Macquarie Island offers a rare land-based cross-section through the deep ocean floor, which covers 60% of our Earth. It formed 11 million years ago as slow spreading crust, which has had minimal study compared to more common fastspreading crust. Does the difference in spreading speed produce different crustal geometry, composition, hydrothermal fluids, and cycling of sulfur between ocean and crust? To gain insights to these and related questions, we propose to study uplifted and eroded sections through a series of fault zones, spaced along the length of Macquarie Island, which were the last magmatic, structural and hydrothermal events to occur before shifting stresses drove the seafloor up to form the Macquarie Ridge mountain chain. This dataset is a summary of samples obtained by Mr Steve Lewis for the purposes of investigating hydrothermal alteration in oceanic crust on Macquarie Island. Samples derive from the major lake, Lusitania Bay, and Caroline Cove areas. Each sample consists of rock chips up to a maximum of 1 kg. Samples were all obtained by hand with a geological hammer. The fields in this dataset are: Sample Easting Northing Date Location Transect Details

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.

Owing to the fact that the principal investigator died before data were able to be archived, the only available data are in the form of the referenced paper, which is available as a PDF download to AAD staff only. From the referenced papers: Macquarie Island is an exposure above sea level of the Macquarie Ridge Complex, on the boundary between the Australian and Pacific plates south of New Zealand. Geodynamic reconstructions show that at ca. 12-9.5 Ma, oceanic crust of the Macquarie Island region was created at this plate boundary within a system of short spreading-ridge segments linked by large-offset transform faults. At this time, the spreading rate was slowing (less than 10 mm/yr half-spreading rate) and magmatism was waning. Probably before 5 Ma, and possibly before the extinct spreading ridge had subsided, the plate boundary became obliquely convergent, and crustal blocks were rotated, tilted, and uplifted along the ridge to form the island. Planation by marine erosion has exposed sections through the oceanic crust. The magmatism that built the oceanic crust produced melts similar in composition to the widespread normal to enriched mid-oceanic ridge basalt (N- to E-MORB) suite found in many spreading ridges, but the melts ranged beyond E-MORB to primitive, highly enriched, and silica-undersaturated compositions. These compositions form one end member of a continuum from MORB but seem not to have been derived from a MORB-source mantle, despite sharing a Pacific MORB isotopic signature. The survival of these primitive melts may be due to their origin in a slow-spreading system that must have been closing down as extension along the plate boundary gave way to transpression, putting a stop to the upwelling of asthenosphere and decompression melting. In a more energetic, faster-spreading system, mixing would have been more efficient, the presence of this end member could not easily have been inferred from its isotopic composition, and the igneous rocks would have resembled a typical N- to E-MORB suite. Macquarie Island may therefore provide a type example of magmatism at a very slow spreading ridge and a clue to the origins of E-MORB. Macquarie Island is an exposure above sea-level of part of the crest of the Macquarie Ridge. The ridge marks the Australia-Pacific plate boundary south of New Zealand, where the plate boundary has evolved progressively since Eocene times from an oceanic spreading system into a system of long transform faults linked by short spreading segments, and currently into a right-lateral strike-slip plate boundary. The rocks of Macquarie Island were formed during spreading at this plate boundary in Miocene times, and include intrusive rocks (mantle and cumulate periodites, gabbros, sheeted dolerite dyke complexes), volcanic rocks (N- to E-MORB pillow lavas, picrites, breccias, hyaloclastites), and associated sediments. A set of Macquarie Island basaltic glasses has been analysed by electron microphobe for major elements, S, Cl, and F; by Fourier transform infrared spectroscopy for H2O; by laser ablation-inductively coupled plasma mass spectrometry for trace elements; and by secondary ion mass spectrometry for Sr, Nd and Pb isotopes. Macquarie Island basaltic glasses are divided into two compositional groups according to their mg-number-K2O relationships. Near-primitive basaltic glasses (Group I) have the highest mg-number (63-69), and high Al2O3 and CaO contents at a given K2O content, and carry microphenocrysts of primitive olivine (Fo86-89.5). Their bulk compositions are used to calculate primary melt compositions in equilibrium with the most magnesian Macquarie Island olivines (Fo90.5). Fractionated, Group II, basaltic glasses are saturated with olivine + plagioclase + or - clinopyroxene, and have lower mg-number (57-67), and relatively low Al2O3 and CaO contents. Group I glasses define a seriate variation within the compositional spectrum of MORB, and extend the compositional range from N-MORB compositions to enriched compositions that represent a new primitive enriched MORB end-member. Compared with N-MORB, this new end-member is characterised by relatively low contents of MgO, FeO, SiO2 and CaO, coupled with high contents of Al2O3, TiO2, NaO2, P2O5, K2O and incompatible trace elements, and has the most radiogenic Sr and Pb regional isotope composition. These unusual melt compositions could have been generated by low-degree partial melting of an enriched mantle peridotite source, and were erupted without significant mixing with common -MORB magmas. The mantle in the Macquarie Island region must have been enriched and heterogenous on a very fine scale. We uggest that the mantle enrichment implicated in this study is more likely to be a regional signature that is shared by the Balleny Islands magmatism than directly related to the hypothetical Balleny plume itself.

This dataset represents the collected work arising from ASAC projects 263, 351, 497 and 716 (ASAC_263, ASAC_351, ASAC_497, ASAC_716). The data are pooled together into a single excel file, and presented by year. Descriptions/explanations of acronyms used are given at the bottom of each spreadsheet. One worksheet also details all publications arising from (and related to) the four ASAC projects. The full titles of the four ASAC projects are: ASAC 263: Metamorphic Evolution and Tectonic Setting of Granulites from Eastern Prydz Bay ASAC 351: The Role of Partial Melting in the Genesis of Mafic Migmatites and Orthogenesis within the Rauer islands ASAC 497: Structural and Chemical Processes in Granulite Metamorphism: the Rauer Group and Brattstrand Bluffs Region, Prydz Bay ASAC 716: Archaean Crustal Accretion Histories and Significance for Geological Correlations Between the Vestfold Block and Rauer Group The fields in this dataset are: Archive Collector Sample Number Location Location Code Latitude Longitude Field description Collected for Reported in Comments Type Grid reference Worker