Crustal Accretion in a Slow Spreading Back‐Arc Basin: Insights From the Mado Megamullion Oceanic Core Complex in the Shikoku Basin

Abstract We use high-resolution and regional geophysical data to study a bathymetric high near the Mohns/Knipovich ridges junction, in the Norwegian-Greenland Sea. Near-seafloor magnetic data over hydrothermal site Loki’s Castle first support the basaltic nature of the seafloor. We then combine this result with regional magnetic and bathymetric considerations to investigate the crustal architecture in the vicinity of the junction. We show that the spreading asymmetry is insufficient to allow the development of Oceanic Core Complexes. Instead, this atypical off-axis hill is dominantly basaltic and should be interpreted as the first inside corner hogback structure identified along an active mid-ocean ridge system. Our conclusion tempers the definition of Oceanic Core Complex and underlines that bathymetric highs located off axis from slow-spreading centers cannot always be interpreted as such. This intermediate type of spreading paves the way to the introduction of a new class of oceanic structure referred to as Proto-Core Complexes.

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Geochemical Variation of Miocene Basalts within Shikoku Basin: Magma Source Compositions and Geodynamic Implications

Minerals ◽

10.3390/min11010025 ◽

2020 ◽

Vol 11 (1) ◽

pp. 25

Author(s):

Shuang-Shuang Chen ◽

Tong Hou ◽

Jia-Qi Liu ◽

Zhao-Chong Zhang

Keyword(s):

Japan Sea ◽

Isotopic Signature ◽

Magma Source ◽

Isotopic Compositions ◽

Enriched Mantle ◽

Shikoku Basin ◽

Depleted Mantle ◽

Parece Vela Basin ◽

Back Arc ◽

Ocean Ridge

Shikoku Basin is unique as being located within a trench-ridge-trench triple junction. Here, we report mineral compositions, major, trace-element, and Sr-Nd-Pb isotopic compositions of bulk-rocks from Sites C0012 (>18.9 Ma) and 1173 (13–15 Ma) of the Shikoku Basin. Samples from Sites C0012 and 1173 are tholeiitic in composition and display relative depletion in light rare earth elements (REEs) and enrichment in heavy REEs, generally similar to normal mid-ocean ridge basalts (N-MORB). Specifically, Site C0012 samples display more pronounced positive anomalies in Rb, Ba, K, Pb and Sr, and negative anomalies in Th, U, Nb, and Ta, as well as negative Nb relative to La and Th. Site 1173 basalts have relatively uniform Sr-Nd-Pb isotopic compositions, close to the end member of depleted mantle, while Site C0012 samples show slightly enriched Sr-Nd-Pb isotopic signature, indicating a possible involvement of enriched mantle 1 (EM1) and EM2 sources, which could be attributed to the metasomatism of the fluids released from the dehydrated subduction slab, but with the little involvement of subducted slab-derived sedimentary component. Additionally, the Shikoku Basin record the formation of the back-arc basin was a mantle conversion process from an island arc to a typical MORB. The formation of the Shikoku Basin is different from that of the adjacent Japan Sea and Parece Vela Basin, mainly in terms of the metasomatized subduction-related components, the nature of mantle source, and partial melting processes.

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Alteration processes recorded by back‐arc mantle peridotites from oceanic core complexes, Shikoku Basin, Philippine Sea

Island Arc ◽

10.1111/iar.12419 ◽

2021 ◽

Author(s):

Ken‐ichi Hirauchi ◽

Izumi Segawa ◽

Yui Kouketsu ◽

Yumiko Harigane ◽

Yasuhiko Ohara ◽

...

Keyword(s):

Philippine Sea ◽

Shikoku Basin ◽

Mantle Peridotites ◽

Alteration Processes ◽

Back Arc

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Shearing within lower crust during progressive retrogression: Structural analysis of gabbroic rocks from the Godzilla Mullion, an oceanic core complex in the Parece Vela backarc basin

Tectonophysics ◽

10.1016/j.tecto.2008.06.009 ◽

2008 ◽

Vol 457 (3-4) ◽

pp. 183-196 ◽

Cited By ~ 34

Author(s):

Yumiko Harigane ◽

Katsuyoshi Michibayashi ◽

Yasuhiko Ohara

Keyword(s):

Structural Analysis ◽

Lower Crust ◽

Backarc Basin ◽

Core Complex ◽

Oceanic Core Complex

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The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽

10.2138/gselements.17.1.23 ◽

2021 ◽

Vol 17 (1) ◽

pp. 23-28 ◽

Cited By ~ 1

Author(s):

Elisabetta Rampone ◽

Alessio Sanfilippo

Keyword(s):

Oceanic Lithosphere ◽

Passive Margin ◽

Crustal Material ◽

Crustal Accretion ◽

Mantle Dynamics ◽

Western Tethys ◽

Mantle Peridotites ◽

Slow Spreading ◽

Tethys Ocean ◽

Basaltic Crust

The Alpine–Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys.

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