Travitonics: using travertines in active fault studies

Late Quaternary travertines deposited from hot springs can reveal much abou t the neotectonic attributes and histories of structures. On the basis of f ield studies in the Aegean region (Turkey and Greece), the northern Apennin es (Italy) and the Basin and Range province (USA) we conclude that the foll owing relationships are of predictive value: (i) travertine deposits are pr eferentially located along fracture traces, either immediately above extens ional fissures or in the hanging walls of normal faults; (ii) the locations of many travertine fissure-ridge deposits coincide with step-over zones (r elay ramps) between fault segments; networks of intersecting tensional fiss ures reflecting the complex strains experienced in such settings are probab ly responsible for enhancing hydrothermal flow; (iii) the morphology of tra vertine deposits overlying extensional fissures is controlled by the rheolo gy of the underlying materials; tufa cones (towers, pinnacles) form on form er and present lake hoots where fissures underlie unconsolidated sediments, whereas fissure-ridges develop where fissures cut bedrocks at the surface; (iv) fissure-ridges comprise outwardly dipping bedded travertine flanking a central tensional fissure filled by vertically banded travertines; fissur es can be used to infer local stretching directions; (v) where there are tr avertines datable by the U-series method it is possible to calculate time-a veraged dilation and lateral propagation rates for individual fissures; (vi ) most fissures cutting fissure-ridges comprise self-similar angular segmen ts with fractal dimensions in the range 1.00-1.12, the properties of bedded travertine combined with stress perturbations at fissure tips probably bei ng responsible for such similar fractal dimensions being inferred from such a wide range of locations. Fissures gradually increasing in width with dep th are products of continuous fracture dilation in contrast to those that f orm during episodic dilation which display stepped increases of width with depth; (vii) travertine deposited from springs along fault zones accumulate in terraced-mounds sited down slope of the spring line; (viii) many post-d epositional fractures cutting travertine deposits are locally oriented at r ight angles to deposit margins; and (ix) systematic joints in travertines a re restricted to those parts of eroded sheet deposits that have been exhume d. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.