UNIVERSITY OF NICOSIA DEPARTMENT OF OIL AND GAS

Observation 1:
Hot liquid lava spilling down from the volcano onto Earth's surface cooled and hardened into solid rock within a few hours (cooled fast).
Observation 2:
sheets of rock that cut across other rock formations also formed by the cooling and solidifying of magma. In these cases, the magma cooled slowly because it had remained buried in Earth's crust
Magma solidification
Before they reach the surface,
Some break through and solidify on the surface.
Both processes produce igneous rocks.
Understanding the processes that melt and re-solidify rocks is a key to understanding the crust formation.
Igneous rocks:
Form at spreading centers (plates move apart) and
At convergent boundaries (one plate descends beneath another)
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Understanding the Exact mechanisms of melting and solidification :
Answer the fundamental questions:
How do igneous rocks differ from one another?
Where do igneous rocks form?
How do rocks solidify from a melt?
Where do melts form?
Igneous processes in the Earth system
Melted rock is transported from magma chambers in Earth's interior to volcanoes.
A variety of gases are also carried along (carbon dioxide and sulfur gases)
Affect the atmosphere and oceans
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How do Igneous rocks differ from one another ?
Classify rock samples by:
Texture
Mineral and chemical composition
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A) Texture:
first division of igneous rocks is made on the differences in mineral crystal size easily see in the field.
Granite: is a Coarse-grained rock. It has separate crystals that are easily visible to the naked eye
Basalt: has Fine-grained crystals that are too small to be seen, even with the aid of magnifying lens.
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1) Volcanic Rocks:
Volcanic rocks are formed from lava during volcanic eruptions.
{Lava is the term that we apply to magma flowing out on the Surface}.
When lava:
Cools rapidly: it forms either:
A) a finely crystalline rock or
B) a glassy one in which no crystals could be distinguished.
Cools slowly: Larger crystals were present.
B) Laboratory study of crystallization: The Ice Cube Experiment
Crystallization process of water: molecules take up fixed positions in the solidifying crystal structure (no longer able to move freely).
All other liquids including magmas crystallize the same way
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2) Laboratory study of crystallization: Magma
The first tiny crystals form a pattern.
Other atoms or ions in the crystallizing liquid also attach themselves and the tiny crystals grow larger.
Time influence:
It takes time for the atoms or ions to "find" their correct places on a growing crystal
large crystals form only if they have time to grow slowly.
Tiny crystals form if a liquid solidifies very quickly (no time to grow).
Result: Large number of tiny crystals form simultaneously
3) Granite: Slow Cooling
Granites cut across and disrupt layers of sedimentary
Can fracture and invade the sedimentary rocks (granite is forced into the fractures as a liquid).
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3) Granite: Study surrounding sedimentary rocks
Minerals of sedimentary rocks in contact with the granite are different from those found in sedimentary rocks at some distance from the granite.
The changes in the sedimentary rocks have resulted from great heat (from the granite liquid form)
Granite is composed of interlocked crystals (evidence of slow crystallization)
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Huttons Proposal:
Granite forms from a hot molten material that solidifies deep in the Earth. The evidence is conclusive and no other explanation could accommodate all the facts.
Today we recognize that:
Granite and many similar coarsely crystalline rocks were the products of magma that had crystallized slowly in the interior of the Earth.
Support the theory:
Intrusive Igneous rocks
Extrusive Igneous rocks
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Intrusive Igneous rocks
Texture is linked to the rate and therefore the place of cooling.
Slow cooling of magma in Earth's interior allows adequate time for the growth of the interlocking of large coarse crystals that characterize intrusive igneous rocks.
An intrusive igneous rock: is one that has forced its way into surrounding rock.
Country rock: is the surrounding rock of an intrusive formation
B) Extrusive Igneous rocks
Rapid cooling at Earth's surface produces the finely grained texture or glassy appearance of the extrusive igneous rocks.
These rocks, form when lava or other material erupts from volcanoes. (volcanic rocks).
They fall into two major categories:
Lavas
Pyroclastic rocks
Porphyry

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Terminology:
Lavas: Are volcanic rocks formed from hot molten rock. They range in appearance from smooth and ropy to sharp, spiky, and jagged, depending on the conditions under which the rocks formed.
Pyroclastic rocks: Are created from violent eruptions.
Pyroclasts form when broken pieces of lava are thrown high into the air.
Volcanic ashes are the finest pyroclasts (extremely small fragments)
Bombs are larger particles, hurled from the volcano
Tuffs are all volcanic rocks lithified from these pyroclastic materials
Examples:
Pumice: a mass of volcanic glass with high porosity.
Obsidian: unlike pumice, it contains low porosity and so is solid and dense.
Porphyry: is an igneous rock with a mixed texture
large crystals (phenocrysts) "float" in a predominantly fine crystalline (formed while magma was still below surface.
Before crystals could grow, a volcanic eruption brought the magma to the surface, where it cooled quickly to a finely crystalline mass.

B) Chemical and Mineral Composition:
Modern classifications now group igneous rocks according to their relative proportions of silicate minerals
The silicate minerals (systematic series)
Quartz,
Feldspar (both orthoclase and plagioclase),
Muscovite
Biotite micas
Amphibole
Pyroxene
Olivine
Felsic minerals are high in silica
Mafic minerals are low in silica.
Felsic = Feldsbar + Silica
Mafic = Magnesium + Ferric "iron".
Mafic minerals: crystallize at higher temperatures (earlier in the cooling of a magma) than Felsic minerals
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Classification of Igneous rocks:
identical in composition and differed only in texture.
Basalt: is an extrusive rock formed from lava.
Gabbro: has exactly the same mineral composition with basalt but forms
deep in Earth's crust
Rhyolite and granite are identical in composition but differ in texture.
Intrusive + Extrusive Rocks
Form 2 chemically and mineralogically parallel sets of igneous rocks
Example:
From the classification model if we know:
The silica content of a rock sample,
We can determine its mineral composition
From composition the type of rock
Rock sample: Granite
70% Silica / 6% Amphibole/ 3% Biotite / 5% Muscovite / 14% Plagioclase Feldspar / 22% Quartz / 50% Orthoclase Feldspar
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Igneous Rocks (Classification model)
Types
Of
Magma

Felsic Rocks Group
Are poor in Fe and Mg / rich in Si minerals.
Si rich minerals:
Quartz,
Orthoclase feldspar,
Plagioclase feldspar.
Mafic minerals crystallize at higher temperatures than felsic
Felsic minerals and rocks tend to be light in color.
Granite: (intrusive igneous rock) contains 70% Si (pink/gray color).
Rhyolite: (extrusive igneous rock) equivalent to granite (brown to gray)
Difference = much more finely grained.
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Intermediate Igneous Rocks Group
Are the midway between the felsic and mafic igneous rocks.
These rocks are not:
Rich in Si as the felsic rocks
Poor as in the mafic rocks.
Intrusive
Granodiorite: Light-colored near felsic rock that looks something like granite. It is also similar to granite in having abundant quartz, but its predominant feldspar is plagioclase, not orthoclase.
Diorite: Dark-colored contains less Si and is dominated by plagioclase feldspar, with little / no quartz.
Extrusive
Dacite: (volcanic equivalent of Granodiorite)
Andesite: (the volcanic equivalent of Diorite)
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Mafic Igneous Rocks Group
Are high in pyroxenes and olivines.
Relatively poor in Si rich Mg/Fe, (dark colors).
Intrusive
Gabbro: (even less silica), is a coarsely grained with dark gray colour. It contains no quartz and only moderate amounts of calcium-rich plagioclase feldspar.
Extrusive
Basalt: (dark gray-black) is the fine-grained equivalent of gabbro. Is abundant igneous rock of the crust and underlies the entire seafloor.
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Ultramafic Igneous Rocks Group
Consist primarily of mafic minerals and contain less than 10% feldspar.
Peridotite: Very low Si of only about 45 %.
Is a coarsely grained,
Dark greenish gray rock
Made up of olivine with smaller amounts of pyroxene.
Dominant rocks of the mantle.
Ultramafic rocks are rarely found as extrusives.
Form at high temperatures (crystallyze at the bottom of a magma chamber)
Rarely liquid and hence do not form typical lavas.
Cyprus is full of Peridotite (Ophiolites)
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There is a strong correlation between:
Mineralogy
Temperatures
Crystallization or melting
Viscosity: The measure of a liquid's resistance to flow
Increases as silica content increases.

How do Magmas Form?
Contradiction:
A) Earth transmits earthquake waves and the bulk of the planet is solid for thousands of km down to the core-mantle boundary.
B) The evidence of volcanic eruptions suggests that there must also be liquid regions where magmas originate.
How do we resolve this apparent contradiction?
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Rock melting (From laboratory experiments):
Rocks melting point depends on:
Composition
Conditions of temperature
Conditions of pressure
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Rock melting (Temperature):
Observation
Discovered that a rock does not melt completely at any given temperature.
Understanding
Rocks undergo partial melting due to the minerals that compose them melt at different temperatures.
Process of partial melting.
As temperatures rise, some minerals melt and others remain solid.
If the same conditions are maintained at any given temperature,
the same mixture of solid rock and melt is maintained.
The fraction of rock that has melted at a given temperature is called a partial melt.
The ratio of liquid to solid in a partial melt depends
Composition
Melting temperatures of the minerals (make up the original rock)
Temperature at the depth in the crust or mantle where melting takes place
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Rock melting (Temperature):
Partial melts (determines different kinds of magma)
Different temperatures
Different regions of Earth's interior.
Composition of a Partial Melt
Which only the minerals with the lowest melting points have melted may be significantly different from the composition of a completely melted rock.
Example
basaltic magmas that form in different regions of the mantle may have different compositions.
Explanation
Different magmas come from different proportions of partial melt
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Rock melting (Pressure):
Pressure increases with depth as a result of the increased weight of overlying rock.
Observation in laboratory
Melting rocks under various pressures, higher pressures led to higher melting temperatures.
Result
rocks that would melt at surface would remain solid at the same temperature in the interior.
The effect of pressure explains why rocks in most of the crust and mantle do not melt.
Rock can melt only
Mineral composition
Temperature
Pressure conditions are right.
Decompression melting
As mantle material rises, the pressure decreases below a critical point and solid rocks melt spontaneously without any additional heat.
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Rock melting (Water content):
Observation
Water is present in some magmas. The compositions of partial and complete melts vary with:
Temperature
Pressure
Water content.
General rule
Dissolving one substance in another lowers the melting point of the solution
Melting temperature of rocks drop considerably in the presence of large amounts of water.
Important knowledge of melting.
Water content is a significant factor in determining the melting temperatures of mixtures of sedimentary (large volume of water) and other rocks.
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Formation of Magma Chambers:
Physical understanding:
Substances are less dense in liquid form than in the solid form.
Density
Melted rock is lower than a solid rock of the same composition.
Understanding
Volume of melt would weigh less than the same volume of solid rock.
Formation (buoyancy driven flows)
The less dense melt moves, in upward layers and rises to the surface.
Being liquid, the partial melt moves slowly through pores and along the boundaries between overlying rocks.
Hot drops of melted rock that move upward mix with other drops, gradually forming larger pools of molten rock within Earth's interior.
The ascent of magmas may be slow or rapid.
Rates of 0.3 – 50 m/year
Periods of 10.000 or even 100.000 of years
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Formation of Magma Chambers:
Magma chambers:
Magma-filled cavities in the lithosphere that form as rising drops of melted rock push aside surrounding solid rock.
Encompasses a volume as large as several cubic kilometers.
Are large, liquid-filled cavities in solid rock, which expand as more of the surrounding rock melts or as liquid migrates through cracks and other small openings between crystals.
Magma chambers contract as they expel magma to the surface in eruptions.
Magma chambers exist because earthquake waves can show us the depth, size, and general outlines of the chambers underlying some active volcanoes
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Magma chambers:

Magma Formation:
Field +Laboratory observation
Volcanoes (land + under the sea) provide molten rocks. Give information about where magmas are located.
Deep drill records of temperatures from holes and mine shafts. This shows that the temperature of Earth's interior increases with depth.
Result
Estimation of the rate at which temperature rises as depth increases.
Example
Temperatures recorded at a given depth in some locations are much higher than other locations.
These indicates that some parts of Earth's (mantle + crust) are hotter than other parts
Realization
Various kinds of rocks can solidify from magmas formed by partial melting.
Increasing temperatures in the Earth's interior could create magmas
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Continue

Magmatic Differentiation:
Discussion about rock melting
Questions?
What accounts for the variety of igneous rocks?
Are magmas of different chemical compositions made by the melting of different kinds of rocks?
Do some processes produce a variety of rocks from an originally uniform parent material?
Answer = Laboratory << Birth of Magmatic Differentiation >>
1) Production of mixture of chemical elements in proportions that simulate compositions of natural igneous rocks
2) Melt these mixtures in high-temperature furnaces.
3) As the melts cool and solidify, we carefully observe and record
The temperatures at which crystals form
The chemical compositions of those crystals
Magmatic Differentiation = process that rocks of varying composition can arise from a uniform parent magma.
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Magmatic Differentiation:
Occurs because different minerals crystallize at different temperatures.
Crystallization process:
The composition of the magma changes as it is depleted of the chemical elements that form the crystallized minerals.
First minerals to crystallize are the ones that were the last to melt from partial melting.
This initial crystallization withdraws chemical elements from the melt and changes the magma's composition.
Repeated crystallization of minerals that had melted at the next lower temperature range during the partial melting changes further the chemical composition until complete solidification.
This is how the same parent magma can give different igneous rocks.
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Fractional Crystallization:
Process by which the crystals formed in a cooling magma are segregated from the remaining liquid.
Scenario
Crystals formed in a magma chamber settle to the chamber's floor and are thus removed from further reaction with the remaining liquid.
The magma then migrates to new locations, forming new chambers.
Crystals that had formed early segregate from the remaining magma, which continues to crystallize as it cools.
Bowen crystallization model
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Example of Fractional Crystallization : Palisades Intrusion

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Evidence of Fractional Crystallization : Palisades Intrusion

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Magmatic Differentiation and Types of Magma
Magma types:
Basaltic (Mafic)
Andesitic/Dacitic (Intermediate)
Rhyolitic (Felsic)
Idea of magmatic differentiation:
Basaltic magma would gradually cool and differentiate into a cooler, more silicic melt by fractional crystallization.
The early stages of this differentiation would produce Andesitic magma, a) Erupt to form andesitic lavas or
b) Solidify by slow crystallization to form Diorite intrusives.
Intermediate stages would make magmas of granodiorite composition.
Process continues, the late stages would form Rhyolitic lavas and Granite intrusions

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Dispute
Magmatic differentiation is a more complex process (Still under divelopment)
Open questions:
A) Much time is needed for small crystals of olivine to settle through viscous magma that they might never reach the bottom of a magma chamber.
B) The source of granite (great volume on Earth) not formed from basaltic magmas and by magmatic differentiation.
Reason:
Large quantities of liquid volume are lost by differentiation. To produce the existing amount of granite, a volume of basaltic magma 10 times the size of a granitic intrusion would be required

Igneous Rocks
Granitic Magma
Source rocks of the upper mantle and crust is responsible for the variation in magma composition:
1. Rocks in the upper mantle might partially melt to produce basaltic magma.
2. A mixture of sedimentary rocks and basaltic oceanic rocks (subduction zones) might melt to form andesitic magma.
3. A melt of sedimentary, igneous, and metamorphic continental crustal rocks might produce granitic magma

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Forms of Magmatic Intrusions
Limitations:
Cannot directly observe the shapes of intrusive igneous rocks formed when magmas intrude the crust.
We deduce their shapes and distributions only by observing them after they have been uplifted and exposed by erosion
Indirect evidence of current magmatic activity from earthquake waves.
Cannot reveal the detailed shapes or sizes of intrusions arising from those magma chambers.
Measurements of temperatures in deep drill holes reveal a crust much hotter than normal, which may be evidence of an intrusion at depth.

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Types of representative Igneous Rocks
Volcanic (Extrusive rocks)
Plutons (Intrusive rocks)
Types of Rocks :
Plutons, Sills, dikes, veins

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Plutons
Are large igneous bodies formed at depth in the crust.
They range in size 1km3 to 100 km3.
Study these large rock bodies when uplift and erosion uncover them Plutons are highly variable, in size and shape (different ways magma makes space for itself).
Observations
Most magmas intrude at depths greater than 8 to 10 km.
At these depths, few holes or openings exist. (great pressure would close them).
upwelling magma overcomes that pressure
Physical process
Magma rising makes space for itself in three ways (magmatic sloping):
1. Wedging open the overlying rock. As magma lifts great weight, it fractures the rock, penetrates the cracks, and flows into the rock. Overlying rocks bow up during this process.

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2. Breaking off large blocks of rock. Magma pushes its way upward by breaking off blocks of the invaded crust (xenoliths), sink into the magma, melt, and blend into the liquid, in some places changing the composition of the magma.
3. Melting surrounding rock. Magma also makes its way by melting walls of country rock.

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Plutons: Batholiths
The largest plutons
Great irregular masses of coarse-grained igneous rock that by definition cover at least 100 km2.
Are found in the cores of tectonically deformed mountain belts.
are thick, horizontal, sheetlike or lobe-shaped bodies
Their bottoms may extend 10 to 15 km deep.
The coarse grains of batholiths result from slow cooling at great depths.
Plutons: Stocks
Are the rest of the plutons, similar but smaller.
Discordant intrusions: rocks that cut
across the layers of the country rock
that they intrude. (batholiths / stocks)

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Sills and Dikes:
Are similar to plutons (smaller) and have a different relationship to the layering of the surrounding intruded rock.
Sill: is a sheet like body formed by the injection of magma between parallel layers of pre-existing bedded rock.
Sills range in thickness from cm to 100m and they can extend over considerable areas.
The 300-m-thick Palisades intrusion is a large sill.
Concordant intrusions: rocks that
their boundaries lie parallel to these
layers, whether or not the layers are
horizontal (Sills).

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Dikes:
Are the major route of magma transport in the crust. They are like sills (sheet like igneous bodies) but cut across layers of bedding in country rock and so are discordant.
Some dikes can be followed in the field for 10 km’s.
Widths vary from m-cm.
Dikes rarely exist alone, hundreds or thousands of dikes are found in a region that has been deformed by a large igneous intrusion.
The texture of dikes and sills varies.
Many are coarsely crystalline, with an appearance typical of intrusive rocks.
Many others are finely grained
and look much more like volcanic
rocks. (texture = rate of cooling).

Igneous Rocks
Veins (Pegmatites):
Are deposits of minerals found within a rock fracture that are foreign to the host rock.
They may be a few mm to several m across, and they tend to be 10m to km long or wide.
Veins of extremely coarse-grained granite cutting across a much finer grained country rock are called Pegmatites.
They crystallized from water-rich magma in the late stages of solidification.
Pegmatites provide ores of many rare elements, such as lithium and beryllium.
Hydrothermal veins
Filled with minerals that contain large amounts of chemically bound water and are known to crystallize from hot-water solutions.
Groundwaters: originate as rainwater seeps into the soil and surface rocks. Hydrothermal veins are abundant along mid-ocean ridges. seawater infiltrates cracks in basalt and circulates down into hotter regions, emerging at hot vents on the seafloor

Igneous Rocks
Veins (Pegmatites):