Sites 1110 through 1113

Site 1110

Hole 1110A (APC):
9°43.599´S, 151°34.511´E; 3246.4 mbsl
0—9.50 mbsf cored; 9.50 m recovered (100%)
Hole 1110B (APC/XCB):
9°43.609´S, 151°34.508´E; 3246.3 mbsl
0—22.30 mbsf cored; 5.37 m recovered (24%)
Hole 1110C (RCB):
9°43.599´S, 151°34.498´E; 3245.8 mbsl
0—15.00 mbsf drilled; no cores taken
Hole 1110D (RCB):
9°43.588´S, 151°34.526´E; 3245.8 mbsl
0—22.7 mbsf drilled; 22.7—28.7 mbsf cored; 0.10 m recovered (2%)

Site 1111

Hole 1111A (RCB):
9°43.059´S, 151°34.533´E; 3200.7 mbsl
0—173.70 mbsf cored; 15.19 m recovered (9%)

Site 1112

Hole 1112A (RCB):
9°44.749´S, 151°36.721´E; 3046.7 mbsl
0—122.4 mbsf cored; 5.85 m recovered (5%)
Hole 1112B (RCB):
9°44.746´S, 151°36.714´E; 3046.6 mbsl
0—126.1 mbsf drilled without coring; 126.1—164.6 mbsf cored; 1.19 m recovered (3%)

Site 1113

Hole 1113A (RCB):
9°45.449´S, 151°36.737´E; 2915.6 mbsl
0—25.20 mbsf cored; 0.44 m recovered (2%)

Sites 1110 through 1113 were drilled in various locations near the foot of Moresby Seamount in an attempt to find a viable alternate location to our primary Site 1108. With the hydrocarbon safety restriction of 485 mbsf, the depth reached at Site 1108, we sought to intercept the Moresby low-angle normal fault in other locations or at shallower depths. We first tried two locations ~6 km west-northwest of Site 1108, near the rift basin depocenter located due north of Moresby Seamount. We then tried two other locations updip of Site 1108, all without success.

At Site 1110, where the fault may be 400—450 mbsf, multiple holes were unable to penetrate below ~29 mbsf because of talus beneath ~9 m of surficial calcareous clay, late Pleistocene in age (<0.22 Ma). The pebbles and cobbles of the talus include micaschists, amphibolites, and rare granite porphyry.

Moving 1 km north, at Site 1111, we cored a single hole through ~154 m of Pleistocene deposits (<1.02 Ma): talus pebbles and cobbles in calcareous ooze, clay, and silty clay with lesser nannofossil-rich silt, sand, and gravel. The talus includes metasediments (micaschist and gneiss) and variably metamorphosed igneous rocks, both basic (diabase, metadiabase, and lamprophyre) and acidic (granite porphyry). Coring was stopped at 174 mbsf in large metamorphic cobbles. Based on temperatures measured at the mudline and at 135 mbsf, the thermal gradient is 95°C/km, similar to that encountered at Site 1108, and the heat flow is 86 mW/m2.

Site 1112 is located.1.5 km west of, and updip from, Site 1108, where the depth to the fault is ~450 mbsf. Another thick pile of talus deposits in Pleistocene (<1.75 Ma) sediments, including silty clay with occasional ash, required two RCB holes to reach 165 mbsf. The recovery consisted of pebbles only, mostly of metadiabase and epidosite, but also minor andesite, granite porphyry, micaschist, and sandstones.

After offsetting 1.3 km south, we attempted a "bare rock" spud at the base of the slope of Moresby Seamount where the fault crops out (Site 1113), but there was enough talus to make the hole unstable and repeatedly refill, and it was abandoned at 25 mbsf in micaschist and epidosite pebbles and cobbles.

Most of the metamorphic rocks recovered from the talus of Moresby Seamount have igneous protoliths. In addition, micaschists and gneisses record an early tectono-metamorphic stage characterized by the development of a foliation under epidote-amphibolite to amphibolite facies conditions. A later retrograde metamorphism in the greenschist facies affected all protoliths. This later stage was coeval to brittle extensional deformation and extensive hydrothermal alteration, probably during the normal faulting of Moresby Seamount and the subsequent unroofing of its basement.


To 180 Site Summary for Site 1117

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