Upwarped Mountains - Structural Geology - Lecture Notes, Study notes of Geology

Download Upwarped Mountains - Structural Geology - Lecture Notes and more Study notes Geology in PDF only on Docsity! 23 2. E.g. Basin and Range Province of Nevada, Utah, Eastern CA, SE Oregon, AZ. 3. Often associated with precursory volcanic activity. C. Upwarped Mountains 1. produced in assoication with broad arching or upwarping of the crust or of vertical uplift along high angle reverse faults. 2. e.g. Black Hills of S.D. and Adirondack Mtns. of NY e.g. of broad arching or uplift 3. Rocky Mtns of CO, NM result of vertical uplift, leave front range in which mantle of sed. rocks are tilted upward along high angle faults. a. results in hogbacks or flat-irons of front range V. MOUNTAIN BUILDING: THE PROCESS OF MOUNTAIN CONSTRUCTION A. Processes of Mountain Building have been studied in a variety of mountainous terrains around the world, some of which are relatively recent developments (Cordillera, Island arcs of S. Pacific, Himalayas), some of which are older remnants of orogenic events (e.g. Appalachian Mtns., Ural Mtns of USSR) B. Charcter of Mountain Belts 1. often include parallel ridges of folded and faulted sedimentary and volcanic rocks a. sedimentary rocks: sed. rx. often included in Mtn-bldg. events were deposited long before the Mtn event, and were subsequently caught up in the deformation process. 2. zones of metamorphosed rock bodies 3. igneous intrusions C. Orogenesis at Subduction Zones TIME AND GEOLOGY I. Law of Uniformitarianism- the present is the key to the past. A basic premise of the study of geology first presented by Scottish Geologist James Hutton in the 1700's. The law states that the geological processes operating at present, have been operating the same throughout geologic history. With many pieces of the geologic puzzle missing, we have to assume that the processes have been operating the same throughout geologic time. Historical Geology is the study of earth history. For geologists to adequately understand the Docsity.com 24 geologic environment of a particular site, a basic sequence of geologic events or history of an area must be put together. RELATIVE VS. ABSOLUTE GEOLOGIC DATING Relative Geologic Time: earth history placed in the context of relative sequences of geologic events. Absolute Geologic Time: uses radioactive elements contained within rock sequences to chemically and quantitatively determine the absolute age of that rock within the framework of statistical and/or experimental error. II. RELATIVE GEOLOGIC TIME A. Law of Original Horizontality- in a layer-cake geologic sequence of rocks, such as sedimentary rocks, it is assumed that the rock layers were first deposited horizontally under the force of the earth's gravity. B. Law of superposition- in an undisturbed sequence of sedimentary rocks, the lowermost rock layers are the oldest, and the uppermost rock layers the youngest. C. Law of Cross-cutting Relationships- " a disrupted pattern is older than the cause of the disruption". E.g. when a fault cross-cuts a sequence of sedimentary rocks, the rocks were deposited first, then cross-cut by the fault, otherwise they would have been undisturbed by the faulting event. 1. Cross-cutting geologic phenomena include: faults, volcanic intrusions, and erosional unconformities. Unconformity- a surface of erosion in which part or all of a rock record may be removed. D. Principles of Rock Correlation: 1. Physical continuity of rock bedding. 2. Similarity of Rock types 3. Correlation/similarity of fossils: based on theory of evolution and distinct periods of life forms on earth. a. Law of Faunal Succession: species of life have historically succeeded one another in a definite and recognizable order. b. Index fossils: a relatively rare fossil, known only to have existed for a very short period of time, also of limited geographic distribution. e.g. trilobites found only in Cambrian and lower Ordovician e.g. sharks found throughout geo-history since Devonian c. fossil assemblage: a series of fossils when found together, indicate a distinct time zone. D. Relative Geologic Time Scale: broken into Eras, Periods, Epochs in decreasing time interval Docsity.com