Banca de DEFESA: Rhander Taufner Altoé

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Rhander Taufner Altoé
DATE: 09/09/2022
TIME: 09:00
LOCAL: Sala de videconferência do IGD
TITLE:

STRAIN LOCALIZATION IN THE LOWER OCEANIC CRUST: THE ATLANTIS BANK OCEANIC CORE COMPLEX, SOUTHWEST INDIAN RIDGE – IODP EXPEDITION 360

KEY WORDS:

gabbro mylonite, fluid-rock interaction, dislocation creep, metamorphism, diffusion creep 

PAGES: 91
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

Detachment faulting has been hypothesized as the main process of tectonic spreading in slow-
spreading mid-ocean ridges, leading to exhumation of lower crustal rocks interlayered with pristine

upper-mantle aggregates through large-scale normal faulting, namely ocean core complexes (OCC).
Although many models have been proposed for the rooting of detachments and the exhumation of
ocean core complexes, the interplay between deformation and fluid-assisted metamorphic reactions
during mylonitizatin and unroofing of OCC is still poorly constrained. Particularly, the role of ductile
shear zones at depth and their potential pathways for melt and/or fluids in enhancing phase
transformation during large-scale faulting is still contentious. Thus, the influence of fluids on the
modes which strain is localized in the oceanic crust is yet to be constrained in terms of their impact
on the mechanical behavior of the lithosphere.
In this contribution, we have investigated the mechanical characteristic of lower crustal rocks through
a detailed tectono-metamorphic analysis of gabbro mylonites recovered in the hole U1473A from the
Atlantis Bank ocean core complex, Southwest Indian Ridge (IODP Expedition 360), to better
understand strain localization processes during uplift of the high-temperature ocean crust, taking into
account the influence of fluids as a potential weakening mechanism.
We have shown that mylonites in gabbroic shear zones localize deformation at granulite facies
conditions by a combination of mechanical fragmentation and viscous flow (e.g., dislocation and
diffusion creep) in the presence of fluids. The percolating fluids promote syn-kinematic hydration
reaction products (i.e., amphibole), and the amount of amphibole produced is intimately linked to the
degree of strain the rock experienced. Our results evidence that fluids contribute to the development
of fine-grained shear zones in ‘dry’ gabbroic rocks and play a crucial role on the overall mechanical
behavior of the lower oceanic crust. Hence, the rheology of the lower crust at slow-spreading ridges
would be best modeled with flow laws for polymineralic aggregates, taking into account the role of
water in promoting reaction-softening. Such fluid-rock interactions are complex and indicate the way
strain is distributed in the footwall of oceanic core complexes during large-scale, detachment faulting
and exhumation of the lower crust/upper mantle boundary.

BANKING MEMBERS:
Externo à Instituição - LEONARDO EVANGELISTA LAGOEIRO - UFPR
Externa à Instituição - ANDREA TOMMASI
Externo ao Programa - 3291096 - CAIO ARTHUR SANTOS
Interna - 1555904 - CATARINA LABOURE BEMFICA TOLEDO
Presidente - 2370895 - LUIS GUSTAVO FERREIRA VIEGAS