Mauzy Ridge is 21 nmi southeast of Site 1276 on the lower continental rise of the Newfoundland margin (Fig. F2). Drilling at Site 1276 (Figs. F1, F2) terminated in Lower Cretaceous alkaline basalt/diabase sills that are believed to be located several tens of meters above a subsediment basement, which could be either attenuated continental crust or subcontinental mantle. The sedimentary cover of Mauzy Ridge at Site 1277 was not sampled because of time constraints at the end of Leg 210. Core recovery began with pieces of micaceous sediment (in a wash core) and fossiliferous, ferromanganiferous crust directly above basement-related rocks and sediments. Beneath this, two contrasting units were recovered, as shown in Figure F3 (Tucholke, Sibuet, Klaus, et al., 2004).
Unit 1 (less than ~104–142.10 meters below seafloor [mbsf]) consists of basalt and is estimated to make up ~50% of the succession as lava flows and intercalated coarse clastic sediments. The sediments contain abundant clasts of serpentinite and lesser amounts of gabbro, together with minor amounts of finer grained clastic and ferruginous sediments. The relative proportions of these constituents vary within the succession, as discussed below. Relatively low recovery of most lithologies allows only estimates of the thicknesses of individual basaltic flows and clastic intervals to be made. The coarse-grained clastic sediments were initially interpreted as slumps, slides, and debris flows (see Shipboard Scientific Party, 2004b).
By contrast, Unit 2 (142.10–180.30 mbsf) is dominated by strongly deformed and altered serpentinized harzburgite and some dunite, together with minor gabbroic injections. The top of the unit is characterized by a gabbro cataclasite, and several thin zones of foliated cataclasite occur beneath this. The shear zones were interpreted by the Shipboard Scientific Party as products of an extensional detachment system related to the exhumation of subcontinental mantle to the seafloor. The serpentinized peridotite is cut by millimeter- to centimeter-wide hydrothermal veins that are mainly composed of talc, magnetite, and calcite. The foliated serpentinite is interpreted as strongly deformed mantle peridotite that was cut by small gabbroic intrusions and then exhumed to the seafloor in response to an advanced stage of rifting and continental breakup (Shipboard Scientific Party, 2004b). Details of the mineralogy and petrogenesis of the plutonic rocks of lithologic Unit 2 have been given by Müntener and Manatschal (2006). In general, the composition of the spinel within the serpentinized peridotite is indicative of a relatively high degree of melting (14%–25%). Gabbroic to monzonitic veins are also present in the basement, and gabbroic clasts ranging from gabbros and gabbronorites to oxide gabbros and anorthosites are present as clasts (Müntener and Manatschal, 2006). An Ar-Ar age of 126.5 separated from gabbroic veins (G. Manatschal, pers. comm., 2006). This is the same age as the nearby M1 anomaly (late Barremian) and suggests that gabbro intrusion was approximately contemporaneous with basement exhumation.