Dynamic accretion beneath a slow-spreading ridge segment: IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex

Henry J.B. J B Dick (1) , Christopher J. J Macleod (2) , Peter Blum (3) , Natsue Abe (4) , Donna K. K Blackman (5) , Julie A. Bowles (6) , Mike J Cheadle (7) , K Cho (8) , J Ciążela (9) , Jeremy R Deans (10) , Virginia P P Edgcomb (1) , Carlotta Ferrando (11) , Lyderic France (12) , Biswajit Ghosh (13) , Benoit Ildefonse (11) , Barbara John (7) , Mark A. A Kendrick (14) , Juergen Koepke (15) , J. A. M. Leong (16) , Chuanzhou Liu (17) , Q. Ma (18) , Tomoaki Morishita (19) , Antony Morris (20) , James H. H Natland (21) , Toshio Nozaka (22) , Oliver Pluemper (23) , Alessio Sanfilippo (24) , Jason B Sylvan (25) , Maurice A Tivey (1) , Ricardo Tribuzio (24) , Gustavo Viegas (26)

1 WHOI - Woods Hole Oceanographic Institution
2 School of Earth and Ocean Sciences [Cardiff]
3 Integrated Ocean Drilling Program
4 JAMSTEC - Japan Agency for Marine-Earth Science and Technology
5 SIO - UC San Diego - Scripps Institution of Oceanography
6 University of Wisconsin - Milwaukee
7 UW - University of Wyoming
8 Pukyong National University
9 Space Research Centre [Torun]
10 USM - University of Southern Mississippi
11 Géosciences Montpellier
12 CRPG - Centre de Recherches Pétrographiques et Géochimiques
13 University of Calcutta
14 ANU - Australian National University
15 Leibniz Universität Hannover=Leibniz University Hannover
16 ASU - Arizona State University [Tempe]
17 CAS - Chinese Academy of Sciences [Beijing]
18 Tongji University
19 KU - Kanazawa University
20 Plymouth University
21 Marine and Atmospheric Chemistry Division [Miami]
22 Okayama University
23 Universiteit Utrecht / Utrecht University [Utrecht]
24 UNIPV - Università degli Studi di Pavia = University of Pavia
25 Texas A&M University [College Station]
26 UnB - Universidade de Brasilia [Brasília]

809 deep IODP Hole U1473A at Atlantis Bank, SWIR, is 2.2 km from 1,508-m Hole 735B and 1.4 from 158-m Hole 1105A. With mapping, it provides the first 3-D view of the upper levels of a 660-km 2 lower crustal batholith. It is laterally and vertically zoned, representing a complex interplay of cyclic intrusion, and ongoing deformation, with kilometer-scale upward and lateral migration of interstial melt. Transform wall dives over the gabbro-peridotite contact found only evolved gabbro intruded directly into the mantle near the transform. There was no high-level melt lens, rather the gabbros crystallized at depth, and then emplaced into the zone of diking by diapiric rise of a crystal mush followed by crystal-plastic deformation and faulting. The residues to mass balance the crust to a parent melt composition lie at depth below the center of the massif-likely near the crust-mantle boundary. Thus, basalts erupted to the seafloor from >1,550 mbsf. By contrast, the Mid-Atlantic Ridge lower crust drilled at 23°N and at Atlantis Massif experienced little high-temperature deformation and limited late-stage melt transport. They contain primitive cumulates and represent direct intrusion, storage, and crystallization of parental MORB in thinner crust below the dike-gabbro transition. The strong asymmetric spreading of the SWIR to the south was due to fault capture, with the northern rift valley wall faults cutoff by a detachment fault that extended across most of the zone of intrusion. This caused rapid migration of the plate boundary to the north, while the large majority of the lower crust to spread south unroofing Atlantis Bank and uplifting it into the rift mountains.

Domaines: Géophysique [physics.geo-ph]; Stratigraphie

Henry J.B. J B Dick, Christopher J. J Macleod, Peter Blum, Natsue Abe, Donna K. K Blackman, et al.. Dynamic accretion beneath a slow-spreading ridge segment: IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex. Journal of Geophysical Research : Solid Earth, 2019, 124 (12), pp.12631-12659. ⟨10.1029/2018JB016858⟩. ⟨hal-02384032v2⟩