Mekhoa ea Petrographic Tlhahlobong ea Lefika
Petrography ke lekala la jeoloji le shebaneng le tlhaloso le tlhaloso ea mafika ho latela sebopeho sa 'ona sa liminerale, sebopeho le sebopeho sa ka hare. Mokhoa oa petrographic ke o mong oa mekhoa ea bohlokoa ka ho fetisisa tlhahlobong ea mafika hobane o ka "bala" nalane ea ho thehoa ha mafika ka ho shebella ka ho toba, haholo-holo ka thuso ea microscope e nang le polarizing. Ho tloha mafikeng a igneous le sedimentary ho ea ho a metamorphic, petrography e thusa litsebi tsa jeoloji ho utloisisa lits'ebetso tsa jeoloji tse kang magma crystallization, deposition, diagenesis, deformation, metamorphism, le hydrothermal alteration.
1. Mehopolo ea Motheo ea Petrography
Ka kakaretso, petrography e arotsoe ka libaka tse peli tse ka sehloohong: macroscopic petrography le microscopic petrography. Macroscopic petrography e etsoa ka ho shebella mafika ka kotloloho (disampole tsa letsoho), mohlala ka ho sheba 'mala, boholo ba lithollo, khanya ea liminerale, masoba, kapa boteng ba makhasi. Ho sa le joalo, microscopic petrography e etsoa ka ho shebella likarolo tse tšesaane tsa mafika tlas'a microscope e nang le polarizing ho khetholla liminerale le metsoako e sa bonahaleng mahlong a hlobotseng.
Matla a petrography a hokahanngoa ha litšobotsi tsa 'mele tsa majoe le lits'ebetso tse a entseng. Mohlala, majoe a igneous a nang le sebopeho sa porphyritic a bontša mekhahlelo e 'meli ea ho pholisa ha magma, ha majoe a metamorphic a nang le makhasi a matla a bontša boteng ba khatello e matla ea phapang.
2. Mehato ea Mokhoa oa Petrographic
Mekhoa ea petrographic bakeng sa tlhahlobo ea mafika ka kakaretso e latela mekhahlelo e 'maloa e meholo: ho nka disampole, ho lokisa karolo e tšesaane, ho shebella ka microscope, tlhaloso le tlaleho. Mohato ka mong o hloka ho nepahala, kaha esita le liphoso tse nyane li ka lebisa litlhalosong tse fosahetseng.
a. Ho etsa disampole
Mokhahlelo oa pele ke pokello ea lisampole tsa lefika tse tsoang tšimong kapa khubung ea drill. Ha e le hantle, lisampole li lokela ho emela lefika le lokelang ho hlahlojoa 'me li se ke tsa senyeha haholo. Lithutong tsa jeoloji ea tšimo, lisampole hangata li tsamaea le rekoto e qaqileng: sebaka, likhokahano, likamano tsa stratigraphic, meaho e potolohileng ea jeoloji, le maemo a phetoho. Bakeng sa mafika a sedimentary, ho bohlokoa hape ho ela hloko tataiso ea meaho ea bethe le ea sedimentary. Bakeng sa mafika a metamorphic, ho lokela ho tlalehoa hore makhasi le tataiso ea mola li ka ba tsa bohlokoa tlhalosong ea microtextural.
b. Tokiso ea Karolo e Tšesaane
Karolo e tšesaane ke lefika le lokisoang ka botenya ba di-micrometer tse ka bang 30 e le hore lesedi le ka kenella diminerale. Ts'ebetso ea ho theha karolo e tšesaane e kenyelletsa ho seha sampole, ho e hokela ho slide ea khalase ho sebelisoa resin, ho sila, ho bentša, 'me ka linako tse ling ho eketsa sekoahelo.
Boleng ba karolo e tšesaane bo bohlokoa haholo. Botenya bo sa lekanang bo ka fetola ponahalo ea mebala ea tšitiso ea liminerale, e leng se etsang hore ho be thata ho tsebahatsa. Ntle le likarolo tse tšesaane tse tloaelehileng, ho na le litokisetso tse khethehileng, tse kang likarolo tse bentšitsoeng, bakeng sa ho sekaseka liminerale tse sa bonahaleng (mohlala, pyrite, magnetite) ho sebelisoa microscope e bonts'ang.
c. Ho shebella ka Microscope e Polarizing
Liteko tsa petrographic tsa microscopic hangata li etsoa ka microscope ea polarizing e nang le mekhoa e 'meli e meholo: leseli le kopantsoeng le nang le polarized (Plane Polarized Light/PPL) le leseli le tšekaletseng le nang le polarized (Cross Polarized Light/XPL).
1. PPL e sebediswa ho hlokomela:
– 'Mala oa diminerale ('mala)
– Pleochroism (phetoho ea 'mala ha e potoloha)
– Phomolo (phapang ea liminerale ho matrix)
– Sebopeho sa kristale (euhedral, subhedral, anhedral)
– Ho petsoha le mapetso
2. XPL e sebediswa ho hlokomela:
– Mebala ea tšitiso
– Twinning, mohlala, ho plagioclase
– Sekhutlo sa ho fela
– Birefringence (tekanyo ea phapang ho refractive index)
- Sebopeho sa kristale le likamano tsa liminerale
Tlhahlobong, litsebi tsa jeoloji li tla khetholla liminerale tsa mantlha (mohlala, quartz, feldspar, pyroxene, amphibole, mica) le liminerale tse thusang (zircon, apatite, titanite) hammoho le liminerale tsa bobeli tse bakoang ke phetoho (sericite, chlorite, epidote, calcite).
d. Tlhahlobo ea Sebopeho le Sebopeho
Ntle le sebopeho sa diminerale, petrography e boetse e totobatsa tlhahlobo ya sebopeho (boholo, sebopeho, le dikamano pakeng tsa dithollo/diminerale) le sebopeho (dikarolo tse kgolo, tse hlophisehileng haholoanyane). Mehlala ya sebopeho sa bohlokwa:
– Sebopeho sa porphyritic: di-phenocryst tse kgolo mobung o nang le dimela tse ntle, tse bontshang nalane ya ho phodisa butle-butle lefikeng la igneous.
– Sebopeho sa di-granular: di-granular tse batlang di tshwana, tse tlwaelehileng majweng a granite kapa majweng a itseng a fetotsweng.
– Sebopeho sa vesicular: masoba a bakoang ke khase, a atileng haholo basalt.
– Sebopeho sa khale: likotoana tsa lefika/diminerale tse tlamilweng ke matrix kapa samente, tse tlwaelehileng majweng a sedimentary.
– Sebopeho sa Lepidoblastic kapa nematoblastic: tataiso ya mica kapa amphibole mafikeng a metamorphic.
– Sebopeho sa Mylonitic: ho fetoha ho matla ka lebaka la ho kuta, ho fellang ka lithollo tse tšesaane le makhasi a matla.
Mafikeng a sedimentary, petrography e ka senola tekanyo ea ho hlopha, ho chitja ha lithollo, mofuta oa samente (silica, calcite, iron oxide), le porosity. Mafikeng a metamorphic, petrography e ka khetholla liminerale tsa metamorphic index tse kang garnet, staurolite, kyanite, le sillimanite, tse thusang ho fumana tekanyo ea metamorphism.
e. Palo: Ho Bala Lintlha le ho li Hlopha
Ho eketsa ho se nke lehlakore, petrography hangata e tlatselletsoa ka mekhoa ea lipalo tse kang ho bala lintlha. Ka mokhoa ona, moshebelli o bala peresente ea liminerale ho latela lintlha tse 'maloa tsa tlhokomelo e hlophisitsoeng likarolong tse tšesaane. Liphetho li sebelisetsoa ho arola, mohlala:
– Setšoantšo sa QAPF bakeng sa mafika a plutonic igneous (quartz–alkali feldspar–plagioclase–feldspathoid)
– Setšoantšo sa TAS (se atile haholo bakeng sa mafika a seretse se chesang a thehiloeng lik'hemik'haleng, empa petrography e ka thusa ka netefatso ea liminerale)
– Ho hlophisoa ha majwe a lehlabathe (mohlala, quartz arenite, arkose, litharenite) ho itshetlehile ka sebopeho sa quartz–feldspar–lithic fragment
– Ho hlophisoa ha mafika a metamorphic ho latela diminerale tse hlahelletseng le sebopeho (schist, gneiss, marble, quartzite)
Ho bala diminerale ho boetse ho thusa ho lekola boleng ba matamo lithutong tsa jeoloji ea oli le khase, mohlala, dikahare tsa samente ea carbonate e fokotsang masoba.
3. Tlhaloso ea Mekhoa ea Jeoloji
Boleng ba mantlha ba petrography ke tlhaloso. Ho tsoa ho data ea mineralology le ea mongolo, litsebi tsa jeoloji li ka haha bocha lits'ebetso tse entseng mafika. Mehlala e meng ea tlhaloso:
– Boteng ba plagioclase e nang le libaka mafikeng a igneous bo ka bontša liphetoho mokhoeng oa magma nakong ea kristale.
– Likarabelo tsa metamorphic tse kang ho thehoa ha garnet ho tsoa ho chlorite le biotite li bontša keketseho ea mocheso le khatello.
– Ho kopanngoa ha silica lejoeng la lehlabathe ho bontša mohato oa diagenetic, ha ho tsosolosoa ha likristale ho ka eketsa kapa ho fokotsa boleng ba masoba.
– Phetoho ea hydrothermal joalo ka ho sericitation, chloritization, kapa silicication e ka ba sesupo sa sistimi ea mineralization ea ore.
Ka hona, petrography ha e arabe feela hore "lefika lena le entsoe ka eng", empa hape e araba "lefika lena le thehiloe le ho fetoloa joang".
4. Melemo le Mefokolo ea Mekhoa ea Petrographic
Petrografiya e na le melemo e 'maloa: e theko e tlase haholo ha e bapisoa le tlhahlobo e felletseng ea geochemical, e fana ka tlhaiso-leseling e ruileng ea mongolo, 'me e sebetsa hantle bakeng sa ho khetholla liminerale le likamano tsa tsona. Leha ho le joalo, petrography le eona e na le meeli. Liminerale tse nang le meedi e menyenyane li ka ba thata ho li khetholla, liminerale tse sa bonahaleng li hloka mekhoa e khethehileng, 'me litlhaloso li ka susumetsoa ke subjectivity ea moshebelli. Ka hona, petrography hangata e kopanngoa le mekhoa e meng e kang XRD (X-ray diffraction), SEM-EDS, tlhahlobo ea geochemical, kapa tlhahlobo ea isotope ho netefatsa liphetho.
5. Qetello
Mekhoa ea petrographic ke motheo oa bohlokoa oa tlhahlobo ea mafika hobane e kopanya tlhokomelo e tobileng, ho tsebahatsa liminerale, tlhahlobo ea sebopeho, le tlhaloso ea lits'ebetso tsa jeoloji. Ka mehato e hlophisehileng—ho tloha ho lisampole le ho arola ka mokhoa o mosesaane ho ea ho tlhokomelo e nyenyane le ho lekanya—petrography e ka hlahisa setšoantšo se felletseng sa botho ba lefika le nalane ea jeoloji. Mokhoa oa sejoale-joale, petrography e ntse e le ea bohlokoa ebile e le matla le ho feta ha e kopantsoe le mekhoa e meng ea tlhahlobo, e fanang ka kutloisiso e nepahetseng haholoanyane ea matla a Lefatše le bokhoni ba mehloli ea jeoloji.
