Eos, Vol. 81, No. 31, August 1,2000

BOOK REVIEW Norumbega Fault System of the Northern Appalachians PAGE 353

ALLAN LUDMAN AND DAVID P . WEST JR., (EDS.)

Geological Society of America Special Paper 331, xii + 202 pp., ISBN 0-8137-2331-0,1999, $55.

Yes,Virginia, the eastern United States can finally claim to have a strike-slip fault of its own on a scale to rival the west coast's San Andreas fault: the Norumbega fault system, which stretches nearly 450 km from central New Brunswick, south to Casco Bay in south­ern Maine, and perhaps even farther into southern Connecticut.The Norumbega fault was active for 100 Ma, five times longer than the San Andreas. Its displacement is reckoned by one author to be as much as 1768 km ( ! ) , five times more than the San Andreas, and it has been exhumed locally to mid-crustal depths.This collection of 12 full-length,stand­alone papers and preface provides a single venue for a rapidly growing body of interdisci­plinary research about a remarkable—though inactive—fault that may prove to be the longest, most long-lived fault with the greatest displacement of any in North America.

The informative preface sets the scene for ensuing papers that proceed logically through the standard litany of topics that should be recited about a fault: How is the slip direction determined (chapter 1)? At what crustal levels is the fault exposed (chapter 2)? What is its regional extent (chapters 4,5)? What are the associated structures (chapter 6)? What is its tectonic significance (chapter 9)? What are

ABOUT A G U

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Citation

"Brilliant minds are not unusual among sci­entists. More uncommon are those who com­bine scientific acumen with a keen apprecia­tion for history and geography, giving their

the ages and timing of displacements along the fault (chapter 10)? How much displacement has occurred (chapter 11)? Is the fault presently active (chapter 12)?

Only chapter 8 seems like a fish out of water, because it concerns geochemical and metal-logenetic contrasts in Paleozoic granitic rocks of the northern Appalachians. One may argue cogently that these data could prove useful to determine regional displacements, but neither the author nor the authors of the other papers use the data for that purpose.

Each paper commences with background information that is neither entirely repetitive nor consistent from paper to paper. Each author regards the Norumbega fault system and its displacement as "significant," yet the cumulative displacement is not mentioned until chapter 9.The eleventh chapter is a con­cise discourse on the timing and displace­ments of multiple shearing events. It is a nice summary for the entire volume, cutting through speculation that flavors some of the other papers to say, in effect, these are the facts, the arguments, the speculations, and the remaining problems. For example, one chap­ter estimates that the dextral displacement ranges from 30 km to 1768 km.The eleventh chapter concludes succinctly "the most gener­ous estimates of dextral slip... amount to less than 150 km," and also,"considering its length and width, the Norumbega fault system appears to have produced remarkably little displacement." Hmm, that doesn't sound like a San Andreas rival.

Few of the authors resisted the temptation to compare the Norumbega and San Andreas fault systems, however—but usually inappro­priately, in my opinion.The Norumbega fault system is an ancient, orogen-parallel strike-slip fault in a convergent plate boundary regime,

work context in time and place. Rarest of all are those who can convey these gifts with humor, common sense, generosity, and style.

"Such a man is this year's Horton Medalist, Professor M. Gordon Wolman, known far, wide, and hereafter as Reds. His career has left sub­stantial legacies in hydrology and geomorphol-ogy as concepts, insights, publications, and,

whereas the San Andreas fault is a youthful transform plate boundary,so the comparison is one between apples and oranges. Some authors characterize the Norumbega fault sys­tem as significant, evidently because it was active for a period five times longer than the San Andreas fault has been so far.The Norum­bega activity began 380 Ma ago and dextral slip evidently ceased 280 Ma ago, although it was reactivated as normal fault during Meso-zoic time. Chapter 12 concludes that the Norumbega fault system is presently inactive; the San Andreas fault is still very much alive and over the next 150 Ma years it may become just as "significant" as the Norumbega.

The book itself is the standard 8 W x 11", softcover, Government Services Administration-style special paper. It is well designed, con­structed, and edited, the presence of the word "lithologies" notwithstanding. Regrettably, a black-and- white figure on page 68 should have been printed in color, so the publisher packaged a corrected page in a plastic sleeve and tipped it into the book as a loose replace­ment sheet that immediately fell on to the floor when I opened my book.

The book is useful in summarizing a decade of research, in drawing comparisons and con­trasts with comparable topics elsewhere in the world, and in pointing to directions for future research. Students of all strike-slip faults will learn a great deal from this book about what their own fault may look like at depth, just as the editors intend. Students of other orogenic belts will find useful criteria to eval­uate the possible role of orogen-parallel strike-slip where the phenomenon has not yet been recognized. As with most books these days, however, I am dismayed that its cost is about double what I might be willing to pay to have it on my library shelf.

Reviewer

Arthur Gibbs Sylvester Department of Geological Sciences, University of California, Santa Barbara, USA

Wolman Receives 2000 Robert E. Horton Medal M. Gordon Wolman was awarded the Robert K Horton Medal at the AGU Spring Meeting

Honors Ceremony, which was held on June 2,2000, in Washington, D.C The medal recognizes outstanding contributions to the geophysical aspects of hydrology.