WA
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Large geochronological and geochemical data sets for the Paleo- to Mesoarchean Pilbara and Meso- to Neoarchean Yilgarn cratons, Western Australia, show that both cratons exhibit similar evolutionary trends in felsic magmatism, providing important constraints on Archean tectonics. The most obvious trend is a transition from sodic magmatismthe ubiquitous tonalite-trondhjemite-granodiorite (TTG) series with their high pressure (high-Al) signatureto potassic magmatism. In the Pilbara craton this transition is marked by two periods of potassic magmatism separated by 50 Myr. In the Yilgarn, the transition is mostly diachronous with potassic magmatism broadly younging to the west, except for one terrane where potassic magmatism begins ~40 Ma earlier. The change from sodic to potassic magmatism is, in part, a continuation of trends observable within the sodic granites themselves, which become more LILE-enriched with decreasing age. It is also evident in both cratons that magmatism derived from basaltic precursors is not confined to high-pressure formation of High-Al TTGs but includes lower pressure variants. The latter include low-Al TTGs (significant in the Pilbara Craton), and a group with high-HFSE and low- to moderate LILE-contents typical of A-type magmas. In the Yilgarn Craton such rocks form a locally common, often bimodal, association, representing formation at high-temperature and low-pressure. They are not often recognised as belonging to the sodic magmatic group but clearly reflect a magmatic pathway that starts with a largely mafic protolith, albeit at lower pressures and, unlike the low-Al TTGs, higher temperatures. Another shared trend is the appearance of a diverse group of rocks not unlike those seen in modern-day convergent tectonic settings. These comprise high-Mg diorites (or sanukitoids) (and related rocks), boninite-like rocks, `calc-alkaline basalts and andesites, calc-alkaline lamprophyres, but also syenites and monzonites. These rocks appear well after the first appearance of high- (and low-) Al TTGs and are most abundant just prior to major onset of potassic magmatism. In both cratons they are largely confined to younger linear geological terranes or marginal to/within the larger generally older terranes, and this, along with their enriched geochemistry permits the interpretation that they tap enriched mantle along crustal scale structures. Such rocks form a significant local component but overall are not abundant. The trends documented above are evident in many Archean terranes. The simplest way to explain the variation in the TTGs (high- and low-pressure variants) and the trends from sodic to potassic magmatism is via progressive reworking (maturation) of existing continental crust (for crustal-derived magmatism) and increasing involvement of felsic crust (for non-crustal magmatism). The chemical and isotopic evidence suggests a role for both mechanisms. It is, however, clear that crustal reworking played an early and persistent role in the compositional evolution of both the Pilbara and Yilgarn cratons (and probably Archean cratons in general), suggesting that models advocating a switch from slab-derived TTGs to crustal-derived potassic magmas are too simplistic. The appearance of magmas with an arc-like signature suggests that proto-subduction-like tectonic processes operated, at least intermittently, but not necessarily that they dominated Archean crustal evolution and crust formation.
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Isogal Gravity Strengthening (P198090) contains a total of 46 point data values acquired at a spacing of None metres. The data is located in ACT, NSW, NT, QLD, SA, TAS, VIC, WA and were acquired in 1980, under project No. 198090 for Bureau of Mineral Resources (BMR).
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Soviet Absolute Gravity (P197999) contains a total of 1 point data values acquired at a spacing between 2000 and 2100 metres. The data is located in ACT, NSW, NT, QLD, SA, TAS, VIC, WA and were acquired in 1979, under project No. 197999 for None.
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Ord Bonaparte Gravity Survey Groundwater (P201760) contains a total of 1403 point data values acquired at a spacing between 100 and 200 metres. The data is located in NT, WA and were acquired in 2017, under project No. 201760 for Department of Agriculture and Food (Western Australia).
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Australia Wide AFGN Absolute 2015 (P201590) contains a total of 35 point data values acquired at a spacing between 200 and 750 metres. The data is located in ACT, NSW, NT, QLD, SA, TAS, VIC, WA and were acquired in 2015, under project No. 201590 for Geoscience Australia.
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Gravity data measure small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. This Wiluna Gravity Survey P201660 Spherical Cap Bouguer Anomaly 1VD is the first vertical derivative of the spheical cap Bouguer anomaly grid for the Wiluna Gravity Survey (P201660). This gravity survey was acquired under the project No. 201660 for the geological survey of WA. The grid has a cell size of 0.0076 degrees (approximately 800m). A total of 4453 gravity stations at variable spacing between 1000m and 2500m were acquired to produce this grid. A Fast Fourier Transform (FFT) process was applied to the original grid to calculate the first vertical derivative grid. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose.
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Gravity data measure small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Wiluna Gravity Survey P201660 Spherical Cap Bouguer Anomaly 267GU is a complete Bouguer anomaly grid for the Wiluna Gravity Survey (P201660) survey. This gravity survey was acquired under the project No. 201660 for the geological survey of WA. The grid has a cell size of 0.0076 degrees (approximately 800m). The data are given in units of um/s^2, also known as 'gravity units', or gu. A total of 4453 gravity stations were acquired to produce this grid.
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Australia Wide AFGN Absolute 2016 (P201691) contains a total of 21 point data values acquired at a spacing of 750 metres. The data is located in ACT, NSW, NT, QLD, SA, TAS, VIC, WA and were acquired in 2016, under project No. 201691 for Geoscience Australia.
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Gravity data measures small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Canning Coastal 2D Seismic Survey Gravity (P201410) contains a total of 1765 point data values acquired at a spacing of 400 metres. The data is located in WA and were acquired in 2014, under project No. 201410 for None.
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Digital Elevation data record the terrain height variations from the processed point-located data recorded during a geophysical survey. This Sir Samuel Throssell Gravity Survey P201460 GRS80HTM is elevation data for the Sir Samuel Throssell Gravity Survey (P201460). This survey was acquired under the project No. 201460 for the geological survey of WA. The grid has a cell size of 0.00477 degrees (approximately 499m). This grid contains the ground elevation relative to the ellipsoid for the Sir Samuel Throssell Gravity Survey (P201460). It represents the vertical distance from a location on the Earth's surface to the ellipsoid. The data are given in units of meters. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose.