on the terrestrial heat transport to the surface. On a regional scale, all of the aquifers are underpressurized due to upstream propagation through high-permeability zones of low hydraulic heads at discharge elevations. The flow pattern is corroborated by salinity distributions, with comparatively lower salinity in each aquifer at recharge in the southwest and at discharge in the northeast caused by mixing with fresher meteoric water, and higher salinity between recharge and discharge areas. Salinity distributions show that the aquifers are not completely flushed of the original formation waters. Dissolution of salt and anhydrite from adjacent strata leads to high salinity in the Elk Point aquifer system and Beaverhill Lake aquifer. Hydrocarbons generated in the southwest in Devonian and Carboniferous strata, at maximum burial depth during the Laramide orogeny, migrated updip to the northeast driven by their own buoyancy and entrained by the flow of formation waters. Unless stratigraphically trapped by reefs and at the edge of semi-open aquifers, migration to the discharge areas led to loss of the volatile components and biodegradation into altered bitumens. The hydrostratigraphy and direction of the flow of formation waters in the northern part of the Alberta basin indicate that hydrocarbons generated in this region did not contribute to the formation of the giant Athabasca oil sand deposit located southeast of the study area.