scholarly journals Global variation of seismic energy release with oceanic lithosphere age

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nicolás Pinzón ◽  
Carlos A. Vargas
Keyword(s):  
Cross Sections ◽  
Thermal Evolution ◽  
Seismic Energy ◽  
Oceanic Lithosphere ◽  
Physical Factors ◽  
Additional Tool ◽  
Mid Ocean Ridge ◽  
Mid Atlantic Ridge ◽  
Spreading Rates ◽  
Ocean Ridge

AbstractVariations in Mid Ocean Ridge seismicity with age provide a new tool to understand the thermal evolution of the oceanic lithosphere. The sum of seismic energy released by earthquakes during a time, and for an area, is proportional to its lithospheric age. Asthenospheric temperatures emerge on ridge centers with new crust resulting in high seismic activity; thus, the energy released sum is highest on the young lithosphere and decreases with age. We propose a general model that relates the systematic variation of seismic energy released with the lithospheric age. Our analysis evaluates the main physical factors involved in the changes of energy released sum with the oceanic lithosphere age in MOR systems of different spreading rates. These observations are substantiated based on three cross-sections of the East Pacific Rise, six sections in the Mid Atlantic Ridge, and three profiles in the Central Indian Ridge. Our global model provides an additional tool for understanding tectonic processes, including the effects of seismicity and mid-plate volcanism, and a better understanding of the thermal evolution for the young oceanic lithosphere.

Subduction initiation-induced rapid emplacement of garnet-bearing peridotites at a nascent forearc: Petrological and Os-Li isotopic evidence from the Purang ophiolite, Tibet

2021 ◽  
Author(s):  
Xiao-Han Gong ◽  
Ji-Feng Xu ◽  
Ren-Deng Shi ◽  
Ben-Xun Su ◽  
Qi-Shuai Huang ◽  
...  
Keyword(s):  
Oceanic Lithosphere ◽  
Garnet Peridotite ◽  
Chemical Compositions ◽  
Close Link ◽  
Geological Evidence ◽  
Subduction Initiation ◽  
Mid Ocean Ridge ◽  
Rapid Ascent ◽  
Melt Percolation ◽  
Ocean Ridge

Garnet-bearing peridotites commonly occur in the deeper parts of mature or thickened oceanic lithosphere, and are rarely exhumed and emplaced onto the seafloor. The Purang ophiolitic peridotites in south Tibet contain rare symplectite pseudomorphs after garnet, offering a unique window into the still poorly understood evolution of the deep oceanic lithosphere. Here, integrated petrologic and Os-Li isotopic data are used to constrain the evolution and dynamics of emplacement for these garnet peridotite protoliths. The Purang peridotites show wide variations of chemical compositions (spinel Cr#: 0.2−0.8) and Os model ages (up to 2.0 Ga), thus representing a piece of heterogeneous oceanic mantle lithosphere. Dunite channels show two distinctive groups of Cr# of spinels and Os-isotope compositions, with the low- to medium-Cr# (0.2−0.6) and high-Cr# (0.7−0.8) dunites reflecting the reaction of host lherzolites/harzburgites with percolating mid-ocean ridge basalt−like and boninitic melts, respectively. This confirms recent subduction initiation-related melt percolation in the Purang peridotites. Coexisting olivines and pyroxenes in the peridotites show systematic Li elemental and isotopic disequilibrium, suggesting fast cooling of the peridotites to Li closure temperature shortly after the melt percolations, likely during exhumation of the peridotites onto the seafloor. This supports a close link between subduction initiation and tectonic emplacement of the Purang peridotites. Combined with other geological evidence, we suggest the Purang peridotites may originate from the deep part of old, thick oceanic lithosphere of the Neo-Tethys. This thick oceanic lithosphere was progressively weakened and thinned likely during widespread plume-lithosphere interaction, triggering the transformation of garnet peridotite protoliths to spinel peridotites. Subsequently, initiation of a new subduction zone along the lithospheric weakness caused rapid ascent and emplacement of the Purang peridotites at a nascent forearc.

Fluids in Submarine Mid-Ocean Ridge Hydrothermal Settings

Elements ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 389-394
Author(s):  
Esther M. Schwarzenbach ◽  
Matthew Steele-MacInnis
Keyword(s):  
Heat Budget ◽  
Oceanic Lithosphere ◽  
Life Forms ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Early Earth ◽  
Geologic Time ◽  
Mid Ocean Ridge ◽  
Time Changes ◽  
Ocean Ridge

Seawater interaction with the oceanic lithosphere crucially impacts on global geochemical cycles, controls ocean chemistry over geologic time, changes the petrophysical properties of the oceanic lithosphere, and regulates the global heat budget. Extensive seawater circulation is expressed near oceanic ridges by the venting of hydrothermal fluids through chimney structures. These vent fluids vary greatly in chemistry, from the metal-rich, acidic fluids that emanate from “black smokers” at temperatures up to 400 °C to the metal-poor, highly alkaline and reducing fluids that issue from the carbonate–brucite chimneys of ultramafic-hosted systems at temperatures below 110 °C. Mid-ocean ridge hydrothermal systems not only generate signifi-cant metal resources but also host unique life forms that may be similar to those of early Earth.

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.

scholarly journals Geothermal heating and episodic cold-seawater intrusions into an isolated ridge-flank basin near the Mid-Atlantic Ridge

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Keir Becker ◽  
Richard E. Thomson ◽  
Earl E. Davis ◽  
Heinrich Villinger ◽  
C. Geoffrey Wheat
Keyword(s):  
Bottom Water ◽  
Ocean Bottom ◽  
Geothermal Heat ◽  
Bottom Water Temperature ◽  
Geothermal Heating ◽  
Mid Ocean Ridge ◽  
Before And After ◽  
Bottom Waters ◽  
Mid Atlantic Ridge ◽  
Ocean Ridge

AbstractSix-year records of ocean bottom water temperatures at two locations in an isolated, sedimented deep-water (∼4500 m) basin on the western flank of the mid-Atlantic Ridge reveal long periods (months to >1 year) of slow temperature rises punctuated by more rapid (∼1 month) cooling events. The temperature rises are consistent with a combination of gradual heating by the geothermal flux through the basin and by diapycnal mixing, while the sharper cooling events indicate displacement of heated bottom waters by incursions of cold, dense bottom water over the deepest part of the sill bounding the basin. Profiles of bottom water temperature, salinity, and oxygen content collected just before and after a cooling event show a distinct change in the water mass suggestive of an incursion of diluted Antarctic Bottom Water from the west. Our results reveal details of a mechanism for the transfer of geothermal heat and bottom water renewal that may be common on mid-ocean ridge flanks.

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.

4. Subduction of oceanic lithosphere

2015 ◽  
pp. 53-76
Author(s):  
Peter Molnar
Keyword(s):  
Oceanic Lithosphere ◽  
Great Depth ◽  
Continental Margins ◽  
Island Arcs ◽  
The Andes ◽  
Mid Ocean Ridge ◽  
Subducting Plate ◽  
Ocean Ridge ◽  
Large Earthquakes ◽  
Adjacent Rock

‘Subduction of oceanic lithosphere’ begins with the notion that for the Earth not to expand, the sum total of new lithosphere made at a spreading centre (or mid-ocean ridge) must be matched by the removal, by subduction, of an equal amount of lithosphere elsewhere. The subduction process is asymmetric: one plate will slide beneath the other at island arcs and continental margins like the Andes of South America. Before it plunges beneath the island arc, the subducting plate of lithosphere bends down gently to cause a deep-sea trench. The subducting plate slides beneath the region between the trench and volcanoes, commonly in large earthquakes, and plunges to great depth, pulled down by gravity acting on the dense slab of subducted lithosphere. Water carried to depth by the subducting plate lowers the melting temperature of the adjacent rock and enables volcanoes to form.

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