BREAKING UP A CONTINENT: TIMING AND SOURCES OF GRANITOID MAGMATISM IN THE OSLO RIFT, NORWAY
Apatite and titanite data from both batholiths exhibit high REE abundances, with ∑REE in titanite up to 44,842 ppm and ∑REE in apatite up to 35,519 ppm. High ratios of La/Sm and La/Ce (~4-15 and ~0.42-0.70ppm, respectively) are consistent with apatite crystallization in a highly-oxidized environment, with several LREE vs HREE discrimination plots indicative of apatites from mafic I type granites (Sha et al., 1999). The ∑REE abundances in titanite range from 29,031 to 43,352 ppm in the cores, and from 33,343 to 43,121 ppm in the rims. Broadly, REE-chondrite normalized patterns display prominent Eu-anomalies, consistent with crystallization in a magmatic environment where plagioclase is crystallizing. However, two titanite crystals exhibit a positive Eu anomaly and clear enrichment in the HREE. This is interpreted as representing alteration from hydrothermal fluids.
Future work will involve isotopic characterization (U-Pb, Hf, O) of the minor phases studied to date. This study therefore offers a unique opportunity to assess the processes, and timescales, associated with granitoid magmatism during continental rifting and associated continental growth.