We report new estimates of transport rates for H2O and Cl between the mantle and surface reservoirs. Our estimates take into consideration alteration of oceanic crust, especially that of plutonic rocks, and possible subduction of sediments. The effect of (hydrothermal) alteration on the Cl budget seems to be negligible, but the effect on the H2O budget is significant. Altered oceanic crust (excluding sediments) contains about 10 times as much H2O as the unaltered crust, and its subduction may result in a net transport of H2O to the upper mantle in subduction zones. However, the rate of expulsion of H2O from the mantle by subduction-zone magmatism is comparable to the amount released by ridge magmatism, and is only about 10% of the amount subducted. Therefore, about 90% of the subducted H2O must be returned to the mantle or returned to the crust by other processes. In addition, subduction of oceanic sediments to mantle depths will result in 1. (1) a further increase in the return rate of H2O to the mantle reservoir, 2. (2) possible net transfer of Cl to the mantle, depending on the rate of pore water expulsion.
|Original language||English (US)|
|Number of pages||12|
|Journal||Geochimica et Cosmochimica Acta|
|State||Published - Sep 1983|
Bibliographical noteFunding Information:
,4cknow[~~g~m~ffts-An early version of the paper formed a chapter of lto’s Ph.D. thesis. A similar, early version was presented by Harris at 1979 IUGG Assembly held at Canberra, Australia. Two later versions were presented by Ito at the Seventh Symposium on Geochemical Cycles held in 1980 at Atlanta, GA, and at the LPI Topical Conference on Planetary Volatiles held in 1982 at Alexandria, MN. Yet another version was presented by Anderson at the 1982 AGU Spring Meeting. Parts of the paper were prepared during Ito’s stay as a Carnegie Fellow at the Department of Terrestrial Magnetism, Carnegie Institution of Washington, and were finally completed at the University of Minnesota. Harris gratefully acknowledges support from American Geophysical Union and International Association of Meteorology and Atmospheric Physics (IAMAP) used to defray travel expenses to attend the IUGC meeting in Canberra. The work was partially supported by NSF grant, No. EAR 76-15016 to Anderson (University of Chicago). We thank J. G. Schilling, J. R. Delaney, J. Honnorez, and an anonymous reviewer for constructive comments.