A number of metamorphic core complexes (MCCs) developed in the North China Craton and adjacent regions in the Early Cretaceous and were characterized by consistent extensional orientations. These MCCs formed in the continental interior and were conceptually attributed to the retreat of the Palaeo-Pacific (Izanagi) Plate, but the exact physical mechanism remains enigmatic. Here we utilize 2-D thermomechanical simulations to study how mechanical conditions of the continental crust respond to stresses derived from oceanic subduction and their roles in the formation of MCCs. Our results demonstrate that pre-existing weaknesses are key for localized formation within the continental interior. These weaknesses first undergo compression to form thrust faults in response to shallow subduction of the oceanic slab. These thrust faults gradually transform into extensional ones as the oceanic slab starts to retreat, eventually causing the synchronous exhumation of middle-to-lower crustal rocks that form the MCCs. The P-T paths of metamorphic rocks in the core of MCCs reveal a two-stage exhumation, with isothermal decompression followed by rapid isobaric cooling. Sensitivity tests show that (1) stronger upper crust and weaker lower crust favour MCC formation, while lithospheric strength could exert an influence on the formation time of MCCs and (2) when the continental crust is hot (TMoho = 800 °C), a new magmatic dome could form along the continental margin. We suggest that pre-existing weaknesses in the North China Craton played a key role in generating the quasi-simultaneous MCC series in response to the retreating Palaeo-Pacific Plate.
Inherited structural, compositional, thermal, and mechanical properties from previous tectonic phases can affect the deformation style of lithosphere entering a new stage of the Wilson cycle. When continental crust jams a subduction zone, the transition from subduction to extension can occur rapidly, as is the case following slab breakoff of the leading subducted oceanic slab. This study explores the extent to which geometric and physical properties of the subduction phase affect the subsequent deformation style and surface morphology of post subduction extensional systems. We focus on regions that transition rapidly from subduction to extension, retaining lithospheric heterogeneities and cold thermal structure inherited from subduction. We present numerical models suggesting that following failed subduction of continental crust (with or without slab breakoff), the extensional deformation style depends on the strength and dip of the preexisting subduction thrust. Our models predict three distinct extensional modes based on these inherited properties: (1) reactivation of the subduction thrust and development of a rolling‐hinge detachment that exhumes deep crustal material in a domal structure prior to onset of an asymmetric rift; (2) partial reactivation of a low‐angle subduction thrust, which is eventually abandoned as high‐angle, “domino”‐style normal faults cut and extend the crust above the inherited thrust; and (3) no reactivation of the subduction fault but instead localized rifting above the previous subduction margin as new rift‐bounding, high‐angle normal faults form. We propose that the first mode is well exemplified by the young, rapidly exhumed Dayman‐Suckling metamorphic core complex that is exhuming today in Papua New Guinea.
more » « less- PAR ID:
- 10458365
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Tectonics
- Volume:
- 38
- Issue:
- 5
- ISSN:
- 0278-7407
- Page Range / eLocation ID:
- p. 1742-1763
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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