Abstract
The Allendale Lake stock is a representative intrusion of the Eocene alkaline igneous province in south-central British Columbia (Canada), which forms the northwestern edge of the Montana-Wyoming alkaline province. The shallow-seated intrusion (~53 Ma), about 4.5 km long and 2 km wide, is composed predominately of feldspar-phyric biotite-clinopyroxene-amphibole-bearing monzonitic/syenitic rocks. The feldspar forms distinct rhomb-shaped phenocrysts, which contain abundant exsolution of perthite and antiperthite. The Allendale Lake rocks are silica-undersaturated with SiO2 ranging from 52 to 63 wt% and high contents of alkalis, particularly K2O (4.5–6.5 wt%), typical of shoshonitic rocks. The rocks show a distinct enrichment of large-ion-lithophile elements relative to heavy rare earth elements and high-field strength elements. Their isotopic compositions are highlighted by high negative ƐNd(t) values (−4.5 to −5.5), Neoproterozoic Nd model ages (750–900 Ma) and high but relatively uniform initial 87Sr/86Sr ratios (~0.706). The rocks were generated by fractional crystallization under oxidizing conditions. The parent magma, a hydrous alkaline basaltic melt, was formed by partial melting of an amphibole-phlogopite-bearing peridotite of the subduction-modified subcontinental lithospheric mantle. The mantle source underwent Neoproterozoic and subsequently Cenozoic metasomatic enrichment events. The alkaline volcanic rocks of the Penticton Group (Marron Formation) from the nearby Eocene Challis-Kamloops volcanic belt are volcanic correlatives of these intrusions. The Eocene alkaline rocks in the south-central part of the British Columbia are related to continental arc rifting.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.