Weds 12th March

12 – 1 pm

Rm 312.222

Korien Oostingh

Curtin Applied Geology PhD Candidate

Using ultra-precise 40Ar/39Ar data for development of new geochronology techniques, in order to model the emplacement and land surface evolution of the Cainozoic Newer Volcanic Province, Victoria, Australia.

Abstract

Young basalts are extremely difficult to date by the K-Ar and U-Th decay series, as they contain low K concentrations and generally lack minerals high in U and Th, such as zircon and titanite. However, our recent installation of a new generation multi-collector mass spectrometer (ARGUSVI) will allow measurement of Ar isotopes with unprecedented levels of precision and vastly improved sensitivity (up to 25 times better analytical precision for young basalts!). The 40Ar/39Ar geochronology technique is already widely used in geology due to its ability to test the reliability of the data via incremental step-heating analysis, but improved analytical precision, along with the recent improvement over the value of the decay constant allow an exceptional step forward in age precision and accuracy.

In this PhD-research, new and ultra-precise ARGUSVI 40Ar/39Ar data will be used to build a robust age database for both olivine lamproites from Western Australia and other overseas locations, and young basalts of the Newer Volcanic Province (NVP) in Victoria, Australia. These data will be used for two purposes:

(1) To cross-calibrate age results obtained from two new techniques that will be developed as part of this research; olivine U/Th-He geochronology and cosmogenic 38Ar exposure dating. Lamproites comprise an exceptional suite of minerals, which favourably partition K as well as U and Th. This makes them ideal for cross-calibration of olivine U/Th-He ages with 40Ar/39Ar ages derived from multiple minerals in the rock. The young basalts of the NVP will be used as a case study to test the potential of the newly developed olivine U/Th-He technique for dating mafic rocks with much lower U/Th concentrations. The presence of original flow top surfaces on samples as well as the limited land cover and erosion in Victoria, potentiates the calibration of the cosmogenic 38Ar exposure dating technique using the young NVP basalts. Development of the 38Ar cosmogenic exposure dating technique could provide enhanced information on landscape evolution, elucidating a history of land mass cover and surface erosion and could be applied to a myriad of geological problems.

(2) A second aspect of this research will combine geochronology with new and existing elemental and isotope geochemistry to develop improved emplacement models for these eruptive features. Current models oppose mantle plume vs. shallow mantle melting scenarios but these are based on very limited datasets. New olivine noble gases (e.g. He, Ne, Ar) and Sr, Nd, Pb and Os isotope analyses will help us decipher between the various available models.