Petrologi 3-difinisi
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Igneous rocks:Igneous rocks: Some definitions
Molten rockMolten rock
when magma reaches Earth’s surface it is called lavalava
in the Earth is magmamagma
Magma is buoyant, rises to surface,& sometimes breaks through
An igneousigneous rock is formed when magma orlava cools and solidifies
Why should we care?
Igneous rocks make up bulk of Earth’s crust
Earth’s mantle is basically one huge igneous rock
Important rocks economically
Striking landscape features
Igneous rocks that form
- at the surface are volcanicvolcanic (extrusive)(extrusive)
Igneous rocks that form
- deep down are plutonicplutonic (intrusive)(intrusive)
Plutonic rocks
Magma bodyMagma body
To see them, they must be uplifted to surfaceAnd softer surrounding rock eroded away
Plutonic rocks
For us to ever see them, they must be uplifted to the surfaceAnd softer surrounding rock eroded away
Plutonic igneousPlutonic igneousrock example:rock example:
El CapitanYosemite Nat. Park,California
As magma cools, atoms arrange in anorderly crystal structure
crystallizationcrystallization
Note: different crystal sizes
Coarse-grained igneous rock
Close up of crystals
Note the variety of crystal sizes
TYPES OF MAGMA
1. granite ------ rhyolite
“coarse” “fine” phaneritic
aphanitic
silica (SiO2) richfeldspar and quartz
2. basalt---------gabbro “fine” “coarse” aphanitic phaneritic
iron – magnesium (Fe – Mg) richferromagnesian minerals,
plagioclase (Ca, Na feldspar)
Minerals to Rocks:Minerals to Rocks:Major Rock GroupsMajor Rock Groups
IGNEOUS SEDIMENTARY METAMORPHIC
Igneous Rock - Molten rock that has Igneous Rock - Molten rock that has cooled and crystallized into sold rock.cooled and crystallized into sold rock.
• Crystal size determined by Crystal size determined by how fast the rock cooled. Due how fast the rock cooled. Due to how crystals grow.to how crystals grow.– Long time = large crystalsLong time = large crystals– short time = small crystalsshort time = small crystals
• Course grain - crystals are Course grain - crystals are easily seen with naked eye.easily seen with naked eye.
• Fine grain - crystals < 1mm, Fine grain - crystals < 1mm, but can still be seen without but can still be seen without magnification.magnification.
• Glassy - no crystals can be Glassy - no crystals can be seen without magnification.seen without magnification.
Forms and Structures of Forms and Structures of Igneous RocksIgneous Rocks
Forms and Structures of Forms and Structures of Igneous RocksIgneous Rocks
Intrusive Intrusive StructureStructure
ss
Extrusive Extrusive StructuresStructures
Cone-sheet,Cone-sheet,Ring DikesRing Dikes
Lens-shaped Lens-shaped IntrusionsIntrusions
Sheet Sheet IntrusionsIntrusions
SubjacentSubjacent PlutonsPlutons Volcanic Volcanic
ConeConeLava PlateauLava Plateau
Columnar Columnar JointingJointing
VesiculaVesicular r
structurstructureePillow lavaPillow lavaAmygdaloidal Amygdaloidal
structurestructure
Ropy lavaRopy lava
DikesDikes SillsSills
Block lavaBlock lava
LaccolithLaccolith
PhacolithPhacolith
DiapirsDiapirs
BatholithBatholith
StockStock
LopolithLopolith
IgneousRocks
Intrusives and Extrusives
Igneous Rock StructuresIgneous Rock Structures
IntrusiveGranite
(large crystals)
Intrusive Igneous RocksIntrusive Igneous Rocks• Also called PlutonicAlso called Plutonic• Rocks form inside Rocks form inside
the earth. Granite is the earth. Granite is the most common. the most common.
• Cools slowly - Large Cools slowly - Large crystals (course crystals (course grain)grain)
• Magma - molten rock Magma - molten rock inside the earth. inside the earth.
Intrusive Igneous Rocks Intrusive Igneous Rocks ExposedExposed
Shiprock California Granite Outcrop, Yosemite
Subjacent PlutonsSubjacent PlutonsSubjacent PlutonsSubjacent Plutons BathoilthBathoilth
Large, irregular, major deep seated intrusive Large, irregular, major deep seated intrusive masses of very large size, elongated parallel to masses of very large size, elongated parallel to major tectonic regime.They have an outcrop major tectonic regime.They have an outcrop areas greater than100km2areas greater than100km2
StockStock Is similar to batholiths, with surface area less Is similar to batholiths, with surface area less
than 100 km2. They have steeply plunging than 100 km2. They have steeply plunging contact with no visible floor. Boss is a term contact with no visible floor. Boss is a term applied to stocks of circular sectionapplied to stocks of circular section
DiapirsDiapirs are bodies of rock and/or magma that are are bodies of rock and/or magma that are
buoyant and moves upwards, piercing rocks buoyant and moves upwards, piercing rocks above them.They appear as ballon like bodies above them.They appear as ballon like bodies intruded and displaced the country.intruded and displaced the country.
ExtrusiveBasalt
(small crystals+
glass)
Block Lava(subareial lava flows, result when volatile in the magma are boiled off in the vent before eruption
Pillow Lava(Submarine lava flows, exhibit a pillow structure that consists of isolated pillowed shaped masses piled one upon another
The Structures of LavasThe Structures of Lavas
Ropy Lava(lava flows with less loss of volatiles show contorted snaky folds)
Vesicular Lava(Lava flows with gas cavities or vesicles which are trapped during solidification, eg. Scoria, Pumice,…)
Amygdaloidal structure(When vesilcles are later filled with secondary minerals such asCalcite, chlorite, chalcedony,..)
Columnar Jointing(fractures that separate polygonal, pencil-like cooling structuresSeveral centimeters across.)
Extrusive Igneous RocksExtrusive Igneous Rocks• Also called volcanicAlso called volcanic• Rocks form at the Rocks form at the
earth’s surface. earth’s surface. Known as BasaltKnown as Basalt
• Cools rapidly - small Cools rapidly - small crystals (glassy)crystals (glassy)
• Lava - molten rock Lava - molten rock at the earth’s at the earth’s surfacesurface
Extrusive Igneous Rocks Extrusive Igneous Rocks form near volcanoesform near volcanoesMt. Pinatubo
Hawaii
Lava flow at Volcanoes National Park, Hawaii
Fig. 4.16Fig. 4.16
Fig. 4.17Fig. 4.17
Vesicular structure
Obsidian - extrusiveObsidian - extrusive
Glassy texture (no defined crystals)Glassy texture (no defined crystals)
Fig. 4.12Fig. 4.12
Pumice - extrusive withvesicles
Fig. 4.28Fig. 4.28
Fig. 4.30Fig. 4.30
Pillow Structure
Fig. 4.29Fig. 4.29