Unroofing of active metamorphic core complexes in the D'Entrecasteaux Islands, Papua New Guinea

Hill, E. J.; Baldwin, Suzanne L.; Lister, Gordon

doi:10.1130/0091-7613(1992)020<0907:uoamcc>2.3.co;2

Cited by 148 publications

(120 citation statements)

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“…Studies of metamorphic core complexes (e.g. Malavieille, 1987a,b;Coney, 1980;Hill et al, 1992) show that shallowly dipping gneissic foliations may develop during crustal extension. In such settings, shear fabrics along extensional detachments may overprint subhorizontal flattening foliations (e.g.…”

Section: Origin Of Shallowly Dipping Foliations In Highgrade Gneiss Tmentioning

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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Section: Origin Of Shallowly Dipping Foliations In Highgrade Gneiss Tmentioning

confidence: 99%

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

Harris

Koyi

Fossen

2002

Earth-Science Reviews

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“…Hill et al, 1992). Orogenic extension can occur if erosion is unable to denude the main part of the upper crust in central sectors of orogenic belts and thereby compensate gravitational instabilities created by crustal thickening during contractional tectonics (Dewey, 1988).…”

Section: Introductionmentioning

confidence: 99%

Rapid Variscan exhumation and the role of magma in core complex formation: southern Brittany metamorphic belt, France

Brown

Dallmeyer

1996

Journal Metamorphic Geology

115

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The high-grade migmatitic core to the southern Brittany metamorphic belt has mineralogical and textural features that suggest high-temperature decompression. The chronology of this decompression and subsequent cooling history have been constrained with 40Ar/39Ar ages determined for multigrain concentrates of hornblende and muscovite prepared from amphibolite and late-orogenic granite sheets within the migmatitic core, and from amphibolite of the structurally overlying unit. Three hornblende concentrates yield plateau isotope correlation ages of c. 303-298 Ma. Two muscovite concentrates record well-defined plateau ages of c. 306-305 Ma. These ages are geologically significant and date the last cooling through temperatures required for intracrystalline retention of radiogenic argon. The concordancy of the hornblende and muscovite ages suggest rapid post-metamorphic cooling. Extant geochronology and the new 40Ar/3'Ar data suggest a minimum time-integrated average cooling rate between c. 725 "C and c. 125 "C of c. 14+4"C Ma-', although below 600 'C the data permit an infinitely fast rate of cooling. Mineral assemblages and reaction textures in diatexite migmatites suggest c. 4 kbar decompression at 800-750 "C. This must have pre-dated the rapid cooling. Emplacement of two-mica granites into the metamorphic belt occurred between 345 and 300 Ma. The youngest plutons were emplaced synkinematically along shallow-dipping normal faults interpreted to be reactivated Eo-Variscan thrusts. A penetrative, west-plunging stretching lineation developed in these granites suggests that extension was orogen-parallel. Extension was probably related to regional uplift and gravitational collapse of thermally weakened crust during constrictional (escape) tectonics in this narrow part of the Variscan orogen. This followed slab breakor during the terminal stages of convergence between Gondwana and Laurasia; detachment may have been consequent upon a change in kinematics leading to dextral displacement within the orogen. Dextral ductile strike-slip displacement was concentrated in granites emplaced synkinematically along the South Armorican Shear Zone. Rapid cooling is interpreted to have resulted from tectonic unroofing with emplacement of granite along decollement surfaces. The high-grade migmatitic core of the southern Brittany metamorphic belt represents a type of metamorphic core complex formed during orogen-parallel extensional unroofing and regional-scale ductile flow.

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“…Metamorphic core complexes on the D'Entrecasteaux Islands and in the Suckling-Dayman massif on the Papuan Peninsula were also exhumed in the Pliocene/Pleistocene (Davies, 1980;Davies and Warren, 1988;Hill, 1990). The best structural studies, geothermometry, geobarometry, and age dating of these complexes have been done on Goodenough and Fergusson Islands (Davies and Warren, 1992;Hill et al, 1992Hill et al, , 1995Hill and Baldwin, 1993;Baldwin et al, 1993;Lister and Baldwin, 1993;Hill, 1994;Baldwin and Ireland, 1995). There, normal movement along a 0.3-to 1.5-km-thick ductile mylonitic shear zone resulted in the uplift of deep metamorphic rocks and the juxtaposition of unmetamorphosed cover rocks.…”

Section: Pliocene/pleistocene Riftingmentioning

confidence: 99%

“…2) show that (A) they are associated with Pliocene/Pleistocene granodiorite intrusions and amphibolite-facies ductile shear zones, (B) they have been rapidly exhumed from ~30 km depth (7-11 kilobar [kb]) in the last 4 m.y., (C) uplift continues (forming topography up to 2.5 km), and (D) they are very three dimensional and regionally discontinuous (or varying in grade) along strike (Davies andWarren, 1988, 1992;Hill, 1987Hill, , 1990Hill, , 1994Hill, , 1995Hill et al, 1992Hill et al, , 1995Hill and Baldwin, 1993;Baldwin et al, 1993;Lister and Baldwin, 1993;Baldwin and Ireland, 1995 Duncan, pers. comm., 1993;Walker and McDougall, 1982) and P4 (late Paleocene) foraminifer-bearing micrites overlying the basalts with tonalite-diorite-dacite intrusions K/Ar dated at 57-47 Ma (Rogerson et al, 1993).…”

mentioning

confidence: 99%

Woodlark Basin

Huchon¹,

Taylor²,

Klaus³

1998

ODP Scientific Prospectus

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This Scientific Prospectus is based on pre-cruise JOIDES panel discussions and scientific input from the designated Co-Chief Scientists on behalf of the drilling proponents. The operational plans within reflect JOIDES Planning Committee and thematic panel priorities. During the course of the cruise, actual site operations may indicate to the Co-Chief Scientists and the Operations Manager that it would be scientifically or operationally advantageous to amend the plan detailed in this prospectus. It should be understood that any proposed changes to the plan presented here are contingent upon approval of the Director of the Ocean Drilling Program in consultation with the Science and Operations Committees (successors to the Planning Committee) and the Pollution Prevention and Safety Panel.Technical Editor: Karen K. Graber Leg 180 will drill a transect of three sites just ahead of the spreading tip: ACE-9a on the down flexed northern margin; ACE-8a through the rift basin sediments, the low-angle normal fault zone, and into the footwall; and ACE-3c near the crest of the footwall fault block (Moresby Seamount).The primary objectives at these sites are (1) to characterize the composition and in situ properties (stress, permeability, temperature, pressure, physical properties, and fluid pressure) of an active low-angle normal fault zone to understand how such faults slip, and (2) to determine the vertical motion history of both the downflexed hanging wall and the unloaded footwall as local groundtruth for input into regional models to determine the timing and amount of extension prior to spreading initiation.

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Unroofing of active metamorphic core complexes in the D'Entrecasteaux Islands, Papua New Guinea

Cited by 148 publications

References 0 publications

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

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

Rapid Variscan exhumation and the role of magma in core complex formation: southern Brittany metamorphic belt, France

Woodlark Basin

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