Stazhevsky Karst Genesis PPT

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1 New Insight into Karst Genesis S.B. Stazhevsky, G.N.Khan, E.P.Rusin

description

Some pieces of factual evidence supporting a new insight into karst genesis

Transcript of Stazhevsky Karst Genesis PPT

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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.