Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Geological Magazine

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by BAHAT, D. Articles by FRID, V. Search for Related Content GeoRef GeoRef Citation

Correlation of plume morphologies on joint surfaces with their fracture mechanic implications

D. BAHAT^*,, A. RABINOVITCH and V. FRID^*

^* Department of Geological and Environmental Sciences Ben Gurion University of the Negev, POB 653 Beer Sheva, 84105 Israel, and the Deichmann Rock Mechanics Laboratory of the Negev
Department of Physics, Ben Gurion University of the Negev, POB 653 Beer Sheva, 84105 Israel, and the Deichmann Rock Mechanics Laboratory of the Negev

Author for correspondence: bahat{at}bgu.ac.il

The fractography and conditions of propagation of joints that cut Devonian siltstones in the Appalachian Plateau, New York, and Eocene chalks from the Beer Sheva Syncline, Israel, are investigated. The joints cutting the siltstones are marked by S-type and C-type plumes, and the joints cutting the Lower Eocene and Middle Eocene chalks are marked by coarse and delicate plumes, respectively. The four plume types propagated under sub-critical (slow propagation) conditions. On the semi-quantitative fracture velocity (v) versus the tensile stress intensity (K_I) curves, the S and C plume types fall in the K_I = 0.073–0.79 MPa m^1/2 and v = 2 x 10^–4–10^–2 m/s and K_I = 0.073–0.79 MPa m^1/2 and v = 10^–6–10^–4 m/s ranges respectively. The coarse and delicate plumes fall in the K_I = 0.03–0.17 MPa m^1/2 and v = 10^–6–4 x 10^–5 m/s and K_I = 0.03–0.17 MPa m^1/2 and v = 10^–4–5 x 10^–3 m/s ranges, respectively. Generally, slow plumes are relatively short, show periodicity, and typically exhibit superposition of arrest marks. On the other hand, faster plumes are longer and continuous, occur particularly in thinner layers, and show no superposition of arrest marks. There is a clear distinction between two en échelon segmentation end-members in the joint fringe, the ‘discontinuous breakdown type’ and the ‘continuous breakdown type’. There are also ‘transitional’ variations between the end-members. Only curved ‘discontinuous breakdown type’ boundaries of en échelon fringes can be equated with mirror boundaries.

Key Words: jointing • plumes • fracture mechanics • boundaries