Thermochronologic constraints on the tectonic and thermal history of the northeastern Aileron Province: Results from 40Ar/39Ar step-heating of hornblende and biotite. NTGS submission to National Argon Map initiative

Abstract

This Record presents 40Ar/39Ar chronologic results acquired from Aileron Province rock samples as part of the AuScope National Argon Map initiative. The data were collected in support of regional geoscientific investigations and mapping programs conducted by the Northern Territory Geological Survey (NTGS). Argon isotopic data were obtained from 10 hornblende and biotite mineral separates from nine samples collected in the HUCKITTA map area in the Aileron Province of the Northern Territory. The data and interpretations are presented herein. The results complement pre-existing chronological constraints derived from previous analyses (U–Pb zircon, monazite and apatite; argon hornblende, biotite and muscovite) from this part of the Aileron Province; together they provide new constraints on the thermal and deformation history of the northeastern Aileron Province.

The northeastern portion of the Aileron Province is subdivided into a series of discrete fault- and shear zone-bounded tectonic domains that preserve evidence for a long-lived period of metamorphism and deformation during the Palaeo- to Mesoproterozoic. The domain-bounding Delny and Entire Point shear zone system has an extensive history of metamorphism and deformation during the Palaeoproterozoic, with the Palaeozoic history dominated by less substantial brittle deformation and episodic fluid flow. The southern margin of these shear zones also form the boundary with the Neoproterozoic–Palaeozoic Irindina Province, which experienced metamorphism and deformation during the Palaeozoic Larapinta Event and Alice Springs Orogeny. Samples were analysed from six of the Aileron Province domains to examine the post-metamorphic cooling history during the Palaeo- to Mesoproterozoic, and also test the extent and degree to which the Larapinta Event and Alice Springs Orogeny affected this portion of the Aileron Province, including the Delny and Entire Point shear zones.

Two samples were analysed from the Bonya Domain. Hornblende in a sample of a calc-silicate para-amphibolite of the Bonya Metamorphics (HU13BLR049z) records final cooling below 520–480°C during the Palaeo- or Mesoproterozoic. Similarly, hornblende and biotite from a sample of metasomatised Kings Legend Metadolerite (HU13JAW207) record final cooling below 320-280°C during the Calymmian Period of the Mesoproterozoic, possibly ca 1.53 Ga.

Two samples were analysed from the Jervois Domain. Hornblende in a sample of Attutra Metagabbro (HU13JAW392) records final cooling below 520–480°C at 1721 ± 9 Ma. Biotite in a sample of porphyroblastic schists of the Bonya Metamorphics (HU14BLR362) records final cooling below 320-280°C at 1592 ± 2 Ma.

One sample was analysed from the Denara Domain. Biotite in a sample of Denara Orthogneiss (HU14JAW433) records isotopic resetting at 468 ± 3 Ma due to reheating of the sample above 320–280°C.

One sample was analysed from the Perenti Domain. Biotite in a sample of Perenti Metamorphics (HU15BLR957) records final cooling below 320–280°C at 1547 ± 5 Ma.

Two samples were analysed from the Kanandra Domain. Hornblende in a sample of Carmencita Metadolerite (HU15BLR978) records final cooling below 520–480°C at 1692 ± 9 Ma. Biotite in a sample of Kanandra Metamorphics records discordant results that suggest initial cooling or a late phase of deformation during the Calymmian Period of the Mesoproterozoic, and reheating above 320–280°C during the Palaeozoic.

One sample was analysed from the Deep Bore Domain. Hornblende in a sample of the Captain Morgan Metadolerite (HU18BLR2038) records cooling below 520–480°C at 1628 ± 4 Ma.

The combined thermochronologic data indicate this portion of the Aileron Province experienced variably slow cooling and deformation until the Calymmian Period of the Mesoproterozoic; evidence for heating above 520–480°C during the Palaeozoic was not observed. Two biotite samples record evidence for variable amounts of isotopic resetting due to heating above 320–280°C in the Palaeozoic. These data demonstrate that the thermal and deformational effects of the Larapinta Event and Alice Springs Orogeny on this portion of the Aileron Province are substantially less than previously interpreted, and that burial and exhumation of the Irindina Province in this area was predominately accommodated by deformation within and at the margins of the Irindina Province as opposed to the currently exposed Aileron Province portion of the Delny and Entire Point shear zones.