WILSON CYCLE STUDIES 

NASA GRANT NAG5-585 

Semi -Annual Report 

July 15, 1986 - January 15, 1987 

Activity concentrated on the study of regional 1 ineaments in continental 

evolution and an extended abstract (Appendix 1 attached) was prepared that 

will be presented at a forthcoming US-India workshop on continental 1 ineaments 

to be held in Bangalore in April 1987 (attendance is at no cost to the project). 

(6ASB-CH-180353) WILSCN CYClE SPUDIES ~a1-15a24 

Semiannual Regort, 15 Jul. 19E6 - 15 Jan. 1587 (Houston Univ.) 7 F CSCL OBG Unclas 

63/46 43555 
. 

REGIONAL LINEAMENTS AND CONTINENTAL EVOLUTION 

Kevin Burke, Lunar and Planetary Institute, 3303 Nasa Road I, Houston, TX 77058 and 

Department of Geosciences, University of Houston, Houston, TX 77001 rnd Cel:l Sen&, 

Lunar Planetary Institute and Istanbul Technical University. 

1. SUMMARY 

Lineaments within continents are attributable to a small number of processes of continent formation and modification, but interactions among these processes may produce 

complex patterns. 

2. FORMATlON AND MODIFICATION OF THE CONTINENTAL CRUST 

Continents originate by the sweeping together of island arcs (Burke and SengEr, 1986). 

Continental and island arc crusts are dominated by rocks of comparable compositional 

and density ranges (SOz 50-7096; 2.6-2.9 gm/cc), evidence of the operation of this process 

is abundant in the geological record, and can be seen in action today in Indonesia. 

Misgivings have been voiced about the simple idea of assembling continents by colliding 

arcs, because some arcs do not closely resemble average continental material and because 

much continental material is very old (> 2.5 Ga) and the world is likely to have operated 

in a different way in the remote past. 

The world must have operated in a different way in the very remote past, but it is 

increasingly being recognized that the record of the rocks as far back as 3.8 Ga ago, is 

consistent with the idea "that many processes have apparently not changed at all" 

(Thompson et al, 1984, p. 404). For this reason, we here employ the hypothesis that as far 

back as the record goes, continents have been assembled by processes fundamentally comparable to those acting today. 

There are within the oceans shallow-water objects distinct from active arcs, extinct 

arcs and micro-continents which have been suggested capable of contributing to the continental crust. One such population is that formed at intra-oceanic hot-spots, e. g., Hawaii 

and Iceland, but although small objects representative of oceanic islands have long been 

repoited from mountain belts of all ages, there are no large Iceland or Hawaii like objects 

with volumes in excess of a thousand cubic kilometers in the mountain belts of the world. 

We therefore infer that it is the fate of such material to be largely removed from the 

surface of the earth by either subduction or obduction. The alternative idea, that older 

oceans did not contain hotspot volcanics seems less likely. A similar argument applies to 

the oceanic plateaus (e. g., Caribbean, Manihiki, Ontong Java, Shatsky Rise, Hess Rise) 
which extend over areas of millions of square kilometers. Evidence both from places 

where slivers have been caught up in accretionary prisms and from their relationship to 

old spreading centers shows that they do not represent continental fragments (as has been 

suggested), but are very thick accumulations of basalt interbedded with pelagic sediments. 

The mountain belts of the world contain slivers of material of this type, but no large 

volumes, and we therefore conclude that, oceanic plateaus do not contribute significant 

volumes of material to the continents. 

Materials that contribute substantial volumes to the continents are parts of Island arc 

systems, including sediments of accretionary wedges which in some areas, for example, 

the Songpan-Ganzi, the Makran and the Barbados wedge may be of enormous volume. 

jected are limited in both number and extent. We distinguish six main processes by which 

continents are modified and summarize them thus: 

(1) The construction of an Andean arc at the continental margin involves a variety of 

phenomena, including: (a) addition of magmatic material from the mantle; (b) partial 

melting of older continental crust and related vertical fractionation; (c) thickening of 

crust by up to a factor of 2 (to 70km) and consequent elevation; (d) compressional 

tectonism (especially on the borders of the arc) with formation of both a forearc and a 

foreland trough; (e) extensional tectonism (especially at the crest of the arc). 

(2) Continental collision, as now in Tibet and the Himalayas, produces effects similar to 

those of Andean collision, but over a much larger area. Indian workers have long 

described the Himalaya and, thanks to recent pioneering efforts by Chinese geologists 

and their French and British colleagues, we are beginning to appreciate some of the ways 

in which continental crust is modified at collision in Tibet. 

Once a continent is assembled by arc collision, the vicissitudes to which it can be sub- 

~~~~ 

Tremendous thrusting of the kind first described from the Alps, Scandinavia, the 

Himalaya and from the North of Scotland about 100 years ago, has accommodated the 

extensive doubling of continental thickness that characterizes both Andean and collisional 

mountain belts. Partial melting of the thickened crust at collision produces compositional 

differentiation with shallow "minimal-melt" granites and deep anhydrous residues. Thickened continents, are unstable being subject to rapid erosion as well as to gravitational 

collapse, two processes that restore continental thicknesses to normal values (30-40 km) in 

8 few tens of millions of years after the cessation of convergence. 

(3) Flooding of the continents by the waters of the ocean produces a sediment thickness 

typically of a few hundred meters and reflects sea level changes dominated by the varying 

average age of the ocean floor and the volume of ice-caps. 

(4) The mature continent records bombardment from outer space, but since the beginning 
ORIGIPSA PAGE rs 

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of the rock record (at 3.8 Ga), the flux has been low, and the most complete record is on 

the oldest continents with Vredefort in South Africa and Sudbury on the Canadian Shield. 

(5) Sporadic non-plate mrrglo (or hot-spot) volcanlrm will modify the continental crust 

from time to time, but these effects generally produce only local modification. 

(6) Rifting (the formation of elongate depressions related to rupture of the lithosphere in 

extension) is one of the dominant ways in which continents are modified. Rifts form in 

diverse tectonic environments: Andean arcs may split along their crestal volcanoes to form 

marginal basins; continents like Africa now and about 200 Ma ago may come to rest over 

the convective circulation of the mantle and rupture. Rifts also form in association 

with continental collision (as in the Rhine and Baikal). 

Continental assembly from island arcs, Andean arc formation, continental collision and 

rifting are the dominant processes of continental evolution which leave their mark in the 

deep structure of the continents. Continental regional geophysical lineaments can be 

related to one or other of all of these processes. 

3. REGIONAL LINEAMENTS WITHIN THE CONTINENTS 

Lineaments related to the various processes that generate and modify continental 

crust are widespread, and I here describe a few examples: 

(1) The almost North-South trend of the greenstone belts of Southern India (Fig. 1) is now 

TbO 78" BOe 

Figure 1. Numerous Archean arc-collisions 

are suggested responsible for the Greenstone 

belt trends (horizontal lines) north of a line 

through Kolsr. Bangalore rnd Mysore. 

The dash-dot line close to the East coast is a 

lineament marking the site of a possible Late 

Proterozoic collision to which the Cuddapah 

Basin is 8 foreland-basin. Late Proterozoic 

strike-slip faults are perhaps associated 

with this collision. From Drury rnd others. 

Journal of Geology, 1984. 
. 

OWEC?~,"iL PAGE IS 

OF POOR QUALITY 

(2) The characteristic trend of an Andean arc can be recognized in the Gangdise intrusive 

and volcanic belt of Tibet (Fig. 2) which represents the arc system associated with northward subduction of Neotethyan ocean floor that preceded the collision of India with the 

rest of Asia in Paleogene times. Ancient examples of arcs of this kind probably exist 

within the Indian Shield, perhaps, for example, in the Aravallis. 

I Mop of -y. 

Figure 2. Structural map of 

the Eastern Himalaya modified 

from Gansser (1980) showing 

parallel lineaments attributable 

to the Indus-Yarlung Tsangpo 

suture (black) and the Gangdise 

intrusives (short dashes) 

representing the roots of an 

Andean arc. 

(3) The Indus-Yarlung Tsangpo suture zone is a familiar feature (Fig. 2) marking the site 

of the collision between India and the rest of Asia. Similar lineaments are recognized in 

many parts of the world as recording collisions between continental and arc blocks and 

fragments. A map of such suture zones in Asia forms Figure 3. 

Figure 3. Sutu res of 

& along which 

blocks and fragments 

(sometimes confusingly 

called terranes) have 

been joined, mainly 

during the Phanerozoic. 
(4) Many of the world's most spectacular lineaments mark the sites of major strike-slip 

fault-zones and some of the most prominent of these faults are related to continental 

collision. New understanding of these features has followed from appreciation of their 

role in the process of "tectonic escape" by which material caught in a collision attempts to 

escape toward an oceanic "free-face". Faults in China and southeast Asia, such as the 

Altyn Tagh fault (Fig. 4) are the best examples of active faults of this kind, although 

more ancient features, such as the New York to Alabama lineament, have also been associated with collisional events. 

Examples of strike-slip related linear features shown in Figure 1 are possibly associated 

with a late Proterozoic collisional event roughly along the site of the present East Coast 

of India. The Cuddapah basin may be a Precambrian foreland basin related to such a 

collision. 

(5) Although rifts occur in a variety of different tectonic environments, many of the most 

familiar are related to collision. For example, in Figure 4 the Baikal and Shansi rifts 

inferred from their ages to be associated with the current Indian-Asian collision. 

Figure 4. Tectonic escape in South-East 

Asia. Modified and simplified from Tapponnicr 

et al. Note that evidence of timing indicates 

an association with the Himalayan collision 

for rifts as far apart as Baik2l ant the 

Sumatran coal basins (at 103 E. 3 S). A-T is 

the Altyn Tagh fault zone I200 km in length. 

7Q W W JUV llQ 

Fjgure 5 is a representation of Gondwana-Land in Late Permian times in which it is 

indicated, following a suggestion of Peter Lehner, that the "Gondwana" rifts of India, 

Madagascar and Australia can be attributed to an arc-collision event recorded in the 

'Sa mf ra u'. 

Although virtually all of the major lineaments of the continents can be ascribed to 

one or other of the processes outlined here, deciphering exactly how the processes have 

operated is generally difficult and may not always be possible. An illustrative example of 
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OF POOR QUALITV 

Figure 5. End Paleozoic Collision of 

arc systems with Gondwana induced 

rifting in Africa, India. Australia and 

Antarctica. The Cimmerian continent 

left Gondwana and an extensive foreland basin (K) was filled by 

Karroo sediments. 

how rifting, strike-slip motion and suturing may interact to yield complex geometric 

patterns is shown in Figure 6. 

Figure 6. Complex lineament patterns within continents (as 

in IV and V) may be produced by rifting (I and 11) and 

strike-slip motion (IIIa) before suturing (IVa) or suturing 

(IIlb) followed by strike-slip motion (IVb). 

Burke, Kevin and CelAl ScngEr, 1986. Tectonic escape in the evolution of the continental 

crust in Reflection Se ismolonv: The Cont inental Crus1 . Geodynamics Series Vol. 14, 

pp. 41-53, American Geophysical Union. 

Thompson, A. B., F. M Richter, H. Ahrendt, M. J. Bickle, K. Burke, R. F. Dymek, H'. Frisch, 

R. D. Gee, A. Kroner, R. K. O'Nions, E. R. Oxburgh, and K. Weber, 1984. The long-term 

evolution of the crust and mantle in Patterns of Channe of Earth EvolutioL edited by 

Holland and Trendall, pp. 389-406.