Contrasting styles of fluid-rock interaction within the West Fissure Zone in northern Chile

Abstract

Geochemical data from three profiles crossing the West Fissure Zone in northern Chile were used to describe the chemical effects of fluids on faulting processes. The results document considerable differences of fluid-rock interactions between the profiles (A-C). Within the area of profile A and C fluid activities have neither led to intensive exchange reactions between fluids and rocks nor to notable changes in whole rock and mineral composition of fault rocks relative to their undeformed host rock. Investigations of stable isotopes (513C, 8180) and fluid inclusions indicate infiltration of predominantly descending (meteoric) fluids and only subordinate involvement of ascending hydrothermal fluids. In the case of profile B, fluid-enhanced weakening mechanisms are dominant. Dissolution transfer has led to the formation of an alteration zone up to 400 m wide. Along profile B we have no indications for warm fluids derived from a deep source. Rather, a number of lines of evidence (e.g. 5180 and ~D) show that fault rock alteration took place due to the infiltration of low temperature meteoric water. For this profile, all geochemical data indicate an open fluid system. Moreover, the chemical variations across the West Fissure Zone agree well with the structural variability observed at this traverse. The application of a variety of geochemical analyses of fault rocks shows the heterogeneity of largescale continental fault zones.

Correlation of electrical conductivity and structural damage at a major strike‐slip fault in northern Chile

“…The spring emanating on the West fault trace proves the availability of surface water in the study area. Furthermore, the presence of fluids of primarily meteoric origin in the younger geologic past is supported by fluid-rock chemistry of the alteration zone material [Janssen et al, 2004].…”

“…Gorila is the study area presented in this paper. Studies of two other segments of the West fault zone are published by Janssen et al [2002Janssen et al [ , 2004. Dotted lines are transects of two regional magnetotelluric studies [Brasse et al, 2002].…”

“…A fault core of the type visible for the WF in the copper pit mine of Chuquicamata, with a black argillitic fault gouge up to 5 m thick [Ossandón et al, 2001], is not exposed (or preserved) in the Gorila region. Instead, a $400 m wide fluid alteration zone of intense material comminution is discernible, in which almost no damage elements can be identified [Janssen et al, 2004; (compare photo in Figure 4d of Janssen et al [2004]). Only larger blocks that are less affected by alteration, contribute to the fault damage data.…”

“…Carbonate precipitation occurs at lower temperatures (<80°C) and depth [Renard et al, 2000;Labaume et al, 2001]. The alteration products exposed at the surface indicate low-temperature alteration conditions (<100°C) and no SiO 2 dissolution processes [Janssen et al, 2004]. The fault fracture mesh is (and was) not sealed at shallow depth, but permeability reduction due to quartz seals likely prevents fluid flow to greater depth ( Figure 13).…”

The role of fluids in faulting deformation:a case study from the Dead Sea Transform (Jordan)

“…In spite of these comprehensive investigations, the understanding of the DST as fluid entrapment and fluid channel is limited even though the characterization of fluid-rock interactions and fluid flow in fault zones is an essential precondition to understanding faulting processes. Especially in large strike-slip fault zones, fluid circulation may play an important role in controlling the mechanical behavior of faults (Sibson1992; Byerlee1993; Rice 1992;Evans and Chester 1995;Muchez and Sintubin1998;Conti et al 2001;Janssen et al 2004a).…”