Hydrothermal process, magma

Norton D. and Dutrow B. L. (2001) Complex behavior of magma-hydrothermal processes role of supercritical fluid. Geochim. Cosmochim. Acta 65, 4009—4017. 

Mineralogically, zeolites are hydrated aluminosilicate minerals, which originate during the formation of igneous, metamorphic, or sedimentary rocks, principally via hydrothermal processes. Hot circulating water leaches out mineral components deep within the Earth, particularly from basalt magmas. Zeolites form in these water-rich geological environments when conditions of low temperature (<200 °C) and low pressure (4 X 10 Pa, equivalent to around 15 km depth of burial) are attained. 

The local stress field in volcanic environments is a combination of the regional tectonic stress and that produced by magmatic and hydrothermal processes. The interaction of these two components leads to the generation of VT earthquakes, which are produced by stress changes, linked to the movement of magma or other fluids. 

Trace elements are useful tracers of geochemical processes mostly because they are dilute their behavior depends primarily on the trace element-matrix interaction (e.g., Rb-host feldspar, Sr-calcite) and very little on the trace-trace interaction (e.g., Rb-Rb, Sr-Sr). Consequently, the distribution of trace elements among natural phases largely obeys the linear Henry s law. The modeling of trace elements in various geological environments (magmas, hydrothermal fluids, seawater,...) relies on three different aspects... 

Some trace metals are transported into the ocean as a component of hydrothermal fluids. This process is discussed further in Chapter 19- To briefly summarize, hydrothermal fluids are produced when seawater penetrates into cracks in the crust near tectonic spreading centers. The seawater is heated as it comes into contact with magma. The hot seawater leaches a number of trace metals from the magma. The resulting hydrothermal fluids are acidic and do not contain O2, so most of the metals are present in reduced form. Because of their high temperatures, the hydrothermal fluids have a lower density than cold seawater. Their increased buoyancy causes them to rise until they are emitted into the deep sea. Admixture with cold, oxic, alkaline seawater causes the hydrothermal metals to undergo various redox and precipitation reactions. 

O, H, C, S, and N isotope compositions of mantle-derived rocks are substantially more variable than expected from the small fractionations at high temperatures. The most plausible process that may result in variable isotope ratios in the mantle is the input of subducted oceanic crust, and less frequent of continental crust, into some portions of the mantle. Because different parts of subducted slabs have different isotopic compositions, the released fluids may also differ in the O, H, C, and S isotope composition. In this context, the process of mantle metasomatism is of special significance. Metasomatic fluids rich in Fe +, Ti, K, TREE, P, and other large ion lithophile (LIE) elements tend to react with peridotite mantle and form secondary micas, amphiboles and other accessory minerals. The origin of metasomatic fluids is likely to be either (1) exsolved fluids from an ascending magma or (2) fluids or melts derived from subducted, hydrothermally altered crust and its overlying sediments. 

Figure 7 Potential physical and chemical processes occurring in a magmatic-hydrothermal system, including the influence of magma dynamics in the chamber-conduit plumbing system, and interactions between magmatic fluids and the crust. These can strongly modulate the speciation and flux of various magmatic components emitted into the atmosphere, compheating the interpretation of geochemical measurements of surface emissions.

Water is the main natural explosive agent on the Earth. This fact is well demonstrated by all forms of volcanic and hydrothermal explosive manifestations, characterized by a sudden and brutal vaporization of water and other dissolved volatiles from a condensed state, either from aqueous solutions or from supersaturated magmas. This paper is mainly devoted to the first case, i.e. the explosivity of aqueous solutions. Explosions can be defined as violent reactions of systems, which have been perturbed up to transient and unstable states by physico-chemical processes. As such, the traditional approach to such problems is to rely on kinetic theories of bubble nucleations and growths, and this topic has been already the subject of an abundant literature (see references therein ). We apply here an alternative and complementary method by... 

---