Mountain Oceanic crust Ocean f + V splacement upper man Uppermost mantle (rigid) Asthencsphere (plastic) Reduction in elevation due to weathering, erosion, and transpc rt of materia Is Deposition of sediments Oceanic crust Ocean Lj...'_„k,...^|iM 1_' Uppermost mantle Slow f lowage toward Asthencsphere region of crustal thinning Sediments Oceanic crust Můhů Ocean I Uppermost mantle Uppermost mantle Subsidence from weight of sediments Asthenosphere^ (c) Asthenosphere r Geologie na konci 20. století přešla od fixistických statických interpretací k dynamickému pojetí vývoje Zemč. Dnes dominující paradigma geologie -tektonika litosferických desek - zdůrazňuje výrazné horizontální přesuny kontinentálních bloků. Za jejich hnací motor je považována tepelná konvekce v plášti Země, která je určována tepelnou výměnou mezi žhavotekutým jádrem Země a poměrně chladným povrchem. Teorie litosferických desek předpokládá, že konvekční tepelné proudy v plastické části zemského pláště vedou v místech vzestupných tepelných proudů ke vzniku divergentních rozhraní a v místech sestupných tepelných proudů ke vzniku konvergentních rozhraní litosferických desek CL Ifl :> V A (1) ĽL o £Z n5 conti nental crust Litosferická deska oceanic crust Outer layers of the Earth. Plates are made of crust and rigid upper mantle. Driving mechanism of plate tectonics * Trench pull ■ Ridge push ■ Thought to be cooling of the planet. * Friction at base of the lithosphere transfers motion from the asthenosphere to the lithosphere. * Convection may have overturned asthenosphere 1-6 times. Mechanisms Types of plate boundaries • divergent: mid-ocean ridges • convergent: collision zones volcanic arcs • strike-slip: San Andreas fault Alpine fault, N.Z. Examples of Plate Boundaries o-c convergent Andes o-o divergent Ocean Mid-Atlantic Ridge fcift c-c o-o divergent divergent crust Rift valley Carlsberg Sea Rit^eRJfi level O-O convergent Japan volcanic arc O-O divergent O-C convergent East Pacific Riie ftifi Andes Fig. 20.8a,b Convergent Plate Boundaries •oceanic-oceanic convergent plate boundary Sediments accumulate in ocean trenches, later lobe folded anchor metamorphosed Beniuff earthquake zone Konvergentní rozhraní představují místa vrásnění, vulkanické činnosti, vzniku pohoří a kolize kontinentů Formation of an accreted terrane •Accretionary Tectonics •Allochthonous Terrains •allochthonous •autochtonous •red - blocks from continents other than N. America dark green - blocks displaced from parts of N. America •Subduction Zone Complex •melange •ophiolite suite Idealized Ophiolite Suite Deep-sea sediments Pillow basalt Gabbro Peridotite Fig. 20.14 •Wilson Cycle •Supercontinent Cycle (500 million years) 1) Initial Rifling 2) Rafting of Continents 3) Subduction of oceanic crust at continental margins Closing Phase Opening Phase •Continent-Continent Collision Regional metamorphism -granulite, amphibolite, greenschist, •blueschist metamorphism, glaucophane •Suture zone- foreland basin, thrust faults regional metamorphism Approaching Arc or Microcontinent Fig. 20.21a Accreted Microplate Terrane Fig. 20.21c Microplate terranes Added to Western North America Over the Past 200 Million Years After Hutchinson, 199Z-1993 Fig. 20.22 Krtpi//geoll:»ť.jFmi ^iwTlchiw/VVilsofi/wlkfidnd html Rock assemblages and plate tectonics • Each plate tectonic environment produces a distinctive group of rocks. • By studying the rock record of an area, we can understand the tectonic history of the region. •Tectonic QFL Distribution Wilson Home | One Page | X-Sects. | B-Rift | E-Volc. Arc | F-Arc-Cont. | G-Cordill. | H-Cont.-Cont. | Self The QFL Distribution Of Sedimentary Rocks In Various Tectonic Regimes FrnsT Two Stages in the Rifting Process Stage B in Wilson Cycle * Wilson Home Page * Stage B * Igneous Home Page * Volcanos may be fissure type or conduit type * Bimodal association: felslc [alkaline) + marie [tholeiitlc] KM 3 Horst Graben _ i /Normal faults — Volcano: mafic If from hot spot Felsk if from melting of continental crust -f Ľ -f V *J -i ^k~7 -A ^ -? -A ^ ^ -1 ^ "7 -Í f "7 -i "7 -i V -J ^ ť -J Hot Spot / Thermal Doming Felsic batfioliths from frartkma] melting of lower continental crust KM 3 Continental Terrace (hinge Töne)--^ AxE^I Rift Alluvial fan « lake deposits V M V -J N A "T-7-4 "^-7^ "^-7^ Founderin? of Rift Valley / Marine Invasion Generation of mafic oceanic crust Volcanic Arc Systcm igneous rocks by fractional melting in a subduction - zone stage E-G KM 3- Horst Graben Volcano: mafic if from hot spot. Felsic if From melting of continental crust A i -? -b -j -i Hl m t) -r M "f ľ J f -l -T Jl/ -) -,r-l "í Hot Spot / Thermal Doming -7 -i "7 -1 f -1 ^v-l "> -T -L *> T -1 ,j-f If ,j -r Ir^-i H rr H -i V ^ -i V -\ FqIsc- btatholiths front fractional melting of lower continental crust km a- Continental Terrace (hinge zone) Axial Rift Alluvial fans lake deposits 4 -ľ ^ -l ^ t -l Foundering of Rift Valley / Marine Invasion Early Divergent Margin Sediment Wedge Nedy Opening Ocean Basin f--*---n Mid Oceanic Rift (Generating Ophiolite Suite) No A*ial rift on this side Early Divergent Margin H 1 í i -t Ír i -f h •f V -i -ŕ V-i -f P j -f V -i -ŕ Y <| -f *-T* 4 -J * * T* * T *■ * T * * -t if i -f ■/ y i -i v i -f Full nitrornant Marnin INTRODUCTION TO QFLQFL stands for Quartz, Feldspar, Lithics Sedimentary rocks are classified on the basis of the texture (grain size) of the rock, and composition. The basic classification only concerned texture, using the Wentworth size scale. But any full rock name must specify both texture and composition. Thus, an arkose sandstone is a rock of sand sized particles, with a high percentage of those particles being feldspar. It might seem that an unlimited variety of particles could end up in a sedimentary rock. After all, there are over 6000 known minerals. In addition, any incompletely weathered piece of igneous, sedimentary, or metamorphic rock can also be found in a sedimentary rock. A composition classification could become very complicated if all of these different particles were considered. But in most cases rock composition can be defined by four compositional components: >>> Quartz >>> Feldspar >>> Lithic fragments (including rock fragments and mineral grains other than quartz) >>> Matrix (a catchall for the silt and clay grains that cannot be easily seen by eye). QFL Diagram: The QFL diagram is to the right. Observe the following: »» Quartz is at the top, feldspar on the lower left, and lithics on the lower right. It is always done this way. »» The ternary diagram is divided into 5 fields, here color coded. The boundaries among the fields, left and right, are at the 50% boundary, and up and down at the 75% and 90% boundaries. »» As you travel toward any apex the quantity of Q, F, or L increases accordingly, with 100% being, of course, right at the apex. »» Notice that as we travel vertically the amount of quartz in the rock increases, and at the 90% boundary and above the rock has so much quartz the rock becomes a • "quartz something", such as a quartz sandstone or quartz conglomerate. >>>> The lower two fields contain rocks that are felspar (red) or lithic (blue) rich. That is, these rocks have more than 25% feldspar or lithics, that is, 25-100% feldspar or lithics. Rocks with this composition have such names as feldspathic (arkosic) sandstone (both terms are used interchangably) and lithic sandstone. >>>> Remember that all feldspar and lithic fragments are going to weather and disappear (to shale or dissolved minerals), leaving only quartz. On the QFL diagram, however, we can only plot the abundance of sand (or larger) particles of various compositions. So, on this diagram, as feldspar and lithics weather the composition of the remaining sandstone migrates toward the quartz apex. No matter where you start on the diagram the sediment is going to evolve in almost a straight line right to the top. QFL Composition Diagram Quartz XQuartz Subariraii^T Vubltthk / * / Arkoslt Little \ /Feldspathic} Is par Rock fLithicJ Fragments One of the things we are very interested in is how close the sediment has gotten along its path of evolution. This is the concept of sediment maturity. Thus, above the arkosic and lithic fields, but below the quartz field are two more fields, subarkosic and sublithic. Rocks in these fields have between 10-25 % feldspar or lithics and are thus farther along in their evolution toward pure quartz than feldspathic or lithic rocks. >>>> In other classsification systems, the boundaries among the fields sometimes differ from this one, and there may be more fields than 5 laid out. It all depends on what the geologist wants to do with them. But for this site we will always have these five fields, in these five places. >>>> Observe that a composition plotted somewhere in the middle of the QFL indicates a mixed composition. For example, the composition of "A" to the right is about 50% quartz, 35% feldspar, and 25% lithics (ternary with percent numbers). We could just call it an arkose since it falls in the feldspar field, but it would be more accurate to indicate that a lot of lithics are present too. Such a name, following the rules for naming rocks, is lithic, feldspathic, quartz. A Tectonic Rock Cycle. The diagram below takes the outline tectonic rock cycle and explores it into its details and rationalle. The Roman numerals in yellow circles are clickable and will take you to more detailed descriptions of the processes operating at that stage. Clicking the igneous rock names will take you to samples. Clicking the tectonic regime names (in blue script) will take you to a stage in the Wilson cycle where the processes are taking place. •Igneous Activity •andesite •island arc •volcanic arc •batholithic core •Metamorphism •regional metamorphism •- granulite - amphibolite - greenschist •blueschist metamorphism Volcanic Arc System •- glaucophane