On- and off-axis chemical heterogeneities along the South Atlantic Mid-Ocean-Ridge (5–11°S): Shallow or deep recycling of ocean crust and/or intraplate volcanism?

2011 ◽  
Vol 306 (1-2) ◽  
pp. 86-97 ◽  
Author(s):  
Kaj Hoernle ◽  
Folkmar Hauff ◽  
Thomas F. Kokfelt ◽  
Karsten Haase ◽  
Dieter Garbe-Schönberg ◽  
...  
Keyword(s):  
South Atlantic ◽  
The South ◽  
Ocean Crust ◽  
Intraplate Volcanism ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Helium isotope geochemistry of mid-ocean ridge basalts from the South Atlantic

1992 ◽  
Vol 110 (1-4) ◽  
pp. 133-147 ◽  
Author(s):  
David W. Graham ◽  
William J. Jenkins ◽  
Jean-Guy Schilling ◽  
Geoffrey Thompson ◽  
Mark D. Kurz ◽  
...  
Keyword(s):  
Isotope Geochemistry ◽  
South Atlantic ◽  
Helium Isotope ◽  
The South ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

scholarly journals Sr–Nd–Pb–Hf Isotopic Constraints on the Mantle Heterogeneities beneath the South Mid-Atlantic Ridge at 18–21°S

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1010
Author(s):  
Yun Zhong ◽  
Xu Zhang ◽  
Zhilei Sun ◽  
Jinnan Liu ◽  
Wei Li ◽  
...  
Keyword(s):  
Isotopic Data ◽  
The South ◽  
Mantle Heterogeneities ◽  
Depleted Mantle ◽  
Mid Ocean Ridge ◽  
Trace Elemental ◽  
Heterogeneous Mantle ◽  
Mid Atlantic Ridge ◽  
St Helena ◽  
Ocean Ridge

In an attempt to investigate the nature and origin of mantle heterogeneities beneath the South Mid-Atlantic Ridge (SMAR), we report new whole-rock Sr, Nd, Pb, and Hf isotopic data from eight basalt samples at four dredge stations along the SMAR between 18°S and 21°S. Sr, Nd, and Pb isotopic data from SMAR mid-ocean ridge basalts (MORBs) at 18–21°S published by other researchers were also utilized in this study. The SMAR MORBs at 18–21°S feature the following ratio ranges: 87Sr/86Sr = 0.70212 to 0.70410, 143Nd/144Nd = 0.512893 to 0.513177, 206Pb/204Pb = 18.05 to 19.50, 207Pb/204Pb = 15.47 to 15.71, 208Pb/204Pb = 37.87 to 38.64, and 176Hf/177Hf = 0.283001 to 0.283175. The 87Sr/86Sr, 143Nd/144Nd, 206Pb/204Pb, and 176Hf/177Hf ratios of these MORBs varied considerably along the SMAR axis. The variable compositions of the Sr–Nd–Pb–Hf isotopes, combined with the corresponding whole-rock major and trace elemental abundances reported in previous studies, suggest that the SMAR MORBs at 18–21°S were probably derived from a heterogeneous mantle substrate related to a mixture of depleted mantle (DM) materials with a small amount (but variable input) of HIMU (high-μ, where μ = 238U/204Pb)- and enriched (EMII)-type materials. The HIMU-type materials likely originated from the proximal St. Helena plume and may have been transported through “pipe-like inclined sublithospheric channels” into the SMAR axial zone. The EMII-type materials possibly originated from a recycled metasomatized oceanic crust that may have been derived from the early dispersion of other plume heads into the subcontinental asthenosphere prior to the opening of the South Atlantic Ocean. In addition, the contributions of subducted sediments, continental crust, and subcontinental lithospheric mantle components to the formation of the SMAR MORBs at 18–21°S may be nonexistent or negligible.

Jump event of mid-ocean ridge during the eastern subbasin evolution of the South China Sea

2016 ◽  
Vol 4 (3) ◽  
pp. SP67-SP77 ◽  
Author(s):  
Yan Qiu ◽  
Yingmin Wang ◽  
Wenkai Huang ◽  
Weiguo Li ◽  
Haiteng Zhuo ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Seafloor Spreading ◽  
The South China Sea ◽  
Magnetic Data ◽  
The South ◽  
Tectonic Event ◽  
China Sea ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

The South China Sea is one of the largest marginal seas in the Western Pacific region, and it has been widely accepted that the evolution of the basin and the development of its oceanic crusts is closely linked to seafloor spreading. A great controversy, however, is around whether or not there was a jump of mid-ocean ridges during seafloor spreading, particularly in the eastern South China Sea subbasin. A tectonostratigraphic interpretation using high-resolution seismic data demonstrated that: (1) a southward jump event of the mid-ocean ridge took place in the eastern subbasin during the seafloor spreading; (2) the orientation of the mid-ocean ridge had dramatically changed after the event resulting in that the abandoned mid-ocean ridge is along an east–west direction, whereas the younger one is generally east–northeast/west–southwest oriented; (3) the corresponding surface caused by the jump tectonic event and the pre-event sequence can be traced throughout the earlier formed oceanic crust; and (4) paleo-magnetic data showed that the event occurred at approximately 25–23.8 Ma. The results of this study could be used to better understand the evolution and filling of the South China Sea and other associated marginal basins.

scholarly journals Abiotic hydrogen (H2) sources and sinks near the Mid-Ocean Ridge (MOR) with implications for the subseafloor biosphere

2020 ◽  
Vol 117 (24) ◽  
pp. 13283-13293 ◽  
Author(s):  
Stacey L. Worman ◽  
Lincoln F. Pratson ◽  
Jeffrey A. Karson ◽  
William H. Schlesinger
Keyword(s):  
Control Volume ◽  
Preliminary Investigation ◽  
Oceanic Lithosphere ◽  
Analytical Framework ◽  
Ocean Crust ◽  
Global Estimate ◽  
Mid Ocean Ridge ◽  
Free Hydrogen ◽  
Microbial Consumption ◽  
Ocean Ridge

Free hydrogen (H2) is a basal energy source underlying chemosynthetic activity within igneous ocean crust. In an attempt to systematically account for all H2within young oceanic lithosphere (<10 Ma) near the Mid-Ocean Ridge (MOR), we construct a box model of this environment. Within this control volume, we assess abiotic H2sources (∼6 × 1012mol H2/y) and sinks (∼4 × 1012mol H2/y) and then attribute the net difference (∼2 × 1012mol H2/y) to microbial consumption in order to balance the H2budget. Despite poorly constrained details and large uncertainties, our analytical framework allows us to synthesize a vast body of pertinent but currently disparate information in order to propose an initial global estimate for microbial H2consumption within young ocean crust that is tractable and can be iteratively improved upon as new data and studies become available. Our preliminary investigation suggests that microbes beneath the MOR may be consuming a sizeable portion (at least ∼30%) of all produced H2, supporting the widely held notion that subseafloor microbes voraciously consume H2and play a fundamental role in the geochemistry of Earth’s ocean–atmosphere system.

A discussion concerning the floor of the northwest Indian Ocean - Heat flow and magnetic profiles on the Mid-Indian Ocean Ridge

1966 ◽  
Vol 259 (1099) ◽  
pp. 262-270 ◽  
Keyword(s):  
Indian Ocean ◽  
Heat Flow ◽  
Magnetic Anomaly ◽  
Lateral Displacement ◽  
High Heat ◽  
South Atlantic ◽  
High Heat Flow ◽  
The South ◽  
Ridge Crest ◽  
Ocean Ridge

Sixty heat flow values were measured along nine profiles across the Mid-Indian Ocean Ridge. The results were roughly of the same character as the ones previously reported for the South Atlantic Ridge. The correlation of high heat flow with the centre of the ridge was less pronounced. The scatter of heat flow values when plotted as a function of distance from the ridge was even greater. The average of all values is 1.35 /tcal cm -2 s -1 , indicating that over the surveyed area the heat flow is normal. The cause for the low values on the flanks of the ridge remains unknown. A right lateral displacement of about 200 km across the Vema Trench was measured from the offset of the magnetic anomaly on the ridge crest.

scholarly journals Geochemistry and Mineralogy of Basalts from the South Mid-Atlantic Ridge (18.0°–20.6°S): Evidence of a Heterogeneous Mantle Source

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 659 ◽  
Author(s):  
Yun Zhong ◽  
Weiliang Liu ◽  
Zhilei Sun ◽  
Chris Yakymchuk ◽  
Kefa Ren ◽  
...  
Keyword(s):  
Magma Mixing ◽  
Primitive Mantle ◽  
Spreading Ridge ◽  
Spinel Lherzolite ◽  
The South ◽  
Depleted Mantle ◽  
Mid Ocean Ridge ◽  
Heterogeneous Mantle ◽  
Mid Atlantic Ridge ◽  
Ocean Ridge

The South Mid-Atlantic Ridge is a typical slow-spreading ridge that represents a modern example to understand mantle composition and the evolution of mid-ocean ridge magmatism. In this paper, we investigate basalt samples dredged from four locations along the South Mid-Atlantic Ridge ranging from 18.0° to 20.6°S. The basalts belong to the tholeiitic series and exhibit normal mid-ocean ridge basalt (N-MORB) geochemical features with variable enrichments of Rb, Th, U, and Pb and depletions of Ba and Sr relative to primitive mantle. Some samples have negative Nb–Ta anomalies whereas others have positive Na–Ta anomalies to average N-MORBs. Plagioclase phenocrysts, microphenocrysts, and microlites occur in the in the matrix; phenocrysts and microphenocrysts are bytownite and labradorite in composition. Olivine phenocrysts are forsterite (Fo87 to Fo96). Chemical zoning in phenocrysts are interpreted to record crystal fractionation and magma mixing. Cores of plagioclase phenocrysts have higher anorthite values (An72–83) and estimated crystallization temperatures (~1180–1240 °C) that may suggest a xenocrystic origin. The lower anorthite proportions of rims of plagioclase phenocrysts (An65–71) and microphenocrysts (An54–72) yield lower estimated crystallization temperatures of ~1090–1120 °C and ~980–1060 °C, respectively. Rims of plagioclase phenocrysts and microphenocrysts may be generated in different environments such as magma chambers or magma channels, respectively. The basalt samples probably originated from partial melting of a depleted mantle spinel lherzolite source with a minor contribution of enriched materials possibly derived from the Saint Helena plume and subcontinental lithospheric mantle in the asthenosphere. Variable compositions of the basalt samples suggest heterogeneous mantle that includes depleted and enriched components at the South Mid-Atlantic Ridge between 18.0°–20.6°S.

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