BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA VOL. 71, PP. 363-398. 34 FIGS. APRIL 1960 DIASTROPHISM AND MOUNTAIN BUILDING BY MAELAND P. BILLINGS (Address as Retiring President of The Geological Society of America) ABSTRACT For many years the terms orogeny and mountain building have been used so loosely that they no longer convey definite meanings. Because of this lack of precision, hypothe- ses of diastrophism are often based on false premises. Folding and thrusting, often referred to as tectogenesis or orogeny, is best displayed by stratified rocks. Some geologists believe that folds and thrusts are due to vertical movements accompanied by lateral spreading, that the strata are stretched an amount commensurate with the intensity of the folding, and that the opposite sides of the sedi- mentary packet do not move toward each other. Most geologists, however, agree that during folding and thrusting the strata are shortened and that the two opposite sides of the sedimentary packet move toward each other by an amount commensurate with the intensity of the folding. But it is not clear to what extent the entire crust in the deformed belt is shortened. In one extreme view, the two opposite ends of the deformed belt do not move toward each other, and the folds and thrusts result from gravity sliding. At the other extreme, the entire crust is believed to be shortened to the same extent as the sedi- mentary strata. An excellent example of broad vertical movements (epeirogenesis) that has never been sufficiently emphasized is in eastern North America, involving the Appalachians, Coastal Plain, and Continental Shelf. During the Mesozoic and Cenozoic the Fall-Line surface was depressed as much as 20,000 feet beneath the Continental Shelf, whereas it was uplifted at least 8000 feet over the Appalachians. The northeastern two-thirds of the Appalachian-Ouachita belt has been going up since the Jurassic, whereas the south- western third has been going down. Thus the present Appalachians are unrelated to the late Paleozoic folding. Certain metamorphic minerals—such as kyanite—or certain metamorphic assemblages—such as jadeite and quartz—form at confining pressures found only at depths of tens of miles, implying tremendous erosion wherever such min- erals or assemblages are exposed. Broad vertical movements, accompanied by high-angle faulting, are illustrated by the fault-block mountains of the Basin and Range Province and by such features as the Rhine graben and the Rift Valleys of Africa. Although the nature of the displacement along the San Andreas fault has been known for more than SO years, only in recent decades have other large strike-slip faults been recognized. But it is now the fad to assign all kinds of faults and even nonexistent faults to the strike-slip category. In recent years seismologists have emphasized the importance of strike-slip faults. The author suggests that in the Fairview Peak-Dixie Valley, Nevada, earthquakes there is evidence that strike-slip movements are invading an area previ- ously characterized by Basin-Range structure. The geologic record indicates that large strike-slip faults have been distinctly subordinate to folding, broad vertical movements, and broad vertical movements accompanied by high-angle faulting. Possible displacement of the crust or the entire earth relative to the axis of rotation has been emphasized in recent years. Continental drift, if it occurs, is one such type of move- ment. Slipping of the entire crust over the mantle is another. Much research has been accomplished in paleomagnetism in recent years, but the data are too scanty and con- flicting to permit any definite conclusions. Among the possible causes of diastrophism are (1) contraction of the earth, (2) con- vection currents, (3) formation of large pockets of magma, (4) sialic material leaking out of the mantle, (5) conversion of sial to mantle by change of low-pressure minerals to high-pressure minerals, or the reverse, and (6) serpentinization or deserpentinization of the upper part of the mantle. Mountain building is merely one manifestation of vertical movements of the crust. In the past mountain building has been erroneously considered by many to be primarily the result of folding and thrusting. Certainly many modern ranges are the result of verti- 363 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/71/4/363/3431890/i0016-7606-71-4-363.pdf by guest on 27 September 2021 364 M. P. BILLINGS—DIASTROPHISM AND MOUNTAIN BUILDING cal uplift unrelated to folding. Many such uplifts are accompanied by high-angle faulting to produce fault-block mountains. Blocks caught between strike-slip faults may be squeezed upward if the blocks move toward each other. Mountainous uplifts have also resulted from folding and thrusting. Conversely, in some folded belts erosion appears to have kept pace with the rise of the folds so that no mountains developed. CONTENTS TEXT Figure Page 16. Folding by vertical uplift and lateral Page spreading 374 Introduction 364 17. Effect of type of folding on thickness and Diastrophism 365 circumference of crust 375 Types of diastrophism 365 18. Map showing deformation of Fall-Line General discussion 365 surface in eastern North America 377 Folding and thrusting 366 19. Cross section showing deformation of Broad vertical movements 376 Fall-Line surface in eastern North Broad vertical movements accompanied America 378 by high-angle faulting 380 20. Buried and emergent Appalachians 379 Large-scale strike-slip displacements 381 21. Stability fields of some high-pressure Displacement of the crust or entire earth minerals 380 relative to axis of rotation 387 22. Horst of the Ruby-East Humboldt Range, Hypotheses of diastrophism 389 Nevada. 381 Mountain building 390 23. Rhine graben 382 Summary and conclusions 393 24. Alpine and related faults of New References cited 394 Zealand 383 25. Magnetic anomalies associated with Murray fracture zone, eastern Pacific ILLUSTRATIONS Ocean 384 26. Fault-plane solutions based on data for Figure Page P waves 385 1. Folded and thrust-faulted strata, Appa- 27. Russian fault-plane solutions based on lachian Valley and Ridge Prov- data for 5 waves 386 ince 367 28 Diastrophism associated with Fairview 2. Folded and thrust-faulted strata, Jura Peak-Dixie Valley earthquakes, Mountains 367 Nevada 387 3. Overthrusts of the Glarus district, Switzer- 29 Nature of net slip on surface faults during land 367 Fairview Peak-Dixie Valley earthquakes, 4. Folding by lateral compression 367 Nevada 388 5. Possible de'collement in the Appalachian 30. Variations of magnetic declination and Valley and Ridge Province 368 inclination within historic time at 6. Folding by gravity sliding 369 London, Boston, and Baltimore 389 7. Some types of gravitational tectonics 369 31. Structural trends in California 392 8. Relation between shortening, thickness 32. Shutter ridges 393 of root, and height of mountains 370 33. Buckling associated with strike-slip 9. Folding in Appalachian Valley and Ridge faulting 393 Province and Appalachian Plateaus. ... 370 34. Thrust fault associated with strike-slip 10. Wathlingen-Hanigsen salt dome, Germany. 371 faulting 393 11. Structure resulting from vertical rise of migmatite in East Greenland 372 12. Chester dome, southeastern Vermont 373 TABLES 13. Injection folding 373 14. Block folding, Causcasus Mountains, Table Page Noukha area 373 1. Tectonic processes, after Von Bubnoff. 365 15. Block folding, Caucasus Mountains, Mt. 2. Tectonic processes, after Sender . 366 Dibrar area 373 3. Types of diastrophism . 366 INTRODUCTION 1890, p. 3). Contrasting, although related, geological processes are volcanism (including "Diastrophism is a general term for the both extrusion and intrusion), erosion, and process or processes of deformation of the sedimentation. earth's crust. Products of diastrophism are For many years the thinking of the geologi- continents, plateaus and mountains, ocean cal profession has been impaired by numerous beds and valleys, faults and folds" (Gilbert, misconceptions concerning diastrophism. The Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/71/4/363/3431890/i0016-7606-71-4-363.pdf by guest on 27 September 2021 INTRODUCTION 365 terms orogeny and mountain building are often One of the principal purposes of this paper is to used so loosely that they no longer have demonstrate that many modern mountain meaning. Hypotheses of orogeny, mountain ranges are not the result of folding and building, and diastrophism are often concerned thrusting. with irrelevant subjects and fail to treat the main problems. It is hoped, therefore, that TABLE 1.—TECTONIC PROCESSES this paper will clarify the problems of diastro- (After Von Bubnoff) phism and mountain building. Professors Francis Birch and John Miller Tectogenesis Diktyogenesis Epeirogenesis kindly read an early draft of this paper and made valuable suggestions for its improve- Narrow span Intermediate Great span ment. Professors George C. Kennedy and Leon span Knopoff sent copies of their manuscripts prior to publication. Dr. Erwin Raisz graciously Structural Structural Structure re- drafted most of the illustrations at a time when change change tained he was heavily engaged with other work. Episodic Episodic and Secular DIASTROPHISM secular Types of Diastrophism Not reversible Partly rever- Reversible sible General discussion.—For many years, geol- ogy, especially in the English-speaking coun- Not autono- Not autono- Autonomous tries, has been limping along with a