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.

A new locality for primary xenolith-bearing nephelinites in northwestern British Columbia

1985 ◽  
Vol 22 (10) ◽  
pp. 1556-1559 ◽  
Author(s):  
Michael D. Higgins ◽  
John M. Allen
Keyword(s):  
British Columbia ◽  
Trace Element ◽  
Volcanic Belt ◽  
Primary Magma ◽  
Similar Composition ◽  
Element Abundances ◽  
Late Tertiary

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.

scholarly journals Origin of alkali olivine basalts and hawaiites in the western Mexican arc: Evidence of rapid phenocryst growth and magma mixing during ascent along fractures

Geosphere ◽  
2021 ◽  
Author(s):  
Juliana Mesa ◽  
Rebecca A. Lange
Keyword(s):  
Magma Mixing ◽  
Olivine Basalt ◽  
Volcanic Belt ◽  
Prolonged Storage ◽  
Compositional Zoning ◽  
Mexican Volcanic Belt ◽  
Alkali Olivine Basalt ◽  
Mafic Lavas ◽  
Unique Composition ◽  
Mafic Lower Crust

A detailed petrological study is presented to constrain the origin of a suite of alkali olivine basalt and hawaiite (>5 wt% MgO) lavas that were erupted in a rift zone within the western Mexican arc (Trans-Mexican Volcanic Belt), adjacent to the Sangangüey andesitic stratovolcano, together with more evolved lavas (mugearites and benmoreites; <5 wt% MgO). As previously documented in the literature, the Sangangüey mafic lavas are devoid of any arc geochemical signature, despite their location within an arc. In this study, a new olivine-melt thermometer/hygrometer, based on the partition­ing behavior of Ni2+ and Mg2+, was applied to the Sangangüey basalts (SB). The results show that the high-MgO (>9 wt%) SB crystallized at higher temperatures and lower melt-water contents (0–1.3 wt%) compared to high-MgO arc basalts (≤5.7 wt% H2O) erupted in the west-central Mexican arc. The Sangangüey lavas with 5–8 wt% MgO display evidence of mixing between high-MgO alkali olivine basalts and low-MgO mugearites. It is proposed that the unique composition of the mugearites (i.e., low SiO2 contents and elevated FeO and TiO2 contents) is the result of partial melting of mafic lower crust driven by the influx of high-MgO intraplate basalts under relatively hot, dry, and reduced conditions. On the basis of crystal textures and compositional zoning patterns, it is shown that both phenocryst growth and magma mixing occurred rapidly, most likely during ascent along fractures, and not slowly during prolonged storage in a crustal magma chamber.

scholarly journals Rhönite in Cenozoic alkali basalt from Changle, Shandong Province, China, and its significance

2020 ◽  
Vol 32 (3) ◽  
pp. 325-346
Author(s):  
Fan-Mei Kong ◽  
Hans-Peter Schertl ◽  
Ling-Quan Zhao ◽  
Xu-Ping Li ◽  
Xiao-Han Liu
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Mantle Xenolith ◽  
Olivine Basalt ◽  
Shandong Province ◽  
Coarse Grained ◽  
Primitive Mantle ◽  
Wide Range ◽  
Alkali Olivine Basalt ◽  
Ree Patterns

Abstract. Four Cenozoic, rhönite-bearing alkali-olivine basalt samples from the Changle area (Shandong Province, China) show an intracontinental character and were generated in an extensional setting. Petrographic studies document different generations of rhönite. In three samples, rhönite occurs either as a reaction product surrounding coarse-grained corundum, spinel and phlogopite or along cleavage planes in phlogopite. In one sample rhönite forms disseminated crystals in a mantle xenolith, possibly formed by a reaction of coarse-grained orthopyroxene or spinel with a melt. Rhönite exhibits a wide range of compositions: 22.9 wt %–33.0 wt % SiO2, 13.3 wt %–19.0 wt % Al2O3, 9.4 wt %–19.9 wt % MgO and 10.210.2 wt %–24.5 wt % FeO. The derived primary substitutions include (1) SiIV + NaVII = (Al, Fe3+)IV + CaVII, (2) MgVI = (Fe2+, Mn2+)VI and (3) TiVI + (Mg + Fe2+ + Mn2+)VI = 2Fe3+VI. Rare-earth-element (REE) patterns of euhedral rhönite crystals from the mantle xenolith (sample SS17) and those surrounding spinel (sample CL04) have a concave-upward shape for the heavy rare-earth elements (HREEs) and are slightly enriched in the light rare-earth elements (LREEs). These patterns resemble those of kaersutitic amphibole and kaersutite reported from basanite, olivine nephelinite, transitional alkali-olivine basalt and hawaiite. In contrast, REE patterns of the other two samples containing fine-grained, anhedral and acicular rhönite crystals (samples CL01 and EGS03) are relatively steep, with lower HREE and higher LREE abundances, similar to those of ocean island basalts (OIBs). All types of Changle rhönite show positive Nb, Ti and V anomalies in spidergrams normalized to primitive mantle. Mineral assemblages of the studied samples indicate that rhönite crystallized at different stages within a temperature range from about 950 to 1180 ∘C and at pressures below 0.5 kbar, with fO2 below the NNO buffer. The chemical composition of Changle rhönite is interpreted to depend on the composition of the initial silicate melt, the redox conditions during crystallization and the composition of the minerals involved in reactions to form rhönite. Similar to metasomatic mantle amphibole, the compositions of Changle rhönites cover the I-Amph (I-amphibole) and S-Amph (S-amphibole) fields, indicating that they may have formed due to an intraplate metasomatic event, overprinting an older metasomatic subduction episode.

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.

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.

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.

Motukoreaite, a new hydrated carbonate, sulphate, and hydroxide of Mg and Al from Auckland, New Zealand

1977 ◽  
Vol 41 (319) ◽  
pp. 389-390
Author(s):  
K. A. Rodgers ◽  
J. E. Chisholm ◽  
R. J. Davis ◽  
C. S. Nelson
Keyword(s):  
New Zealand ◽  
Olivine Basalt ◽  
Unit Cell ◽  
Rock Fragments ◽  
Alkali Olivine Basalt ◽  
Beach Rock ◽  
Wet Chemical ◽  
O 19 ◽  
Olivine Sand ◽  
Sand And Gravel

Motukoreaite occurs as relatively abundant, white, clay-like cement in both beach-rock and basaltic volcanic tuffs on the flanks of a small, extinct, late Pleistocene, basaltic cone at Brown's Island (Motukorea), within Waitemata Harbour, Auckland, New Zealand (36° 50′ S., 174° 35′ E.). The occurrence was originally recorded by Bartrum (1941) as ‘beach limestone’ found at two places of the island's shore. The beach-rock consists of a grain-supported fabric of poorly sorted, well-rounded, alkali-olivine basalt pebbles and granules, subangular to sub-rounded fresh olivine sand and abraded sand- and gravel-sized bioclasts in a colourless to pale yellow-green aphanocrystalline matrix of motukoreaite. Additional detritals include quartz, feldspar, and sedimentary rock fragments. Stereoscan examination of the surface of pieces of the cement prised from the beach-rock showed a box-work of plate-like crystals with a hexagonal form in which individuals measured about 3×3×0·02 microns (fig. 1).Wet-chemical analysis of a separate of the cement containing some 5 % quartz and traces of calcite and goethite gives SiO2 5·55, Al2O3 17·87, Fe2O3 0·73, CaO 0·92, MgO 22·98, MnO 0·70, ZnO 0·56, Na2O 0·71, K2O 0·10, CO2 9·32, SO3 10·00, H2O+ 19·62, H2O- 10·35, sum 99·41 %. The unit-cell formula using obtained unit-cell constants and measured specific gravity 1·43) is (Na0·73K0·07)∑0·80(Mg18·13Mn0·32Zn0·21)∑18·66Al11·15(CO3)6·22(SO4)3·97 (OH)51·1927·20H2O. Of several idealized formulae that may be proposed NaMg19Al12(CO3)6.5 (SO4)4(OH)54·28H2O is preferred.

Model of evolution of the Bella Coola – Ocean Falls Region, Coast Mountains, British Columbia

1968 ◽  
Vol 5 (6) ◽  
pp. 1429-1441 ◽  
Author(s):  
A. J. Baer
Keyword(s):  
British Columbia ◽  
Granitic Rocks ◽  
Coast Mountains ◽  
Early Tertiary ◽  
Upper Paleozoic ◽  
Late Tertiary ◽  
Bella Coola

Granitic rocks and metavolcanics underlie most of the Coast Mountains of British Columbia between the fifty-second and the fifty-third parallel, about half-way between Vancouver and Prince Rupert. The age of most rocks is unknown. The area has been involved in at least two orogenic cycles. The oldest known supracrustal rocks (Upper Paleozoic?) have been metamorphosed to gneisses, deformed along northeasterly trends, and intruded by granitic plutons, probably early in the Mesozoic Era. These rocks formed the basement of disconformable Mesozoic sediments and volcanics. The basement and its Mesozoic cover were metamorphosed and deformed along northwesterly trends in the early Tertiary. In the late Tertiary (Pliocene?) post-kinematic granites were emplaced and basalts were extruded for a period extending to postglacial times. The model is possibly applicable to all of the Coast Mountains in Canada.

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