Qin:

Kindly have a look at these links for insights:

http://usoceandiscovery.org/wp-content/uploads/2016/05/Christeson_ActiveMidOceanRidges.pdf

https://tos.org/oceanography/assets/docs/20-1_tivey.pdf

Best

Syed

Dear Zanghie: You posed a difficult question to answer. The expansion of the midoceanic ridges really doesnt cause changes in the sea water composition but in the sea water level, causing transgressions and flooding of continental platforms. Very long range changes in the ocean redox conditions are really related to the changes operating in the atmosphere, the most relevant was the "great oxygenation event of the Mesoproterozoic", due to the photosynthesis by cyanobacteria. In shorter periods, such as the Mesozoic-Tertiary, the chemical changes are caused by the sea water altering the MORB basalts (and submarine island arcs and seamounts), in what is called sea floor weathering and sea floor "metamorphism" (which actually is metasomatism..). The latter process occurs at a very large scale, even generating apparent regional "isogrades" of zeolite, greenschist and amphibolite facies in the oceanic crust to depths over 6-7 km below the sea floor; also all sorts of deeply metasomatised rocks are produces such as rodingites, serpentinites, chloritocites, epidosites, spilites and keratophyres. Another well known process generates Cyprus-type massive volcanogenic sulfides related to the metasomatic alteration of oceanic crust too. So, I believe that the effect is backwards: it is not the sea composition what changes but the oceanic crust composition and mineralogy! With regards. Sebastian.

There will a change in composition of seawater...

Spreading centers are very good location for hydrothermal and seafloor massive sulfide deposits. Hydrothermal vents obviously release a lot of material and it react with seawater and those slurry like amterial are resposible for the formation of FE-Mn encrust.

Interaction of seawater near to hydrothermal will be different.

Dear Syed Abbas Jafar, Sebastián Grande, Ashkan Vafadar, Drishya Girishbai,

Thanks very much for your great answers. Because my attention is mainly about the deposits of evaporites, I don`t think it has the ability to change all global seawater by MORB-RELEASE frequently. But, there are two papers（Heinrich D. Holland et al., 1996; Lawrence A. Hardie, 1996）, which give me a viewpoint that different type of marine evaporites in different geological times are caused by "seawater-basalt interaction", "seafloor generation rate" and "dolomitization". It`s remain difficult to difinite quantities of contributions by MORB. I believe it is a complicated exchange system.

Best wishe,

Qin

The volcanoes of the ridges must be responsible for the halogen elements dissolved in sea water. The combine with the "salts" that come from weathering to form the evaporites, I would think. Since there are thousands of volcanoes under the sea they affect the composition of seawater globally.