Shatter cones and planar deformation features confirm Santa Marta in Piaui State, Brazil, as an impact structure

Autor(es)

Goncalves de Oliveira, Grace Juliana ^[1] ; Rodrigues Vasconcelos, Marcos Alberto ^[1] ; Crosta, Alvaro Penteado ^[1] ; Reimold, Wolf Uwe ^{[2, 3]} ; Goes, Ana Maria ^[4] ; Kowitz, Astrid ^[3]

Afiliação do(s) autor(es)

^[1] Univ Estadual Campinas, Inst Geosci, BR-13083870 Sao Paulo - Brazil

^[2] Humboldt Univ, D-10099 Berlin - Germany

^[3] Museum Nat Kunde Berlin, D-10115 Berlin - Germany

^[4] Univ Sao Paulo, Inst Geosci, BR-05508080 Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: METEORITICS & PLANETARY SCIENCE; v. 49, n. 10, p. 1915-1928, OCT 2014.
• Citações Web of Science: 8

Resumo

A total of 184 confirmed impact structures are known on Earth to date, as registered by the Earth Impact Database. The discovery of new impact structures has progressed in recent years at a rather low rate of about two structures per year. Here, we introduce the discovery of the approximately 10km diameter Santa Marta impact structure in Piaui State in northeastern Brazil. Santa Marta is a moderately sized complex crater structure, with a raised rim and an off-center, approximately 3.2km wide central elevated area interpreted to coincide with the central uplift of the impact structure. The Santa Marta structure was first recognized in remote sensing imagery and, later, by distinct gravity and magnetic anomalies. Here, we provide results obtained during the first detailed ground survey. The Bouguer anomaly map shows a transition from a positive to a negative anomaly within the structure along a NE-SW trend, which may be associated with the basement signature and in parts with the signature developed after the crater was formed. Macroscopic evidence for impact in the form of shatter cones has been found in situ at the base around the central elevated plateau, and also in the interior of fractured conglomerate boulders occurring on the floor of the surrounding annular basin. Planar deformation features (PDFs) are abundant in sandstones of the central elevated plateau and at scattered locations in the inner part of the ring syncline. Together, shatter cones and PDFs provide definitive shock evidence that confirms the impact origin of Santa Marta. Crystallographic orientations of PDFs occurring in multiple sets in quartz grains are indicative of peak shock pressures of 20-25GPa in the rocks exposed at present in the interior of the crater. In contrast to recent studies that have used additional, and sometimes highly controversial, alleged shock recognition features, Santa Marta was identified based on well-understood, traditional shock evidence. (AU)

• Processo FAPESP: 12/04191-2 - Modelamento numérico e geofísico de estruturas de impacto brasileiras
• Beneficiário: Marcos Alberto Rodrigues Vasconcelos
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 12/50368-1 - Caracterização geológica e geofísica da potencial estrutura de impacto de Santa Marta (PI)
• Beneficiário: Alvaro Penteado Crósta
• Modalidade de apoio: Auxílio à Pesquisa - Regular