CLASSIFICATION OF LAMPROPHYRES, LAMPROITES, KIMBERLITES' AND THE
Kimberlites vs Volcanoes.ppt
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Transcript of Kimberlites vs Volcanoes.ppt
KIMBERLITE
DIATREMES
AND
VOLCANOS:
SIMILARITIES
AND DIFFERENCES
CONTENT(preliminary version)
• 1. Geography & Tectonics• 2. Geomorphology• 3. Channel of eruption• 4. Petrology & Microstructure• 5. Mineralogy and Mineral resources• 6. Volcanology• 7. Genesis & Conclusions
Part 1
Geography
&
Tectonics
Fact:
Geographical distribution of kimberlites and
volcanoes is different with 100% negative
correlation.
Kimberlites occur within ancient cratons while
volcanoes – within young mobile belts.
Ancient cratons and folded belts are the two main tectonic elements of the Earth’s crust
Kimberlites occur within cratons
(After O.R.Eckstrand et al, 1995, Geology of Canada No. 8, GSC.)
Volcanoes occur within folded belts
Kimberlites vs. volcanoes by region.North & South Americas
Volcanoes (red dots) Kimberlites
No volcanoesin NWT Canada
No volcanoesin Brazil
No kimberlites in Ring of
Fire
Kimberlites vs. volcanoes by region. Yakutia, India and Australia
KimberlitesVolcanoes (red dots)
No volcanoesin Yakutia
No volcanoesin India
No volcanoesin Australia
No kimberlitesin Ring of Fire
India
Kimberlites vs. volcanoes by region. Europe and Africa
Volcanoes (in red) Kimberlites
No kimberlites in Iceland
SouthernAfrica
Iceland
No volcanoes in Southern Africa
N.Tanzaniavolcanoes
W.Tanzaniakimberlites
White Seaprovince
No volcanoesin White Sea
province
N.Tanzaniavolcanoes
Part 2
Geomorphology
Fact: Kimberlites and volcanoes create
diametrically opposite topographic forms:
volcanoes – positive
kimberlites – negative
There are no volcanoes with negative forms,
and there are no kimberlites with positive
forms of relief.
Volcanoes create positive forms of relief (Mt. Mayon, Philippines)
Kimberlite pipes create negative forms of relief (composite sketch)
(After Dr. A.R.Chakhmouradian
Geomorphology
There are no volcanoes without a cone: Klyuchevskoi volcano (left).
There are no diatremes with a cone: model of kimberlite pipe (right). Red dashed line indicates the same level for volcano and for diatreme: the end of a diatreme is a beginning of a volcano
Geomorphology
Simultaneous (?)
accumulation (volcano)
and excavation (pipe),
(386 km between them)
• Kilimanjaro (rhyolite volcano)
Age - 40 Ma
Height (Kibo) = 5,895 m (in air)
Crater size = 2.7 x 1.9 km
• Mwadui (kimberlite pipe)
Age – 41 Ma (C. Jennings, 1990)
Depth of crater 400 m (in granites)
Crater size = 1.5 x 1.2 km
GeomorphologyOl Doinyo Lengai
Part 3
Channel of eruption
Three-dimensional model of the Misery kimberlite complex
5034 kimberlite pipe, Canadaconsists of four lobes
Volcano has a simple pipe-like vent and a rounded crater filled with homogeneous rock (left)
Model of channel of eruption
Kimberlite pipes
have a complex
inner structure(previous slide as well)
Du Toit’s Pan pipe consists of dozen of kimberlite rocks with different grade
Kimberlite pipe walls structure
“Grooves or striae which appear after
mechanical abrasion of the pipe walls by
intruded kimberlite could be inclined or even
horizontal” (C.R.Clement, 1986). That means
that kimberlite magma had different directions
during its eruption which is impossible for
volcanoes.
Petrology…
Part 4
Petrology…
• Diatremes can be composed with rhyolites,
dacites, andesites, basalts, ultrabasic rocks
and carbonatites – the whole range of
effusive / hypabyssal rocks
• Volcanoes are filled up with rhyolites, dacites,
andesites, basalts and carbonatites. There are
no kimberlite rocks were found in volcanoes
Geological contacts between different kimberlites are very graduate. They do not conform to the classic structure of magmatic contacts, which must include zones of endo- and exo-contacts. They rather look like accumulative zones between different portions of the same batch of kimberlite magma.
Classic contact zone between broken and baked siltstone (bottom) and mafic sill with frozen endocontact
…inner structure
Xenoliths in effusive rocks are quite rare, because they were washed away by final batches of ascending lava. There is clear contact reaction rim around xenolith (black arrows)
“Volcaniclastic” kimberlite overfilled with xenoliths. There are no contact rims between xenoliths and cold magma
Xenolith gabbro in basalt. Hawaii. C.Benrley, 2010
Part 5
Mineralogy…
Mineral resources
• Diatremes can contain high quality
deposits of the long list of minerals like
gold, copper, iron, uranium, diamonds,
zinc, lead, etc
• Volcanoes themselves directly produce
mostly breakstone, some perlite, and also
some sulphur.
VolcanologyPart 6
Ol Doinyo Lengai Carbonatite
Kilauea Volcano
Kilauea VolcanoBasalt
Kimberlite should be between them
Types of volcanoes:kimberlite should be close to Hawaiian and Icelandic types,
far from Plinian
Eruption Type
VEI Main Rocks SiO2 (%)
Viscosity
Eruption Mode
VolcanicProducts
PlumeHeight
TroposphericInjection
Plinian 8 Rhyolites
65
Very high Mega-Colossal
Tephra
50 km Substantial
Pelean 7 Dacites 62
High
Colossal
Tephra
> 25 km Substantial
Vesuvian 5-6 Andesites
59
Intermediate
Paroxysmal
Tephra
10-25 km Substantial
Vulcanian 3-4 Rhyolito- Basalt
54
Moderate
Severe
Tephra, minor lava
3-15 km Substantial
Strombolian 1-2 Andesito- Basalt
51
Moderate
Mildly explosive
Tephra, minor lava
1-5 km Minor
Hawaiian 0 Basalt 48
Low
Gentle, Effusive
Lava, very little tephra
0.1-1 km Negligible
Icelandic 0 Basalt 45
Low
Non-ExplosiveMost peaceful
Lava, rare tephra
< 0.1 km Negligible
Kimberlitic Close to zero
Picrite-Carbonatite?
35?
Should be low
Should benon-explosive
Tephra should be rare
About 0.1 km?
Negligible?
Carbonatitic(Ol Doinyo)
0-3 Carbonatite
3-10
Very low Non-Explosive
Lava, rare tephra
0.01-0.1 km Negligible
Types of volcanoes and their main parameters
Blocks, no ash
Lapilli Ash, no blocks
Volcanic ash can’t make a deposit inside its own crater (Natural separation by size & weight)
wind
tephra
Volcanic ash makes deposits a hundreds kilometers away from the crater.
Volcanic ash
Solid, well-rounded kimberlite pellets of the TK- kimberlite, covered by 70 m of granites, 5034N, Canada (left), clearly differ from sharply angular porous pieces of volcanic ash, Brokeoff Volcano, California (right).
Pseudo-pyroclastic TK-kimberlite Volcanic ash
Some important numbers
Kimberlite magma was extremely cold:
below 200 degree (Davidson, 1964) to
400 degree (Dawson, 1980)
Volcanic lava has a temperature
between 1000 -1300 degree.
Tephra which was not found among kimberlites
Ribbon bomb “Bread crust” bomb
Rotation bomb Porous bomb
Autoliths which were not found in tephra
Autolith with stratified structure in the center and concentric structure around. Maliutka pipe, Yakutia. Slab
Concentric-zoned autolith. Dal'naya pipe. Yakutia. Thin section.
“Lapillus”. Victor-North“pyroclastic”kimberlite.Canada. B. vanStraaten et al.
Lapilli (?) unit in the El Guayal KT site.
(Salge and Claeys, 2000)
Which magic force could keep lapilli in suspended condition and protect them against falling down before the solid supporting matrix was created?
The Natural History Museum, 2000.Thin section.
Around - Liquid magma,Fine-grained fully crystallizedgroundmass of hypabyssalrock
Minerals
Kimberlite autolith
To
aut=To
mag
To
aut=3000
Kimberlite “lapillus”
Victor-North “pyroclastic” kimberlite with completelycrystallized groundmass.Ontario, Canada.
B. van Straaten, M. Kopylova, K. Russell, K. Webb, B. Scott Smith
Volcanic tephra
Around - Gases/air,Porous glassy groundmassof volcanic rock
Pores
Volcanic glassT
o
lap>>To
air
To
lap=10000
Minerals Pores
Porous volcanic bomb
Volcanic lapillus
Around - Gases/air,Porous glassy groundmassof volcanic rock
Around - Liquid magma,Fine-grained fully crystallizedgroundmass of hypabyssalrock
Pores
Volcanic glass
Minerals
Kimberlite autolith
To
lap>>To
air To
aut=To
mag
To
lap=10000 To
aut=3000
Minerals
Genesis & Conclusions
Part 7
Genesis.
• During the flight in atmosphere volcanic tephra obtained the
hard crust of the frozen surface (“bread crust”). This crust
has prevented lapilli against their tight junction into solid
magmatic rock. Such crust was never observed in kimberlite
rocks.
• Kimberlite pellets had never left their original magmatic
environment as far as they represent the silicate part of the
initially homogeneous kimberlite magma. These pellets are
cemented by an immiscible carbonatite (Kryvoshlyk, 1976,
2008).
Genesis
1. Volcano was created by eruption of a simple homogeneous magma.
2. Diatreme is a result of eruption of a composite magma, which fragmentation is a product of a liquid immiscibility. Liquid immiscibility is a wide spread natural phenomenon which can be observed by everybody everyday (oil in water).
3. Kimberlite “tuff” (TK, VK,…) is a mixture of picritic melt which was fine-dispersed starting from a molecular level within carbonatitic melt.
Conclusions
1. Natural sequence of volcanic events in modern
theories is broken: tephra must be generated
first, before lava, and lava must appear later,
after tephra. In kimberlite pipes we see lava (HK-
kimberlite) first and tephra (TK-kimberlite) later.
2. If the HK-kimberlite represents kimberlite lava, so
why there are no clear sharp contacts between HK and TK-kimberlites which should represent tephra? The fact is: there are many meters of HKt and TKt kimberlites between TK and HK