Geometry and kinematics of shear zones formed during continental extension in eastern Papua New Guinea

Hill, E. J.

doi:10.1016/0191-8141(94)90054-x

Cited by 54 publications

(111 citation statements)

References 21 publications

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“…The granodiorite includes leucogranites and is more leucocratic than the host quartzofeldspathic gneiss. The bulk of the quartzofeldspathic gneiss and eclogites have a gently dipping foliation and gently plunging E-W lineation formed at amphibolite-facies conditions [Hill, 1994;Little et al, 2011]. At the highest structural levels, near the tops of the domes, this fabric crenulates an older, steeply dipping foliation.…”

Section: D'entrecasteaux Islandsmentioning

confidence: 99%

Predicted velocity and density structure of the exhuming Papua New Guinea ultrahigh-pressure terrane

et al. 2011

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[1] New electron backscatter diffraction measurements show that the Papua New Guinea (PNG) ultrahigh-pressure (UHP) terrane is dominated by rocks with weakly oriented quartz and feldspar and less abundant strongly oriented hornblende, clinopyroxene, and mica. Velocities measured at high pressures (600 MPa) show that V P is 5.8-6.3 km/s for gneiss samples, 6.5-7.7 km/s for amphibolite, and 7.7-8.2 km/s for eclogite and V S is 3.4-3.9 km/s for gneiss, 4.0-4.4 km/s for amphibolite, and 4.5-4.6 km/s for eclogite. Velocities and anisotropies calculated from mineral crystal preferred orientations (CPOs) are equivalent to within 5% of the measured values. The highest seismic anisotropy for the PNG terrane is in amphibolite at 8% and 7% for V P and V S , respectively. Calculations of seismic velocities at depth based on predicted mineral assemblages indicate that the exhuming UHP terrane is of dominantly mafic composition below ∼20 km depth. Anisotropy in the PNG terrane is expected to be quite low and is controlled by the orientation of the foliation. If observable, changes in anisotropy across the exhuming body may be used to differentiate among the different proposed mechanisms of UHP exhumation.

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Section: D'entrecasteaux Islandsmentioning

confidence: 99%

Predicted velocity and density structure of the exhuming Papua New Guinea ultrahigh-pressure terrane

et al. 2011

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“…Mafic eclogites are inferred to have originated as dikes that were metamorphosed in situ and now occur as eclogite boudins within strongly folded and isoclinally folded garnet-bearing quartzofeldspathic host gneisses (23)(24)(25)(26). Foliation in the mafic eclogites is roughly concordant with that in the host gneiss.…”

Section: Geologic Setting and Sample Descriptionmentioning

confidence: 65%

Atmospheric Ar and Ne returned from mantle depths to the Earth’s surface by forearc recycling

Baldwin¹,

Das²

2015

Proc. Natl. Acad. Sci. U.S.A.

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In subduction zones, sediments, hydrothermally altered lithosphere, fluids, and atmospheric gases are transported into the mantle, where ultrahigh-pressure (UHP) metamorphism takes place. However, the extent to which atmospheric noble gases are trapped in minerals crystallized during UHP metamorphism is unknown. We measured Ar and Ne trapped in phengite and omphacite from the youngest known UHP terrane on Earth to determine the composition of Ar and Ne returned from mantle depths to the surface by forearc recycling. An 40 Ar/ 39 Ar age [7.93 ± 0.10 My (1σ)] for phengite is interpreted as the timing of crystallization at mantle depths and indicates that 40 Ar/ 39 Ar phengite ages reliably record the timing of UHP metamorphism. Both phengite and omphacite yielded atmospheric 38 Ar/ 36 Ar and 20 Ne/ 22 Ne. Our study provides the first documentation, to our knowledge, of entrapment of atmospheric Ar and Ne in phengite and omphacite. Results indicate that a subduction barrier for atmosphericderived noble gases does not exist at mantle depths associated with UHP metamorphism. We show that the crystallization age together with the isotopic composition of nonradiogenic noble gases trapped in minerals formed during subsolidus crystallization at mantle depths can be used to unambiguously assess forearc recycling of atmospheric noble gases. The flux of atmospheric noble gas entering the deep Earth through subduction and returning to the surface cannot be fully realized until the abundances of atmospheric noble gases trapped in exhumed UHP rocks are known.subduction | UHP metamorphism | geochronology | noble gas | atmosphere

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“…These islands are composed of shear zone bounded, possibly diapiric (e.g. Little et al, 2011), gneiss domes (Hill, 1994;Little et al, 2007) whose core zones preserve a polymetamorphic history dating back to~68 Ma (Zirakparvar et al, 2011). The cores of these domes contain rocks that can be traced to the eastern Australian margin in Gondwana as well as those that are related to the more recent history of metamorphism and magmatism during subduction, rifting, and exhumation (Zirakparvar et al, 2012).…”

Section: Tectonic Evolution Of the Woodlark Riftmentioning

confidence: 98%

Cathodoluminescence guided zircon Hf isotope depth profiling: Mobilization of the Lu–Hf system during (U)HP rock exhumation in the Woodlark Rift, Papua New Guinea

Zirakparvar

2015

Lithos

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Geometry and kinematics of shear zones formed during continental extension in eastern Papua New Guinea

Cited by 54 publications

References 21 publications

Predicted velocity and density structure of the exhuming Papua New Guinea ultrahigh-pressure terrane

Predicted velocity and density structure of the exhuming Papua New Guinea ultrahigh-pressure terrane

Atmospheric Ar and Ne returned from mantle depths to the Earth’s surface by forearc recycling

Cathodoluminescence guided zircon Hf isotope depth profiling: Mobilization of the Lu–Hf system during (U)HP rock exhumation in the Woodlark Rift, Papua New Guinea

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