Jim,

Ferrarri (2003) VOLCANIC EPISODES IN THE TRANSMEXICAN VOLCANIC BELT:
IMPLICATIONS FOR SUBDUCTION DYNAMICS
http://gsa.confex.com/gsa/2003CD/finalprogram/session_4513.htm

"...(2) From 11 to 6 Ma voluminous mafic lava flows were emplaced across
the whole central Mexico through major extensional fault systems. They
show ages progressively younger from west to east. This episode is
related to a slab detachment event triggered by the end of subduction
off southern Baja California. "

Ferrari starts the slab breakoff (the one I described in Rogers, et al.
2002, Geology) as trench-ridge interaction off westernmost Mexico. The
slab "tear" from west to east along the trace of the TMVB. The tear
dynamics of slab break-off associated w/ end of subduction are described
in Wortel and Spakman (Science, 2001). Essentially the slab tears like
"opening zipper" allowing hot asthenosperic mantle to rise in the tear
giving rise to the unusual mafic flows of TMVB that young to the east.

It would seem that as the tear reaches the eastern TMVB (6-7 Ma),
approaching the subducted continuation of the Tehuantepec ridge, the
slab tear proceeds southward parallel to the MAT. Ferrari provides the
triggering mechanism for producing the slab breakoff. I never knew what
triggered it.

Point. The TMVB existed prior to slab detachement.

In the same session, Guzman-Speziale GEOMETRIC ASPECTS OF THE SUBDUCTION
OF THE COCOS PLATE: IMPLICATIONS FOR THE ORIENTATION OF THE
TRANS-MEXICAN VOLCANIC BELT
<http://gsa.confex.com/gsa/2003CD/finalprogram/abstract_51780.htm>:
discusses how the TMVB may have attained it's orientation.

-Rob

James Pindell wrote:

>Hi Rob,
>
>This line caught my eye in your meeting summary....
>
>....the eastward younging mafic sequences of the TransMexican Volcanic
Belt
>trace the tear of the Cocos slab breakoff imaged beneath Central America.
>
>Would you be able to expand upon that for me please? Are you saying that
>the eastward younging is not due to migration of Chortis, but rather to
>tearing of the slab? Or are they effectively the same? I am curious!
>Thanks, Jim
>
>--
>
>Dr. James Pindell, Director Tectonic Analysis, Ltd. Cokes Barn West
Burton,
>Pulborough, West Sussex RH20 1HD ENGLAND (44) 1798 831110 (phone/fax;
work)
>jim@... (preferred) JamesPindell@... (alternate)
>Website: www.tectonicanalysis.com Also: Research Scientist, Rice
>University
>
>
>
>
>
>

--
Robert D. Rogers
Dept. of Geological Sciences
Institute for Geophysics
The University of Texas at Austin
4412 Spicewood Springs Rd. bldg 600
Austin, TX 78759-8500


Honduras Geology:
http://www.ig.utexas.edu/research/projects/honduras/index.htm

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