Albitization and Amphiboles in the Idefjorden Terrane, Billdal: a geochemical study of Monzonite in SW Sweden

Abstract

This Paper investigates and maps a rocky outcrop in southwestern Sweden previously mapped by the Swedish geological survey (SGU) as porphyritic granite intruded by a gabbro in the Billdal area of Västra Götalands municipality SW Sweden. As found by this paper the mineralogy is not consistent with existing SGU maps and is infract a monzonite containing large amounts of plagioclase and calcic amphiboles, exhibiting a petrology and chemistry consistent with a granite metamorphosed by hydrothermal fluids rich in sodium causing albitization and amphibolite facies metamorphism. This paper argues the metamorphism was driven by the heat produced by the nearby gabbro intrusion. A geochemical study of three nearby outcrops were performed along with U-pb dating with the purpose of accurately dating the outcrop and finding the boundary between the Hisingen suite and Kungsbacka bimodal zone. Although the U-Pb dating failed due to metamict samples a tentative pattern was found in zircon morphology and magnetic susceptibility that may provide guidance for future study.