This award will support an integrated magnetic and thermochronometric study of gabbroic rocks from Hole U1309D (Atlantis Masif, on the western flank of the Mid-Atlantic Ridge at 30degreesN. The distribution (relative to igneous contacts) and temperature stability of the normal polarity magnetic overprints will give valuable constraints on the spatial scales of intrusions as well as the temperature of the country rock when these plutons were emplaced. Single zircon U-Pb dating will define the emplacement age of crust forming melts (including leucocratic dikes, oxide gabbro and some gabbro) found throughout the upper 1250m of IODP Hole U1309D. (U-Th)/He thermochronometry on zircon and apatite, with closure temperatures between ~200- 70degreesC, will delimit the low temperature cooling and denudation history of these rocks. The combined U/Pb chronometry and remanent magnetic data will be used to constrain the timing and rate of cooling/denudation resulting from low-angle normal faulting as proposed for Atlantis Massif. Remanence directions (particularly from core pieces reoriented using formation microscanner images) will be used to estimate the amount of tectonic rotation since the remanence was acquired and where may help constrain the range of possible rotation axes. The study involves international collaboration and the participation of graduate students.
