Abstract
It is well known that seawater that migrates deep into the Earth’s crust will pass into its supercritical domain at temperatures above 407°C and pressures above 298 bars. In the oceanic crust, these pressures are attained at depths of 3 km below sea surface, and sufficiently high temperatures are found near intruding magmas, which have temperatures in the range of 800°C to 1200°C. The physico-chemical behaviour of seawater changes dramatically when passing into the supercritical domain. A supercritical water vapour (ScriW) is formed with a density of 0.3 g/cc and a strongly reduced dipolar character. This change in polarity is causing the ScriW to lose its solubility of the common sea salts (chlorides and sulphates) and a spontaneous precipitation of sea salts takes place in the pore system. However, this is only one of many cases where the very special properties of ScriW affect its surroundings. The objective of this paper is to increase awareness of the many geological processes that are initiated and governed by ScriW. This includes interactions between ScriW and its geological surroundings to initiate and drive processes that are of major importance to the dynamics and livelihood of our planet. ScriW is the driver of volcanism associated with subduction zones, as ScriW deriving from the subduction slab is interacting with the mantle rocks and reducing their melting point. ScriW is also initiating serpentinization processes where olivines in the mantle rocks (e.g. peridotite) are transformed to serpentine minerals upon the uptake of OH-groups from hydrolysed water. The simultaneous oxidation of Fe2+ dissolved from iron-bearing pyroxenes and olivines leads to the formation of magnetite and hydrogen, and consequently, to a very reducing environment. ScriW may also be the potential starter and driver of the poorly understood mud and asphalt volcanism; both submarine and terrestrial. Furthermore, the lack of polarity of the water molecules in ScriW gives the ScriW vapour the potential to dissolve organic matter and petroleum. The same applies to supercritical brines confined in subduction slabs. If these supercritical water vapours migrate upwards to reach the critical point, the supercritical vapour is condensed into steam and dissolved petroleum is partitioned from the water phase to become a separate fluid phase. This opens up the possibility of transporting petroleum long distances when mixed with ScriW. Therefore, we may, popularly, say that ScriW drives a gigantic underground refinery system and also a salt factory. It is suggested that the result of these processes is that ScriW is rejuvenating the world’s ocean waters, as all of the ocean water circulates into the porous oceanic crust and out again in cycles of less than a million years. In summary, we suggest that ScriW participates in and is partly responsible for: 1) Ocean water rejuvenation and formation; 2) Fundamental geological processes, such as volcanism, earthquakes, and meta-morphism (including serpentinization); 3) Solid salt production, accumulation, transportation, and (salt) dome formation; 4) The initiation and driving of mud, serpentine, and asphalt volcanoes; 5) Dissolution of organic matter and petroleum, including transportation and phase separation (fractionation), when passing into the subcritical domain of (liquid) water.
Highlights
One of the last century’s greatest discoveries was done in the late 1970s [1] with the direct observation of deep-sea active hydrothermal venting: “The typical basaltic terrain at the ridge axis is bleak
All mud volcanoes are associated with gas venting, and from this fact it is evident that the generation of gas at depth is an important and necessary contributor to the lifting force inside the conduits
The main questions we have presented, here, are 1) can locally extreme heat-flows occurring at the basement of sedimentary basins, where there may be a juxtaposition of intersecting deep fractures and faults cause the formation of Supercritical Water (ScriW) trigger and drive mud volcanism; and 2) is the role of gas lift inside the vertical transport conduits of mud volcanoes important for lifting the multi-component material of solids and liquids to the surface? the whole question may be simplified as one of sediment thickness below the mud volcano and the correct temperature gradient
Summary
One of the last century’s greatest discoveries was done in the late 1970s [1] with the direct observation of deep-sea active hydrothermal venting: “The typical basaltic terrain at the ridge axis is bleak . What was not realized at that time was that a few hundred metres away from the observers, was perhaps the most lethal fluid imaginable—supercritical water (ScriW) In this brief article, we will discuss some of the properties of ScriW, its occurrences and some of its geological effects and consequences. The ionic dissociation constant declines from the normal water value of 10−14 down to 10−23 at CP, and the density of water attains a value of ~0.3 g/cm3 [8,9] This strongly influences the inter-molecular behavior of water, and Raman spectra of deuterated water in the supercritical region show only remnants of hydrogen bonding [10,11]. The physico-chemical properties of ScriW with its high diffusivity, allows it to permeate into nanoscale voids, fissures, and cracks, and alter the surrounding rocks. This lead to the formation of a new numerical “Deep Earth Water” (DEW) model [7], on which further exciting results will undoubtedly be based
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