Very sorry for the late reply, Roger. I can add one reference:



Decker et al. 2008: Tectonics of the NE Al Kufrah Basin (Libya). Geology of East Libya, vol. 4, pp. 139-152.



I hope, it still helps.

All the best,



Heike R. Gröger, PhD

Geologist, Exploration Research

Global Basin Analysis

Statoil ASA



Mobile: +47 91753553

Telephone: +47 51997293

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Visitor address: Svanholmen 8, Stavanger-Forus, Norway

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-----Original Message-----

From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of Stephen Rippington

Sent: 7. november 2013 17:08

To: [log in to unmask]

Subject: Re: Age of normal faulting in SE Libya



Hi Roger,



CASP undertook numerous expeditions to the Kufra and Murzuq regions before the Arab Spring. It would be worth contacting Guido Meinhold at Goettingen, Dan Le Heron at Royal Holloway, or Andy Whitham at CASP, to see if they can help. I'm sure a quick Google search will throw up their email addresses.



Good luck!



Stephen Rippington, PhD

New Ventures Interpretation Geoscientist



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-----Original Message-----

From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of Roger Gibson

Sent: 07 November 2013 15:19

To: [log in to unmask]

Subject: Age of normal faulting in SE Libya



Dear Geotectonics List Members,



In 2010 I was invited by Libyan colleagues to be part of an expedition to the Oasis impact structure (24o34’N, 24o24’E) located NE of Kufra in SE Libya. The reconnaissance study was supposed to be followed up in 2011 by a larger study; however, political events in Libya quashed any hopes of a return.



One of the aspects of the region is that the impact structure is cut by a prominent set of WNW-trending lineaments that extend over 200 km to the N and NW of the structure. Koeberl et al. (2005) claimed that the impact structure overprinted these 'sandstone dykes", however, our mapping has showed that these features are small normal faults with localised but extreme drag  at their margins, and displacements likely of no more than a few metres. The faults have coarse, gritty, silicified and manganiferous to ferruginous sand infillings and common pipe-like tubes that are steeply plunging, suggesting significant fluid volumes. The latter may explain the term "sandstone dyke" used previously - they stand slightly higher than the surrounding landscape as low knife-like ridges up to kilometres long. North of the main Oasis hills, the ferruginous plugs reach several tens of metres across. They remind me of fluid-escape structures formed in the high-strain-incompatibility terminations of faults. I am not familiar with whether they would be more likely in volcanic areas with high groundwater flow. If anyone is interested, I can send them some photos.



In discussion with one of our Libyan colleagues it was suggested that the faults were cut by 39 Ma intrusive dykes elsewhere in Libya; thus giving an age limit for the faulting. However, the GoogleEarth image does not show much in the way of igneous features in the Oasis inlier, which is surrounded by extensive sandy desert, and the neighbouring inliers with volcanic features do not show conclusive evidence of a similar fault pattern. The faults postdate the so-called Nubia Formation, although the gritty/sandy infill reminiscent of the Nubia Formation may suggest the latter was not fully consolidated at the time. Thus far, my colleague has been unable to tell me whether the 39 Ma age is reliable, and what the source is. I am also aware that the Jurassic-Cretaceous history of the region is one of extension, so differentiating generations of faults may be difficult to impossible. It is also clear that getting further information out of Libya is unlikely, so I am appealing to anyone who may have knowledge of this rarely-visited region for any clues that could confirm or refute the age or of the significance of the fault swarm North of Kufra in terms of the regional tectonics, and its relation to volcanism and/or intrusive activity in the region?



In anticipation of your reply,



Thanks,



Roger Gibson



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