Igneous stratigraphy and rock-types from a deep transect of the gabbroic lower crust of the Atlantis Bank core complex (SW Indian Ridge); preliminary results from IODP Expedition 360

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Author(s): Sanfilippo, Alessio; France, Lyderic; Ghosh, Biswajit; Liu, Chaun-Zhou; Morishita, Tomoaki; Natland, James H.; Dick, Henry J.; MacLeod, Christopher J.
International Ocean Discovery Program, Expedition 360 Scientists
Author Affiliation(s): Primary:
Kanazawa University, Kanazawa, Japan
Other:
University of Pavia, Italy
Centre de Recherches Pétrographiques et Géochimiques, France
University of Calcutta, India
Chinese Academy of Sciences, Institute of Geology and Geophysics, China
University of Miami, United States
Woods Hole Oceanographic Institution, United States
Cardiff University, United Kingdom
Texas A&M University, United States
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: International Ocean Discovery Program (IODP) Expedition 360 represents the first leg of a multi-phase drilling programme ('SloMo' project) aimed at investigating the nature of the lower crust and Moho at slow spreading ridges. As an initial phase of the SloMo project, IODP Exp. 360 intended to recover a representative transect of the lower oceanic crust formed at Atlantis Bank, an oceanic core complex on the SW Indian Ridge. During this expedition, 89 cores of gabbroic rocks were recovered at Hole U1473A, drilled to 789.7 m below seafloor. This hole was subsequently deepened to 809.4 mbsf during transit Expedition 362T, which recovered additional 7 cores. The gabbroic section recovered at Hole U1473A consists of several types of gabbro, diabase, and felsic veins. The main lithology is dominated by olivine gabbro (76.5% in abundance), followed by gabbro containing 1-2% oxide (9.5%), gabbro with >2% oxide (7.4%), gabbro sensu stricto (5.1%), felsic veins (1.5%) and diabase (<0.5%). The different lithologies appear randomly distributed throughout the section, although oxide abundance seems to decrease slightly downhole, except for the lowermost intervals where oxide gabbros are more abundant. Based on changes in rock types, grain size, texture, and the occurrence of felsic material, we identified eight lithologic units, which locally define separate geochemical trends. Each unit is characterized by meter-scale heterogeneity which classically characterizes gabbros formed at slow spreading ridges. Reaction textures in olivine gabbros, crosscutting relationships between oxide gabbros and host rocks, the presence of intrusive to sutured contacts, igneous layering and the widespread occurrence of felsic veins and segregations indicate that the evolution of this section was controlled by complicated interactions of magmatic processes, e.g., fractional crystallization, melt-rock reaction, late-stage melt migration, which were active in a crystal mush formed by multiple injections of magma. This contribution describes the main features of these rocks and discusses the complexity of the igneous processes producing this ∼800 m-long transect of oceanic crust that was formed in a robust magmatic segment of an ultraslow spreading ridge.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 05 Petrology, Igneous and Metamorphic; Atlantis Bank; Expedition 360; Gabbros; IODP Site U1473; Igneous rocks; Indian Ocean; International Ocean Discovery Program; Lithostratigraphy; Plutonic rocks; SloMo; Southwest Indian Ridge
Coordinates: S324222 S324222 E0571641 E0571641
S324225 S324220 E0571645 E0571635
Record ID: 2017068229
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