CHNG 6 nh ngha bin chtMc bin chtNguyn nhn gy bin cht Cc kiu bin chtTng bin chtBin cht v kin to mng

Thut ng bin cht xut pht t ting Hy Lp: Meta = bin i, Morph = hnh dng thay i hnh dngNhng thay i v t hp khong vt v kin trc l kt qu ca s thay i nhit v p sut trn cc c trc. 1. nh ngha bin cht

Qu trnh rn kt thnh cng l s bin i ca xy ra trn trm tch, gii hn nhit

2. Mc bin chtKhi nhit v p sut tng b bin cht prograde = mc bin cht tng

Mc bin cht: iu kin nhit v p sut tng i lm c trc b bin i v hnh dng v kin trc

Mc bin cht thp

Xy ra nhit t 200 to 320oC, p sut tng i thp, c trng bi s phong ph cc khong vt c chc nc trong kin trc tinh th.Td:Cc khong vt st Al2Si2O5(OH)4Serpentine H4(Mg,Mn,Zn)3Si2O9Chlorite (Mg,Fe)3(Si,Al)4O10(OH)2(Mg,Fe)3(OH)6

Mc bin cht cao xy ra nhit > 320oC v p sut tng i cao. Do mc bin cht tng, cc khong vt cha nc gim do mt nc. Td:Muscovite - H2KAl3(Si04)3. Biotite - K(Mg,Fe++)3[AlSi3O10(OH,F)2 kv cha nc vn bn trong qu trnh bin chtPyroxene - Ca(M, Fe) (SiO3)2 Garnet - X3Y2(SiO4)3

3.Cc yu t bin cht Qu trnh bin cht xy ra do mt s khang vt ch bn iu kin nhit v p sut nht nh. Khi nhit v p sut thay i, cc khong vt trong s thay i thnh mt t hp khc n nh trong iu kin nhit v p sut mi.Nhit Nhit gia tng theo su theo a nhit b chn vi s chu tc dng nhit cao.Nhit c th gia tng do khi magma xm nhp t di ln.

p sut tng theo su c nhit v p sut s thay i theo su.p sut: p sut thy tnh- ng hng (p sut tc dng bng nhau theo mi hng) v p sut nh hng d hng (p sut khc nhau theo nhng hng khc nhau)

p sut s lm thay i kin trc trong qu trnh bin cht.

Cc ht trn s b dp theo hng p sut - ng sut cc i

Cc khong vt kt tinh c th b nh hng (cc khong vt silicat lp nh biotite v muscovite, chlorite, talc, v serpentine).Cc lp ny s pht trin thng gc vi phng ng sut cc i, lm d b v theocc mt song song vi lp to kin trc phn phin.

Dung dch: trong l hng gia cc ht trong c th cha cc dung dch.Dung dch ch yu l H2O v cc kv ha tan.Dung dch quan trng lm tng tc ca cc phn ng ha hc. Do p sut tng, th tch cc l hng gim dung dch that ra dung dch khng hin din khi p sut v nhit gim.Thi gian Cc phn ng ha hc xy ra trong qu trnh bn cht c lin quan vi thi gian, vi s ti kt tinh v pht trin cc kv mi. Thi gian bin cht cng di cc kv kt tinh c tinh th cng ln bin cht ht th Cc thc nghim cho thy qu trnh bin cht thi gian c th hng triu nm.

4. Phn ng ca khi mc bin cht tng. Slate- phin st hnh thnh mc bin cht thp pht trin cc chlorite ht mn v kv st. S nh hng ca cc kv silicat lm d b v theo cc mt song song.

ng sut cc i tc dng mt gc trn mt lp nguyn thy cc ct khai ca phin pht trin, theo mt gc so vi mt lp nguyn thy

phn mica Kch thc cc ht kv c khuynh hng tng theo mc bin cht pht trin cc phin ca cc kv silicat (biotite v muscovite). Cc ht thch anh v feldspar khng b nh hng.

Gneiss Khi mc bin cht tng, cc tm silicat tr nn khng bn vng cc kv sm mu nh hornblende v pyroxene bt u xut hin thnh cc di cu to di. Cc kv sm mu xp thnh cc di thng gc vi ng sut cc i.

Granulite - mc bin cht cao nht, tt c cc kv cha nc v silicat dng tm tr nn khng bn mt vi kv s nh hng to kin trc granulitic tng t nh kn trc kt tinh ca magma.

Bn cht ca Basalts v Gabbros phn lc - Olivine, pyroxene, v plagioclase trong basalt c trc bin i thnh amphiboles and chlorite (c mu lc) do nc trong l hng phn ng vi cc kv nguyn thy nhit v p sut thp. Amphibolite Khi nhit v p sut tng n mc bin cht trung bnh, ch c kv mu amphiboles v plagioclase tn ti amphibolite.Granulite - mc bin cht cao nht cc amphiboles b thay th bi pyroxenes and garnets, s phn phin bin mt v to thnh kn trc granulite

Bin cht vi v ct kt hoa vi cu to ch yu bi calcite - v calcite bn trong mt gii hn di ca nhit v p sut cc tinh th calcite nguyn thy s c kch thc ln hn v khng phn phinQuartzite Ct kt gm thch anh b bin cht thch anh s ti kt tinh hnh thnh quartzite khng phn phin

5. Cc kiu bin cht Bin cht c nt b bin dng c hc do 2 th trt theo 2 bn mt t gy. Nhit pht sinh do s ma st dc theo i trt, b c nt. Bn dng c nt t ph bin. Bn cht chn vi- khi trm tch b chn vi vi trm mt, nhit s >300oC kv mi s pht trin nh Zeolites. i khi bin cht chn vi chng ln vi qu trnh rn kt thnh bn cht khu vc do nhit v p sut tng.

Bin cht tip xc xy ra gn khi magma xm nhp s bin cht ch xy ra quanh khi xm nhp do nhit cao ca khi magma xm nhp i bin cht tip xc. Xa i tip xc, khng b bin cht.Mc bin cht tng theo mi hng v pha khi xm nhp. Do nhit khc bit ln gia vy quanh v khi magma xm nhp ti v tr nng ca V Tri t, bin cht tip xc thng lin quan n nhit cao v p sut thp hnh thnh sng vi ht mn khng phn phin.

Bin cht khu vc xy ra trn quy m ln chu tc dng p sut nh hng cao hnh thnh bin cht phan phin mnh nh slates, schists, and gniesses. ng sut nh hng thng l kt qu ca chuyn ng kin to hnh thnh lc np p (2 mng lc a va chm nhau) bin cht khu vc xy ra nhn ca cc dy ni ln hay cc dy ni b xm thc. ng sut nn p l kt qu ca s un np V Tri t dy c khuynh hng y xung su ni m chu tc dng bi nhit v p sut cao.

6. Tng bin cht Nhng thay i ca t hp kv do thay i nhit v p sut cc c im ca t hp kv l du hiu bit mi trng nhit v p sut m chu tc dng nhit v p sut lin quan n tng bin cht (Tng t nh tng trm tch c hnh thnh trong nhng iu kin mi trng trong qu trnh trm tch).

Lat cc tng bin cht ty thuc vo a nhit (geothermal gradient) hin din trong qu trnh bin cht. a nhit cao A trong hnh di y c trng cho mi trng quanh khi xm nhp tng sng. a nhit bnh thng B tng zeolite n phin lc, amphibolite, v eclogite khi mc bin cht (hay su chn vi) tng. Nu a nhit thp "C pht trin t tng zeolit thnh tng phin xanh n tng eclogite. nu bit tng trong khu vc c th xc nh a nhit ti thi im xy ra bin cht

7. Bn cht v kin to mng Hin nay, a nhit ch yu lin quan n kn to mng. Dc theo cc i ht chm, magma hnh thnh gn i ht chm v xm nhp nng. Do nhit cao gn b mt, a nhit tr nn cao (A) v bin cht tip xc (tng sng)

Do s nn p xy ra dc theo i ht chm (v i dng dch chuyn v cung o ni la) b y xung su a nhit bnh thng hay cao hn mt cht (B). a nhit cao hn khu vc B do magma i ln qua V tri t c khuynh hng t nng V. Trong nhng vng ny c phin lc, amphibolite, v tng granulit bin cht.Dc i ht chm, V i dng tng i lnh b ko xung su a nhit thp (nhit tng theo su), hnh thnh tng phin xanh v eclogite vng C.

V tr cc tng bin cht i ht chm: 1) zeolite, 2) prehnite-pumpellyite, 3) glaucophane schist, 4) eclogite, 5) greenschist, 6) amphibolite, 7) granulite, 8) pyroxene hornfels, 9) hornblende hornfels, v 10) albite-epidote hornfels.