Ashley Heath, Gary Girty‘s, and Crystal Repolge’s poster presentation at the 2014 GSA Annual Meeting in Vancouver, British Columbia.
CHARACTERIZING THE EFFECTS OF ILLUVIATION ON THE PETROLOGY AND CHEMISTRY OF TONALITIC SAPROCK: IMPLICATIONS FOR INTERPRETING COMPOSITIONAL LINEAR TRENDS
The above effects of eluviation contrast markedly with the statistically significant additions of Si, Al, Fe, Mn, Ti, Sc, Cr, Cu, Rb, Y, and Yb mass produced by illuviation. Such additions translate into an overall statistically significant 12-15% increase in bulk mass. The above increases in elemental and bulk mass are a reflection of eluvial processes operating in the now eroded overlying ≥6.7 m section of regolith. Within that overlying section, kaolinite; minute particles of biotite, hornblende, and ilmenite; and ions derived from leaching of these mineral were suspended into downward percolating fluids. The dominance of kaolinite, along with the apparent severity of leaching implied by the downward transfer of significant elemental mass, suggest a climatic regime that is unlike that currently existing in the Peninsular Ranges, or during the Quaternary, ~35,000 years ago, the exhumation age of a nearby corestone. Though poorly constrained, after removal of ~300 km of displacement along the San Andreas fault, the section of regolith studied during this investigation, may reflect Paleocene weathering within a subtropical setting.
On centered p(A)-p(CN)-p(K) ternary diagrams, illuviation resulted in a compositional linear trend anchored by the geometric mean of the corestone samples and the projected composition of kaolinite at the p(A) apex. Notably, this trend is unlike that documented for biotite-controlled and plagioclase-controlled weathering.
Session No. 31–Booth# 51