1 

.' 

WILSON CYCLE STUDIES 

NASA GRANT NAG5-585 

Semi-Annual Report 

January 15, 1986 to July 15, 1986 

(Delayed inadvertently because of an over1 ooked typographical 

error in the previous report which read July 15, 1986 - where 

it should have read July 15, 1985) 

The main activity relating to the study during this half year was a 

three week field trip to study Chinese sedimentary basins (June 10 to 

July 3, 1986) at no cost to the project. 

character, permitted progress in understanding how the processes of island 

arc-collision and micro-continental collision operated during the Paleozoic 

in far western China (especially the Junggar and Tarim basins and in the 

intervening Tien Shan Mountains). 

India- and Asia on the area were also studied. 

in the elevation of the Tien Shan to more than 4 km above sea level and the 

depression of Turfan to move 150m below sea level. 

large-scale strike-sl ip motion are important in producing these elevation 

changes. 

This study, while of a reconnaissance 

The effects of the continuing collision of 

Most specifically, these result 

Both thrusting and 

Some effort during the half year was also devoted to the study of 

greenstone-belts in terms of the Wilson Cycle and an abstract was contributed 

to an LPI workshop on greenstone-belts (Appendix 1 attached). 

Kevin Burke 

April 10, 1987 

(NASA-CR- 3802137) YILSCE CYCLE SIlUDIES He 7- I st3 23 

Semiannual GeFort, 15 Jan. - 15 Jul, 1986 (kcuston Univ,) 5 F CSCL 086 

Unclas 

G3/46 43654 

' L. 
/’. . . 

WORKSHOP ON 

TECTONIC EVOLUTION OF GREENSTONE BELTS 

Edited by 

4 M. J.deWit 

and 

Lewis D. Ashwal 

Sponsored by 

The Lunar and Planetary Institute 

A Lunar and Planetary Institute Workshop 

January 16-18,1986 

Lunar and Planetary Institute 3303 NASA Road 1 

LPI Technical Report 86-10 

Houston, Texas 77058-4399 
. 

GREENSTONE BELTS ARE NOT INTRACONTSNENTAL RIFTS. WHAT THEN ARE THEY? 

Celal Sengor 

- I 

Kevin Burke, Lunar and Planetary Institute, 3303 NASA Road One, Houston, Texas 

77058 and Geosciences, University of Houston, University Park. 

also Lunar and Planetary Institute, and Maden Fakultesi , ITU, Istanbul. 

Hundreds of intracontinental rifts ("elongate depressions [within 

continents] overlying places where the lithosphere has ruptured in extension" 

ref. 1) with ages between 3.0 and 0 Ga have been recognized on earth (2,3,4). 

Compressional features are either absent or insignificant in the vast majority 

of these rifts. 

few rifts. (Notably: the Benue trough (5) the Dneipr-Donetz rift (Fig. 1) (6) 

the Southern Oklahana rift (7) and the rift occupying East Arm of Great Slave 

Lake (8)). 

Intense canpression is the rule in greenstone belts and preservation of 

regional extensional structures is rare. (Abstracts at this meeting). Whatever 

greenstone belts are they do not satisfy the definition of intracontinental 

rifts. 

Wilson (9) showed that a common fate of intracontinental rifts is to 

develop into oceans and that oceans are likely to close. Mountain belts mark 

places where oceans have closed. 

mountain belts and greenstone belts are dominated by canpressional structures. 

Pursuing Wilson's idea I therefore sGest that it might be useful for students 

of greenstone belts to test the hyp@hesis that: "Greenstone belts are 

mountain-belts markin laces where OCEANS have closed". Oceaozg is a 

canplicated proIFef.~a~offh~g~canplexities that may be 

recorded in greenstone belts are indicated in Fig. 2. 

other becguse sane who describe greenstone belts as intracontinental rifts may 

be consciously concentrating on an early episode in greenstone belt evolution 

and recognize that the belts have a later oceanic and collisional history. I 

suggest that this practise is confusing and is rather like describing Ronald 

Reagan as a movie actor and ignoring more significant later episodes in his 

career. 

Prainent canpressional features are reported fran only a very 

In contrast to intracontinental rifts both 

There is a possibility that students of greenstone belts are confusing each 

References 

1. Basaltic Volcanism Study Project (1981). Basaltic Volcanism on the 

I Terrestrial Planets. Pergamon Press, Inc., New York, 1286TpT 

2. Morgan, P. and Baker, B.M. (1983). Processes of continental rifting. 

3. Burke, K., Kidd, W.S.F. and Kusky, T.M. (1985). The Pongola structure of 

Tectonophysics, 94, 680 pp. 

south-eastern Africa: The World's oldest preserved rift? Journ. of 

Geodvnamics, - 2, 35-49. 

I 

- 

4. Burke, K., Delano, L., Dewey, J.F., Edelstein, A., Kidd, W.S.F., Nelson, 

K.D., Sengor, A.M.C. and Stroup, 3, (1978). Rifts and sutures of the 

World. Contract Report NAS5-24094. Geophysics Branch, ESA Division, 

Goddard Space Flight Center, Greenbelt, Maryland. 238 PP. 

5. Benkhelil, J., Dainelli, P., Ponsard, J.F., Popoff, M. and Saugy, L. (1986) 

The Benue trough in press AAPG special publication Sediments in Rifts 

ed. Warren ManspeEer . 
. GREENSTONE BELTS ARE NOT INTRACONTINENTAL RIFTS 

Burke, K. and Sengor, C. 

- 

6. Sengor, A.M.C. (1985). Die Alpiden und die Kimneriden: Die verdoppelte 

7. Ham, W.E., Denison, R.E. and Merritt, C.A. (1964). Basement rocks and 

Geschichte der Tethys. Geol. Rundsh., 74, 181-213 pp. 

structural evolution of Southern Oklahoma. Oklahoma Geol. Surv. Bull 

- 95, 302pp. 

- - 

- - ., 

8. Hoffman, P.E. (1980). Wopmay Orogen: a Wilson cycle of early Proterozoic 

age in the northwest of the Canadian Shield. In - The Continental Crust 

of the Earth and its Mineral De osits (D.W. Strangway, ed.). p.523-549. 

GeorAc GadaSpec. Paper _e_f 20, oronto, Ontario. - 

9. Wilson, J.T. (1968). Static or Mobile Earth: the current scientific 

revolution. In Gondwanaland Revisited, p.309-320. her. Phi 10s. SOC. 

Proc. vol. 112. 

B 

Figure 1. (from ref. 6) Ill 

(such as the Dneipr-Donetz 

continental coll isions (as 

coll isions in North Dobrudj 

has shown that folding and 

much less intense than that 

greens tone bel ts . 

ustration of how rifts within a continent 

rift) have been affected by neighboring 

the Dneipr-Donetz structure responded to 

a in the Early Jurassic). Observation 

thrusting developed in this environment is 

with which we are becoming familiar in 
.. 

GREENSTONE BELTS ARE - NOT INTRACONTINENTAL RIFTS 

Burke, K. and Sengor, C. 

Figure 2. (from ref. 6) A possible origin for some greenstone belts. 

Rifting (I) takes a continental fragment out into an ocean (11). Major strike-slip motion (IIJa) is depicted as preceding collision between 

Slivers of the continental fragment and the main continent (IVa). As an 

alternative suturing my take place (IIIb) before major strike-slip 

motion (IVb). In either case the preserved suture zones may end abruptly 

at stri ke-sl ip faults and late rotation may preserve puzzling polarities 

(Vb).