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Extensional tectonics associated with convergent plate boundaries
365 highly recommend Maill's "Discussion" sec-
Group in the Brooks Range, northern Alaska.
tion (pp. 2 6 - 28) which contains some proba-
Nilsen considers these sequences to be both
ble answers but entertains many more intriguing questions. F.B. Van Houten's article, pp. 35 48, is
allochthonous and autochthonous. Depositional environments are described and several possible explanations for the present
an
distribution of the redbeds are discussed.
excellent study
and
definition
of the
Molasse in its type area, the northern Alps. His reference section for this area is excel-
272, discusses, all aspects, of the Eureka
lent.
Sound Formation of Upper Cretaceous to
B.R. Rust, pp. 4 9 - 7 6 , compares alluvial sequences of the Lower and Middle Devonian w i t h those of Late Devonian and Carboniferous time, eastern Gasp~, Canada. The older sequence resulted from mild compression in a shallow subduction zone; the younger formed as the North American Continent rode over this subduotion zone creating considerable relief along strike-slip faults. P.W. Fralick and P.E. Shank, pp. 77-97, discuss the relationship between tectonics and sedimentation in the late Paleozoic rocks of the eastern Cumberlain Basin, Maritime Canada. They feel that the rock assemblages studied (Devonian-Carboniferous) are a result of N W - S E
compression and wrench
faulting rather than rifting. A.C. Donaldson and R.C. Shumaker, pp. 9 9 - 124,
discuss
the
late
Paleozoic
The final article, by A.D. Miall, pp. 221-
Oligocene (?) age which occurs in the Canadian Arctic region. The author attempts to reconcile some apparent discrepancies between outcrop data and marine geophysical data by presenting his own tentative synthesis of plate tectonic evolution of this vast area. He hopes that additional data will bring future enlightenment. When
considering
clastic-tectono-sedi-
mentary facies, this publication takes its place next to that edited by Lajoie (1970) which was concerned with flysch sedimentation. Good show A.D.! Lajoie, J. (Editor), 1970. Flysch Sedimentology in North America. Geol. Assoc. Can. Spec. Pap., ~. H.W. Dodge Jr., Lakewood, Colo.
" m o l a s s e " (Devonian-Permian) of the Central
Appalachians. They describe two consecutive clastic wedges whose dispersal patterns and clepocenters were related to plate convergence and probably subblock tilting. G.H. Eisbacher, pp. 125-151, likens, in m o s t respects, the Late M e s o z o i c Paleogene molasse facies of the Bower Basin, Canadian C o r d i l l e r a , to the
F.J. Vine and A.G. Smith (Organizers), 1981. Extensional Tectonics Associated with Convergent Plate Boundaries. Proceedings of a Discussion of the Royal Society held in
London, March 19 and 20, 1980. The Royal Society of London, 224 pp. £stg.29.75 (overseas £stg.31.25).
type-molasse of the Alps. He calls for "collision, suturing and transcurrent faulting, involving an island-arc complex .... oceanic c o m p l e x . . . , and the outer sedimentary terrace wedge along the western margin of the North American craton." D.GF. Long, pp. 152-186, discusses the relationship of coal basins to plate tectonically produced right lateral faults of the Canadian Cordillera. His paper presents some excellent descriptions of various depositional environments of intermontane basins and their relationship to coal formation. Tor H. Nilsen, pp. 187-219, mainly describes redbed sequences of the Upper Devonian to Upper Mississippian Endicott
This is an elegant big volume containing 100 illustrations, 3 plates, 5 large pull-out illustrations or maps, 6 tables, and a grand total of 792 references (many duplicated), the youngest of which dates from 1981. Its 13 articles treat at all levels of thoroughness with the geology and geophysics of extensional processes occurring in "behind the a r c " settings in the western Pacific, the southwestern Atlantic (Scotia Sea), the Mediterranean, and the Basin and Range province of western United States (where the " a r c " , of course, has disappeared). It also includes a short entry by Molnar, Tapponier and Chen that is, by their own description, and "annotated bibliography" of their pub-
366 lished work on the neotectonics of central
tion of models, perhaps briefly mentioning
and eastern Asia. In addition, several entries
ideas by Karig, Molnar and Atwater, Uyeda
catalog geological evidence for presumed "behind the arc" extensional processes in the Mesozoic that resulted in ophiolite com-
and Kanamori, Jurdy, etc., but few commit themselves, or even speculate forthrightly on the set of conditions that lead to back-arc
plexes that are now beached on the con-
extension. It is all driver~, from below, by sec-
tinental margins of Oman and Chile. As an introduction to the geology of these many
ondary thermal convection or something else? What effect does subduction-angle
areas, and as a condensation of facts underlying discussions of back-arc extensional
have, if any? Are absolute plate velocities the whole answer? Frankly, it was the hope that
models, this book is excellent. I found the article by Dalziel on back-arc extension in
questions like these would be answered that
the southern Andes particularly useful, and the entry by Zoback, Anderson and Thompson on extension in the Basin and Range province is overwhelming in its thorough-
induced me to review the book. My payoff was not exciting. Only the European students of Mediterranean arcs seemed much interested in mechanisms, although Weissei does provide a useful one-page summary of
ness. This book will find its way into the
models (western Pacific), and Molnar and
hands of many graduate students over the next few y e a r s - - although more often
co-authors assure us that models will be discussed, if only we read more elsewhere. In
through the library than the book-seller, I
short, this was a valuable Discussion of the what of back-arc extension. Perhaps now we need one on why.
suspect, considering its price. As a serious attack on the question of
why back-arc extension takes place, however, this book is a severe disappointment. Most authors fence gingerly with the ques-
M.E. Beck, Bellingham, Wash.
Group in the Brooks Range, northern Alaska.
tion (pp. 2 6 - 28) which contains some proba-
Nilsen considers these sequences to be both
ble answers but entertains many more intriguing questions. F.B. Van Houten's article, pp. 35 48, is
allochthonous and autochthonous. Depositional environments are described and several possible explanations for the present
an
distribution of the redbeds are discussed.
excellent study
and
definition
of the
Molasse in its type area, the northern Alps. His reference section for this area is excel-
272, discusses, all aspects, of the Eureka
lent.
Sound Formation of Upper Cretaceous to
B.R. Rust, pp. 4 9 - 7 6 , compares alluvial sequences of the Lower and Middle Devonian w i t h those of Late Devonian and Carboniferous time, eastern Gasp~, Canada. The older sequence resulted from mild compression in a shallow subduction zone; the younger formed as the North American Continent rode over this subduotion zone creating considerable relief along strike-slip faults. P.W. Fralick and P.E. Shank, pp. 77-97, discuss the relationship between tectonics and sedimentation in the late Paleozoic rocks of the eastern Cumberlain Basin, Maritime Canada. They feel that the rock assemblages studied (Devonian-Carboniferous) are a result of N W - S E
compression and wrench
faulting rather than rifting. A.C. Donaldson and R.C. Shumaker, pp. 9 9 - 124,
discuss
the
late
Paleozoic
The final article, by A.D. Miall, pp. 221-
Oligocene (?) age which occurs in the Canadian Arctic region. The author attempts to reconcile some apparent discrepancies between outcrop data and marine geophysical data by presenting his own tentative synthesis of plate tectonic evolution of this vast area. He hopes that additional data will bring future enlightenment. When
considering
clastic-tectono-sedi-
mentary facies, this publication takes its place next to that edited by Lajoie (1970) which was concerned with flysch sedimentation. Good show A.D.! Lajoie, J. (Editor), 1970. Flysch Sedimentology in North America. Geol. Assoc. Can. Spec. Pap., ~. H.W. Dodge Jr., Lakewood, Colo.
" m o l a s s e " (Devonian-Permian) of the Central
Appalachians. They describe two consecutive clastic wedges whose dispersal patterns and clepocenters were related to plate convergence and probably subblock tilting. G.H. Eisbacher, pp. 125-151, likens, in m o s t respects, the Late M e s o z o i c Paleogene molasse facies of the Bower Basin, Canadian C o r d i l l e r a , to the
F.J. Vine and A.G. Smith (Organizers), 1981. Extensional Tectonics Associated with Convergent Plate Boundaries. Proceedings of a Discussion of the Royal Society held in
London, March 19 and 20, 1980. The Royal Society of London, 224 pp. £stg.29.75 (overseas £stg.31.25).
type-molasse of the Alps. He calls for "collision, suturing and transcurrent faulting, involving an island-arc complex .... oceanic c o m p l e x . . . , and the outer sedimentary terrace wedge along the western margin of the North American craton." D.GF. Long, pp. 152-186, discusses the relationship of coal basins to plate tectonically produced right lateral faults of the Canadian Cordillera. His paper presents some excellent descriptions of various depositional environments of intermontane basins and their relationship to coal formation. Tor H. Nilsen, pp. 187-219, mainly describes redbed sequences of the Upper Devonian to Upper Mississippian Endicott
This is an elegant big volume containing 100 illustrations, 3 plates, 5 large pull-out illustrations or maps, 6 tables, and a grand total of 792 references (many duplicated), the youngest of which dates from 1981. Its 13 articles treat at all levels of thoroughness with the geology and geophysics of extensional processes occurring in "behind the a r c " settings in the western Pacific, the southwestern Atlantic (Scotia Sea), the Mediterranean, and the Basin and Range province of western United States (where the " a r c " , of course, has disappeared). It also includes a short entry by Molnar, Tapponier and Chen that is, by their own description, and "annotated bibliography" of their pub-
366 lished work on the neotectonics of central
tion of models, perhaps briefly mentioning
and eastern Asia. In addition, several entries
ideas by Karig, Molnar and Atwater, Uyeda
catalog geological evidence for presumed "behind the arc" extensional processes in the Mesozoic that resulted in ophiolite com-
and Kanamori, Jurdy, etc., but few commit themselves, or even speculate forthrightly on the set of conditions that lead to back-arc
plexes that are now beached on the con-
extension. It is all driver~, from below, by sec-
tinental margins of Oman and Chile. As an introduction to the geology of these many
ondary thermal convection or something else? What effect does subduction-angle
areas, and as a condensation of facts underlying discussions of back-arc extensional
have, if any? Are absolute plate velocities the whole answer? Frankly, it was the hope that
models, this book is excellent. I found the article by Dalziel on back-arc extension in
questions like these would be answered that
the southern Andes particularly useful, and the entry by Zoback, Anderson and Thompson on extension in the Basin and Range province is overwhelming in its thorough-
induced me to review the book. My payoff was not exciting. Only the European students of Mediterranean arcs seemed much interested in mechanisms, although Weissei does provide a useful one-page summary of
ness. This book will find its way into the
models (western Pacific), and Molnar and
hands of many graduate students over the next few y e a r s - - although more often
co-authors assure us that models will be discussed, if only we read more elsewhere. In
through the library than the book-seller, I
short, this was a valuable Discussion of the what of back-arc extension. Perhaps now we need one on why.
suspect, considering its price. As a serious attack on the question of
why back-arc extension takes place, however, this book is a severe disappointment. Most authors fence gingerly with the ques-
M.E. Beck, Bellingham, Wash.