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Can we relate the surface expression of dike-induced normal faults to subsurface dike geometry?

Craig Magee and Christopher A. L. Jackson
Can we relate the surface expression of dike-induced normal faults to subsurface dike geometry?
Geology (Boulder) (November 2020) 49 (4): 366-371

Abstract

Many igneous dikes do not reach the surface, instead triggering normal faulting and graben formation in overlying rock. The surface expression of these dike-induced faults provides important records of active and ancient diking. For example, surface measurements of graben half-widths have been used to estimate dike upper-tip depths by projecting faults straight downdip, whereas extension measured at the surface across dike-induced fault pairs (i.e., their cumulative heave) is considered a proxy for dike thickness. We use three-dimensional seismic reflection data to test how the surface expression of two buried dike-induced faults relates to dike geometry. The dike-induced faults are nonplanar, suggesting fault dips should not be assumed constant when using graben half-widths to estimate dike depth. Multiple displacement maxima occur across the dike-induced faults, but rarely at their lower or upper tips, suggesting they formed through linkage of isolated faults that nucleated between the dike and free surface. Fault heave is greatest where these subsurface displacement maxima occur, meaning the cumulative heave of the dike-induced fault pair measured at the syn-faulting free surface underestimates their total extension and poorly reflects dike thickness. Our results imply that at-surface analyses of dike-induced fault geometry cannot be used to estimate key dike parameters without a priori knowledge of fault structure and kinematics or host rock lithological variations.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 49
Serial Issue: 4
Title: Can we relate the surface expression of dike-induced normal faults to subsurface dike geometry?
Affiliation: University of Leeds, School of Earth Science and Environment, Leeds, United Kingdom
Pages: 366-371
Published: 20201125
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 35
Accession Number: 2021-005276
Categories: Igneous and metamorphic petrologyStructural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sect., sketch maps
S19°48'00" - S19°31'60", E113°42'00" - E114°19'00"
Secondary Affiliation: Imperial College, GBR, United Kingdom
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202104
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