MICROSTRUCTURAL FEATURES OF A SUBAQUEOUS LAVA FROM BASALTIC CRUST OFF THE EAST PACIFIC RISE (ODP SITE 1256 , COCOS PLATE)

Authors

  • Laura Crispini DIPTERIS, Dipartimento per lo Studio del Territorio e delle sue Risorse, Università di Genova, Italy
  • Paola Tartarotti Dipartimento di Scienze della Terra “A. Desio”, Università degli Studi di Milano, Italy
  • Susumu Umino Institute of Geosciences, Faculty of Science, Shizuoka University, Japan

Keywords:

Abstract

This work examines a massive basaltic lava emplaced in a subaqueous environment and drilled at ODP Site 1256. Site 1256 was drilled on the eastern flank of the East Pacific Rise during ODP Leg 206 (6°44N, 91°56W; Guatemala Basin), located in 15 Ma old oceanic crust created by superfast seafloor spreading (ca. 220 mm/yr). The massive lava lies between thin sheet flows and caps pillow lavas, sheet flows with minor hyaloclastite, breccia and dikes. The massive basalt was encountered in two holes, 1256C and 1256D, which are 30 m apart, and has a thickness of 35 m in Hole 1256C and 75 m in Hole 1256D. It can be interpreted as a ponded lava, originated by rapidly erupted lava accumulated in a off axis >3-5 km depression of a steep paleotopography (Teagle et al., 2004). The Hole 1256 lava pond has been divided into distinct petrographic units and structural units. Five main structural units with different key flow-related textures and syn-magmatic or late magmatic structures were recognized. Ductile and brittle-ductile structures attributed to the flow gives constraints about the emplacement mechanism of the lava and possibly seafloor topography. Unusual textural features related to the flow kinematics were recognized mainly in the top and in the bottom parts of the lava pond, whereas brittle-ductile and brittle deformations occur throughout the whole ponded body. Microstructures in the base may be interpreted as flow-related deformation of hot ductile coalesced spatter clasts erupted during the first stages of emplacement. Alternatively, they may have been formed during lava drain-back, in the final emplacement stages.

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Published

2006-07-01

How to Cite

Crispini, L., Tartarotti, P., & Umino, S. (2006). MICROSTRUCTURAL FEATURES OF A SUBAQUEOUS LAVA FROM BASALTIC CRUST OFF THE EAST PACIFIC RISE (ODP SITE 1256 , COCOS PLATE). Ofioliti, 31(2), 117-127. Retrieved from https://www.ofioliti.it/index.php/ofioliti/article/view/334

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