DATA REPORT: GEOCHEMISTRY AND MINERAL CHEMISTRY OF ULTRAMAFIC ROCKS FROM THE KANE AREA (MARK)

Carl-Dietrich Werner and Joachim Pilot

ABSTRACT

A suite of serpentinized peridotites from Leg 153 was analyzed for major and trace elements. All the rocks are less-refractory peridotites. The mineral chemistry of olivines (Mg# = 90.3), orthopyroxenes (Mg# = 90.4), clinopyroxenes (Mg# = 91.6), and some Cr spinels (Mg# = 68.4; Cr# = 29.7) shows the characteristic features of minerals from less-depleted mantle peridotites. Some geothermometric calculations gave temperatures for the pyroxene system of about 1300C, reflecting the prekinematic to synkinematic crystallization of the pyroxenes, and gave a range from 1180 to 1075C for the mineral pair orthopyroxene and spinel. Oxygen-isotope determinations show delta18O values of about 6 for olivine, orthopyroxene, and clinopyroxene; delta18O values from chromian spinel/magnetite vary between 2.9 and 3.8, values from serpentine vary between 2.8 and 5.3, and whole-rock values vary between 2.9 and 4.6. Two temperatures could be calculated from the oxygen-isotope exchange for the mineral pair clinopyroxene and spinel: about 1100 and about 900C. The 1100C value nearly corresponds to the data obtained using the orthopyroxene-spinel mineral thermometer, and may indicate subsolidus deformation and recrystallization. The temperature range of the serpentinization could only be estimated. It depends upon the rock/water ratio, and may not have exceeded ~300C. Finally, a calculation of possible rock/water ratios is given.

Date of initial receipt: 24 August 1995
Date of acceptance: 27 February 1996


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