Large-magnitude continental extension: An example from the central Mojave metamorphic core complex

Fletcher, J. M.; Bartley, John M.; Martin, Mark W.; Glazner, Allen F.; Walker, J. Douglas

doi:10.1130/0016-7606(1995)107<1468:lmceae>2.3.co;2

Cited by 88 publications

(72 citation statements)

References 52 publications

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“…The fault corrugations have map view wavelengths of 40-50 km and amplitudes of 5 -15 km, which is comparable to those at many other Cordilleran core complexes. Slip perpendicular folds in the fault have been reported at several other core complexes [e.g., Reynolds and Lister, 1990;Fletcher et al, 1995] but we have not identified such folds at Sierra Mazatán, although most of the updip exposures of the fault have been eroded.…”

Section: Main Low-angle Normal Faultcontrasting

confidence: 56%

“…[77] Many detachment faults associated with core complexes have broad corrugations or folds with axes that are parallel to the extension direction [e.g., John, 1987;Fletcher et al, 1995], a geometry that defines the distinctive basin and dome topography characteristic of many core complexes. This fault geometry has been interpreted either as folds of an initially planar fault [e.g., Spencer, 1982;Yin and Dunn, 1992] possibly as a result of crustal shortening perpendicular to extension [Holm et al, 1994;Fletcher et al, 1995] or as original corrugations in the fault surface [John, 1987;Spencer, 1985].…”

Section: Detachment Fault Corrugationsmentioning

confidence: 99%

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Geologic, structural, and thermochronologic constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation

Wong

Gans

2008

Tectonics

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The Sierra Mazatán in northwestern Mexico is the southernmost metamorphic core complex in the North American Cordillera. Large‐magnitude Tertiary extension at Sierra Mazatán involved both ductile and brittle slip along a major normal fault that presently dips 10°–15° west. Extension was polyphase and involved an early period of extension from 25 to 23 Ma followed by major slip from 21 to 16 Ma. Total slip was ≤20 km and occurred at rates of 3–4 mm/a. This extension predated the plate boundary change to transtension at ∼12 Ma and was largely decoupled from relative Pacific–North American plate motion. Numerous lines of evidence suggest that the presently low‐angle normal fault initiated at a steep dip (50°–60°) and was rotated to lower angles during slip. When corrected for this tilting, fault corrugations at Sierra Mazatán had a similar geometry to the segmentation of many active normal faults, which is compatible with their origin as primary fault features. Many aspects of the Sierra Mazatán are comparable to large active normal faults, indicating that this core complex formed owing to prolonged extension on an otherwise typical high‐angle normal fault. Therefore, core complexes need not represent a fundamentally unique mode of crustal extension.

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Section: Main Low-angle Normal Faultcontrasting

confidence: 56%

Section: Detachment Fault Corrugationsmentioning

confidence: 99%

Geologic, structural, and thermochronologic constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation

Wong

Gans

2008

Tectonics

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“…[Fletcher et al, 1995], and footwall volume expansion during unloading [Spencer, 1982]. With respect to tectonic configuration, at midocean ridges we expect horizontal, isochron-parallel extension rather than compression because of contraction of the cooling lithosphere [Collette, 1974;Turcotte, 1974].…”

Section: Interpretation Of Megamullionsmentioning

confidence: 99%

Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid‐Atlantic Ridge

Tucholke¹,

Lin²,

Kleinrock³

1998

J. Geophys. Res.

494

539

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Abstract. In a study of geological and geophysical data from the Mid-Atlantic Ridge, we have identified 17 large, domed edifices (megamullions) that have surfaces corrugated by distinctive mullion structure and that are developed within inside-corner tectonic settings at ends of spreading segments. The edifices have elevated residual gravity anomalies, and limited sampling has recovered gabbros and serpentinites, suggesting that they expose extensive cross sections of the oceanic crust and upper mantle. Oceanic megamullions are comparable to continental metamorphic core complexes in scale and structure, and they may originate by similar processes. The megamullions are interpreted to be rotated footwall blocks of low-angle detachment faults, and they provide the best evidence to date for the common development and longevity (-1-2 m.y.) of such faults in ocean crust. Prolonged slip on a detachment fault probably occurs when a spreading segment experiences a lengthy phase of relatively amagmatic extension. During these periods it is easier to maintain slip on an existing fault at the segment end than it is to break a new fault in the strong rift-valley lithosphere; slip on the detachment fault probably is facilitated by fault weakening related to deep lithospheric changes in deformation mechanism and mantle serpentinization. At the segment center, minor, episodic magmatism may continue to weaken the axial lithosphere and thus sustain inward jumping of faults. A detachment fault will be terminated when magmatism becomes robust enough to reach the segment end, weaken the axial lithosphere, and promote inward fault jumps there. This mechanism may be generally important in controlling the longevity of normal faults at segment ends and thus in accounting for variable and intermittent development of inside-corner highs.

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“…1. Schematic cross sections portraying the rolling hinge model for folding of extensional shear zones and exhumation of medium to high grade rocks during asymmetric rifting (after Fletcher et al, 1995). (a) A discrete normal fault in the upper, brittle crust widens into a ductile shear zone with depth.…”

Section: Collapse Of a Thrust-thickened Orogenmentioning

confidence: 99%

“…Numerical modelling indicates that the stress reduction itself in the extension direction is insufficient for extension-parallel folds to develop unless the magnitudes of the horizontal principal stresses (r 1 and r 2 ) are relatively close (Yin, 1991). In this case, reduction of the vertical stress and increase of horizontal stress by tectonic denudation may cause r 1 to switch from vertical to horizontal during or after extension (Fletcher et al, 1995). Yin (1991) also shows that detachment shear zones may be deformed by folds with axes parallel and orthogonal to the transport direction, forming dome and basin structures.…”

Section: Formation Of Folds With Axes Parallel To the Maximum Extensimentioning

confidence: 99%

Mechanisms for folding of high-grade rocks in extensional tectonic settings

Harris

Koyi

Fossen

2002

Earth-Science Reviews

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This review of structures developed in extensional high-grade terrains, combined with results of centrifuge analogue modelling, illustrates the range of fold styles and mechanisms for folding of amphibolite to granulite facies rocks during rifting or the collapse of a thrust-thickened orogen. Several extensional fold mechanisms (such as folding within detachment shear zones) are similar to those in contractional settings. The metamorphic P -T -t path, and not fold style or mode of formation, is therefore required to determine the tectonic setting in which some folds developed. Other mechanisms such as rollover above and folding between listric normal shear zones, and folding due to isostatic adjustments during crustal thinning, are unique to extensional tectonic settings. Several mechanisms for folding during crustal extension produce structures that could easily be misinterpreted as implying regional contraction and hence lead to errors in their tectonic interpretation. It is shown that isoclinal recumbent folds refolded by open, upright folds may develop during regional extension in the deep crust. Folds with a thrust sense of asymmetry can develop due to high shear strains within an extensional detachment, or from enhanced back-rotation of layers between normal shear zones. During back-rotation folding, layers rotated into the shortening field undergo further buckle folding, and all may rotate towards orthogonality to the maximum shortening direction. This mechanism explains the presence of many transposed folds, folds with axial planar pegmatites and folds with opposite vergence in extensional terrains. Examples of folds in high-grade rocks interpreted as forming during regional extension included in this paper are from the Grenville Province of Canada, Norwegian

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Large-magnitude continental extension: An example from the central Mojave metamorphic core complex

Cited by 88 publications

References 52 publications

Geologic, structural, and thermochronologic constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation

Geologic, structural, and thermochronologic constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation

Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid‐Atlantic Ridge

Mechanisms for folding of high-grade rocks in extensional tectonic settings

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