The Antarctic Creek impact structure is an

impact structure An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surface e ...

in the Pilbara Craton of

Western Australia Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...

. With an age of around 3.47 billion years dating to the Paleoarchean, it is the oldest known impact structure on Earth by over a billion years and the only one known from the

Archean The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...

. The structure is found in the East Pilbara Terrane, one of the oldest parts of the Pilbara Craton. A geological dome called the North Pole Dome likely represents the central uplift of the structure. Evidence of the impact is

shatter cones Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite impact craters or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the ran ...

and impact spherules (formed from condensed impact vapour) found in the Antarctic Creek Member, a thick layer of sedimentary rock including "

felsic In geology, felsic is a grammatical modifier, modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted ...

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

volcaniclastic Volcaniclastics are geologic materials composed of broken fragments (clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...

rocks,

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a prec ...

argillite Argillite () is a fine-grained sedimentary rock composed predominantly of Friability, indurated clay particles. Argillaceous rocks are basically lithified muds and Pelagic sediment, oozes. They contain variable amounts of silt-sized particles. T ...

arenite Arenite (from the Latin ''arena'', "sand") is a sedimentary clastic rock with sand grain size between 0.0625 mm (0.00245 in) and 2 mm (0.08 in) and containing less than 15% matrix. The related adjective is ''arenaceous''. The e ...

and jaspilite intruded by

dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grain ...

", located within the otherwise entirely volcanic Mount Ada Basalt, which is thick, with the Antarctic Creek Member being overlain by pillow basalts of the Mount Ada Basalt.

Uranium–lead dating Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...

of detrital zircons within the Antarctic Creek Member as well as separate dating of the overlying and underlying volcanic strata, have tightly constrained the age of the Antarctic Creek Member and thus the impact to 3470 million years ago, ± 2-3 million years. The diameter of the dome suggests that the now long eroded impact crater was over in diameter when it formed. A spherule bed found in the Barberton Greenstone Belt of South Africa of roughly the same age may have formed as a result of the impact.

See also

References

See also