T»chiDIACTlATI<MIA.sA340. l-2Ai014.lr. I-IO
470 TRIfU NAM GABBRO - DIABAS VUNG NUI NU'A D 6 I CAU TRUC SONG MA VA Y NGHIA KIEN TAO
PHAM-TRUNG HIEU', LA MAI SON' LE TEN DUNG', NGO XUAN-THANH'
Trudng Dgi hpc Khoa hpc Tu nhien, Nguyin Van Cir. Phudng 4. Quan 5, TP Hd Chi Minh Trudng Dgi hpc Md - Dia chdt, Ddng Nggc. TiiLiem. Hd Ndi
Lien doan Bdn do Dia chdt Miin Bdc. Gia Lam. Hd Noi
Tdm tdt: Zircon dupe tuyen tir cdc dd gabbro - diabas vimg Nui Nua - Thanh Hoa, dupe xdc dinh tudi bdng phuang phdp L4-ICP-MS U-Pb cho tudi 470 trieu nam (Tr.n), tudi ndy duac coi Id tudi kit linh cua chiing. Cdc Ihdnh tao gabbro-diabas xuyen cdt cdc dd sieu mcrfic phdc he Ndi Nua. vi vpy co thi khdng dinh tudi kit tinh cua cdc dd sieu mafic thupe ddi ophiolit Sdng Md phdi CO han 470 Tr.n (ky Ordovic). Cong trinh nghien cuu nay coy nghia quan trpng trong vi^c hgn dinh tudi thdnh tgo cho cdc dd sieu mafic Niii Nua khu vuc Song Md, mpt trong nhiing nghien cuu con nhiiu quan diim khdc nhau trong thdi gian qua.
LMd^DAU
Cic da gabbro - diabas phan bo rpng rai trong vo Trai dAt, chung co quan he gin gQi v(W cac qui trinh tien h6a magma kien tao. Chiing dugrc chap nhan rong rai nhu li v$t chat co ngu6n g6c manti nong chiy dira len vk thanh tao 6 phin vo Trai dat, chiing bj cac v$t chat ngudn vo tac dpng thong qua qua trinh dong hoa ho^c trpn lin vat chat. Vi?c nghien ciru ddng vi vi xic djnh tuoi thanh t ^ ciia chiing la nhi?m v\f quan trpng trong nghien cuu dia chit khu vvrc. Tiiy timg loai da khic nhau vi^c lya chpn doi tupmg phan tich co y nghia "quyet djnh syr thanh cong cua moi phuong phip. Gabbro-diabas hay diabas la mpt trong nhiing lo?u di kh6 xic dinh ni6i nhit bang phuong phip U-Pb zircon do chung chiia rat it lupng don khoing zircon so voi cic di trung tinh va da axit, thong thucmg phii Iva chpn kh6i lupng mau Ion moi CO the tuyen dii zircon tir da g6c. Cac nghien ciru tnnyc day deu cho tliay ring rat nhieu khoang v^t zircon trong cic da mafic c6 nguon goc ti^ cic da vay quanh dua vao, mpt phin zircon dupe hiiih thanh moi trong qua trinh ho?it dpng magma mafic.
Dpc theo doi khau Song Ma cac the mafic, sieu mafic dupe cho la nguon gdc dai duong hien tai phan bo tren vo luc dia thong qua qua trinh va cham, x6 hue cua cac doi kien tao Ion thanh tao nen cac phirc he ophiolit xen lan cac the biSn chat cua cac da nguon goc trim tich va magma (Nguyen Vin Chien, 1964; Le Tiin DQng va nnk 1991, 2010; Nguyen Vin Vupng va nnk, 1999, 2012; Ngo Xuan Thanh et al., 2011).
Cac the mafic, sieu mafic thupe phirc he ophiolit thucmg bi bien chit manh me thong qua cac dong nhi?t dich co su tac dpng Ion ciia yeu to ap suat cao xuit hien dpc cic doi hiit chim, va cham. Tuy nhien ve tuoi thanh tao cua cac thi ophiolit dpc doi Song Ma van con nhieu quan diem khac nhau nhu: 1/
Chiing dutjrc thanh tao vao giai doan Paleozoi sdm Dao Dinh Thuc, Huynh Trung, 1995; Tran Vin Tri, 1977); 2/ Vao Trias mupn (Fromaget, 1952; Dojikov et al., 1965); 3/ Neoproterozoi Paleozoi sdm (Trin Vin Tti, Vu Khuc va nnk, 2009; Biii Minh Tam, 2010).
Vimg nghien ctiu nim trong pham vi g h ^ ndi ciia cac vi mang luc dia khac nhau, hai qua nhieu giai doan tiin hda phirc tap.
chinh VI thi cac da thudc td hpp ophiolit khu vuc Sdng Ma khd bao tdn kiin tnic va ciu tai nguyen thuy. Vi vay, viec xac dinh moi quan he giOa chiing vtji da vay quaiih ciing nhu xac dinh tudi thanh tao bing phuong phap ddng vi gap nhiiu kho khan trong viec lua chpn ddi hipng phan tich, do cac da sieu mafic chii yiu bi biin ddi thanh serpentinit Nhiing nghien ciiu tnroc kia ciia chiing tdi thuc hien bing phuong phap Sm-Nd xac dinh duong ding thdi thdng qua da tdng, nhung do nhiiu nguyen nhan khac nhau daii den viec thuc hien khdng thanh cdng trong hai lan cac tac gia tu phan tfch tai phdng thi nghiem thudc Vi?n Han lam Khoa hpc Trung Qudc, mdt lin giii sang Nhat Ban va mdt Ian giii sang Dai Loan. Trong nghien cuu niy chiing tdi hjui dinh hidi thanh tao sieu mafic Niii Nua bing phuong phap giin tiep thdng qua viec xac dinh tudi ket tinh U-Pb zircon LA-ICP-MS cac da gabbro-diabas, ngoii thyc dia chiing cd quan h§ xuyen cit cac thanh tao sieu mafic Ntii Nua. Chiing tdi hy vpng ring viec xac dinh tuoi thanh t^io cac da gabbro-diabas xuyen cat cic di sieu mafic (peridotit) vimg Niii Nua, Thanh Hda gdp phin hiiu biit them qua hinh hinh thinh cac di thupe td hpp ophiolit khu vvc Sdng Ma, mpt trong nhimg nghien ciiu cdn nhieu quan diim khac nhau trong thdi gian qua.
II. 0|A CHAT K H U V I / C , VI TRi LAY MAU
VA PHUONG PHAP PH^N^TfeH U4CP.,Ifs 1. Dia chit khu v^c v i vj tri liy miu Khu vyc Tay Bic Vi?t Nam la noi kit hpp cua nhieu vi luc dja t ^ nen trong dd bao gom cac vi lye dja chinh: Ddng Duong Vi?t-Trung va Sibumasu (Hinh la) Day li khu vyc rpng Ion cd Hch sti tiin hda lau dai vi phuc tap, phia bac dupe khdng chi boi Art gay Sdng Chay, phia nam bdi diit gay Song Ma, phia tay la diit gay Di?n Bien Phti.
X?," IT ^^^ Bac bao gdm ddi khau Sdng Ma, Idiu vyc Day Nui Con Voi, khu vy^
Phan S. Pan_ va khu vuc Tu Le la nhiing noi cd nhieu mot quan tam nghien cuu ciia dc
tac gia trong va ngoai nude. Phin ria ddng bac ciia khu vuc Tay Bic thuemg dupe xem la mdt phan ciia phiic nip ldi thupe Day Ntii Con Voi vdi phan nhan la cac da biin chit tuong amphibolit tudi Proterozoi, bao gdm cac da paragneis, orthogneis va migmatit, phia nam ciia diit gay Sdng Hdng dupe phii boi cac thanh tao tudi Mesozoi va Kainozoi (Tran Thanh Hai va nnk, 2005), tiip theo dd la khu vuc Tii Le hi phu chii yiu bdi cic thanh t^o magma, trim tich phun trio hrong ling tudi cudi Permi dau Trias va cdc thanh tao magma - phun trao tudi Creta sdm. Khu vuc Sdng Da bao gdm cac thanh tao dia chat cd mdi dia chat khac nhau tii Paleozoi sdm - giiia, Paleozoi mupn - Mesozoi. Khu vyc ddi khau Sdng Ma Ip ra nhiiu cac thanh t ^ mafic va sieu mafic phan bd theo phuong re-DN dupe coi la tan du ctia vd dgi duong CO. Cac da mafic, sieu mafic trong phirc h?
ophiolit nky thudng xuit hi?n dpc theo ckc dk bien chat h$ ting Nam Cd, h§ ting Ngm Su Lu cd tudng bien chit tir thip tdi hrdng amphibolit va dupe xip vko tudi Proterozoi [4,5]. Vimg Di?n Bien Phii cdn cd sy xuit hien ctia cdc dd biin chit dp suit cao den sieu cao (Nakano et al., 2010). Ngodi ra cdn phan bd kha rdng rai cdc thanh tao xam nh?p va phun trdo tuong ung tudi cudi Penni diu Tnas dupe thdnh t?o trong boi cdnh cung magma (Lan et al., 2000).
Mau phSn tich V1255 trong nghien citu nay dupe lay frong cac the gabbro - diabas xuyen cdt cdc thi peridotit bj serpentin hda m^ mS cua phirc h? Niii Nua tgi tpa dp 19''39'46" vT dp Bic, 105''39'49" kinh d$
Dong, vimg huy?n Ndng Cong, Thanh Hda (Anh 1). Cdc the gabbro - diabas hay diabas Id dudi dang thi tudng, via phdn b6 rpng rSi d vimg Niii Nua, be rpng ttr 80 cm den 2-3 m (Anh 2), ddi noi cd thi dgt tdi vdi chyc met h o ^ khodng 50 m.
Nghien ciiu thdnh phin thach hpc dudi kinh cho thdy thdnh phin khodng v^t cua cdc the gabbro-diabas ndy bao g6m piagiocia (50-60 %), pyroxen (20-25 %)
oHvin (10-15 9c). ngoai ra cdn cd cac khoang vat phu nhu: manhetit, zircon, sphen... Cac khoang vat trong da cdn dupe bao tdn tdt. It bj bien ddi, bien dang. Ngoai thuc dia cac the gabbro-diabas nay xuyen cit cdc da sieu mafic Niii Nua.
2. Phirang phap phan tich LA-ICP-MS
Zircon dupe tuyen bang phucmg phap nghien, dai va nhat hat dudi kinh hiin vi soi ndi. Dai bd phan zircon cd dang lang try ngdn, trdn canh, chieu ddi khodng 80-200 ^m. Sau khi tuyen, zircon dupe gdn vdo mpt vdng trdn nhya epoxy, va dupe ddnh bdng bang giiy rdp, ki'ch cd khdc nhau, de Ip phdn
trung tam hgt, khi phan Hinh X.Sado dia chdt vung nghiin cdu vd vi tri lay mdu (a) theo Lepvrier et ai. 2004 [14], (b) theo Nakano
va nnk 2006 [17] co sua chiia.
Anh 1. Peridotit bf serpentin hoa manh me
cua khoi Niii Nua (Nguon: La Mai San, 2012). Anh 2. Gabbro-diabas phong hoa hoc vo, dgng the tuang, via xuyen cat cdc thdnh
tgo sieu mafic khoi Nui Nua (Ngudn; La Mai San, 2012).
tich bang phuong phdp LA-ICP-MS mau thudng dupe mai khoang 1/3 bi ddy hgt. Mdu zircon sau khi ddnh bdng, dupe phan tich dac diim ciu triic phaii ddi zircon bang phuong phap kinh hiin VI dien tti quel (SEM) tai Vien Dia chit vd Dm cau Vien Han lam Khoa hoc Trung Qudc. Diim phan tich LA-ICP-MS U-Pb thuc hien cho cdc vi tri diem phan tich cd dudng kinh 32 um' thudng chpn tgi nhan tinh thi va tai riim' mpc chdng ctia mdt sd tinh thi idii da quan sdt, phan u'ch dnh am cue phdt quang. Diem phan tich thudng dupe chpn be mat cdc hgt zircon sach, khdng chua vet mit, khdng chiia bao thi. Cdc Uu nghiem phan tich duoc tiin hdnh tgi Phong thi nghiem MC-LA-ICP-MS Vien Dia chat va Dia vat ly Vien Han lam Khoa hpc Trung Qudc. Quy trinh chuan bi mau, ky thuat phan tich va tinh toan bang cdc phan mim phuong phdp LA-ICP-MS U-Pb trong nghien c L ndy hoan toan tuong ty ky thuat dd dupe Chung tdi trinh bay chi tiit d [23].
III. Ket QUA PHAN TfCH 1. Anh am eye phdt quang (SEM) Don khodng zircon tir giOa thi ky XX tro Ig, day dupe coi nhu mpt cdng cy hihi ich trong vile dinh tudi ddng vi nhjn myc dich Igp Igi lich su tiin hda vd Trdi dat vd gid. quyet nhiiu vin di trong inh vyc dia chit [22]. Kit qua phdn tich 2 atn eye phdt.quang cd thi cho ta h iu d L l h l T ^ " ^ ° ' = ^^ "l"^ '^"h 'i^n hda dia chat, cdc giai dogn nhiet kiin sinh.
Anh 3 Id anh SEM cOa 6 hgt zircon dai d.?n tu miu VI255. Mpt sd hgt zircon
^ong mau cd dgng trdn cgnh (hg't 02 05;
A.^ 3), cac hgt cdn Igi (hgt 07, 09; At^h 3 LT^T,^ " " ' ' '^^'^ bi^t cdc hat 13 15
„^J*^''J'^-.C^c hgt cd kich thudc v i a v j nho, mpt so hat khdng thi hi^n ciu tnic phdn dd. ben trong mpt cdch rd net (ha^J?- A n h 3 ) m p t s d h g t c h o t h i y e i u t r ^ c b € n
Anh 3. Anh SEM zircon tir gabbro-diabas Nm Nua. Cac vdng trdn nho Id vi tri phdn
tich tuoi va ket qud tudi Ma (Tm.).
Anh 4. Anh CL zircon tugneis Sin Quyin Cac vong trdn nhd la v/ tri phdn lich tudi vd
ket qua tudi Ma (Tr.n.) (theo [25]).
trong cd riim trdn cgnh vd chiing dupe mpc chong bdi mpt thi h$ zircon khdc phan nem ngoai (hgt 15; Anh 3). Ngupc Igi, cdc hgt vira va Idn cd ciu tnic phan d<H ben
^ong rd rdng, cau tnic phan ddi d nhdn cd
£ l ^ u ' ^ ' I ' ' ^ ^^ "^ ^^' ^^^ ^V hinh ITt^l T "J^/•'^'" '"'?'= '=''^"8 '^n nhan cott^dc (hgt 15; Anh3).Ki.qud phdn tich cau tnic zircon ndy cho thiy cdc khodng . L " ? " . ' ' ° " ? ^ Sabbro - diabas bao f Z -* 5 " " " ° " ' = * ^ " e u 6 n g 6 c k h d c nhau, mpt phin cua chting Id cdc hgt zircon
thupe the h? zircon hinh thdnh trong qiS trinh hogt dpng ctia magma
4K
2. Tnoi U-Pb zircoii Trong n ^ e n ciiu nay chiing tdi lya chpn mpt mau phan tich tuoi ddng vi U-Pb dgi di«i cho gabbro-diabas viing Ntii Nua (V1255), miu lya chpn cd dac diem cdn tuoi vd it bj biin ddi.
Tdng sd phan tich dupe thuc h i ^ tren 20 hat zircon, kit qud phan t'ch dupe the hien d Bdng 1 vd biiu dd triing hpp (Hinh 2).
Cdc ket qua tudi ddng vi
^ b / ^ ' U dao dOng tit 2631 Tr.n den 234 Trji. Kit qud phan tich dao dpng trong phgm vi rOng, nhiing hat cd nhan cd bieu hien tu6i ciia cdc vdt lieu trim tich
^ trong vd Trdi dit, kit qud 234 Tr.n cd thi ghi nhdn giai dogn nhift kien sinh diu Trias (xem phin thdo ludn sau). Tr6n bieu do trung hpp biiu dien tudi
^bPhj - ^Pb/^'U (Hinh 2), chiing t^ trung gin vdi dudng cong Concordia vd cho tuoi tnmg binh tuong img v(W 470±47 Tr.n, tu6i ndy dupe coi Id tuoi kit tinh ciia gabbro-diabas.
IV.THAOLUAN
1. Sv ghi nh$n cOa giai dogn biin chit Trias sdm l§n cdc thdnh t^o Paleozoi s6m
Cdc kit qud phdn tich LA-ICP-MS U-Pb trong nghi€n cihi ndy cho thiy zircon tuyin tir cdc dd gabbro-diabas khdng cung mpt thi hi. it nhit cd ba thi h? zircon khdc nhau Uong miu nghi&i ciiu. Thi hf thii nhit gdm cdc hgt zircon trdn cgnh vd cd ciu ttiic ben trong khdng r5 rdng, cd mpt riem trong md, khd trdn cgnh vd cho khodng tudi 743-2631 Tr Ji. Trong khu vyc Sdng Md ndi rieng vd trfn lanh thd Vift Nam ndi chung, cdc thi h?
zircon cho khodng tu6i cd tir Neo-Proterozoi din Meso-Arkei da dupe bdo cdo khd nhieu
0.6
0.4
0.2
nn V1255
2 ^ 4 j ^ ; ^ ^
1400/ , ' • '
^ ^ 2 — - - ' ' ' 470 ±42 Ma
^ p - ' * " ^ (MSWD = 1.8, 95% conf.)
.
300ftr—-,-'
s
207c
12 16 20
'Pb/"=y
Hinh 2. Gian dd Concordia kit qua phdn tich LA-ICP-MS U-Pb zircon cho gabbro-diabas Niii Nua.
o.s
0.4
0.3
0.2
0.1
0 0
V0753
1200
tOOfI
1 6 0 0 ^ 2 0 0 0
a04M
OKIU » /
014
2 4 0 0 , , - - - '
/
J3,
' ^ 25013 MI r^ MswD-i.s.9s%conr.
r
O-M 0 U 0,M
0 2 4 6 8 10
Hinh 3. Gian dd Concordia kit qud phdn tich LA-ICP-MS U-Pb zircon cho da gneis
Sin Quyin (tham khdo [25]).
trong cdc cdng trinh trudc day (Lan et al., 2001; Trin Ngpc Nam et al., 2003; Phgm Tnmg Hiiu et al., 2010, 2012; Hd Thdnh Nhu vd nnk, 2011). Nhu vay, cdc gjd trj tudi phan tich LA-ICP-MS cho tudi 2,6 ty nam, 1,8 ty nam vd 760 Tr Ji trong nghien ctiu nay cd le phdn dnh zircon ciia vgt lifu trim tich trong vd Trdi dit, khi gabbro-diabas kit tinh chting mang theo cdc vat lifu tren, cdc s6 lifu ndy cui^ cho thiy vd Trdi dit khu vyc nghien cthi tdn tai c ^ vgt chit cd Uioi co, (Igt tdi 2,6 ty ndm (Arkei mupn).
Bang 1. Kit qua phdn tich tu6j^«ang ^ U^b zircon miu V1255 g,bb«>-.i,b„
Thi hf ^thti hai Id nhan cua cdc tinh thi
^ n cd cau taic phan ddi hrong d6i tu hinh,
^ , " 1 ^ . * " ° ' ' ^ " ^ g 400-500 Tr.n. (hidi u - Pb tmng binh ctia 7 diim phan tich M470±42Tr.n.,Hinh2),vdthiheSiubaS hcttula na mpc choiig len cdc tinh thi ciia thi h?ttiuha^chotu6i%^06pbeuathihfM ba 234 Tr.n (Anh 3, diim phdn tich 16).
K ^ u « al., 2010 da phdn tich tudi U-Pb cho cdc Unh the zircon tuy&i hi miu V0753 bdng phuong phdp LA-ICP-MS h ^ don khodnf arcon dupe lya chpn tir cdc thdnh tao gneis
S;,§t^.;??3«hihi^cdckit';s
LA-ICP-MS U-Pb zucon miu V0753 1251 theo do cd sdu tinh thi da phan tieh d ria S;^"/'^'^5<>"^250±3Trj,(Anh4),edc kit qud ndy cd ty sd Th/U < 0,1 thi hifi^^giai
S"riffi-'''^A^*'^'^8tn,£g
«ia nem bien chit (Rubatto. 2002; Moller I
^??l'Sni'-'°^^^^^°^
Tgi Vtet Nam, cdc khu vyc nhu Phan Si Pan, 4 a khu Kon Tum, khdi Sdng Chdy, Tam Ky - Phudc Son, ddi Tmdng Son vd khu vyc Sdng Ma xudt hifn cdc thdnh tgo magma vd bien chdt cho tuoi tir 230 Tr n din 260 Tr.ii. Nhu vgy tudi zircon ghi nh|n dupe tu mau dmh tuoi trong nghien ciiu ndy cd thi the hi?n tudi ciia m$t pha kien tgo khd Idn tac dOn| den qud trinh thdnh tgo magma, bien chat trfn mpt khu vyc Idn thufc dia khdi Ddng Duong vd mf t phin ciia khii Viet-Tnmg (Sino-Vietnam). Nhiiu tdc gid cho rang cdc pha magma, biin chit ndy cd tJie hen quan tdi giai doan hpi ty (hiit chlm va va chgm) giiia hai mdng Ddng Duong vd khoi Vift-Tning Trong mOt s6 nghifn ciiu ttudc day cd nhiiu tdc gid cho iftig vdo Wiodng 230 Tnn, hai mdng Ddng Duong vd Vi?t-Tnmg hodn todn gh^p n6i (Lepvrier et al., 1997,2004). Tuy nhien cd y kiin Igi cho rang giai doan kiin tgo Trias ghi nh|n dupe
rpng khip cdc khdi Dong Dirong va Vift-Trung, chiing khdng lien quan din {dia va diani gjiia hai khdi ndy ma chi la mpt pta nhift kioi tao lien quan din mot pha kiin tao hogt hda (Carter et al., 2007; Trin Van fri vd nnk., 2009).
2. t nghia kiln tgo
Troiig nhieu cdng trinh nghien ciiu cho thay tudi thanh tgo cdc dd sieu mafic Niii Nua cdn nhiiu y kiin khdc nhau: 1/ Tudi Neoproterozoi mupn - Paleozoi giiia (Trin Vdn Tri, Vu Khiic va nnk, 2009; Biii Minh Tdm, 2010); 2/ Tudi Paleozoi sdm (Ddo Dinh Thyc, Huynh Trung 1995); 3/ Tudi Peimi Trias (Fromaget, 1952; Doyjikov, 1965). C ^ tudi tren dupe xac dinh dya vdo moi quan hf giiia cdc the ophiolit vdi da vSy quanh vd mpt sd phuong phdp tudi ddng vj Sm-Nd dd tdng cho cdc dd biin chat mafic vd Ar-Ar tudi ngupi Ignh cho cdc thdnh tgo amphibolit vd tilm tich biin chit (Lepvrier et al., 2004), vd gin day dupe xdc djnh bdng mpt sd phuong phdp cd dp chinh xdc cao Sm-Nd vd U-Pb cho khodng vat titanit (Nguyen Vdn Vupng et al., 2012), cho cdc thanh tgo dd thudc ddi ophiolit khu vyc Sdng M l
Trong n ^ f n ciru ndy chiing tdi lya chpn phucmg p h ^ U-Pb zircon xdc djnh tudi thdnh tgo gidn tiip cho cac dd sieu mafic Ntii Nua bing vifc xdc djnh tudi thdnh tgo ciia cdc dd gabbro-diabas, ngodi thyc dia chiing cd quan hf xuyen cit cdc thdnh tgo sieu mafic Niii Nira.
Tu 20 diim phan tich mau nghifn ciiu V1255 cho thiy tudi cua chiing dao dpng trong phgm vj rpng, tir 2,6 ty ndm tdi 234 TrJi, 7 diim phdn tich ndm trfn ditdng tiling hpp cho gid trj tudi trung binh 470 Trji, biiu thj tu6i kit tinh cua dd. Cdc gid tri zircon cd tuoi c6 2,6 ty ndm, 1,8 ty nam, 980 Trji, 760 Tr.n dupe coi Id cdc hpp phin di sdt cac dd tram tich ndm trong vd Tidi dit, khi cac thanh t^o gabbro-diabas ket tinh, di len mang theo chiing. N ^ f n ciiu ndy kit hpp vtii cdc
ng}iien cuu trudc kia ciia cac tac gid khdc (Lan et al., 2001; Nam et al., 2003; Pham Tnmg Hi&i et aL, 2010, 2012; Ha Thdnh Nhu va nnk, 2011) vd tai lifu gin day cua ta^ the tac gid (tai hf u chua cdng bd), cho thay vd Trai dit khu vyc Tay Bdc Viet Nam ft nhit phdi cd hon 3,5 ty nam. Thdng qua ket qud i^ian tich tudi vd kh hpp nghioi ciiu cau tnic cdc hat zircon, chiing tdi kit luan cdc dd gaUiro - diabas trong khu vuc dupe hinh thdnh vao khoang 470 Tr.n trudc day.
Cdc ng^en cuu tiudc day diu cho ting td hpp cdc da mach diabas trong khu vuc thudc mdt phin trong td hpp ophiolit vimg Sdng Ma, tuy nhien ciing cin cd them sy nghien ciiu sau hon ve dia hda vd dia hda dong vi cua chiing di cd kit ludn ro htm.
Nhiing nghien ciiu trudc day vi dd peridotit viing Bd Xinh (Ngd Xuan Thdnh et al., 2011) vd nhiing nghifn oiu gdn day ciia nhdm tdc gid vi dd sif u mafic Niii Nua (so lifu chua cdng bd) cho thiy cdc thi sifu mafic d day la nhiing thi peridotit Mnh thdnh d ddi trudc cung hiit chim. Cdc nghifn cim tren the gidi h i ^ nay ch%) nhgn rpng rdi ring cdc thf magma trudc cung dupe thdnh tgo trong giai dogn sdm cua su kifn hiit chim khi mdng tiiach quyen dgi duong hut chim xuong dudi manti. Nhu vay, niu cdc mgch gabbro-diabas trong khu vyc thupe mpt phin cua thgch quyen dgi duong trong td hpp ophiolit, khi dd tudi 470 Tr.n cd thi dupe coi Id tudi bit diu cua qud trinh hiit chim giiia dja khdi Ddng Duong vd Vift-Trung. Kit qua nay cimg phii hpp vdi cdc nghien ciiu gin day cua tdc gid Nguyoi Van Vupng vd nnk (2012) dio cdc thanh tao ophiolit khu vyc Sdng Ma, cho thiy tudi ciia cdc thdnh tao sieu mafic khu vuc Sdng Md phdi cd hon giai dogn Ordovic, khdng dinh vd dgi duong khu vyc Sdng Ma dupe hinh thdnh c6 hon giai dogn Ordovic - Silur.
Tuy nhien, qud trinh hpi nhdp ciia ddi khau S«ig Ma, cd thi gdm nhiiu giai dogn khdc nhau. Ckc so lifu nghioi ciiu gin ddy cua mpt so tdc gid cho idng the biin chit cao
tudng eclt^t vung Dien Bien cd tudi khodng 240 Trji chiing td qua trinh hpi nhap giua hai mdng Ddng Duong va Vift-Trung xdy ra vao khodng Trias sdm. Tap thi tdc gia da phan tich cho cdc thdnh tao plagiogranit khu vyc Sdng Ma, chiing cd tudi -260 Tr.n.
Tudi nay (tdi lifu chua cdng bd) minh chiing cho tudi phin vd dgi duong khu vuc nghien ciiu dupe thdnh tgo vao giai doan Permi.
Phin vd trudc cung chi hinh thanh trong giai dogn ddu cua qua trinh hut chlm vd chiing ngimg nghi khi qua trinh hiit chun da xdy ra sdti va thyc thy. Nhu vay mdi 260 Tr.n khdng the la tudi ciia cdc thi ophiolit trudc cung. Bdn triing dgi duong khu vuc nay ciing CO thi dupe thdnh trong nhiiu giai doan ddng thdi vdi qud trinh hiit chim.
Trong gud trinh hiit chun va chgm cd thi mpt phdn vd dgi duong thyc thu bi diy len vd lye dia giua hai mdng.
Do dia chit khu vuc nghifn ctiu khd phiic t^, qud trinh tiin hda lau ddi vd trdi qua nhieu sy kifn dia chit khdc nhau, vi vdy trong thdi gian tdi cin tiip tuc diu Ur nghifn cim cdc thdnh tgo thufc dai ophiolit khu vyc Sdng Md, mdi cd thi cd nhimg nh|n x6t vd hieu biit thiu ddo hon vi lich su hf n hda ciia chiing.
V.KetLUAN
1/ Tuii kit tinh U-Pb zircon If'I^IV^ gabbro-diabas vung Niii Nua L J'." ^ ^ ' ° ^ ° * ' ' • ^ ) - Tu6i nay khdng dinh cdc dd sifu mafic Nui Nua I't nhat phdi cd hon 470 Tr.n.
2/ Vao 234±6 Tr.n, pha nhift Win sinh da
^ dpng 1«, cdc dd gabbiOKliabas (hidi Paleozoi sdm) xdy ra trong thdi gian Trias W , T ^ J ^ " ° ' ^^ hai i g Viet-Tnmg vd Ddng Duong
yjf t " T ^^^ t6i xin cdm on T^.
x . ^ . ^ ' ' ^ " ^ ' Pl^ng thi nghifm l l ^ ^ u - ^ ^"P <» trong qud trinh thuc hi?a thi nghifm vd nhiing h^o ddi quy bdu
trong thdi gian cdng tdc thyc dja ciia GS Sun Maomrag, GS. Wang Pigun Dgi hpc Cat Lam Tnmg Qudc, cdm on nhiing gdp v quy bdu ciia GS. Trdn Van Tri trong qud tnnh hoan thifn bdi bdo, cdm on (Juy phat tafn Khoa hpc va Cdng nghf qudc gia (NAFOSTED), da tai titr cho Di ^ m d ^ 105.03-2011.23.
VANLI?U
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Caledonides of Western Norway Contribution to Mineralogy and Petrolosn
147.671-683. '^' 2. Biii Minh Tam (Chu biin), 2010.
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F-48-XX),/jp. 123. HdNdi
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mdi ve tuoi dong vj U-Pb zircon trong granodiorit, phiic he Chieng Khuong khu vuc . huyf n Sdng Ma. TC Khoa hpc Ky thugt Md - Dia chdt, 35/7:38-42. Ha Npi
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12. U Tien DOng, Phgm Thj Van Anh, 2008. Ddc diim dja chit cdc khoi metaophiolit khu vyc Mudng Ldt (phia Tay Thanh Hda). TC Khoa hpc Kp thugt Md - Dia chdt. 21/01;30-38 Hd Npi
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HdNgi
22. Nguyen Van Vuong, Hansen BT, Wemmer K et al, 2012. U/Pb and Sm/Nd dating on ophiolitic rocks of the Song Ma suture zone (northern Vietnam): Evidence for upper paleozoic paleotethyan lithospheric remnants. Journal of Geodynamics.
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25. Pham Trang Hieu, Chen Fukun, Zhu Xiyan, Wang Fang, 2010. Zircon ages of paragneisses from the Sin Quyen Fomation in northwestern Viehiam and their geological significances Earth Science-Joumgl of China University of Geosciences, 35/2:201-210.
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Bien dgng uon nip-chdm nghich vd kiin
^o phu chdm trong qud trinh tao niii d Tay Bac Bf: sy hifn tlifn vd tdc dpng cda Chung len binh dh ciu tnic khu vyc, Tuyin tgp Bdo cdo Hpi nghi khoa hpc Dia chdtky mem 60 nam thdnh Igp „gdnh Dia chdt
Vi^tNgm, tr. 49-62.
19. Trin Van Tri, 1977, Dja chit Vift Nam phan mien Bdc. Nxb Khoa hpc Kv thugt. Ha Npi, 354 trang
^^^.":.J'",^".V»» Trj, Vu Khiic (BSng Chu bien) vd nnk., 2009. Dja chit vd Tai nguygn Vift Nam. Nxb Khog hpc Tv nhien vg Cdng ngh?. Ha Npi 590 tr
SUMMARY
470 Ma aged flabbro-diabase in Ntii Nu-a area of Song Ma structural zone and Its tectonic significances
Phgm Trung Hiiu. LaMgiSm. Le TiinDUng, NgdXu&n Thdnh
hy^rs^prrxS'te^r^or^^rM^-T^^^^^^
s s t ; ^ i ^ ; i s ^ i ~ -
Sdng Md ophiolite zone I s t ^ S r ^ h l dTnT. ' '^*J°" '^' "^ *^ ""^'™««<= ''^^ i" the significance in delimitingTe emplacement a i o f l ' (Ordovician). This sUidy is of important SangMdstnicturalzone,^oneof7oLurr3:sit
Nguori bien tStp: GS TS Trdn Vgn Trf.