New U-Pb SHRIMP zircon ages of the Cape Granite Suite: implications for the magmatic evolution of the Saldania Belt

Abstract

This paper presents new U-Pb (SHRIMP) age data determined on zircon populations from the Cape Granite Suite. Three peraluminous granites of the Saldanha batholith, namely the Hoedjiespunt granite, the Seeberg granite and the Trekoskraal granite, representative of Phase I of the Cape Granite Suite magmatism, were selected for the study. The data obtained indicate magmatic crystallization ages of 552±4 Ma (Hoedjiespunt granite), 54±4 Ma (Seeberg granite) and 539±4 Ma (Trekoskraal granite). The maximum age of the Cape Granite Suite is therefore about 552 Ma, significantly younger than previous age determinations for the oldest Cape granite (the Hoedjiespunt granite). The Phase I ages for magmatism in the Saldanha batholith correspond with ages for the early phases of granite migmatism in the Darling batholith and the Peninsula pluton. Phase I magmatism, which lasted for approximately 5 to 21 million years (beginning at 552±4 Ma and ending at 539±4 Ma), was characterized by the emplacement of peraluminous granites. This stage was followed by metaluminous magmatism with the entire time span of granitic magmatism in the Saldania Belt being restricted to about a 30 to 44 million year duration i.e. the difference between the ages of the 552Ma Hoedjiespunt granite and the 515 Ma Postberg ignimbrites. Show more