Teleseismic travel-time anomalies and deep crustral structure in central Australia

Abstract

Teleseismic travel times have been recorded along two lines of instruments traversing the Amadeus Basin and southern Arunta Block of central Australia for the purpose of examining the deep crustal and upper-mantle structure underlying these features. Pronounced differential travel times, approaching 1.5 s, and with major azimuthal variation, have been recorded. Most of the useful observations originated from events to the north (JapanMarianas) and to the east (Fiji-Tonga) at epicentral distances of 40-65". A few observations of southerly azimuth events (Macquarie Ridge and South Sandwich Islands) were also recorded. The inferred structure beneath the basin and block exhibits major lateral variations, the essential aspects of which are: (1) a zone of relatively high-velocity material dipping steeply northwards such that the continuation of its southern edge to the surface coincides approximately with a mylonitic shear zone known as the Redbank Deformed Zone;(2) a steeply dipping zone of relatively low-velocity material immediately to the south of this shear zone and partly underlying the high-velocity zone. If the travel times are interpreted in terms of an undulating Moho, variations in Moho depth of 20 km occur over horizontal distances of less than 50 km with relatively shallow Moho depths occurring immediately to the north of the Redbank Deformed Zone. Such an interpretation is consistent with the gravity anomalies observed across the geological structures. The inferred structure is out of hydrostatic equilibrium and departures from local isostasy approach 150 MPa. These stress-differences must have persisted during the 300 Ma following the Alice Springs Orogeny that led to the present crustal structure. Evidence, in the form of the surface topography and seismicity, suggests that some stress relaxation has occurred and still is occurring but not at the shear zone itself. At the time of the orogeny the structure may have been close to isostatic equilibrium, but as erosion took place complete local rebound did not occur, either because horizontal compressive forces still operated or because the strength of the lithosphere increased with time.

Lithospheric Framework of Australia

“…The initial application of mapping of the relative delay times of seismic arrivals was to investigate the major gravity anomalies in central Australia ( Figure 5) by using linear profiles of portable instruments (Lambeck et al, 1988). These studies revealed the need for substantial, but localised, variations in crustal thickness, to satisfactorily model the seismic results.…”

Constrained potential field modeling of the crustal architecture of the Musgrave Province in central Australia: Evidence for lithospheric strengthening due to crust‐mantle boundary uplift

“…[19] Current knowledge of the crustal architecture of the Musgrave Province at depth is based on a single teleseismic transect across the province [Lambeck and Burgess, 1992;Lambeck et al, 1988], supplemented by deep seismic reflection data in the Amadeus Basin [Korsch et al, 1998] and at the southern margin of the Musgrave Province [Lindsay and Leven, 1996] (Figure 2). The model based on teleseismic data (Figure 3) is characterized by steep Moho penetrating shear zones, corresponding to the Mann Fault, Wintiginna Lineament and Lindsay Lineament, that accommodate an upward Moho offset of up to 30 km beneath the central Musgrave Province [Lambeck and Burgess, 1992].…”

“…[4] Seismic and gravity data over the Arunta Inlier have provided a reasonable degree of constraint on the crustal architecture of this province and have demonstrated that the crust-mantle boundary is uplifted by $25 km along the lithospheric scale Redbank Thrust Zone, and that this offset is sufficient to cause the relative gravity high [Goleby et al, 1989[Goleby et al, , 1990Korsch et al, 1998]. A similar but less well constrained model derived from teleseismic data over the Musgrave Province proposes up to 30 km of crust-mantle boundary uplift, occurring along steep lithospheric scale reverse shear zones during the Petermann Orogeny [Lambeck and Burgess, 1992;Lambeck et al, 1988].…”

Constraining Crustal Properties With Bayesian Joint Inversion of Vertical and Radial Teleseismic P‐Wave Coda Autocorrelations

“…Moho depth varies between 37 and 53 km along the BILBY transect. The crust beneath the Musgrave Province, Officer Basin, and Arunta Block is characterized by a Moho uplift, which might be due to the presence of crustal‐scale faults and shear zones (e.g., Redbank shear zone in Arunta block [Goleby et al., 1989; Lambeck & Penney, 1984; Lambeck et al., 1988; Sippl, 2016]). A distinct and systematic pattern of Moho variation is recognizable along the transect across the crustal domains.…”