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 (Ͻ10 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.Varne, R., Brown, A.V., and Falloon, T., 2000, Macquarie Island: Its geology, structural history, and the timing and tectonic setting of its N-MORB to E-MORB magmatism, in Dilek, Y.

Ocean Drilling Program hole 504B revealed an ocean crust hydrothermal sulphur anomaly on the dyke–lava transition, with implications for global sulphur sinks. Here we confirm the presence of the anomaly sporadically along 7.5 km of dyke–basalt contact on the Macquarie Ridge at Macquarie Island, a 39–9.7 Ma slow‐spreading setting. Background contact‐zone pyrite S contents average 1845 p.p.m. across ∼50 m. However, zones of small‐scale brittle faulting that commonly occur on and above the dyke–basalt contact average between 5000 and 11 000 p.p.m. S (20–30 m widths). These consist of steep ridge‐parallel faults and fault splays on the contact, overlain by up to 50 m of linked pyritic fault trellis. The contact zone faults are haloed by disseminated pyrite–chlorite, cross‐cut by quartz–chlorite–sphalerite and epidote‐cemented breccias, containing evidence of turbulent flow. The structural control on sulphur deposition is attributed to the active extensional slow spreading setting. With increasing extension, diffuse mixing across the contact was replaced by channellized flow and dynamic mixing in fault arrays. The magnitude of the dyke–lava transition sulphur sink must be reassessed to take account of this heterogeneity.

Because large bibliographies on mafic intrusions in other parts of the world were being compiled concurrently, time has not been available for inspection and verification of many of the citations; for this we apologize. Users of these bibliographies are encouraged to report any errors to Gerald K. Czamanske so that they may be corrected. In a similar spirit, users are encouraged to send notice of any reports published before 1987 that have been inadvertently omitted. Consistency of citation style has benefited from review by George Havach of the U.S. Geological Survey. The efforts of Pauline C. Bennett during early stages of compilation are gratefully acknowledged. This report is being issued in two forms, representing slightly differing versions. Version A, issued as paper copy, incorporates foreign diacritics. Version B, issued as an IBM-compatible diskette, affords users the great benefit of an online bibliography, but is formatted only in the standard ASCII character set.