Bouguer anomaly inversion and hydrocode modeling of the central uplift of the Araguainha impact structure

MIYAZAKI, MARCELLE R.; LEITE, EMILSON P.; VASCONCELOS, MARCOS A.R.; WÜNNEMANN, KAI; CRÓSTA, ALVARO P.

doi:10.1590/0001-3765202120210081

MARCELLE R. MIYAZAKI

Instituto de Geociências, Universidade Estadual de Campinas, Rua Carlos Gomes, 250, 13083-855 Campinas, SP, Brazil

http://orcid.org/0000-0002-4528-7565

EMILSON P. LEITE

Instituto de Geociências, Universidade Estadual de Campinas, Rua Carlos Gomes, 250, 13083-855 Campinas, SP, Brazil

http://orcid.org/0000-0003-1691-6243

MARCOS A.R. VASCONCELOS

Universidade Federal da Bahia, Instituto de Geociências, Departamento de Geofísica, Av. Adhemar de Barros, s/n, 40170-110 Salvador, BA, Brazil

http://orcid.org/0000-0002-4970-0484

KAI WÜNNEMANN

Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstraße 43, 10115 Berlin, Germany

Freie Universität Berlin, Malteserstr., 74-100, Haus D, 12249 Berlin, Germany

http://orcid.org/0000-0001-5423-1566

ALVARO P. CRÓSTA

Instituto de Geociências, Universidade Estadual de Campinas, Rua Carlos Gomes, 250, 13083-855 Campinas, SP, Brazil

http://orcid.org/0000-0003-0485-1147

Correspondence to: Emilson Pereira Leite E-mail: emilson@unicamp.br

AUTHOR CONTRIBUTIONS

Marcelle Rose Myazaki: Data acquisition; Data processing and analysis; Gravity inversions; Geological interpretations; Writing. Emilson Pereira Leite: Data acquisition; Computer programming; Data analysis; Gravity inversions; Writing. Marcos Alberto Rodrigues Vasconcelos: Data collection; Numerical modelling; Geological interpretations; Writing. Kai Wünnemann: Numerical modelling; Writing. Alvaro Penteado Crósta: Geological interpretations; Writing.

Figures (6)
Tables (1)

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Figure 1
Simplified geological map of the Araguainha impact structure (after Lacerda Filho et al. 2004Lacerda Filho JW, Abreu Filho W, Valente CR, Oliveira CC & Albuquerque MC. 2004. Geologia e Recursos Minerais do Estado de Mato Grosso. Programa Integração, Atualização e Difusão de Dados de Geologia do Brasil. CPRM/SICME-MT, MME, 235 p.). The central square depicts the location of the study area, where data were collected from gravity stations.

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Figure 2
Residual Bouguer anomaly map of the Araguainha impact structure’s center, showing the 300+ gravity stations from which the data was collected. Color scale is in mGal. Stations are closest to each other at the center of the structure. Thin black lines correspond, from the innermost to the outermost, to: granite, Furnas Formation, and Ponta Grossa Formation, respectively. All of them comprise the central uplift. Ends of profiles A-B and C-D are indicated on the map.

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Figure 3
3D gravity inversion model of the central uplift. (a) Complete model. From top to base: (b) Intermediate density sources (2.2 - 2.3 g/cm³), likely where breccias and sandstones of the Furnas Formation occur. (c) Low density sources (~2.1 g/cm³), mostly located beneath the top block, and possibly related to sandstones of the Furnas Formation and/or to highly-cracked granites at the center. (d) High-density sources (~2.4 g/cm³) representing the granites. This bottom block extends outward, beneath the Furnas Formation, as mentioned in the text.

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Figure 4
Sections obtained from the gravity inversion, detailing the area of the central granite. (a) N-S profile, (b) E-W profile. The location of both profiles is shown in Figure 2. B – Polymictic breccias/Melts, F – Furnas Fm., MG – Massive porphyritic granite, FG – Fractured granite. Dashed lines mark high density contrasts and are associated with the changes in geology.

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Figure 5
Best-fitting model for the impact event, showing the right-hand side of the model. (a) 15 sec after the impact, the crater reaches ~16 km diameter and ~7 km depth. (b) After 30 s, the formation of the central uplift begins. (c) The basement rises and remains exposed after 90 sec. (d) After 280 s, the structure reaches gravitational stability. CR = crater’s rim. Number 1 corresponds to sedimentary rocks, and number 2 to the granitic basement. The solid tracer lines connect the positions of the tracer particles that marked the center of each computational cell at the beginning of the simulation, following the paths of the material in that cell. Where the separation between tracer particles that were originally horizontally adjacent to each other exceeds ten times the initial separation (250 m), there is no line connecting these points. The extreme deformation in the sedimentary collar around the central uplift is highlighted by folding and discontinuities in the tracer lines at radial distances of 5-15 km. A similar deformation is observed in the real strata of the Furnas Formation.

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Figure 6
(a) Last timeframe obtained by iSALE showing the temperature range (in K) within a 7.5 km radius. The dashed white line corresponds to the same area (5 km x 2 km) of the gravity inversion presented in Figure 4. The temperature peaks in this area are likely related to the formation of melts in the granite. The upper figure shows the Bouguer anomaly estimated by the porosity model (dashed line) and the real Bouguer anomaly obtained from Figure 2 in the E-W direction. (b) Linear downward pressure trend at the innermost center. The pressure peak is around 53 GPa after 0.5 s, falling to 15 GPa after 1 s, and to less than 10 GPa after 1.5 s.

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Table I
Parameters of the best fitting numerical model of the Araguainha impact structure.

PARAMETERS	ASSUMPTIONS
Impactor:
Diameter	3000 m
Impact velocity	12 km.s^-1
Material/EOS	granite/ANEOS
Density	2.65 g.cm^-3
Upper sedimentary layers	Quartzite/ANEOS
Material/EOS	Intact	Damaged
Cohesion C_s	1 MPa	0.01 MPa
Dry friction coefficient ϕ_S	2.0	0.01
Thickness	1750 m
Granitic Basement	Granite/ANEOS
Material/EOS	Intact (Y₀)	Damaged (Y_d0)
Cohesion C_B	10 MPa	1 KPa
Dry friction coefficient ϕ_B	2.0 (FricInt)	0.6 (FricDam)
Model setup
Number of cells nx x ny (radial, vertical)	300 x 330 cells (high res. zone)
Spatial increment (high resolution area)	60 m
Resolution in cells per projectile radius (CPPR)	10
Acoustic fluidization parameters	Granite	Sedimentary rocks
*Dimensionless Acfl. fluidized viscosity g_h	0.01	0.0008
*Dimensionless Acfl. acoustically fluidized decay time g_b	115	150

[1] Correspondence to: Emilson Pereira Leite E-mail: emilson@unicamp.br

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Bouguer anomaly inversion and hydrocode modeling of the central uplift of the Araguainha impact structure

Abstract