GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 202-26
Presentation Time: 9:00 AM-6:30 PM


KULIGIEWICZ, Artur, Institute of Geological Sciences - Research Centre in Krakow, Polish Academy of Sciences, Senacka 1, Krakow, 31-002, Poland, SKIBA, Michal, Institute of Geological Sciences, Jagiellonian University, Golebia 24, Krakow, 31-007, Poland, SZCZERBA, Marek, Research Centre in Cracow, Institute of Geological Sciences, Polish Academy of Sciences, ul. Senacka 1, Kraków, 31-002, Poland and HALL, Chris M., Earth and Environmental Sciences, University of Michigan, 2534 C.C. Little Building, 1100 N. University Ave, Ann Arbor, MI 48109

In this study seven clay gouges from Tatra Mountains, Poland were investigated for using X-ray diffraction and Ar-Ar dating. Constraining timing of fault activity using radiometric dating is often based on the assumption that dioctahedral mica (“illite”) polytypes in fault zones form following the sequence: 2M1 polytype the oldest, followed by 1M and 1Md. A key aim of this study was to test this assumption.

The bulk mineral composition of gouge materials was quartz, plagioclase, K-feldspar, dioctahedral mica (2M1, 1M, and 1Md), smectite, and chlorite. Investigation of clay size fractions indicated the presence of mixed-layer R1 illite-smectite and kaolinite along with phases present in bulk. Large variability of gouge compositions among the investigated zones was noted.

Vacuum encapsulated Ar-Ar dates were obtained for four size fractions of one feldspar-free gouge. Three different approaches were used for extracting end-member ages (Tab. 1), including a three-component model proposed in this study.

Tab. 1. Preliminary age values of illite polytypes present in the clay gouge sample (in Ma) obtained with different approaches.


Illite Age Analysis*


3 component system


204.6 ± 31

183.8 ± 29

33.1 ± 23


10.4 ± 11

5.4 ± 13

189.8 ± 21


2.8 ± 5

* Pevear (1992)

**Szczerba and Środoń (2009)

Timing of fault activity was highly dependent on the method used for age calculation. Methods handling two-component system returned age values in rough agreement, pointing towards a young age of the authigenic component and at least a partial age reset of the “inherited” component during Alpine orogeny. The results of three-component age modeling indicated, however, that the assumption underlying conventional age analysis i.e. that 1M and 1Md illite polytypes form at the same time, may not be always valid.


AK thanks the Clay Minerals Society for founding the research with a Student Research Grant.


Pevear, D.R. (1992) Illite age analysis, a new tool for basin thermal history analysis Pp. 1251-1254 in: Water-Rock Interaction (Y.K. Kharaka and A.S. Maest, editors). A.A. Balkema, Rotterdam, The Netherlands.

Szczerba, M. and Środoń, J. (2009) Extraction of diagenetic and detrital ages and of the 40Kdetrital/40Kdiagenetic ratio from K-Ar dates of clay fractions. Clay Clay Miner, 57, 93-103.