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Two-stage Subduction Initiation around the Caribbean Plumehead Plate Bob Stern (U TX Dallas USA) Scott Whattam (Korea U., Korea) Taras Gerya (ETH, Switzerland) James Pindell (Rice U., USA) T224 Tuesday 8:05am Mile High Ballroom 2C Induced Nucleation of a Subduction Zone (INSZ) 2 types Spontaneous Nucleation of a Subduction Zone (SNSZ) 3 types Induced Nucleation of a Subduction Zone (INSZ) 2 types Spontaneous Nucleation of a Subduction Zone (SNSZ) 3 types Induced Nucleation of a Subduction Zone (INSZ) 2 types Spontaneous Nucleation of a Subduction Zone (SNSZ) 3 types SNSZ requires lithospheric failure. It requires a lithospheric weakness to exploit and density inversion between lithosphere and asthenosphere. 3 types of SNSZ 1. Passive Margin Collapse Unlikely; no Cenozoic examples 2. Transform/Fracture Zone Collapse Ex. modern IBM, Late Cretaceous SW Asia) 3. Plume Induced Subduction Initiation (PISI) Late Cretaceous of SW Caribbean 1. Passive Margin Collapse No Cenozoic examples. Seems difficult to accomplish. Wilson cycle ocean closing vectors probably ~90° to opening vectors because new subduction zones form on transforms, not along rifted continental margins Look at Gulf of Mexico example The Gulf of Mexico USA Cuba Mexico Dallas Houston Modified after Pindell and Kennan 2009 Gulf of Mexico vertical gravity gradient map from satellites (CryoSat-2 and Jason-1) reveals the Jurassic spreading ridge. Uninterpreted Interpreted The VGG reveals the extinct spreading ridges and fracture zones as well as a significant change in amplitude across the boundary between continental and oceanic crust (COBs). This is a Mercator projection; grayscale saturates at T20 eotvos units. (Sandwell et al., 2014) North-south (dip) cross-section of the NW Gulf of Mexico continental margin. 165 Ma oceanic crust + 20 km sediments = no lithospheric failure or even earthquakes). Late Jurassic (M16; 141 Ma) reconstruction of the Proto-Caribbean Good place for transform margin collapse and formation of new subduction zone (Greater Antilles Arc). Pindell et al. 2011 Interested to learn more about Subduction Initiation and the Greater Antilles? Pardee Symposium P4. Geologic Evolution of Cuba Wed., 28 Sept., 8 a.m.-noon Mile High Ballroom 2A/3A Induced Nucleation of a Subduction Zone (INSZ) 2 types Spontaneous Nucleation of a Subduction Zone (SNSZ) 3 types 2. Transform margin collapse (Uyeda & Ben Avraham model*) Eocene ~50 Ma Problem: Old lithosphere is very strong, but a properly oriented fracture zone could allow it to begin to sink. *of course it’s more complicated, see Leng and Gurnis GRL 2015 A. Exploitation of Lithospheric Weakness B. Lithospheric Collapse & Formation of Infant Arc (proto-forearc*) by seafloor spreading *Nursery of most ophiolites C. Proto-forearc widens by seafloor spreading as lithospheric subsidence continues spreading Trench rollback Trench rollback draws in more asthensophere Interested to learn more about IBM SNSZ? Studying an Ophiolite in its Natural Environment: IODP Leg 352 Drilling in the Izu-Bonin-Mariana (IBM) Forearc T209 Wed. 3:20 pm Room 203 D. Forearc cools soon after true subduction (downdip motion of plate) begins When and why lithospheric subsidence develops down-dip motion is not understood. Mature arc system begins as forearc cools Stern & Bloomer 1992 E. Mature Subduction Zone Induced Nucleation of a Subduction Zone (INSZ) 2 types Spontaneous Nucleation of a Subduction Zone (SNSZ) 3 types Late Cretaceous evolution of the Caribbean plate Galapagos Hotspot Plume- induced SI: the Late Cretaceous Caribbean example Cartoon depicting construction of (a) the early 140–110 Ma oceanic plateau followed by the subsequent evolution of subduction zones around the plume head through Late Cretaceous time. Whattam and Stern 2014 Plume- induced SI: the Late Cretaceous Caribbean example Numerical experiments of mantle plume impinging on oceanic lithosphere The initial model setup impinges a thermal mantle plume (100-300 km in diameter) into an oceanic lithosphere with 8-30 km thick mafic crust composed of 3 km basalts and 5-27 km gabbro (Gerya et al., Nature 2015). PISI early stage: Plume head impinges on base of lithosphere 20 Ma lithosphere; modern Earth Plume head impingment: oceanic plateau development formation of an incipient trench and a nearlycircular slab at the plateau margins PISI late stage: Lithosphere ruptures and collapses into Subduction Zone as plume head expands tearing of the circular slab formation of four retreating subduction zones Induced Nucleation of a Subduction Zone (INSZ) 2 types Spontaneous Nucleation of a Subduction Zone (SNSZ) 3 types