Crustal structure and apparent tectonic underplating from receiver function analysis in South Island, New Zealand

Abstract

[1] We utilize seismic converted phases on more than 700 receiver functions calculated for 42 stations in the South Island, New Zealand, to infer crustal and uppermost mantle structure. We determine the crustal thickness from direct observations of conversion from the Moho interface and infer zone of the maximum thickness being located along the axis of the Southern Alps, just east from the Alpine fault. The crustal root widens from north to south in the direction perpendicular to the Alpine fault and appears to have an asymmetric structure. Stations in the alpine portion of island show evidence for prominent midcrustal conversions. Significant crustal thickening is developed in response to both the convergent component of the motion on the Alpine fault and subduction in the Fiordland region. We propose two models for a strong uppermost mantle conversion that occurs at depths between 33 and 83 km on 16 stations and forms a large continuous feature along the east coast and in the central portions of the South Island. Our preferred model attributes upper mantle conversion to tectonically underplated oceanic crust formed by late Oligocene-Miocene spreading between the Australian and Pacific plates, which was detached from the Australian plate and tectonically underplated under the South Island. An alternative model attributes the upper mantle conversions to long-lived seismic fabric created by subduction of the Gondwanaland margin.

Continental and oceanic crustal structure of the Pampean flat slab region, western Argentina, using receiver function analysis: new high-resolution results

“…6). Tectonic underplating has been observed, although generally at shallower depths, in subductions zones such as Alaska (Fuis et al 2008), Cascadia (Calvert et al 2006), Japan (Kimura et al 2010) and New Zealand (Spasojevic & Clayton 2008). In Indonesia, Singh et al (2008) seismically imaged broken oceanic crust and interpreted very strong coupling, which lead to brittle failure of mantle rocks in the subduction zone, and the great megathrust earthquake of 2004 in Sumatra.…”

Lithospheric shear velocity structure of South Island, New Zealand, from amphibious Rayleigh wave tomography

“…The crustal thickness model of Salmon et al . [] incorporates results from onshore/offshore refraction and reflection studies dating to the 1980s and includes Moho depth estimates from recent onshore receiver function analyses [ Spasojević and Clayton , ]. Where data are sparse (i.e., offshore), they are interpolated using the Crust2.0 model [ Bassin et al ., ].…”

“…Plate reconstructions indicate that the Zealandian Australia/Pacific plate boundary likely initiated at this time, cutting across the Challenger Plateau [ Cande and Stock , ], possibly in the location of the present‐day Alpine Fault [ Sutherland et al ., ]. Eocene rifting along the Resolution Ridge (Figure b) beginning approximately 45 Ma likely created oceanic crust eastward of the present‐day Alpine Fault, which is no longer present in surface rocks and is inferred to have been overridden by the Campbell Plateau (Figure b) during Cenozoic convergence [ Spasojević and Clayton , ; Sutherland et al ., ]. The Eocene rifting episode requires a pair of passive margins, one of which is evidently preserved at the western edge of the Campbell Plateau.…”

“…Much of the continental lithosphere of Zealandia is below sea level and not easily accessible for seismic studies to probe the nature of the plate boundary and adjacent mantle lithosphere. Previous work using New Zealand land‐based seismic stations has produced images of crustal structure from ambient noise surface wave tomography [ Lin et al ., ], Moho depth from receiver functions [ Spasojević and Clayton , ], and body wave tomography for crust and mantle structure [ Kohler and Eberhart‐Phillips , ]. Teleseismic shear wave splitting analysis [ Zietlow et al ., ] and Pn travel time residuals [ Collins and Molnar , ] reveal a pattern of lithospheric anisotropy consistent with strain distributed across an ~200 km region parallel to the Alpine Fault, but uncertainty persists as to the depth extent of localized versus distributed shear as revealed by seismic anisotropy.…”

Crustal Structure Along Sunda-Banda Arc Transition Zone from Teleseismic Receiver Functions

“…The number of receiver functions for the stacking varies from about 16 to 257 at each individual station. The quality of the stacks may depend on the number of receiver functions at each station, similarity and coherence signal from subsurface structure on the receiver functions derived from different events at the same station and stability of the computed receiver function (Spasojevic and Clayton 2008). Stacking N number of traces will improve the signal to noise ratio by a factor of N (Owens 1984).…”