I. R. Barker

• Western University

Northwest Africa (NWA) 7042 is an intermediate, permafic shergottite consisting of two generations of olivine (early zoned olivine Fo41-76, and late-stage fayalitic olivine Fo46-56), complexly zoned pyroxene (En35-64Fs22-46Wo5-34), shock-melted or maskelynitized feldspar (An5-30Ab16-61Or1-47), and accessory merrillite, apatite, ilmenite, titanomagn...

The timing of the wane in heavy meteorite bombardment of the inner planets is debated. Its timing determines the onset of crustal conditions consistently below the thermal and shock pressure limits for microbiota survival, and so bounds the occurrence of conditions that allow planets to be habitable. Here we determine this timing for Mars by examin...

Granulitic lunar meteorites offer rare insights into the timing and nature of igneous, metamorphic and impact processes in the lunar crust. Accurately dating the different events recorded by these materials is very challenging, however, due to low trace element abundances (e.g. Sm, Nd, Lu, Hf), rare micrometer- scale U-Th-bearing accessory minerals...

Identifying and dating large impact structures is challenging, as many of the traditional shock indicator phases can be modified by post-impact processes. Refractory accessory phases, such as zircon, while faithful recorders of shock wave passage, commonly respond with partial U–Pb age resetting during impact events. Titanite is an accessory phase...

Constraining the timing and intensity of Solar System bombardment is critical to understanding planetary formation, evolution and habitability. However, the identification and dating of shockmetamorphic events in the mafic igneous lithologies that dominate planetary materials remains highly challenging, particularly at relatively modest shock press...

Strength and deformation microstructure of zircon were investigated to 32 GPa at room temperature using a diamond anvil cell (DAC). The obtained X-ray diffraction data were analyzed using the lattice strain theory. The high-pressure quenched samples were analyzed by electron backscatter diffraction (EBSD). Our results show a bulk modulus of 203 ± 1...

The accurate dating of igneous and impact events is vital for the understanding of Solar System evolution, but has been hampered by limited knowledge of how shock metamorphism affects mineral and whole-rock isotopic systems used for geochronology. Baddeleyite (monoclinic ZrO2) is a refractory mineral chronometer of great potential to date these pro...

The mechanism by which olivine grains became embedded within iron-nickel alloy in pallasite meteorites continues to be a matter of scientific debate. Geochemical and textural observations have failed to fully elucidate the origin and history of the olivine crystals; however, little research attention has been devoted to their crystallographic orien...

The corrosion of the Ni-Cr-Mo alloy C22, has been studied in a simulated crevice corrosion environment (3 M NaCl + 1.5 M HCl at 75 • C). Analyzing the corroded surface by electron backscatter diffraction showed that corrosion damage localized predominantly in random as opposed to 3 grain boundaries. Scanning transmission electron microscopy and ele...

div class="title">Atom Probe Tomography of Zircon and Baddeleyite Geochronology Standards - Volume 21 Issue S3 - D.A. Reinhard, D.E. Moser, I.R. Barker, D. Olson, I. Martin, Katherine P. Rice, Y. Chen, D. Lawrence, T.J. Prosa, D.J. Larson

Abstract Copper coated steel containers are being developed for the disposal of high level nuclear waste using processes such as cold spray and electrodeposition. Electron Back-Scatter Diffraction has been used to determine the microstructural properties and the quality of the steel-copper coating interface. The influence of the nature of the cold-...

The Northwest Africa (NWA) 7475 meteorite is one of the several stones of paired regolith breccias from Mars based on petrography, oxygen isotope, mineral compositions, and bulk rock compositions. Its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten. Other clast types include crystal...

Newly designed miniature Compact Tension (CT) specimens, designed according to standard ASTM dimension ratios, and machined out of previously in-service X65 pipeline steel were exposed to super-imposed cyclic loading at high mean stresses in NS4 solution to determine the behaviour of X65 steel to ripple loading under near neutral pH conditions. Ele...

Detrital shocked minerals can provide valuable residual records of eroded impact structures. Recent studies have reported shocked minerals in modern alluvium in a subtropical climate from the deeply eroded 2.02 Ga Vredefort Dome impact basin in South Africa. To evaluate the detrital shocked mineral record at a large impact structure in a temperate...

Melting by impact heating is thought to have been a significant process in the modification of early planetary crusts; however, crustally derived melt bodies in ancient terrestrial crust are frequently presumed to be absent due to erosion. Here we demonstrate that in the central basement uplift of the 2.020 Ga Vredefort impact basin (South Africa),...

An unusual basaltic specimen found at low elevation in Morocco contains measurable levels of cosmogenic nuclides and may be a rare type of lunar meteorite.

The effects of shock metamorphism on the U-Pb systematics of baddeleyite (ZrO2) in basaltic shergottite Northwest Africa 5298 have been investigated by combining electron beam microstructural techniques (CL, EBSD) with in-situ U-Pb SIMS analyses.

We present the first age and microstructure information from our discovery of regolith zircons and accessory minerals in a relatively water-rich sample of Mars.

In order to investigate the textural relationships among olivine and phosphorus-bearing phases in the Springwater pallasite, we determined olivine crystal orientations with EBSD and analyzed phosphates and phosphoran olivine with electron microprobe.

Nano- to atomic-scale records of impact processes on Earth, Moon, Asteroids and Mars; integration of microstructure and isotope geochronology of inner solar system minerals such as zircon and baddeleyite.

Testing the impact origin of a gabbronorite dyke at Vredefort, evidence includes; contact relationships, shock microstructural state of major and accessory phases, U-Pb and Hf isotopic analysis of zircons, and Ti-in-zircon thermometry.

Invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites. However, the interpreted ages of the ejected igneous crust of Mars differ by up to four billion years, a conundrum due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and t...

The record of meteorite impacts on Earth is incomplete due to the destruction of impact craters by erosion and burial. Shocked minerals residing in sediments may help further document the impact record. To evaluate the survival of shocked minerals in fluvial systems we investigated ∼10,000 sand grains from seven sites along the Vaal River in South...

Microstructural and geochronological analysis of shocked zircon has greatly advanced understanding the formation and evolution of impact structures. However, fundamental aspects of shock-produced planar microstructures in zircon remain poorly known, such as their deformation mechanisms, crystallographic orientations, and how planar microstructures...

Spodumene pegmatites occur in the southeastern sector of the 2.02 Ga Vredefort impact structure in South Africa. Moser et al. (published in 2011) presented an isotope dilution – thermal ionization mass spectrometry (ID–TIMS) age of 1136 ± 47 Ma for these spodumene pegmatites. This discussion questions the reliability of this age. Field relations in...

We document detrital shocked grains from the mouth of the Orange River in South Africa. These grains require long (1200 to 2000 km) distances of transport, diverse sedimentary processes, and originate from multiple impact basins.

Resolution of the shergottite "age paradox" through integrated SIMS and electron nanobeam (e.g., CL, EBSD) analysis of primary igneous baddeleyite and later metamorphic zircon.

Analysis has led to identification of mafic impact melts at the Vredefort impact. Using microstructural analyses of zircon we were able to distinguish igneous grains for dating and the U-Pb geochronology support crystallized at the time of impact.

EBSD, CL, EDS and EPMA investigations of shock-deformed enstatite in MET 00783 (EH4, S4) reveal microstructures including heterogeneous lamellar fabrics corresponding to subtle differences in Kikuchi band contrast, and amorphous feldspathic material.

We describe a single detrital shocked zircon from modern sand that records a 3 Ga history of the evolution of the giant Vredefort Dome impact basin. This result highlights the importance of detrital mineral records for reconstructing ancient impact events.

The stratigraphy of Cretaceous rocks in the Western Canada Foreland Basin is well constrained by dense borehole data that allow three-dimensional mapping of transgressive-regressive events, paleogeography, and subsidence patterns. However, it is difficult to estimate rates of change or to place events in a precise temporal framework because very fe...

Integrated electron nanobeam (EBSD, CL, EDS) and isotopic measurements (U-Pb, (U-Th)/He) of zircon from the collar and centre of the 80 km wide central uplift of the 2020 +/- 3 Ma Vredefort impact structure reveal new shock features in a microstructural progression related to impact basin formation and degree of U-Pb age resetting: (1) planar fract...

The Tagish Lake meteorite, an ungrouped C2 chondrite that is related to CI and CM chondrites, is a heterogeneous accretionary breccia with several distinct lithologies that, in bulk, are thought to represent the first known sample of a primitive carbonaceous D-type asteroid. Textural and chemical zoning of clasts and matrix have been little studied...

Meteorites fell in the area of Grimsby, Ontario on the early evening of Sept. 25, 2009. The bright fireball event was well recorded by a camera network, radar and infrasound and thus far 13 fragments of a fresh H5 chondrite have been recovered.

Colour + UV SEM-CL imaging reveals variations in at least three constituents of Tagish Lake. Intra- and inter-grain differences appear to be uncorrelated with major element chemistry, but may identify trace element records of thermochemical evolution.

Fall event On the early evening of Sept 25, 2009 (01:03 UT Sept. 26, 2009), a brilliant fireball showing three major bursts was observed over southwestern Ontario and adjacent regions, with reports of sonic booms or simultaneous sound. The event was recorded by a network of automated cameras, radar and infrasound sensors operated by the University...