Nd and Sr isotopic systematics of central Australian granulites: chronology of crustal development and constraints on the evolution of lower continental crust

Windrim, Donal; McCulloch, Malcolm T.

doi:10.1007/bf00371438

Cited by 55 publications

(11 citation statements)

References 89 publications

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“…(1984), which is within the range of model ages calculated for other granulites from the Strangways Metamorphic Complex (e.g. Windrim & McCulloch, 1986). The mafic sequence therefore most likely represents part of the Palaeoproterozoic stratigraphy of the Strangways Metamorphic Complex.…”

Section: Geochronologymentioning

confidence: 99%

Exhumation of the lower crust during crustal shortening: an Alice Springs (380 Ma) age for a prograde amphibolite facies shear zone in the Strangways Metamorphic Complex (central Australia)

Ballèvre

Möller

Hensen

2000

Journal Metamorphic Geology

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Foliated garnet‐bearing amphibolites occur within the West Bore Shear Zone, cutting through granulite facies gneisses of the Strangways Metamorphic Complex. In the amphibolites, large euhedral garnet (up to 3 cm) occurs within fine‐grained recrystallized leucocratic diffusion haloes of plagioclase–quartz. The garnet and their haloes include a well‐developed vertical foliation, also present in the matrix. This foliation is the same as that cutting through the unconformably overlying Neoproterozoic Heavitree Quartzite. The textures indicate syn‐ to late kinematic growth of the amphibolite facies mineral assemblages. All mineral assemblages record an arrested prograde reaction history. Noteworthy is the growth of garnet at the expense of hornblende and plagioclase, and the breakdown of staurolite–hornblende to give plagioclase–gedrite. These dehydration reactions indicate increasing P–T conditions during metamorphism, and suggest heating towards the end of a period of intense deformation. Temperature estimates for the garnet–amphibolite and related staurolite–hornblende assemblages from the shear zone are about 600 °C. Pressure is estimated at about 5 kbar. An Sm–Nd isochron gives an age of 381±7 Ma for the peak metamorphism and associated deformation. This age determination confirms that amphibolite facies conditions prevailed during shear zone development within the Strangways Metamorphic Complex during the Alice Springs Orogeny. These temperature conditions are significantly higher than those expected at this depth assuming a normal geothermal gradient. The Alice Springs Orogeny was associated with significant crustal thickening, allowing exhumation of the granulite facies, Palaeoproterozoic, lower crust. Along‐strike variations of the tectonic style suggest a larger amount of crustal shortening in the eastern part of the Alice Springs Orogeny.

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Section: Geochronologymentioning

confidence: 99%

Exhumation of the lower crust during crustal shortening: an Alice Springs (380 Ma) age for a prograde amphibolite facies shear zone in the Strangways Metamorphic Complex (central Australia)

Ballèvre

Möller

Hensen

2000

Journal Metamorphic Geology

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“…Windrim and McCulloch (1986) rejected crust recycling (citing Reymer & Schubert 1984) and advocated mixing of depleted and primitive mantle to explain the £Nd growth curve. Chase and Patchett (1988) offer the novel explanation that the large and substantially light rare earth enriched reservoir is ancient ocean crust, stored in the mantle.…”

Section: Neodymium Initial Ratiosmentioning

confidence: 99%

The persistent myth of crustal growth

Armstrong¹

1991

Australian Journal of Earth Sciences

304

107

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From the extraterrestrial telescopic, space probe, meteorite and returned sample studies of planetary evolution, and terrestrial evidence for early differentiation of core and fluid spheres and continental crust, I feel the conclusion is inescapable that large terrestrial planets of our solar system underwent essentially immediate differentiation into relatively constant-volume core, depleted mantle, enriched crust and fluid reservoirs. Differentiation was an early event, carried rapidly to completion. It is a false premise to have the formation of sialic crust on Earth dragged out over billions of years after hot accretion. The uniqueness of the Earth arises from its size, retention of water and dynamic surface-renewal processes, which have effectively erased all vestiges of the first several hundred million years of its crustal history. A large volume of depleted mantle always existed and an isotopically nearly homogeneous character for mantle and crust in early times was only sustained by rapid convective stirring of the silicate Earth. The sigmoidal continental crust age curve that is recorded in whole rock Nd and zircon U-Pb dates is a predictable consequence of the highly exponential decline in stirring rates. It represents survival, not the original extent of crustal domains. Positive The idea that the Earth's crust has grown is a myth dating from the 19th century and was established as geochemical dogma in the 1950s and 1960s. It has survived by inertia and repetition and endless self-citation. The alternative no-growth view has been sometimes ignored, frequently questioned and downplayed, often cited only as an end member hypothesis (on the presumption that the truth must lie between extremes), and sometimes acclaimed and supported. Evidence in its favour has been accumulating. The growth myth has survived, however, as the consensus.In science, conventional wisdom is difficult to overturn. After more than 20 years some implications of plate tectonics have yet to be fully appreciated by isotope geochemists who advocate crustal growth, and by geologists and geophysicsts who have followed their lead.

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“…The SOB is composed of a well-layered (on a scale of metres to kilometres) sequence of supracrustal granulite facies rocks dominated by mafic and quartzofeldspathic gneisses. These have an Sm-Nd model age of approximately 2000-2100 Ma (Windrim & McCulloch, 1986). Interleaved metasediments include a banded iron formation, quartzite, carbonate, calc-silicate rock and a wide variety of aluminous and pelitic gneisses.…”

Section: Tectonic F R a M E W O R Kmentioning

confidence: 99%

Silica‐undersaturated sapphirine, spinel and kornerupine granulite facies rocks, NE Strangways Range, Central Australia

Goscombe

1992

Journal Metamorphic Geology

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Small pods of silica-undersaturated Al-rich and Mg-rich granulite facies rocks containing sapphirine, pleonastic spinel, kornerupine, cordierite, orthopyroxene, corundum, sillimanite and gedrite are scattered throughout the NE Strangways Range, Central Australia. These are divided into four distinct rock types, namely orthopyroxene-rich aluminous granofels and metapelitic gneisses containing sapphirine, spinel or kornerupine. Two granulite facies metamorphic events are recognized, of which only the first (Ml) is considered in this paper.Peak metamorphic mineral parageneses indicate that the MI thermal maximum occurred at approximately 900-950°C and 8-9 kbar. All samples are characterized by profuse and diverse coronitic and symplectic reaction textures. These are interpreted as evidence for the sequential crossing of the following reactions in the system FMAS:Phase stability relationships in FMAS and MASH indicate an anticlockwise P-T path terminated by isobaric cooling. Such a path is exemplified by early low-P mineral parageneses containing spinel, corundum and gedrite and the occurrence of both prograde and retrograde corundum. Reaction textures preserve evidence for an increase in a,,,, and ae,o, with progressive isobaric cooling. This hydrous retrogression resulted from crystallization of intimately associated M1 partial melt segregations. There is no evidence for voluminous magmatic accretion giving rise to the high M1 thermal gradient. The M1 P-T path may be the result of either lithospheric thinning after both crustal thickening and burial of the supracrustal terrane, or concomitant crustal thickening and mantle lithosphere thinning. Abbreviationscd OPX S P = cordierite = orthopyroxene = pleonastic spinel = gedrite = corundum = sapphirine = kornerupine = sillimanite = K-feldspar = plagioclase = phlogopite = garnet rut = rutile chl = chlorite tm = tourmaline zr = zircon mon = monazite aP = apatite an = anorthite enden = enstatite endilm-hem,,= ilmenitepember member

show abstract

Nd and Sr isotopic systematics of central Australian granulites: chronology of crustal development and constraints on the evolution of lower continental crust

Cited by 55 publications

References 89 publications

Exhumation of the lower crust during crustal shortening: an Alice Springs (380 Ma) age for a prograde amphibolite facies shear zone in the Strangways Metamorphic Complex (central Australia)

Exhumation of the lower crust during crustal shortening: an Alice Springs (380 Ma) age for a prograde amphibolite facies shear zone in the Strangways Metamorphic Complex (central Australia)

The persistent myth of crustal growth

Silica‐undersaturated sapphirine, spinel and kornerupine granulite facies rocks, NE Strangways Range, Central Australia

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