The role of axial discontinuities in oceanic crustal evolution: Evidence from elemental and Mo Sr Nd Pb Hf isotopic compositions of rock suites from the Southwest Indian Ridge (42°–53°E)

Abstract Mantle source heterogeneity and magmatic processes have been widely studied beneath most parts of the Southwest Indian Ridge (SWIR). But less is known from the newly recovered mid-ocean ridge basalts from the Dragon Bone Amagmatic Segment (53°E, SWIR) and the adjacent magmatically robust Dragon Flag Segment. Fresh basalt glasses from the Dragon Bone Segment are clearly more enriched in isotopic composition than the adjacent Dragon Flag basalts, but the trace element ratios of the Dragon Flag basalts are more extreme compared with average mid-ocean ridge basalts (MORB) than the Dragon Bone basalts. Their geochemical differences can be explained only by source differences rather than by variations in degree of melting of a roughly similar source. The Dragon Flag basalts are influenced by an arc-like mantle component as evidenced by enrichment in fluid-mobile over fluid-immobile elements. However, the sub-ridge mantle at the Dragon Flag Segment is depleted in melt component compared with a normal MORB source owing to previous melting in the subarc. This fluid-metasomatized, subarc depleted mantle is entrained beneath the Dragon Flag Segment. In comparison, for the Dragon Bone axial basalts, their Pb isotopic compositions and their slight enrichment in Ba, Nb, Ta, K, La, Sr and Zr and depletion in Pb and Ti concentrations show resemblance to the Ejeda–Bekily dikes of Madagascar. Also, Dragon Bone Sr and Nd isotopic compositions together with the Ce/Pb, La/Nb and La/Th ratios can be modeled by mixing the most isotopically depleted Dragon Flag basalts with a composition within the range of the Ejeda–Bekily dikes. It is therefore proposed that the Dragon Bone axial basalts, similar to the Ejeda–Bekily dikes, are sourced from subcontinental lithospheric Archean mantle beneath Gondwana, pulled from beneath the Madagascar Plateau. The recycling of the residual subarc mantle and the subcontinental lithospheric mantle could be related to either the breakup of Gondwana or the formation and accretion of Neoproterozoic island arc terranes during the collapse of the Mozambique Ocean, and is now present beneath the ridge.

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Heterogeneous upper mantle Ne, Ar and Xe isotopic compositions and a possible Dupal noble gas signature recorded in basalts from the Southwest Indian Ridge

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2012.10.017 ◽

2012 ◽

Vol 359-360 ◽

pp. 227-239 ◽

Cited By ~ 39

Author(s):

R. Parai ◽

S. Mukhopadhyay ◽

J.J. Standish

Keyword(s):

Upper Mantle ◽

Noble Gas ◽

Southwest Indian Ridge ◽

Isotopic Compositions ◽

Indian Ridge

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Isotopic Compositions of Helium and Argon in Hydrothermal Sulfides from Southwest Indian Ridge and their Geological Inferences

Acta Geologica Sinica - English Edition ◽

10.1111/1755-6724.12380_37 ◽

2014 ◽

Vol 88 (s2) ◽

pp. 1298-1299

Author(s):

Yan WANG ◽

Xiaoming SUN ◽

Zhongwei WU ◽

Xiguang DENG

Keyword(s):

Southwest Indian Ridge ◽

Isotopic Compositions ◽

Indian Ridge ◽

Hydrothermal Sulfides

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Os isotopic compositions of MORBs from the ultra-slow spreading Southwest Indian Ridge: Constraints on the assimilation and fractional crystallization (AFC) processes

Lithos ◽

10.1016/j.lithos.2013.07.020 ◽

2013 ◽

Vol 179 ◽

pp. 28-35 ◽

Cited By ~ 15

Author(s):

Alexandra Yang Yang ◽

Tai-Ping Zhao ◽

Mei-Fu Zhou ◽

Xi-Guang Deng ◽

Gui-Qin Wang ◽

...

Keyword(s):

Fractional Crystallization ◽

Southwest Indian Ridge ◽

Isotopic Compositions ◽

Slow Spreading ◽

Indian Ridge

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Macrofaunal burrowing enhances deep-sea carbonate lithification on the Southwest Indian Ridge

Biogeosciences ◽

10.5194/bg-15-6387-2018 ◽

2018 ◽

Vol 15 (21) ◽

pp. 6387-6397 ◽

Cited By ~ 1

Author(s):

Hengchao Xu ◽

Xiaotong Peng ◽

Shun Chen ◽

Jiwei Li ◽

Shamik Dasgupta ◽

...

Keyword(s):

Deep Sea ◽

Driving Force ◽

Carbonate Rocks ◽

Sedimentary Rock ◽

Southwest Indian Ridge ◽

Ocean Ridges ◽

Tremendous Amount ◽

Indian Ridge ◽

Carbonate Area

Abstract. Deep-sea carbonates represent an important type of sedimentary rock due to their effect on the composition of the upper oceanic crust and their contribution to deep-sea geochemical cycles. However, the role of deep-sea macrofauna in carbonate lithification remains poorly understood. A large lithified carbonate area, characterized by thriving benthic faunas and a tremendous amount of burrows, was discovered in 2008, blanketing the seafloor of the ultraslowly spreading Southwest Indian Ridge (SWIR). Benthic inhabitants – including echinoids, polychaetes, gastropods and crustaceans – are abundant in this carbonate lithified area. The burrowing features within these carbonate rocks, as well as the factors that may influence deep-sea carbonate lithification, were examined. We suggest that burrowing in these carbonate rocks enhances deep-sea carbonate lithification. We propose that active bioturbation may trigger the dissolution of the original calcite and thus accelerate deep-sea carbonate lithification on mid-ocean ridges. Macrofaunal burrowing provides a novel driving force for deep-sea carbonate lithification at the seafloor, illuminating the geological and biological importance of bioturbation in global deep-sea carbonate rocks.

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