A critical review of tectonic processes at continental margin orogens

Tectonophysics, Elsevier

199

191 (1991) 199-212

Science Publishers

B.V., Amsterdam

A critical review of tectonic processes at continental margin orogens Steven Department

H. Edelman

of Geological Sciences, University of Tennessee, Knoxville,

(Received

November

30, 1987; revised version accepted

TN 37996-1410,

August

USA

20, 1988)

ABSTRACT Edelman, S.H., 1991. A critical review of tectonic processes at continental margin orogens. Coward (Editors), Deformation and Plate Tectonics. Tectonophysics, 191: 199-212.

In: A. PCrez-EstaCn

and M.P

A “cordilleran-type” orogen has previously been defined as contractional deformation of a continental margin due to subcontinental subduction. The plate tectonic setting of cordilleran-type orogenesis is fundamentally different from that of “collisional” orogenesis. Intracontinental orogens such as the Himalayas and Alps form by collision between a continental margin and a continental margin subduction zone. Orogens at continental margins may form due to subcontinental subduction (cordilleran-type orogeny), or due to collision of a continental margin with an intra-oceanic subduction zone which is typically followed by a reversal of subduction polarity. In the latter case, collisional orogenesis may proceed along with the reversed, subcontinental subduction. Modem arcs are mostly extensional or neutral, so subduction hangingwall contraction is not a necessary consequence of subduction. Crustal contraction in known collisional orogens lasts for tens of millions of years, so collisional deformation at a continental margin may last for tens of millions of years after arc-continent collision and subduction reversal. Collisional orogenesis is a predictable consequence of subduction, and collisional deformation is kinematically linked to the kinematics of subduction. Noncollisional cordilleran-type orogenesis is not predicted by plate theory. A geologic history that would demonstrate noncollisional orogenesis is a magmatic arc built into a passive margin sequence with strong deformation but without an earlier arc or ophiolite accretion event; this history has not been recognized in the geologic record. The classic examples of cordilleran-type orogens, including the Cretaceous-Cenozoic of the Andes and the Jurassic-early Tertiary of the western United States, may be interpreted as arc-continent collisions. However, the youngest increments of deformation in these two orogens occurred 100 million years after the youngest collisions and are thus difficult to ascribe to collisional processes. Notwithstanding the long time scales, these deformations occurred at the end of space-time continua of probable collisional orogenies. Alternatively, these deformations may represent lithosphere-scale fault-bend folding, duplex folding, backthrusting, and/or out-of-sequence forethrusting during shallow subduction.

Introduction

In

their

tween plate Phanerozoic sively studied,

Bird (1970) proposed

erogenic belts have been intenand the structural complexity of

Archean and Proterozoic basement terranes cates that the erogenic processes of crustal

indicon-

0 1991 - Elsevier Science Publishers

that mountain

beand

belts develop

in two fundamentally different plate tectonic settings: (1) A “collisional” orogen forms when a continental margin intersects a subduction zone. The subduction may be at a continental margin subduction zone in a continent-continent collision (Fig. la), an intra-oceanic subduction zone with an oceanic arc in an arc-continent collision (Fig. lb), or an intra-oceanic subduction zone without an arc in an ocean-continent (ophiolite emplacement) collision (Fig. lc). These three types

traction, metamorphism, uplift, and erosion have been fundamental aspects of the thickening and tectonic stabilization of continental crust throughout earth history. However, the problem of the plate tectonic settings of erogenic deformation is unresolved. The problem is most acute for continental margin orogens. 0040-1951/91/$03.50

classic paper on the relationships tectonics and orogenesis, Dewey

B.V.

S.H. EDELMAN

200

(a) Continent-continent

collision

review processes with emphasis

SUTURE

duced

by

produced

of continental

margin

on distinguishing

subcontinental by earlier

orogenesis,

deformation

subduction

pro-

from

that

arc collision.

EANIC CRUST

Previous ideas on cordilleran-type (b) Arc-continent

Dewey

MOLASSE

orogen

sJiFi~b*o~;zgFTA,

and

evolved

thotectonic Ocean (ophiolitekcontinent collision

orogen

“Andean

(1970)

cordilleran-type

from Dewey’s (1969) “or-

which

was

“Atlantic

associated

with

type” margin

type” margin.

to

The concept

of a cordilleran

orogen was inspired

pable thrust

from the western Americas that folding, and cleavage formation

evidence faulting,

occurred (d) Cordilleran-type

directly

of a passive

a convergent

SEA‘CW

Bird’s

orogen”

conversion (cl

orogenesis

collision

contemporaneously

subduction.

with

by the inesca-

subcontinental

Dewey and Bird (1970) suggested

that

high heat flow and plutonism

in the marginal

caused

of a “mobile

the rise and expansion

arc core”

(Fig. Id) beneath an “erogenic welt.” The mobile core would expand toward the continent and drive

Fig. 1. Plate tectonic leran-type development continent (1970).

settings

(d) orogens.

of collisional

Situations

of an arc edifice; collisions”

with

dashed

reversal

both

in this paper. lines

(a, b, c) and cordil-

(b) and

representing

(c) differ

are referred From

only

in

to as “arc-

Dewey

incipient

and

Bird

subduction

in (b) and (c) from Dewey (1976).

thrust sheets in that direction, and gravity slides would move in the same direction. This kinematic picture does not require any bulk shortening of the continental crust; any crustal thickening may be by addition of igneous rocks to the system. Variations of Dewey and Bird’s (1970) “mobile core” idea (Fig. Id) included a ductility contrast between Davis, of

of collisional orogen are mechanically driven by partial subduction of buoyant continental crust. (2) A “cordilleran-type” orogen forms above a continental margin subduction zone and is thermally driven (Fig. Id). The arc-continent and ocean-continent collisions (Fig. lb,c) differ only in whether an arc edifice forms, so both will hereafter be referred to as arc-continent collisions. In these collisions, subduction must reverse polarity and dip beneath the continent if convergence is to continue. Any deformation of the continental margin would then occur in a cordilleran-type setting (Fig. Id), but it is then unclear whether the deformation is driven by the subcontinental subduction or by the earlier collision. The purpose of this paper is to critically

heated

and unheated

crust (Burchfiel

1975), a push from the “hydrostatic

a fluid-like

rock

welt”

(Smith,

1981)

and head and

forceful arc to

injection and spreading of plutons drive thrust sheets (Allmendinger

in the and

Jordan, pointed

1981; Hamilton, 1985). Rutland (1973) out that circum-Pacific orogenies were not

due to repeated opening and closing of the Pacific Ocean in Wilson cycles; he also suggested that accretion of crustal fragments was not of importance. Mechanical explanations for cordilleran-type deformation in a subduction hangingwall have also been proposed. Coney (1972, 1973a,b) pointed out that the ages of erogenic events in western North America in the late Mesozoic and Cenozoic correspond to times of changes in sea-floor spreading geometry in the Atlantic Ocean. He interpreted this correlation as compressional failure at the leading (western) edge of an “ac-

TECTONIC

PROCESSES

tively driving”

North

sively overrode east-dipping

AT CONTINENTAL

MARGIN

American

relatively

Benioff

plate that succes-

tion of younger

lithosphere.

subcontinental,

wall orogenesis

due to shallowly

orogenesis

tion was suggested

passive,

zones.

201

OROGENS

This

was

specifically noncollisional (Coney, 1973a), and the dominant erogenic vergence was considered to be against

the “absolute”

hot spot reference plate

(Coney,

interpreted

frame,

1973b). oceanic

orogens

in terms

reference plates,

plate motion

of the actively

Wilson arcs

of active

and

and

Roeder’s between

at convergent

(1973) treatment

subduction

belts interpreted thetic” in that particularly

Burke

in a

driving (1972)

cordilleran-tie

motion,

frame, of the subducting

respectively,

direction,

in a mantle

of the relationships in erogenic

cordilleran-type orogens as “antithe erogenic vergence direction,

in foreland

settings,

was opposite

to

that of the coeval subduction (Fig. Id). This situation contrasts with the “synthetic” collisional orogens (Fig. la-c). Roeder (1975) suggested that antithetic lithospheric deformation above a subduction zone (cordilleran-type due to changes in subduction dip would above

spreading

the subduction

overlying back-arc

cause

lithosphere, spreading.

zone

orogenesis) may be dip. A decrease in

cordilleran-type

Moores

(1970)

western

Americas

collisions

orogenesis

-

would

occur during episodes of decreasing subduction rate. This analysis contrasts with the suggestion of Dalziel (1986) that cordilleran-type orogenesis in the Andes was caused by an increased subduction rate which may increase the horizontal compressive stress. Molnar and Atwater (1978) pointed out a rough correlation between the ages of actively subducting oceanic lithosphere at various convergent margins and the type of tectonic regime active in the associated arc. They concluded that arc spreading is associated with subduction of lithosphere older than 50-100 Ma, and that cordilleran-type orogenesis is associated with subduc-

the

subduc(1977),

et al. (1983)

subduction

proposed

that

was due

as in Fig.

ophiolite away from

lb,c,

with

subsequent

A continental

be due to the collision.

margin

after each reversal,

emphasized

the similarities

sions

subduction

arc

but orogenesis

Dickinson

(1971)

of arc-continent

colli-

reversal

orogenesis.

in the

dipped

develop

and

orogenesis,

orogenesis

to arc and

would

(cordiller~)

hangingwall

margin

would

to

Dewey

“activation”

and

Horsfield

(1970) suggested that arc accretion and subduction reversal may be a “partial explanation” for continental margin orogens. Gill (1982) suggested that “‘erogenic andesite’ rarely accompanies orogeny,” thus emphasizing that magmatism, even at “Andean-style” accreted

in dip would cause

Jordan

continental

reversals.

of the as

dipping

and Reynolds

in which subduction

and extension

An increase

to for

characteristic

type orogen. Because higher subduction rates may lead to shallower subduction and visa versa (Luyendyk, 1970) extension would occur during episodes of increasing convergence rate, and con-

contrast

wedge

contraction of the mantle wedge and of the lithosphere, and would be manifested as a cordilleran-

traction

In

mechanisms

of the mantle

and would be manifested

hanging-

Bird (1988), and Isacks (1988).

subduction

margins.

by Coney

et al. (1983)

the continent

and overriding

dip and vergence

Allmendinger

Subduction

margins,

should

not

of orogenesis.

With

fragments

prompted

crustal

a defining

the interest

in

by Coney

et

al. (1980), some workers have proposed that collisions of displaced terranes may be responsible for all orogenesis

that was previously

ascribed

ple subduction in cordilleran-type Avraham et al., 7981; Nur and 1982).

to sim-

orogens (BenBen Avraham,

Modem are-trench systems and oceanic plateaus

Cordilleran-type

orogenesis

is not a necessary

consequence of subduction. Modern arc systems display a variety of tectonic regimes, but most are sites of subduction hangingwall extension. Hamilton (1981) concluded that “magmatic arcs are extensional at all crustal levels.” In their synthesis of arc structure, Karig and Sharman (1975) cited repeated arc rifting and formation of back-arc basins and remnant arcs as characteristic of arc settings. This rifting is not restricted to intra-oceanic arcs, as evidenced by formation of the Sea of Japan. Some arcs are not deforming appreciably, and the controlling factors of arc extension are

S.H. EDELMAN

202

incompletely

known

(1981) reviewed

(Uyeda,

evidence

not characterized

1986).

Matthews

that arcs in general

by compression

normal

Geometry and tectonic setting

are In collisional

to the

“synthetic”

trench.

finally

The only part of a typical arc that is “erogenic” is the accretionary all arc-trench tional,

prism which is contractional

systems.

or neutral

regions

The extensional,

tectonics

is independent

tional

tectonics

With

the

modern, orogen.

actualistic Active

contrac-

of the arc and rear-arc

Some

proponents theory

and fold overturning,

direction

This

and

Well known

examples

Himalayan

orogen

is no

the

subduction

and Tapponnier, Mattauer, resulting (Milnes,

applicable

emphasized

south-vergent

from northward

arcs in Middle

of a universally

the

thrust from

(1970)

beneath

1975; Coward

subduction

1978;

1980),

Roeder,

northward

include resulting

Tibet (Molnar 1985; orogen

beneath

Italy

the south-vergent

Guinea

subduction

collisional

Alpine

from southward in the New

was

and Butler,

1986), the north-vergent

belt

to the

concept

in Dewey

there

Bird’s

The

of over-

is opposite

of subduction.

is

that

basin.

or direction

(Fig. la-c).

margin

of orogenesis

thrusting

ocean

direction,

orogens

America and the Cascade Range of North America do not maintain subduction hangingwall orogens. collisional

vergence

implicit

of a cordilleran-type

continental

the intervening

dominant dip

vergence

contrac-

of the Andes, example

closes

the dominant

1973) to the subduction

plate boundary.

of the universally

of the convergent

exception

in

orogens,

(Roeder,

region beneath

resulting the

New

modem abundance of oceanic plateaus and the inevitability of their active and future collisions

Guinea

with continental margin subduction zones (BenAvraham et al., 1981; Nur and Ben-Avraham,

al., 1987), and the west-vergent Taiwan thrust belt resulting from the east-dipping Manila Trench

1982). Collisions of oceanic plateaus with subduction zones must be an important tectonic process, but whether these collisions cause strong deformation of subduction hangingwalls is not clear. These

subduction (Page and All orogens, to various gences. Examples of “antithetic” vergence zone”, which is a late,

collisions magmatism

may cause temporary cessation of in the upper plate (Nur and Ben-

and Timor

and Pfiffner, Canadian

Cordillera

dominant

erogenic

collision

matics of collisional

of the Sula platform subduction

(plateau)

zone

in

with an

Indonesia,

is

manifested by imbrication of the lower plate plateau rather than by deformation of the upper plate (Silver et al., 1983a). Accretion of oceanic plateaus and other crustal fragments probably causes major orogenesis only if the plateaus are bounded by active subduction subduct continental masses.

zones that partially

Tectonic mechanisms morphism (Oxburgh

(Price,

beneath

wedges”

1986).

vergence

The

mimics

in the earlier

the

kine-

subduction.

thickening results

1979; Karig et

Suppe, 1981; Ernst, 1982). degrees, display two verthe opposite, subordinate, include the Alpine “root south-vergent fold (Milnes

1980), and “tectonic

Avraham, 1981; McGeary et al., 1985). But deformation in modern plateau collisions, such as the intra-oceanic

arcs (Hamilton,

by thrust faulting

in burial and

and Turcotte,

in

and other

and Barrovian

meta-

front

suture

of the

1974; Oxburgh

and

En-

gland, 1980). Erosion and possibly normal faulting (Platt, 1986) results in exposure of these metamorphic rocks in the “metamorphic core zone” of the orogen. Collisional orogens do not display associ-

relevant to con-

ated magmatic arcs. The limited crustal melting that occurs in collision zones is a second order consequence of collisional crustal thickening (En-

In order to evaluate in detail the similarities of continental margin orogens to well known collisional orogens, a brief overview of the geometry and chronology of collisional orogens is presented here.

gland and Thompson, 1986). Collisional processes can form erogenic belts without the operation of subduction hangingwall processes. Well known collisions between continents (Fig. la) cannot be followed by subduction reversal in the vicinity of the orogen and deformation thus occurs without subduction of oceanic lithosphere.

Aspects of collisional orogenesis tinental margin orogens

TECTONIC

PROCESSES

AT CONTINENTAL

MARGiN

203

OROGENS

ChXWUlOgy

berlain,

Deformation

Caribbean,

in

from the internal the external

collisional

fold-thrust

of years.

sional

implies

orogenesis

margins

millions

after

reversal.

tion of collisional

may

initial

began

curred

arc collision

Several examples

orogenesis

collision

in the Eocene

and

of the dura-

are reviewed

The continent-continent layas

orogeneof

is still

active today, indicating a minimum duration of 40 million years of crustal contraction (Molnar and Tapponnier, 1975; Powell, 1.979; Klootwijk and Radha~s~amurty, continent collision late Eocene

1981). The microcontinentin the Alps began no later than

(40 Ma) and lasted until

(5 Ma) indicating

a minimum

duration

the Pliocene of 35 mil-

lion years of crustal contraction (Dewey 1973; Milnes and Pfiffner, 1980; Trtimpy, Butler,

1986)

and the collision

et al., 1982;

may have begun

as

system

hangingwall

succession

or other accretion

type of orogen;

sive margins

to convergent

mechanisms

crustal

orogens

and subduction

margin

(Dewey,

a convergent sonably

ini-

margins.

lies

of pas-

There are two

continental

margin

(Fig. 2a,b). This process is compartly because the oldest, most

Australia

margin

of orogenesis”

subduction may initiate (Fig. 2) (Dickinson, 1971): (1) Subduction may initiate at a previously

This type of subduction

Continental

If the orogen

for conversion

by which

since the younger collision. The active arc-continent collision between New Guinea and northern 1979).

events.

problem

a mechanism

dense oceanic lithosphere generally located along

(Hamilton,

em-

such that the absense of is established, then any

deformation there lasted from the Late Jurassic until at least the Paleocene (60 Ma) (Price and Mountjoy, 1970) an interval of at least 40 m. y.

Ma) and is still in progress

not

ophiolite

Dewey (1969, pp_ 189) suggested

that the “fundamental in discovering

passive margin monly invoked

(5-24

which does

to cordiller~-type erogenic processes. Subduction must initiate at a continental margin to form this

Jurassic and the second (about 100 Ma)(Monger

no later than the Miocene

contact

contraction within and behind the conmargin arc could reasonably be ascribed

early as 100-130 Ma (Gillet et al., 1986). Terrane accretion in the Canadian Cordillera may have involved two major collisions, the first in the Late

began

the volcanic-pluto~c

for arc collision,

is preserved and exposed an early accretion event crustal tinental

oc-

The crucial

depositional-int~sive

margin

evidence

placement,

an orogen

contraction

arc collision.

in which

is in primary

display

of cordilleran-type

of such an orogen would be a paired

basic

in the mid-Cretaceous et al., 1982). Foreland

operation

would be to identify

without an earlier

arc-trench

of the northern

1979).

subduction

characteristics arc

the

with a passive

here.

in the Hima-

(40 Ma) and

for

processes

of colli-

last for tens

Mattson,

A test erogenic in which

The duration that collisional

sis at continental of years

migrates

core zone toward

belt and lasts for several

tens of millions

subduction

orogens

metamorphic

1988; Jurassic-Cretaceous

1969; margin

contraction linked

in an ocean basin is the rifted continental

Smith,

1976;

initiation without

would

1988). produce

a collision,

in this setting

to subcontinental

Ellis,

could subduction

and

be rea(Fig.

2b). This situation has not been clearly documented in the geologic record, so there is no clear

tiation

evidence that direct conversion to a convergent margin has ever occurred. This test does not dis-

Subduction may reverse and dip beneath the continent after arc-continent collision (Fig. lb,c). Examples of active subduction reversal have been reported from the southwest Pacific (New Guinea

prove the cordilleran-type erogenic model, but rather that the tectonic situation that would demonstrate its operation, i.e. continental margin subduction without pre-existing collisions, has not been realized. (2) Subduction may initiate within an ocean basin and approach a passive margin, in which case a component of subduction must dip away from the continent (Fig. 2a,c). Intra-oceanic subduction initiation is documented in the Aleutian

Trench, Hamilton, 1979; Cooper and Taylor, 1987; Flores and Wetar thrusts, Silver et al., 1983b) and have been inferred for erogenic belts (Nevadan orogen, Moores, 1970, 1972; Schweickert and Cowan, 1975; Cretaceous of British Columbia, Tempelman-Kluit, 1979; Lambert and Cham-

S.H. EDELMAN

204

PASSIVE

MARGIN

DIRECT CON-VERSION TO CONVERGENT MARGIN

c2= I//

Cordilleran-type orogenesis

Cordilleran-type OR collisional orogenesis Fig. 2. Two mechanisms Schematic oceanic

passive

for converting

margin.

Random

crust. (b) Subduction

be cordillerantype, lithosphere

and an arc (“v”

subduction

flips to form

deformation

initiates

but this geologic pattern)

a passive

pattern

at passive history

to a convergent

margin

basement;

prism-arc collision.

or ophiolite

plate. pair

tectonically

margin, and subduction may reverse (Fig. 2d). This tectonic history is well documented, but it is whether ensuing crustal contraction

due to subcontinental

(c) Passive

(d) Passive

margin

as in (b). Orogenesis

The two mechanisms

fragment

and their implications lines = shelf-slope-rise

and forms an accretionary

arc-trench system (Cooper et al., 1976) and in several parts of the southwest Pacific (Hamilton, 1979; Ben-Avraham and Uyeda, 1982). The continental margin eventually enters the subduction zone, the intra-oceanic arc is thrust over the

uncertain

margin

horizontal

has not been documented.

in the overriding

an accretionary

or the earlier arccontinent

margin

= continental

is

subduction and cordilleran-

type erogenic processes, or to the arc collision and collisional erogenic processes (Fig. 2d).

prism-arc

pair. Orogenesis

margin

is on a subducting

enters

subduction

in this setting

are distinguished

emplaced

for erogenic sedimentary

could

by the absence

over the continental

processes. wedge;

in this setting plate,

zone, arrests

would

with oceanic

subduction,

be due either (b) or presence

(a)

black =

and

to cordilleran (d) of an arc

margin.

larly crucial because this system represents the only candidate for an active cordilleran-type orogen and thus the only actuahstic example. Andes The

Andes display a well developed, Cretavolcanic-plutonic continental

ceous-Cenozoic,

margin arc related to subduction, and a Cretaceous-Cenozoic fold and thrust belt along the continental

side of the arc (Fig. 3a) (Ham and

Examples of cordilleran-type orogens revisited

Herrera, Faucher

1963; Ahlfeld, 1970; Gansser, and Savoyat, 1973; Audebaud

1973; et al.,

Dewey and Bird’s (1970) classic examples of cordilleran-type orogens were the CretaceousCenozoic of the Andes, the Jurassic-early Tertiary of the western United States, and the early Paleozoic Taconic _orogeny of the northern Appalachians. Interpretation of the Andes is particu-

1973). Deformation “peaks” occurred in the Late Cretaceous, Eocene, and Miocene-Pliocene (Martinez, 1980). Andean deformation has generally been attributed to subcontinental subduction (Hamilton, 1969a,b; James, 1971) and several studies have shown a correlation between late Cenozoic deformation and the geometry of sub-

TECTONIC

PROCESSES

AT CONTINENTAL

MARGIN

OROGENS

205

Cretaceous-

ene-Holocene

Cretaceous-

REVERSED

(a)

Subduction

SUBDUCTION

SYSTEM

Continental

zone COLLISIONAL

Fig. 3. Sketch

maps

Jurassic-early

Tertiary

diagram)

followed

showing

major

by subduction

examples,

features

of the western

Trrv

the oceanic

reversal

States.

(“reversed

arcs and ophiolites

probably

ducting oceanic lithosphere (Nur and Ben-Avraham, 1981; Allmendinger et al., 1983; Jordan et al., 1983). There is evidence for arc and ophiolite collisions

immediately

preceeding

the main

orogens

Both examples subduction

Creta-

Foreland fold and thrust belt

Metamorphic core zone

of the “cordilleran-type”

United

of (a) the Cretaceous-Cenozoic

can be interpreted system”

formed

arc

OROGEN

::I::.;.*..; Oceanic arcs and ophiolites

margin

as arc collisions

in diagram).

a fringing

From

Andes (“collisional

references

cited

arc system near the continenta

and (b) the orogen”

in text.

in

In both

margin.

continental margin (Bruhn, 1979; Dalziel and Palmer, 1979). In contrast, Dalziel and Forsythe (1985) stated that “accretion of oceanic terranes is not known

to have occurred”

Mesozoic-Cenozoic

during

the late

of the Andes.

ceous-Cenozoic Andean orogenesis, but their full extent is unknown (Fig. 3a). The basement for the

The “metamorphic core” of the Andes includes cleaved rocks associated with Cretaceous arc and

Andean orogeny is a Proterozoic-Paleozoic

ophiohte accretion in the southern Andes (Bruhn,

ter-

rane amalgam that was consolidated before the end of the Paleozoic (Ramos et al., 1986). The earliest event in the Andean orogeny was emplacement of ophiolite and oceanic arc complexes in the mid-Cretaceous in the southernmost Andes (Bruhn, 1979; Dalziel and Palmer, 1979; Saunders et al., 1979) and the northern Andes (Bourgois et al., 1982; Aspden and McCourt, 1986; Spadea et al., 1987) (Fig. 3a). Accreted oceanic terranes may be more extensive but concealed by volcanic cover (Howell et al., 1985; Aspden and McCourt, 1986). Gansser (1973, pp. 97) stated that strong deformation was preceeded by ophiolites. The accreted arc and ophiolite fragments probably formed near the

1979; Dalziel and Palmer, 1979) and in the northem Andes (Aspden and McCourt, 1986) and Late Cretaceous and Eocene schistosities in part of the central Andes (Martinez, 1980; Farrar et al., 1988) (Fig. 3a). Barrovian metamorphism (kyanite and garnet + staurolite), and Late Cretaceous with mid-Cretaceous in the “collision-style (Nelson et al., 1980; The late Cenozoic foreland fold and

continent-directed

nappes,

foreland thrusting associated arc collision is documented orogeny” of Tierra de1 Fuego Nelson, 1982). orogeny is restricted to the thrust belt in the Eastern

Cordillera, Sub-Andes, and Pampean Ranges. This deformation is dominated by east-vergent (conti-

206

S.H. EDELMAN

nent-directed)

and by subduction

thrust faults of Eocene-Holocene

reversal

represented

by the

age, with block fault uplifts in the Pampean Ranges

Sierra-Franciscan

(Herrero-Ducloux,

Moores, 1984). The presence of ophiolites (Saleeby,

1963; Ham and Herrera, 1963;

Martinez, 1980; Allmendinger et al., 1983; Jordan

1982,

et al., 1983; Roeder, 1988).

Schweickert

The

Andean

orogeny

Cretaceous-early

apparently

reflects

a

Cenozoic arc and ophiolite colli-

sional orogen, and a Cretaceous-Cenozoic

fore-

land fold and thrust belt with substantial

late

Cenozoic activity that could be a continuation

of

the collisional

orogenesis

of

subcontinental

subduction (cordilleran-type

or a manifestation

orog-

1983)

arc-trench system (Edelman and

and blueschists et al., 1980)

(Hotz et al., 1977; in the Nevadan

belt

require ocean basin closure. Probable accreted arcs include Klamath

the

Rattlesnake

Mountains

Creek

(Irwin,

and parts of the Foothills

terrane

1972;

in

Gray,

the

1986)

terrane in the Sierra

Nevada (200 Ma belt of Saleeby, 1982; Tuolumne River and Slate Creek terranes press).

These

terranes

represent

of Edelman, Early

in

Jurassic

eny) or both.

volcanic-plutonic ensimatic arcs and ophiolites that accreted before the Late Jurassic. Previous

Western United States

suggestions

of Late

Jurassic

collision

(Moores,

1970, 1972; Schweickert and Cowan, 1975; Gastil The late Mesozoic orogen of the western United States consists of, from east (continental side) to west (Fig. 3b): a Late Jurassic-early Tertiary foreland fold and thrust belt (Sevier foreland and Laramide belts), an Early Cretaceous metamorphic core zone characterized by penetrative deformation and both medium P/T Barrovian facies series and low P/T facies series (Sevier hinterland), and a complex zone of Jurassic ophiolites

et al., 1978; Ingersoll and Schweickert, 1986; Edelman, 1987) have been ruled out based on terrane linkage criteria (Mortimer, 1985; Sharp, 1988; Edelman, 1991, this volume). The geometries and chronologies of the remainder of the late Mesozoic erogenic features are compatible with a Nevadan collisional model (Fig. 3b). The Sevier hinterland contains Barrovian metamorphic overprints and other evidence of late Mesozoic crustal thickening

and ensimatic arcs (Nevadan orogen). Middle Jurassic-Cretaceous igneous rocks including the

(Coney and Harms, 1984). The large-scale

Sierra Nevada batholith

depicted in Fig. 2d. In addition, the coeval Canadian Cordillera, which contains extensive late

are widespread and are

associated with a belt of Late Jurassic-Early tiary subduction

melanges, blueschists,

Ter-

and eclo-

gite blocks (Franciscan Complex). These features have been attributed to cordilleran-type orogenesis in the late Mesozoic, with many analogies made to the Cenozoic Andes (Hamilton, 1969a,b, 1985; Coney, 1972, 1973a,b; many others). The Sierra Nevada batholith and associated rocks would represent the marginal arc and the Franciscan Complex would represent the subduction complex. These paired belts, hereafter called the “Sierra-Franciscan arc-trench system,” would represent the subcontinental subduction that caused Nevadan-Sevier-Laramide deformation by subduction hangingwall processes. However, the late Mesozoic erogenic features in the western United States may also be explained by arc-continent collision in the Nevadan belt, followed by contraction of the continental margin in the Sevier and Laramide belts (Fig. 3b)

struc-

ture and cross-cutting relations are similar to those

Mesozoic batholithic complexes, is now widely interpreted as collisional (Tempelman-Kluit, 1979; Brown and Read, 1983; Price, 1986; Lambert and Chamberlain, 1988). Taconic orogeny Dewey and Bird (1970) interpreted reported “gravity slides” in the Taconic allochthons in the northern

Appalachians

as evidence

for cordil-

leran-type orogenesis. Later data argued strongly against both interpretations, the Taconic orogeny being subsequently interpreted as arc (Rowley and Kidd, 1981; Stanley and Ratcliffe, 1985) and ophiolite (Nelson and Casey, 1979; Williams, 1985) collisions. In the central and southern Appalachians, widespread Barrovian metamorphism and coeval deformation are chiefly Taco& (Ordovician; But-

TECTONIC

PROCESSES

AT CONTINENTAL

MARGIN

207

OROGENS

ler, 1972; Glover et al., 1983). The Taconic orog-

earlier

eny in the southern Appalachians

another change in plate motions occurs.

buted to arc-continent Lash,

1982;

Hatcher,

has been attri-

collision (Shamugan 1987)

arc collisions,

may operate

stably

until

and

Marginal basins may be underlain by trapped

whereas no cordil-

oceanic lithosphere as described above and/or by

leran-type models have been proposed.

new

oceanic

spreading.

lithosphere

formed

The mechanisms

by

back-arc

by which marginal

Synthesis and problems

basins close is an important unresolved problem.

Synthesis

Wright, 1984) orogens. Thrust faults must cut the back-arc lithosphere resulting in continentward

This process has been cited in the Andean (Dalziel and Palmer,

The above discussion suggests a simple view of orogenesis in which continents, as passive riders in plate tectonics, are periodically deformed at their margins when they enter subduction zones. When the subduction zones are themselves at continental margins (Andean-style

margins), a continent-con-

tinent collision results. When the subduction zones are intra-oceanic, an arc-continent collision results and subduction reverses to create a convergent

Andean-style

margin

with

a continental

margin orogen. This simple view is predicted by plate theory and is supported by the geologic record. However, problems of marginal basin closure, the long time scales of continental margin orogens in the westem Americas, and deep lithospheric displacement compatibility remain unresolved. Closure of marginal

(Dalziel

1979)

and Nevadan

and Palmer, 1979;

(Harper

and

Nelson et al., 1980;

Bourgois et al., 1982) or oceanward (Harper and Wright, 1984) ophiolite emplacement, but whether these thrust faults are bona fide subduction zones, and the circumstances

under which they might

lead to strong deformation

of the adjacent

con-

tinental margin, are uncertain. This problem hinges in part on whether marginal basin closure is a spontaneous

subduction

hangingwall

contraction

or the result of a buoyant mass entering the subduction zone to cause subduction reversal behind the arc.

Time scales of continental low subduction

margin orogens and shal-

Late Cenozoic deformation in the Andes and Late Cretaceous-early Tertiary deformation of the western United States (Laramide orogeny) are re-

basins

Intra-oceanic subduction zones that dip away from continents are inherently unstable features

stricted to the external parts of the orogens and occurred about 100 million years after the youn-

because they can operate only until the continent enters the subduction zone. When a system of

gest collisions. Although both examples are spatial and temporal continuations of probable collisional

subduction zones initiates in an intra-oceanic

orogenies, the time scales are longer than in better

vironment

en-

during a global or regional plate re-

organization, those subduction zones that face a continent will be preferentially choked while those

known collisions. be associated

Both deformational

events may

with shallowly dipping subduction

that face open ocean continue to operate in a quasi-steady state. The choked subduction zones may cause collisional orogenesis and subduction

as indicated by continentward migration of magmatism in the western United States and the present dips of Benioff zones beneath western South America (Coney and Reynolds, 1977; Al-

reversal, whereas the oceanward-facing subduction zones may form a system of fringing island arcs separated from the continent by marginal basins. The resulting configuration of oceanward facing oceanic arcs and/or continental margin arcs, the latter being built into basement deformed by the

lmendinger et al., 1983; Jordan et al., 1983; Bird, 1988). During shallow subduction, the entire continental margin is a relatively thin thrust sheet and may be subject to lithosphere-scale fault-bend folding, duplex folding, backthrusting, and outof-sequence forethrusting.

208

S.H. EDELMAN

In addition,

the thickeness

of the “erogenic

walls. This deformation

may result from arc- and

wedge” (Davis et al., 1983; Platt, 1986; Jamieson

ophiolite-continent

and Beaumont, 1988) may increase by addition of

versal and/or

processes

magma and thus drive orogenesis.

subcontinental

subduction.

This process

would be an updated version of the “magmatic welt” (Dewey and Bird, 1970;

Hamilton,

1985).

tion is a predictable

collisions

and subduction

resulting

directly

Collisional

consequence

re-

from

deforma-

of subduction;

imbrication and thickening of continental

margins

However, this process must be treated with cau-

when they enter subduction zones is a kinematic

tion becuase, despite the impressive dimensions of

continuation

the granitic-dacitic

oceanic sediments in accretionary

batholiths and volcanic fields

of the imbrication

and thickening of prisms. In con-

of the western Americas, these materials are prob-

trast, cordilleran-type

ably transferred from lower to higher crustal levels

diction of plate theory nor an attribute

with only mafic material being added to the wedge

modem

convergent

orogenesis is neither a premargins.

maintains

is the

from beneath the crust.

only modem

Displacement

hangingwall orogen, and there are no demonstrably noncollisional orogens.

compatibility

arc that

of most

The Andes

a subduction

The outstanding kinematic problem with continental margin orogens is how the finite, oppositely-verging ,displacement fields of the coeval

The late Cenozoic Andean orogeny and the Late Cretaceous-early Tertiary Laramide orogeny occurred 100 m.y. after the youngest possible collisions. These deformations are restricted to fore-

oceanic subduction and the continental subduction (continent-directed thrust faulting, Bally,

scales, are space-time

1981)

orogenies. Alternatively,

interact

at

depth.

whether cordilleran-type

This (Fig.

problem

arises

2b) or collisional

land regions and, notwithstanding

the long time of collisional

these extended deforma-

tional events and other components of continental

(Fig. 2d) processes are ultimately operative. If the

margin deformation

down-dip continuations

deformation

of the thrust faults in Fig.

continuations

may be due to hangingwall

during

shallow

subduction.

The

2b,d had been drawn, a displacement compatibility problem would become obvious. In both the Laramide and Andean orogenies, the oceanwarddirected thrust systems accommodated shortening one or two orders of magnitude greater than that of the continent-directed systems.

primary kinematic problem with continental margin orogens is how displacements on the oppositely directed subduction and foreland thrust belts interact at depth. Resolution of this problem is critical to elucidating tectonic processes at continental margin orogens.

If orogenesis is accompanied by no crustal contraction as implied by Dewey and Bird’s (1970)

Acknowledgments

cordilleran-type orogen (Fig. Id) and suggested explicitely by Hamilton (1985), no displacement compatibility problem arises. If there is contraction (Allmendinger et al., 1983; Roeder, 1988) then continental thrust faults may terminate against the coeval subduction zone to form backthrusts and tectonic wedges (Price, 1986). Determination of this deep structure may be critical to understanding erogenic processes at continental margins. Conclusions Continental margin orogens appear to represent crustal contraction in subduction hanging-

I thank Eldridge M. Moores Beard for stimulating discussions,

and James S. and a Univer-

sity of Tennessee grant to Robert D. Hatcher, Jr. for supporting my trip to Oviedo and for manuscript preparation. Comments by two reviewers were very helpful. References Ahlfeld, V.F., 1970. Zur Tektonik des andinen Bolivien. Geol. Rundsch., 59: 1124-1140. Allmendinger, R.W. and Jordan, T.E., 1981. Mesozoic evolution, hinterland of the Sevier erogenic belt. Geology, 9: 308-313.

TECTONIC

PROCESSES

Allmendinger,

R-W.,

and Hacks, J.A.

terrane

Ramos,

MARGIN

V.A., Jordan,

B.L., 1983. Paleogeography

ural geometry, Aspden,

AT CONTINENTAL

northwest

and

in the central

W.J.,

Andes

T.E.,

Palma,

and Andean

Argentina.

McCourt,

Tectonics, 1986.

209

OROGENS

M.

struct-

of Colombia.

oceanic

Geology,

14:

415-41s. Audebaud,

E.. Capdevila,

Laubacher,

G.,

Mattauer. Les

C., Marocco,

M., Megard.

F., Paredes,

geologiques

essentiels

traits

(Perou-Bolivie). Bally, A.W.,

R., Dolmayrac,

Lefevre,

Rev. Geogr.

1981. Thoughts

B., Debelmas,

J.,

R., Martinez,

C.,

J. and Tomasi, des

P., 1973.

Andes

Centrales

Phys. Geol. Dyn., 15: 73-113.

on the tectonics

of folded

In: N.J. Price and K. McClay

(Editors),

Tectonics.

Spec. Publ., 9: 13-32.

Geol. Sot. London,

Ben-Avraham,

2. and Uyeda,

margmal

seas. In: T.W.C.

Geodynamics

belts.

and Nappe origin

Hilde

(Editors),

Union/Geol.

and

S. Uyeda

of

Pacific-Indonesian

Region.

Sot. Am., Geodyn.

Ser., 11:

Ben-Avraham,

2..

Continental thonous

Nur,

A., Jones,

accretion:

terranes.

from

Science,

P., 1988. Formation

United

States:

D. and

oceanic

Cox,

A.,

plateaus

1981.

to alloch-

of the Rocky

Mountains,

computer

western

model. Science,

239:

J., Calle, B., Tournon,

J. and Toussaint,

Andean

ophiolitic

megastructures

Ventura

transverse

(Western

Tectonophysics, Brown,

on

the

J., 1982. The

Cordillera-Valte

“core complex”.

1979. Rock

structures

in the Andes

terrane

of British

Geology,

11: 164-

formed

during

of Tierra

back-arc

de1 Fuego.

Ged.

Sot. Am. Bull.. 90: 998-1012. Burchfiel,

orogenesis,

of an earlier synthesis.

1975. Nature

western

United

Carolinas,

lachians.

1986.

subduction

London, P.J.,

Implications P.J.,

thrust-fold

southern

in

Appa-

M.P. and Butler,

deep

structure

in the Alps and Himalayas.

and

J. Geol. Sot.

I.W.D.,

Andean

tectonics

and

tectogenesis

Turling

and

of Continental

Drift

1973b.

Plate

tectonics

belts. Geology, Harms,

North

America

Cenozoic

sion. Geology,

extensional

12: 550-554.

1986. Collision

basin.

J.

1985. Thrust

tectonics

and

Himalaya.

Geology,

13:

orogonesis:

an

tors), Collision

and cordilleran

In: M.P. Coward

Tectonics.

Geol.

and A.C. Ries (Edi-

Sot. London,

Spec. Pub].,

19: 3899404. Dalziel,

I.W.D. the

and

Forsythe,

terrane

R.D.,

concept.

Tectonostratigraphic gion. Circum-Pac.

1985. Andean

In:

Terranes Count.

Dalziel,

I.W.D.

D.G.

evolution

Howell

(Editor),

of the Circum-Pacific

Ener. Miner.

S.K.

Runcom

to the Earth of

and Palmer,

tion and erogenic Davis,

Resour.,

Re-

Earth

Sci.

1984. Cordilieran

North

(Editors), Sciences. foreland

D., Suppe,

J. and

Dahlen,

relics of Mesozoic

com-

compres-

F.A..

deforma-

extremity

1983.

belts and accretionary

J.F.,

1969. Continental

sion of Atlantic

of the

Mechanics

wedges.

of

J. Geophys.

type

margins:

to Andean

a model

type.

Earth

for converPlanet.

Sci.

Lett., 6: 189-197. J.F.,

1976. Ophiolite

abduction.

Tectonophysics,

31:

93-120. Dewey, J.F. and Bird, J.M., 1970. Mountain Dewey,

tectonics.

J. Geophys.

J.F. and Horsfield,

and continental Plate

growth.

tectonics

B., 1970. Plate Nature,

tectonics,

orogeny

225: 521-525.

W.C., Ryan, and

belts and the new

Res., 75: 262552647.

W.B.F.

the evolution

and Bon&J.,

1973.

of the Alpine

system.

Geol. Sot. Am. Bull., 84: 3137-3180. W.R.,

continental Edelman, fomia: Edeiman,

1971. Plate tectonic

margins.

Nature,

S.H., 1987. Evidence in the Sierra

plate kinematic S.H.,

1991.

arc-continent folds, shear

zones,

for orogeny

for two Mesozoic

Nevada interpretation Progr., and

belt,

of a terrane

Cah-

analysis.

19: 651-652. between

kinematics

and foliations

Nevada,

at

arc-continent

metamorphic

Relations~ps

colhsion

Sierra

models

232: 41-42,

kinematics of thrust

in the Nevadan

California.

of

faults, orogen,

Tectonophysics,

191

(this vol.): 223-236. Edelman,

core

1979. Progressive

at the southern

Geol. Sot. Am. Bull., 90: 259-280.

northern marginal

K.F.,

uplift

Geol. Sot. Am., Abstr. in western

1: 131-134.

T.A.,

R.W.H.,

Sea marginal

of the Pakistan

perspective.

collisions

Am. J. Sci., 272: 603-628. D.H.

of New

arc-continent

417-420.

Dickinson,

Press, New York. pp. 713-727.

P.J. and

plexes:

Tennessee

tectonics,

1972. Cordilleran

In:

Academic

Coney.

Thrust

P.J., 1973a. Non-collision

America.

Coney,

and

in the Bearing

the deep structure

Dewey, J.F., Pitman,

363-396. metamorphism

143: 857-873.

plate motion. Coney,

Georgia,

regional

of

extensions

Am. J. Sci., 272: 319-333.

R.W.H.,

crustal

and controls

States:

Am. J. Sci., 275-A:

Butler, J.R., 1972. Age of Paleozoic

Coney,

Res., 81: 1916-1934.

global

B.C. and Davis, G.A.,

Cordilleran

following

6: 53-67.

lineations

Dewey,

a Mesozoic

basin deformation

Seismotectonics

M.S. and Scholl, D.W., 1976. Mesozoic

magnetic

Dewey, R.L.,

B., 1987.

Geophys. Coward,

1980. Cordil-

Res., 88: 1153-1172.

Colombia).

168. Bruhn,

Butler,

Tectonics,

J.W.H.,

288: 329-333.

for arc reversal

A.K., Marlow,

fold-and-thrust

Buga-Buena-

82: 207-229.

R.L. and Read, P.B., 1983. Shuswap

Columbia:

the

collision.

Monger,

Nature,

Taylor,

a model

Andes.

1501-1507. Bourgois,

P. and

Cooper,

Benioff zones.

Ser., 1: 565-581.

213: 47-54.

a continuum

D.L. and

terranes.

Guinea:

and

91-104.

Bird,

P.J., Jones,

Cooper,

S.J., 1977. Cordilleran

270: 403-406.

leran suspect

Dalziel,

S., 1982. Entrapment

of the Western

Am. Geophys.

Thrust

P.J. and Reynolds,

Nature, Coney,

2: I-16.

Mesozoic

Coney,

S.H. and Moores,

sion orogen Progr.,

E.M., 1984. Late Mesozoic

in the western

USA.

Geol.

Sot.

Am.,

colliAbstr.

16: 498.

Ellis, M.. 1988. Lithospheric

strength

in compression:

initiation

S.H. EDELMAN

210

of subduction, ing,

and

flake tectonics,

an

origin

foreland

of displaced

migration

terranes.

of thrust-

J. Geol.,

96:

thermal

and

P.C. and

Thompson,

models

for crustal

tectonic

zones. In: M.P. Coward Tectonics. W.G.,

Building

A., 1986.

and A.C. Ries (Editors),

Collision

Herrero-Ducloux,

building

Academic

and metamorphism:

a

A.H.,

1988. Zongo-San of the central B. and

Andes

Kontak,

Gaban

Andean

east Peru. Geology, Faucher,

pp. 247-

D.J. and

zone:

Eocene

orogen,

Archibald, foreland

northwest

D.A.,

E., 1973. Esquisse

de 1’Equateur.

Gansser,

Rev. Geogr.

Phys.

geologique Geol.

A., 1973. Facts

des

Dyn.,

15:

G., Morgan,

of California.

McDougall

(Editors), United

J.B.,

J. Geol.

D.G.

Mesozoic

Symp.,

1982. Mountain (Editor),

In:

D., 1978. Meso-

and related

areas east

Howell

and

Paleogeography

States. Sot. Econ. Paleontol.

Paleogeogr.

Hsu

California

H.A. of

Mineral.

the Pac.

building

and

Building

volcanism.

In: K.J.

Processes.

Academic

P., Choukroune.

Thickening

P., Ballerre,

history

M. and Davey,

of the western

Alps.

Earth

P., 1986.

Planet.

Sci.

Lett., 78: 4452. L., Speer,

J.A.,

the central G.G.,

1986.

system Hamilton,

terranes

California.

S.S., 1983.

and ductile deformation

Tectonics,

Klamath

5: 1043-1054.

of eastern

Peru

and

Equador.

for the Cretaceous America.

central

Oreg.

Dept.

Andes

-

and tectonics Geol.

Miner.

mantle.

Mesozoic

Geol. Surv., Profess. W.,

Philos. Trans. Hamilton,

1981.

a modem of westInd. Bull.,

In:

D.G.

graphic

Terranes

Ener. Miner.

G.D.

region.

U.S.

Pap., 1078: 345 pp. Crustal

evolution

R. Sot. London,

Count. Harper,

fomia. Isacks,

magmatic

and Wright,

arcs, and foreland

(Editor),

of the Circmn-Pacific Resour.,

magmatism.

Ser. A, 301: 279-291.

Howell

Tectonostrati-

Region.

Circum-Pac.

Earth Sci. Ser., 1: 259-262.

J.E., 1984. Middle

Sci., 15:

Argentina.

to Late Jurassic

D.A., 1977. Triassic and

north-central

Schermer,

Tectonostratigraphic

1985. region.

Terranes

Circum-Pac. R.A.,

genesis,

Count.

of

Ener.

1986. A plate-tectonic

Nevadan

California. Terranes

orogeny

Tectonics,

of the

in the southern

western

Paleozoic

orocline.

and

Mountains,

Pap., 800-C:

of the central

of the Bolivian

and forearc

5: 901-912.

Klamath

U.S. GeoI. Surv., Profess.

bending

E.R.,

of the circum-Pacific

Sci. Ser., 1: 3-30.

B.L., 1988. Uplift

CaIi-

C103-Clll.

Andean

Plateau

J. Geophys.

and

Res.,

93:

3211-3231. James, D.E., 1971. Plate tectonic Andes.

Jamieson,

paths

of the

Tectonics,

to the central

to geometry

and south-

7: 417-445.

B.L., Allmendinger,

V.A. and Ando,

and meta-

and pressure-tempera-

with applications

T.E., Isacks,

lated

C., 1988. Orogeny

a mode1 for deformation

em Appalachians. Jordan,

model for the evolution

Geol. Sot. Am. Bull., 82: 3325-3346.

R.A. and Beaumont,

morphism:

R.W.,

Brewer,

C.J., 1983. Andean

of subducted

Nazca

J.A.,

tectonics

plate.

re-

Geol.

Sot.

Am. Bull., 94: 341-361. Karig,

D.E. and Sharman,

tion in trenches.

G.F.,

A.J., Charlton,

D.M., 1987. Nature

across

1975. Subduction

the

Banda

T.R.,

Arc-Australian

CT.

and

of the Indian

collision.

McElhinney

In: M.W.

Paleorcconstruction

Comm. Lambert, visited,

Martinez,

Geodyn., R.J.

and

with

zone

at

C., 1981. Phaneroplate and the India-Asia

and

D.A. Valencio

of the Continents.

Geodyn.

(Edi-

Inter-Union

Ser., 2: 93-105.

Chamberlain,

V.E.,

a three-dimensional

in British Columbia.

1988. CordiIIeria mode1

for

re-

Cretaceous

J. Geol., 96: 47-60.

B.P., 1970. Dips of downgoing

lithospheric

plates

island arcs. Geol. Sot. Am. Bull., 81: 3411-3416. C., 1980. Gtol.

O.R.S.T.O.M., Mattauer,

S. and

of deforma-

collision

Radhakrishnamurty,

zoic paleomagnetism

beneath

Klemperer,

and distribution

GeoI. Sot. Am. Bull., 98: 18-32.

Klootwijk,

Luyendyk,

and accre-

Geol. Sot. Am. Bull., 86: 377-389.

D.E., Barber,

tectonics

by arc

Earth

1972. belt

tion

and the underflow

of the Indonesian

W., 1985. Subduction,

deformation.

California

and

Region.

northern

W.P.,

Am.

Geol. Sot. of Am. Bull., 80: 2409-2430.

W., 1979. Tectonics

Hamilton,

Irwin,

tors),

W., 1969b.

of Pacific

D.L. terranes

for ophiolite

Hussong,

65: 175-184.

Hamilton,

model

Timor.

batholiths

of western

California

R.V. and Schweickert,

fault

Petr. Geol., Mem., 2: 47-61.

em North Hamilton,

Resour.,

Ingersoll,

Karig,

L.J., 1963. Role of Subandean

in tectonics

in

Lithos, 16: 223-245.

of the central

W.. 1969a. The volcanic

model

Farrar,

Appalachians.

Native

C.K. and Herrera,

Assoc.

G.S. and

metamorphism

and southern

Mountains, Ham,

Russell,

Jones,

Circum-Pacific

Ramos,

Ages of regional Gray,

the

ture-time

Press, New York, pp. 13-17.

Glover,

D.G.,

central

2: 107-115.

Mountain

northern

Tectonostratigraphic

Triassic

G.J. and Krummenacher,

of peninsular

the Gulf

Western

on the Andes.

129: 93-131.

zoic history

Coast

and theories

and central

Planet.

Geol., 5: 659-663.

initiation,

Sot. London,

Gillet,

Oregon.

Miner.

16: 55-58.

Savoyat,

Rev. Earth

M.A. and Swanson,

from

In: D.G. Howell (Editor),

boundary

Bolivia and south-

115-142.

Gill,

Hotz, P.E., Lanphere,

Howell, E., Clark,

of the southern

Annu.

A., 1963. The Andes

blueschist

Mountain

Press, New York,

Califomia-

Am. Assoc. Pet. Geol., Mem., 2: 16-28.

Spec. Publ., 19: 83-94.

In: K.J. Hsu (Editor),

Mountains,

3: 759-772.

internides.

337-362.

from Taiwan.

of the Klamath

R.D., Jr., 1987. Tectonics

Appalachian

collision

1982. Mountain Processes.

Some

256. Farrar.

of

Tectonics,

in continental

melting

Geol. Sot. London,

case history

Gastil,

evolution

Oregon. Hatcher,

91-100. England,

Ernst,

tectonic

des Andes

M., 1986. Intracontinental

decollement and other

boliviennes.

Trav.

Dot.

119: 352 pp. and crustal

collision

belts.

stacking

subduction, wedge

crust-mantle

in the Himalayas

In: M.P. Coward

and A.C. Ries

TECTONIC

PROCESSES

(Editors),

AT CONTINENTAL

Collision

Tectonics.

MARGIN

Geol.

OROGENS

Sot.

London,

211

Spec.

Matthews.

V., III,

associated

1981.

with

foreland

Regional

arc-trench

province:

stresses

and

complexes

a different

view.

the Wyoming

Contrib.

Geol.,

19:

P.H.,

1979. Subduction, faulting

buoyant

in the northern

breaking.

flipping,

Caribbean.

J. Geol.,

S., Nur, A. and Ben-Avraham,

in arc volcanism: oceanic

plates.

and

the central Eclogae Molnar,

Pfiffner.

Alps

Geol.

collision,

1980. Tectonic

cross

section

oceanic

evolution

of

St. Gallen-Como.

Interarc

as alternates lithosphere.

Asia:

spreading

related

Earth

and

to the age of

Planet.

Sci. Lett., 41:

Tapponnier,

P., 1975. Cenozoic

effects

of a continental

J.W.H..

Price, R.A. and Tempelman-Kluit,

Tectonic

accretion

and plutonic

and

collision.

the origin

tectonics

D.J., 1982. metamorphic

Cordillera.

the U.S. Cordillera Moores,

and the Tethys.

E.M., 1972. Model

margin

collision

and orogeny,

10:

with models

of

in California.

228: 837-842.

island

Geol. Sot. Am., Abstr. Progr.,

N., 1985. Structural

Mountains,

metamorphic

Count.

aspects

northeastern

In: D.G. Howell (Editor),

Terranes

cum-Pac.

and

terrane juxtaposition,

California.

stratigraphic

of the Circum-Pacific

Ener. Miner.

CM.,

erogenic

core

complex:

Resour.,

of erogenic

metamorphic

1979.

with

Mineral.

Lichi melange origin.

of:

Am. J.

wedges

and the uplift

rocks. Geol. Sot. Am. Bull.,

A speculative

history

some constraints

and K.A. DeJong

faulting,

tectonic

Karachi,

Geol.,

Rocky

Rivers -

and

Ocean.

Geodyn.

In:

of Pakistan.

pp. 5-24. Canadian

Cordillera:

and delamination

thrust

of the litho-

8: 239-2.54.

R.A. and Mountjoy,

the Canadian

of Pakistan

from the Indian

(Editors),

wedging,

sphere. J. Struct.

E.W., 1970. Geologic Mountains

a progress

between

report.

structure

Bow and

of

Atha-

Geol. Assoc. Can., Spec.

Pap., 6: 7-25. V.A., Jordan,

Kay,

T.E., Allmendinger,

S.M.. Cortes,

J.M.

of the central

and

R.W., Mpodozis,

Palma,

C.,

M.. 1986. Paleozoic

Argentine-Chilean

Andes.

Tecton-

ics, 5: 855-880. D.H.,

Roeder,

1973.

Subduction

D.H., 1975. Tectonic

E.P., Dalziel,

ural geology orogenesis

377.

Cir-

Sci. Ser.. 1:

from

fission

temperature-time

Darwin

track

geo-

relationships.

J.

139: 755-761. I.W.D.

Roeder,

of the Cordillera in the southernmost

K.D. and Casey,

Upper Ordovician on the tectonic

A.G.,

Darwin

-

1980. Struct-

collisional-style

Chilean

Andes.

Eclogae

1980.

system:

and

orogeny.

J. Geophys.

effects of dip changes

J.F., 1979, Ophiolitic

detritus

in the

of western

Newfoundland.

Geol.,

7: 27-31.

Geodynamics

a synthesis.

in subduc-

and

detrital

R.W.R.,

erogenic Saleeby,

of the Taconic

consumption

of aseismic

Z., 1981. Volcanic ridges

in South

gaps

and the

America.

Geol.

Sot. Am., Mem., 154: 729-740. Ben-Avraham,

Saleeby,

building.

ing Processes.

In: K.J. Hsu (Editor),

Academic

terranes

Mountain

Press, New York, pp. 73-84.

and Build-

implications

1973. On the interpretation ophiolite

geochronological

for the tectonic 89: 199-218. of Cordilleran

J. Geophys.

Annu.

A.D.,

tectonostratigraphic

Res., 87: 180331824.

Rev. Earth

Tarney,

belt of the California

and

J.B., 1983. Accretionary

cordillera. Saunders,

J. Geol.,

reiationOrdovician

belts. Am. J. Sci., 273: 811-849. Nevada:

tectonics PIanet.

J., Stern,

of the North

Am.

Sci., 15: 45-73.

CR.

of Mesozoic

neous rocks from southern

and

marginal

Dalziel, basin

I.W.D., floor

ig-

Chile. Geol. Sot. Am. Bull., 90:

237-258. Schweickert,

Z., 1982. Displaced

of the medial

orogeny.

J.B., 1982. Polygenetic

Sierra

Cordillera

7: 23-39.

1981. Stratigraphic

composition

1979. Geochemistry

A. and Ben-Avraham,

W.S.F..

Helv., 73: 353-

of eastern

Tectonics,

flysch of western New England: evolution

Alpine-Mediter-

Geol.

structure

of La Paz, Bolivia).

D.B. and Kidd,

ships

of the

Eclogae

D., 1988. Andean-age

(province

development.

flysch of Notre Dame Bay and its bearing evolution

D.H.,

Rutland,

and Milnes,

Geol. Helv., 73: 727-751.

A. and

Roeder,

Tectono-

Region.

Earth

of

ranean

uplift of the Cordillera

evidence

and closing

Geol. Sot. London,

mountain

Schweiz.

and olistostromal

Price. R.A., 1986. The southeastern

Rowley,

E.P., 1982. Post-tectonic

chronology

Nur,

its plate-tectonic

surroundings:

Klamath

201-214.

Nur,

Alps.

gradients

terranes

tion zones. Am. J. Sci., 275: 252-264.

Middle Jurassic

Nelson,

1974. Thermal

in over&rust

Res.. 78: 5005-5024.

4: 202. Mortimer.

the

Geol.

97: 1037-1053.

Roeder,

arc-continental

D.L.,

to the eastern

J.P., 1986. Dynamics

Ramos,

Geology,

Nature,

for Jurassic

flow and

Alps. Eclogae

Mitt., 54: 641-662.

terranes E.M., 1970. Ultramafics

1980. Heat

Sci., 281: 193-227. Platt,

baska

Sci., 189: 419-426.

of the major

welts in the Canadian

of

70-75. Moores,

Nelson,

Petrogr.

Price,

Monger,

Nelson,

reference

A. Farah

330-340. P. and

Turcotte,

metamorphism

Geol. Surv. of Pakistan,

T., 1978.

P.C.,

of the eastern

Page, B.M. and Suppe, J., 1981, The Phocene

Poweil,

47: 369-392.

O.A.,

Atwater, tectonics

subducted Molnar,

regional

of high-pressure

zones and continental

in the

of

Helv. 73: 619-633.

P. and

cordilleran

or subduction

119: 195-221.

Alps. Tectonophysics.

A.G.

Z., 1985. Spatial gaps

of collision

Tectonophysics,

A.G., 1978. Structural

central Mimes,

the effect

England,

evolution

E.R. and

and

Taiwan:

87: 293-304.

Milnes,

Oxburgh, special

and strike-slip McGeary,

E.R. and

Helv., 73: 379-398.

deformation

and

123-126. Mattson.

Oxburgh,

metamorphic

Publ., 19: 37-50.

tectonic

R.A. evolution

and

Cowan,

D.S.,

of the western

1975.

Early

Sierra Nevada,

Mesozoic California

Geol. Sot. Am. Bull., 86: 1329-1336. Schweickert,

R.A., Armstrong,

R.L. and

Harakal,

J.E., 1980.

212

S.H. EDELMAN

Lawson&e fornia.

blueschist

Shanmugan,

G. and

evolution

Lash,

Geol.,

W.D.,

Sierra

1988.

Nevada

Prentice

foredeeps,

Evolution

Ophiolite

Sula platform

1982.

southern

Cali-

tectonic and central

Ernst

evolution (Editor),

of the

Metamor-

Back

donesia:

United

States.

Cliffs, N.J., pp. 824-864.

R., Joyodiwiryo, island

between

arc,

S., the

Indonesia.

J.

R. and Joyodiwiryo,

A.G.,

1976.

Tectonophysics, Smith,

A.G.,

particular

Plate

in the eastern

of arc-continent

Sot. London,

(Editors),

from La Tetilla,

Sunda

arc,

collision.

and

orogeny:

to North Thrust

orogeny

Triimpy,

America. and Nappe

Spec. Publ., 9: 111-124.

thrust

belts,

with

In: N.J. Price and Tectonics.

Geol.

1985. Tectonic

in Yukon:

synthesis

New England.

of

Geol. Sot.

cataclasite,

evidence

Geol. Surv., Can., Pap. 79-14,

R., 1982. Alpine

K.J. Hsu (Editor),

27 pp.

paleogeography:

Mountain

Building

ophio

of arc-continent a reappraisal.

Processes.

In:

Academic

Press, New York, pp. 149-156. S., 1986. Facts,

ideas

systems.

problems

on trench-

In: F.C. Wezel (Editor),

and open

The Origin

Geotectonics,

21) Elsevier,

Amsterdam,

pp. 435-460. ranes

H., 1985. Paleozoic of the North

sons. In: D.G. and coeval

N.M.,

D.J., 1979. Transported

of Arcs. (Develop.

a review.

southwestern

J. Geol., 95: 377-395.

in western

lite and granodiorite

In-

J. Geo-

A. and Wagner,

Am. Bull., 96: 1227-1250.

arc-backarc

33: 215-285.

reference

A., Orrego,

complex

R.S. and Ratcliffe,

Williams,

tectonics

1981. Subduction

K. McClay

M., Espinosa,

South America.

Y.,

phys. Res., 88: 7429-7448. Smith,

Stanley,

Uyeda,

D.L., McCaffrey,

arc thrusting

Colombia,

collision.

Y. and Stevens,

by collision

the Sulawesi

a consequence

P.. Delaloye,

Tempelman-Kluit,

Res., 88: 9419-9435.

E.A., Reed,

Spadea,

the Taconian

of the Western

emplacement and

Analogous

crustal

In: W.G.

Hall, Englewood

Geophys. 1983b.

G.G.,

Pre-Cretaceous

E.A., McCaffrey,

1983a.

Silver,

Nevada,

10: 562-566.

region.

phism and Crustal Silver,

Sierra

J.J., 1987. Ophiolite

of the Ordovician

Appalachians. Sharp,

in the northern

Geol., 8: 27-31.

ranes

Howell

region:

(Editor),

of the Circum-Pacific

Ener. Miner. Wilson,

miogeoclines

Atlantic

Resour.,

Y.T. and

building.

Nature,

Burke,

Earth

and

suspect

Cordilleran

Tectonostratigraphic

Region.

Circum-Pac.

ter-

compariTerCount.

Sci. Ser., 1: 71-75.

K., 1972.

239: 48-449.

Two

types

of mountain