Interactive property of large thrust sheets with footwall rocks—the Sub thrust interactive duplex hypothesis: A mechanism of dome formation in thrust sheets

231

Teczo~oph.~s~~s, 191 (1991) 237-242 Elsevier

Science Publishers

B.V., Amsterdam

Interactive property of large thrust sheets with footwall rocks- the Subthrust Interactive Duplex Hypothesis: a mechanism of dome formation in thrust sheets Robert D. Hatcher, Jr. Departmeni

of Geological Sciences, University of Tennessee, Knoxville, TN 379961410, and Environmental Oak Ridge National Laboratory, P.O. Box X, Oak Ridge, TN 37831, USA * (Received

August

25,1988;

accepted

August

Sciences Division,

30,1988)

ABSTRACT Hatcher, Jr.. R.D., 1991. Interactive property of large thrust sheets with foot wall rocks- the subthrust interactive duplex hypothesis: a mechanism of dome formation in thrust sheets. In: A. Phrez-Estarin and M.P. Coward (Editors), Deformation and Plate Tectonics. Tectonophysics, 191: 237-242. Recently acquired Appalachian Uttradeep Core Hole (ADCOH) Project site investigation seismic reflection data and geolo$ic data from the Appalachians and several other erogenic belts suggest an important mutually interdependent relationship exists between emplacement of large crystalline thrust sheets and the deforming foreland rocks beneath. This relations~p suggests isolated domes beneath crystalline thrust sheets may be produced by passive folding of the sheet as a result of formation of an antiformal stack duplex in the platform sedimentary sequence beneath. Suggestions that domes in crystalline thrust sheets formed by interference of late open folds is doubtlessly still valid in places, but the platform duplex mechanism is probably also valid to explain the late doming of many crystalline and other large thrust sheets. The dome beneath the Shooting Creek and Brasstown Bald windows in the ADCOH site region is imaged as an antifonnal stack duplex at depth. The Tallulah Falls dome, Grandfather Mountain and Mountain City windows, and Smokies Foothills duplex in the site region and elsewhere in the southern Blue Ridge are all late isolated domes and all are probably or demonstrably underlain by antiformal stack duplexes beneath the Blue edge-~edmont composite crystalline thrust sheet. The Assynt window and footwall duplex benath the Arnabol and Moine thrusts in Scotland, and the Engadine window in the Alps may be similar structures.

data were collected from within the Blue RidgePiedmont composite crystalline thrust sheet in an area where several isolated domes occur. Interpretation of arching reflector packages in presumed foreland sedimentary rocks beneath the crystalline

Intmductioe The purpose of this paper is to outline a hypothesis related to the process of duplex formation in overthrust terranes and ultimately to plate collision processes. This hypothesis, called the Subth~t mulated

~ntera~t~~~ Dupfex Hypothesis, was forduring analysis of seismic reflection data

from the Appalachian Ultradeep COH) Project site investigation Appalachians

* Operated

sheet revealed that these arching reflector packages may be duplexes. Their locations are precisely

(Coruh

by Martin

U.S. Department

beneath

et al., 1987). All of these

Marietta

of Energy

Energy

Systems,

under contract

Inc., for the

No. DE-AC05-84

0 1991 - Elsevier Science Publishers

domes.

above duplexes, but assumed the processes of thrusting, metamo~~sm and cleavage formation in the internal parts of an orogen are coeval and interrelated. Detailed studies of timing of fabric development and metamorphism in most orogens have shown that assumption to be incorrect. A

oR21400.

0040-1951/91/$03.50

some of the isolated

Boyer and Elliott (1981) discussed the formation of folds and culminations in the roof thrusts

Core Hole (ADin the southern

B.V.

R.D. HATCHER

238

basic assumption by abundant is emplaced structures

of the present

paper,

data, is that the dominant cold and transports formed

during

and

events

related

here also apply Boyer

and

nature

to roof

thrusts

in foreland

belts where the original Elliott

(1981)

related

to the

sheets

crystalline

of crystalline

earlier

events

simpler

and

thrust

rocks

may contain

sheets

consist

sheets

of several

sheets, ophiolites,

of western

the Blue Ridge-Piedmont and central Appalachians

Canada

collision. dominantly

a more internal

zone of transpression,

nant

strike-slip

(Eisbacher,

BLUE

1985;

and

spatial

in overthrust

ter-

occur

4: 1 and 1 : 1; they com-

on the hinterland belts.

Boyer

sides of foreland and

Elliott

(1981)

reflection

data

acquired

Appalachian

Ultradeep

investigation

has revealed

as part

of the

Core Hole (ADCOH) the presence

site

of antifor-

ma1 stack duplexes probably composed of Paleozoic platform margin rocks beneath isolated domes in

the

Blue

Ridge-Piedmont

crystalline

thrust

that crystalline

sheets,

sheet (Fig. 1). It was recently

then domi-

because

and

RIDGE

proposed

they are some of the largest

CHAUGA 1BELT j

6 10 _ Horizontal and Vertical 20

strength,

form where the ratios of weak to

units are between

Seismic

into

Hatcher

and

(1985) recog-

Boyer and Elliott (1981) and Mitra (1986) called antiformal-stack and foreland-dipping duplexes.

and

partitioned

1970;

of roof thrusts occurs as a result of duplex formation, and particularly the formation of the types

These structures commonly dip-slip continent-directed

that is frequently

is the

1986; Mitra

and Hatcher

formation

strong

thrust

terranes

(Dahlstrom,

Mitra,

are scale,

continental

Elliott and Johnson (1980) and Diegel (1986) and others have constructed sections that show arching

sheet of the and the Moine

sense of motion

there

monly

fold and

sheet in Scotland. All, except the Yukon-Tanana sheet may be directly attributable to continentcontinent have a

1981;

of duplex

ranes. Duplexes

blocks. Examples include the Austroalpine sheet in the Eastern Alps, the Yukon-Tanana sheet in Alaska, southern

of overthrust

may

early colli-

the

structures

di-

during

Diachroneity and/or

with

property of duplex

that

controls

ural features on the Earth, comparable in size with large accreted terranes and microcontinental

Cordillera

promontories

of

nized

of

by a series of

and tectonic slides, that are moved together in the later-formed composite sheet (Hatcher and Williams, 1986). These are some of the largest struct-

the northern

sion

event.

dip-

be slightly

are produced

collision

Boyer, 1986). Costello

formed

types, e.g., thin-skinned

to oblique

Boyer and Elliott,

coeval

of events is best applied.

Composite

collision

be related

formation

of

may

but all elements

margin(s). Another

fold

assumption

of the respective

components

the same major

to

peak. This is clearly the

case for the Blue Ridge-Piedmont, Moine, Jotun, and Austroalpine sheets. The principles outlined and thrust

1987). The timing

strike-slip

achronous,

earlier penetrative

earlier

the rnet~o~~c-the~al

Edelman,

supported roof thrust

Jr.

tectonic

fea-

INNER PIEDMONT

Kilometers

Fig. 1. Cross section through part of the Blue Ridge, Brevard fault wne and western Piedmont of the Carolinas and Georgia southern Appalachians

based upon ADCOH

Project site investigation

seismic reflection and surface geologic data. The large duplex at the

west end of the section is shown in greater detail in Fig. 3.

INTERACTIVE

PROPERTY

tures in mountain fluid

as they

margin

tion pathway.

FOOTWALL

onto

239

ROCKS

of

thought

to be the result

collision

a continental

(see

Hatcher

references

therein).

and foreland

and hydrocarbons structures

migration

if the crystalline

low temperature

recently

in the migra-

The antiformal-stack barriers

that may

duplexes

beneath

may

crystalline

unconventional

source

for the notion belt deformation

by the crystalline

sheet was emplaced

at a

Recently the internal

( < 300 o C). The antiformal-stack

consequently

except thrust

par-

1986,

sheets

process

for

was thought

mechanically that

and until

independent,

the foreland

was driven

fold and

ahead

of and

sheet.

acquired seismic reflection data from parts of the southern Appalachian

may prove

to be a future

Blue Ridge-Piedmont

of methane

and other

(Coruh

hy-

Williams,

The emplacement

to be largely

of hydr~arbons,

of continent-continent

and

crystalline

suitable

duplexes

WITH

1986). These fluids may carry with

sheets to impede ticularly

SHEETS

expel1 huge volumes

emplaced

in appropriate

constitute

THRUST

metals

(Oliver,

be trapped

chains,

are

them dissolved

OF LARGE

composite

et al., 1987) indicate

crystalline

sheet

a significant

amount

drocarbons.

of interaction between the crystalline sheet and the foreland beneath, with each affecting the other

Interactive property of large thrust sheets

during

Large onto

thrust

a continental

earlier period of a passive

sheets

are

platform

commonly that

emplaced

experienced

an

of rifting followed by development margin stratigraphy (Fig. 2). This

emplacement

of the crystalline

formation

of both

the crystalline

foreland

has occurred

(Fig.

assemblage

of the crystalline

sheet

to

move.

resulted

the

duplexin doming

as the crystalline Seismic

De-

and

1). Extensive

ing of the platform continued

sheet.

sheet

sheet

reflection

data

stratigraphy contains weak units into which the master detachment propagated as it ramped from the ductile-brittle transition into the platform rift and passive margin stratigraphic assemblage. Foreland thrusts are driven ahead of the advanc-

acquired during the Appalachian Ultradeep Core Hole (ADCOH) Project site investigation (Coruh et al, 1987) provide greater resolution than any collected previously in a crystalline terrane. In particular, these data provide the strongest evi-

ing crystalline sheet(s), except those forming outof-sequence. The crystalline sheet utilizes the same weak units as the foreland sheet as it moves over

dence without drilling that platform sedimentary rocks were deformed into antiformal stack duplexes during emplacement of the crystalline

the platform of both ferences strength. crystalline

assemblage,

and the overall

types becomes similar, with related mostly to relative The emplacement of large thrust sheets has for some

TRAJECTORY

behavior major size

sheet, and in turn

difand

into broad ADCOH

composite time been

deformed

the crystalline

domes (Fig. 3). Consequently, site

combination

study with

seismic

surface

reflection

geologic

sheet the new

data,

data,

in

suggest

that @‘reevolution of stnrctures during emplacement

OF FUTURE

FRAGMENT Fig. ‘2. Development continent-continent the rifted margin

of a passsive collision,

margin

stratigraphy

the master detachment

elastic sediments

on continental

propagates

crust

following

from the ductile-brittle

and then into the weak unit(s) within sequence.

a period

of rifting

transition

as a crystalline

the basal elastic-carbonate

and extention.

assemblage

thrust, within

During

ramps

into

the patfrom

R.D. HATCHER

Jr.

240 IN SECTION

1350

1400

1

4

VL9 P

Hayesvile

HAYESVILLE THRUST t7Gu I

1800

HAYEWLLE

lSzrI=T

Fold cHJNKY GAL

MOUNTAIN FAUT,

in Section i

1400 15501:

1Sm

1350

KM

KM

‘\I

I I

II

C”h,Pl

B-

lhlC

CRYSTALLINE

8

p8 BASEMENT GRABEN

(7)

Fig. 3. Part of the west end of ADCOH seismic reflection line 3 (top) beneath the Shooting Creek and Brasstown Bald windows along the North Carolina-Georgia the reflectors

border in the southern Appalachian Blue Ridge (Coruh et al., 1987). The middle frame is a tracing of

in the seismic section and the bottom frame is an interpretation of the data. If the interpretation crystalline sheet was arched by construction of the duplex in the platform rocks.

is correct,

the

INTERACTIVE

PROPERTV

OF LARGE

Crystalline

THRUST

SHEETS

WITH

FOOTWALL

the

Sheet

241

ROCKS

external

worldwide

L

Platform -Autochthonous

Crystalline

amples

include

Moine

thrust

Elliott

Basement

Sheet

----_

window

Cove/

Tuckaleechee

(Diegel,

et al.,

the 1923;

City/Limestone and

Cove/Wear

the

Cove

in the

Cades

windows

southern

window

in the eastern

example. Duplexing beneath crystalline

beneath et al.,

and Reed, 1970; Boyer 1986),

1986b)

Ex-

the ~r~dfather

Mountain

The Engadine

retta nappe

window (Peach

(Bryant

sheets

by duplexes.

1980) and

19X1),

windows

crystalline

cored

Scotland

Cove

lachians.

large

the Assynt in

Elliott,

(Hatcher

Basement

of

and Johnson,

Mountain and Doming of Crystalline

fringes

are commonly

through

Appathe Silv-

Alps may be a further

of foreland sedimentary rocks sheets has been described by

Hossack (1983) and observed by Hatcher (unpublished) in Sweden and Norway. The interactive property

is implicit

in sections

through

many

of

these structures (see figs. 1X and 24 in Elliott and Johnson, 1980, and fig. 29 in Boyer and Elliott, 1981). The interactive doming property appears to be most commonly associated with the emplacement Snakehead in Platform Fig. 4. Subthrust interaction

Duplex Rocks

Interactive

of a crystalline

ing the development

Basement Duplex

thrust

of large crystalline

Hypothesis.

Progressive

sheet with its platform

of first a thrust in the platform

show-

(top), then

a duplex that arches the crystalline

sheet (middle)

which evolves

into an antiformal

that enhances

the arching

stack (bottom) the crystalline

of

sheet.

of a crystalline thrust sheet onto a continental platform is a rn~t~a~~y ~ntera~~~ve process between the sheet and the platform beneath (Hatcher et al., 1986a), a statement of the Subthrust Interactive Duplex

Hypothesis.

Antiformal

stack

duplexes

sheets. There is no obvious this process should not thrust sheets, particularly considered,

been interpreted

the crystalline

of additional

late domes

earlier structures transported sheet (Fig. 4). Isolated domes

deforming

by the composite in crystalline thrust

to indicate

occur beneath where relative

is commonly

not

that

smaller size is

observed.

The

Numerous isolated domes that have not been breached by erosion to expose the basal detachment and the foreland rocks beneath occur in crystalline thrust sheets. These have traditionally and-basin,

into

but

reason

thrust

interactive process may be triggered by threshold values of thickness of dominant unit(s), area, trapped fluid, or other critical parameters.

form in the platform in response to emplacement of the crystalline thrust sheet which in turn arch sheet

sheets and large foreland

to be the result of Type 1, dome-

fold interference nearby

domes

(Ramsay, and basins

1967). Lack belonging

to the same set has always left some doubt whether this is the correct interpretation,

as to or if

sheeets previously throught to be formed by fold interference should be reexamined with this hy-

some other mechanism is responsible for the formation of these structures. That they are isolated

pothesis in mind. Extensive duplexing beneath the unbreached Tallulah Falls dome and Shooting Creek/Brasstown Bald windows imaged in the Applalachian Ultradeep Core Hole (ADCOH) Project site investigation seismic reflection data (Fig. 3) provide stong evidence that this is a viable mechanism. Erosionally breached antiforms along

both in space and time should indicate another mechanism may be responsible for their formation. The subthrust interactive duplex hypothesis provides an explanation for formation of these structures. The fact that these structures are also potential hydrocarbon traps provides the basis for more than purely scientific interest.

R.D. HATCHER

242

Conclusions

Dahlstrom,

C.D.A.,

margin

(1) Doming sheets

occurs

of crystalline

as the sheet interacts

forms its footwall mation

rocks during

of antiformal

rocks beneath and

stack

isolated

interactive

(2) Isolated duplexing

emplacement.

duplexes

domes. duplex

domes

of platform

a large thrust migration (primarily

with and deFor-

in footwall

large thrust sheets deforms

produces

subthrust

and other large thrust

This

the sheet

is called

the

hypothesis.

formed

sheet may provide

interactive

rocks beneath barriers

to fluid

and serve as untapped hydrocarbon gas) reservoirs where excessive tempera-

tures have not been reached

in the platform

rocks.

F., 1986. Topological

networks,

examples

nessee. J. Struct. Eisbacher, and

I am grateful to the organizers of the conference on Deformation and Plate Tectonics for inviting me to present this paper in Oviedo, Spain, to S.H.

Edelman

for

presenting it for me because of a schedule conflict. Support by the U.S. National Science Foundation Grant EAR-8417894 is gratefully acknowledged. Reviews by R.A. viewer significantly 1 am responsible tation.

Price and an anonymous improved the manuscript;

rebut

for all errors of fact or interpre-

Elliott,

Trans. Hatcher,

systems.

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Mountain

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