The relationship between the hawaiites and basalts of the itcha Volcanic Complex,central British Columbia |
| |
| Authors: | Anne Charland Don Francis John Ludden |
| |
| Institution: | (1) Département de Géologie, Université de Montréal, Centre-ville, C.P. 6128, succ, H3C 3J7 Montreal, Québec, Canada;(2) Department of Earth and Planetary Sciences, McGill University, 3450 University St., H3A 2A7 Montreal, Quebec, Canada;(3) Centre de recherches pétrographiques et géochimiques (CRPG) 15 rue N.D. des Pauvres, B.P. 20, F-54501 Vandoeuvre-les-Nancy, France |
| |
| Abstract: | Volumetrically subordinate alkaline mafic lava flows form a late capping stage over the earlier felsic lavas that form the
shield of the Itcha Volcanic Complex (IVC), of the Anahim Volcanic Belt (AVB) in central British Columbia (B.C.). The mafic
capping stage of the IVC is dominated by hawaiites which are the earliest of the mafic lavas, and are succeeded by alkali
olivine basalts (AOB) and then by basanites. The alkali olivine basalts can be subdivided into high-, intermediate- and low-MgO
AOB groups, all of which share similar HFSE ratios (e.g. Nb/Zr) with the hawaiites. High Al contents and Sr/Zr ratios indicate
that hawaiites and Fe-rich evolved AOB were derived from primitive AOB parental magmas by crystal fractionation of a wehrlitic
assemblage at pressures on the order of 8 to 10 kbar. High Si and low Fe contents indicate that the majority of the evolved
AOB lavas, however, do not represent an intermediate stage in the liquid line of descent to hawaiites, but were most likely
produced by gabbroic fractionation from primitive AOB magmas at relatively low pressures. The parental magmas of the majority
of these lavas were distinct from those of the observed high-MgO basalts, having higher HFSE contents and being more Si-under-saturated.
The high Al, high Sr/Zr signature of high-pressure fractionation of a clinopyroxene-dominated assemblage in the IVC is shared
by hawaiites of other alkaline volcanic suites of the Canadian Cordillera, such as the Edziza Volcanic Complex in northern
B.C. and appears to be a feature of hawaiites in many localities, including Hawaii and Iceland. Viscosities calculated for
both high- and low-pressure crystal fractionation models suggest that aphyric hawaiites are residual liquids escaped from
a wehrlitic crystalline network, at elevated pressures, possibly at the base of the crust.
Editorial responsibility: T.L. Grove |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
