SAG meeting in Oman
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SAG meeting in Oman

This year (2019) the twenty-fourth gathering of the Science Advisory Group (SAG) for the International Continental scientific Drilling Program (ICDP) took place. This time the SAG-group gathered in Muscat, Oman. This country is a Mecca for geologists, as Oman host so much fantastic geology. Thanks to the dry conditions the exposures are amazing. Before three long days of evaluating applications, we went on an excursion led by Peter Kelemen. On this absolutely brilliant field trip he took us to the Oman ophiolite, which has been thrusted over the Hawasina sediments (Fig 1). We also learned more about the Oman Drilling Project. As the field trip started 7 AM, and the flight was scheduled to arrive at 10 PM the previous evening, I decided to arrive one day earlier. However, the first challenge was getting to Oman! 

First part of my travel was to fly KLM to Amsterdam, departing 6 AM from Gothenburg. Waking up at 3:40 AM after a few hours of “sleep” I read a text message from KLM – my flight from Gothenburg had been cancelled! I was re-booked on a Lufthansa flight 7:15 AM. Still taking the ordered taxi at 4:00 AM, I got to the airport and tried to check in. At KLM they sent me over to the SAS check-in desk (representing Lufthansa). They informed me something was wrong with the ticket and forwarded me to the SAS service desk. Here they told me my ticket was incomplete and sent me back to the KLM service desk. KLM complained about Lufthansa not doing their job and then sent me back to SAS where I finally got my boarding cards, both to Frankfurt and Muscat. All employees were nice and did a good job, so thanks!
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Arriving one day in advance turned out to be fortunate as Peter even arranged an excursion to the mantle rocks located around the oldest part of Muscat the day before the main excursion. The mountains consist of harzburgite intruded by dunites (Fig 2). We saw rocks transacted by a fault zone, and these were rich in magnesite vein fillings. The next day the official excursion started and we travelled to the southern ophiolite massive. We followed the highway [no. 15] south to the town Izki along the Samail Wadi, turning towards the east to the first locality with active alkaline springs. Water passes through the peridotite rock (completely dominated by Mg-rich olivine) that gets serpentinised and leaches out Mg into alkaline water enriched in Mg(OH)2 and with a pH of 11 (Fig. 3). If calcite is present, the Ca originated from the clinopyroxene.

Some vegetation uses (likes, tolerates) this alkaline water, e.g. grasses and Dade palms growing next to the springs. Next locality was a valley at the village Falaij, where alkaline springs are emerging from the peridotite and forming travertine. At this locality the waterfall of alkaline water had dried up as the local landowner had re-directed the water to his palm tree plantation. The locality was, however, not completely devastated as it still has several beautiful stalagmites of travertine. The excursion continued to a locality of layered gabbros. After the gabbros, the excursion travelled back into the peridotite outcrops, which had experienced total carbonation. The fluids have removed all Mg from the olivine to make magnesite. With the Mg gone, the Si is used to form quartz, making a network of fine quartz veins in the rock and making it extremely hard. A complete carbonation of the peridotite means that all the Mg and Ca in the rock, and some of the Fe, is combined with CO2. This forms a red listwanite rock consisting of magnesite and calcite minerals in a quartz network (Fig 4). In addition, this rock contains a Cr-muscovite called fuchsite. The first day of the excursion finished at the place where Wadi Mansah intersected with road no. 15. Here we saw sheeted dykes in a fresh cut (Fig. 5).
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The next day started with a long drive along road no. 23 towards the town of Ibra. At Ibra we turned northwards travelling to the drill hole BA2 that is part of the Oman drilling project. This valley is within the mantle peridotite, and the drill holes aimed at exploring alteration processes. From this locality we followed a dirt road dissecting the peridotite massive. The probable reason for this road existing is the two power lines that it follows. At the second stop of the day, we hiked down a wadi (dried-up riverbed) to a locality with extensive fractured peridotite filled with large magnesite bodies. After a short ride we stopped and hiked down a wadi and climbed up to a plateau. From this plateau we had a fantastic view over the peridotite massive, and we also had our lunch at this incredible place. The next stop was also a wadi where the riverbed conglomerate had been cemented by carbonate-rich solutions (Fig 6). In the harzburgite, magnesite had filled fractures and through weathering produced flakes so the ground was littered with magnesite like potato chips. We continued to the Dima Wattayeen valley and drove over a pass down to the highway no. 23 again. As soon as we left the highway and followed a wadi (again) we saw layered gabbros and higher up in the wadi we crossed over the Moho boundary and came back into the peridotite. Next stop was the so called 5 o’clock Moho (Fig. 7) where the mountain had perfect light (at 5 PM) displaying its lower part with peridotites and the top with the layered gabbros, separated by the Moho. The second day of excursion ended at a locality with sheeted dykes. The excursions fulfilled all expectations of fantastic geology and Peter Kelemen being an excellent guide!

After the excursion, the SAG committee withdrew to a conference room and spend three days evaluating, ranking and commenting the many workshop- and drilling proposals. We finished our recommendations for each application at 10:38 PM on the third day. As the KLM flight (an airbus) departed at 11:25 PM in the evening, I had to stay one more night, which was used for sleeping in and some sight seeing in Muscat. The return trip was eventless and I arrived home Saturday morning.

References

Nicolas, A., Boudier, F., Ildefonse, B., & Ball, E., 2000. Accretion of Oman and United Arab Emirates Ophiolites – Discussion of a new structural map, Marine Geophysical Researches, 21, 174–179.

Fig 1. A geological map of the area south of Muscat showing the ophiolite rocks of the southern massive, drawn after an original by Nicolas et al. (2000). The approximately location of localities visited are marked with triangles.

Photo: Erik Sturkell

Fig 2.  The ophiolite massive, that surrounds the old part on Muscat, consists of the dark brown harzburgite and the light brown dunites. Note the conspicuous holes that are frequent in particular in the dunite.

Photo: Erik Sturkell

Fig 3. Alkaline springs with water that has passed through the peridotite rocks. The water seeping out has a pH of 11. At stop 1:1

Photo: Erik Sturkell

Fig 4. The red mountain consists of listwanite that is Fe-rich carbonised ultramafic rock. At the stop 1:4

Photo: Erik Sturkell

Fig 5. Sheeted dykes at dry spillway of the Wadi Mansah. At stop 1:5

Photo: Erik Sturkell

Fig 6. In riverbeds in the peridotite massive, the conglomerate is often cemented and gives a concrete impression. At stop 2:3

Photo: Erik Sturkell

Fig 7. The 5 o’clock Moho, where the lower part is peridotite and the top consists of gabbros separated by Moho. The photo is taken from highway no. 23. At stop 2:7