BAN DO KIEN TAO - DIA DONG LlTC VUNG BIEN NGOAI KHOI NAM TRUNG BO VA PHU CAN
TECTONIC AND GEODYNAMIC SKETCHIVIAP OFFSHORE OF SOUTHERN PART OF CENTRAL VIETNAM
Phiing Van Phach, Do Chien ThSng, Nguyen The Tiep, Hoang Van Vuong, Duffng Quoc Hung, Tran Anh Tuan, Tran Van Kha, Ngo Bich Hucmg, Trinh Hoai Thu
Vien Dja chat va dja vat ly bien, 18 - Hoang Qude Viet, Cau Giay, Ha Ndi, Email: pvphach(a'vahoo.com
Tom tat:
Khu vuc biin Nam Trung Bd vd phu can cd cdu tnic kien tgo vd dia ddng lire khd phire tgp. Cdc nghien ciru chi tiit cdc tdi lieu mdi thu thdp gdn ddy nhdt ve dia chdt, dia mgo, vien thdm, cdu triic kiin tgo vd dia ddng lire cho phep di den mot sd nhdn dinh, Idm sdn^ td them mdi quan he giira cdc dan vi cdu triic trong khu vuc. Ddc biet Id vdn di vi bdn chdt vo chuyin tiep ciia phdn ddu miit tay nam cua triing nuac sdu Biin Ddng. Diiu ndy mot Idn nua khdng dinh dnh huang mgnh me ciia kiin tgo xd hiic din ddc diem cdu tnic-kiin tgo vd dia ddng lire ciia khu vuc Ddng Duang-Biin Ddng Viet Nam ndi chung vd khu vuc Nam Trung Bd ndi riing.
Viec chinh xdc hda cdu tnic chuyin tiep ciia phdn ddu miit TN ciia trung nuac sdu Biin Ddng cd y nghia rdt quan trong trong viec xdc dinh ranh giai ngodi thim luc dia Viet Nam, gdp phdn bdo vi chii quyin ciia Viet Nam trin Biin Ddng.
Abstract:
Continental shelf of southern part of Centred Viet Nam and adjacent area has quite complicated tectonics and geodynamic regime. Our detail analysis of new- data of geology, geomorphology, remote sensing, tectonic structures and geodynamics led to some new interpretations that help to make the relationship
betix'een the structures of the region clearer. In particular it concerns a transition crust on the SW tip of East Viet Nam Sea. This once more confirms the strong influence of collision tectonics on tectonic structures and geodynamic conditions of Indochina in general, and continental shelf of Southern part of Central Vietnam in particular.
The precision of transitional character of the SW tip of deep water basin of East Viet Nam Sea has an important role in establishment of outer limit of continental shelf of Viet Nam that has contributed to affirm a sovereignty of Viet Nam at East Viet Nam Sea.
1. Mddau
Them luc dja Viet Nam la khu vuc chuyen tiep giiia vd Trai Dat kieu luc dja va kieu dai duang, vdi mot ben la khdi luc dja Ddng Duong va mot ben la Bien Ddng Vict Nam.
Ban dd kien tao va dja ddng lire la san pham dau tien can phai thanh lap trong viec xac djnh ranh gidi ngoai them luc dja Viet Nam.
De xac djnh ranh gidi ngoai them luc dja Viet Nam theo Cdng udc luat bien qude tl 1982, tmdc tien chiing ta phai xac djnh dugc ranh gidi giua vd luc dja va vd dai duang. Ranh gidi dd triing vdi diem chan ddc luc dja, nai xay ra cac bien ddng ve dja hinh, trudng trgng lire, tmdng tir manh nhat. Cac diem chan ddc luc dja dugc xac djnh cho cac khu vuc cd su chuyen tiep tir vd luc dia sang vd dai duang.
Hgi nghi Khoa hgc ky mem 35 ndm Vien Khoa hgc vd Cong nghe Viet Nam - Hd Ngi 10 2010
Tren Biin Ddng Viet Nam tdn tai cac miln cd che do ddng hgc khac nhau. dd la: mien tach gian ria luc dja Bdc Biin Ddng; miln tmgt bang Tay Bien Ddng; mien trdi tmgt- huy hoai vd luc dja viing Tmdng Sa - Reed Bank; Mien nen ep - hdi tu Borneo-Palawan va Manila; Mien vd dai duang Kainozoi tmng tam Bien Ddng.
Bien Ddng Viet Nam la mot bien ria ddc dao, vdi sir hinh thanh va phat trien mot mien vd dai duong thue thu, cd tudi tir 32 - 15,5 trieu nam. Sir hinh thanh va phat trien Bien Ddng trong Kainozoi lien quan mat thiet den sir tuong tac giiia cac mang thach quyen, vdi sir tham gia tich cue eiia cac mang luc dja An Do, Tmng Qude, Ddng Duong, cac tieu mang Ddng Nam A, mang vd dai duong Thai Binh Duong.
Viec thanh lap ban dd kien tao va dja ddng lire can xuat phat tir mot quan diem kien tao - dja ddng lire nhat quan. Trong khi hien nay tdn tai nhieu quan diem khac nhau lien quan den su hinh thanh va tien hda Bien Ddng trong Kainozoi.
2. Cac quan diem kien tao cff ban ve sy hinh thanh va tien hoa Bien Dong
Hien tdn tai mot sd md hinh kien tao ddng lire Kainozoi. Cac md hinh kien tao khu vuc chu yeu tap vao giai quyet mdi lien he ddng lire ciia cac mang, hudng chuyen djch ciia cac dirt gay TB-DN, a kinh tuyen va vai trd ciia ehiing ddi vdi sir tien hoa ciia vd dai duong Bien Ddng trong Kainozoi.
Theo Taylor va Hayes (1983) [10] thi sir hinh thanh vd dai duong Bien Ddng Kz lai gan lien vdi qua trinh hut chim vd dai duong cd (Mesozoi) d ranh Palawan. Theo md hinh nay dirt gay Tay Bien Ddng cd kieu tmgt phai.
Theo md hinh ciia Tapponnier P., Peltzer, G., (1986), Hall, R., (1996, 2002), Leloup, Ph., (2001) [2, 5, 9...] trong giai doan dau cua Tan Kien tao dja khdi Ddng Duong di chuyen ve phia DDN, tao nen sir tmgt trai manh me cua he dirt gay phuang TB-DN dac biet la dirt gay Sdng Hdng. Trong md hinh nay dirt gay kinh tuyen TBD dugc coi nhu ranh gidi phia ddng cua dja khdi Ddng Duong va lien hoan vdi dirt gay Sdng Hdng nd ciing cd kieu tmgt trai. Tapponnier va cac ddng sir coi dd la ddng lire chinh hinh thanh vd dai duong Bien Ddng Kz (32-15,5 tr.n.).
Mot nhdm cac nha khoa hgc khac nhu Rangin, C.(1990), Le Pichon, X. (1995), Briais A. (1993), Roques, D. (1996), Huchon (1998) [1, 4, 7, 8] lai cd quan dilm tmng gian. Mot mat hg khang djnh kieu hinh ddng hgc tmgt trai manh me ciia cac dirt gay phuang TB-DN, va cho rang he nay ddng vai trd dot pha khau trong viec md vd dai duong Bien Ddng Kz. Tuy nhien, hg cho rang vao giai doan sau (sau dj thudng tir 7) dirt gay TBD cd kieu tmgt phai thuan trong bdi canh vd dai duong hinh nem tien ve phia TN. Ddng thdi cac nha khoa hgc nhdm nay cdn cho rang cd the tdn tai cac tam xoay (Euler poles), lam cho vd dai duong Bien Ddng phat trien ve phia them luc dja Viet Nam dudi dang mot hinh nem, lan ve phia tay nam, ngan each quan dao Tmdng Sa vdi them luc dja Viet Nam.
Cac bang chung ve cau tnic kien tao, dja ddng lire tren dja phan Ddng Duong, cho thay khu vuc nay vao giai doan Eocene - Miocene chju tac ddng cua cac lire nen a vT tuyen, lam cho cac dut gay phuong TB-DN tmgt trai manh me, ddng nghTa vdi sir tmgt phai ciia cac dii't gay phuong DB-TN. Cac triing keo toac (pull- apart) thudng dugc hinh thanh dgc theo cac ddi dirt gay phuang TB - DN. Cae tning De Tam nhu Ciru Long va Bac Vjnh Bac Bd dac tmng cho qua trinh tach gian bac - nam trong tmdng ling suat vdi cac nen ep cue dai dinh hudng theo phuong a vT tuyen. Cae tning De Tam dgc cac ddi dirt gay phuong TB-DN nhu Cao Bang-Tien Yen, Sdng Chay, Sdng Hdng, Sdng Ca, Sdng Rao Nay, lasir-Sdng Ba ciing la cae tach gian dia phuong dien hinh trong tmdng nen ep a vT tuyen. Chinh vi nhirng le dd ma md hinh kien tao-dja ddng lire ciia Tapponnier la md hinh dugc chiing tdi lu chgn de thanh lap ban dd Kien tao-Dia ddng lire viing bien ngoai khoi Nam Trung Bd.
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Vo luc dia bi vat mong Vo dai diTdng r\r\n<bi KIEN lAr)
Mien kien lac trircft bang Vung ria luc dia cang gian Kz
Vung vo luc dja bj cang gian, pha huy
Mang trung Borneo-Palawan Vung nen ep Borneo - Palawan Oia khoi Tien Cambri Indosinia Oia khoi Tien Cambri Cardamon Ddi uon nep Pz muon Viel-iao
I ^ p T r -f » -I
Mien uon nep Pz-Mz Tay Bac VN Dai nui Itjra Mz Triet Giang-Da Lat B l tram tich n6i mang
Khoi Tien Cambri Viet Bac
Mien uon nep Pz sdm Katasia Ddi khau Song Hong Mien kien true Indosini Shan Thai
: KY niKu KII.VC
Cac trung tSm sut lun cua be tram tich Kz True gian day Bien Dong Kainozoi Duong di thudng tuc6 Cac ddi nang
Pha kien tao E-N Pha kien tao Neogen Pha kien tao Plio-Q
V 5
Hinh 1: Bdn dd Kien tgo thim luc dia Nam Trung Bd vd phu can (CSL07)
Hgi nghi Khoa hgc ky mem 35 ndm Vien Khoa hgc vd Cong nghe Viet Nam - Hd Ngi 10 2010
Tren thirc te viec cho rdng phdn dudi TN eiia tning bien sau cua Bien Ddng, tir tga do 112 do kinh ddng va 10 do vT bdc vl phia TN la vd dai duong, la khdng du can cir.
Trudc tien can phai ndi rang viec xac djnh ranh gidi vd luc dja-vd dai duong chu yeu dira vao cac tai lieu dj thudng trgng lire, tir tmdng, cac mat cat dja chan cdng nghiep, tai lieu phan tich dja hinh-dja mao. Trong khi cac sd lieu true tiep nhu van tdc tmyen sdng cua cac Idp thach quyen thi lai chua dugc xac djnh bang cac tai lieu dja chan sau (sir diang sdng khue xa chang han).
Cac md hinh phan tich trgng lire cua nhieu tac gia cdn mang tinh chii quan, phu thudc vao each dat dieu kien bai toan md hinh. Theo tac gia Briais (1993) va Nguyen Nhu Tmng (2004) [1, 11] vd dai duong Bien Ddng khdng vugt qua kinh do 112 ve phia tay nam. Tai lieu dj thudng tir cua vd dai duong theo tai lieu Briais chi dugc ghi nhan vl phia ddng kinh do 112. Theo Nguyen Nhu Tmng (2004) viec cac tac gia nhu Taylor va Hayes (1983) [10] xac djnh tdn tai vd dai duong tai khu vuc kinh do 109 la chua chinh xac, do thilu tai lieu. Ngay trong bai bao cua Taylor va Hayes (1983) ve ngudn gdc va sir tiln hda cua Biin Ddng Viet Nam, ciing da chi ra rang neu vach ranh gidi vd dai duong-vd lijc dja sir dung cac dudng ddng sau day bien, thi d khu vuc nay cd sir tjnh tien dang ke ciia ranh gidi ve phia nude sau (cd the vai tram met), do dd dudng ranh gidi vd dai diron^ d khu vuc tay nam triing nude sau cd the ling vdi cac dudng dang sau 3800-3900 m, tire la ve phia ddng eiia kinh do 112.
Hon nira xem xet Ijch sir tien hda ciia vd dai duong Bien Ddng, chiing ta thdy rdng ve CO ban sir gian day xay ra ddi xiing ve hai ben tir triic gian day tmng tam, ke ca ddi vdi phdn tay nam cua triing nude sau Bien Ddng, do su dang len cua ddng ddi luu tir manti. Cho nen rat khd giai thich sir tdn tai nem vat nhgn ciia vd dai duong d khu vuc dau mut tay nam triing nude sau. Ngugc lai, ve nguyen tac, thdng thudng vd dai duong dugc khdng che bdi cae dirt gay chuyen dang, cd phuang ga vudng gdc vdi true gian day (d day phuong true ^ian day la DB-TN). Md hinh kien tao dja ddng lijc theo Tapponnier hoan toan phii hgp vdi dieu nay, vdi sir tdn tai ciia mot dirt gay phuong TB-DN, ddng vai trd gidi han su tdn tai vd dai duong d phia TN .
Cac tai lieu ve mat cat dja chan, dja hinh day bien deu phan anh SIJ: tdn tai loat cac dirt gay phuong TB-DN d viing bien nay. Tren ban dd dja hinh phan giai cao cd the thay dugc sir hien dien cua mot loat cac khe ranh dang canion phuong TB-DN, phan anh sir tdn tai va hoat ddng cua cac dirt gay ciing phuong. Cac dirt gay nay nhu la su ndi dai ciia he thdng dirt gay Sdng Hdng phuong TB-DN, ddng vai trd quyet djnh trong su hinh thanh va phat trien ciia vd dai duong Bien Ddng (tir 32 den 15,5 trieu nam tmdc).
3. Sff do kien tao - dia dong lu-c viing bien ngoai khoi Nam Trung Bo trong viec xac djnh ranh gidi ngoai them luc dja
Tren eo sd cac tai lieu hien cd, vdi quan diem kien tao-dja ddng luc nhu tren chiing tdi da tien hanh thanh lap ban dd kien tao-dja ddng lire viing bien ngoai khoi Nam Tmng Bd va cac viing bien khac ciia Viet Nam. Cd the nhan thay rang phan tay nam ciia triing nude sau Bien Ddng cd ban chat la vd chuyen tiep, chir khdng phai la vd dai duong.
4. Ket luan
1. Sir hinh thanh va phat Bien Ddng Viet Nam lien quan chat che den kien tao xd hue, do sir va cham ciia mang An Do vao Chau A mang lai: sir tmgt trai manh me ciia dirt gay phuong TB-DN Sdng Hdng da tao ra tach gian va hinh thanh vd dai duong Kainozoi Biin Ddng.
2. Sir phat trien ve phia TN cua vd dai duong Biin Ddng la su phat triln tilp Uic trong tmdng irng suat chung, tao nen sir tmgt trai manh me ciia he thdng dirt gay Sdng Hdng va cac
3. Vd dai duong Bien Ddng d khu vuc phia tay nam triing nude sau Bien Ddng, gan thim luc dja NamTmng Bd, dugc gidi han bdi mot dirt gay phuong TB-DN. Vd dai duong Biin Ddng chi tdn tai ve phia ddng cua kinh tuyen 112 do ddng.
TAI LIEU THAM KHAO
1. Brias, A., Patnat,P. and Tapponnier, P. (1993). - Updated interpretation of magnetic anomalies and seafloor spreading stages in the South China Sea: implications for the Tertiary tectonics of Southeast Asia. J. Geophys. Res. 98, 6299- 6328.
2. Hall R., 2002. Cenozoic geological and plate tectonic evolution of SE Asia and the SW Pacfic: computer-based reeonstmetions, model and animation. Journal of Asian Earth Sciences 20 (2002) pp. 543-531.
3. HoUoway, N.H., 1982. North Palawan block, Philippines - its relationship to Asian mainland and role in evolution of South China Sea. AAPG Bull. 66, 1355- 1383.
4. Huchon P., Nguyen Thj Nggc Hai, Rooke C , 1998. Finite extension across the South Vietnam basins from 2D gravimetric modelling] relation to South China Sea kinematics. Marine and Petroleum Geology, 15 (1998) 619-634.
5. Leloup, P.H., et al, 2001. New constraints on the stmcture, thermochronology and timing of the Ailao Shan-Red River shear zone, SE Asia. J. Geophys. Res.
6. Nguyen Thi Ngoc Hai, 1997. Stmchire et cinnematique de 1 extremite de la Mer de 1 est (Mer de Chine mDridionale). Et des bassins du sud Vietnam. These de doctoral.
L Universite Paris 6.
7. Rangin C , Jolivet, Pubellier M., 1990. A simple model for the tectonic evolution of southeast Asia and Indonesia region for the past 43 m.y. Bull.Soc.Geol.France, 1990 (8).t.VI,pp889-905.
8. Roques, Delphine. 1996. Tectonique Cenozoique de la marge Centre Vietnam : Implications pour I'ouverture de la Mer de Chine Meridionale. These de Doctotat de L'Universite Pierre et Marie Curie. Paris 6.
9. Tapponnier P., Peltzer G. & Armijo R. (1986). "On the mechanics of the collision between India and Asia." in M.P. Coward and A.C. Ries (eds.) "Collision Tectonics Vol. 19", Geol. Soc. Spec. Publ., 115-157.
10. Taylor, B., Hayes, D.E., 1983. Origin and history of the South China Sea Basin. In:
Hayes, D.E. (Ed.), The Tectonic and Geologic Evolution of Southeast Asian Seas and Islands. Geophys. Monogr., AGU, Washington, D.C., vol. 27, pp. 2 3 - 56.
11. Tmng Nguyen Nhu, Sang-Mook Lee and Que Bui Cong.2004. Satellite gravity anomalies and their correlation with the maj tectonic features in the South China Sea.
Gondwana Research, V.7, No.2, pp407-424.
