skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Role of isostasy in the evolution of normal fault systems

Abstract

The footwalls of west-dipping normal faults that separate the west-central Colorado Plateau from the Basin and Range province record at least 5-7 km, and perhaps as much as 15-20 km, of west-side-up Neogene uplift, with an axis just 10-20 km west of undeformed plateau strata. The uplift is expressed as folding and steep faulting in pre-Tertiary cratonic and disconformably overlying Neogene strata, forming a basement-cored anticline and coincident topographic high on the western margin of the plateau. The authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin. Profound, isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains, calling into question several assumptions fundamental to existing models of the evolution of normal fault systems.

Authors:
;
Publication Date:
Research Org.:
Harvard Univ., Cambridge, MA (USA)
OSTI Identifier:
6765075
Alternate Identifier(s):
OSTI ID: 6765075
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geology; (United States); Journal Volume: 16:9
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GEOLOGIC FAULTS; GEOLOGIC MODELS; COLORADO; DEFORMATION; GEOLOGIC HISTORY; GROUND UPLIFT; ORIGIN; STRATA MOVEMENT; FEDERAL REGION VIII; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; NORTH AMERICA; USA 580100* -- Geology & Hydrology-- (-1989)

Citation Formats

Wernicke, B., and Axen, G.J.. Role of isostasy in the evolution of normal fault systems. United States: N. p., 1988. Web. doi:10.1130/0091-7613(1988)016<0848:OTROII>2.3.CO;2.
Wernicke, B., & Axen, G.J.. Role of isostasy in the evolution of normal fault systems. United States. doi:10.1130/0091-7613(1988)016<0848:OTROII>2.3.CO;2.
Wernicke, B., and Axen, G.J.. Thu . "Role of isostasy in the evolution of normal fault systems". United States. doi:10.1130/0091-7613(1988)016<0848:OTROII>2.3.CO;2.
@article{osti_6765075,
title = {Role of isostasy in the evolution of normal fault systems},
author = {Wernicke, B. and Axen, G.J.},
abstractNote = {The footwalls of west-dipping normal faults that separate the west-central Colorado Plateau from the Basin and Range province record at least 5-7 km, and perhaps as much as 15-20 km, of west-side-up Neogene uplift, with an axis just 10-20 km west of undeformed plateau strata. The uplift is expressed as folding and steep faulting in pre-Tertiary cratonic and disconformably overlying Neogene strata, forming a basement-cored anticline and coincident topographic high on the western margin of the plateau. The authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin. Profound, isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains, calling into question several assumptions fundamental to existing models of the evolution of normal fault systems.},
doi = {10.1130/0091-7613(1988)016<0848:OTROII>2.3.CO;2},
journal = {Geology; (United States)},
number = ,
volume = 16:9,
place = {United States},
year = {Thu Sep 01 00:00:00 EDT 1988},
month = {Thu Sep 01 00:00:00 EDT 1988}
}
  • From a geometric analysis of the fault pattern in the Reconcavo basin, Brazil, supported by a reinterpretation of the early opening history of the South Atlantic Ocean, it is inferred that the basin formed as a result of Valanginian (Early Cretaceous) motion on a major N40/sup 0/E-striking left-lateral transform fault located offshore between Salvador and Recife. This left-lateral motion was due to the location of the Valanginian pole of South American - African plate rotation within northern Brazil, at 2.5 /sup 0/S, 45.0/sup 0/W, rather than farther north as interpreted previously. 13 figures, 2 tables.
  • From a geometric analysis of the fault pattern in the Reconcavo basin, Brazil, supported by a reinterpretation of the early opening history of the South Atlantic Ocean, it is inferred that the basin formed as a result of Valanginian (Early Cretaceous) motion on a major N40/sup 0/E-striking left-lateral transform fault located offshore between Salvador and Recife. Left-lateral movement along the inferred transform created three fault sets. Geohistory curves for Early Cretaceous units in the Reconcavo basin indicate that the syn-tectonic Valanginian shales of the lacustrine Candeias Formation began to generate hydrocarbons during the earliest subsequent deposition of the Ilhas Formationmore » (.Hauterivian). Rejuvenation as normal faults of earlier formed strikeslip and normal faults occurred in the latest Aptian. Rejuvenated faults tapped earlier filled Sergi Formation reservoirs, which then leaked earlier reservoired hydrocarbons up these fault planes into higher reservoirs in the Ilhas and Sao Sebastiao Formations.« less
  • Discrepancies in right-lateral strike-slip separation of pre-Tertiary and Tertiary geologic features along the northern San Andreas fault give rise to two contrasting views of the evolution of the fault system. One model entails two stages of right slip on the San Andreas fault, one Late Cretaceous-early Tertiary and one post-Oligocene. The other model required significant right slip on multiple faults of the Neogene San Andreas fault system. Several lines of evidence now suggest that major Neogene right slip occurred on several faults of the San Andreas transform-fault system in addition to the San Andreas fault proper. Furthermore, these data indicatemore » that the magnitude of proto-San Andreas right slip probably was far less than previously suggested. Integration of the fault studies and regional geologic relations, especially in the central Salinian block, permits reconstruction of the tectonic evolution of the San Andreas fault system and the central California margin. A relatively modest amount of right slip on a proto-San Andreas fault, possibly the consequence of oblique plate convergence, emplaced granitic basement of the Salinian block west of the fault in Paleocene time. Following an initial rise-trench encounter in the Oligocene, migration of a triple junction from south to north past central California resulted in coordinate termination of subduction and propagation of the San Andreas transform-fault system. Initially, the Salinian block experienced extensional tectonism, perhaps related to the passage of the triple junction. Right slip on the San Andreas fault and on faults cutting the Salinian block probably began in middle Miocene time. Since a late Miocene change of pole of rotation of the Pacific-North American plate pair, motion has been increasingly absorbed on the San Andreas fault proper.« less
  • In order to help understand the evolution of stacking fault tetrahedra (SFTs) in a cascade producing irradiation environment, the available information on the behavior of SFTs observed under different experimental conditions has been briefly reviewed. Effects of thermal annealing and irradiations on the stability of pre-existing SFTs produced by quenching and aging are also included in the review. Some results on the effects of thermal annealing of irradiation-induced SFTs are presented and discussed. The analysis of these observations leads to three significant conclusions: (a) during irradiation SFTs produced in the cascades are likely to interact with vacancies, self-interstitial atoms (SIAs)more » and SIA clusters, (b) interaction with SIAs and their clusters may cause both shrinkage and transformation of SFTs into Frank loops and (c) both during irradiation and annealing the lifetime of SFTs is determined not only by their thermal stability but also by their stability against transformation to loops. These facts must be taken into account in the theoretical treatments of damage accumulation.« less
  • Normal fault zones play a major role in the development of basins and in the migration and trapping of hydrocarbons. The mapping of normal fault systems using seismic data requires careful correlation of faults on adjacent sections, a procedure that often leads to the interpretation of faults as having long, continuous, sinuous traces. Recent work involving detailed mapping of fault traces, first by using land exposures but more recently using three-dimensional seismics, has demonstrated that faults are usually made up of many overstepping segments, linked by areas of complex deformation, termed transfer zones or relay ramps. Relay ramps occur betweenmore » normal fault segments that overstep in map view. The geometry and evolution of exposure-scale relay ramps are described from the Somerset coast, England, and are compared with larger scale ramps from elsewhere. Relay ramps can be classified into four groups based on the degree of interaction and linkage between the overstepping segments; these groups are interpreted as being evolutionary stages. In stage 1, the segments do not interact. Stage 2 involves the reorientation of bedding between two interacting faults to produce a relay ramp. In stage 3, connecting fractures start to break the relay ramp. Stage 4 is when the relay ramp is destroyed to produce a single fault that has an along-strike bend. These evolutionary stages can develop through time, but they can also be seen spatially. A branch line between normal faults or an along-strike bend may represent a stage 4 relay, with progressively earlier stages occurring updip or downdip. Characteristic variability in displacement-distance profiles for fault segments and linked faults accompanies the interaction and linkage processes. Displacement transfer by relay ramps is accompanied by steep displacement gradients along fault segments at oversteps. Relay ramps often contribute to a minimum in total fault displacement at a linkage point. 47 refs., 16 figs.« less