Monday, March 26, 2018 11:30 am 12:30 pm Miller Hall, Room 105 All - PDF document

The Department of Geological Sciences & Geological Engineering Distinguished Speaker Program presents: Monday, March 26, 2018 11:30 am – 12:30 pm Miller Hall, Room 105 All are welcome to attend! Reception with food and refreshments to follow talk

Introduction My fascination with the nature, origin, and evolution of mountains began during the summer of 1952, when, after only one course in geology, I had the good fortune to be employed on Dr. Geoffrey B. Leech’s GSC (Geological Survey of Canada) field party in the Purcell Mountains of southeastern British Columbia. Having never before been in the mountains, I was enthralled and intrigued by their majesty, formidable beauty, and mystery. Fortunately for me, Geoff Leech was a superb mentor and role model. He nurtured my fascination with the mountains and my latent interest in geology, with the result that my scientific focus shifted from physics and chemistry to geology. My principal scientific quest became: “Whence the Mountains?” particularly the mountains of the southeastern Canadian Cordillera. Geoff arranged for me to acquire diverse GSC field experience during the three following summers in the southwestern Canadian Rockies, the Precambrian Shield north of Lake Athabasca, and the southern Alberta Foothills. Thanks to Geoff and to R.J.W. (“Bob”) Douglas, who became my GSC thesis supervisor and prime mentor, I was able to obtain a GSC PhD thesis research project that straddled the Lewis thrust sheet and the Flathead Valley graben at North Kootenay Pass. In 1958, having completed my PhD at Princeton, I joined the GSC. Between 1958 and 1968, with Bob’s support, I was assigned two GSC mapping projects that spanned the Rockies; one along the U.S.A. border in the Fernie area; and the other, Operation Bow-Athabasca, a large helicopter-supported project to map the region between Banff and Jasper, which included my esteemed colleague and close friend Eric Mountjoy and six other young GSC geologists. In addition to these exceptional opportunities for a hands-on regional overview of the southern Canadian Rockies, I was also authorized to spend several summers studying both thrust-related folding and the tectonic significance of meso-scale faulting and fracturing within this region. As one of many individual scientists who benefitted immeasurably from serving Canada by conducting scientific research for the Geological Survey of Canada, it was my honour, duty, and privilege to interrupt my research from 1981 to 1988 to assume responsibility for management of the GSC during an interval of fundamental change. Since becoming a member of the faculty of Queen’s University in 1968, I have been inspired and enlightened by working with many gifted graduate students and research associates; and also by collaborating with stimulating colleagues like Dugald Carmichael, John Dixon and Herb Helmstaedt. Co-supervision of eight graduate students with Dugald enhanced my appreciation of metamorphic petrology and its utility in elucidating tectonic processes. My fruitful collaboration with Jim Monger on the evolution of the Canadian Cordillera began after I first moved from the GSC to Queen’s and is still flourishing 50 years later. Sixty - five years after switching from physics and chemistry to geology, I am now equipped with a wealth of new information and many new conceptual models, (some of my own making), and I now can comfortably offer credible explanations for the nature, origin, and evolution of the southeastern Canadian Cordillera, and thereby for some other mountain belts elsewhere. These words are taken (with a few minor updates) from the introduction to my November 2012 Geological Society of America Penrose Gold Medal Lecture . My March 26 th lecture will be a 2018 updated version of the 2012 lecture. The attached pdf, which is the revised final page of the 2012 lecture, has been and still is “a work in progress”.

Ray Price ---FinalVersion:27Feb2018 How the dynamic solid Earth works and evolves: --- Planet Earth is a ‘gravity drive’ heat engine Because of gravity, thermal convection within Earth’s molten metallic outer core heats the base of the mantle, and also generates a magnetic field that protects humanity (and the rest of the biosphere) from harmful cosmic radiation. Because of gravity, hotter, more buoyant rock within the lower mantle also rises vertically. Because of gravity, the rising buoyant hot rock is constrained to diverge symmetrically as it approaches Earth’s spherical surface. Then, as it rotates ‘horizontally’ along that spherical surface, it gradually ‘freezes’ from the top down; thereby creating symmetrical, diverging, stiff, spherical ‘plates’ of new ocean-floor lithosphere. This process, which is continuously creating new ocean-floor lithosphere , is called “ seafloor spreading” . Because of gravity, progressively cooler, thicker, more negatively buoyant ocean-floor lithosphere is continuously being bent where it begins to sink asymmetrically (edge-wise) below Earth’s spherical ‘horizontal’ surface, while en route to the lower mantle. The descending side of this ‘migrating’ flexure is commonly marked by a deep-sea trench. This process of consumption of older, colder, thicker, negatively buoyant ocean-floor lithosphere along a continuously migrating flexure is called “ subduction ” . Asymmetrical subduction consumption of ocean-floor lithosphere is the down-flow counterpart of the symmetrical seafloor spreading up-flow process that continuously creates new ocean-floor lithosphere. Because of gravity , hot, liquid magma (generated, during subduction, by partial melting within the over-riding mantle and/or crust) rises buoyantly toward the surface, creating volcanoes, granitic batholiths, and thus, new crust. Because of gravity , fragments of buoyant continental lithosphere separate and diverge (“drift” apart) symmetrically as new ocean-floor lithosphere is created between them by seafloor spreading. Because of gravity , buoyant fragments of continental lithosphere ultimately converge, “collide”, and are “welded together,” as all intervening older, colder negatively buoyant ocean-floor lithosphere is consumed by subduction. Because of gravity, almost all ocean-floor lithosphere (which comprises about two thirds of the surface of Planet Earth) is less than 200 Ma old; whereas, large tracts of the buoyant continental lithosphere under North America, and elsewhere, are more than 2,500 Ma old; and at one locality in northern Canada it is more than 3,580 Ma old. Because of gravity, vertical rock-uplift occurs mainly in the zones of crustal convergence above subducting slabs of lithosphere, where buoyant crust is thickened by magmatism and/or by horizontal contraction (for example by tectonic overlap and/or tectonic wedging during convergence of relatively more buoyant crustal rocks. Vertical rock uplift creates steep regional topographic-surface-elevation gradients that induce lateral gravitational spreading within the crust. Flow is in the direction of decreasing regional surface elevation . Lateral gravitational spreading involves extending flow and extrusion within an ‘upslope domain’, that is beneath regions of higher surface elevation; this is transitional lateraly into compressing flow and intrusion within a ‘downslope’ domain that is beneath adjacent regions of lower surface elevation. The deformation within extending flow domains is distinguished by stretching and thinning, and increasing displacement in the direction of decreasing regional surface elevation ; for example by: recumbent isoclinal folding, sheath folding, pervasive stretching lineations in metamorphic rocks, boudinage of layers of less ductile rock, listric extensional (‘normal’) faulting at various scales, and by extensional high-strain detachment zones. The deformation within compressing flow domains is distinguished by shortening and thickening, and by decreasing displacement in the direction of decreasing regional surface elevation ; for example by: imbricate listric contractional (’thrust’) faulting, thrust-fault-propagation folding, tectonic wedging, and by thrust (and/or fold) contractional detachment zones. I suspect that the diachronous superimposed deformation, that must occur while rock that has been extruded from the extending flow domain is being intruded into the adjacent compressing flow domain, is commonly misinterpreted as evidence of superimposed separate “episodes” of polyphase mountain-building.