stazhevsky karst genesis ppt
DESCRIPTION
Some pieces of factual evidence supporting a new insight into karst genesisTRANSCRIPT
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New Insight into Karst Genesis
S.B. Stazhevsky, G.N.Khan, E.P.Rusin
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What is karst? Karst is a system of processes and phenomena occurring and
developing underground and/or on Earth’s surface as a result of interaction
(dissolution, transfer and deposition of substances) of natural waters with
soluble rock.
Karst falls into two main categories:
– exokarst (“cold” karst) caused by meteoric water penetration from the earth’s
surface into its depths;
– hydrothermal (or endo-) karst emerging under action of internal high-pressure
water from the earth’s interior upwards.
Incentives for karst study by the mining science. There is obvious
connection of karst with minerals. Deposits of lead and zinc, antimony and
mercury, bauxites, phosphorites, uranium, nickel, gold, diamonds, oil and gas
collectors may be of karst origin. Karst manifestations often cause
complications in mining.
Unintelligible aspects to investigate. First of all, principles of karst formation
and, second, a whole range of karst related issues – including nature of a
number of its kinds such as ore-bearing karst, karst in insoluble rock (silicate
one), karst isolated from the surface, nature of stylolites etc – do not find non-
contradictory explanation.
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Define the research scope
Main conditions for exo- and endokarst formation:
1) rock solubility – which is an intrinsic feature of karstifying rock;
2) presence of large amounts of water (in particular, contained in
fluids) – which is an intrinsic feature of the Earth’s lithosphere
because the volume of Н2О entrapped in the Earth’s mantle is
commensurable with the Н2О amounts contained in the
planet’s hydrosphere;
3) rock mass permeability which is defined by porosity and
fissuring. Between the two factors, the karst science gives the
palm of supremacy to fissuring whose origin still needs
explanation.
That is why in this study we deal with principles of the origin of
karst inducing rock fissuring.
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NEW GEOMECHAICAL HYPOTHESIS
OF KARST GENESIS
Karst of all kinds is of depth nature and its
initial cause is not solubility of rock or
simple separation or shear fissures but
formation of rock mass discontinuities
accompanying evolution of endogenic ring
structures (R-structures) being a tool for
Earth’s degassing and defluidization.
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Simplified model of a ring structure formation (“floating-up”)(profile of strained rock mass area)
An interior area disturbed by degassing and, therefore, being “loosely” packed collapses. This
causes subsidence of a conic block Q, sequential subsidence of a cylindrical block G and formation
of an R-structure with diameter D. The blocks are outlined with anomalously porous and fissured
slip surfaces 1 and 2. They play role of channels for water, fluids and gases.
Thus, a potential R-structure tends to float-up to the surface which results in defluidization and
compaction of underlying geomedium. Depending on the location depth of an R-structure “loosely”
packed seat, the elementary deformation cycle may repeat. The process begins developing from
the bottom of the area disturbed by degassing and propagates upwards by repeating the cycle in
the course of time.
The way it goes is seen in the following “chronicle” of a physical experiment with sodium
chloride.
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Physical modeling of an R-structure “floating-up”(“loosely” packed area collapse is imitated by a piston downward movement)
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Final stage of the experiment with an R-structure “floating-up”.
Note that the process has not reach the surface yet, thus representing
(1) an endokarst occurrence and (2) an example of an isolated cave.
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Stilolite origin
Rock sample microsection with stilolites
Rock outcrop with stilolites
Schematic diagram of stilolites
Fragment of the modeling media
deformation pattern (see darker area
at slide 10). Note traces of earlier
open and then closed fissures
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Model of an isolated cave
Q – conical block;
h – intact rock bridge thickness;
1 – fractured rock zone;
2 – cave upper part filled with gas;
3 – cave lower part filled with water
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Ayalon isolated cave, Israel
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Digital modeling of an R-structure “floating-up”
Q – conical block; D – ring structure diameter
Modeling method used: discrete element method [Cundall&Strack, 1979]
with modifications [Khan, 2008]
Rock mass deformation pattern at one of the stages
of an R-structure “floating-up”
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Comparison of the results of an R-structure “floating-up”
modeling with field observation data
a) DEM modeling (fragment – see lighter area at slide 14);
b) physical modeling (fragment – see lighter area at slide 12);
c) profile of Kievskaya cave;
d) profile of Snezhnaya cave;
e) profile of Krubera cave.
Qualitative resemblance between the images shows morphological similarity of
geomedium under an R-structure and karstified rock mass
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Examples of R-structure spatial coincidence
with karst manifestations
Example 1. R-structure overlaying a karstified area (Texas, USA)
a) shaded relief map of Texas, USA;
b) an R-structure identified in the surface relief (see lighter area);
c) fragment of the USA karst map (karst shown in black) .
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Examples of R-structure spatial coincidence
with karst manifestations
Example 2. Hydrothermal karst ore deposits adjacent to the contours
of R-structures (Ireland)
a) shaded relief map of Ireland. Every deposit is connected with an R-structure contour;
b) some of the R-structures highlighted in the surface relief (see lighter areas).
- hydrothermal karst ore deposit.
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Examples of R-structure spatial coincidence
with karst manifestations
Example 3. Hydrothermal karst lead-and-zinc ore deposit adjacent to the
contour of an R-structure (Gays River, Nova Scotia, Canada)
a) shaded relief map (with topography) of Gays River mine area;
b) an R-structure identified in the surface relief (see lighter area).
– Gays River lead-and-zinc mine.
a b
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Examples of R-structure spatial coincidence
with karst manifestationsExample 4. Pinnacle karst (tsingy) reserve on the contour of an R-structure
(Tsingy de Bemaraha, Madagascar)
a b c
d
a) shaded relief map of Madagascar with bathymetry; b) Madagascar geological map;
c) physical map of Madagascar; d) tsingy landscape.
- R-structure contour; - limestone outcrop; - point of the R-structure contour
intersection with limestone outcrop; - tsingy reserve location.
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Examples of R-structure spatial coincidence
with karst manifestations
Example 5. Heavily karstified area coinciding with R-structures
(Kungur, Russia)
Co
nto
urs
of
R-s
tru
ctu
res
KUNGUR
KUNGUR
Fragments of cosmogeological maps showing different size large R-structures
superimposed upon the territory of Kungur.
- location of Kungur
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Examples of R-structure spatial coincidence
with karst manifestations
Example 5 (continued). Heavily karstified area
coinciding with R-structures (Kungur, Russia)
The territory of Kungur
(Google Earth image)
Shaded relief map
of Kungur with identified
R-structures
Karst manifestations (marked
with dots) and identified
R-structures in Kungur
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Sum up,
1) configuration patterns of discontinuities under ring
structures are similar to the internal structure of
karst systems;
2) locations of karst manifestations of various kinds
and sizes coincide with ring structure areas.
This supports the new hypothesis on endogenous
nature of karst and its connection with evolution of
ring structures.