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Title: Geochemical evidence of an extraterrestrial component in impact melt breccia from the Paleoproterozoic Dhala impact structure, India
Author: Jayanta Kumar Pati, Wen Jun Qu, Christian Koeberl, Wolf Uwe Reimold, Munmun Chakarvorty, Ralf Thomas Schmitt

The Paleoproterozoic Dhala structure with an estimated diameter of ~11 km is a confirmed complex impact structure located in the central Indian state of Madhya Pradesh in predominantly granitic basement (2.65 Ga), in the northwestern part of the Archean Bundelkhand craton. The target lithology is granitic in composition but includes a variety of meta-supracrustal rock types. The impactites and target rocks are overlain by ~1.7 Ga sediments of the Dhala Group and the Vindhyan Supergroup. The area was cored in more than 70 locations and the subsurface lithology shows pseudotachylitic breccia, impact melt breccia, suevite, lithic breccias, and postimpact sediments. Despite extensive erosion, the Dhala structure is well preserved and displays nearly all the diagnostic microscopic shock metamorphic features. This study aimed at identifying the presence of an impactor component in impact melt rock by analyzing the siderophile element concentrations and rhenium-osmium isotopic compositions of four samples of impactites (three melt breccias and one lithic breccia) and two samples of target rock (a biotite granite and a mafic intrusive rock). The impact melt breccias are of granitic composition. In some samples, the siderophile elements and HREE enrichment observed are comparable to the target rock abundances. The Cr versus Ir concentrations indicate the probable admixture of approximately 0.3 wt.% of an extraterrestrial component to the impact melt breccia. The Re and Os abundances and the 187Os/188Os ratio of 0.133 of one melt breccia specimen confirm the presence of an extraterrestrial component, although the impactor type characterization still remains inconclusive.

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The Allahabad University (AU) is set to get the first "crater core library" in the country to store samples from the asteroid impact site at Dhala in Madhya Pradesh's Shivpuri district.

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Dhala crater is an impact crater in the Madhya Pradesh state of India. Its age is estimated between 1.7 and 2.1 billion years. Its diameter is estimated at 11 km. It is exposed at the surface.

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The news of the discovery of one of the oldest impact structures in Shivpuri district of Madhya Pradesh by an Allahabad University geologist could open up new vistas of research in India as well as in the Asian continent on meteorites that strike the Earth.
It is worth mentioning here that Dr Jayanta K Pati of the planetary science department of Allahabad University has recently discovered the Dhala impact structure believed to have been created by an asteroid of the size of about one Km in diameter about 2,500 million years ago which is being considered of great significance with regard to widening the field of occurrence of impact structures in Asia.

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DhalaB.gif
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Digital Elevation Model of Dhala impact structure, India based on Survey of India topographic contour data (54K/3, 4, 7 and 8). The estimated diameter (~25 km) based on remote sensing  data is shown in dotted line. Linear ridges are quartz veins (GQV).

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The Dhala structure  (N25°17'59.7" and E78°8'3.1") is situated in Shivpuri district, Madhya Pradesh State, India. Currently, the diameter of the structure is estimated at 11 km based on field observations. The basement rocks are predominantly composed of granitoids, and in the central most part of the structure voluminous melt breccia containing target rock clasts with shock metamorphic features are directly overlain by a post-impact silt-stone-shale-sandstone sequence of the Vindhyan Supergroup.
Recent geochronological dates suggest that the age of the impact event lies in the range between 1.6 and 2.5 Ga.

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-- Edited by Blobrana at 12:52, 2009-01-11

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One of the oldest impact structures in the world, created by an asteroid of the size of about one km in diameter about 2,500 million years ago, has been discovered by an Indian geologist in Madhya Pradesh's Shivpuri district.
The newly discovered Dhala structure, second in India after Lonar, has been named after the village near which it was discovered. It is the eroded remnant of the an impact structure with an estimated present day diameter of 11-km, the largest in Asia. Till date not a single confirmed impact structure has been reported from Japan and China.

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This structure was discovered by Dr. Jayanta K. Pati, University of Allahabad, India. The age is estimated to be 2000 million years old.

-- Edited by Blobrana at 21:30, 2006-04-22

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The Dhala structure is a newly discovered impact structure in central India, that had an estimated diameter of 15 km.
Proterozoic age impact occurred in the western fringe of Bundelkhand craton, Shivpuri district, Madhya Pradesh, India. The impact structure has unequivocal evidences of diagnostic shock metamorphic features; extensive deformational imprints and a large impact melt vein. It is a complex structure with a clearly defined central uplift and a breccia ring. The crater fill sediments, occurring around the central uplift, preserve excellent soft sediment deformation structures.
The age is estimated to be 650 million years old.


Position: 25.3000 N 78.1342 E

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