Keyword

EARTH SCIENCE > SOLID EARTH > ROCKS/MINERALS/CRYSTALS > ELEMENTS > MAJOR ELEMENTS

3 record(s)
 
Type of resources
Topics
Keywords
Contact for the resource
Provided by
From 1 - 3 / 3
  • 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

  • At Loewe Massif and Amery Oasis, samples were taken; - for sediment analysis (XRF geochemistry and grain size) - for geochronology (cosmogenic isotope analysis). The custodian for these samples is Dr Damian Gore, Macquarie University. Lake sediment samples were taken from Lake Terrasovoje, Radok Lake and Beaver Lake. The custodian for these lacustrine samples is Dr Martin Melles, Leipzig University. The dataset also includes weather/meteorological observations. Further work in project 1071 was also completed as part of PCMEGA. The fields in this dataset are: Date Site Latitude Longitude Time Altitude Temperature Pressure Wind direction Wind Speed Cloud Relative Humidity