TITLE:
Buried Hydrothermal Systems: The Potential Role of Supercritical Water,“ScriW”, in Various Geological Processes and Occurrences in the Sub-Surface
AUTHORS:
Martin Hovland, Håkon Rueslåtten, Hans Konrad Johnsen
KEYWORDS:
Supercritical Seawater; Hydrothermal Salt Model; Rifting Sediment Basins; Salt Precipitation from Supercritical Seawater; Petroleum Migration; Volcanism; Mud Volcanoes
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.5 No.2,
January
27,
2014
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.