Teknologi Kebumian(MGD 421)
GDG 10
Program Studi Teknik GeologiFakultas Teknologi Kebumian dan EnergiUniversitas Trisakti2011
Materi GDG 10PendahuluanPENGERTIAN GEOLOGI, Proses, Hukum BUMI SEBAGAI PLANETLITHOSFERA - MINERALBATUAN : BT, BEKU BT SEDIMENBT, METAMORP STRUKTUR GEOLOGI P E TATEKNOLOGI KEBUMIAN
Land SeismicOffshore Seismic
Evidence from Seismic Waves
Earths Internal StructureThe CrustThe MantleThe Core
Seismic ReflectionControlled by:
Snells LawElastic properties of the layers
Seismic RefractionRay paths arebent acrossvelocity or seismicdiscontinuities.
Bend away fromboundary normalif V2 > V1
Bend towardboundary normalif V1 > V2V1V2
Modified from: Brown & Mussett, 1981V2V1In this example, V2 > V1
Locating Boundaries By Refraction
Radial Distribution of Ray PathsRays curveupward becauseof generallyincreasingvelocitywith depthVp and Vs
Internal Earth Structure from SeismologyCrust: 0-60 km
Mantle: 60-2900 km
Core: 2900-6370 km
Seismic Moho and LVZ
Summary Crustal Properties
Mantle TomographyBlue = Fast (cold)
Red = Slow (hot)
Deep Earth Velocity StructureNB that velocity is measured from earthquake waves, but density mustBe inferred from inversion of the velocity combined with elastic modulii
P wave Shadow Zone
S wave Shadow Zone
OlivineFe-NiMetal AlloyPallisite meteorites are classified as stoney-irons and are thoughtto be derived from the CMB region of an asteroidal parent body.Non-seismologicalevidence of core - mantleexchange!
From: Garnero, E.J., Ann. Rev. Earth Planetary Sci., 28 , 509-37, 2000.
Isostasy and GravityIsostasy is the gravitational equilibrium of bodies of different density.Isostatically compensated uplift zones are stabilized by low density roots.Isostatic re-adjustment can be caused by many different processes.
IsostasyCompensation depth is arbitrary and selected for convenience. Total column mass (or gravitational acceleration) must be equal.Low densityHigh density
Isostatic Readjustment: Erosion
Post-glacial Crustal Rebound
From: http://www.uni-geophys.gwdg.de/~gkaufman/work/onset/onset_ice3g.html
Isostatic Uplift due to Crustal ThickeningNB that uplift would depend on the amount and density ofaccumulated magma accreted to the base of the crust.
Gravitational Attraction
Gravity Meters Response to Density VariationsLocal gravity high can be related to a high density body within the crust,while a gravity low can be related to a lower than average density.gravityhighgravitylowLow densityHigh density
Gravity Profile in Isostatic Equilibrium
Non-isostatically Compensated Profile
Negative Gravity Anomaly
Chapter 8
Time and Geology
Sir Charles LyellImage source: www.mnsu.edu/emuseum
Simple Geologic Time Scale
Absolute or Numerical AgeIsotopic DatingUses of Isotopic Dating
Combining Relative and Absolute AgesThe Age of the EarthComprehending Geologic Time
Radioactive Decay MechanismsOperates when Z 58
222Rn86 -> 218Po84 + (5.5 MeV) + n0 = p+ + e-
40K19 -> 40Ca20 + (1.3 MeV) + e- + p+ = n0
125I53 -> 125Te52 + (~3 KeV)
87Rbb87SrRadioactive decay and radiogenic IsotopesRadiogenic isotope ratios are functions of both time and parent/daughter ratios. They can help infer the chemical evolution of the Earth.
Radioactive decay schemes87Rb-87Sr (half-life 48 Ga)147Sm-143Nd (half-life 106 Ga)238U-206Pb (half-life 4.5 Ga)235U-207Pb (half-life 0.7 Ga)232Th-208Pb (half-life 14 Ga)
Extinct radionuclidesExtinct radionuclides have half-lives too short to survive 4.55 Ga, but were present in the early solar system.
Uranium 238 Decay Scheme
Instruments and TechniquesMass Spectrometry: measure different abundances of specific nuclides based on atomic mass.Basic technique requires ionization of the atomic species of interest and acceleration through a strong magnetic field to cause separation between closely similar masses (e.g. 87Sr and 86Sr). Count individual particles using electronic detectors.TIMS: thermal ionization mass spectrometrySIMS: secondary ionization mass spectrometry - bombard target with heavy ions or use a laserSample Preparation: TIMS requires doing chemical separation using chromatographic columns.
http://www.es.ucsc.edu/images/clean_lab_c.jpg
From: http://www.es.ucsc.edu/images/vgms_c.jpg
Half-life and exponential decayExponential decay:Never get to zero!Linear decay:Eventually get to zero!
Pt = Po exp - (to t)1st order rate law
Where
Pt
quantity of the parent isotope (i.e. 87Rb) at time t;
Po
quantity of the parent isotope at some earlier time to, when the isotopic system was closed to any additional isotopic exchange;
is the characteristic decay constant for the system of interest, which is related to the half-life, t1/2, by the equation below:
ln 2 / t1/2
t1/2
is defined as the half-life, which is the amount of time required for 1/2 of the original parent to decay and is a constant.
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87Rbt = 87Rbo e -to t)
(Assume that t = 0, for the present)
87Rbo + 87Sro = 87Rbt + 87Srt
(Conservation of Mass, with 87Sro as the initial
concentration and 87Srt as the concentration today)
87Srt - 87Sro = 87Rbt (e to 1)
M1M2M3
Basic Geochronological AssumptionsDecay constants remain constant through geological time. Good reasons to believe this is correct based on nuclear physics.Measurements of decay sequences in ancient supernovae yield the same values as modern lab measurements.System remains closed to addition or subtraction of parent or daughterDepends on the isotopic system and type of rock (mineral) being measured. Careful sample preparation and thorough characterization of the materials is essential to correct interpretation of results.
Half-lives for common parents
Independent Checks on Radiometric AgesCorrelation of erosion with age on Hawaiian Island Chain: Dates increase in age to the NW as does erosion.Annual growth bands in Devonian corals: 400/yr yields date that is similar to radiometric date. Consistent with slowing of Earth rotation with time.Independent determination of Pacific plate motion yields age progression that is consistent with K/Ar dates of the islands.Agreement between magnetic age from deep marine sediments and radiometric ages of tuffs in East African Rift
Relative and Absolute dates combined
Modern Geological Time Scale
The Age of the EarthEarly Methods: Long debated among intellectuals1625 Archbishop James Usher determined the Earth was created 4004 B.C. by counting generations in the Bible. Young Earth was commonly accepted by western countries.Hindus regarded the Earth as very old. 2000 A.D. would be 1.97 million years according to their calendar.1866 Lord Kelvin calculated the age of the earth based on physical principles. Assumed that the Earth was entirely molten and had to cool to become a solid. Estimated the age between 20-40 million years old.Unknown sources of heat - radioactive decayAssumed that all heat was dissipated by conductionEarly Isotopic Methods: 1905 First crude estimates yielded 2 billion year ageMeteorites gave dates of 4.5 to 4.6 billion years oldModern U-Pb methods yield a consensus value of 4.55 By old
Comprehending Geological Time
SIG atau Geographic Information System (GIS) : menyimpan, dan menganalisis objek dan fenomena geografis merupakan karakteristik yang penting dianalisis
Bentuk SIG Komponen SIG
Tol TomangSelat SundaTerminal Sukarno HattaSenayan
GEOLOGIPENGELOLAAN SUMBER DAYA ALAM DARI BIDANG GEOLOGI, PERTAMBANGAN DAN MIGASTAMBANGNON TAMBANGLOGAMMIGASNON MIGASGEOTHERMALVOLKANOLOGILINGKUNGANGEODINAMISTEKNIK SIPILDLL
Eksplorasi Geologi Permukaan TanahFoto Udara / Foto Satelit Geologi Bawah Permukaan TanahPeta Topografi
Peralatan survai well loggingKegiatan survai lapangan, Pengambilan data Geofisika dan Geokimia
Kegiatan Survei Geofisika (seismik) dalam eksplorasi Migas
Kegiatan Pengolahan dan Interpretasi Data Geologi (di Laboratorium)Pengolahan dan Interpretasi Data di Laboratorium
Ahli Geologi meneliti sampel batuan dari inti pemboran (core)KEGIATAN PENGEBORAN SUMUR EKSPLORASIPeralatan survai well logging
PENGEBORAN DI DARAT dan DI LEPAS PANTAI
Energi Alternatif Ramah Lingkungan Geothermal
GALIAN TAMBANG TEMBAGA FREEPORT
Bagaimana di masa depan?? ???Ada di tangan kita !!
Pustaka dan Acuan : - Prodi Teknik Geologi FTKE Usakti- Museum Geologi- Pusat Survei Geologi Pusat Lingkungan Geologi - Berbagai Situs Internet
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