#porcellanite

[geoworldtravel]

Today was the penultimate day of our tour. We awoke in our desert camp in the Wahiba Sands (pic2), and had to first navigate the dunes to reach a road again. The first stop was to see rocks of the Precambrian crystalline basement (800-1,000 million years old). Here we saw granites that formed as terranes were accreted together, cut by huge gabbro dykes (pic3) that were intruded as the basement went through a later period of extension. All of these rocks were themselves intruded by granitic pegmatite (containing large crystals) dykes (pic4). Our next stop was to see an ultramafic rock outcrop on the beach (pics 5&6), which contained volcanic fragments (lapilli) that formed due to the ascent of magma. Some authors have called the rock a kimberlite, which is the deepest mantle derived volcanic rock of all, and sometimes contains diamonds, although this outcrop contains no diamonds. Others argue this outcrop is actually a carbonatite which is also derived from deep in the mantle but less deep than kimberlite. After our picnic lunch, we then visited one of Oman’s most famous outcrops informally known as the ‘mother of all outcrops’ (pics 1,7&8). Here, red radiolarian chert is interbedded with white porcellanite. These sediments were deposited in water 4,000-4,500 metres deep, which is too deep for limestones to form so, but rocks can form from radiolaria plankton because their skeletons are made of silica. Our group discussed at length why the outcrop consisted of alternating white and red layers, was it a secondary diagenetic process? or was it directly due to cycles of sedimentation? However the sediments were deposited, they were later folded and faulted as they were thrust onto Arabia as part of the Batain Nappe, (along with the Oman’s other ophiolite, the Masirah Ophiolite), 15-20 ma after the emplacement of the main Semail Ophiolite. At our next stop, we saw an outcrop of manganese ore (pic9), which contained crystals of pyrolusite (MnO2). The final stop of the day was an outcrop of carbonite volcanic rock (pic10). The rock appeared to be a tuff (volcanic ash) rather than lava. The rock also contained beautiful veins of amethyst. (at Oman) https://www.instagram.com/p/B9oV6CPJ9Gk/?igshid=tzmrobeuec2u

[environmentguru]

Petrological study of the early Mesoproterozoic Glauconitic Sandstone and Olive Shale members from the Semri Group, Vindhyan Supergroup in Central India: Implications to input from intrabasinal felsic volcanic source and glauconitization

The Semri Group of the Vindhyan Supergroup contains widespread intrabasinal felsic volcanic rocks in the Porcellanite Formation formed during the early Mesoproterozoic. This widespread felsic volcanism was followed by the deposition of siliciclastic https://www.environmentguru.com/pages/elements/element.aspx?utm_source=dlvr.it&utm_medium=tumblr&id=5207387

#CO2 #Sedimentation #Detritus

[geoworldtravel]

Today was the penultimate day of our #oman #geology tour. Our first stop (picture 5) was to see rocks of the precambrian crystalline basement (800 - 1000 million years old). At this site granites were intruded by basalts which were themselves cut by #pegmatite veins. Our next stop (pictures 6 & 7) was to see a rare volcanic rock called #kimberlite that brings rock up from very deep in the mantle and sometimes contains diamonds (although not in this case). We then visited the #motherofalloutcrops seen in pictures 1-4. Here red radiolarian chert is interbanded with white porcellanite. These sediments were deposited in water 4000-4500 meters deep. They are folded and faulted and were trusted onto Arabia as the Batain Nappe 15-20ma after the emplacement of the Semail Ophiolite. We then had our picnic lunch before heading to a Manganese Pit which is located in the same sediments. Our final stop was Ras al Hadd where there is a Bronze Age settlement and a turtle nesting beach. Here we are spending the night. (at Oman) https://www.instagram.com/p/BuRGGTygfCP/?utm_source=ig_tumblr_share&igshid=1jxxej0tt3f1r

#oman #geology #pegmatite #kimberlite #motherofalloutcrops