p2 pembentukan & komposisi magma
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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).
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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?
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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
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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
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1) Increase the temperature
No reamecha
the gen
case
Local h
OK (jar
terbata
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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.
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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).
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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 (
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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
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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
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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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Pergerakan lempeng secara tidak langsung dipengaruhi olehbagian-nagian bumi
Pelelehan parsial mantel mengambilPT-path yang berbedatatanan tektonik
Mantel tidakhomogen
Rangkuman
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Rangkuman
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