Variable lithospheric drips and their surface expressions: exploring the role of viscosity with analogue modelling
Abstract
A density instability can exist between the colder/denser mantle lithosphere and the underlying sub-lithospheric mantle. Inferred from geological and geophysical interpretations (i.e., surface subsidence, uplift, and shortening) it is suggested that the mantle lithosphere drips or sinks into the underlying mantle due to a contrast in density. This process is responsible for the removal or thinning of the lithosphere in intraplate (e.g., Great Basin) and active orogenic regions (e.g., Cordilleran magmatic arcs, Anatolia). In this study, we conducted a series of scaled 3D analogue/laboratory experiments with quantitative analyses using the high-resolution Particle Image Velocimetry (PIV) technique. The purpose was to define conditions for observable crustal thickening and shortening from a lithospheric drip. We explore how the attachment vs. semi-attachment of a drip to the upper mantle lithosphere (i.e., a variable amount of material participating in the drip) affects deformation in the upper crust. The models include a sub-lithospheric mantle (Polydimethylsiloxane-PDMS), mantle lithosphere (PDMS and plasticine), and upper crust (Si spheres and e-spheres) in a Plexiglass box. We varied the viscosity of the mantle lithosphere between experiments and in some cases, introduced a lower crust (PDMS and plasticine). Results show that a semi-attached drip only yields subsidence, with no surficial evidence of shortening; whereas attached drips will produce subsidence followed by thickening/shortening of the upper crust. At the later stages of the attached drip-mantle lithosphere experiments, the drip thins and necks, and the surface topography increases as a response to the upwelling sub-lithospheric mantle. Meanwhile, regions of surface extension develop as a response to the convergence. Importantly, we observe a correlation between the ratio of viscosity of the mantle lithosphere with respect to the sub-lithospheric mantle, and the development of convergent structures in the crust. A higher ratio produces more deformation than a lower ratio. Our results are applicable to areas where lithospheric drips have been postulated on Earth (e.g., rift margins and extensional zones) and to planets that show no evidence of surface plate tectonics but have deformed crusts (e.g., coronae formation on Venus).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T13F0251A
- Keywords:
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- 8110 Continental tectonics: general;
- TECTONOPHYSICS;
- 8122 Dynamics: gravity and tectonics;
- TECTONOPHYSICS;
- 8169 Sedimentary basin processes;
- TECTONOPHYSICS;
- 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS