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.

Late Cenozoic tectonics offshore western Mexico and its relation to the structure and volcanic activity in the western Trans-Mexican Volcanic Belt

1993 ◽  
Vol 32 (4) ◽  
pp. 543-559
Author(s):  
Hugo Delgado Granados
Keyword(s):  
Volcanic Activity ◽  
Volcanic Belt ◽  
Late Cenozoic ◽  
Western Mexico ◽  
Mexican Volcanic Belt ◽  
Cenozoic Tectonics ◽  
Trans Mexican Volcanic Belt

La tasa de convergencia calculada indica que la tectónica del occidente de México ha sido tensional durante los últimos 3 Ma. Este estilo de deformación se ve reflejado en la formación de estructuras rift en la parte occidental de la Faja Volcánica Trans-Mexicana [FVTM]. Los valores obtenidos para la tasa de convergencia predicen que, a través del tiempo, se verifica una tectónica menos tensional (con tendencia a la neutralidad) en la parte sureste de la zona de interacción de las placas de Rivera Y Norteamérica, mientras que en la parte noroccidental se vuelve más tensional. Por otra parte, un análisis cualitativo de las tasas de esparcimiento muestra que éstas fueron más rápidas antes de los 6.5 Ma de lo que fueron posteriormente. Después de analizar diferentes parámetros cinemáticos, se concluyó que la tasa de esparcimiento de la cresta del Pacífico Oriental en su sector Pacífico-Rivera, influye fuertemente sobre la tasa de convergencia. De esta manera se puede establecer una correlación positiva entre la evolución de la tasa de esparcimiento de la cresta Pacífico-Rivera y la geología continental. Esta correlación muestra que tasas de esparcimiento relativamente rápidas coinciden con la presencia de volcanismo monogenético calci-alcalino en la parte occidental de la FVTM cuando menos desde hace 10 Ma y que este tipo de volcanismo continúa hasta nuestros días. Sin embargo, cuando la tasa de esparcimiento se ha hecho más lenta (y por tanto la tasa de convergencia se ha hecho menor) durante el periodo comprendido entre 6.5 Ma y 3.5 Ma, se ha verificado en la región una tectónica extensional ampliamente distribuida, volcanismo explosivo y sedimentación lacustre en los sistemas rift de Colima, Tepic-Zacoalco y de Chapala; particularmente entre los 4.6 Ma y 3.9 Ma ha coincidido con volcanismo alcalino en los rifts fr Colima y Tepic-Zacoalco. Un leve incremento en la tasa de esparcimiento después de los 3.5 Ma coinciden con el decremento de actividad volcánica (principalmente alcalina). Durante el periodo entre 1.6 Ma y 0.7 Ma, la tasa de esparcimiento disminuyó de nuevo coincidiendo con un fallamiento normal continuo en las tres estructuras rift mencionadas y en parte, con otra etapa de volcanismo alcalino (entre 1.4 Ma y 0.2 Ma) en los rift de Colima y Tepic-Zacoalco. Después de los 0.7 Ma, la tasa de esparcimiento se ha incrementado levemente. Por otra parte, se observa una relación genética entre el contenido de elementos compatibles en rocas volcánicas de la región con la tasa de convergencia, lo cual implica que tasas de subducción mayores aportan una mayor cantidad de sedimentos acrecionados a la cuña del manto. Esto explica las diferencias geoquímicas entre las rocas volcánicas a lo largo del frente volcánico de la parte occidental de la FVTM.

Rare earth element concentrations in Quaternary volcanic rocks of southwestern British Columbia

1984 ◽  
Vol 21 (6) ◽  
pp. 731-736 ◽  
Author(s):  
Nathan L. Green ◽  
Paul Henderson
Keyword(s):  
British Columbia ◽  
Earth Element ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Lake Area ◽  
Calc Alkaline ◽  
Lower Light ◽  
The Individual ◽  
High Level ◽  
Ree Patterns

A suite of hy-normative hawaiites, ne-normative mugearite, and calc-alkaline andesitic rocks from the Garibaldi Lake area exhibits fractionated, slightly concave-upward REE patterns (CeN/YbN = 4.5–15), heavy REE contents about 5–10 times the chondritic abundances, and no Eu anomalies. It is unlikely that the REE patterns provide information concerning partial melting conditions beneath southwestern British Columbia because they have probably been modified substantially by upper crustal processes including crustal contamination and (or) crystal fractionation. The REE contents of the Garibaldi Lake lavas are not incompatible with previous interpretations that (1) the hawaiites have undergone considerable fractionation of olivine, plagioclase, and clinopyroxene; and (2) the individual andesitic suites were derived from separate batches of chemically distinct magma that evolved along different high-level crystallization trends. In general, however, the andesites are characterized by lower light REE contents than the basaltic andesites. These differences in LREE abundances may reflect different amounts of LREE-rich accessory phases, such as apatite, sphene, or allanite, assimilated from the underlying quartz diorites.

Eocene Challis-Kamloops volcanism in central British Columbia: an example from the Buck Creek basin

1998 ◽  
Vol 35 (8) ◽  
pp. 951-963 ◽  
Author(s):  
J Dostal ◽  
D A Robichaud ◽  
B N Church ◽  
P H Reynolds
Keyword(s):  
British Columbia ◽  
Rare Earth ◽  
Rare Earth Element ◽  
Fractional Crystallization ◽  
Earth Element ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
The United States ◽  
Calc Alkaline ◽  
Heavy Rare Earth Element

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.

scholarly journals Detailed mapping and lithogeochemistry of Neoarchean volcanic rocks: Beaulieu volcanic belt, Slave Craton, NWT

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Shelby Brandon Austin-Fafard ◽  
Michelle DeWolfe ◽  
Camille Partin ◽  
Bernadette Knox
Keyword(s):  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Massive Sulfide ◽  
Lake Area ◽  
Density Currents ◽  
Volcanogenic Massive Sulfide ◽  
The South ◽  
Slave Craton ◽  
Volcaniclastic Rocks ◽  
Tuff Breccia

Neoarchean volcanic rocks of the Beaulieu River volcanic belt structurally overlie basement rocks of the Sleepy Dragon Complex (ca. 2.85 Ga), approximately 100 km east northeast of Yellowknife. The volcanic belt is comprised of complex lithofacies, including basalt, andesite, rhyolite, and associated volcaniclastic rocks, and hosts the Sunrise volcanogenic massive sulfide deposit. The absolute age of the volcanic strata is not known, nor is the stratigraphy well-defined; therefore, the Beaulieu River volcanic belt cannot be easily correlated to other greenstone belts within the Slave craton. The main objective of this study is to document the litho- and chemo-stratigraphy of the volcanic rocks, and particularly the rhyolite dome, located at the south end  of Sunset Lake to reconstruct their volcanic and petrogenetic evolution, and determine their relationship to the volcanic strata that hosts the Sunrise VMS deposit, located ~6km to the north of the study area. Detailed mapping (1:2000) was completed over two field seasons (2018 and 2019) and shows that the volcanic rocks in the south Sunset Lake area comprise a complex stratigraphy consisting of basaltic, andesitic and rhyolitic lithofacies. This includes massive to pillow basalt and andesite, with lesser amounts of massive to in-situ brecciated, weakly quartz-plagioclase porphyritic rhyolite, heterolithic tuff to lapilli- tuff and felsic tuff to tuff breccia. The felsic clasts within the felsic volcaniclastic rocks are similar in composition to the coherent rhyolite. Units have a trace element geochemical signatures that vary from tholeiitic to calc-alkaline, arc-like rocks. Volumetrically, the volcanic strata in the south Sunset Lake area has a significant amount of volcaniclastic rocks, ranging from tuff to tuff breccia units. The volcaniclastic rocks are interpreted to have been deposited by a series of debris flows and eruption-fed density currents. The stratigraphy of the volcanic rocks in south Sunset Lake is very similar to that of the stratigraphy that hosts the Sunrise VMS deposit. Evidence of a vent proximal environment (e.g. rhyolite dome, peperite, syn-volcanic intrusions) and porous, volcanic debris accumulating on the seafloor highlight conditions favourable for volcanogenic massive sulfide-type mineralization in the south Sunset Lake area.

Chronostratigraphy of Eocene volcanism, central British Columbia

2014 ◽  
Vol 51 (1) ◽  
pp. 56-103 ◽  
Author(s):  
Esther Bordet ◽  
Mitchell G. Mihalynuk ◽  
Craig J.R. Hart ◽  
Jim K. Mortensen ◽  
Richard M. Friedman ◽  
...  
Keyword(s):  
British Columbia ◽  
Volcanic Activity ◽  
Volcanic Rocks ◽  
Early Eocene ◽  
Isotopic Age ◽  
The North ◽  
Felsic Volcanism ◽  
Magma Compositions ◽  
Age Determinations

Onset and termination of Eocene felsic volcanism in the Chilcotin Plateau of central British Columbia is constrained between 54.6 and 46.6 Ma by 33 new U–Pb and 40Ar/39Ar isotopic age determinations. Dates were obtained from representative felsic coherent and fragmental volcanic rocks that comprise the Ootsa Lake Group. The resulting chronostratigraphy shows that magma compositions evolved from felsic to intermediate, with no spatial migration of the volcanic activity. Rhyolitic compositions are oldest; and are overlain by dacitic rocks with varied phenocrysts assemblages. In many parts of the Chilcotin Plateau, the Eocene stratigraphy is capped by distinctive vitreous black dacite lavas, which are contemporaneous with andesitic lavas of the Endako Group in the Nechako Plateau to the north. Crystallization ages from Ootsa Lake Group rocks of the Chilcotin Plateau overlap age determinations from correlative rocks of the Nechako Plateau and southern BC. Collectively, this geochronological dataset supports previous suggestions of a voluminous Early Eocene-aged (∼55–46 Ma) period of volcanism in the Intermontane Belt. The abrupt initiation of volcanism, as well as the wide extent, thickness, and compositions that characterize Eocene volcanic rocks may be explained by cessation of subduction and formation of a slab gap beneath British Columbia in the Early Eocene.

Lillooet Glacier basalts, southwestern British Columbia, Canada: products of Quaternary glaciovolcanism

2017 ◽  
Vol 54 (6) ◽  
pp. 639-653 ◽  
Author(s):  
Alexander M. Wilson ◽  
James K. Russell
Keyword(s):  
British Columbia ◽  
Sea Level ◽  
Basaltic Andesite ◽  
Volcanic Rocks ◽  
Volcanic Belt ◽  
Storage Conditions ◽  
Ice Thickness ◽  
Pillow Basalt ◽  
Phenocryst Assemblage ◽  
Ice Surface

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.

The Cheslatta Lake suite: Miocene mafic, alkaline magmatism in central British Columbia

2001 ◽  
Vol 38 (4) ◽  
pp. 697-717 ◽  
Author(s):  
Robert G Anderson ◽  
Jonah Resnick ◽  
James K Russell ◽  
G J Woodsworth ◽  
Michael E Villeneuve ◽  
...  
Keyword(s):  
British Columbia ◽  
Olivine Basalt ◽  
Volcanic Belt ◽  
Primitive Mantle ◽  
Alkaline Magmatism ◽  
Type Area ◽  
Late Tertiary ◽  
Alkali Olivine Basalt ◽  
Trace Element Contents ◽  
Geochemical Studies

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.

Geochemistry and tectonic significance of the mafic volcanic blocks in the Dunnage mélange, north central Newfoundland

1985 ◽  
Vol 22 (9) ◽  
pp. 1248-1256 ◽  
Author(s):  
Janusz J. Wasowski ◽  
Robert D. Jacobi
Keyword(s):  
Chemical Composition ◽  
Alkali Basalt ◽  
Volcanic Rocks ◽  
Pillow Lava ◽  
Calc Alkaline ◽  
North Central ◽  
Head Formation ◽  
Tectonic Significance ◽  
Low Potassium ◽  
Tuff Breccia

Abundant volcanic blocks are present in the Dunnage mélange. These mafic volcanic rocks consist predominantly of pillow lava, tuff breccia, isolated pillow–tuff breccia, and minor amounts of ropy lava.Major- and trace-element compositions of the basalts reveal that these volcanics do not resemble calc-alkaline or low-potassium island-arc suites. Rather, the majority of the samples are enriched-type ocean-floor tholeiites, whereas some show alkali basalt affinities. Discrimination diagrams suggest that these basalts may have been erupted as within-plate basalts. However, the chemical composition of the volcanic blocks is most similar to that of basalts generated at bathymetric highs located astride (or slightly off) mid-ocean ridges.The geochemistry of the Dunnage mélange basalts is very similar to that of the mafic volcanic rocks from the nearby Summerford Group and the Lawrence Head Formation. This correlation is further supported by sedimentary and petrographic evidence and by partial age equivalency.

The Petrology of Late Tertiary Dolerite Plugs in the South Cariboo Region, British Columbia

1973 ◽  
Vol 10 (2) ◽  
pp. 205-225 ◽  
Author(s):  
R. B. Farquharson
Keyword(s):  
British Columbia ◽  
Trace Element ◽  
Chemical Nature ◽  
Major Element ◽  
Basaltic Magma ◽  
Olivine Basalt ◽  
Coarse Grained ◽  
Basalt Magma ◽  
Late Tertiary ◽  
High Level

The petrology of four plugs of fresh, coarse-grained olivine dolerite, of Pliocene age, is described in this paper. Two plugs, which exhibit textural and mineralogical variations, are described in detail. Major element analyses and selected trace element analyses for fifteen samples illustrate the chemical nature of the dolerite as well as fractionation in small marginal portions of the plugs. Strontium isotope values indicate that the plugs represent basaltic magma that was not contaminated by crastal matter. Both the mineralogy and the chemistry of the plugs indicate that the magma was mildly alkaline, and suggest that it was a differentiate of a primary olivine basalt magma, perhaps derived through crystal fractionation in a high-level magma chamber.

A Tertiary Lamprophyre Dike Province in Southeastern Alaska

1973 ◽  
Vol 10 (3) ◽  
pp. 408-420 ◽  
Author(s):  
James G. Smith
Keyword(s):  
British Columbia ◽  
Mantle Source ◽  
Olivine Basalt ◽  
Volcanic Rocks ◽  
Alkali Content ◽  
Topographic Features ◽  
Total Alkali ◽  
Alkali Olivine Basalt ◽  
Basalt Composition ◽  
Dike Swarms

Mapping in southeastern Alaska along the British Columbia border has shown the presence of hundreds of aligned Tertiary Lamprophyre dikes. Most dikes occur in northeast-trending swarms that cut across northwest-trending structures in the bedrock. More than 60% of the dikes dip within 10° of vertical and strike between N35°E and N80°E. Major topographic features such as fjords and streams have the same trend; differential erosion along the dike swarms and parallel joint sets, not faulting, is responsible for this northeast topographic grain.The dikes show various degrees of deuteric alteration. In relatively unaltered rocks, phenocrysts are subcalcic augite and rarely plagioclase, altered olivine, or amphibole. Deuterically altered dikes have a texture of interlocking milky plagioclase and black amphibole needles.The dikes form an undifferentiated homogeneous suite of alkali olivine basalt composition with an average SiO2 content of 48.8% and a total alkali content of 5.3%. Their chemistry closely resembles Quaternary volcanic rocks in British Columbia and Alaska.Structural setting, extent, and chemistry of the dikes suggest a mantle source and rapid intrusion without time for differentiation.

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