Absolutely spectacular HUGE volcanic dykes in Libya!

Thread on the latest awesome geology I’ve stumbled onto in Google Earth - and a rare foray for me into ‘normal’, rather than mud, volcanism.

Paging @seis_matters @SimonHolford @MagmaFingers @janinekrippner

These are Pliocene-Pleistocene age basalts on the SW edge of the 42000km2 Al Haruj Volcanic Province.

Location: https://goo.gl/maps/iDst86jSpxPAAGXB8
25°38'52.1"N 16°48'54.9"E

The 2 large parallel dykes are oriented NE-SW and are ~2.5km apart.

The larger dyke is ~23km long and ~1.5km wide at its widest part. The smaller dyke is ~13km long and ~800m wide at widest part.

There is a central volcanic vent right between the two, with visible connection feeders into the two dykes.

These dykes are briefly described in Elshaafi & Gudmundsson (2016), who also attempt to mechanically model them: https://doi.org/10.1016/j.jvolgeores.2016.06.025

The dykes are highly segmented, & appear to be made up of dozens of small, short NW-SE to E-W segments. The smaller vent is comprised of over 80 segments, with an average spacing of ~150m. The larger dyke is also highly segmented, though the segments are generally merged.

These vents are orthogonal to the ~WNW-ESE regional alignment of volcanic vents in the Al Huraj Province (& likely maximum horizontal stress direction at the time), which is also approximately the same orientation as the dyke segments & feeder to dykes from central volcanic vent.

It has been proposed that these dykes have intruded along pre-existing fault planes, as they are sub-parallel to regional faults mapped in nearby exposures.

I may be imagining it, but the segments also look like they vary in orientation along the dyke – being ~NW-SE in the thicker, central parts of the dykes and rotating to ~E-W near the tips. This could be a ‘snapshot’ of the stress reorientation that occurs near fracture tips.

These dykes are fascinating! If forcing open a fault, its a poorly aligned fault in the prevailing stress. Hydraulic fracs will often simply cross or arrest at such high approach angles. The internal segmentation is amazing.

I’m still trying to figure out the mechanics of this!