On water in nominally anhydrous minerals from mantle peridotites and magmatic rocks

Abstract

Trace amount of water associated with the lattice defects of nominally anhydrous minerals (NAMs) can be measured using Fourier transform infrared spectroscopy (FTIR) and secondary ion mass spectrometry (SIMS). Lots of data on water in NAMs from different lithologies, especially mantle peridotite xenoliths, have been published. The water distribution in olivine from peridotite xenoliths often displays a diffusion profile with high water concentration in the core and low at the rim, which indicates water loss via diffusion during the ascent of host magma. On the other hand, water is homogeneously distributed in pyroxene and its concentration is typically interpreted to represent a mantle value. The water concentration of magma in equilibrium with NAM can be estimated using specific partition coefficient, from which the water content of parental magma and the mantle source can be inferred. The accuracy of this method, however, depends on the selection of appropriate partition coefficient for the system. Using hydrogen isotope compositions and H 2 O/Ce ratios of mantle NAMs, water source regions can be traced and water heterogeneity can be mapped in the upper mantle. Water plays an important role in the stability of cratonic mantle. The water contents and vertical distribution patterns can be significantly different among different cratonic mantles, which may result from different geologic activities. However, the mantle-plume interaction may not necessarily result in significant change of water content in cratonic mantle. The estimation of the water content in the upper mantle is still largely based on geochemical models due to the limitations of data on water in mantle NAMs.Keywords Nominally anhydrous minerals, Fourier transform infrared spectroscopy, Craton stability, Water in the upper mantle, Magma ascent rate, Water in magma Citation:Hui H J, Xu Y J, Pan M E. 2016. On water in nominally anhydrous minerals from mantle peridotites and magmatic rocks.

Atomic Spectroscopy

“…5A). The H2O contents in minerals or melt inclusions were measured by SIMS, using the relative signal intensity of 1 H or 16 O 1 H (to 16 O, 18 O, or 30 Si) with a calibration curve. 51,59,[62][63][64][65][66][67][68][69][70][71] In this study, the H2O content calibration curves were established by comparing the Fourier transform infrared spectroscopy (FTIR) results with the SIMS 16 O 1 H/PI ratios obtained for a series of newly introduced zircon H2O content reference materials (Fig.…”

“…17 Nominally anhydrous minerals (NAMs), which do not contain hydrogen in their chemical formulas, usually contain trace amounts of water in the form of structural bonds (H + , NH4 + , OHgroups). [18][19][20] Over the past decades, there has been an increased focus on NAMs because they may represent an important water reservoir in the Earth's interior. [21][22][23] They could potentially play a major role in the distribution, cycling, and inventory of water between and within the mantle, crust, and exosphere.…”

Investigation of copper sulfate pentahydrate dehydration by terahertz time-domain spectroscopy*

“…[1][2][3] These features of CuSO 4 •5H 2 O are similar to nominally anhydrous minerals (NAMs). [4] NAMs, with tens to hundreds of parts per million (ppm) water entering the structure of minerals, have widely raised the interests of scientists for the considerable geological significances. [5] Despite the trace amounts of hydrous component of NAMs, it can possess a disproportionately large influence on the physical and chemical properties of mantle minerals.…”