Steven M. Reddy

Curtin University

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Denis Fougerouse

Curtin University

David W. Saxey

Curtin University

Nicholas E. Timms

Curtin University

William D.A. Rickard

Curtin University

Chris Clark

Parkland Health & Hospital System

Timmons M. Erickson

Johnson Space Center

Aaron J. Cavosie

Curtin University

Christopher L. Kirkland

Curtin University

Mark A. Pearce

Commonwealth Scientific and Industrial Research Organisation

P. A. Bland

Curtin University

Cooperative Institutions

Curtin University

114

Planetary Science Institute

University of Western Australia

Centre National de la Recherche Scientifique

Commonwealth Scientific and Industrial Research Organisation

Australian National University

ARC Centre of Excellence for Core to Crust Fluid Systems

Australian Resources Research Centre

Mineral Resources

Australian Research Council

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Trench-parallel fast axes of seismic anisotropy due to fluid-filled cracks in subducting slabs

Earth and Planetary Science Letters (2009)

David Healy Steven M. Reddy Nicholas E. Timms Erin M. Gray Alberto Vitale Brovarone

Slab

Forearc

Seismic anisotropy

Blueschist

Brittleness

Caldera

10.1016/j.epsl.2009.03.037

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Citations (110)

Mechanisms of deformation-induced trace element migration in zircon resolved by atom probe and correlative microscopy

Geochimica et Cosmochimica Acta (2016)

Steven M. Reddy Arie van Riessen David W. Saxey Tim Johnson William D.A. Rickard

Trace element

10.1016/j.gca.2016.09.019

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Citations (82)

Isotopic constraints on the cooling history of the Nanga Parbat‐Haramosh Massif and Kohistan arc, western Himalaya

Tectonics (1995)

Mark George Steven M. Reddy Nigel Harris

Nineteen 40 Ar/ 39 Ar and 22 Rb‐Sr mineral ages are presented for metamorphic rocks and granites collected from the northern part of the Nanga Parbat‐Haramosh Massif (NPHM) and adjacent parts of the Kohistan arc, western Himalaya. The majority of these ages are interpreted as exhumation‐related cooling ages, and they therefore place important constraints on the exhumation history of the region. The 40 Ar/ 39 Ar and Rb‐Sr mica cooling ages for areas of the NPHM to the north of the Indus River lie in the range 2–8 Ma and are similar to previously published ages from the Indus gorge itself. Cooling histories for these areas show little systematic variation from east to west, suggesting that the basement may have been exhumed as a relatively rigid block, after the main stages of folding. Mica ages increase dramatically from the NPHM westward into the Kohistan arc, where ages lie in the range 13–30 Ma. The contrast in both cooling ages and the age differential between mineral pairs between the two terranes indicates rapid cooling of the NPHM in the last 10 m.y. compared with the Kohistan arc. The relationship between rates of cooling and exhumation is poorly constrained in regions of rapid uplift, where the characteristics of the evolving geotherm are not well understood. However, the results are consistent with an anomalously rapid exhumation history of the NPHM during the last 10 m.y. compared with the adjacent Kohistan arc. The interpretation of some of the ages documented in this study is problematical. Two biotite samples from contrasting lithologies within the NPHM have yielded higher 87 Sr/ 86 Sr ratios than the corresponding whole rocks, but the cause of this isotopic disequilibrium remains unclear. Other biotite samples from the region have consistently yielded younger Rb‐Sr ages than 40 Ar/ 39 Ar ages, which may be a reflection of either preferential leaching of 87 Sr during fluid infiltration on a regional scale or the presence of excess argon. Alternatively, the relative ages indicate slightly lower closure temperature for strontium diffusion in biotite than for argon diffusion in biotite where samples have undergone rapid cooling.

Massif

Island arc

Basement

Indus

10.1029/94tc02906

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Citations (30)

Trace-element segregation to dislocation loops in experimentally heated zircon

American Mineralogist (2021)

Emily M. Peterman Steven M. Reddy David W. Saxey Denis Fougerouse M.Z. Quadir

Abstract To evaluate the mechanisms driving nanoscale trace element mobility in radiation-damaged zircon, we analyzed two well-characterized Archean zircons from the Kaapvaal Craton (southern Africa): one zircon remained untreated and the other was experimentally heated in the laboratory at 1450 °C for 24 h. Atom probe tomography (APT) of the untreated zircon reveals homogeneously distributed trace elements. In contrast, APT of the experimentally heated zircon shows that Y, Mg, Al, and Pb+Yb segregate to a set of two morphologically and crystallographically distinct cluster populations that range from 5 nm tori to 25 nm toroidal polyhedra, which are confirmed to be dislocation loops by transmission electron microscopy (TEM). The dislocation loops lie in {100} and {001} planes; the edges are aligned with <100>, <101>, and <001>. The largest loops (up to 25 nm diameter) are located in {100} and characterized by high concentrations of Mg and Al, which are aligned with <001>. The 207Pb/206Pb measured from Pb atoms located within all of the loops (0.264 ± 0.025; 1σ) is consistent with present-day segregation and confirms that the dislocation loops formed during our experimental treatment. These experimentally induced loops are similar to clusters observed in zircon affected by natural geologic processes. We interpret that differences in cluster distribution, density, and composition between experimentally heated and geologically affected zircon are a function of the radiation dose, the pressure-temperature-time history, and the original composition of the zircon. These findings provide a framework for interpreting the significance of clustered trace elements and their isotopic characteristics in zircon. Our findings also suggest that the processes driving cluster formation in zircon can be replicated under laboratory conditions over human timescales, which may have practical implications for the mineralogical entrapment of significant nuclear elements.

Trace element

10.2138/am-2021-7654

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Citations (30)

Geochemical modification of plastically deformed zircon

Geochimica et Cosmochimica Acta (2006)

Steven M. Reddy Nicholas E. Timms P. D. Kinny

10.1016/j.gca.2006.06.961

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Citations (1)

Micro- and nano-scale textural and compositional zonation in plagioclase at the Black Mountain porphyry Cu deposit: Implications for magmatic processes

American Mineralogist (2019)

MingJian Cao Noreen J. Evans Steven M. Reddy Denis Fougerouse Pete Hollings

Textural and compositional microscale (10–100 μm) and nanoscale (10–100 nm) zoning in a plagioclase phenocryst from a fresh, syn-mineralization diorite porphyry (Black Mountain porphyry Cu-Au deposit, Philippines) was characterized for major and trace elements using electron microprobe, laser ablation-inductively coupled plasma-mass spectrometry, and atom probe tomography. The complex plagioclase crystal (3.0 × 5.4 mm) has a patchy andesine core (An41–48 mol%), eroded bytownite mantle (An71–80 mol%), and oscillatory andesine rim (An39–51 mol%). Microscale variations with a periodic width of 50 to 200 μm were noted for most major and trace elements (Si, Ca, Al, Na, K, Fe, Mg, Ti, Sr, Ba, Pb, La, Ce, and Pr) with a ΔAn amplitude of 4–12 mol% in both the core and rim. The mantle has a distinct elemental composition, indicating the addition of hotter mafic magma to the andesitic magma. Atom probe tomography shows an absence of nanoscale variations in the andesine rim but alternating nanoscale (25–30 nm) Al-rich, Ca-rich, and Si-rich, Na-rich zones with a Ca/(Ca+Na)at% amplitude of ~10 in the bytownite mantle.

Phenocryst

Microprobe

Diorite

10.2138/am-2019-6609

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Citations (26)

Ductile Zircon Dating of Lithosphere Flow

AGU Fall Meeting Abstracts (2007)

D. Moser Bill Davis Steven M. Reddy R. L. Flemming R. J. Hart

Source

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Citations (1)