Abstract
Pillow lava is a common feature of volcanic stratigraphy throughout geologic time. A comparison is made between the morphology of oceanic pillows from the FAMOUS area of the Mid-Atlantic Ridge, recent pillows from Iceland, and Archean pillows from the Rouyn-Noranda area of northwestern Quebec. In two dimensions the shapes and sizes of pillows from the three areas are similar but not identical. Abyssal and subglacial lava flows, when viewed in three dimensions, appear to be tubular lava forms similar to subaerial pahoehoe flows. Archean pillows also appear to be interconnected. Evidence of this includes broken selvages, lenticular quartz-filled cavities representing fossil lava levels, and the "pinch and swell" nature of elongate pillows. The stratigraphy of Archean volcanics and modern-day oceanic crust as seen in DSDP holes is similar. Both consist of interlayered massive, pillowed, and breccia units in an apparent random order. However, there appears to be a preponderance of pillowed flows in the modern volcanics compared to the ancient examples. Archean flows appear to be longer and, possibly, thicker than those at present-day ocean ridges and individual Archean pillows are in some places flattened and welded. These observations suggest that the rate of eruption in the Archean may have been greater than in known areas of the Mid-Atlantic Ridge. Pillow morphology and vesicle size and distribution in the Archean examples are consistent with a relatively shallow depth of eruption for the Archean sequences. Overall, the styles of eruption of both the Archean and modern pillow sequences appear to have been similar.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call