TY - JOUR

T1 - Dynamic accretion beneath a slow-spreading ridge segment

T2 - IODP Hole 1473A and the Atlantis Bank Oceanic Core Complex

AU - Dick, H. J. B.

AU - MacLeod, C. J.

AU - Blum, P.

AU - Abe, N.

AU - Blackman, D. K.

AU - Bowles, J. A.

AU - Cheadle, M. J.

AU - Cho, K.

AU - Ciazela, J.

AU - Deans, J. R.

AU - Edgcomb, V. P.

AU - Ferrando, C.

AU - France, L.

AU - Ghosh, B.

AU - Ildefonse, B.

AU - John, B.

AU - Kendrick, M. A.

AU - Koepke, J.

AU - Leong, J. A. M.

AU - Liu, C.

AU - Ma, Q.

AU - Morishita, T.

AU - Morris, A.

AU - Natland, J. H.

AU - Nozaka, T.

AU - Pluemper, O.

AU - Sanfilippo, A.

AU - Sylvan, J. B.

AU - Tivey, M. A.

AU - Tribuzio, R.

AU - Viegas, G.

N1 - Funding Information: The authors would like to acknowledge the Crew, and operational and technical staff of the JOIDES Resolution, particularly the ships master, Terry Skinner, and Offshore Installation Manager, James Samuel McLelland, as well as JRSO shipboard personnel and technical representatives, particularly Stephen Midgley, operations superintendent, and Roy Davis, laboratory officer. Support for all science personnel was provided by members of the Ocean Discovery Program at-sea, and post-expedition. The first author wishes to also recognize grants OCE1434452 and OCE1637130 from The National Science Foundation (NSF) for synthesis of the Atlantis Bank site survey data and post-cruise rock analysis and for analysis of Expedition 360 and 362T cores and data. Additional support was also gratefully received from The Investment in Science Fund at WHOI. The paper was beneficially reviewed by Jack Casey and one anonymous reviewer, for which we are grateful. Stephen Parman acted as Editor and provided many useful suggestions that improved the manuscript. Thank you Steve. There are no real or perceived financial conflicts for any author. The data used in this paper may be found in Dick et al. (), MacLeod, Dick, Blum, and Expedition-360-Scientists (), and https://www.iodp.org/resources/access-data-and-samples.

PY - 2020/1/23

Y1 - 2020/1/23

N2 - 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-km2 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.

AB - 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-km2 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.

KW - crust-mantle boundary

KW - crustal accretion

KW - lower ocean crust

KW - Ocean core complex

KW - ocean drilling

KW - SW Indian Ridge

UR - http://www.scopus.com/inward/record.url?scp=85076608107&partnerID=8YFLogxK

U2 - 10.1029/2018JB016858

DO - 10.1029/2018JB016858

M3 - Article

AN - SCOPUS:85076608107

VL - 124

SP - 12631

EP - 12659

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 12

ER -