Inherited lithospheric structures control arc-continent collisional heterogeneity

Abstract

From west to east along the Sunda-Banda arc, convergence of the Indo-Australian plate transitions from subduction of oceanic lithosphere to arc-continent collision. This region of eastern Indonesia and Timor-Leste provides an opportunity for unraveling the processes that occur during collision between a continent and a volcanic arc, and it can be viewed as the temporal transition of this process along strike. We collected a range of complementary geological and geophysical data to place constraints on the geometry and history of arc-continent collision. Utilizing ~4 yr of new broadband seismic data, we imaged the structure of the crust through the uppermost mantle. Ambient noise tomography shows velocity anomalies along strike and across the arc that are attributed to the inherited structure of the incoming and colliding Australian plate. The pattern of anomalies at depth resembles the system of salients and embayments that is present offshore western Australia, which formed during rifting of east Gondwana. Previously identified changes in geochemistry of volcanics from Pb isotope anomalies from the inner arc islands correlate with newly identified velocity structures representing the underthrusted and subducted Indo-Australian plate. Reconstruction of uplift from river profiles from the outer arc islands suggests rapid uplift at the ends of the islands of Timor and western Sumba, which coincide with the edges of the volcanic-margin protrusions as inferred from the tomography. These findings suggest that the tectonic evolution of this region is defined by inherited structure of the Gondwana rifted continental margin of the incoming plate. Therefore, the initial template of plate structure controls orogenesis.

A Detailed Earthquake Catalog for Banda Arc–Australian Plate Collision Zone Using Machine-Learning Phase Picker and an Automated Workflow

“…It is also approximately concordant with a geodetic block boundary (e.g., Nugroho et al, 2009), with the Timor-Wetar block in the east accommodating up to 63% motion of the Australian plate relative to southeast Asia compared to an amount of 21%-41% in the west (Nugroho et al, 2009). A recent ambient noise tomography study also observes contrasting crustal structure on the two sides, with more slower materials observed in the crust beneath the Timor (Porritt et al, 2016;Zhang and Miller, 2021;Miller et al, 2021). Combined, we interpret the abundant crustal seismicity beneath the Alor-Timor segment to reflect the strong and complex crustal shortening and subduction of Australian continental materials.…”

Slow Geodynamics and Fast Morphotectonics in the Far East Tethys

“…This result partly explains the ubiquitous uplifted Pleistocene coral reef sequences that festoon the islands of the Banda arc (Figure 1). Although some are uplifted due to tectonic contraction (for instance, Sumba island, Authemayou et al., 2018, Miller et al., 2021, or SE Sulawesi, Pedoja et al., 2018), the background uplift of the region is induced by the relaxation of the dynamic topography. This motion is well localized around the basin, while the Australian margin conversely continues to subside at present.…”

Tectonic Fabric in the Banda Arc‐Australian Continent Collisional Zone Imaged by Teleseismic Receiver Functions

“…This array (coded as the YS network) includes the first broadband seismometer deployment in Timor-Leste and on the islands of Lomblen, Savu, Rote, and Alor in eastern Indonesia (Figure 1b; Miller et al, 2016). Using this data set, new imaging of crustal and mantle structure suggests continent subduction/underthrust is the dominant lithospheric structure beneath the region (Miller et al, 2021;Porritt et al, 2018;, in line with conclusions of other regional seismic tomography studies (e.g., Fichtner et al, 2010;Harris et al, 2020;Zenonos et al, 2019Zenonos et al, , 2020. The pronounced along-strike structural variations at shallow lithospheric depths may either result from the diachronous (progressive) collision as a result of the oblique convergence (Porritt et al, 2018; or from inherent structural heterogeneities of the incoming and colliding Australian (lower) plate (Miller et al, 2021), or both.…”

“…Using this data set, new imaging of crustal and mantle structure suggests continent subduction/underthrust is the dominant lithospheric structure beneath the region (Miller et al, 2021;Porritt et al, 2018;, in line with conclusions of other regional seismic tomography studies (e.g., Fichtner et al, 2010;Harris et al, 2020;Zenonos et al, 2019Zenonos et al, , 2020. The pronounced along-strike structural variations at shallow lithospheric depths may either result from the diachronous (progressive) collision as a result of the oblique convergence (Porritt et al, 2018; or from inherent structural heterogeneities of the incoming and colliding Australian (lower) plate (Miller et al, 2021), or both. The present-day seismic structure may be further complicated by exotic terranes or microplates formed during the Jurassic breakup of eastern Gondwana (e.g., Supendi et al, 2020;.…”