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23 octubre 2014 4 23 /10 /octubre /2014 19:32

The combined data set shows that the Målingen structure formed in conjunction with the Lockne crater in the same marine setting. The shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz, slumped sediments, and resurge deposits support an impact origin.

 

Dos cráteres suecos son la primera prueba del doble choque de un asteroide contra la Tierra

 

Hace unos 470 millones de años ocurrió una gran catástrofe cósmica en el sistema solar: un asteroide de unos 200 km de longitud se rompió en fragmentos, dos de los cuales viajaron juntos 12 millones de años hasta impactar en la Tierra los dos a la vez. Lo hicieron en lo que hoy es Suecia, creando los cráteres Lockne y Målingen. Ahora un geólogo del Centro de Astrobiología ha encontrado las evidencias, en lo que constituye el primer caso confirmado de impacto de asteroide binario en nuestro planeta.

 

Los cráteres suecos Lockne, de 7,5 km de ancho, y Målingen, de unos 0,7 km, fueron originados a la vez por el choque de un asteroide doble, formado por un objeto de unos 600 m y otro más pequeño de 150 m. Ambos surgieron tras la explosión de un enorme asteroide de 200 km por alguna colisión en el cinturón de asteroides principal hace 470 millones años.

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141023_mapasueciacrater2_Scientific Reports-Ormö et al

 

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Localización de los cráteres Lockne y Målingen en Suecia. / Scientific Reports-Ormö et al.

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Así lo apunta un estudio que esta semana publica en la revista de acceso abierto Scientific Reports un equipo de investigadores liderados por Jens Ormö, del Centro de Astrobiología (INTA-CSIC).

“Por primera vez se ha datado con tan alta precisión una pareja de cráteres de este tipo, ambos creados hace 458 millones de años, y que constituyen el único ejemplo terrestre conocido que puede atribuirse sin lugar a dudas al impacto de un asteroide binario”, destaca Ormö a Sinc. “Todos los otros posibles candidatos dobles tienen edades con lapsos de tiempo que no permiten descartar que se hayan formado por separado”.

El buen estado de conservación de Lockne y Målingen, separados unos 16 km, ha permitido conseguir las pruebas geológicas necesarias para relacionarlos.

“El impacto doble se produjo en un mar poco profundo y los dos objetos chocaron sobre una misma configuración estratigráfica rocosa situada bajo una columna de agua de unos 500 m”, explica Ormö.

El investigador subraya el valor de estos datos “como referencia para las simulaciones numéricas de estos eventos, y por tanto, para evaluar los riesgos potenciales de los impactos de asteroides en el mar”.

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141023_crateres_suecos_JensOrmo

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Gran roca eyectada por el impacto del asteroide desde el antiguo fondo del cráter Lockne hasta varios kilómetros de su borde. / Jens Ormö

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Además, las formas de los dos cráteres están en consonancia con el impacto de un proyectil fragmentado, lo que lleva a los científicos a suponer que el asteroide binario pertenece al tipo denominado ‘pila de escombros', formado con piezas diversas unidas por fuerzas gravitacionales.

Las observaciones de asteroides cercanos a la Tierra indican que alrededor de un 16%  viajan en parejas; sin embargo, solo se han identificado unos pocos y controvertidos pares de cráteres asociados en la superficie de nuestro planeta.

Según los autores, es muy raro que un cráter de impacto pueda asociarse a un evento de ruptura datado en un tiempo concreto en el cinturón de asteroides, y en este caso se ha conseguido el único ejemplo doble conocido. Este, a su vez, servirá de referencia para analizar otros impactos dobles, así como la formación y evolución de los asteroides binarios en el sistema solar.

 

 

Fig. 3 – Map of the Siljan structure with inset showing the position of the seismic lines.

Map of the Siljan structure with inset showing the position of the seismic lines in A) Mora area and B) Orsa area.

 

 

The geology of the Målingen structure: A probable doublet to the Lockne marine-target impact crater, central Sweden

http://onlinelibrary.wiley.com/doi/10.1111/maps.12251/abstract

 

J. Ormö, E. Sturkell, J. Nõlvak, I. Melero-Asensio, Å. Frisk and T. Wikström
Article first published online: 4 MAR 2014

The Målingen structure is an approximately 700 m wide, rimmed, sediment-filled, circular depression in Precambrian crystalline basement approximately 16.2 km from the concentric, marine-target Lockne crater (inner, basement crater diameter approximately 7.5 km, total diameter in sedimentary strata approximately 13.5 km). We present here results from geologic mapping, a 148.8 m deep core drilling from the center of the structure, detailed biostratigraphic dating of the structure's formation and its age correlation with Lockne, chemostratigraphy of the sedimentary infill, and indication for shock metamorphism in quartz from breccias below the crater infill. The drill core reveals, from bottom to the top, approximately 33 m of basement rocks with increased fracturing upward, approximately 10 m of polymict crystalline breccia with shock features, approximately 97 m of slumped Cambrian mudstone, approximately 4.7 m of a normally graded, polymict sedimentary breccia that in its uppermost part grades into sandstone and siltstone (cf. resurge deposits), and approximately 1.6 m of secular sediments. The combined data set shows that the Målingen structure formed in conjunction with the Lockne crater in the same marine setting. The shape and depth of the basement crater and the cored sequence of crystalline breccias with shocked quartz, slumped sediments, and resurge deposits support an impact origin. The stratigraphic and geographic relationship with Lockne suggests the Lockne and Målingen craters to be the first described doublet impact structure by a binary asteroid into a marine-target setting.

 

 

 

Fig. 4 – Map of the Siljan structure indicating sedimentological distribution and the position of the Ordovician carbonate mounds.

 

Map of the Siljan structure indicating sedimentological distribution and the position of the Ordovician carbonate mounds. The three Igrene drill sites are indicated. Transpression ridges superimposed following the suggestion by Kenkman & von Dalwigk (2000). Map modified from Ebbestad & Högström (2007).

 

 

 

Concentric Impact Structures in the Paleozoic

 

Principal Investigators:
     Erik Sturkell, Gothenburg University, Sweden.
     Anette E.S. Högström, Tromsø University Museum, Norway.
     Jan Ove R. Ebbestad, Uppsala University, Sweden.

 

In 2009, CISP was one of two projects within the Swedish Deep Drilling Program (SDDP) that was granted funds for site investigations in the Swedish Research Council’s (VR) annual call for scientific projects.  The project received about 1/2 of the applied funding, for the period 2010 – 2012, although the funds were available until the end of 2013.
The main objectives of CISP have been fulfilled with great success (see summary under 2012), and has led to some quite revolutionary discoveries. The new facies distribution in the Siljan area revealed by Oliver Lehnert and his group and large scale tectonic implications should be mentioned.
As expected new research questions have arisen, and following the unsuccessful application to VR 2013 it was decided by the principal investigators, in understanding with co-workers, that future research under the umbrella of the new SSDP project should take different directions.
New proposals for pilot studies under CISP management will therefore not be made, and because the main objectives have been reached the CISP project is therefore declared ended. We, the principal investigators, are extremely thankful to everyone involved for their enthusiastic and engaging participation during these years. Even though CISP ceases, research will continue in the Lockne and Siljan craters, albeit regrouped and with different specific aims.

Large impact structures are a key to understanding a diverse set of scientific problems since they record essentials about the geological history where they occur. The ambition of CISP was to characterize the large Lockne and Siljan crater structures, with decisive features in common. The Siljan structure, the largest impact structure in Western Europe, and Lockne, which is the best accessible and studied impact formed in relatively deep sea, occurred at the supposedly Himalayan-type Caledonian mountain front in Sweden. Their development therefore expresses interaction between a gigantic over-thrust plate and Baltica through about 80 Ma. The most important apparent interaction was depressing Baltica’s west flank to form the trough where both craters formed. Another was tectonic stress that influenced shape and mineralization in the craters. It is all the more important to elucidate the less understood complications that can help to understand other craters. Major issues are the importance of basement lithology and structure, depth of water or sediment cover at the time of impact.
In addition to impact tectonics, the effect on life from the impact event can be studied in the Lockne area where records of post-impact re-colonization are found. The Siljan crater, with its renowned carbonate mud mounds, also contains unique sedimentological and palaeontological records preserved solely within the crater structure.

In 2009 CISP was one of two projects within the Swedish Deep Drilling Program (SDDP) that was granted funds for site investigations in the Swedish Research Council’s (VR) annual call for scientific projects.  The project received about 1/2 of the applied funding, for the period 2010 – 2012, although the funds were available until the end of 2013.
Dr. Erik Sturkell was the main applicant, with drs Jens Ormö (Centro de Astrobiología, Madrid, Spain), Christopher Juhlin (Uppsala University, Sweden), Reinhard O. Greiling (Karlsruhe Institute of Technology, Germany) and Anette Högström listed as co-workers. Administration of the project was handled by the principal investigators. The project was presented in the SDDP Science & Technology Plan in May 2010 (http://www.sddp.se/sciencetechnology), as well as in Högström et al. (2010).

 

 

Fig. 9 – Geological map

 

Geological map of the Lockne area with location of the suspected Proterozoic shear zone (black line), sample locations for 2012 and 2013 sampling campaigns (map kindly provided by E. Sturkell, University of Gothenburg).

 

 

 

READ MORE

 

http://www.ssdp.se/projects/cisp.html

http://www.ssdp.se/projects/cisp.html

 

* Malcolm Allison H  2014

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  • : Ecología y sostenibilidad socioambiental, énfasis en conservación de ríos y ecosistemas, denuncia de impacto de megaproyectos. Todo esto es indesligable de la política y por ello esta también se observa. Ecology, social and environmental sustainability, emphasis on conservation of rivers and ecosystems, denounces impact of megaprojects. All this is inseparable from politics, for it, the politics is also evaluated.
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  • Malcolm Allison H malcolm.mallison@gmail.com
  • Biólogo desde hace más de treinta años, desde la época en que aún los biólogos no eran empleados de los abogados ambientalistas. Actualmente preocupado …alarmado en realidad, por el LESIVO TRATADO DE(DES)INTEGRACIÓN ENERGÉTICA CON BRASIL
  • Biólogo desde hace más de treinta años, desde la época en que aún los biólogos no eran empleados de los abogados ambientalistas. Actualmente preocupado …alarmado en realidad, por el LESIVO TRATADO DE(DES)INTEGRACIÓN ENERGÉTICA CON BRASIL

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