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Dive into the research topics where John F. Pernet-Fisher is active.

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Featured researches published by John F. Pernet-Fisher.


International Geology Review | 2014

The secondary origin of diamonds: multi-modal radiation tomography of diamondiferous mantle eclogites

Geoffrey H. Howarth; N. V. Sobolev; John F. Pernet-Fisher; Peter H. Barry; Dayakar Penumadu; Stephen B. Puplampu; Richard A. Ketcham; Jessica A. Maisano; Dawn Taylor; L. A. Taylor

Three-dimensional neutron and X-ray tomography reveals the textural and spatial relationship of diamonds and associated minerals in situ, in a unique suite of 17 diamondiferous eclogites. We emphasize the reporting of X-ray imaging on mantle xenoliths, which in combination with neutron imaging enables the clear identification of diamonds and interstitial metasomatic secondary minerals. In particular, neutrons are highly sensitive to hydrogen (H), allowing for the identification of OH- and H2O-bearing metasomatic minerals. The identification of metasomatic minerals allows for the delineation of distinct metasomatic pathways through the eclogite xenoliths. Diamonds are readily identified as the darkest greyscales due to their low attenuation, and are typically surrounded by secondary minerals, never in contact with primary minerals, and always confined within metasomatic pathways. The ubiquitous occurrence of diamonds in association with pathways suggests a potential genetic link. Both octahedral and dodecahedral diamonds are observed within individual xenoliths, suggesting multiple heterogeneous growth and dissolution processes at small scales. The distinct age dichotomy between eclogite xenoliths and metasomatic mineral assemblages implies that the observed textural relationship of diamonds and late-stage metasomatic pathways for this suite of 17 eclogites casts doubt on the theory that eclogitic diamonds formed billions of years ago. Diamonds are interpreted to have formed from multiple growth episodes, with the last of these episodes represented by the metasomatic assemblages observed in this study. This further indicates that eclogitic diamond inclusions may span large time scales from ancient ages (>2 Ga) all the way to the last growth event, perhaps even close to the time of kimberlite emplacement (~360 Ma), which has significant implications for age-dating of diamonds and the study of diamonds as a whole.


Scientific Reports | 2017

Assessing the shock state of the lunar highlands: Implications for the petrogenesis and chronology of crustal anorthosites.

John F. Pernet-Fisher; K. H. Joy; Dayl J. P. Martin; K. L. Donaldson Hanna

Our understanding of the formation and evolution of the primary lunar crust is based on geochemical systematics from the lunar ferroan anorthosite (FAN) suite. Recently, much effort has been made to understand this suite’s petrologic history to constrain the timing of crystallisation and to interpret FAN chemical diversity. We investigate the shock histories of lunar anorthosites by combining Optical Microscope (OM) ‘cold’ cathodoluminescence (CL)-imaging and Fourier Transform Infrared (FTIR) spectroscopy analyses. In the first combined study of its kind, this study demonstrates that over ~4.5 Ga of impact processing, plagioclase is on average weakly shocked (<15 GPa) and examples of high shock states (>30 GPa; maskelynite) are uncommon. To investigate how plagioclase trace-element systematics are affected by moderate to weak shock (~5 to 30 GPa) we couple REE+Y abundances with FTIR analyses for FAN clasts from lunar meteorite Northwest Africa (NWA) 2995. We observe weak correlations between plagioclase shock state and some REE+Y systematics (e.g., La/Y and Sm/Nd ratios). This observation could prove significant to our understanding of how crystallisation ages are evaluated (e.g., plagioclase-whole rock Sm-Nd isochrons) and for what trace-elements can be used to differentiate between lunar lithologies and assess magma source compositional differences.


Lithos | 2014

Superplume metasomatism: Evidence from Siberian mantle xenoliths

Geoffrey H. Howarth; Peter H. Barry; John F. Pernet-Fisher; Ioannis P. Baziotis; N. P. Pokhilenko; Lyudmila N. Pokhilenko; Robert J. Bodnar; L. A. Taylor; A. M. Agashev


Contributions to Mineralogy and Petrology | 2014

Komsomolskaya diamondiferous eclogites: evidence for oceanic crustal protoliths

John F. Pernet-Fisher; Geoffrey H. Howarth; Yang Liu; Peter H. Barry; Laura Carmody; John W. Valley; Robert J. Bodnar; Zdislav V. Spetsius; L. A. Taylor


Geochimica et Cosmochimica Acta | 2015

Evidence for the exsolution of Cl-rich fluids in martian magmas: Apatite petrogenesis in the enriched lherzolitic shergottite Northwest Africa 7755

Geoffrey H. Howarth; John F. Pernet-Fisher; Robert J. Bodnar; L. A. Taylor


Astronomy & Geophysics | 2016

The lunar highlands: old crust, new ideas

John F. Pernet-Fisher; K. H. Joy


Lithos | 2015

Helium isotopic evidence for modification of the cratonic lithosphere during the Permo-Triassic Siberian flood basalt event

Peter H. Barry; David R. Hilton; James M. D. Day; John F. Pernet-Fisher; Geoffrey H. Howarth; Tomas Magna; A. M. Agashev; N. P. Pokhilenko; Lyudmila N. Pokhilenko; L. A. Taylor


Geochimica et Cosmochimica Acta | 2014

Estimating the lunar mantle water budget from phosphates: Complications associated with silicate-liquid-immiscibility

John F. Pernet-Fisher; Geoffrey H. Howarth; Yang Liu; Yang Chen; L. A. Taylor


Lithos | 2015

Plume impingement on the Siberian SCLM: Evidence from Re–Os isotope systematics

John F. Pernet-Fisher; Geoffrey H. Howarth; D.G. Pearson; S. Woodland; Peter H. Barry; N. P. Pokhilenko; Lyudmila N. Pokhilenko; A. M. Agashev; L. A. Taylor


Meteoritics & Planetary Science | 2014

Two-stage polybaric formation of the new enriched, pyroxene-oikocrystic, lherzolitic shergottite, NWA 7397

Geoffrey H. Howarth; John F. Pernet-Fisher; J. Brian Balta; Peter H. Barry; Robert J. Bodnar; L. A. Taylor

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L. A. Taylor

University of Tennessee

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K. H. Joy

University of Manchester

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Yang Liu

California Institute of Technology

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A. M. Agashev

Russian Academy of Sciences

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