Northward motion of the Whitehorse Trough: paleomagnetic evidence from the Upper Cretaceous Carmacks Group

1988 ◽  
Vol 25 (12) ◽  
pp. 2005-2016 ◽  
Author(s):  
Guy Marquis ◽  
Brian R. Globerman
Keyword(s):  
British Columbia ◽  
Upper Cretaceous ◽  
Middle Eocene ◽  
Critical Evaluation ◽  
Volcanic Rocks ◽  
Rocky Mountain ◽  
Andesitic Lava ◽  
Western Cordillera ◽  
Kinematic Models ◽  
Volcaniclastic Deposits

The Upper Cretaceous Carmacks Group (70.4 ± 2.4 Ma) comprises gently dipping basaltic and andesitic lava flows overlying volcaniclastic deposits of the Intermontane Belt in the Whitehorse Trough. The sampling area is in southern Yukon and northern British Columbia; it lies west of the Tintina – Northern Rocky Mountain Trench fault and Teslin Suture Zone and east of the Denali – Shakwak fault. Volcanic sections were sampled in three regions spread over 300 km, providing the first paleomagnetic data from pre-Tertiary volcanic rocks in the northern Canadian Cordillera. Alternating-field and thermal demagnetization revealed stable magnetization for 18 of the 27 sites collected. The overall mean direction (D = 166.7°, I = −71.4°, k = 53, α95 = 4.8°, N = 18 sites) is pre-folding and is most probably primary (latest Cretaceous). This gives a paleopole at 109.4°E, 82.1°N, K = 21, A95 = 7.8°. A critical evaluation of North American cratonic data yields a reference paleopole for the latest Cretaceous at 185.8°E, 77.7°N, A95 = 7.7°, implying 13.4 ± 8.5 °(1500 ± 950 km) northward displacement and 10.2 ± 20.7 °(not significant) clockwise rotation of the Whitehorse Trough. The displacement occurred between 70.4 ± 2.4 and 59 – 54 Ma, the "docking" time suggested by other paleomagnetic studies in Alaska. The amount and timing of this displacement are consistent with Gabrielse's estimate of cumulative dextral displacements along the Northern Rocky Mountain Trench fault and associated lineaments. As expected, it is intermediate between the low paleolatitudes observed from middle Cretaceous rocks and the concordant paleolatitudes observed in Middle Eocene rocks of the Western Cordillera farther south, in British Columbia and in northern Washington. The estimated displacement is consistent with those predicted by kinematic models of Engebretson and Umhoefer based on North Pacific Basin plate motions.

Petrology and geochemistry of the Kamloops Group volcanics, British Columbia

1981 ◽  
Vol 18 (9) ◽  
pp. 1478-1491 ◽  
Author(s):  
Thomas E. Ewing
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Primary Source ◽  
Low Pressure ◽  
Rock Types ◽  
South Central ◽  
High K ◽  
Petrology And Geochemistry

The Kamloops Group is an alkali-rich calc-alkaline volcanic suite of Early to Middle Eocene age, widespread in south-central British Columbia. Rock types in the suite range from high-K basalt through andesite to rhyolite. The suite is characterized by relatively high K2O, Sr, and Ba, but low Zr, Ti, and Ni concentrations, only moderate Ce enrichment, and little or no Fe enrichment. Initial ratios 87Sr/86Sr are about 0.7040 in the western half, and about 0.7060 in the eastern half of the study area. No difference in chemistry or mineralogy marks this sharp transition. Chemically similar suites include the Absaroka–Gallatin suite in Wyoming and the lower San Juan (Summer Coon) suite in Colorado. The content of K2O at 60% SiO2 increases regularly eastward across southern British Columbia. The chemical data support the subduction-related continental arc origin of the Kamloops Group volcanics.The volcanic rocks consist in the main of augite–pigeonite andesites ranging from 52 to 62% silica, with subordinate quantities of olivine–augite–pigeonite basalt and biotite rhyodacite and rhyolite. The andesites and basalts were derived by a combination of low-pressure fractional crystallization, higher pressure fractional crystallization, and variable parental magmas, whereas low-pressure fractional crystallization of plagioclase, biotite, and apatite from parental basalt and andesite produced the rhyolites. The parental magmas were basalts and basaltic andesites with high K, Sr, and Ba. The primary source of these magmas is inferred to have been an alkali-enriched hydrous peridotite with neither plagioclase nor garnet present in the residuum.

scholarly journals An Eocene brontothere and tillodonts (Mammalia) from British Columbia, and their paleoenvironments

2017 ◽  
Vol 54 (9) ◽  
pp. 981-992 ◽  
Author(s):  
Jaelyn J. Eberle ◽  
David R. Greenwood
Keyword(s):  
British Columbia ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Open Water ◽  
Late Eocene ◽  
Mean Annual Precipitation ◽  
Mean Annual Temperature ◽  
Forested Landscapes ◽  
Radiometric Ages ◽  
Age Range

We describe Eocene fossils of the tillodont Trogosus from the Allenby Formation in Princeton, British Columbia (B.C.), as well as teeth of Brontotheriina from the lower Australian Creek Formation near Quesnel, B.C. These fossils represent the only occurrence of Tillodontia and Brontotheriidae in B.C. Further, the presence of the largest species of Trogosus — T. latidens — as well as a smaller species identified only as Trogosus sp. supports a late early – early middle Eocene (Bridgerian) age for the Vermilion Bluffs Shale of the Allenby Formation. Based on their morphology and large size, the teeth referred here to Brontotheriina represent one of the larger, more derived brontothere genera, and suggest a Uintan–Chadronian (middle–late Eocene) age range for the lower Australian Creek Formation that is consistent with radiometric ages of underlying volcanic rocks. Paleobotanical data from sediments correlative to those that produced these Eocene mammal fossils suggest they inhabited forested landscapes interspersed with swamps and open water environments, under mild and wet temperate climates (mean annual temperature (MAT) ∼10–16 °C; cold month mean temperature (CMMT) −4–4 °C; mean annual precipitation (MAP) >100 cm/year). These mixed conifer–broadleaf forests included tree genera typical of modern eastern North American forests (e.g., Tsuga, Acer, Fagus, and Sassafras), together with genera today restricted to east Asia (e.g., Metasequoia, Cercidiphyllum, Dipteronia, and Pterocarya). The paleobotanical evidence is consistent with the hypothesized habitats of both tillodonts and brontotheres.

Interpretation of structures in the southeastern Nechako Basin, British Columbia, from seismic reflection, well log, and potential field data1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia.2Geological Survey of Canada Contribution 20100002.

2011 ◽  
Vol 48 (6) ◽  
pp. 1000-1020 ◽  
Author(s):  
Nathan Hayward ◽  
Andrew J. Calvert
Keyword(s):  
British Columbia ◽  
Potential Field ◽  
Seismic Reflection ◽  
Middle Eocene ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Late Eocene ◽  
Strike Slip ◽  
Potential Field Data ◽  
The North

The structure and stratigraphy of the southeast Nechako Basin, which are poorly understood primarily because of substantial volcanic cover, are investigated in an analysis of seismic reflection, well, and potential field data. Formation and development of the SE Nechako Basin resulted in sub-basins containing Cretaceous and Eocene rocks. Interpretation reveals that dextral transtension in the Early to Middle Eocene created NNW-trending, en echelon, strike-slip faults linked by pull-apart basins, which locally contain a thickness of Eocene volcaniclastic rocks of >3 km. This structural pattern is consistent with regional observations that suggest the transfer of slip from the Yalakom fault to the north via a series of en echelon strike-slip faults. In the Middle to Late Eocene, faults associated with a change in the direction of stress, echoed by the north-trending right-lateral Fraser fault, reactivated and cut earlier structures. A simple model agrees with local observations, that northeast-directed compression was subparallel to the relic Cretaceous grain. Cretaceous rocks are discontinuous throughout the basin and may be remnants of a broader basin, or a number of contemporaneous basins, formed in a regional transpressional tectonic setting that caused northeast-directed thrusting along the eastern side of the Coast Plutonic Complex. Results suggest that thrusting affected most of the SE Nechako Basin, as observed across the Intermontane Belt to the northwest and southeast. The pattern of deposition of Neogene volcanic rocks of the Chilcotin Group was in part controlled by the Eocene structural grain, but we find no evidence of Neogene deformation.

Syngenetic magnetic anomaly sources: Three examples

Geophysics ◽  
1991 ◽  
Vol 56 (7) ◽  
pp. 902-913 ◽  
Author(s):  
S. Parker Gay ◽  
Bronson W. Hawley
Keyword(s):  
Central America ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Rocky Mountain ◽  
Magnetic Anomalies ◽  
Magnetic Minerals ◽  
Subsurface Geology ◽  
South Central ◽  
Different Types ◽  
Source Materials

Aeromagnetic anomalies encountered in three areas, two in the western United States and one in Central America, are shown to arise from magnetic sedimentary formations. These examples are selected from a larger number of similar areas surveyed by Applied Geophysics, Inc. in various places in the U.S. Midcontinent and Rocky Mountain regions. The first area discussed is the northwest corner of Nebraska where the Miocene Arikaree formation, comprised of magnetic airfall and windblown tuffs, causes anomalies in areas of incised topography. The second area is located in south central Utah, where the Upper Cretaceous Kaiparowits sandstones contain detrital magnetite that causes large anomalies in tilted structures and over incised topography. The third area treated covers over half of southern Belize in Central America, including much of the offshore portion. Here, the Toledo formation of Paleocene‐Eocene age contains a thick section of clastic detritus rich in lithic grains of volcanic rocks that produce magnetic highs over thrusted and folded anticlinal axes. These three examples of magnetic anomalies due to syngenetic magnetite in widely scattered areas and from different types of source materials bring into question the assumption of so‐called “diagenetic magnetite” (or other magnetic minerals) as a cause of magnetic anomalies in other petroleum basins. It is necessary in all cases to determine the magnetic source from surface or subsurface geology, as was done here, rather than making assumptions strictly from magnetic profiles or mathematical models.

Petrology of a supra-subduction zone ophiolite (Elaz1g, Turkey)

2000 ◽  
Vol 37 (10) ◽  
pp. 1411-1424 ◽  
Author(s):  
Melahat Beyarslan ◽  
A Feyzi Bingöl
Keyword(s):  
Upper Cretaceous ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Island Arc ◽  
Granitic Rocks ◽  
Late Triassic ◽  
Geochemical Data ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Magmatic Suite

The Elaz1g region in eastern Taurus, Turkey, exposes Paleozoic-Tertiary metamorphic, magmatic, and sedimentary units. Contacts between the different units are mostly tectonic, but there are also primary sedimentary, and intrusive contacts. The metamorphic rocks of the Elaz1g region are the Bitlis-Pütürge and Keban-Malatya massifs, which are a single tectonostratigraphic unit that has been tectonically disrupted and fragmented during the Upper Cretaceous. Magmatic rocks in the region are represented by ophiolitic units, magmatic arc products, and young volcanic rocks. The sedimentary units are represented by Upper Cretaceous - Tertiary marine and lacustrine sedimentary rocks. In the study area, the metamorphic units are represented by the Paleozoic Pütürge metamorphic rocks composed of phyllite, slate, mica schist, quartz-muscovite schist, calc-schist, and low-grade metamorphite. The ophiolite that is described in this paper is composed of wehrlite-pyroxenite, gabbro, diabase dykes, and dykes cutting gabbro. These units are cut by the granitic rocks of the Upper Cretaceous Elaz1g magmatic suite. The lithological and geochemical data on the rocks of Kömürhan ophiolite indicate that these rocks were derived from crystallization of an enriched mid-ocean ridge basalt (MORB)-type magma. The Kömürhan ophiolite formed in a supra-subduction spreading zone during the Cretaceous; related to this event is the north-dipping subduction of the southern branch of Neo-Tethys ocean, which began spreading in the Late Triassic. The crust was thickened by the development of an island arc and by the thrusting of the Pütürge metamorphic rocks onto this island arc in response to north-south compression during the Late Cretaceous. The magma formed by partial melting of the subducted slab giving rise to granitic rocks that cut the upper parts of the ophiolite. The ophiolite and the Elaz1g magmatic suite attained their present position after the Middle Eocene.

Tip Top Hill volcanics: Late Cretaceous Kasalka Group rocks hosting Eocene epithermal base- and precious-metal veins at Owen Lake, west-central British Columbia

1992 ◽  
Vol 29 (5) ◽  
pp. 854-864 ◽  
Author(s):  
Craig H. B. Leitch ◽  
C. T. Hood ◽  
Xiao-Lin Cheng ◽  
A. J. Sinclair
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Lake Area ◽  
Vein Deposit ◽  
Type Area ◽  
Lake Formation ◽  
Host Rocks ◽  
Polymictic Conglomerate

Rocks hosting the Silver Queen epithermal Au–Ag–Zn–Pb–Cu vein deposit near Owen Lake, British Columbia, belong to the Tip Top Hill volcanics. They are lithologically similar to the informally named Upper Cretaceous Kasalka Group rocks exposed in the type area at Tahtsa Lake, 75 km southwest of the deposit, and at Mount Cronin, 100 km northwest of the deposit. The Kasalka Group rocks in the Tahtsa Lake area give questionable dates of 105 ± 5 Ma by K–Ar on whole rock but are cut by intrusions dated at 83.8 ± 2.8 Ma by K–Ar on biotite. The sequence at the Silver Queen deposit includes a polymictic conglomerate, followed upward by felsic fragmental rocks and a thick porphyritic andesite flow and sill unit, cut by microdiorite and quartz–feldspar porphyry intrusions. The porphyritic andesite and the microdiorite have been dated as Late Cretaceous (78.3 ± 2.7 and 78.7 ± 2.7 Ma, respectively, by K–Ar on whole rock), close to previous dates for these rocks (77.1 ± 2.7 and 75.3 ± 2.0 Ma, respectively). The quartz–feldspar porphyry intrudes the porphyritic andesites but has an older U–Pb zircon date of 84.6 ± 0.2 Ma, probably due to underestimation of the true age of the host rocks by the K–Ar whole-rock method. Later dykes correlate with younger volcanic rocks belonging to the Ootsa Lake and Endako groups. Eocene pre- and postmineral plagioclase-rich dykes (51.9 ± 1.8 to 51.3 ± 1.8 Ma) and late diabase dykes (50.4 ± 1.8 Ma; all by K–Ar on whole rock) may be correlative with trachyandesite volcanics of the Goosly Lake Formation, part of the Eocene Endako Group. These volcanics have been dated elsewhere at 55.6 ± 2.5 to 48.8 ± 1.8 Ma by K–Ar on whole rock and biotite, respectively. Mineralization at Silver Queen is therefore similar in age to, but slightly younger than, the producing Equity mine located 30 km to the northeast, which is estimated at 58.5 ± 2.0 Ma by K–Ar on whole rock.

scholarly journals Cretaceous stage boundaries in the southern Interior Plains of Canada

1984 ◽  
Vol 33 ◽  
pp. 57-69
Author(s):  
W. G. E. Caldwell ◽  
B. R. North
Keyword(s):  
British Columbia ◽  
Upper Cretaceous ◽  
Rocky Mountain ◽  
Successive Stage ◽  
Planktonic Foraminifers ◽  
Lower Upper ◽  
Peace River ◽  
Western Flank ◽  
Mountain Front ◽  
Stage Boundaries

Marine Cretaceous rocks of Berriasian to Aptian age are restricted to northwestern Alberta and north­eastern British Columbia where many stage and substage boundaries may be drawn only tentatively on the basis of limited molluscan faunas. A complete marine Albian succession is similarly restricted, although the middle and upper divisions of the stage are much more widespread. The complete Albian succession of the Peace River district contains a refined and well-documented sequence of ammonite and foraminiferal zones and would be a most suitable continental standard. The Albian-Cenomanian (Lower-Upper Cretaceous) boundary has been reliably established in the continuous foraminifer- and mollusc-bearing sequences of the northwestern plains, but eastward it becomes enclosed in a hiatus. The same is true of successive stage boundaries from the Cenomanian­Turonian to the Santonian-Campanian. The bases for establishment of these boundaries, therefore, can be fully considered only on the western flank of the basin. The Campanian-Maastrichtian boundary may be precisely drawn in western Saskatchewan and traced westward to the Rocky Mountain front. Zones based on ammonites and inoceramid bivalves form· the cornerstone of the biostratigraphy and chronostratigraphy of the southern Interior Plains and hold the key to the stage boundaries. Zones based on assemblages of benthonic foraminifers, rarely of planktonic foraminifers, supplement the molluscan zones. The foraminiferal zones are less reliable and less useful, however, because some benthonic assemblages are weakly diachronous, most foraminiferal zones span several molluscan zones, and many stage boundaries fall within individual foraminifer zones.

The conglomerate of Churn Creek: Late Cretaceous basin evolution along the Insular–Intermontane superterrane boundary, southern British Columbia

2001 ◽  
Vol 38 (1) ◽  
pp. 59-73
Author(s):  
J W Riesterer ◽  
J Brian Mahoney ◽  
Paul Karl Link
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Volcanic Rocks ◽  
Clastic Rocks ◽  
South Central ◽  
Lower Member ◽  
Volcanic Source ◽  
Braided Stream ◽  
Bridge Group

Upper Cretaceous coarse clastic rocks exposed in the canyon of Churn Creek, south-central British Columbia, record active basin tectonism and coeval volcanism adjacent to the boundary between the Intermontane and Insular superterranes. Mid to late Albian (~104 Ma U–Pb), calc-alkaline andesite and basaltic andesite flows, with minor conglomerate and reworked epiclastic deposits and tuffs correlative with the Spences Bridge Group of the Intermontane superterrane are exposed in the canyon. In depositional contact above the volcanic rocks is the conglomerate of Churn Creek, which contains a thick (>1 km) sequence of complexly intertonguing conglomerate and sandstone that is divided into two members composed of four lithofacies. The lower member was deposited unconformably on the underlying Albian volcanic unit and contains late Albian–Cenomanian chert-pebble (>50% chert) conglomerate and interbedded chert- and volcanic-lithic sandstone. It is interpreted to have been deposited in a braided stream system flowing from southeast to northwest. The source for the chert was most likely the Bridge River terrane, a Mississippian to Jurassic ocean floor assemblage located to the southwest of Churn Creek, south of the Yalakom fault. Gradationally overlying the lower member throughout much of the basin is a mixed chert, plutonic, and volcaniclastic lithofacies of the upper member. Plutonic debris was provided to the mixed and plutonic lithofacies of the upper member by the Little Basin pluton, which was uplifted along the northeast-directed Little Basin thrust fault on the southwest margin of the basin. The upper member also contains a volcanic-rich lithofacies composed of chaotic volcanic conglomerate and local lithic tuff derived from a coeval proximal volcanic source. The conglomerate of Churn Creek records active northeast-vergent compressional tectonism and development of piggyback basins along the boundary between the Insular and Intermontane superterranes during Albian–Santonian time. The conglomerate of Churn Creek has been correlated to the Silverquick – Powell Creek succession of the Methow terrane, based on age, stratigraphic, lithologic, structural, geochemical, and paleomagnetic similarities, and may, therefore, represent an overlap assemblage linking the superterranes in the Late Cretaceous.

Regional stratigraphy and structural setting of the Kamloops Group, south-central British Columbia

1981 ◽  
Vol 18 (9) ◽  
pp. 1464-1477 ◽  
Author(s):  
Thomas E. Ewing
Keyword(s):  
British Columbia ◽  
Basaltic Andesite ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Local Flow ◽  
Fault Movement ◽  
South Central ◽  
Type Area ◽  
Slip Displacement ◽  
Fault Network

The Kamloops Group is redefined as an assemblage of Lower to Middle Eocene volcanic and sedimentary rocks widespread in south-central British Columbia. In the type area west of Kamloops, the basal Tranquille Formation consists of 500 m of lacustrine and deltaic sediments, pillowed flows, and hyaloclastites. Elsewhere, basal coal-bearing nonvolcanic fluvial and lacustrine units occur, such as the Coldwater Formation at Merritt, the Chu Chua Formation at Barriere, and the Shorts Creek Formation west of Vernon. Overlying these formations are dominantly volcanic units. At the type area, the Dewdrop Flats Formation includes over 1000 m of interstratified basaltic andesite flows, andesitic flow-breccia sheets and cones, basaltic tuff rings, and an andesitic composite cone. Elsewhere, flat-lying basaltic andesite flows about 600 m thick with local flow breccias are common.The basal sediments accumulated in separate fault-bounded basins initiated immediately before the onset of volcanism. These volcanic rocks filled the basin and formed a widespread volcanic blanket, which was disrupted by continued fault movement. The numerous basins are linked by a throughgoing fault network with up to 12 km of net right-lateral strike-slip displacement.

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