Diverse Styles of Lithospheric Dripping: Synthesizing Gravitational Instability Models, Continental Tectonics, and Geologic Observations.

Density instabilities in the lithosphere can founder gravitationally via viscous dripping and decoupling from overlying crust. The lithospheric dripping concept has been invoked across the globe, but the diversity of crustal effects, observable evidence, and tectonic settings involved in dripping remain underexplored. Here, we synthesize numerical and analogue modeling studies and geologic data from the literature, including all proposed lithospheric dripping events to‐date. We argue that two distinct styles of dripping can occur depending on crustal strength (relative to that of the mantle lithosphere). Near‐surface contraction and subsidence of strong crusts contrasts with near‐surface extension and uplift of weak crusts. We discuss these events in terms of tectonic setting, timing, size, and the main types of data associated with each event. We also find that lithospheric dripping is associated with a distinct suite of geological observations including sedimentological, structural, volcanic, and geophysical data, which can be used to distinguish strong crusts from weak crusts. We find 27 events for which lithospheric dripping is a key hypothesis, including 9 with clear evidence for strong‐crust dripping and 3 with clear evidence of weak‐crust dripping. We review emerging research methods have the potential to detect the signals of dripping in the geologic and geophysical record, and we suggest additional techniques in light of our strong‐crust versus weak‐crust framework. The diverse tectonic settings and inferred consequences of these lithospheric drips, if confirmed, would demand a shift in our understanding of continental geology to emphasize the role of vertical removal of continental lithosphere. Plain Language Summary: If part of the lithosphere (Earth's crust and the rigid upper part of the mantle) increases in density, it may become heavier than the underlying mantle and sink, or founder. Foundering results in the removal of blobs of lithosphere from overlying crust, a process called dripping. Dripping may have occurred in several locations across the globe, but the effects it is capable of producing are not well understood. We synthesize numerical models of dripping with studies of real‐world locations and compile available evidence to better understand the dripping process. We suggest that key observable effects are driven by the strength of the crust relative to the foundering lithosphere. In particular, when the crust is weak and able to flow in response to a lithospheric drip, complex patterns of deformation and sedimentation can result. For the 27 events that have been discussed to date, 9 have clear evidence for strong‐crust behavior, and 3 for a weak‐crust behavior. This framework will help researchers understand what lithospheric dripping looks like in geological and geophysical data, and we discuss avenues for further research on this topic. Key Points: Lithospheric dripping has been proposed for 27 locations throughout the globe and may be responsible for a wide range of observable effectsA synthesis of modeling studies suggests two distinct types of dripping depending on crustal strength relative to mantle lithosphereExisting data support the strong‐crust versus weak‐crust drip framework and suggest future research opportunities [ABSTRACT FROM AUTHOR]