Petrologi-5-batuan-beku-piroklastik.pdf

Semester 2, 2017-2018

petrologi 2 SKS teori 1 SKS praktikum by: hill. gendoet hartono

[TGS7208]

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Siklus Batuan, Kontrak Kuliah, Kelulusan, & Praktikum Magma, Diferensiasi, Viskositas, Gas dan Komposisi Batuan Beku, Intrusi Dalam & Karakteristiknya Batuan Gunung Api, Intrusi Dangkal & Karakteristiknya Batuan Gunung Api, Lelehan, Letusan & Karakternya Klasifikasi Batuan Beku & Gunung Api Batuan Alterasi

Batuan Sedimen, Jenis & Proses Pembentukan Batuan Sedimen Silisiklastika Batuan Sedimen Karbonat Klasifikasi Batuan Sedimen Batuan Metamorf, Jenis & Proses Pembentukan Batuan Metamorf Derajat Rendah, Menengah & Tinggi Klasifikasi Batuan Metamorf

Minerals to Rocks: Major Rock Groups

Extrusive Rocks: Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include andesite, basalt, obsidian, pumice, rhyolite, scoria, and tuff. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface. Extrusive igneous rocks cool much more rapidly than intrusive rocks. The rapid cooling time does not allow time for large crystals to form. So igneous extrusive rocks have smaller crystals than igneous intrusive rocks. Extrusive igneous rocks are also called volcanic rocks.

Pembentukan batuan gunung api (Hartono, 2010)

Extrusion (ɪkˈstruːʒən) n 1. the act or process of extruding 2. (Geological Science) a. the movement of magma onto the surface of the earth through volcano craters and cracks in the earth's crust, forming igneous rock b. any igneous rock formed in this way Extrusion in British. (ɪkˈstruːʒən ) the act or process of extruding. a. the movement of magma onto the surface of the earth through volcano craters and cracks in the earth's crust, forming igneous rock. Dictionary

Extrusion In geology, the breaking-out of igneous rock from below the Earth's surface. Any volcanic product reaching the surface becomes extrusive material whether it is ejected through a volcano's cone or through pipe-like channels or fissures in its crust.

Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and metamorphic rocks and constitute an important element of some sediments and sedimentary rocks. For these reasons, in geology, volcanics and shallow hypabyssal rocks are not always treated as distinct. In the context of Precambrian shield geology, the term "volcanic" is often applied to what are strictly metavolcanic rocks. Volcanic rocks are among the most common rock types on Earth's surface, particularly in the oceans. On land, they are very common at plate boundaries and in flood basalt provinces. It has been estimated that volcanic rocks cover about 8% of the Earth's current land surface. From Wikipedia, the free encyclopedia

Extrusive Basalt (small crystals + glass)

Igneous bodies (Beneath the surface)

Extrusive bodies or Volcanic bodies (On the surface of earth) Example: Lava flows

Plutonic bodies

Hypabyssal bodies Transverse intrusives Parallel intrusives

Example: Batholith Stock and Boss

Example: Example: Sill, Laccolith, Dyke, Volcanic neck Lopolith and Phacolith

Forms and Structures of Igneous Rocks Intrusive Structures

Sheet Lens-shaped Cone-sheet, Intrusions Intrusions Ring Dikes

Dikes

Sills

Extrusive Structures

Subjacent Plutons

Laccolith

Batholith

Phacolith

Stock

Lopolith

Diapirs

Lava Plateau

Volcanic Cone

Ropy lava Vesicular structure

Columnar Jointing

Pillow lava Amygdaloidal Block lava structure

Extrusive Igneous Rocks form near volcanoes

Extrusive Igneous Rocks Also called volcanic rocks form at the earth’s surface. Known as Basalt Cools rapidly - small crystals (glassy) Lava - molten rock at the earth’s surface

The Structures of Lavas Block Lava (subareial lava flows, result when volatile in the magma are boiled off in the vent before eruption) Ropy Lava (lava flows with less loss of volatiles show contorted snaky folds) Pillow Lava (Submarine lava flows, exhibit a pillow structure that consists of isolated pillowed shaped masses piled one upon another 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 as calcite, chlorite, chalcedony,..) Columnar Jointing (fractures that separate polygonal, pencil-like cooling structures several centimeters across.)

Once the surface skin becomes solid, the lava can continue to flow beneath the surface in lava tubes. The surface skin insulates the hot liquid lava form further cooling. When the eruption ends, liquid lava often drains leaving an open cave Once the surface skin becomes solid, the lava can continue to flow beneath the surface in lava tubes. The surface skin insulates the hot liquid lava form further cooling. When the eruption ends, liquid lava often drains leaving an open cave Once the surface skin becomes solid, the lava can continue to flow beneath the surface in lava tubes. The surface skin insulates the hot liquid lava form further cooling. When the eruption ends, liquid lava often drains leaving an open cave

Struktur kolom pada lava, Randubang, Selogiri

Amygdaloidal structure

Amygdaloidal structure

Lava bantal Kalipuru, Bayat, Klaten

Lava bantal Watuadeg, Berbah, Sleman

Explosive eruptions are favored by high gas content & high viscosity magmas (andesitic to rhyolitic magmas). The explosive bursting of bubbles fragments the magma into clots of liquid that cool as they fall through the air. These solid particles become pyroclasts or volcanic ash.

Pyroclastic Material If the magma has high gas content and high viscosity, the gas will expand in an explosive fashion and break the liquid into clots that fly through the air and cool along their path through the atmosphere. Alternatively it blast out solid pieces of rock that once formed the volcanic edifice. All of these fragments are referred to as Pyroclasts = hot, broken fragments. Loose assemblages of pyroclasts called tephra. Depending on size, tephra can be classified as bombs. blocks, lapilli, or ash.

Classification of Volcaniclastic rocks and sediments Clast size in mm

Pyroclast

> 64 mm

Bomb, block

64 to 2 mm

Lapillus

2 to 1/16 mm

Coarse ash grain Fine ash grain (dust grain)

< 1/16 mm

Pyroclastic deposit Primarily unconsolidated: tephra Agglomerate, bed of blocks or bomb, block tephra Layer, bed of lapilli or lapilli tephra Coarse ash Fine ash (dust)

Primarily consolidated: pyroclastic rock Agglomerate, pyroclastic breccia Lapilli tuff Coarse (ash tuff) Fine (ash) tuff (dust tuff)

2-64mm

<2mm

Material gunung api produk letusan (vide Compotn, 1985)

>64mm

Bom gunung api, Tiyaran, Wonogiri

Bom gunung api pada aglomerat, G. Gajahmungkur, Wonogiri

Bomb gunung api

Block gunung api

Lapilli gunung api

Ash gunung api

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