FN Archimer Export Format PT J TI Evolution of a Cold Intra‐Transform Ridge Segment Through Oceanic Core Complex Splitting and Mantle Exhumation, St. Paul Transform System, Equatorial Atlantic BT AF Vincent, Clément Maia, Marcia Briais, Anne Brunelli, Daniele Ligi, Marco Sichel, Susanna AS 1:1;2:1;3:1,2;4:3,4;5:5;6:6; FF 1:;2:;3:;4:;5:;6:; C1 Geo‐Ocean UMR6538 CNRS‐IFREMER‐UBO‐UBS Institut Universitaire Européen de la Mer IUEM Brest ,France Géosciences Environnement Toulouse—GET Université Toulouse III—Paul Sabatier Toulouse, France Dipartimento di Scienze Chimiche e Geologiche Università di Modena e Reggio Emilia Modena ,Italy IGAG‐CNR Istituto di Geologia Ambientale e Geoingegneria Rome, Italy ISMAR‐CNR Instituto di Scienze Marine Bologna, Italy LAGEMAR Universidade Federal Fluminense Niteroi, Brazil C2 UBO, FRANCE UNIV TOULOUSE, FRANCE UNIV MODENA & REGGIO EMILIA, ITALY CNR IGAG, ITALY CNR ISMAR, ITALY UNIV FED FLUMINENSE, BRAZIL UM GEO-OCEAN IN WOS Cotutelle UMR DOAJ copubli-france copubli-europe copubli-univ-france copubli-int-hors-europe copubli-sud IF 3.5 TC 0 UR https://archimer.ifremer.fr/doc/00838/94960/102533.pdf https://archimer.ifremer.fr/doc/00838/94960/102534.docx LA English DT Article CR COLMEIA BO L'Atalante DE ;Mid-Atlantic Ridge;intra-transform spreading;detachment faults;oceanic core complex AB Accretionary processes at mid-ocean ridge segments with low magma input have seldom been investigated over the long term. The evolution of such magma-starved segments over time is still largely unknown. We present a study on the structure and evolution of the southernmost intra-transform ridge segment of the St. Paul Transform Fault System in the Equatorial Mid-Atlantic Ridge, based on new bathymetry, gravity, and rock sampling data. We show that this area evolves differently from previously described tectonics along ridge segments of similar spreading rate. On the flanks of the axial ridge segment, we observe a succession of structures exhumed by detachment faulting, evolving from east-facing, long-lived, corrugated oceanic core complexes (∼6 Ma ago), to short-lived detachment faults exposing lower crust and mantle rocks and facing alternatively east and west in the more recent part of the segment. The oldest detachment faults have been repeatedly split and partially transferred to the opposite flank through the formation of new detachments into the footwall. The terminations of three old, east-facing detachments are observed on the east flank of the segment. The westward relocations of the plate boundary appear to compensate for the asymmetry of accretion through detachment faulting, overall creating the same amount of lithosphere on both flanks of the ridge. We interpret the observed changes in the time of the accretionary processes to reflect a decrease of the melt supply over the last ∼6 Myr. Key Points The southern intra-transform ridge segment in the St. Paul transform fault system, over the last ∼6 Myr is dominated by detachment faulting Several detachments have been split and partly transferred to the opposite ridge flank through ridge axis relocation The change in the accretionary processes, from Oceanic Core Complexes to mantle exhumation, suggests a decrease in the time of the melt supply Plain Language Summary The generation of new seafloor at mid-ocean ridges where cold underlying mantle delivers low magma supply has not been investigated over the long term. Here we present the analysis of new bathymetry, gravity, and rock sampling data over such a ridge segment located within the St. Paul Transform Fault system in the Equatorial Mid-Atlantic Ridge, which allowed us to bring constraints on its structure and evolution over the last ∼6 Myr. We show that this area evolves differently from previously described ridge segments of similar spreading rate. We observe the remnants of very large normal faults called detachment faults, which have been active for very long times, forming domes called oceanic core complexes. The fault surfaces have been dissected by further extensional deformation, until the plate motion became accommodated along a new detachment fault formed west of the previous plate boundary. The emergence lines of the detachment faults are observed on the eastern flank of the ridge segment. We also observe a change in time of the structures, from typical oceanic core complexes to shorter ridges formed by the exhumation of mantle rocks. We interpret these changes to possibly reflect a decrease in the melt supply in the last 6 Myr. PY 2023 PD MAY SO Geochemistry Geophysics Geosystems SN 1525-2027 PU American Geophysical Union (AGU) VL 24 IS 5 UT 000999803300001 DI 10.1029/2023GC010870 ID 94960 ER EF