Njira za Petrographic mu Kusanthula kwa Mathanthwe
Petrografiya ndi nthambi ya geology yomwe imayang'ana kwambiri kufotokozera ndi kutanthauzira miyala kutengera kapangidwe kake ka mchere, kapangidwe kake, ndi kapangidwe kake ka mkati. Njira ya petrografiya ndi imodzi mwa njira zofunika kwambiri pakusanthula miyala chifukwa imatha "kuwerenga" mbiri ya mapangidwe a miyala kudzera mu kuwona mwachindunji, makamaka pogwiritsa ntchito maikulosikopu yozungulira. Kuyambira pa igneous ndi sedimentary mpaka pa miyala ya metamorphic , petrography imathandiza akatswiri a geology kumvetsetsa njira za geological monga magma crystallization, deposition, diagenesis, deformation, metamorphism, ndi hydrothermal alteration.
1. Malingaliro Oyambira a Petrography
Kawirikawiri, petrography imagawidwa m'magawo awiri akuluakulu: macroscopic petrography ndi microscopic petrography. Macroscopic petrography imachitika mwa kuyang'ana mwachindunji miyala (zitsanzo za manja), mwachitsanzo poyang'ana mtundu, kukula kwa tirigu, kuwala kwa mchere, porosity, kapena kukhalapo kwa masamba. Pakadali pano, microscopic petrography imachitika mwa kuyang'ana magawo opyapyala a miyala pansi pa microscope yozungulira kuti mudziwe mchere ndi mawonekedwe omwe sangawonekere ndi maso.
Mphamvu ya petrography ili mu kuthekera kwake kogwirizanitsa mawonekedwe a miyala ndi njira zomwe zidapanga. Mwachitsanzo, miyala ya igneous yokhala ndi mawonekedwe a porphyritic imasonyeza magawo awiri a kuzizira kwa magma, pomwe miyala ya metamorphic yokhala ndi masamba amphamvu imasonyeza kukhalapo kwa mphamvu yayikulu yosiyana.
2. Magawo a Njira ya Petrographic
Njira zoyezera miyala nthawi zambiri zimatsatira magawo akuluakulu angapo: kutengera zitsanzo, kukonzekera magawo ochepa, kuyang'ana pa microscope, kutanthauzira, ndi kupereka malipoti. Gawo lililonse limafuna kulondola, chifukwa ngakhale zolakwika zazing'ono zingayambitse kutanthauzira kolakwika.
a. Kusankha
Gawo loyamba ndi kusonkhanitsa zitsanzo za miyala kuchokera kumunda kapena pakati pa bowo. Mwachiyembekezo, zitsanzo ziyenera kukhala zoyimira thanthwe lomwe liyenera kufufuzidwa osati kuwonongedwa kwambiri. Mu maphunziro a za nthaka, zitsanzo nthawi zambiri zimatsatiridwa ndi zolemba mwatsatanetsatane: malo, ma coordinates, ubale wa stratigraphic, kapangidwe ka nthaka kozungulira, ndi kusintha kwa zinthu. Pa miyala ya sedimentary , ndikofunikiranso kuzindikira komwe bedi ndi kapangidwe ka sedimentary zikuyendera. Pa miyala ya metamorphic , masamba ndi mzere ziyenera kulembedwa chifukwa zitha kukhala zogwirizana ndi kutanthauzira kwa microtextural.
b. Kukonzekera Gawo Loonda
Gawo lopyapyala ndi miyala yophikidwa mpaka makulidwe a pafupifupi ma micrometer 30 kuti kuwala kulowe mu mchere. Njira yopangira gawo lopyapyala imaphatikizapo kudula chitsanzocho, kuchilumikiza ku galasi pogwiritsa ntchito utomoni, kupukuta, kupukuta, ndipo nthawi zina kuwonjezera chophimba.
Ubwino wa gawo lopyapyala ndi wofunika kwambiri. Kukhuthala kosagwirizana kungasinthe mawonekedwe a mitundu yosokoneza mchere, zomwe zimapangitsa kuti kuzindikirika kukhale kovuta. Kuwonjezera pa magawo opyapyala wamba, palinso zinthu zina zapadera, monga magawo opukutidwa, kuti afufuze mchere wosawoneka bwino (monga pyrite, magnetite) pogwiritsa ntchito maikulosikopu yowunikira.
c. Kuyang'anitsitsa pogwiritsa ntchito maikulosikopu yozungulira
Kuyang'ana kwa petrographic pogwiritsa ntchito microscope ya polarizing nthawi zambiri kumachitika pogwiritsa ntchito maikulosikopu ya polarizing yomwe ili ndi njira ziwiri zazikulu: kuwala kofanana kwa polarized (Plane Polarized Light/PPL) ndi kuwala kophatikizana kwa polarized (Cross Polarized Light/XPL).
1. PPL imagwiritsidwa ntchito poona:
– Mtundu wa mchere (mtundu)
- Pleochroism (kusintha kwa mtundu ukazunguliridwa)
- Mpumulo (kusiyana kwa mchere ndi matrix)
– Mawonekedwe a kristalo (euhedral, subhedral, anhedral)
- Kusweka ndi ming'alu
2. XPL imagwiritsidwa ntchito poona:
- Mitundu yosokoneza
- Twinning, mwachitsanzo mu plagioclase
- Ngodya ya kutha
- Birefringence (kusiyana kwa refractive index)
- Kapangidwe ka kristalo ndi ubale wapakati pa mchere
Mu kusanthula, akatswiri a za nthaka adzazindikira mchere woyambira (monga quartz, feldspar, pyroxene, amphibole, mica) ndi mchere wowonjezera (zircon, apatite, titanite) komanso mchere wachiwiri womwe umabwera chifukwa cha kusintha (sericite, chlorite, epidote, calcite).
d. Kusanthula Kapangidwe ndi Kapangidwe kake
Kuwonjezera pa kapangidwe ka mchere, petrography imagogomezeranso kusanthula kapangidwe kake (kukula, mawonekedwe, ndi ubale pakati pa tirigu/minerals) ndi kapangidwe kake (zinthu zazikulu, zokonzedwa bwino). Zitsanzo za kapangidwe kofunikira:
– Kapangidwe ka porphyritic: ma phenocryst akuluakulu mu nthaka yopyapyala, zomwe zikusonyeza mbiri yozizira pang'onopang'ono mu miyala ya igneous.
– Kapangidwe ka tinthu tating'onoting'ono: tinthu tating'onoting'ono tofanana, tomwe timapezeka m'miyala ya granite kapena miyala ina yosinthika.
– Kapangidwe ka vesicular: mabowo chifukwa cha mpweya, omwe amapezeka kwambiri mu basalt.
– Kapangidwe kake kakale: zidutswa za miyala/mineral zomangidwa ndi matrix kapena simenti, zomwe zimakhala ngati miyala ya sedimentary.
– Kapangidwe ka Lepidoblastic kapena nematoblastic: momwe mica kapena amphibole imaonekera m'miyala yosinthika.
– Kapangidwe ka Mylonitic: kusintha kwakukulu chifukwa cha kudulidwa, zomwe zimapangitsa kuti tinthu tating'onoting'ono tipezeke komanso masamba olimba.
Mu miyala ya sedimentary, petrography imatha kuwonetsa kuchuluka kwa kusanja, kuzungulira kwa tirigu, mtundu wa simenti (silika, calcite, iron oxide), ndi porosity. Mu miyala ya metamorphic, petrography imatha kuzindikira mchere wa metamorphic index monga garnet, staurolite, kyanite, ndi sillimanite, zomwe zimathandiza kudziwa kuchuluka kwa metamorphism.
e. Kuwerengera: Kuwerengera Mfundo ndi Kugawa
Kuti zinthu ziyende bwino, petrography nthawi zambiri imathandizidwa ndi njira zowerengera monga kuwerengera mfundo. Ndi njira iyi, wowonera amawerengera kuchuluka kwa mchere kutengera mfundo zingapo zowunikira m'magawo ochepa. Zotsatira zake zimagwiritsidwa ntchito pogawa, mwachitsanzo:
- Chithunzi cha QAPF cha miyala ya plutonic igneous (quartz–alkali feldspar–plagioclase–feldspathoid)
- TAS diagram (yodziwika kwambiri pa miyala ya volcano yopangidwa ndi mankhwala, koma petrography ingathandize kutsimikizira za mineralization)
- Kugawa miyala yamchenga (monga quartz arenite, arkose, litharenite) kutengera kapangidwe ka quartz–feldspar–lithic fragment
- Kugawa miyala ya metamorphic kutengera mchere ndi kapangidwe kake (schist, gneiss, marble, quartzite)
Kuwerengera mchere kumathandizanso poyesa ubwino wa malo osungiramo mafuta ndi gasi m'maphunziro a geology, mwachitsanzo kuchuluka kwa simenti ya carbonate yomwe imachepetsa ma porosity.
3. Kutanthauzira kwa Njira za Dziko
Kufunika kwakukulu kwa petrography ndi kutanthauzira. Kuchokera ku deta ya mineralological ndi textural, akatswiri a geology amatha kukonzanso njira zomwe zinapanga miyala. Zitsanzo zina za kutanthauzira:
– Kupezeka kwa zoned plagioclase m'miyala ya igneous kungasonyeze kusintha kwa kapangidwe ka magma panthawi ya crystallization.
– Kusintha kwa zinthu monga kupangika kwa garnet kuchokera ku chlorite ndi biotite kumasonyeza kuwonjezeka kwa kutentha ndi kupanikizika.
– Kulimbitsa silika mu mchenga kumasonyeza gawo la diagenetic, pomwe kubwezeretsanso kwa kristalo kumatha kuwonjezera kapena kuchepetsa ubwino wa ma pore.
– Kusintha kwa kutentha kwa madzi monga sericitation, chloritization, kapena silicication kungakhale chizindikiro cha dongosolo la mineralization ya ore.
Motero, petrography sikuti imangoyankha kuti "mwala uwu ndi chiyani", komanso "mwala uwu umapangidwira bwanji komanso umasinthidwa bwanji".
4. Ubwino ndi Zofooka za Njira Zofufuzira Zinthu
Petrografiya ili ndi ubwino wambiri: ndi yotsika mtengo poyerekeza ndi kusanthula kwathunthu kwa geochemical, imapereka chidziwitso chochuluka cha kapangidwe kake, ndipo ndi yothandiza kuzindikira mchere ndi ubale wawo. Komabe, petrography ilinso ndi zolepheretsa. Miyala yopyapyala ingakhale yovuta kuzindikira, mchere wosawoneka bwino umafuna njira zapadera, ndipo kutanthauzira kumatha kukhudzidwa ndi zomwe owonera akuwona. Chifukwa chake, petrography nthawi zambiri imaphatikizidwa ndi njira zina monga XRD (X-ray diffraction), SEM-EDS, kusanthula kwa geochemical, kapena kusanthula kwa isotope kuti zitsimikizire zotsatira.
5. Mapeto
Njira zofufuzira miyala ndi maziko ofunikira pakusanthula miyala chifukwa zimaphatikiza kuyang'ana mwachindunji, kuzindikira mchere, kusanthula kapangidwe kake, ndi kutanthauzira njira za geological. Kudzera mu njira zokhazikika—kuyambira kutengera zitsanzo ndi kugawa magawo pang'ono mpaka kuwona ndi kuwerengera zinthu zazing'ono—petrography ikhoza kupanga chithunzi chokwanira cha umunthu wa thanthwe ndi mbiri ya geological. M'machitidwe amakono, petrography imakhalabe yofunikira komanso yamphamvu kwambiri ikaphatikizidwa ndi njira zina zowunikira, zomwe zimapereka kumvetsetsa kolondola kwa mphamvu za Dziko Lapansi ndi mphamvu ya geological.
