Crustal structure of the Kermadec arc from MANGO seismic refraction profiles

Abstract

Three active‐source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the Kermadec subduction zone. These observations are used to test contrasting tectonic models for an along‐strike transition in margin structure previously known as the 32°S boundary. We use residual bathymetry to constrain the geometry of this boundary and propose the name Central Kermadec Discontinuity (CKD). North of the CKD, the buried Tonga Ridge occupies the fore‐arc with VP 6.5–7.3 km s−1 and residual free‐air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110 ± 20 km), and strike (~005° south of 25°S). South of the CKD the fore‐arc is structurally homogeneous downdip with VP 5.7–7.3 km s−1. In the Havre Trough back‐arc, crustal thickness south of the CKD is 8–9 km, which is up to 4 km thinner than the northern Havre Trough and at least 1 km thinner than the southern Havre Trough. We suggest that the Eocene arc did not extend along the current length of the Tonga‐Kermadec trench. The Eocene arc was originally connected to the Three Kings Ridge, and the CKD was likely formed during separation and easterly translation of an Eocene arc substrate during the early Oligocene. We suggest that the first‐order crustal thickness variations along the Kermadec arc were inherited from before the Neogene and reflect Mesozoic crustal structure, the Cenozoic evolution of the Tonga‐Kermadec‐Hikurangi margin and along‐strike variations in the duration of arc volcanism.

Quantitatively Tracking the Elevation of the Tibetan Plateau Since the Cretaceous: Insights From Whole‐Rock Sr/Y and La/Yb Ratios

“…Strong correlations ( R 2 > 0.85) between the elevation and Moho depth in modern subduction and collision zones confirm the effectiveness of Equations – (Figure 1). The differences in equations for subduction zones and equations for collision zones are interpreted to be caused by the variations in crust and upper mantle density (Figure 1; Bassett et al, 2016; Lee et al, 2015). Previous studies that calculating paleo‐elevation based on Airy isostasy and paleocrustal thickness (e.g., Chapman et al, 2020; Zhu et al, 2017) implicitly assume that the crust and upper mantle density have not changed, which may not be valid for ancient orogens.…”

Source Process for Two Enigmatic Repeating Vertical‐T CLVD Tsunami Earthquakes in the Kermadec Ridge

“…The tsunami waveforms can be well reproduced with a RMSE of 0.0612 ( Figure S8c) by a CLVD source model at depth of 1.5 km with a total length of 7 km, thickness of 1 km, and a nonuniform distribution of vertical expansion and horizontal compression amounts ( Figure S8a). If we assume a rigidity at this depth of 10 GPa ( Figure S9), based on the velocity model of Bassett et al (2016), then the total seismic moment of the shallow CLVD source model from the tsunami waveform analysis is 1.5 times that of GCMT solution. Kanamori et al (1993) suspected that this kind of tsunami earthquake was a result of hydrofracturing by heated water in a sediment layer above a shallow magma chamber.…”

Dating Oceanic Subduction in the Jurassic Bangong–Nujiang Oceanic Arc: A Zircon U–Pb Age and Lu–Hf Isotopes and Al-in-Hornblende Barometry Study of the Lameila Pluton in Western Tibet, China

“…Alternatively, magmatism may play a considerable role in the thickening of the Jurassic oceanic arc within the BNO. Studies on modern oceanic arcs, such as the Izu-Bonin-Marina [70][71][72][73], the Lesser Antilles [74][75][76], the Tonga-Kermadec [77][78][79], and the Aleutian [80][81][82] arcs show a variation of crustal thickness (9-35 km) within a single arc or between different arcs. In addition, an important finding of these studies is that the thick part of an arc is always related to high magmatic flux.…”