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Mountain Building Chapter 10 Learning Standard: I will analyze the theories associated with geologic events that change the earth’s physical environment. Learning Target: I will compare different types of mt-building processes and the resulting structures of each process. Deformation __________________ is a general term that refers to all changes in the original form and/or size of a rock body Most crustal deformation occurs along plate margins Factors that influence the strength of a rock • • • _______________ and confining _________________ _________________ ______________ _____________ •Types of deformation: •1. _________________ – change that can be recoverable, like a rubber band. Stress is gradually applied but when released, earthquakes are generated (elastic rebound) •2. ________________ – rock fractures, •temps and pressure are low •Happens near the Earth’s surface •3. _______________ – rock changes in size and shape without fracturing •Temps and pressure are high •Happens deep under the Earth’s surface •Brittle and Ductile deal with mountain building processes and occur due to temperatures and confining pressures. Folds Rocks bent into a series of waves Most folds result from compressional forces which shorten and thicken the crust Types of folds • • _________________ – upfolded, or arched, rock layers _________________ – downfolded rock layers Anticlines and synclines can be • ________________________ - limbs are mirror images • ________________________ - limbs are not mirror images • ________________________ - one limb is tilted beyond the vertical • Where folds die out they are said to be plunging Other types of folds • ____________________ • Circular, or slightly elongated • Upwarped displacement of rocks • Oldest rocks in core • Younger rocks on the outer ends • ____________________ • Circular, or slightly elongated • Downwarped displacement of rocks • Youngest rocks in core • Oldest rocks on the outer ends • • Illinois is considered a basin. – Pennsylvanian age rocks (286 million years) • South-central part of the state – – – Mississippian age rocks (320 million years) Devonian age rocks (362 million years) Ordovician age rocks (441 million years) • Northern part of the state Ozark Dome – Encompasses most of Missouri – Oldest rocks start in Southeastern Missouri with the St. Francois Mts. – Precambrian rocks in the center (544 million years and older) – Cambrian (505 million years) – Ordovician (441 million years) – A little Silurian/Devonian (362-418 million years) – Mississippian (320 million years) – A lot of Pennsylvanian (286 million years) Faults Faults are fractures (breaks) in rocks along which appreciable displacement has taken place Types of faults • ___________-______________ fault • Movement along the inclination (dip) of fault plane • Parts of a dip-slip fault • ________________ wall – the rock above the fault surface • ________________ – the rock below the fault surface Types of dip-slip faults (Normal and Reverse • ____________________ fault • Hanging wall block moves down • Associated with fault-block mountains • Grand Tetons of Wyoming • Prevalent at spreading centers • Caused by tensional forces • Create horsts and grabens • Series of uplifted blocks and downward valleys Second type of dip-slip fault ________________ and thrust faults • • • • Hanging wall block moves up Caused by strong compressional stresses Reverse fault - dips greater than 45º Thrust fault - dips less than 45º ______________-__________ faults • Dominant displacement is horizontal and parallel to the trend, or strike • Transform fault • Large strike-slip fault that cuts through the lithosphere • Often associated with plate boundaries Other Fractures in the crust _____________ • Fractures along which no appreciable displacement has occurred • Most are formed when rocks in the outer-most crust are deformed Mountain belts ____________________ refers to processes that collectively produce a mountain belt Mountain building at ________________ boundaries • • Most mountain building occurs at convergent plate boundaries Aleutian-type mountain building • Where two oceanic plates converge and one is subducted beneath the other _______________________refers to processes that collectively produce a mountain belt These events are called ________________________ ______________________ at convergent boundaries • • Types of Mountains: • • • • • 1. _______________ Mountains 2. _______________ Mountains 3. _______________ Mountains 4. _______________Mountains Other Structures • • • Most mountain building occurs at convergent plate boundaries 1. _________________ 2. _________________ Plateaus ________________________ Mountains • • • Mountain ranges made from igneous/volcanic activity Usually associated with subduction zones Examples: • Cascades • Western Andes • Japan • Philippines • ____________________ Mountains • • • • • Occur when rock strata is twisted and folded Regional, high-grade metamorphism Associated with some continental-continental convergence Compressional stresses with reverse and thrust faulting Anticlines and synclines are present • Examples: Himalayas, Appalachians, N. Rockies __________________________________ • • • • • Third mechanism of mountain building Small crustal fragments collide with and accrete to continental margins Accreted crustal blocks are called terranes Occurred along the Pacific Coast _____________________________ Mountains – Tensional stresses pulling crust apart – Associated with normal faulting – Formed by the displacement of rock along a single fault – Horsts and grabens • • Examples: Grand Tetons (WY), Sierra Nevada (CA), Basin and Range (UT, NM, AZ, CA) _________________________ Mountains – Associated with doming episodes – Associated with reverse faulting and compressional stresses – Faults on two sides of the mt. range • Examples: Southern/Colorado Rockies, Black Hills, Adirondacks Rocky Mountains • Southern Rockies – Colorado Rockies, Sangre de Cristo Range in New Mexico, and Big Horns in Wyoming • Upwarped Mountains – Different from the Northern Rockies • N. Rockies are Folded – Formed during the Laramide Orogeny (60 million years ago) • Was not associated with mt. building at plate margins • Orogenesis that occurred within a plate • Due to nearly horizontal subduction, not vertical • One of the last Mt. building episodes of western N. America (Cordilleran) How these Rockies Possibly Formed A nearly horizontal subducting plate (Farallon plate) moved eastward under western N. America This type of subduction caused compressional stresses and major thrust faults in western N. America The plate broke off from the lithosphere and sank into the asthenosphere As the plate sank, it melted causing hot rock to replace it This hot rock provided the buoyant force necessary to raise the southern Rockies, the Colorado Plateau, and The Basin and Range province This upwelling lifted ancient basement/igneous rocks and provided tensional forces to form high angle normal faults Thus leading to a mountainous topography surrounded by sediment filled basins • • • • • • • • Other Structures – ________________: uplift of flat land with little deformation. – Generally created behind mt ranges – Features of plateaus: • Mesas and Buttes • Example: Colorado Plateau • ____________________ Plateau – A highly eroded plateau – Erosion by streams and rivers cutting through the uplifted area – Examples • Ozark Plateau • Cumberland Plateau Ozark nonMountains • • Ozark Dissected Plateau A highland dome – Encompasses most of Missouri – Oldest rocks start in Southeastern Missouri with the St. Francois Mts. • Igneous rocks • (544 million years and older) – The surrounding rocks are primarily limestone and dolostone • Range from 505 million years to 286 million years • Deposited by a vast sea in the Paleozoic era (540 m.y to 250 m.y) • Separated into three sections – Salem Plateau • Central to SE Missouri – Springfield Plateau • SW Missouri – Boston Mountains • Northern Arkansas Mountain belts Buoyancy and the principle of _____________________________ • • Evidence for crustal uplift includes wave-cut platforms high above sea level Reasons for crustal uplift • Not so easy to determine • Isostasy • Concept of a floating crust in gravitational balance • When weight is removed from the crust, crustal uplifting occurs • Process is called ____________________________