Regional Metamorphism within a Creationist Framework: What Garnet Compositions Reveal
by Andrew A. Snelling, Ph.D.
Presented at the Third International Conference on Creationism, Pittsburgh, Pennsylvania, July 18–23, 1994. Published in: Proceedings of the Third International Conference on Creationism, R. E. Walsh (editor), pp. 485–496.
© 1994 Creation Science Fellowship, Inc. Pittsburgh, Pennsylvania, USA. All Rights Reserved.
The “classical” model for regional metamorphic zones presupposes elevated temperatures and pressures due to deep burial and deformation/tectonic forces over large areas over millions of years— an apparent insurmountable hurdle for the creationist framework. One diagnostic metamorphic mineral is garnet, and variations in its composition have long been studied as an indicator of metamorphic grade conditions. Such compositional variations that have been detected between and within grains in the same rock strata are usually explained in terms of cationic fractionation with changing temperature during specific continuous reactions involving elemental distribution patterns in the rock matrix around the crystallizing garnet. Garnet compositions are also said to correlate with their metamorphic grade.
However, contrary evidence has been ignored. Compositional patterns preserved in garnets have been shown to be a reflection of compositional zoning in the original precursor minerals and sediments. Compositional variations between and within garnet grains in schists that are typical metapelites at Koongarra in the Northern Territory, Australia, support this minority viewpoint. Both homogeneous and compositionally zoned garnets, even together in the same hand specimen, display a range of compositions that would normally reflect widely different metamorphic grade and temperature conditions during their supposed growth. Thus the majority viewpoint cannot explain the formation of these garnets. It has also been demonstrated that the solid-solid transformation from a sedimentary chlorite precursor to garnet needs only low to moderate temperatures, while compositional patterns only reflect original depositional features in sedimentary environments. Thus catastrophic sedimentation, deep burial and rapid deformation/tectonics with accompanying low to moderate temperatures and pressures during, for example, a global Flood and its aftermath have potential as a model for explaining the “classical” zones of progressive regional metamorphism.
Regional Metamorphism, Grade Zones, Garnets, Compositional Zoning, Sedimentary Precursors
For Full Text
Please see the Download PDF link above for the entire article.