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Radioactivity and Matter
Published in Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff, Radiation and Radioactivity on Earth and Beyond, 2020
Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff
The term “radiogenic” denotes any effect resulting from radioactive decay. When the radiations emitted by radionuclides are absorbed in matter, their energy is converted into heat. Radioactive materials are therefore warmer than their surroundings, and when the heat transfer is efficient the temperature of the environment rises. This occurs in celestial bodies and is achieved on an enormous scale inside the Earth, where the temperature has steadily increased since its formation as a result of energy liberated by radioactive decay.
Geological setting of exceptional geological features of the Flinders Ranges
Published in Australian Journal of Earth Sciences, 2020
Many of the granites, especially the Moolawatana Suite, contain minerals exceptionally rich in radiogenic potassium, uranium and thorium, which have been generating radioactive heat since their hosts’ intrusion. This heating effect was enhanced and trapped when insulating strata of the Adelaide Geosyncline were deposited on these basement rocks in the Neoproterozoic and Cambrian, and this resulted in a protracted and possibly unique history of melting, alteration and hydrothermal activity as exhumation progressed throughout the Paleozoic, Mesozoic and Cenozoic. Significantly, it appears that this was achieved without the obvious involvement of crustal magmas. The inherent heating may also have significantly promoted and influenced tectonic activity during the Cambrian Delamerian Orogeny and subsequent uplift. The heating effect persists until the present day as the Paralana Hot Springs. Details are given in following sections.
Mafic intrusions in southwestern Australia related to supercontinent assembly or breakup?
Published in Australian Journal of Earth Sciences, 2022
H. K. H. Olierook, F. Jourdan, C. L. Kirkland, C. Elders, N. J. Evans, N. E. Timms, J. Cunneen, B. J. McDonald, C. Mayers, R. A. Frew, Q. Jiang, L. J. Olden, K. McClay
The dyke at the Elephant Rocks dyke is structurally distinct from the other six dyke samples in this study, namely that it strikes northeast (Figure 3). The implication is that this dyke emplaced during either northwest–southeast extension or northeast–southwest compression. The Elephant Rocks dyke also has a negative Pb anomaly, which is distinctly different to the strongly positive Pb anomalies in the other six samples (Figure 5c). The youngest concordant zircon grain is ca 940 Ma but there is one additional grain with two mildly discordant analyses (ER1-6 and -7) that yielded 206Pb/238U dates of ca 250 Ma (Figures 6d and 7c). This grain has relatively high U concentrations (∼1050 ppm), which makes its U/Pb systematics susceptible to radiogenic Pb loss owing to crystal defects induced from alpha radiation during radioactive decay of U to Pb. There are three possible explanations for the ca 250 Ma dates from this grain. (1) The grain may have experienced recent Pb loss, which would retain the 207Pb/206Pb ratio at the time of crystallisation and disturb the 206Pb/238U ratio towards younger dates (Andersen et al., 2019). If this scenario were correct, the 207Pb/206Pb dates at ca 342 ± 40 Ma (Table B) would record crystallisation of the zircon grain. (2) A complex interplay of U-gain and Pb loss could serve to disturb the original U/Pb systematics (Andersen et al., 2019; Olierook, Taylor, et al., 2019), rendering any interpretation of the age of the grain obsolete. (3) The grain may have experienced partial ancient Pb loss, forming a trajectory between the original age of the grains (likely Meso- or Neoproterozoic) and an age younger than ca 250 Ma. Although scenario (2) is possible, the third scenario is the most plausible given the potential discordia through these grains, which would yield a lower concordia intercept of 232 ± 35 Ma; such an array is incompatible with scenario 1 (recent Pb loss).