The St. Paul Transform System offsets by 630 km the Equatorial Mid Atlantic Ridge at 1° N. It consists of four major faults separating three intra transform ridge axes. This region shows a transition from a transpressive, hot spot affected, regional-scale shear zone to the North to a region dominated by a particular oceanic core complex spreading to the South (Vincent et al., this congress). Samples collected in the region during the COLMEIA cruise (Maia et al., 2016) were studied for textures and whole-rock major and trace element contents. All samples experienced pervasive deformation at ductile to brittle conditions overprinted by late low-T alteration. Mylonitic and ultramylonitic rocks can be grouped in three main types: peridotitic, gabbroic and talc-chlorite schist. Peridotitic ultramylonites preserve few opx, cpx and sp porphyroclasts; they have homogeneous nano-micro grain size groundmass, banded foliation and late amphibole and sulfide crystallization. Locally S-C fabric overprints the mylonitic texture. Micro cracks, filled with serpentine, chlorite and oxides are common, as well fluid inclusions trails in olivine and plagioclase crystals of peridotite and gabbros respectively. Major and trace element content of the peridotitic mylonites plot in the depleted field of the abyssal peridotites; however, they present marked LREE enrichment and Eu positive anomaly. Gabbroic and talc-chlorite mylonites display REE-enriched patterns (up to 100x CI) and variable Eu anomalies. Major elements show a remarkable linear trend in the talc-chlorite group suggesting mixing of pure talc and chlorite end-members. These compositional characteristics suggest variable assimilation of MORB and E-MORB during mylonisis or early melt-rock interaction and hydrothermal evolution at variable metamorphic conditions. Vincent et al., 2017. Particular Oceanic Core Complex evolution …; this congress Maia et al., 2016. Extreme mantle uplift and exhumation ... Nat. Geo. doi:10.1038/ngeo2759

MECHANICAL MIXING AND METAMORPHISM OF MAFIC AND ULTRAMAFIC LITHOLOGIES DURING MYLONISIS AT THE ST. PAUL TRANSFORM SYSTEM, MID-ATLANTIC RIDGE - T33D-2618 / Álden, Adrião; Marcia, Maia; Hemond, Christophe, Andrè, Michel; Mary-Alix, Kaczmarek; Anne, Briais; Clément, Vincent; Brunelli, Daniele. - (2017). ((Intervento presentato al convegno AGU FALL MEETING tenutosi a NEW ORLEANS - USA nel 13/12/2017.

MECHANICAL MIXING AND METAMORPHISM OF MAFIC AND ULTRAMAFIC LITHOLOGIES DURING MYLONISIS AT THE ST. PAUL TRANSFORM SYSTEM, MID-ATLANTIC RIDGE - T33D-2618

HEMOND, Christophe, Andrè, Michel;Daniele Brunelli
2017

Abstract

The St. Paul Transform System offsets by 630 km the Equatorial Mid Atlantic Ridge at 1° N. It consists of four major faults separating three intra transform ridge axes. This region shows a transition from a transpressive, hot spot affected, regional-scale shear zone to the North to a region dominated by a particular oceanic core complex spreading to the South (Vincent et al., this congress). Samples collected in the region during the COLMEIA cruise (Maia et al., 2016) were studied for textures and whole-rock major and trace element contents. All samples experienced pervasive deformation at ductile to brittle conditions overprinted by late low-T alteration. Mylonitic and ultramylonitic rocks can be grouped in three main types: peridotitic, gabbroic and talc-chlorite schist. Peridotitic ultramylonites preserve few opx, cpx and sp porphyroclasts; they have homogeneous nano-micro grain size groundmass, banded foliation and late amphibole and sulfide crystallization. Locally S-C fabric overprints the mylonitic texture. Micro cracks, filled with serpentine, chlorite and oxides are common, as well fluid inclusions trails in olivine and plagioclase crystals of peridotite and gabbros respectively. Major and trace element content of the peridotitic mylonites plot in the depleted field of the abyssal peridotites; however, they present marked LREE enrichment and Eu positive anomaly. Gabbroic and talc-chlorite mylonites display REE-enriched patterns (up to 100x CI) and variable Eu anomalies. Major elements show a remarkable linear trend in the talc-chlorite group suggesting mixing of pure talc and chlorite end-members. These compositional characteristics suggest variable assimilation of MORB and E-MORB during mylonisis or early melt-rock interaction and hydrothermal evolution at variable metamorphic conditions. Vincent et al., 2017. Particular Oceanic Core Complex evolution …; this congress Maia et al., 2016. Extreme mantle uplift and exhumation ... Nat. Geo. doi:10.1038/ngeo2759
AGU FALL MEETING
NEW ORLEANS - USA
13/12/2017
Álden, Adrião; Marcia, Maia; Hemond, Christophe, Andrè, Michel; Mary-Alix, Kaczmarek; Anne, Briais; Clément, Vincent; Brunelli, Daniele
MECHANICAL MIXING AND METAMORPHISM OF MAFIC AND ULTRAMAFIC LITHOLOGIES DURING MYLONISIS AT THE ST. PAUL TRANSFORM SYSTEM, MID-ATLANTIC RIDGE - T33D-2618 / Álden, Adrião; Marcia, Maia; Hemond, Christophe, Andrè, Michel; Mary-Alix, Kaczmarek; Anne, Briais; Clément, Vincent; Brunelli, Daniele. - (2017). ((Intervento presentato al convegno AGU FALL MEETING tenutosi a NEW ORLEANS - USA nel 13/12/2017.
File in questo prodotto:
Non ci sono file associati a questo prodotto.
Pubblicazioni consigliate

Caricamento pubblicazioni consigliate

Licenza Creative Commons
I metadati presenti in IRIS UNIMORE sono rilasciati con licenza Creative Commons CC0 1.0 Universal, mentre i file delle pubblicazioni sono rilasciati con licenza Attribuzione 4.0 Internazionale (CC BY 4.0), salvo diversa indicazione.
In caso di violazione di copyright, contattare Supporto Iris

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11380/1167664
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact