scholarly journals The 2007 Nazko, British Columbia, Earthquake Sequence: Injection of Magma Deep in the Crust beneath the Anahim Volcanic Belt

2011 ◽  
Vol 101 (4) ◽  
pp. 1732-1741 ◽  
Author(s):  
J. F. Cassidy ◽  
N. Balfour ◽  
C. Hickson ◽  
H. Kao ◽  
R. White ◽  
...  
1985 ◽  
Vol 22 (10) ◽  
pp. 1556-1559 ◽  
Author(s):  
Michael D. Higgins ◽  
John M. Allen

High Ni abundances (420–500 ppm) and Mg* values (100 × Mg/(Mg + Fe2+) = 69–71) and the presence of mantle-derived xenoliths indicate that a subvolcanic nephelinite intrusion in northwestern British Columbia represents an unmodified primary magma. A separate, closely associated nephelinite intrusion shows evidence of minor olivine fractionation from a similar composition. Only three other occurrences of primary nephelinite have been described. This new occurrence suggests that these magmas may not be so rare as previously supposed. The trace-element abundances closely resemble those of primary nephelinites of similar La content from Freemans Cove, Canada. Such compositions are usually taken as evidence of intraplate rifting and doming. Therefore, these rocks are further evidence of late Tertiary or Quaternary rifting in the Stikine volcanic belt.


1998 ◽  
Vol 35 (8) ◽  
pp. 951-963 ◽  
Author(s):  
J Dostal ◽  
D A Robichaud ◽  
B N Church ◽  
P H Reynolds

Eocene volcanic rocks of the Buck Creek basin in central British Columbia are part of the Challis-Kamloops volcanic belt extending from the United States across British Columbia to central Yukon. The volcanic rocks include two units, the Buck Creek Formation, composed of high-K calc-alkaline rocks with predominant andesitic composition, and the overlying Swans Lake unit made up of intraplate tholeiitic basalts. Whole rock 40Ar/39Ar data for both units show that they were emplaced at 50 Ma. They have similar mantle-normalized trace element patterns characterized by a large-ion lithophile element enrichment and Nb-Ta depletion, similar chondrite-normalized rare earth element patterns with (La/Yb)n ~4-14 and heavy rare earth element fractionation, and overlapping epsilonNd values (2.4-3.1) and initial Sr-isotope ratios ( ~ 0.704). These features suggest derivation of these two units from a similar mantle source, probably garnet-bearing subcontinental lithosphere. The differences between tholeiitic and calc-alkaline suites can be due, in part, to differences in the depth of fractional crystallization and the crystallizing mineral assemblage. Fractional crystallization of the calc-alkaline magmas began at a greater (mid-crustal) depth and included fractionation of Fe-Ti oxides. The volcanic rocks are probably related to subduction of the Farallon plate under the North American continent in a regime characterized by transcurrent movements and strike-slip faulting.


2016 ◽  
Author(s):  
A M Wilson ◽  
J K Russell ◽  
M C Kelman ◽  
C J Hickson

1984 ◽  
Vol 21 (5) ◽  
pp. 599-608 ◽  
Author(s):  
Alan M. Jessop ◽  
J. G. Souther ◽  
Trevor J. Lewis ◽  
A. S. Judge

Measurements at seven sites in the Intermontane region of northern British Columbia and southern Yukon show heat flow of 63–100 mW/m2 and heat generation, obtained from intrusive rocks at three of these sites, of 1.8–6.5 μW/m1. These few data cannot define a linear relation between heat flow and heat generation for this region, but the plotted points lie between the lines of the stable crust of the eastern United States and of the Basin and Range Province. Conductive thermal models of the crust, assuming a basalt composition for the lower crust, predict at 35 km depth a heat flow of 30 mW/m2 and temperatures between 645 and 775 °C at most sites.At two sites conductive models based on reasonable properties do not yield reasonable temperatures. The site on the axis of the Stikine Volcanic Belt shows a probable component of convectively enhanced heat flow or the presence of a young intrusion at depth. The site in the Bowser Basin shows the probable effect of water movement in the sediments.


2017 ◽  
Vol 54 (6) ◽  
pp. 639-653 ◽  
Author(s):  
Alexander M. Wilson ◽  
James K. Russell

The retreat of Lillooet Glacier (LG) has exposed a succession of pillow basalt and subordinate amounts of breccia and hyaloclastite. The lithofacies and physiographic setting suggest that the deposits have a glaciovolcanic origin and represent a partially dissected basaltic pillow-dominated tindar. Chemically, the LG volcanic rocks are basalt to basaltic andesite, and, as a group, they represent the highest-silica, Quaternary mafic products in the Garibaldi volcanic belt (GVB). Like other northern GVB (alkaline) basalts, they lack the Nb–Ta depletion signature typically associated with subduction-related products. Geochemical and petrologic analysis indicates that the LG basalts are comagmatic and that chemical variations within the suite are consistent with sorting of the observed phenocryst assemblage: olivine + plagioclase. Thermodynamic modeling establishes shallow, crustal, pre-eruptive storage conditions at <2 kbar (1 kbar = 100 MPa; or 7.5 km) and an H2O content of 0.5–1 wt.%. We estimate that the LG basalts were erupted at the peak of, or during the waning stages of, Fraser glaciation (17–13 ka). The eruption produced an englacial lake that was >150 m deep and that appears to have been sustained throughout the entire eruption (i.e., no discernible passage zone). Using hydrostatic constraints, we calculate a minimum overlying paleo-ice thickness of >645 m and a paleo-ice surface elevation of >1895 m above sea level.


2001 ◽  
Vol 38 (4) ◽  
pp. 697-717 ◽  
Author(s):  
Robert G Anderson ◽  
Jonah Resnick ◽  
James K Russell ◽  
G J Woodsworth ◽  
Michael E Villeneuve ◽  
...  

New mapping, mineralogical, and geochemical studies help characterize late Tertiary primitive, alkaline, sodic basanite, alkali olivine basalt, transitional basalt, and diabase in the Nechako River, Whitesail Lake, and McLeod Lake map areas of central British Columbia and distinguish the Miocene Cheslatta Lake suite. The suite encompasses scattered erosional remnants of topographically distinct, columnar-jointed, olivine-phyric basalt and diabase volcanic necks, dykes, and associated lava flows north of the Anahim volcanic belt and west of the Pinchi Fault. Volcanic centres at Alasla Mountain and at Cutoff Creek, near Cheslatta Lake, are proposed as type areas. Olivine, plagioclase, and pyroxene phenocrysts, megacrysts, and (or) xenocrysts; common ultramafic xenoliths; and rare but significant plutonic and metamorphic xenoliths are characteristic. Basanite, transitional basalt, and alkali olivine basalt groundmass contain plagioclase, clinopyroxene, Fe-Ti oxides, feldspathoid, olivine, and apatite. The Cheslatta Lake suite is characterized by its alkaline character, olivine-rich (>10 wt.%) normative mineralogy, and silica-undersaturated nature (>1 wt.% normative nepheline; hypersthene-normative rocks are uncommon). Mg numbers vary between 72–42. Some samples encompass near-primitive mantle melt compositions. Cheslatta Lake suite rocks in the Nechako River area are distinguished from the underlying Eocene Endako and stratigraphically higher Neogene Chilcotin groups basaltic andesite lavas within the study area, and from the Chilcotin Group basalt in the type area south of the Anahim volcanic belt, by form, preserved thickness, phenocryst–xenocryst mineralogy, amygdule abundance, included xenoliths, isotopic age, and major and incompatible, high field strength, and rare-earth trace element contents.


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