New K-Ar age determinations on basalts, basaltic andesites, and ash flow tuffs from the central Western Cascades in

No abstract

We use quantitative X-ray diffraction to determine the mineralogy of late Quaternary marine sediments from the West and East Greenland shelves offshore from early Tertiary basalt outcrops. Despite the similar basalt outcrop area (60 000-70 000 km 2 ), there are significant differences between East and West Greenland sediments in the fraction of minerals (e.g. pyroxene) sourced from the basalt outcrops. We demonstrate the differences in the mineralogy between East and West Greenland marine sediments on three scales: (1) modern day, (2) late Quaternary inputs and (3) detailed down-core variations in 10 cores from the two margins. On the East Greenland Shelf (EGS), late Quaternary samples have an average quartz weight per cent of 6.2 AE 2.3 versus 12.8 AE 3.9 from the West Greenland Shelf (WGS), and 12.02 AE 4.8 versus 1.9 AE 2.3 wt% for pyroxene. K-means clustering indicated only 9% of the samples did not fit a simple EGS vs. WGS dichotomy. Sediments from the EGS and WGS are also isotopically distinct, with the EGS having higher e Nd (À18 to 4) than those from the WGS (e Nd ¼ À25 to À35). We attribute the striking dichotomy in sediment composition to fundamentally different long-term Quaternary styles of glaciation on the two basalt outcrops.