BASALTS, GRANITES, VOLCANOES AND XRF (Invited Presentation)

From age 14 I knew I wanted to be a geologist: especially a field geologist. At University my reaction to a short course on XRF analysis was “Thank God that’s over”. But, ironically, my first job with the Bureau of Mineral Resources in Australia, mapping in the outback of the Northern Territory for 9 months of the year, provided all the field work I needed. But it was here I first became interested in granites. I did this at ANU with Bruce Chappell who was developing highly quantitative XRF analyses for all types of rocks. I was hooked and came to appreciate the vital importance of good data. Your ideas may be flawed, but if the data is sound, it remains invaluable.

Bruce recommended me to NASA to run an XRF lab at the Johnson Manned Spacecraft Center analyzing rocks returned by the Apollo missions. These were exciting, heady but stressful times. The focus of my research switched from granites to the lunar mare basalts. At this time, the Glomar Challenger, was drilling the world’s oceans, recovering samples of the oceanic crust. A major outcome of our research on these ocean crust basalts was that their compositions were dominated by magma mixing due to magmatic recharge. It was an idea whose time had come and is now recognized as important in most volcanic systems. Although drill cores provide some temporal control, the magnitude of the time interval between successive eruptive units is unknown.

It was time to work on active volcanoes. Collaboration with Pete Lipman and Jack Lockwood (USGS) on Mauna Loa, Hawaii, provided the answer, adding geochemical data to their careful mapping and C14 dating of flows. About this time, I was invited to establish a Regional XRF Analytical Facility at the University of Massachusetts. Studies on Mauna Loa continued, including the 1984 eruption, and more recently that of 2022. Simultaneously, work with Mike Garcia on the 39 year long Puu Oo eruption of Kilauea, and Mauna Loa submarine lavas by dredging and with submersibles has proved most fruitful

Granites were not forgotten! Work on the Maine granites of Vinalhaven and Isle au Haut, showed that these granites had been intruded by basaltic magmas, producing quenched pillow lavas and sills. Strong evidence that basaltic magmatism provides the driving engine for granite batholiths and large volume silicic eruptions.