sign in sign up
<<
Home , Araguainha crater

Large Impacts (2003) 4096.pdf

NEW LABORATORY RESULTS ON FIELD SECTIONS AT THE OF ARAGUAINHA (MT, GO, ). AREA OF PROXIMAL AND DISTAL IMPACT EJECTA, INCLUDING MICROSPHERULES DATED FROM THE END OF PERMIAN. J. M. Théry1, A. Crosta², E. Veto Akos3, E. Bilal4, K. Gal-Solymos5 and E. Dransart6. 1 9, Jardin Gabrieli 3700 Tours France – [email protected] - 2IG, Unicamp 13081-970, Campinas (SP), Brazil – [email protected] 3 E. Veto Akos, II Budapest 1026, ut Baloch Adam 18-6, Hungary - [email protected] 4Ecole Mines St Etienne – Centre Spin, 158 cour Faurel 42023 St Etienne France [email protected] 5 Eötvös University, Dept. Petrology H-1117 ELTE, 1088 Budapest Churum krt 4/A Hungary. [email protected] - EMTT6 (Etudes Métalurgiques et de Traitement) - 1 avenue du Chater 69340 Francheville France – [email protected].

Introduction: The Araguainha Impact crater is lo- 500 to 530 Ma, the red dikes and the ejected cated in Brasil in the northeastern part of Parana Basin: and deposited around the area are of the same age. latitude -16°77’, longitude –52°58’. Its diameter is 40 According to field observations on sample locations 6 Km. and 8 (E Veto Akos, written information), the impact W.Engelhardt1 (1992) and A.P. Crosta2 (1981) are related breccias, present in the impact products, are amist the first with Dietz and French (1972) to re- mixed with rhyolitic debris. A volcanic eruption was conize, this crater as astrobleme. We have to give a caused by the at PTB. right credit to all geologists, who worked there before. We have established the geological build up of the On the impact crater at Araguainha and neighbour- target rocks at the time of the impact event, the severe ing areas [1], we have obtained new data during our modification of this build up after the impact and the field survey carried out in July 1998 with A. Crosta. erosion and weathering phases since the Permian time The purpose of the present paper is to give an outline by studying the signs of shock-waves observed during of our research. The samples collected within the cra- our field trip and from aerial photographs. ter and in neighbouring localities have provided a clear A large, 3 to 4 km in diameter, iron-rich bearing understanding of the stratigraphy of the Permian- meteorite, fell at Araguainha at the end of the Per- Triassic boundary (PTB) at the time of impact. mian., very close to a mega structure known as the As a result of a careful choice of twelve new sam- Tranbrasilian Lineament [6] at the boundary between ple locations in the area of the crater itself, we have the Guapore Plate (U. Precambrian) and the Goias been able to discern some of the nature and constitu- Plate (Archean to Precambrian). Shearing and thrust- tions of the and dikes. Subsequently, the con- ing took place at the boundary of an old Cambro- stituents were studied thoroughly by petrographic granitic trend and the Arnica Mts. The analyses. The layered nature of the breccia allowed us latter were folded during the Guandacol- and subse- to establish an order in the deposits. The results from quent Ocloyica orogenies, the Famatinian cycle, petrographic thin sections and Scanning Electron Mi- probably at the end of the Ordovician but definitively croscopy/EDAX studies were compared. We system- at the end of Lower time ([7], [8] and [9]). atically analysed the Landsat MSS and the Landsat According to detailed maps of the DNPM of the state Thematic Mapper images (already studied in [2], and of Goias (1986), the Serra Negra Rift in the Ara- [3]), from the outcrop areas, in order to obtain a cor- guainha area and at Piranhas near Bom Jardim of rect map base for our interpretations. Goias was formed along this line of weakness in Results: Western Gondwana. This event took place as early as The most important results have been obtained from Lower Llandovery [10]. This tectonic process was the use of the petrographic diagrams of [4] and [5]. initiated by the collision of the Precordillera of Argen- Plots in the Total Alkali Silicates diagram (TAS) are tina, separated from Laurentia, against the western consistent with the QAPF modal classification of gran- margin of Western Gondwana [11]. ites and of eruptive rock and proposals published be- With the ejection of molten granite and rhyolites, a fore were revised and updated. layer of breccia was formed with the largest particles In this framework, some of the alkali-rich K gran- and ejecta near the front of the Arnica Mts. already ites collected at Araguainha are in reality rhyolites formed in Devonian times. Those old ranges are at with all their various constituents, rhyo-dacites and present eroded but retain their former outlines and fold andesites. It has become evident that the uplifted K axis. The finer sized ejecta are believed to have been granite of the target rock (basement dated at present thrown in a southern direction in accordance with the Large Meteorite Impacts (2003) 4096.pdf

scheme of [12] and revised by [13], following simula- portant mass extinction of flora and fauna. This world- tion studies of the growth and movement of particles. wide catastrophic event can be emphasized by the im- As a last stage, we assume a process of volcanism fol- pressive belt of extraterrestrial material of the same lowed by a hydrothermal stage at the northeastern pe- age around the old Tethys Ocean ([17] and [18]) and if riphery of the crater (sample locations 11 and 12) with we consider all material containing exraterrestrial mi- a characteristic fluid phase (OHmol, F, CI). crospherules known at Sassayama [19] (Japan), Me- Microspherules Within The Proximal And Distal ishan [20] (South China) and in the Bukk Mountains Ejecta: (hungary)[21], as impact fallout material at the end of The microspherules ejected from the crater are Pemian time. We can also add one more recently dis- probably included within the smallest ejected particles. covered location in the western Caucasus (pers. com) We have many examples of this within the Araguainha where we found -Ni/Cr spinels at the Pemian Triassic crater itself and surrounding areas, e.g. at Balneario boundary. 60 km away from the crater location and in Mon- References: tividiu, 196 km. towards the southeast. The investiga- [1] Engelhardt W. et al. (1992) Meteoritics, 27, tions on proximal ejected particles were carried out at 442-457. [2] Crosta A. P. et al. (1981) Rev. Bras. a hill site in the breccia belt identified by the presence Geosciences, 11, 139-146. [3] Crosta A. P.and Thomé of a TV antenna. Here, we have collected some sam- Filho (2000) Post Congr. field trip, Aft 47, Rio de Ja- ples (Nb 5) which show the presence of Ni-rich) when neiro. [4] Mc Donald et al. (1992) US Geol. Survey Prof. analysed by ionic probe IMS (1500 ppm Ni), SEM and Paper 1523. [5] Le Bas et al. (1986) J. of Petro., 27, P3, elemental spectra. At the same emplacement Hipperttet 745-754. [6] Brito Neves and Cordani (1991) Precambr. et Lana (1998 MPS 33, 1303-1309) observed a Rh and Res., 53, 23-40. [7] Rapela et al. (1992) in Gutierrez et al., Ir enrichment (4x) relative to the indigenous target Merida, Extramadura; 21-68. [8] Pankhurst and Rapela sediments, where Ir content is only 0.4 ppb. (1998) in “The proto Andean Morgin of Gond- In Balneario near Alto Garças (MT), just above the wana”.Geol. Soc. Special Publ. 142; 383p.-London.. thick- stromatolite beds [14], we found nice PDF with 1-2 [9] Thery JM. (1978) inter. rept. unpublished. microns-thick laminae. According to E. Dransart they con- S.N.P.A. 120p. Trompette R., 1994 A.A. Balkema tain small fluid inclusions, less than 1 micron in size. We Edit. Rotterdam/Brookfield 350p. [10] Gray J. et al. have also observed oval quartz, 30 micron in size forming a (1982) Geology, 13, 7, 521-525. [11] Astini R. A. "ballen", structure. They are "crackled" [15] and provide (1996) XIII Congr. Geol. Argentina, III Congr. Expl. evidence of an impact origin of the Araguainha crater. They Hidrocarburos, Actas V, 509-736. [12] Stoeffler D. are considered as small ejecta included in the deposits and (1974) Forschritte Mineralogie, 51, 256-289. [13] mixed with gravels and probably pseudotachylites [14]. We Artiemeva (2002) IX Int. Conf. on , Imp. have also found diaplectic glass along a dike close to the TV Glass, and Imp. Proc. Frantiskovy-Lazne, Abstract. hillside (written information from thin section studies by E. [14] Théry et al. (2002) Ibid.,Frantöskovy-Lazne. Veto Akos). According to Jean Dejax (Museum d'Histoire [15] French B. M. (1998) LPI Contr. 954, Houston. Naturelle, Paris ) and Rodolfo Dino (Petrobras, Rio, Brazil), [16] Visscher et al. (1996) US Nat. Acad. of Sciences a palynological assemblage found in a recent determina- Proceed. 8, 93, 2155-2158. [17] Retallack G. et al. tion, precises the top of Tatarian to Lower Triassic at Mon- (1998) Geology, 26, 11, 979-982. [18] Chateauneuf et tividiu (GO) (written pers.com). We identified, precisely the Stampfli (1978) Notes Labo Paleont Univ. Genève, extraterrestrial microspherules, the and the Fasc. 2, l-l3. [19] Miono et al. (1973), Nuclear Meth- detailed stratigraphy of the PTB. In addition, these data con- ods in Physics Research B75 p 435-439. [20] Jin Y.G. firm the age of 247-251 Ma for the distal ejecta in Mon- et al. (2000) Science, 289, 432-437. [21] G.H. tividiu (GO), which had been formerly determined by data- Bachmann et H.W. Kozur ,Conf. 19 int. 2002 tion of observed fungal event [16]. Frantiskovy, abstact. Summary: The presence of distal ejecta at the south of the Araguainha impact point at the PTB up to 10-60 Km and even 196 km distant, suggests a large area of dis- tribution of characteristic fallout ejecta. In addition, according to map data, three to four secondary craters are believed to exist around the main crater in the form of a cluster 25 to 35 km in size. It shows the importance of the Araguainha impact at PTB, already well known as the time of the most im-