Microcontinents and Continental Fragments Associated With Subduction Systems

Abstract

Microcontinents 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.

Back‐Arc Dynamics Controlled by Slab Rollback and Tearing: A Reappraisal of Seafloor Spreading and Kinematic Evolution of the Eastern Algero‐Balearic Basin (Western Mediterranean) in the Middle‐Late Miocene

“…Obviously, the tectonic evolution of the ABB has resulted in the splitting of an initially Greater Alboran block into several pieces that were first formed during the southward rollback of the slab (Figures 12a and 12b) and then reworked and fragmented again during the westward rollback phase (Figures 12c and 12d). This process is interpreted to be linked with rapid changes in complex subduction dynamics (van den Broek & Gaina, 2020). That is exactly the situation in the present case study at 16‐15 Ma, at the moment when the Balearic slab began to tear bilaterally to the west and southeast (Figures 12b and 12c), thus triggering dispersal of small continental fragments and significant stretching of the GALB by a fast westward rollback (Figures 12c and 12d).…”

“…The process of slab segmentation and tearing, as proposed in recent geodynamic models of the western Mediterranean Sea (van Hinsbergen et al., 2014; 2020), offers the most likely mechanism to explain the two last stages of opening of the Algero‐Balearic domain. The EABB case study illustrates how collision‐induced rotations following slab rollback and the associated increase of arc curvature may lead to complex back‐arc rifting systems with highly variable geometry and strain rates and may foster fore‐arc fragmentation in a short geological time scale (van den Broek & Gaina, 2020; van Hinsbergen et al., 2020; Guillaume et al., 2010; Wallace et al., 2005).…”

Generation of Continental Lithospheric Mantle by Tectonic Isolation of Oceanic Plate

“…We envisage that a variety of other tectonically driven isolation processes (e.g., rifting to isolate the plate) may also lead to formation of new CLM. Van den Broek & Gaina (2020) suggested that extension and rifting play an important role in the formation of microcontinents, and proposed southern Baja California to be a “proto‐microcontinent”. Here, we provide evidence for such a process on the Baja California margin.…”