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Principal Investigators: Paul Mann and Fred Taylor
Funding agency: NSF EAR.

Paul Mann and Fred Taylor completed five weeks of field work in Papua New Guinea (PNG) in July and August, 2002, under an NSF-funded study called "Active continental extension of eastern Papua New Guinea: Geologic Studies of Emerged Coral Reefs and Marine Sedimentary Rocks."

Papua New Guinea is about the size of England and has a population of 4 million people. The study area was Milne Bay Province which is at the tip of the Papuan Peninsula. Historically, the areas is best known for events related to the early phases of World War II. The Papuan Peninsula and Owen Stanley Range formed a high (3-4 km), elongate natural barrier that formed the high water mark of the 1941-42 Japanese invasion of the SW Pacific. The area is geologically significant because the lateral transition from active oceanic spreading to active rifting of continental crust occurs in only three localities worldwide: Red Sea, Gulf of Aden, and the Papuan Peninsula. These three areas are critical for understanding a variety of tectonic and sedimentary processes associated with the spatial and temporal transition between oceanic ridge propagation and continental rupture. Of these three rifted zones, only the Papuan Peninsula exhibits a close spatial association between: 1) the tip of the propagating Woodlark spreading ridge; 2) low- angle normal fault earthquakes; and 3) late Neogene metamorphic core complexes very similar to those described in ancient exhumed belts of intracontinental extension.

We mapped emergent, late Quaternary coral reefs and Neogene sedimentary sections over hundreds of kilometers of coastlines of islands and peninsulas to determine the pattern and rate of uplift, style of deformation, and tectonic mechanisms of rift propagation. Since there are very few roads in this part of PNG, we used two modes of transportation: a 22-foot fiberglass boat powered by a 55 hp outboard engine and a 60-foot wooden hulled island freighter chartered for our study. These boats allowed us to visit areas of the mainland as well as remote outlying islands including the Trobriand Islands, made famous by reports of early cultural anthropologists like Margaret Mead. The local people are Melanesians who commonly speak three languages: English (PNG was part of the UK commonwealth til 1975), pidgin (local dialect based many languages but mainly English) and local languages (PNG has about 700 local languages; there are about a dozen languages in the region we traveled; some language clans are separated by distances of a few kms). Outside the main towns and villages, the people are mainly self-subsistence farmers and fishermen. Most are at the fringes or completely outside the cash economy.

The main results of our fieldwork include: 1) the best-known area of core complexes on Goodenough and Fergusson Islands is stable or subsiding and is interpreted as a now abandoned spur of ridge propagation active about 3.5 Ma; 2) the main locus of active rifting associated with rapid uplift of Holocene reefs and late Neogene basinal sedimentary rocks is parallel to the Gwoira north-dipping, normal fault system on the Papuan Peninsula and beneath Goodenough Bay; 3) the Milne Bay "graben" is inactive as previously predicted by GPS results showing the Milne Bay area moving as part of the stable Australian plate; 4) the process of rift propagation in PNG appears presently focussed on the Gwoira fault zone within Goodenough Bay and the Papuan Peninsula and is not diffuse across the entire region as depicted in previous models; GPS predicts about 11 mm/yr of extension across this fault.

Our study complements well other NSF-funded studies in the region: a passive broadband seismometer study by Geoff Abers (Boston Univ.) of the core complex area and a thermochronology study by Suzanne Baldwin (Syracuse Univ.) of the uplift history of the core complexes on Fergusson Island (fieldwork in Jan, 2003). Results of the Abers study are to appear in an upcoming issue of Nature.

In the capital of Port Moresby, we visited with various agencies and presented our preliminary results to geologists at the University of Papua New Guinea.

Coral samples are now being processed for dating by Lisa Watson, a UT undergraduate working at the coral sample lab at PRC 131. We will present a poster on the project at the fall AGU meeting.