Mapping the Structure and Metasomatic Enrichment of the Lithospheric Mantle Beneath the Kimberley Craton, Western Australia

Abstract

The lithology, geochemistry, and architecture of the continental lithospheric mantle (CLM) underlying the Kimberley Craton of north‐western Australia has been constrained using pressure‐temperature estimates and mineral compositions for >5,000 newly analyzed and published garnet and chrome (Cr) diopside mantle xenocrysts from 25 kimberlites and lamproites of Mesoproterozoic to Miocene age. Single‐grain Cr diopside paleogeotherms define lithospheric thicknesses of 200–250 km and fall along conductive geotherms corresponding to a surface heat flow of 37–40 mW/m2. Similar geotherms derived from Miocene and Mesoproterozoic intrusions indicate that the lithospheric architecture and thermal state of the CLM has remained stable since at least 1,000 Ma. The chemistry of xenocrysts defines a layered lithosphere with lithological and geochemical domains in the shallow (<100 km) and deep (>150 km) CLM, separated by a diopside‐depleted and seismically slow mid‐lithosphere discontinuity (100–150 km). The shallow CLM is comprised of Cr diopsides derived from depleted garnet‐poor and spinel‐bearing lherzolite that has been weakly metasomatized. This layer may represent an early (Meso to Neoarchean?) nucleus of the craton. The deep CLM is comprised of high Cr2O3 garnet lherzolite with lesser harzburgite, and eclogite. The peridotite components are inferred to have formed as residues of polybaric partial mantle melting in the Archean, whereas eclogite likely represents former oceanic crust accreted during Paleoproterozoic subduction. This deep CLM was metasomatized by H2O‐rich melts derived from subducted sediments and high‐temperature FeO‐TiO2 melts from the asthenosphere.

Petrology, Age, and Rift Origin of Ultramafic Lamprophyres (Aillikites) at Mount Webb, a New Alkaline Province in Central Australia

“…A mantle isentrope of 1330°C and crustal thickness of 40 km were assumed for the paleogeotherm. Our mantle isentrope value follows recent petrological and geophysical studies by , Sudholz et al (2023), Hoggard et al (2020) and Mather et al (2011). A 40 km crustal thickness is validated by recent crustal thickness models (AusMoho) (i.e., B. L. Kennett et al, 2023).…”

“…Similar intervals comprising strong negative seismic receiver function amplitudes within the mid‐lithosphere were observed beneath the Gawler Craton and Adelaide Fold Belt of South Australia (Birkey et al., 2021; Ford et al., 2010; Sudholz, Yaxley, et al., 2022) and Kimberley Craton of north‐western Australia (Birkey et al., 2021; Sudholz et al., 2023). The mid‐lithospheric layer observed beneath the Webb Province occurs at a depth similar to most MLDs observed globally, which are commonly marked by sharp decreases in seismic velocities, higher attenuation of seismic waves, and higher electrical conductivity, commonly between 80 and 120 km (Aulbach et al., 2017; Rader et al., 2015; Selway et al., 2015).…”

“…In the context of the Webb Province, the absence of Cr diopside between 70 and 85 km, coupled with the strong‐negative seismic receiver function amplitudes recorded at nearby permanent seismic stations (i.e., WRKA; Birkey et al., 2021), may correspond to a narrow layer of pargasite‐bearing lherzolite. We suggest that the formation of pargasite took place along the dehydration solidus (80 km) of relatively depleted peridotite (>$${\text{Mg}\#}_{\text{olv}}^{91}$$) in response to the upward percolation of H 2 O‐bearing melts or fluids from the asthenosphere (Sudholz, Yaxley, et al., 2022; Sudholz et al., 2023; Figure 13).…”

“…The mid‐lithospheric layer observed beneath the Webb Province occurs at a depth similar to most MLDs observed globally, which are commonly marked by sharp decreases in seismic velocities, higher attenuation of seismic waves, and higher electrical conductivity, commonly between 80 and 120 km (Aulbach et al., 2017; Rader et al., 2015; Selway et al., 2015). Several explanations have been proposed for the cause of MLDs, including (a) layers of partial melt (Kumar et al., 2012; Thybo, 2006; Thybo & Perchuć, 1997), (b) elastically accommodated grain boundary sliding (Karato, 2012; Karato et al., 2015), (c) accumulation of hydrous‐seismically slow minerals, including pargasite and phlogopite (Aulbach et al., 2017; Kovacs et al., 2017; Kovács et al., 2021; Rader et al., 2015; Saha et al., 2021; Selway et al., 2015; Smart et al., 2021; Sudholz, Yaxley, et al., 2022; Sudholz et al., 2023), (d) high density fluids such as brines (Aulbach, 2018; Bettac et al., 2023) and (e) thermal anomalies related to lithological changes and melt‐wall rock interactions (Z. Liu et al., 2021). A pargasite‐amphibole model for the MLD has received petrological support in recent years because the high‐pressure stability limit of pargasite (amphibole) occurs at a depth similar to most seismic MLDs (80–120 km), and the formation of pargasite is known to take place beneath the metasomatized roots of cratons (Mandler & Grove, 2016; Niida & Green, 1999).…”