Transformation of Serpentinite to Listvenite as Recorded in the Vein History of Rocks From Oman Drilling Project Hole BT1B
Abstract
Oman Drilling Project Hole BT1B intersected 191 m of listvenite (magnesite + quartz rock) and serpentinite in the hanging wall of the basal thrust of the Oman ophiolite. Recovery was 100%. Listvenite is the dominant lithology in the upper plate rocks (166 m). Its shows wide color and textural variation, including pseudomorphic replacement of serpentinized peridotite. Serpentinite was encountered in two main contiguous intervals totaling 25 m. In light of the strongly metasomatic nature for the origin of listvenite, a substantial portion of the core description effort was dedicated to characterization of the complex veining history recorded in the hole. Dense veining is recorded in both lithologies. The density of <1 mm veins is >200/m. The density of veins >1 mm was 50-100/m, with somewhat higher densities recorded in serpentinite than in listvenite. In order of oldest to youngest, the main vein types in serpentinite are microscopic mesh-textured serpentine veins, macroscopic serpentine veins, carbonate-oxide veins, and carbonate veins. The vein paragenesis in listvenite is: early carbonate-oxide veins, followed by carbonate and carbonate-quartz veins, then late carbonate veins. The carbonate-oxide and carbonate veins are shared by the lithologies and hold clues to the transformation of ultramafic rocks to listvenite. Carbonate-oxide veins form a distinctive set that is interpreted to be the earliest record of carbonate formation in serpentinite. They contain Fe-oxide, usually hematite, on a medial line, with antitaxial magnesite crystals growing outward and showing terminations against wall rock minerals. Antitaxial textures may be evidence of positive reaction volumes. In serpentinite, secondary serpentine after earlier serpentine is common at vein margins. Carbonate-oxide veins are the earliest observed in listvenite, where they may form isolated veins to dense, aligned networks that impart a foliated texture. In some cases, they appear to predate replacement of serpentine by microcrystalline quartz. Both lithologies record later, coarser, through going carbonate ± quartz veins. Preliminary vein petrology in BT1B rocks indicates that fracture formation and filling by secondary minerals is integral to the metasomatic replacement of altered peridotite by listvenite.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.V24E..08M
- Keywords:
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- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL;
- 8115 Core processes;
- TECTONOPHYSICS;
- 8140 Ophiolites;
- TECTONOPHYSICS