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    Proses Pembentukan Magm

    dan Tatanan Tektonik

    Vulkanologi P2

    Bacaan penting!

    John D. Winter (Principles of Igneous and Metamorphic Petr

    Robin Gill (Igneous Rocks and Processes).

    03/10/2015

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    Manakah yang benar dari pernyataan beriku

    Pengeboran sudah mencapai inti bumi

    Pengetahuan kita akan mantel banyak berasal dari guagua dan tambang-tambang

    Bagian bumi yang telah dipahami dengan baik hanyakerak-nya saja

    Gelombang energy memberikan gambaran yang tepatapa ayang ada di dalam bumi

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    Interior Bumi

    Diameter bumi sekitar 12,756 km, dan manusia baruberhasil mencapai kedalaman 9.6 km

    Yang kita ketahui sejauh ini berasal dari pengamatantidak langsung (terimakasih Geofisika dan gelombang

    seismik-nya!)

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    Jarak

    Semakin jauh, atenuasi lebih kuat

    Densitas

    Lebih tinggi, lebih cepat

    Suhu

    Dingin, lebih cepat

    Liquid vs. solid

    Solid, lebih cepat, gelombang P dan SLiqud, lebih lambat, tidak bias ditembus oleh gelombang S

    Sudut

    Berapa banyak di-refleksikan dan di-absorbsi

    Susunan vertikal lapisan

    Mengontrol resultan

    Faktor yang mempengaruhi gelombang se

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    Fig. 17.7Observa

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    Pressure, Temperature, Composition

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    Struktur Bumi

    Copyright 2006. M. J. Krech. All rights reserved.

    I

    Ma

    Ke

    Aste

    Lito03/10/2015

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    Kerak-kerak litosferik

    Lempmen

    di atasten

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    Kerak tersusun oleh batuan padat.

    Kerak samudra, 0-10 km, komposisi utamanya basaltik.

    Kerak benua, 30-85 km, tersusun oleh magma felsik-intermdensitas lebih rendah.

    Bagaimana pengaruh komposisi dan densitas di batas lempekonvergen?

    03/10/2015

    Kerak-kerak litosferik

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    Batas antara kerak dan mantle

    disebut Moho (MohorovicicDiscontinuitypada 670 km,zonapenghantar gelombang seismikyang lemah).

    Mantle bersifat semi

    padat/molten rock (hinggakedalaman 3000 km).

    Bagian teratas mantel disebutasthenosphere (molten material)

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    Batas kerak-mantel

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    Inti bagian luar berupa likuid

    (tidak bisa dilalui gelombang S,tersusun terutama oleh Ni danFe.

    Inti bagian dalam berupapadatan (bisa dilalui olehgelombang P), dengan komposisiyang serupa (Fe dan Ni)

    Rotasi inti bumi yang likuidmenciptakan gelombangelektromagnetik

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    Inti bumi bagian luar

    dan dalam

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    Batas lempeng tektonik tempat terbentuknya gunun

    Ekstrusif (km3/a) 3 0.4 0.6 0.1

    Intrusive 18 2 8 1.5

    MOR

    Oceanic

    Intraplate

    Margin

    Subduction

    Zone

    Cont

    Intra

    Marg

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    Tholeiites dihasilkan di MOR

    Juga di oceanic islands, subduction zones

    Alkaline basalts dihasilkan di ocean islands

    Juga di subduction zones

    Calc-Alkaline basalts dihasilkan di subduction

    Masing-masing magma berbeda secara kimiawi

    --> Jawabannya ada di mantel

    Evolve via FX as separate series along different paths

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    Ophiolites

    Slabs of oceanic crust and upper

    mantle

    Thrust at subduction zones onto edge

    of continent

    Dredge samples from oceanic crust

    Nodules andxenoliths in some

    basalts

    Kimberlite xenoliths

    Diamond-bearing pipes blasted up

    from the mantle carrying numerous

    xenoliths from depth

    Dari mana kita mengetahui material ma

    Diambil dari www.deeps

    1500 m

    03/10/2015

    http://www.deepseadrilling.org/about.htmhttp://www.deepseadrilling.org/about.htm
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    15

    10

    5

    0

    0.0 0.2 0.4

    Wt.%Al2O3

    Wt.% TiO2

    Dunite

    Harzburgite

    Lherzolite

    Thole

    Residuum

    Lherzolite is probably

    fertile unaltered mantle

    Dunite and harzburgite are

    refractory residuum after

    basalt has been

    extracted by partial

    melting

    Figure 10-1 Brown and Mussett,

    A. E. (1993), The Inaccessible

    Earth: An Integrated View of Its

    Structure and Composit ion.

    Chapman & Hall/Kluwer.

    Komposisi mantel

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    LherzolitePeridotit dengan

    Olivine > Opx + Cpx

    Olivine

    Orthopyroxene

    Lherzolite

    Websterite

    Orthopyroxenite

    Clinopyroxenite

    Olivine Websterite

    90

    40

    10

    Dunite

    Komposisi mantel

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    Fase diagram lherzolite

    Plagioclase shallow (< 50 km)

    Spinel

    50-80 km

    Garnet 80-400 km

    Al-phase =

    Figure 10.2 Phase diagram of aluminous lherzolite with melting interval (gray), sub-solidus reactions,and geothermal gradient. After Wyllie, P. J. (1981). Geol. Rundsch. 70, 128-153.

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    Bagaimana kita melelehkan mante

    03/10/2015

    http://rumahgunung.files.wordpress.com/2011/12/magmatism-1.pnghttp://rumahgunung.files.wordpress.com/2011/12/magmatism-1.png
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    1) Increase the temperature

    No reamecha

    the gen

    case

    Local h

    OK (jar

    terbata

    03/10/2015

    2) Lower the pressure

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    2) Lower the pressure

    Adiabatic rise of mantle with no conductive heat loss

    Decompression partial melting could melt at least 30%

    Melti(adiab

    reduc

    Melti

    the ad

    the so

    travemelti

    Dashe

    repre

    appro

    melti

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    3) Add volatiles (especially H2O)

    Figure 10.4.compared to

    H2O-saturat

    Dramatic lo

    of melting p

    peridotite

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    Konveksi skala besar?

    Upper depleted mantle = MORB source

    depleted by MORB extraction > 1 Ga

    Lower = undepleted & enriched OIB

    source

    Boundary = 670 km phase transitionSufficient density to impede convection

    so they convect independently

    Homogeneous vs Layered mantle?

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    Review of REE

    Figure 9.4. Rare Earth concentrations

    (normalized to chondrite) for melts produced

    at various values of F via melting of a

    hypothetical garnet lherzolite using the batch

    melting model (equation 9-5). From Winter

    (2001) An Introduction to Igneous and

    Metamorphic Petrology. Prentice Hall.

    03/10/2015 increasing incompatibi

    Enrich LREE > HREE

    Greater enrichment

    for lower % PM

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    REE data for oceanic basalts

    Figure 10.14a. REE diagram for a typical alkaline ocean island basalt (OIB) and tholeiitic mid-ocean ridge basalt (MO(2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (1989).

    03/10/2015

    increasing incompatibility

    Ocean Islan

    (Hawaiian a

    basalt)

    Looks li

    melt of

    mantle

    Mid Ocean

    (tholeiite)How ge

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    Spider diagram for oceanic basalts

    Figure 10.14b. Spider diagram for a typical alkaline ocean island basalt (OIB) and tholeiitic mid-ocean ridge basalt (MOWinter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall. Data from Sun and McDonough (

    03/10/2015

    increasing incompatibility

    Same approach

    variety of eleme

    Still OIB lo

    melt of ~ typMORB stil

    Looks like two m

    reservoirs

    MORB sou

    by melt extrOIB source

    is it enr

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    REE data for UM x

    Figure 10.15 Chondrite-normalized REE diagrams for spinel (a) and garnet (b) lherzolites. After Basaltic VolcanismStudy Project (1981). Lunar and Planetary Institute.

    LREE enriched

    LREE depleted

    or unfractionated

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    Depleted types (+) slope

    Fertile types (-) slope --> Enriched?

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    Nd and Sr isotopes of Ocean Basalts

    Figure 10.16a. Initial

    143

    Nd/

    144

    Nd vs.

    87

    Sr/

    86

    Sr for oceanic basalts. From Wilson (1989). Igneous PetrogenesUnwin Hyman/Kluwer. Data from Zindler et al. (1982) and Menzies (1983).03/10/2015

    Mantle Array MORB at depTahiti, Gough

    at enriched eTruly enriche

    Earth

    Array = mixin

    Two cmixed

    How m

    liquid

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    Figure 14-6. After Zindler and Hart (1986), Staudigel et al. (1984), Hamelin et al.(1986) and Wilson (1989).03/10/2015

    Partial Melting

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    Partial Melting

    in a Plume

    Figure 14.20. Diagrammatic plume-tail

    melting model. Rising plume material

    (heavy arrows are flow lines) is hotter

    toward the axis. Fluid-present melting of

    mantle lherzolite may begin at depths of

    about 350 km (stippled area), but the

    extent of such melts depends on the

    amount of fluid present and is probably

    minor. Melting of recycled crustal pods

    and stringers (red to green streaks) may

    also begin near this depth and such

    melting may be more extensive locally.

    Major lherzolite melting occurs at depths

    near 100 km. The melt fraction is

    greatest near the plume axis, producing

    picrites and tholeiites. The extent of

    plume asymmetry depends on plume

    flux and plate velocity. Plume-head

    melting is much more extensive (Chapter

    15). Based on Wyllie (1988b).

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    MORB Petrogenesis

    Separation of plates

    Upward motion of mantle materialinto extended zone

    Decompression partial meltingassociated with near-adiabatic rise

    N-MORB melting initiated ~ 60-80

    km depth in upper depleted mantlewhere it inherits depleted traceelement and isotopic char.

    Generation

    Figure 13.14. After Zindler et al. (1984) Earth

    Planet. Sci. Lett., 70, 175-195. and Wilson (1989)

    Igneous Petrogenesis, Kluwer.03/10/2015

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    Sekuen Ofiolit

    03/10/2015

    A Model for Oceanic Magmatism

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    A Model for Oceanic Magmatism

    Figure 1

    oceanic

    Zindler

    Zindler03/10/2015

    Island Arc Petrogenesis

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    Phlogopite is stable beyond

    amphibole breakdown

    Wedge P-T-t paths reach phlogopite

    dehydration at ~ 200 km depth

    Island Arc Petrogenesis

    03/10/2015

    Struktur pada zona subduksi IA)

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    Figure 16.2. Schematic cross section through a typical island arc after Gill (1981), Orogenic Andesites

    and Plate Tectonics. Springer-Verlag. HFU= heat flow unit (4.2 x 10-6joules/cm2/sec)

    Note mantle

    (induced dra

    wedge, and

    back-arc bas

    system

    Beniof

    seismic z

    Volcan

    h is re

    depth

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    03/10/2015

    Pergerakan lempeng secara tidak langsung dipengaruhi olehbagian-nagian bumi

    Pelelehan parsial mantel mengambilPT-path yang berbedatatanan tektonik

    Mantel tidakhomogen

    Rangkuman

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    03/10/2015

    Rangkuman

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