Abstract
AbstractMicrocontinents and continental fragments are small pieces of continental crust that are surrounded by oceanic lithosphere. Although classically associated with passive margin formation, here we present several preserved microcontinents and continental fragments associated with subduction systems. They are located in the Coral Sea, South China Sea, central Mediterranean and Scotia Sea regions, and a “proto‐microcontinent,” in the Gulf of California. Reviewing the tectonic history of each region and interpreting a variety of geophysical data allows us to identify parameters controlling the formation of microcontinents and continental fragments in subduction settings. All these tectonic blocks experienced long, complex tectonic histories with an important role for developing inherited structures. They tend to form in back‐arc locations and separate from their parent continent by oblique or rotational kinematics. The separated continental pieces and associated marginal basins are generally small and their formation is quick (<50 Myr). Microcontinents and continental fragments formed close to large continental masses tend to form faster than those created in systems bordered by large oceanic plates. A common triggering mechanism for their formation is difficult to identify, but seems to be linked with rapid changes of complex subduction dynamics. The young ages of all contemporary pieces found in situ suggest that microcontinents and continental fragments in these settings are short lived. Although presently the amount of in‐situ subduction‐related microcontinents is meager (an area of 0.56% and 0.28% of global, non‐cratonic, continental crustal area and crustal volume, respectively), through time microcontinents contributed to terrane amalgamation and larger continent formation.
Highlights
In the geological record, continental breakup and subsequent seafloor spreading sometimes resulted in smaller blocks being sliced and carried away from the margins of the parent continent
We present a global catalogue of microcontinents and continental fragments associated to convergent margins
We investigate microcontinents in regions affected by subduction in the following locations: (1) the Coral Sea; (2) the South China Sea; (3) the central Mediterranean Sea; (4) the Scotia Sea; and (5) the Gulf of van den BROEK AND GAINA
Summary
Continental breakup and subsequent seafloor spreading sometimes resulted in smaller blocks being sliced and carried away from the margins of the parent continent. The various continental pieces bordering the Coral Sea, NE of Australia (Gaina et al, 1999; Taylor & Falvey, 1977), the Reed and Macclesfield Banks in the South China Sea (Cullen et al, 2010; Pichot et al, 2014), the Corsica‐Sardinia block in the Central Mediterranean (Advokaat et al, 2014; Faccenna et al, 2001), and various fragments in the Scotia Sea (Carter et al, 2014; Trouw et al, 1997) (Figure 1) all formed close to active continental margins and related subduction systems. The formation of microcontinents and continental fragments formed in convergent and/or subduction systems is an overlooked aspect of active margin evolution. Both the South China Sea and the Gulf of California where reconstructed according to Matthews et al (2016)
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