Nazko cone: a Quaternary volcano in the eastern Anahim Belt

1987 ◽  
Vol 24 (12) ◽  
pp. 2477-2485 ◽  
Author(s):  
J. G. Souther ◽  
J. J. Clague ◽  
R. W. Mathewes
Keyword(s):  
British Columbia ◽  
North America ◽  
Volcanic Activity ◽  
Mantle Source ◽  
Volcanic Belt ◽  
Lava Flows ◽  
Radiocarbon Dates ◽  
Depleted Mantle ◽  
Late Neogene ◽  
Cordilleran Ice Sheet

Nazko cone, located in central British Columbia at the eastern end of the Anahim Volcanic Belt, is the product of at least three episodes of Quaternary volcanic activity. An eroded Pleistocene subaerial flow at the base of the pile is overlain by a subglacial mound of hyaloclastite that is, in turn, partly covered by a younger composite pyroclastic cone and associated lava flows. A whole-rock K–Ar date of 0.34 ± 0.03 Ma on the oldest flow is consistent with a hotspot model for the Anahim Belt and implies absolute late Neogene motion of 2.6 cm/year for North America. The hyaloclastite mound was erupted beneath the Cordilleran Ice Sheet during the Late Pleistocene, perhaps during the Fraser Glaciation (25 000 – 10 000 years BP). Radiocarbon dates from peat above and below Nazko tephra in a bog near the cone suggest that the volcano last erupted about 7200 years BP.Nazko basalt has 10–15% normative nepheline and is classified as basanite. This is significantly more undersaturated than basalts farther west in the Anahim Belt and may indicate an eastward shift toward a deeper or less depleted mantle source.

Archean volcanoes in southwestern Abitibi Belt, Ontario and Quebec: form, composition, and development

1982 ◽  
Vol 19 (6) ◽  
pp. 1140-1155 ◽  
Author(s):  
A. M. Goodwin
Keyword(s):  
Mantle Source ◽  
Volcanic Belt ◽  
Second Order ◽  
Lava Flows ◽  
Basalt Lava ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
Thermal Pulses ◽  
Stratigraphic Thickness ◽  
Water Depths

Southwestern Abitibi Volcanic Belt is composed of numerous deformed volcanoes that were originally circular to subcircular in outline, 100–200 km in diameter, and 10–16 km in stratigraphic thickness. Tholeiitic (TH) lava flows with local komatiitic (KM) flows and intrusions predominate in the lower parts of each volcano and calc-alkalic (CA) lava flows or pyroclastic rocks in the upper parts. Subsidence of the volcanoes more or less kept pace with magma extrusion such that volcano slopes remained mainly horizontal to subhorizontal. The lower TH parts accumulated rapidly at substantial water depths. The upper CA parts also accumulated rapidly but at decreasing water depths with possible local, brief, island emergence.The lower TH division is dominated by thick, uniform TH basalt lava flows. This changes abruptly at about volcano mid-thickness to the conformably overlying CA andesite-rich division characterized by irregularly recurring basalt–andesite– dacite–rhyolite flow or pyroclastic alternations that become increasingly felsic upwards. Multicyclic volcanoes include second-order internal TH–CA subdivisions. The generalized Abitibi succession is represented by a simplified, composite Abitibi volcano.The salient control in volcano development is attributed to diapiric ascent within a heterogeneously layered Archean mantle. TH and CA components are attributed to direct mantle sources. The major TH–CA volcano pattern represents a full Archean thermal cycle. The TH–CA discontinuity reflects the switch from an earlier, mainly depleted mantle source to a later, mainly undepleted mantle source. Second-order volcano subdivisions (subgroups) represent thermal pulses in diapiric ascent. Such a system of recurring, migrating mantle plumes gave rise, in due course, to the volcano-dominated greenstone belt.

Ice-free conditions in southwestern British Columbia at 16000 years BP

1988 ◽  
Vol 25 (6) ◽  
pp. 938-941 ◽  
Author(s):  
John J. Clague ◽  
Ian R. Saunders ◽  
Michael C. Roberts
Keyword(s):  
British Columbia ◽  
Ice Sheet ◽  
Radiocarbon Dates ◽  
Maximum Extent ◽  
Late Wisconsinan ◽  
Cordilleran Ice Sheet

New radiocarbon dates on wood from two exposures in Chilliwack valley, southwestern British Columbia, indicate that this area was ice free and locally forested 16 000 radiocarbon years ago. This suggests that the Late Wisconsinan Cordilleran Ice Sheet reached its maximum extent in this region after 16 000 years BP. The Chilliwack valley dates are the youngest in British Columbia that bear on the growth of the Cordilleran Ice Sheet.

Late Cenozoic volcanic rocks of the Clearwater – Wells Gray area, British Columbia

1984 ◽  
Vol 21 (3) ◽  
pp. 267-277 ◽  
Author(s):  
Catherine J. Hickson ◽  
J. G. Souther
Keyword(s):  
British Columbia ◽  
Volcanic Activity ◽  
Olivine Basalt ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Pillow Lava ◽  
Late Cenozoic ◽  
Gray Area ◽  
High Level ◽  
Tuff Breccia

The Clearwater – Wells Gray area of east-central British Columbia includes a succession of late Cenozoic, alkali olivine basalt flows that lie east of the extensive Chilcotin lavas and define the eastern end of the Anahim Volcanic Belt. The rocks are petrographically similar to but less altered than the Chilcotin basalts. The volcanic activity spanned at least two episodes of glacial advance and produced both subaerial flows and a subaqueous facies comprising pillow lava, pillow breccia, and tuff breccia, locally intercalated with fluvial gravels and sand. Four morphological assemblages have been recognized. An early glacial assemblage, characterized by tuyalike forms, gives K – Ar dates of 0.27 – 3.5 Ma. These circular features are surrounded by a deeply dissected valley-filling assemblage of subaerial and minor subaqueous flows and tuff breccia that rest locally on lag gravel and till. Subaerial flows in this assemblage give K – Ar dates of 0.15 – 0.56 Ma. Whitehorse Bluffs, a volcanic centre composed of crudely laminated tuff cut by high-level dykes, may be a source of some of these valley-filling flows. A late interglacial assemblage is composed of subaerial pyroclastic material, transitional deposits, and deposits that are clearly subaqueous. Volcanic activity in the area culminated with the formation of pyroclastic cones, blocky lava flows, and pit craters that postdate the last Cordilleran glaciation.

Paleointensity study of late Miocene igneous rocks from British Columbia, Canada

1970 ◽  
Vol 7 (1) ◽  
pp. 176-181 ◽  
Author(s):  
D. T. A. Symons ◽  
E. J. Schwarz
Keyword(s):  
Magnetic Field ◽  
British Columbia ◽  
North America ◽  
Late Miocene ◽  
Igneous Rocks ◽  
Lava Flows ◽  
Basaltic Lava ◽  
Remanent Magnetism ◽  
South Central ◽  
Demagnetizing Fields

Sixty-nine specimens representing 49 late Miocene (10–15 m.y. ago) basaltic lava flows and 4 associated gabbroic intrusive plugs were studied in an attempt to estimate the paleointensity of the earth's magnetic field in south-central British Columbia. The paleointensity determination was based on the comparison of the decay of natural remanent magnetism intensity with that of an artificial thermoremanent magnetism (H = 0.35 Oe) in progressively higher alternating demagnetizing fields (peak: 800 Oe). Only 22 of the 69 specimens were considered to yield reliable paleointensity determinations which give an estimated average equatorial intensity for the late Miocene earth's field of 0.18 Oe ± 0.11. This result agrees reasonably well with those from contemporaneous rocks from North America, Japan, and Iceland. Several low determinations with consistent, normal, or reversed remanence directions suggest that the intensity of the non-dipole components of the late Miocene earth's field must have been very small in the sampled area.

Geochemistry of Cenozoic basaltic and silicic magmas in the central portion of the Loei–Phetchabun volcanic belt, Lop Buri, Thailand

1995 ◽  
Vol 32 (4) ◽  
pp. 393-409 ◽  
Author(s):  
Suporn Intasopa ◽  
Todd Dunn ◽  
Richard StJ. Lambert
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Mantle Source ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Central Portion ◽  
Alkali Basalts ◽  
Crustal Rocks ◽  
Depleted Mantle ◽  
Silicic Magmas

Cenozoic volcanic rocks outcrop in the central portion of the Loei–Phetchabun volcanic belt in central Thailand in the Lop Buri area. The volcanic rocks range in composition from basalt to high-silica rhyolite. In general, the volcanic rocks decrease in age from south to north. The oldest rocks studied are 55–57 Ma rhyolites that are isotopically and geochemically distinct from younger (13–24 Ma) rhyolites that occur farther north. Intermediate rocks (andesite and dacite) are less voluminous than rhyolite. Basalt occurs in the central and northern parts of the area and ranges in composition from olivine tholeiites to nepheline normative alkali basalts. The isotopic, major, and trace element compositions of the andesites, dacites, and younger rhyolites are consistent with an origin for these rocks by variable degrees of partial melting of metabasaltic crustal rocks, themselves derived from a depleted mantle source at approximately 530 ± 100 Ma. The apparent extent of partial melting of metabasalt increases from rhyolite to andesite. The isotopic and trace element systematics of the basalts are consistent with a refertilized depleted mantle source with characteristics of a mixture of normal mid-ocean ridge basalt source mantle and enriched mantle II type mantle.

scholarly journals Relative Sea-Level Change in the Northern Strait of Georgia, British Columbia*

2007 ◽  
Vol 59 (2-3) ◽  
pp. 113-127 ◽  
Author(s):  
Thomas S. James ◽  
Ian Hutchinson ◽  
J. Vaughn Barrie ◽  
Kim W. Conway ◽  
Darcy Mathews
Keyword(s):  
British Columbia ◽  
Sea Level ◽  
Sea Level Change ◽  
Relative Sea Level ◽  
Radiocarbon Dates ◽  
Strait Of Georgia ◽  
Level Change ◽  
Decay Times ◽  
Crustal Uplift ◽  
Cordilleran Ice Sheet

Abstract Twenty-four new radiocarbon dates from isolation basin cores, excavations and natural exposures, and an archeological site, constrain relative sea-level change since the last glaciation in the northern Strait of Georgia, British Columbia. Relative sea level fell rapidly from about 150 m elevation to 45 m elevation from 11 750 to 11 000 BP (13 750 to 13 000 cal BP), then its rate of fall slowed. The initial rapid emergence began soon after the transition from proximal to distal glaciomarine sedimentation, when the glacial front retreated from the Strait of Georgia and the Earth’s surface was unloaded. A sea-level lowstand a few metres below present-day sea level may have occurred in the early Holocene, but sea level was near its present level by 2000 BP. Sea-level change in the northern Strait of Georgia lagged the mid Strait of Georgia, 80 km to the south, by a few hundred years during initial emergence. The lowstand in the northern strait was later and probably shallower than in the mid strait. Isostatic depression inferred from the sea-level observations can be fit with two decaying exponential terms with characteristic decay times of 500 and 2600 years. The faster decay time corresponds to a shallow mantle viscosity of about 1019 Pa s, consistent with previous glacio-isostatic modelling. The present-day crustal uplift rate from the residual isostatic effects of the Cordilleran Ice Sheet is about 0.25 mm/a. Crustal uplift is not expected to significantly ameliorate projected sea-level rise in the mid and northern Strait of Georgia because present-day vertical crustal movements are inferred to be small.

Advance of the Late Wisconsin Cordilleran Ice Sheet in Southern British Columbia Since 22,000 Yr B.P.

1980 ◽  
Vol 13 (3) ◽  
pp. 322-326 ◽  
Author(s):  
J. J. Clague ◽  
J. E. Armstrong ◽  
W. H. Mathews
Keyword(s):  
British Columbia ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Major Advance ◽  
Radiocarbon Dates ◽  
Coast Mountains ◽  
Growth History ◽  
Glacier Ice ◽  
History Of ◽  
Cordilleran Ice Sheet

AbstractRadiocarbon dates from critical stratigraphic localities in southern British Columbia indicate that the growth history of the late Wisconsin Cordilleran Ice Sheet was different from that of most of the Laurentide Ice Sheet to the east. Much of southern British Columbia remained free of ice until after about 19,000 to 20,000 yr ago; only adjacent to the Coast Mountains is there a record of lowland glacier tongues in the interval 22,000 to 20,000 yr B.P. A major advance to the climax of late Wisconsin Cordilleran glacier ice in the northern States was not begun until after about 18,000 yr B.P. in the southwest of British Columbia and after about 17,500 yr B.P. in the southeast. The rate of glacier growth must have been very rapid in the two to three millennia prior to the climax, which has been dated in western Washington at shortly after 15,000 yr B.P.

McNaughton Lake seismicity—more evidence for an Anahim hotspot?

1981 ◽  
Vol 18 (4) ◽  
pp. 826-828 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
British Columbia ◽  
North America ◽  
Coastal Zone ◽  
Volcanic Belt ◽  
Canadian Cordillera ◽  
Lake Region

The only notable concentration of earthquakes in the Canadian Cordillera away from the coastal zone occurs in the McNaughton Lake region of British Columbia, off the eastern end of the Anahim volcanic belt. The association of these two phenomena strengthens the hypothesis that the origin of the Anahim belt is due to North America overriding a mantle hotspot and provides a possible explanation for the concentration and character of the seismicity.

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