Ann M. Therriault

Natural Resources Canada | NRCan

Abstract— The circular Cloud Creek structure in central Wyoming, USA is buried beneath ˜1200 m of Mesozoic sedimentary rocks and has a current diameter of ˜7 km. The morphology/morphometry of the structure, as defined by borehole, seismic, and gravity data, is similar to that of other buried terrestrial complex impact structures in sedimentary targ...

Abstract— Hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near-surface volume of the target body. Local geology of the target area tends to be of secondary importance, and the net result is that impacts of similar size on a given planetary body produce similar results. Th...

Modeling the effects of differential scaling of impact melt and transient cavity volumes indicates that impact melt volumes exceed transient cavity volumes at transient cavity diameters greater than similar to 500 km on the Earth. This condition is not realized on the Moon until transient cavity diameters are greater than similar to 3000 km. A reas...

Previous models of the effects of larger scale impacts on early (~ 4.6 - 3.8 Ga) terrestrial crustal evolution have relied on analogies with the moon. There are, however, some important differences. Due to the Earth's larger gravitational cross-section, it will have been subjected to more impacts of unit mass and these impacts will have a higher re...

Hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near-surface volume of the target body. Local geology of the target area tends to be of secondary importance, and the net result is that impacts of similar size on a given planetary body produce similar results. This is the...

Vredefort, Sudbury, and Chicxulub are the largest known terrestrial impact structures. All have been cited as multi-ring basins. The available data indicate that all have some form of multiple-ring attributes, most commonly structural features. Chicxulub, however, is the only example with morphological ring features. There are also commonalities in...

The circular Cloud Creek structure in central Wyoming, USA is buried beneath 1200 m of Mesozoic sedimentary rocks and has a current diameter of similar to7 km. The morphology/morphometry of the structure, as defined by borehole, seismic, and gravity data, is similar to that of other buried terrestrial complex impact structures in sedimentary target...

The Sudbury structure, Ontario, is the remnant of a 1.85 Ga old impact crater, which originally had a diameter of 200 to 250 km. The Sudbury Igneous Complex occurs within the Sudbury structure. The Sudbury Igneous Complex is a 2.5- to 3.0-km-thick, similar to60- X 27-km elliptical igneous-rock body, which consists of four major lithologies (from to...

The Earth is the most endogenically active of the terrestrial planets and, thus, has retained the poorest sample of impacts that have occurred throughout geological time. The current known sample consists of approximately 160 impact structures or crater fields. Approximately 30% of known impact structures are buried and were initially detected as g...

Large impacts on Earth have generated pools of melt rocks. These early impact melts were deep, cooled slowly, and may have produced felsic differentiates in a "near-surface" environment, which may have played a role in the formation of continents. Additional information is contained in the original extended abstract.

The SIC is a layered body within the Sudbury Structure, Canada. A detailed mineralogical and petrological study reveals that the original SIC melt crystallized in a water-rich environment. Its unusual petrology is evidence of its derivation from an impact melt.

Eleven samples (mostly of the Onaping Formation) from the 1.85-Ga Sudbury impact structure were examined with respect to their carbon phases. Six impact diamonds, <0.6 mm in diameter, were discovered in two samples of the Black Member of the Onaping Formation. These diamonds occur in a variety of colors, are cubic, and are generally friable due to...

The 66 km wide Tookoonooka impact structure (27 degrees 07'S, 142 degrees 50'E) was first recognised, from seismic profiles, as a circular structure consisting of a concentric arrangement of anticlines and synclines, which surround a complex central dome, approximately 22 km wide. A gravity low and a central magnetic high characterize the structure...

The Vredefort impact structure contains a suite of granophyric dykes, referred to as the Vredefort Granophyre, occurring within and at the edge of the Archaean basement core. New whole-rock chemical analyses, together witb previous data, represent a complete suite of the Granophyre occurrences. These data show that the Vredefort Granophyre has a re...

Abstract— Historically, there have been a range of diameter estimates for the large, deeply eroded Vredefort impact structure within the Witwatersrand Basin, South Africa. Here, we estimate the diameter of the transient cavity at the present level of erosion as ∼124–140 km, based on the spatial distribution of shock metamorphic features in the floo...

A unique melt rock, the Vredefort Granophyre, occurs in the Vredefort structure, South Africa, as a series of vertical dykes either extending northwest - southeast and northeast - southwest within the granitic core or straddling along the contact between the Proterozoic collar and the core of Archaean gneisses. A field study of the Vredefort Granop...

— Microscopic planar deformation features (PDFs) in quartz grains are diagnostic of shock meta-morphism during hypervelocity impact cratering. Measurements of the poles of sets of PDFs and the optic axis of 25 quartz grains were carried out for a sample of the Loftarsten deposit from the Lockne area, Sweden. The most abundant PDFs observed in the s...

Consisting mainly of uplifted crystalline basement, the 40-50 km Vredefort Dome is in a near-central position within the Witwatersrand Basin [1,2](Fig. 1). The Vredefort impact structure (27 degrees 00'S, 27 degrees 30'E) consists of the Vredefort Dome and a wide "collar" of metasediments and metavolcanic rocks. Prior to the 1970's the diameter of...

Approximately 150 terrestrial impact structures are currently known, representing a small, biased sample of a much larger population. The spatial distribution indicates concentrations in cratonic areas - in particular, ones where there have been active search programs. The majority of the known impact structures are <200 m.y.old, reflecting the inc...

The Vredefort structure is located approximately 120 km southwest of Johannesburg, South Africa, and is deeply eroded. Controversies remain on the origin of this structure with the most popular hypotheses being: (1) by impact cratering about 2.0 Ga; (2) as a cryptoexplosion structure about 2.0 Ga; and (3) by purely tectonic processes starting at ab...

A model is presented for the evolution of the Vredefort structure, based on reasoned constraints on the original size of the Vredefort structure from observational data and comparison with other terrestrial impact craters. The models for complex craters (ring and multi-ring basins) of Croft, Grieve, and co-workers, and Schultz and co-workers, were...

The Vredefort Dome is located near the center of the Witwatersrand Basin, about 120 km southeast of Johannesburg, South Africa. Its origin is enigmatic, ranging from a major impact event to endogenous processes, either igneous or tectonic. A unique melt rock, the 'Bronzite' Granophyr, occurs in the Vredefort structure as vertical ring dikes along t...