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National Parks 6 WONDERS OF THE NATIONAL PARKS CARVING THE GRAND CANYON (THE COLORADO PLATEAU) APRIL 7, 2017 TO THINK ABOUT • How can brittle rock layers be stretched by hundreds of miles? • Why and how did the Sierra Nevada and the Southern Rocky Mountains emerge? • How did the Colorado Plateau form and what holds it up now? • Why was there such an extensive outpouring of lava and ash? • When and how did the canyons on the Plateau form and where did the rock go? (What is erosional exhumation?) • What caused the Laramide Orogeny and where is the Farallon Plate now? WESTERN UNITED STATES RIO GRANDE RIFT RIO GRANDE RIVER WEST OF TAOS NEW MEXICO RIO GRANDE RIVER ISLETA PUEBLO-NEAR ALBUQUERQUE HURRICANE FAULT EAST OF KINGMAN ARIZONA MOGOLLON RIM CENTRAL ARIZONA "The Colorado Plateau is to the geologist a paradise. Nowhere on the earth’s surface, so far as we know, are the secrets of its structure so fully revealed as here.” John Strong Newberry, 1859 WINGATE SS/CHINLE FORMATION/MOENKOPI FORMATION/CUTLER GROUP/HONAKER TRAIL FORMATION SOME HIGHLIGHTS ON THE COLORADO PLATEAU • Grand Canyon NP Petrified Forest NP • Zion NP Bryce Canyon NP • Canyonlands NP Arches NP • Black Canyon of the Gunnison NP Mesa Verde NP • Capitol Reef NP Monument Valley TP • Canyon de Chelley NM Grand Staircase-Escalante NM • Cedar Breaks NM Hovenweep NM • Bears Ears NM Natural Bridges NM • Valley of the Gods SP Goosenecks SP • San Rafael Swell Comb Ridge THE COLORADO PLATEAU SECTIONS RED ROCK SP NEAR SEDONA ARIZONA PAINTED DESERT NEAR WINSLOW ARIZONA PETRIFIED FOREST NP NEAR HOLBROOK ARIZONA MANCOS SHALE CUTLER GROUP NEAR MOAB UTAH BIDAHOCHI FORMATION NORTHERN ARIZONA CANYON DE CHELLEY NM ARIZONA MONUMENT VALLEY TP ARIZONA- UTAH VALLEY OF THE GODS UTAH GOOSENECKS SP SAN JUAN RIVER UTAH NATURAL BRIDGES NM UTAH BLACK CANYON OF THE GUNNISON NP DINOSAUR NATIONAL MONUMENT UTAH MESA VERDE FORMATION BOOK CLIFFS UTAH LA SAL MOUNTAINS NEAR ARCHES NP ARCHES NP UTAH ARCHES NP NEAR MOAB UTAH ARCHES NP UTAH CANYONLANDS NP UTAH COMB RIDGE NEAR BLUFF UTAH ENTERING THE SAN RAFAEL SWELL I-70 WEST OF GREEN RIVER UTAH CEDAR BREAKS NM UTAH ZION NP THE GRAND STAIRCASE ARIZONA-UTAH GRAND STAIRCASE ESCALANTE NM UTAH UTAH VERMILLION CLIFFS NM ARIZONA GRAND CANYON--TONTO PLATFORM TAPEATS SS, BRIGHT ANGEL SH, MUAV LS DVD CARVING THE GRAND CANYON FORD COCHRANE "The Colorado Plateau is to the geologist a paradise. Nowhere on the earth’s surface, so far as we know, are the secrets of its structure so fully revealed as here.” John Strong Newberry, 1859 VEXING QUESTIONS • When did the Colorado River actually form? • Why is there a Colorado Plateau? Oligocene Late Miocene PRESENT DRAINING THE PLATEAU • Prior to 30 Ma water on the Plateau primarily drained to the east or internally into lakes • As the north and eastern Plateau rose the the drainage divide moved eastward • 16 Ma Lake Bidahochi began to form on the Plateau • 5-6 Ma the level of Lake Bidahochi overtopped the Kaibab Arch—spillover occurred and a river cut through the Kaibab Arch • About 6 Ma this river began to cut the Grand Canyon DEROOFING THE PLATEAU • Prior to 6 Ma the Colorado River did not exit the Plateau through the lower Grand Canyon • Post 5-6 Ma the Colorado River created the lower Grand Canyon • The Colorado River exited the Grand Canyon forming a chain of fresh water lakes (?) and into the Gulf of California • The Green, Gunnison, San Juan, and Little Colorado Rivers integrated with the Colorado River contributed to deroofing the Plateau • The East Pacific Rise spreading center extended northward forming a basin for depositing sediment from the plateau VEXING QUESTIONS • When did the Colorado River actually form? • Why is there a Colorado Plateau? PLATE BOUNDARIES FARALLON SUBDUCTION CHRONOLOGY • Before 80 Ma---”ordinary subduction” • 70-40 Ma Laramide flat slab subduction • 35-25 Ma the Farallon Plate fragments • 20 Ma A large pocket of hot mantle rock wells up behind the collapsing Farallon Plate • About 10 Ma spreading center is subducted • Post 10 Ma – Convective sinking of the Plate – Detachment of the lower lithosphere – Asthenosphere uplifting THE COLORADO PLATEAU SOME DISTINCTIVE FEATURES • Elevated with respect to terrain to its south or west • Surrounded with deformed structures but relatively undeformed itself • Edges generally more elevated than the center • Extensive volcanism largely confined to the perimeter of the Plateau IGNEOUS CENTERS WHAT LIFTED THE PLATEAU? SOME HYPOTHESES • Isostatic rebound due to unroofing • Upwelling of the asthenosphere • Delamination of the lower mantle • Chemical alteration of the lithosphere G Zandt & P Reiners Nature 472 420 2011 A Levander, B Schmandt, M. S. Miller, K Liu, K. E. Karlstrom, et al Nature 472, 461-465 (2011) INTERPRETATION • Rocky Mountains and the edges of Plateau are elevated “by a combination of low density crust and upper mantle buoyancy” • Data is consistent with – Delamination or distributed foundering of dense lithosphere – Replacement by asthenosphere READING THE ROCKS .
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