Robert F. Dymek
Campus Box 1169
1 Brookings Dr
Saint Louis MO 63130-4899
Metamorphic and Igneous Petrology
Professor Dymek utilizes field, chemical, and phase petrology in the study of igneous and metamorphic processes. More recently, he has begun to examine trace elements in sedimentary and metasedimentary rocks as recorders of crustal evolution. Professor Dymek has carried out extensive field studies in West Greenland investigating high-grade Archaean gneisses, and in the Grenville Province of Canada investigating Proterozoic massif anorthosites and related rocks. He supervises the Department's X-ray fluorescence laboratory and applies data obtained by this method in his research. Dr. Dymek is especially interested in geological problems that have a fundamental bearing on Precambrian Earth history, as follows:
(1) Storo, Greenland - Several lines of evidence, including radioactive element budgets, indicate that terrestrial heat production during the Archaean Era (before 2.5 billion years ago) was 3-4 times the present-day value. What are the consequences of this fact for the thermal structure and tectonic style in ancient crust?
Metamorphic mineral assemblages provide one of the few direct indicators of thermal regimes in Archaean crust. Do these reveal steep thermal gradients in ancient crust and/or unique styles of regional metamorphism during the Archaean?
(2) Some models hold that the average composition of the continental crust has changed significantly from the Archaean to the present. Does this reflect a change in the nature and/or rate of crust-forming processes over the course of geological time?
Clastic sediments and metasediments provide one way of testing these hypotheses because such rocks furnish information on the "average" composition of their source regions, and possibly information on lithologies no longer available for direct study. Are observed differences between Archaean and younger sediment suites an artifact of variable tectonic settings or of selective preservation of certain types of ancient terranes, or do they reflect real changes in the chemistry of the upper crust exposed to erosion? In what ways are any conclusions compromised by elemental dispersion and mobility during metamorphism?
(3) Igneous rocks consisting predominantly of plagioclase feldspar (massif anorthosite) are unusually abundant in mid-Proterozoic crustal terranes (ca. 1000-1600 million years old), but otherwise are quite rare. As such, massif anorthosites represent one of the better examples of secular magma genesis in the geological record. Prof. Dymek and students from EPSc 318, Development of the North American Landscape, at Dante's View, Death Valley National Park
Does the time and space distribution of massif anorthosites reflect unique stages and/or processes in the growth of the continents? What special circumstances are required for extreme enrichment in plagioclase? Are anorthosites simply cumulates from a common magma type (gabbro or diorite), are they the products of a distillation process involving separation of immiscible liquids, or were anorthositic magmas involved? Why are Fe-Ti oxide ores commonly found with anorthosites? Why are associated pyroxene-bearing granitoids ("jotunites" and "mangerites") so enriched in Ti, P, and most incompatible trace elements compared to orogenic granite suites?
Owens, B. E. & Dymek, R. F. (1997) Comparative petrology of Archaean anorthosites in amphibolite and granulite facies terranes, SW Greenland. Contributions to Mineralogy and Petrology, 128, 371-384.
Owens, B. E. & Dymek, R. F. (1999) A geochemical reconnaissance of the Roseland anorthosite complex, Virginia, and comparisons with andesine anorthosites from the Grenville Province, Quebec. In: A.K. Sinha (editor), Basement Tectonics, 13, 217-232.
Owens, B. E. & Dymek, R. F. (2001) Petrogenesis of the Labrieville alkalic-anorthosite massif, Greenville Province, Quebec. Journal of Petrology,42, 1519-1546.
Dymek, R. F. & Owens, B. E. (2001) Petrogenesis of apatite-rich rocks (nelsonites and oxide-apatite gabbronorites) associated with massif anorthosites. Economic Geology, 96, 797-815.
Dymek, R. F.& Owens, B. E. (2001) Chemical assembly of Archaean anorthosites from amphibolite- and granulite-facies terranes, West Greenland. Contributions to Mineralogy and Petrology, 141, 513-528.
Earth Materials; Petrography; Advanced Physical Geology; Chemical Petrology; Geology of National Parks