Transcript Carib PISI Stern GSA Denver 2016

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