187Re – 232Th – 238U nuclear geochronometry is a new dating method for astronomy, earth
and planetary sciences [1-4]. Nucleogeochronometric Rhenium-Osmium two-point-isochron
(TPI) ages are calculated using a nuclear geochronometer as one data point in a
two-point-isochron diagram [5-7]. The IVREA chronometer, for example, is one of
five terrestrial nuclear geochronometers identified so far [8]. Here, it is used to
constrain the magmatism of the Ferrar flood basalt province, which has been related to
continental rifting and the break-up of Gondwana in the Jurassic.TPI ages for seven
(basaltic) andesite whole rock samples from the Prince Albert Mountains (Victoria
Land, Antarctica) are calculated. An isochron age of 172 ± 5 Ma (187Os/188Osi
= 0.194 ± 0.023) has previously been published for these rocks [9]. Initial TPI
187Os/188Osi ratios show only minor scatter between 187Os/188Osi = 0.2149 ±
0.0064 and 187Os/188Osi = 0.22231 ± 0.00080, in agreement with the enigmatic,
suprachondritic 187Os/188Osi = 0.194 ± 0.023 from the isochron [9]. TPI ages for
the Mount Joyce samples range from 125.4 ± 9.9 Ma to 139 ± 17 Ma and thus
constrain the youngest magmatic event(s) in the Transantarctic Mountains. For the
Thumb Point basalt, a TPI age of 219 ± 81 Ma is calculated. Despite of its large
uncertainty, the age itself is in agreement with the Triassic 224 Ma and 240 Ma
events reported from North Patagonia [10]. The TPI age of 186.1 ± 8.1 Ma from the
Ricker Hill basalt can be clearly distinguished from the Mount Murray TPI age of
158 ± 14 Ma, while at Brimstone Peak two TPI age groups of 155 ± 14 Ma and
175.3 ± 3.1 Ma are observed. From this it may be concluded that the seven TPI
ages indicate episodic magmatic activity in East-Antarctica between 125 Ma and
219 Ma, leading to the break-up of Gondwana. This picture is consistent with the
geochronology of the Antarctic Peninsula, Patagonia, the Karoo and the Ferrar mafic
rocks [10]. Thus, besides constraining planetary crust formation in general, nuclear
geochronometry may also become an additional powerful tool in constraining not only
magmatic activity in Antarctica but also the assembly and break-up of Pangaea and
subsequently Gondwana from the Carboniferous on, as revealed by means of nuclear
geochronometry for the ultramafic dykes within the Balmuccia peridotite (Ivrea Zone, NW
Italy).
[1] Roller (2015), Goldschmidt Conf. Abstr. 25, 2672. [2] Roller (2016), Goldschmidt
Conf. Abstr. 26, 2642. [3] Roller (2015), Geophys Res. Abstr. 17, 2399. [4] Roller (2016),
Geophys Res. Abstr. 18, 33. [5] Roller (2016), JPS Conf. Proc., Nuclei in the Cosmos (NIC
XIV), Niigata, Japan, subm. (NICXIV-001); NICXIV Abstr. #1570244284. [6] Roller (2016),
JPS Conf. Proc., Nuclei in the Cosmos (NIC XIV), Niigata, Japan, subm. (NICXIV-002);
NICXIV Abstr. #1570244285). [7] Roller (2016), JPS Conf. Proc., Nuclei in the Cosmos
(NIC XIV), Niigata, Japan, subm. (NICXIV-003); NICXIV Abstr. #1570244281. [8]
Roller (2015), Geophys Res. Abstr. 17, 17. [9] Molzahn et al. (1996), Earth Planet.
Sci. Lett. 144, 529 – 546. [10] Pankhurst et al. (2000), J. Petrol. 41, 605 – 625. |