This project exploited the unique exposures of the uppermost oceanic crust found on Macquarie Island as a window into the internal structure of the oceanic crust. The form of rock units and the way in which they are arranged on the Island provided a means of understanding how they were assembled. This assembly occurred beneath a mid-ocean ridge spreading center, an area that can probably never be directly investigated. The general process by which this crust has formed is responsible for the creation of about 60% of the bedrock geology of the Earth. The Macquarie Island ophiolite is an uplifted block of oceanic crust formed at the Australia-Pacific spreading centre between 12 and 9 Ma. The sense of motion and geological processes across this plate boundary reflect an evolution from orthogonal spreading through progressively more oblique spreading to the present-day transpressional regime. The crust that makes up the island was formed during an interval of oblique spreading along east-trending spreading segments punctuated by a series of northwest-trending discontinuities. The discontinuities are accommodation zones marked by oblique-slip dextral-normal faults, localised dikes and lava flows, and extensive hydrothermal alteration, indicating that these zones were active near the spreading axis. These features provide a window into the internal structure of oceanic crust generated by oblique spreading. The download file contains: I. Publication folder (PDF files): 1. Alt, J.C., G. Davidson, D.A.H. Teagle and J.A. Karson, The isotopic composition of gypsum in the Macquarie Island Ophiolite: Implications for sulfur cycle and the subsurface biosphere in oceanic crust, Geology, 31, 549-552, 2003. 2. Rivizzigno, P.A. and J.A. Karson, Mid-ocean ridge fault zones preserved on Macquarie Island: Faulting, hydrothermal processes and magmatism in an oblique-spreading environment, Geology 32, 125-128, 2004. 3. Rivizzigno, P. A., The Major Lake Fault Zone: An Oblique Spreading Structure Exposed in the Macquarie Island Ophiolite, Southern Ocean, MS Thesis, Duke University, Durham, NC USA, 2002, 59 pp. II. Macca Maps folder (TIFF files): 1. Helicopter Video: Macca map showing the path and view direction from a video made during a helicopter trip over the island in 2000 during an unusually clear day. Copies of the video were left with ANARE and with various people at UTas (R. Varne, G. Davidson and others). 2. JAK2000Samples: Macca map with locations of samples collected by J.A. Karson during the 2000 field season. Samples are numbered MAC00-XX. Samples are under study at Duke University. 3. JAKMK2000Samples: Macca map with locations of samples of dike rocks collected for geochemicial studies by J.A. Karson during the 2000 dield season. Samples are numbered MK-XX. They were left with Dr. R. Varne (UTas) in 2000. 4. PAR2000Samples: Macca map with locations of samples collected by P.A. Rivizzigno during the 2000 field season. Samples are under study at Duke University and reported in Rivizzigno (2002) and Rivizzigno and Karson (2004). 5. PARMK2000: Macca map with locations of samples of dike rocks collected for geochemicial studies by J.A. Karson during the 2000 dield season. Samples are numbered MK-XX. They were sent to Dr. R. Varne (UTas) in 2000. 6. Geological map from Rivizzigno (2002) in vector art (Canvas 8.0) and bitmap (jpeg) formats. New data are plotted on a base map by Goscombe and Everard (1998). III. Other Information folder (WORD files): 1. References: citations of journal articles, theses, abstracts from this project. 2. JAK Sample Log: List of samples, locations, etc. for Karson samples from 2000.

Although oceanic crust covers about 60% of the Earth, relatively little is known of its geology and the processes that have created it. Macquarie Island represents a unique subaerial exposure of the seafloor, and an exceptional environment for active study and research into the ocean crust. We plan to utilise geological and geophysical techniques to help us better understand the lithological complexity and evolution of the oceanic crust. Project objectives: Our primary objective is to conduct coordinated ground- and air-based magnetic and electromagnetic surveys of the oceanic crust that comprises Macquarie Island and the surrounding seafloor for ~ 5 km from the island. We will integrate these geophysical data with the results of our recent studies of the Island and additional follow-up geological investigations. Together these data will improve our understanding of the tectonic and hydrothermal evolution of Macquarie Island ocean crust and through it, the evolution of oceanic crust in a more general sense. We believe the acquisition of these data will allow us to: (1) better resolve the complex geologic structure of the island; (2) determine the three-dimensional extent of the hydrothermal alteration of this example of oceanic crust; (3) map active fault zones across the island; and (4) correlate the geology of the Island with the offshore geology, linking it to regional data sets and the nearby active plate boundary. The dataset has two forms. The main dataset is magnetic field data recorded in the Bauer Bay to Boot Hill area of Macquarie Island, on 200 m line spacings (csv file). The subsidiary dataset are sample locations for the same area for a small set of rock samples obtained to check on magnetic character (word file). Data were collected using a GEM Systems GSM-19 Overhauser Magnetometer. The fields in this dataset are: Easting Northing Sample Rock Type Magnetic Intensity (nT) Taken from the 2008-2009 Progress Report: Progress against objectives: This project was in abeyance for the 2007-8 season due to our scientific field program being postponed as a necessity of the rabbit eradication program on Macquarie Island. A detailed study of the formation of specific magnetic lows from our regional ground magnetic survey, with the aim of determining their cause, and gaining insight into interpretation of magnetic lows in ocean crust in general. Hydrothermal alteration in ocean crust typically results in magnetic lows because it involves magnetite destruction. However, it is apparent that on Macquarie Island this is not the only cause of magnetic lows. There are 5 principal study sites: (1) Prion Lake to Brothers Point, and including the Mt Tulloch summit and slopes; (2) Waterfall Lake and surrounds; (3) Hurd Point to the coast immediately east of Mt Jefferies; (4) East Ainsworth area, east of the Caroline Cove protection zone; (5) Whisky Creek area, cutting through the eastern escarpment ~ 5 km north of Hurd Point. The 2008-9 season has involved (1) compiling of geological mapping from each site and rectification with the available topographic base and most recent satellite imagery; (2) processing of magnetic data from each of the detailed surveys; (3) extraction of field observations into a digital database that can be accessed within his GIS platform; (4) petrographic description of ~100 polished thin sections to evaluate magnetite behaviour; and (5) a brief return to Macquarie Island to attempt to infill areas of geological data/sample deficiency. In terms of the objective of correlating the geology of the island with the offshore geology, this has been in process within the USGS under the supervision of Dr Carol Finn. This part of the project is employing heli-magnetics obtained with the cooperation of AAD during resupply, using a USGS instrument The data was partly processed at Utas by Dr Michael Roach, and then transferred on for more detailed processing at the USGS.