9655239
Persistent Identifier: https://pid.geoscience.gov.au/sample/AU9655239
| Property | Value |
|---|---|
| id | 9655239 |
| igsn | 10.60494/1afn-zd40 |
| sample_id | R516532 |
| eno | 912534 |
| sampling_feature_name | R516532 |
| sampling_feature_type | field site |
| sample_type | outcrop specimen |
| sampling_method | outcrop sampling |
| material_class | rock |
| stratigraphic_unit | Oodla Wirra Volcanics |
| geological_province | Stuart Shelf |
| sample_remark | Fabris et al. (2005): Volcaniclastic/tuffaceous samples (such as R516532 and R509072) typically have a quartz + sericite + tourmaline +/- zircon (minor) +/- undifferentiated opaques (possibly hematite) assemblage, with sericite and quartz as the dominant mineralogy. The only primary minerals identified were quartz and trace amounts of zircon. Primary quartz occurs as equant subhedral crystals, magmatically corroded crystals and angular crystal fragments, which are evidence for a fragmental volcanogenic deposit. Detailed examination of the pseudomorph textures now represented by these alteration minerals indicates that the precursor material was originally deposited as part of a fragmental volcanogenic deposit. Evidence for relic ignimbrite textures include wispy elongate anhedral quartz grains up to several centimetres long that represent flattened pumice fragments (fiamme). These define a relic bedding parallel foliation. There are also silicified blocky lithic fragments scattered throughout some specimens. In thin section they are seen as large angular patches of granular mosaic quartz. Mason (2002) observed quartz replacement of sparsely scattered blocky sites and some uncommon large angular fragments. The precursor material was thought to represent altered crystals such as feldspar or large angular lithic fragments, however no primary material is preserved. Banding of quartz in these large angular fragments suggests primary flow banding and a coherent facies precursor. A small amount of quartz in samples described as vitroclastic rocks form ovoid grains, which Mason (2002) suggested was of devitrification origin. Devitrification is a process that typically occurs in shallow intrusions, lavas and welded pyroclastic deposits, where on cooling, the glasses become thermodynamically unstable and are replaced by the growth of fine-grained quartz or feldspar (McPhie, et al., 1993). Flecks of sericite were randomly oriented and often concentrated along foliated horizons that appear to have mimicked a precursor banding through the rock, including elongated lenticular patches (fiamme), confirming the sericite post dates the igneous layering. Tourmaline prisms (~100-200 um) are located on the margin of the quartz-altered sections of the rock. The tourmaline is virtually colourless (suggestive of a Fe-poor composition) and very fine grained, which makes it very difficult to identify. It is considered that these samples originally formed as part of a felsic fragmental/tuffaceous volcanogenic deposit. Rapid deposition produced a non-layered deposit of vitric materials, pumiceous lithic fragments, large lithic fragments (probably flow-banded rhyolite), blocky crystals (probably plagioclase) and trace small zircon crystals distributed throughout a fine vitric matrix. Some samples have developed indistinct layering defined by flattening of the pumiceous lithic fragments suggesting that some of these samples formed by an ignimbritic mechanism i.e. rapid eruption and fragmentation of felsic lava with subsequent rapid deposition and compaction. |
| earth_materials | Y |
| structural_measurements | None |
| inorganic_geochemistry | None |
| organic_geochemistry | None |
| geochronology | None |
| isotope_groups | None |
| hydrochemistry | None |
| rock_properties | None |
| mineralogy | None |
| thin_sections | None |
| repository_samples | None |
| mineral_deposit_samples | None |
| mineral_deposit_waste_samples | None |
| linked_files | None |
| other_geological_data | None |
| project_name | EFTF - Isotopic Atlas of Australia |
| gda94_longitude | 139.1056098 |
| gda94_latitude | -32.8603649 |
| sample_originator | Geological Survey of South Australia |
| date_acquired | 2000-01-01 00:00:00 |
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