Prediction of weathering development in metarhyolites of the Ilgın (Konya) area, SW Turkey

Abstract

Fresh to weathered metarhyolites crop out in the Ilgın (Konya) area of the Afyon-Bolkardağ Zone. Determination of the development of weathering was studied by physical (i.e. specific gravity, dry unit weight, saturated unit weight, porosity, void ratio, and degree of saturation by weight) and mechanical (i.e. point load) properties and the \"point rock change value\" (RCV_p) and \"point rock change ratio\" (RCR_p) values of the metarhyolite rock samples. The samples were classified in 3 groups (i.e. A, B, and C) representing degree of weathering from weathered to fresh rocks based on their RCV_p and RCR_p values. The K_2O values are 7.09 wt.%, 8.62 wt.%, and 8.75 wt.% and the matrix ratios are 60%-70%, 50%-60%, and 20%-25% for groups A, B, and C, respectively. The RCV_p and RCR_p values of the studied samples range between 0.952 and 0.99 and 4.973% and 0.989%, respectively. Calculations show that metarhyolites will be completely changed by weathering at a 9.01% RCR_p value according to metarhyolite alkali values varying in the 8.12%-9.40% range, with the average value being 8.89%. At the end of the rock change processes by weathering, the rocks remain chemically as metarhyolite, while their physico-mechanical properties and mineralogical compositions change to become soil. The average K-Ar ages vary between 60.4 ± 0.9 Ma and 64.1 ± 2.00 Ma. The whole-rock alteration can furthermore be predicted by the relationships between the RCR_p and K-Ar ages of the 3 groups, which indicate that the rocks will be fully altered in the next 4.593 and 9.393 Ma. The whole-rock alteration will be completed for group A rocks in 4.6 Ma, for group B rocks in 7.2 Ma, and group C rocks in 9.4 Ma, provided that all the weathering agents take effect under the same conditions across the area.