Summary of results: Joint NTGS-GA geochronology project: Constraining cooling and deformation in the eastern Aileron Province through 40Ar/49Ar step-heating of hornblende, muscovite and biotite

This Record presents 40Ar/39Ar chronologic results acquired in support of collaborative regional geoscientific investigations and mapping programs conducted by Geoscience Australia (GA) and the Northern Territory Geological Survey (NTGS). Argon isotopic data and interpretations from hornblende, muscovite, and biotite from seven samples collected from the Aileron Province in ALCOOTA , HUCKITTA, HALE RIVER, and ILLOGWA CREEK in the Northern Territory are presented herein. The results complement pre-existing geochronological constraints from U–Pb zircon and monazite analyses of the same or related samples, and provide new constraints on the thermal and deformation history of the Aileron Province.
Three samples (2003082017, 2003082021, 2003083040) were taken from ALCOOTA in the northeastern portion of the Aileron Province. Biotite in sample 2003082017 from the ca 1.81 Ga Crooked Hole Granite records cooling below 320–280°C at 441 ± 5 Ma. Biotite in sample 2003082021 from the ca 1.73 Ga Jamaica Granite records cooling below 320–280°C at or after 414 ± 2 Ma. Muscovite in sample 2003083040 from the Delny Metamorphics, which were deposited after ca 1.82 Ga and preserve evidence for metamorphism at ca 1.72 Ga and 1.69 Ga, records cooling below 430–390°C at 399 ± 2 Ma. The fabrics preserved in the samples from the Crooked Hole Granite and Delny Metamorphics are interpreted to have formed due to dynamic metamorphism related to movement on the Waite River Shear Zone, an extension of the Delny Shear Zone, during the Palaeoproterozoic. Portions of the northeastern Aileron Province are unconformably overlain by the Neoproterozoic–Cambrian Georgina Basin, indicating these samples were likely at or near the surface by the Neoproterozoic. Together, these data indicate that rocks of the Aileron Province in ALCOOTA were subjected to heating above ~400°C during the Palaeozoic.
Two samples (2003087859K, 2003087862F) of exoskarn from an indeterminate unit were taken from drillhole MDDH4 in the Molyhil tungsten–molybdenum deposit in central HUCKITTA. The rocks hosting the Molyhil tungsten–molybdenum deposit are interpreted as ca 1.79 Ga Deep Bore Metamorphics and ca 1.80 Ga Yam Gneiss. They experienced long-lived metamorphism during the Palaeoproterozoic, with supersolidus metamorphism observed until at least ca 1.72 Ga. Hornblende from sample 2003087859K indicates cooling below 520–480°C by 1702 ± 5 Ma and may closely approximate timing of skarn-related mineralisation at the Molyhil deposit; hornblende from sample 2003087862F records a phase of fluid flow at the Molyhil deposit at 1660 ± 4 Ma. 
The Salthole Gneiss has a granitic protolith that was emplaced at ca 1.79 Ga, and experienced alteration at ca 1.77 Ga. Muscovite from sample 2010080001 of Salthole Gneiss from the Illogwa Shear Zone in ILLOGWA CREEK records cooling of the sample below ~430–390°C at 327 ± 2 Ma. This may reflect the timing of movement of, or fluid flux along, the Illogwa Shear Zone.
An unnamed quartzite in the Casey Inlier in HALE RIVER has a zircon U–Pb maximum depositional age of ca 1.24 Ga. Muscovite from sample HA05IRS071 of this unnamed quartzite yields an age of 1072 ± 8 Ma, which likely approximates, or closely post-dates, the timing of deformation in this sample; it provides the first direct evidence for a Mesoproterozoic episode of deformation in this part of the Aileron Province.

Tags: Aileron Province, EARTH SCIENCES, GEOCHEMISTRY, GEOLOGY, Isotope Geochemistry, Northern Territory, Published_External, geochronology, geology
Organization: Geoscience Australia Data