scholarly journals Structural Evidences for Present-day Compressive Tectonics at the St. Peter and St. Paul Archipelago (Equatorial Atlantic Ocean)

2021 ◽  
Author(s):  
Thomas Campos ◽  
Kenji Motoki ◽  
Susanna Sichel ◽  
Leonardo Barão ◽  
Marcia Maia ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Average Rate ◽  
High Angle ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Joint System ◽  
Conjugate System ◽  
The North ◽  
Equatorial Atlantic Ocean ◽  
Load Release

This paper discusses the tectonics of the St. Peter and St. Paul Archipelago (SPSPA) in the Equato-rial Atlantic Ocean, based on the joint-system geometry which show a North-South shorten-ing/transpressional uplift tectonism, is active leading to exhumation of the sub-oceanic mantle. These islets are the summits of a sigmoidal submarine ridge formed by mantle ultramafic rocks. The ridge is crossed by the principal transform deformation zone of the northern transform fault of the St. Paul Multifault System. The South flank ridge exposes serpentinized mantle perido-tites, while the North flank exposes strongly deformed/fractured ultramylonites, recording duc-tile and brittle deformation at lithospheric conditions. The SPSPA show multiple joint systems cutting mylonitic foliation of the exposed rocks, forming three main families: high-angle paral-lel joints of tectonic origin, serpentinization-related joints with random direction and load-release low-angle parallel joints. The tectonic joints show an average direction of N31°E and N28°W, forming a conjugate system with a N1ºW compression axes, coherent with a trans-pressive stress field. Accordingly, the earthquakes focal mechanism close to the islets also shows N-S compression. The previously reported active uplift with an average rate of 1.5 mm/year and the directions of the joint system here reported agreeing with a present-day active N-S compres-sive field at a high angle with the direction of the transform fault.

Mapping of a segment of the Romanche Fracture Zone: A morphostructural analysis of a major transform fault of the equatorial Atlantic Ocean

Geology ◽  
1991 ◽  
Vol 19 (8) ◽  
pp. 795 ◽  
Author(s):  
José Honnorez ◽  
Jean Mascle ◽  
Christophe Basile ◽  
Pierre Tricart ◽  
Michel Villeneuve ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Fracture Zone ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Equatorial Atlantic Ocean ◽  
Romanche Fracture Zone

scholarly journals Gravimetric structure for the abyssal mantle massif of Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean, and its relation to active uplift

2014 ◽  
Vol 86 (2) ◽  
pp. 571-588 ◽  
Author(s):  
KENJI F. MOTOKI ◽  
AKIHISA MOTOKI ◽  
SUSANNA E. SICHEL
Keyword(s):  
Atlantic Ocean ◽  
Saint Paul ◽  
Tectonic Uplift ◽  
Plate Motion ◽  
Ultramafic Rocks ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Data Set ◽  
Equatorial Atlantic Ocean ◽  
Saint Peter

This paper presents gravimetric and morphologic analyses based on the satellite-derived data set of EGM2008 and TOPEX for the area of the oceanic mantle massif of the Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean. The free-air anomaly indicates that the present plate boundary is not situated along the longitudinal graben which cuts peridotite ridge, but about 20 km to the north of it. The high Bouguer anomaly of the peridotite ridge suggests that it is constituted mainly by unserpentinised ultramafic rocks. The absence of isostatic compensation and low-degree serpentinisation of the ultramafic rocks indicate that the peridotite ridge is sustained mainly by active tectonic uplift. The unparallel relation between the transform fault and the relative plate motion generates near north-south compression and the consequent tectonic uplift. In this sense, the peridotite massif is a pressure ridge due to the strike-slip displacement of the Saint Paul Transform Fault.

scholarly journals Ocean variations associated with fishing conditions for yellowfin tuna (Thunnus albacares) in the equatorial Atlantic Ocean

2011 ◽  
Vol 68 (6) ◽  
pp. 1063-1071 ◽  
Author(s):  
Kuo-Wei Lan ◽  
Ming-An Lee ◽  
Hsueh-Jung Lu ◽  
Wei-Juan Shieh ◽  
Wei-Kuan Lin ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Net Primary Productivity ◽  
Principal Component ◽  
Yellowfin Tuna ◽  
Subsurface Water ◽  
Thunnus Albacares ◽  
Equatorial Atlantic ◽  
Catch Per Unit Effort ◽  
The North ◽  
Equatorial Atlantic Ocean

Abstract Lan, K-W., Lee, M-A., Lu, H-J., Shieh, W-J., Lin, W-K., and Kao, S-C. 2011. Ocean variations associated with fishing conditions for yellowfin tuna (Thunnus albacares) in the equatorial Atlantic Ocean. – ICES Journal of Marine Science, 68: 1063–1071. In this study, the Taiwanese longline (LL) fishery data were divided into two types: regular LL and deep LL. Furthermore, we collected environmental variables, such as sea surface temperature (SST), subsurface temperature, chlorophyll a concentration, net primary productivity, windspeed, and the north tropical Atlantic SST index (NTA) during the period 1998–2007 to investigate the relationship between LL catch data and oceanic environmental factors using principal component analysis (PCA). After the daily LL was separated into two types of LL, the results indicated that the deep LL was the major fishery catching yellowfin tuna (YFT) in the equatorial Atlantic Ocean. In 2003–2005, especially in 2005, the monthly catch by deep LL was double those of other years. The spatial distribution of the nominal catch per unit effort (cpue) by deep LL showed the maximum aggregation of YFT in waters with temperature above 24–25°C. The YFT mainly aggregated in the equatorial Atlantic, extending east in the first and second quarters of the year. In the third quarter of the year, the SST decreased off West Africa and the YFT migrated westwards to 15°W. Results of PCA indicated that higher subsurface water temperatures resulted in a deeper thermocline and caused a higher cpue of YFT, but the influence of NTA on the cpue of YFT seemed to be insignificant.

scholarly journals Serpentinized peridotite versus thick mafic crust at the Romanche oceanic transform fault

Geology ◽  
2021 ◽  
Author(s):  
Emma P.M. Gregory ◽  
Satish C. Singh ◽  
Milena Marjanović ◽  
Zhikai Wang
Keyword(s):  
Mantle Peridotite ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Low Velocity ◽  
Transform Faults ◽  
Velocity Anomaly ◽  
The North ◽  
Serpentinized Peridotite ◽  
Equatorial Atlantic Ocean ◽  
Alteration Processes

The crust beneath transform faults at slow-spreading ridges has been considered to be thin, comprising a thin mafic layer overlying serpentinized peridotite. Using wide-angle seismic data, we report the presence of a Moho at ~6 km depth and a low-velocity anomaly extending down to 9 km beneath the 20-km-wide Romanche transform valley floor in the equatorial Atlantic Ocean. The low crustal velocities above the Moho could be due to either highly serpentinized mantle peridotite or fractured mafic rocks. The existence of clear Moho reflections and the occurrence of a large crustal-depth rupture during the 2016 magnitude 7.1 earthquake suggest that the crust likely consists of fractured mafic material. Furthermore, the presence of low velocities below the Moho advocates for extensive serpentinization of the mantle, indicating that the Moho reflection is unlikely to be produced by a serpentinization front. The crust to the north of the transform fault likely consists of mafic material, but that in the south appears to be more amagmatic, possibly containing serpentinized peridotite. Our results imply that the transform fault structure is complex and highly heterogeneous, and thus would have significant influence on earthquake rupture and alteration processes.

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