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Structural Geology Introduction/Review of Basic Principles I. Introduction A. Definitions
- Geology- study of lithospheric portion of the earth and its interaction withthe biosphere, hydrosphere and atmosphere
- Structural Geology- study of the architecture of rocks as related todeformation. a. Structure = Latin Struere - to build b. Study of the architecture of the Earth's crust (1) Architecture = form, symmetry, geometry and the eleganceof the components of the Earth's crust on all scales.
c. Rock Mechanics (Science) = strength and mechanical propertiesof crustal materials, both now and at the time they were formed and deformed.
- Tectonics (Greek Tektos - builder) a. Study of the forces and motion that result in rock deformation and structure b. Tectonic Deformation of Rock (1) Rigid Body Translation- transportation without any permanent change in size and shape (2) Deformation - permanent change in the size and shape of rock by breaking or flow. (a) Brittle Deformation- brittle fracture and cracking ofrocks
i) low temperature, low pressure (b) Ductile Deformation- flowage and solid-statechange of shape
i) high temps, high pressure, but belowmelting point of rock. B. Goal of Structural Geologist
- To interpret and define, on the basis of scientific data, crustal dynamics. a. Complex interaction of natural elements
b. Large-scale in both time and space c. Large time scale = "non-repeatable" experiments
- Geologic Reconstruction a. Time is the limiting factor (1) slow rates of process, very large scale b. Solving jig-saw puzzle (1) no picture on cover of box (2)(3) some pieces may be missing?Geologists reconstruct the picture with limited data and the complicating factor of time C. Scientific Method
- Observations of Nature
- Hypothesis Construction: I.D. Relationships in Nature 3.4. Experimentation, Hypothesis Testing, More ObservationAccept or Reject Hypothesis 5.6. Creation of Model to Explain ObservationsFurther Model Testing
- Accept or Reject Model as Proven Theory
- Science works by formulating observation-based models that can be tested by postdiction and prediction, then refined and tested again. The game is endless. D. Goals of This Course
- To learn the terms and concepts of structural geology 2.3. To fine-tune your skills of observation and conclusionTo orient rock structures in 4-dimensions of space and time
- To learn about processes of rock deformation
- To develop your cognitive skills (i.e. thinking!!) II. Approaches to Structural Geology A. Models of Analysis
- Geometric Model of deformation a. 3d interp. of form and orientation of struct b. based on data obtained from field studies (mapping, geophysical c. data)represented by cross sections and maps.
- Kinematic Model a.b. Reconstructing specific history of motionModel of plate tectonics is a kinematic model
orientation, size and shape of a body of rock.
- Products of Analysis a.b. Restored Sections,partical paths, c.d. plate motion vectors,sense-of-shear, e. rotation, f. velocity
- Strain Analysis a. Evaluating the changes in a body that result from dilation and distortion (1)(2) dilation = volume changeDeformation > order in a structural system. D. Mechanical Models
- Goal a. To reconstruct forces, stresses, and mechanical aspects of the system. b. To I.D. "The power and workings of the engine driving the deformation."
- Analysis by Delineation of: a. Rock strength, b.c. Deformation rate, andBoundary conditions of structural system.
E. Applying the Scientific Method to Geologic Problems: The approach of a goodscientist
- admits own ignorange, hence need for research
- Finds own field difficult and full of holes
- Advances by posing and investigating new problems4. Welcomes new hypothese and methods
- Proposes and tests new hypotheses6. Searches for counter examples
- relies on logic
- uses mathematics9. Cherishes the unity of science
- relies on primary source, gathers and reduces data11. Looks for counter examples
- Attempts to find and apply universal laws
- Settles disputes by experiment and computation14. Is current
- Seeks critical comments from others
EARTH MATERIALS: MATTER, MINERALS AND ROCKS
I. Basic definition of rocks and minerals
or lithfied into an aggregate or rock.A. Rock - an aggregate of one or more minerals, i.e. mineral crystals are bound together B. Mineral - a naturally occurring inorganic solid, which possess a definite internal atomic structure, and a specific chemical composition. II. Composition of Matter A. Definitions
Elements include O, Au, Ag, N, H, C and have a unique, and identifiable atomic structure.1. Elements - all matter are made of elements, over 100 elements are known.
- Compounds - combination of two or more elements joined together at the atomic level.
- Atom - the smallest recognized particle of matter that retains the properties of a given element. Atoms of elements are combined together to form compounds. V. ROCKS AND THE ROCK CYCLE
- Three Rock Types (based on their mode of origin) a. Igneous Rocks- a rock (or agglomeration of one or more minerals) that results from the cooling of magma, or molten rock. As the magma cools, minerals crystallize from the molten rock. Magma - molten or liquid rock beneath the earth's surface. Lava -magma extruded onto the earth's surface via a volcanic vent.
- Basic Terminology
miles beneath), composed of elements found in silicate minerals, water vapor, and gases.A. Magma - molten or hot liquid rock, originates beneath the earth's surface (up to 120 B. Lava - magma that is extruded onto the earth's surface via volcanic eruptions (hot magma is confined at depth beneath surface, relatively lighter than confining rock, rises upward, may eventually erupt onto earth surface).
were extruded onto earth's surface)C. Extrusive Igneous Rocks or Volcanic Ig. Rocks - rocks which solidify from lava (or
beneath the earth's surface.D. Intrusive Igneous Rocks or Plutonic Ig. Rocks - rocks which solidify from magma III. Magma Crystallization Process
magma cools, the ions slow and begin to form atomic bonds, arranging themselves in orderlyA. Hot, molten magma: ions of elements are moving freely in a fluid, unordered state, as patterns --- known as process of crystallization.
earth, fragmenting rock into particlesB. Weathering - disintegration and decomposition of rock at or near the surface of the
of pre-existing rockC. Sediment - fragments of rocks and/or minerals that are produced from the weathering D. Erosion - incorporation and transportation of sediment by a mobile agent, usually water, wind, or ice. VI. SEDIMENTARY ROCKS A. Introductory statements/definitions:
chemical and physical weathering settling or being deposited from a fluid.1. Sedimentary derives from latin root meaning "settling" as in products of
- Visualization - physical and chemical weathering attacks rock, breaks and dissolves it into small particles, sediment, then subject to transportative forces (gravity, water, wind, ice), generally moved downslope under force of gravity, to a resting place (ocean orsedimentary basin), where deposited, buried, compacted, lithified, converted into sedimentary rock. 2a. Lithification - refers to the process of converting loose sediment or mud into solid rock.
time, the weight of overburden compress the deeper sediments and squeeze out fluids and1) compaction - as sediments accumulate and become buried with compact the sediment, compressing clays together, clays act as binding agents.
- cementation - solutions carry ions into pours between sediments, with time ions may be precipitated as cements under appropriate chemical condition.Common cements include calcite, silica, and iron oxide.
cover 75% of the earth's surface exposures. The sedimentary environment is a surface3. Sed. rocks account for only 5% of the earth's crust/lithosphere, however they environment (at surface pressures and temperatures)
- As geologists we can examine modern day sedimentary processes, look at depositional forms and life in sediments, and then go to ancient lithified sequences of sed. rockand interpret their environment of deposition (e.g. river, shallow ocean, deep ocean, lagoon, lake, swamp). Sed. rocks are also where fossils are found providing evidence of past life onearth. (do not find fossils in igneous environment, may find remnants in met. env. in which sed. rocks have been deformed).
- Sedimentary rocks are where we find many natural resources such as coal and oil, also many ore minerals are found in sedimentary rock "hosts". B. Sedimentary Rock Types/Classification Detrital vs. Chemical Sedimentary Rocks.
