T ^ chi DIA CHAT- l o t A. so 317-318.3-6Q01Q. Ir-S3.59
ATLAS KIEN TRUC - CAU TAO DA BIEN CHAT VIET NAM
NGUYEN VAN HOC
Vien Khoa hpc Dja cha va Khodng sdn. Km 9. Thar^Xudn. HaNoi Tom /flt Atlas kien true - cdu tgo dd biin chdt Viet Nam Id cdng trinh phuc vu true dip cho cdng tdc nghien cuu khoa hgc vd pdng day d cdc Yien nghien cuu. cdc Lien dodn Dja chdt cSng nhu cdc trudng Dgi hgc chiiyen nganh
Phdn logi cdc dd biin chdt la mgt vdndildnmd hiin nay tren thiguji chua cd sir phm chia thdng nhdt vi cdc qud trinh biin ch^ vd cdc dd biin chdt. D\ta tren sw chiim uu the cua yiu Id ndy hay yiu td khdc vd bg smi lo^ mdu hen cd d Viit Nam, cdc hen trdc vd cdu tea) du^ ching tdi xip vdo ndm nhdm biin cfuSt chinh: 1) Nhdm dd bien chdt nhiit dgng khu v^ (56 dnh); 2} Nhdm dd sieu bien chdt (15 dnh); 3) Nhdm dd biin chdt nhi^t tiip xuc (12 dnh); 4) Nhdm dd biin chdt d^g hie (8 dnh); 5) Nhdm dd biin chdt nhiit dfch vd trao ddi (40 mh).
Atlas dugc trinh bd)/ trong 95 tnmg gdm 131 dnh mmh hga cho cdc hiu kiin true, m Igo cdc logi ddphd biin d Viet Nam vd diin gidi kem theo.
5. Nhom da bien chit nhiet dich va trao doi
Hi?n nay tren th^ gidi chua co su phan chia th6ng nhit cac qua trinh bi6n chat vk cdc 6A bien chat [\-7\. V i ^ phan chia cac da bien chat nhiet dpng khu vuc trong atlas cdc tdc gid chii yeu dua vao bdng phan loai cua Miyashiro [2], Tuy nhi&i, kifiu biin chit phiic vd bien chit giat lU Id mpt kigu bifin chat p h ^ tgp c6n nhieu tranh cai, cin thifit phdi c6 nhflng c6ng trinh nghifin cuu sau, nfin trong atlas chiing toi khong c6 tham vgng de cdp t<5i. Kifiu bifin chit trao d6i se dugc dfi C£q) tdi trong nh6m bifin chit nhiet djch vd trao d6i. Kieu t\r bifin chat lien quan den ho?t dOng magma dd dirge mo td trong phdn thgch hgc cac da m ^ m a nen kh6ng de clip den trong atlas nay.
Nhu v§y, cac da bifin chit ph6 bifin a Viet Nam dugc gOp vao 5 nh6m da chinh:
1. Nh6m dd bifin chit nhiet d6ng khu virc 2. Nh6m dd sieu b i ^ chdt
3. Nh6m dd bifin chit nhiet tifip xiic 4. Nh6m da bien chit d^ng luc
7. Bien chdt nhift d^ng khu virc: Ld kifiu bifin chat phdt trien trfin dign rfing v6i quy mo to Ion va gin bo ch^t chfi voi cac mifin uon nep. Yfiu to chinh tac dgng len cac da nguyfin thuy la nhiet dg va sep suit, ddng thoi cua nuoc vd axit cacbonic, gdy nen cdc phan lin^ hoa hpc, Tu do kl^ng nhflng ddn dfin bien d6i kifin tnic, ciu tao, thanh phin khodng vat md ca thanh phin h6a hpc cua cic dd nguyen thuy. Nhu v^y, trong qud trinh hinh thanh da bien chit khu vuc cung c6 the tham gia qua trinh bifin chil trao doi.
2. Sieit bien chdt: Trong thifin nhien, cdc dd set bien chat a tuong amphibolit thuong bi nong chay timg phin tao nen nhflng thfi c^
gom hai phin: phan cu (paleosom) la dd set hien chat chua bj nong chay co mau slm vd phln mm (neosom) sang mau co thanh phln tuong tu granit sang mau xen ke nhau gpi Id migmatiL
3. Bien chdt nhiit tiep xuc: La kieu bifin chat xay ra a nhflng vanh tifip xiic vay quanh cdc khdi xdm nhap do huong cua
su nung ndng cua nhiet thoat ra tir khdi magma dang kfit tinh. Cac da nguyen thuy bi bifin ddi vfi kifin true, ciu tao va ca thanh phdn khoang vdL
4. Biin chdt ^ng lire: La dang bifin chit duoc hinh thanh do cdc chuyfin ddng pha hiiy kifin tao. Tdc dgng chii yfiu len cac dd nguyfin thuy la dp suit dinh hirong, gay ca nat ca hgc dpc theo cdc phay kien tao, do dd lam bifin doi kifin tnic va cdu tao, nhimg khong thay ddi thdnh phan khoang vat cua da.
5. Biin chdt nhiet dich vd trao doi: La hogt ddng bifin chat ldm thay ddi thdnh phdn boa hgc cua cac dd nguyen thuy dudi tac dyng hoa hpc ciia cdc dung dich nhiet dich (bifin chit nhiet djch). Dang bifin chat xay ra d ria tiep xuc vdi cdc khdi magma xam nhap dudi tdc dung ciia dung djch bifin chdt thodt ra tii sau qud trinh kfit tinh magma, gdy ra su trao ddi cdc nguyfin td hda hpc giua khdi magma vd dd vay quanh. tao nen mpt logi da cd Ihdnh phin hda hoc hoan toan khac vdi da ban ddu (bien chat trao ddi).
1. Rieng cdc da bien chit nhifit ddng khu vvc dugc phan chia chi tifit thdnh cdc tudng da tren co sd phan loai cua Miyashiro [2).
n. NHdM oA BI£N CHAT NHirr QQNG KHUVI/C
Nhom dd bifin chit nhiet dpng khu v\rc la nhdm da pho bifin nhit vd phat trifin rdng r^
d yi?i Nam. Cho dfin nay cd rit nhifiu quan difim khdc nhau ve difiu ki?n dia chil va hda- ly hinh thdnh cac loai da thupc nhdm nay.
Tuy nhifin, nft thdng nhit Id trong qua trinh biin chdt nhi?t dgng khu vuc, cac dd nguyen thuy ehju tac ddng chu yeu bdi yfiu td nhigt dp va dp suit, dong thdi cua nude vd axit carbonic. Dya Uen co sd nhiet dp va dp suit, ngudi ta phan ra cac tudng bifin chit khdc nhau, Phan loai cac tudng bien chit nhifit dgng khu nrc trong atlas dua theo bdng phdn logi cua Miyashiro [2] cd bo sung:
1. Tudng prehnit-pumpelyit
2. Tudng da phifin luc
3. Tuong epidot-amphibolit (hay tudi^
dk phien hai mica theo dd set biin chat) 4. Tudng amphibolit (hay tudng di phien va gneis biotit-sillimanit theo (^ sei bien chat)
5. Tudng granulit (tudng gneis granai - cordierit; tudng h>persthen-sillimanit theo da set bien chat)
1. Tirong prehnit-pumpelyit Ld kifiu bifin chit metamafic. Chiing thay the chua Iron ven nen vdn cdn tan du cac khoang vat nguyfin sinh. Ddng thoi kifin tnic nguyfin sinh tan du van c6n dugrc gifl nguyen. Trfin thuc tfi cdc da thuOc tudng nay dugfc md ta nhu Id cdc da mafic bi bifin ddi nen da duoc de c§p trong atlas cdc da magma Vi^t Nam.
Trong atlas ndy chiing tdi chi dfi cap den loai dd tram tich va tram tich phun trdo bi phifin hda cd dieu kifin nhiet dO vd ap suSt tuong ling tudng bifin chat nay. Nhin chung, cdc da ndy cd kien tnic biin tinh yiu, vin con tdn du cua kiln triic dd t r ^ tich ban ddu, trong dd cdc hgt vyn cdt it nhifiu bi fip dai va ximang bj fip phiin I90 thanh ldp hpp vi vdy sericit vd thgch anh, felspat hat nhd sdp xfip dinh hudng. Dl^u khdc biet vdi cac dd bien chat tiip xiic nhifit la chiing bdo ton ciu tgo djnh hudnij;
song song hodc phan phifin tir cdc dd tr^;' tich ban dau.
2. Tu^ng da phi^n luc
Miic dp bien chdt tdng len, vgl Ii§u trim tich tdi kit tinh hoan todn tgo nfin kiln tnic vi vay, vi hat blln tinh. D6ng thdi da c6 cdu tao phan phifin rd nfit. Du6i anh hudng ciia hogt dgng kifin tao dd bj vd nhau, udn nip. Qua trinh tdi kit tinh xay ra manh me tgo nfin cdc khodng v§t cd kich thude ldn hinh thanh kien true h^l - vay biin tinh hodc ban bien tinh thu$c ddi chloritoid-granat. Kifin tnic hgt bien tinh d^c Irung cho dd quarzit vd dd hoa.
Ddi vdi cac da j^un trao trung tinh va baza H bien chit den tudng da p^fin IIK CO kiln tnic ban bifin tinh va spi bifin tinh vdi cau tao phan jrfiifin - vi udn nip, sgi- hat biin tinh vdi ciu tao phan dai, hoflc spi-que bi&i tinh vdi cau tao dinh hudng phan phiIrL Dd phien talc TO kien tnic vi vay bifin tinh vd ciu tao dinh hudng phan phifin. Trong da phifin talc-tremolit cd c ^ tim, que tremolit ndi trpi tao nen kifin tnic ban biin tinh trfin nfin vi vdy bien tinh.
3. Tu>dTig epkiot-amph'tbolit
La sdn phim cua qua trinh bifin chit nhifit dgng khu v ^ d mdc do trung binh, xuit hifin trong sir cong sinh ddng thdi ciia biotit, muscovit, granat, staurolit, disthen. Nhflng logi da frfiifin actinoHt, da hoa cd tremolit vd phlogopit xen k?p trong cdc loai (K tren
^ ^ ^ nipt sd h^ tdng nhit djnh cung dupe xep vdo loai da ndy.
Kien tnic chii yfiu ciia cdc dd phifin anthoFhyliit-staurolit vd anthophyllit- cordierit Id hat tim bifin tinh vd hat que bifin tinh. Cdu tao chii yfiu Id phan phifin song song.
Cdc loai dd hoa cd calcit bi fip ddi, cdc tam phlogopit s ^ xep dinh hudng tao nen kifin true hgt-vdy bien tinh, ciu tao dinh hudng. Hat-vdy-que biin tinh trong dd hoa chiia tremolit vd pWogopit, trong dd cdc hat calcit bi cp ddi, cac que tremolit vd vdy phlogopit s ^ xfip theo phuong keo ddi, tao nen ciu tao djnh hudng.
Cac da phien hai mica chiia granat kha phd bien, cdc hat granat dgng ban bifin tinh va khdm - ban bien tinh ndi trdi trfin nfin hat- vay bien tinh. Nhui chung, chung cd ciu tao phdn phien dang mit.
Cac dd phifin hai mica cd granat, disthen vd staurolii thudng cd kiln tiiic ban biin tinh, trong dd cdc ban tinh chu yeu Id granat, disthen vd staurolit kich thuoc ndi trdi iren nfin hgt \ay bifin tinh. Phan ldn cd cau tao dinh hudng song song va dinh hudng jrfian d^ khdng rd rdng. Kiln tnic kham bifin tinh
cui^ thudng gSp trang cdc loai da nay.
Tror^ truong phat trifin tuong epidot- amp^bolit cd cac ^ da quarzit sit chiia amjMx)! d Lang My vdi kiln tnic hat biin tinh, cau tao dinh hudng. 6 viing Ban Xeo (Ldo Cai) trong he tdng Lung Po phat trien da ptnea actinolit-phlogopit vai kifin tnic kham bien tinh, c ^ tao phan phien song song. Cdn trong da phien actinolil d Khdm Diic, kiai tnic que biai tinh vdi ciu tao phan phien song song dien hinh. Kifin tnic hat bien tinh, cau tgo kbdi gap trong da quarzit
4. Ti}>6ng amphibolit
Thupc tudng amphiboHt cd cdc dd phiin thgch anh - biotit, plagjogneis biotit, da phien thach anh - biotit - sillimanit, amphiboht va grarutogneis.
Cdc da ftden thach anh - biotit cd kiln tnic hgt vdy bifin tinh, ciu tao phdn phiin.
Plagiogneis biotit tiiudng cd kiln tnic hgt vdy bien tinh, cdu tao khdi. Trong da phifin thach anh - biotit - sillimanit ham lupng felspat giam di rd ret. Khoang vdt sang mdu chu yeu la thach anh. Xen kep vdi cdc vdy biotit la cac que sillimanit x ^ xip dinh hudng tgo nen kim tnic hat -^jue-vdy biin tinh, cau tgo jrfidn phifin song song. Ddi vdi cdc da amphiboht cung cd nhung net khac nhau ve kien tnic va ciu tao nhu cdc Idng tiu amphibol keo ddi dinh hudng tgo nfin kiln tnic que-hgl bifin tinh va cdu tao tuyfin song song, cdc hgt amphibol va plagioclas luong ddi ddng thude tao nen kifin tnic hat bien tinh, cdu tao khdi hodc ciu t£U) dinh hirdng.
Trong cdc dd amphibolit kiln tiiic chii yiu Id hgt, tim bien rinh, ciu tao dinh hudng.
Mgt trong nhflng loai da difin hinh cho tudng amphibolit Id granitogneis. Vfi thanh phln kha luong ddng vdi granit nhung dtrdi Unh hifin vi cd kiln tiiic hat biin linh vd cdu tao gneis.
5.103n true vi ciu tao cua cdc da thu$c tu>dng amphibolit
Bang phan loai cua Phan Trudng Thi [4]
chia ldm 2 ludng da: tudng gneis granat-
COTdierit ftAin dp suit trung biidi ciia tirong granulit dwo dd mafic biin chit) va tudng hypCTSthoi-siUimanit (hrong duong phan nhifit dp cao ciia tiidng granulit). Trong atlas n ^ , diiing ldi gdp chung rao hrdng granulit Cho dfin nay chi mdi phat hifin ducrc cdc da thupc tudng bien chat cao nay trong mdng cd dia khdi Indosinia (khdi nho Kon Tum). Mgt sd ldi lieu cd dfi cap tdi su xuit hien cdc da tudng bien chat nay d ddi bifin chit Sdng Hdng. Tuy nhifin, bp suu tap mlu cua chiing toi chira diy dii nen chua thfi khdng dinh chic chin vfi vin de nay. 6 day chi dl cap tdi mpt so loai da Ihudc tudng granulit phat trifin d cdc viing Kan Nak va Kroong,
Dd gneis biotit-sillimanit-cordieril cd kiln tnic hgt-spi-vay biin tinh,' cdu tgo khoi. Trong cdc da gneis hyperslhen vd gneis hai pyroxen thirdng cd kien tnic hat biin tinh, khdm biin tinh ho3c su mgc ghfip cua pyroxen va plagioclas, tao nfin kiln tiiic hpp kfip. Dong thdi cd thfi xay ra CO chi gidm dp Wnh thdnh mOt biin thfi cua kiln tiiic hpp kfip la kiln tnic simplectit (rilm mgc ghfip giiia plagioclas vd pyroxen bao quanh cdc hat granat).
Doi vdi cdc dd SEphirin-corindon, corindon-spinel, saphirin-corindon- fAlogopit-spinel kiln tnic chu yiu Id ban bien tinh tten nen vi vdy. C:dc bai biin tinh chu yfiu Id saphirin, corindon vd cac vdy phlogopit nii ti^i tiwi nfin pinit (cordierit bj sericit hod). Kien ttiic hgt bifin tinh phd biin trong dd corindon- spinel vd kiln ttiic khung xuong xuit hi^n frong dd cordierit-saphirin- phlogopil, ttong dd saphirin tao thanh khung xuong tifin nen pinit xen cdc vdy phlogopit
Jrotig qua ttinh sieu biin chit, cdc dd set tt&i chat d n ^ g amphiboht tiiudng bj ndng chay.titng phan tgo nfin logi da khdng ddng nhdt ve tiidnh phdn: phln cfl id vat Ufu slm mdu tuong ung vqi tiidnh phln dd phiin vd
gneis mica va amphibolit, phin mdi la v$
lieu sang mdu hicmg ung vdi granit, ^ hoac pegmatit (da mdu trdng, hgt tho, chi^
day tii vdi mm din hang dm hodc Idn hon).
Yeu td quan trpng tirong qua trinh sifiu biin chit la nhifit dd cao vd dp suit thiiy fiih, ddng tiidi qua trinh mang din vd mang <fi vgt chit hda hgc. Vfi ngudn goc vd (S|y kifin thanh tao migmatit cho den nay vii cdn nhifiu quan diem khdc nhau nfin trong alias nay chiing tdi khdng bdn lugn sau va van de nay.
Sederholm cho ring doi vdi cdc dfi migmatit vi?c nghifin ciiu du&i kinh hien vj il dac trung, md chii yiu Id quan sat ngoii th\ic dia. Do sir phdn bd ciia phin cu sSra mdu paleosom) va phln mdi sang mdu (neosom) khd da dang, nen tgo nfin cdc cau tgo rat khdc nhau. Viec phan logi ciu tgo cOa migmatit tucmg doi phiic lgp. 6 dfiy, chiing tdi chi nfiu mpt sd kifiu migmatit pho biin b Vifit Nam ma dai dien la migmatit d cdc ddi biin chit co Sdng Hdng va Song Chdy, noi dupe coi Id cdc dd migmatit phdt tiiln ijiit.
Migmatit dgng ldp la loai migmatit xen ldp gitta cac ddi slm mdu (paleosom) vi dai sdng mau (neosom) chgy song song nhau. Vdt chdt sdng mdu cd thi chgy song song, cit cheo mdt 16p ho^c mdt phiin cia da. Chieu ddy cac ldp sdng mdu c6 th^
Uiay doi tir vdi miltmet din hdng chyc centiraet hoJic Idp thd.
Migmatit dang mil cd cac 6 sdng mdu dang thdu kinh h o ^ ding ihudc bj cdc ddi sam mdu xen sang mdu u6n lupn bao quanh tgo nen dang mat
Ptygma-migmatit dang rugt, trong 66 phan sdng mdu dgng rugt ngodn ngofio u^W't_
1..U/.n J* *_ J 1 _ ! _ 1 . _ . .11 I > ll_»tdp[f,
fi
khiic, dogn to, dogn nhd ndm chinh hpp cit chfio mat ldp.
Migmatit md Id logi migmatit md ranh gidi giOa hai phdn sam mdu vd sang mdu bj xda nhda Miic dg migmatit hda mgnh, phin cu cdn sdt lai it, vi v^y ddi khi cdn gpi Id migmatit loang Id, cdu tgo dang gneis rd.
Do dnh hudng ciia hogt ddng kiln tao, cdc migmatit dgng ldp va migmatit md, bifin dgng bi udn lupn tgo nen cac n i p udn ggi Id itu^matit vi udn nip hay migmatit uon nep. 6 vdm Sdng Chay rit phdt trifin dd granit-miginatit, trong dd chiia cac Ihl sdt dd phifin ket tinh.
Ciing trong atlas nay the hifin kiln tnic ciia migmatit dudi kinh hien vi, da cd thanh phan tuong img vdi granit vdi kiln ttiic hat vdy bifin tinh, cau tao dinh hudng,
IV. NHOIW DA BI^N C H A T Tiep XOC NHI$T
Dd bifin chit nhiet tifip xiic lien quan trirc tiep voi hogt dong magma vd gdn hfin vdi cdc vdnh tiep xiic ciia cac than xam nhap do dnh hudng cua su nung ndng nhd nhiet tiiodt ra lir khoi magma dang kit tinh. Miic dd bita chit nhiet tiip xiic cua cac dd dupe xdc dinh bdi hdng logt nguyfin nhan dia chit vd hod ly. Trong dd phai kfi dai dd sau hinh thdiih thdn magma, ngudn nhi?t khi magma ket tinh, tinh chit cua magma (magma mafic gdy biin chat kfim hon so vdi magma axJt), kha ndng dan nhi^ ciia da vay quanh phu thugc vdo tiidnh phan vd kiln true ciia chiing, difiu ki$n kiln tao ciia dd vdy quanh.... Dua vdo yiu td nhi$t dp ngudi la phan chia ra cdc tudng khac nhau. Trong atias ndy chung tdi khdng cd tham vpng phan chia chi till ma chi dfi chung vdo ohom dd bifin chil tu i h ^ din cao.
0 giai doan diu tien cila qua trinh biin chat, cdc dd set phdn bd xa ddi tiip xiic, do dnh hudng cua nhi^l dp thip Mnh thdnh da phien dom vdi kiln tnic biin du pelit vd ciu tao dom phdn ldp. S\r phan ldp ban diu ciia dd sfit mat di va chuyen din sang ciu lao khoi, cdc ban biin tinh granai vd cordierit ndi tr^i tren nen sericit tgo nfin kiln tiiic ban bien linh vdi nfin vdy biin tinh va ban biin linh granat tren nfin hgt-vdy bifin tinh albit vd muscovit Kiln tnic hgt-vdy biin tinh kiiu men ran xuit hien trong d^ simg coidierit- andalusit vd cordierit-biotit-andalusit Kiln
tnic hgt-vay b i ^ tinh vdi d u tao (finh hudng I^ian i^fin kit tinb dac trung cho (deu siing andalusit-biotit vd sung biotit Mdt trong nhiing kiln tnic dac tnmg cho da bien ciidt nhi^ tiep xuc la kifin tnic sflng (hat nhd bifin tinh), cau tao £ n h hudng irong da siing epidot Kiln true hat bien tinh vdi ciu tao khdi va cdu lao tan du phdn (diifin rit hay gEq) trong cac da sung amphibol. Kien tnic men rgn cua da sung pyroxen duoc thfi hifin kha rd. Mdt logi da ciing hay gap d ddi tiep xuc giua cac khdi ganit vd da vay quanh la da tha:h anh - biotil-sillimarut- cordierit- granat cd kifin triic hgt-vay bien tinh vd cau tao dinh hudng phan d^.
V. NHOM D A B I £ N C H A T D O N G L I / C
Qud trinh biin chit ddng IIK: xay ra d phdn tren cvia vd trdi dit dudi tac ddng ciia dp sudt mdt chifiu hay cdn ggi Id img luc frong difiu kien nhifit dg thip din din dd bi biin dang co hgc mgnh mfi. Kiiu bifin chat ndy thirdng xdy ra dgc theo phuong phd hiiy kiln tao nhu dul gdy chdm nghjch, chdm trupt vd ddi milonit hda. Anh hudng cua iing lire gdy nen phd huy dat da ciing nhu cdc khoang vgt tao da. Cdc khodng vsit ddn bj d ^ vd vd cdc khodng vgt dfio nhu mica, chlorit uon lupn. Kem theo dp suat mgt chifiu Id S\T nung ndng dd nen khdng nhflng ldm tiiay ddi kien triic, ciu lao md cdn thay ddi thdnh phin khodng vdt tao dd, xuit hi?n cac khodng vdt mdi nhu sericit, chlorit, epidot-zoisil...
C!:ac tdm plagioclas Idn bi ca vd dgng tidn canh ndi trdi tren nfin hat vdy bi cd nat nhfl tdi ket tinh udn lupn tao nen kiln true cd ndt trong da granit Dd pla^ogneis biotit bi ca ndt va mylonit hda yiu tao nen kiln tnic myionit Ihd, ciu tao phan phiin. Hioi tupng ca ndt vd mylonit hda khd irfid bifin d cdc dd granitoid, miic dO milonit hda yiu thudng tao nfin cac tdm felspat Idn cdn t ^ hpp hat nhd gom tfiach jmh, felspat, biotit va homblend s ^ xip # i h hudng u6n lupn quanh cdc tam felspat lao nen kiln tiiic 57
mylonit thd. Da quarzit cung tiiudng bi mylonit hda. Trinh do bien chit mylonit hda tdng cao, cac da granitogneis, migmatit yd granit bi ca frupt mgnh tao nen kiln tiiic mylonit min, cac tim f e l ^ va muscovit nhd, tidn canh dupe vifin bdi tap hc^ hgt vdy nhd mia Ciu tao chii yiu ciia cac logi dd nay Id phan f^ln va [rfian phien dgng sdng, ddi khi tgo thdnh dang mit
VI. NH6M DA BI^N CHAT NHIET DICH - TRAOoi^
Qm trinh bien chit nhiet dich trao ddi khac, cdc kiiu biin chat khac la kem tiieo sy:
thay doi mgnh mfi thanh phln da ban dau do lac dung ciia dung dich nhifit djch va khi Ihanh lien quan chdt chfi vdi hogt dpng magma vd h^u magna. Yfiu Id quan trpng quyfit dinh cac kieu bien chat nhifit dich - trao doi Id nhi^t dp, thanh phin dung dich nhi^ djch - khi thanh va chat bdc. Phan trfin, khi xem xet kien tnic ciia cac kieu bifin chdt khdc nhau da it nhifiu de cap dfin su xuat lu?n ciia cdc khoang vgt bien chit trao ddi chdng gdi nhung chua dugc md la chi tilt. 6 ddy, chiing tdi chi dua ra cdc kieu kifin tiiic dd bifin chat - tiao ddi th^c thy,
Cdc dd phun oao ryolit khi bi biin ddi nhi?t dich igo nen quarzit thii sinh vdi kiln tnic tdn du porphyr vdi nfin vdy bifin tinh, ho$c kien ttiic hgt-vdy biin tinh, lap hpp vi vdy pyrophyllit-kaolinil vdi kiln tnic tan du porphyr ttong cdc da pyrophyilit d viing Tdn Mai. Miic dg bifin chit tdng cao, kiln tiiic ban dau bi xod nhod hodn todn tgo nfin kiln ttiic vi vdy biin tinh. Dudi tdc dyng ciia dung djch nhi?i djch cac da bi biin ddi mgnh hinh tiidnh cdc khodng vgt cao nhdm nhu corindon, diaspor vdi kifin tnic biin du poiphyr vdi nen lap hpp vi hgt vi viy ho§c bifin du porphyr. Trong qud tiinh beresit hod 1^0^ nen kien ttue tdn du, hat- vay bifin tinh Kien ttiic que biin tinh. ban biin tinh vd hgt vay bien tinh ttong da propylit Dudi tdc dyng cua nhifit dp frong qua frinh kit tinh magma giau chat bdc, cac dd vdy quanh b|
simg hod va greisen hod chdng gdi tao nen
cdc tam muscovit ldn tdi 2 mm cd kiln tnic kham bifin tinh kem theo tourmalin trfin n^i hat -vdy biin tinh.
Kien tnic hgt-vay bien tinh ddc trung cho hiu hfit cdc da greisen thuc thu. Rat phd in^
cdc khoang vat fluoril. cassiterit trong cdc di greisen giau chit bdc chiia thiec.
Listvenil phat tiien tren cdc dd xam nh^
thanh phin sieu mafic dudi tdc dyng oa dung dich nhifit dich tao nen tSp hgp serpentin-tremolil-magnesit vdi kiln true hat spi biin tinh.
Trong qua trinh nhJet dich - trao ddi, cac khoang vat dolomit dupe thay till boi magnesit tao nfin cdc hat magnesit dgng tdm.
Id- Kiln tnic hgt biin tinh.
Pyroxen hlnh thdnh mudn dgng hat nho khdng hoan chinh phat trien frong cac h^i granat phdn ddi rat dgc trung cho kifiu kiin tnic frao doi.
Bien chit frao ddi natii tao nfin dd albitit, ttong dd albit dang tim meo md, ranh giin rdng cua hinh ihanh kifin tnic tdm biin linh.
Cac tim felspat kali Idn cd khdm cac h?l zoisit dgng tiv luong thap ihudc kieu ttao doi kali tgo nfin cac kiln triic kham biin tinh.
Trong cdc da dgng nephrit, actinolil-ttiemolil dang spi tgo nen kien tnic spi biin tinh.
Kiln tnic hat bien tinh vd hat lam vw bifin linh xuat hien Uong cdc dd biin chat frao ddi kifiu skam vdi, lim hgt bien tinh.
Dong thdi xuit hifin kiln tnic hpp kfip vi kifin tnic dudng riem phdn iing.
Su xudt hien cua cac khodng vJt clinohumit, monticelUt, phlogopit tgo nen kien tnic hgt biin tinh vd hat-vdy bien tinh frong cdc dd skam magnesi.
Mdt kiiu biin chit fr-ao ddi d mire do cao hinh thdnh cdc khodng vat sillimanit, corindon va spinel tgo cho da cd klcn tnic hgt biin tinh.
Kien tnic dudng rian phdn iing dupe thfi iiifin khd ro trong atlas. Mpt Uong nhflng
kifin tiiic hay gdp trong dd bien chdt trao ddi id kiln QTJC hop k ^ .
VII. Ktr LUAN
Atlas kien trie - cdu lao da biin chit Viet Nam da phan dnh khd da dang cdc kifiu da bien chat phd bien trfin lanh thd vd cd gid tri tiiyc lien cao. Tuy nhien do difiu kien tiidi gian va kinh phi, nfin chua tfifi hien diy dii cdc kieu kifin tnic. cau tgo dac trung. Vi vdy hang ndm can dupe bo sung tiifim nhung kien tiiic va ciu tao mdi phat hifin dfi ldm phong phu vd nang cao chit lupng cua atias.
VAN LIEU L Marakusev A.A., 1973. Thach luan cdc da bifin chit. Nxb MGU. Mo.skva (tiing Nga)
2. Miyashiro A., 1976. Bien chdt vd cac dai bien chat Nxb Mir. Moskx'a (tieng Nga).
3. Nguyen Van Chien, Trinh Ich, Phan Tnrtmg Thj, 1999. TTiach hpc. Nxb Giao thdng van tdi. Hd Ndi
4. Phan T n i ^ g Thi, 1999. Thgch hpc, Quyen II!. Thach hpc da bifin chdt Dgi hgc Qudc gia Hd Sgi. Hd Ngi.
5. Polovinkina Yu.I., 1966. Kifin triic va cdu tao cdc dd magma va bi&i chat Nxb Nedra. Moskva (tiing Nga).
6. Sarantrina G.M., Shinkarov N.F., 1967. Thach hpc cac da magma va bien chat Nxb Nedra. Leningrad
7. Tenter F., Ferfaugen Dz., 1961.
Thach luan cdc da magma va bien chit, Nxb Vdn hgc nude ngodi Moskva.
SUMMARY
Atlas of stmcture and texture of metamorphic rocks in Viet Nam Nguyen Vdn Hgc The atlas of stt^ictiirc and texture of metamorphic rocks in Viet Nam is a work serving directly scientific researches and education in research institutes, geological divisions and specialized universities as well.
The classification of metamorphic rocks is a great problem, however in tiie present worid there still is not a unified division of metamoiphic pnacesses and metamorphic rxKks.
On the basis of eitiier factor or otiier one and the available collection of samples in Vifit Nam. metamorphic rocks in Vi?t Nam can be divided into 5 main groups as follows:
1. Group of regional Uiermodynamic metamorphic rocks (56 photos) 2. Group of ulttTimetamorphic rocks (15 photos)
3. Group of Uiennal confract metamorphic rocks (12 photos) 4. Group of dynamic metamorphic rocks (8 photos) 5. Group of hydrolhermal metamorphic rocks (40 photos)
The atlas is presented in 95 pages wiUi 131 photos illusttating different sfructures and textures of popular rocks in Viet Nam accompanied by explanations.
iXgin'ri bien tgp. KS. Phgm Binh
