Geol 120 1st Edition Exam 1 Study Guide Midterm One Plate Tectonics 1 The outermost layer of the Earth is broken up into tectonic plates 2 Tectonic plates move relative to each other 3 The boundary between two tectonic plates can be convergent moving towards each other divergent moving away from each other or transform sliding past each other 4 The movement and interaction of tectonic plates helps to explain many of Earth s features Oceanic Crust Thinner more dense in subduction zones oceanic plates will slide under continental Continental Crust Thicker less dense Divergent Plates Plates moving apart from each other most common in ocean plates Continental rift Creation of a divergent boundary on a continent 1 Initial uplift from rising magma 2 Stretching faulting from rift melting forms magma 3 Can lead to seafloor spreading new ocean basin 4 Ocean widens from spreading example Atlantic ocean Convergent boundary Plates moving towards each other Ocean Continent Ocean slides under Continental subduction zone Ocean Ocean One plate the thicker denser of the two is subducted Continental Collision 2 continental masses converging produces huge mountain ranges solidified magma in crust is present deformation causes mountain belts Transform boundary Plates sliding against each other Earthquakes in belts and along mid ocean ridges trenches and mountain belts Volcanoes not in plateaus ocean ocean divergent ocean continent convergent Mountains anywhere but transform boundaries Three driving forces of plate motion 1 Gravity 2 Slab pull pulling subducting plate under 3 Ridge push force pulling each side of the divergent plate down Plates move 1 15cm a year about as fast as fingernails grow Earth Materials minerals 1 Minerals are the building blocks for rocks 2 Minerals have defined chemical compositions and internal structures which give them their characteristics 3 Silicate minerals are the most common minerals in Earth s crust 4 The types of minerals present in a rock give us information about how that rock formed 5 Minerals have many uses in society Characteristics that define a mineral natural inorganic solid ordered internal structure and specific chemical composition Mineral characteristics that are used to identify minerals crystal shape cleavage hardness streak luster and effervescence Major classes of rock forming minerals key elements underlined Silicates silica tetrahedron SiO4 Carbonates CO3 Oxides metal oxygen FeO4 Halides metal Halide Nacl Sulfates SO4 Sulfides metal sulfur FeS2 Native metals Metal by itself4 Know that silicates are the most common minerals in Earth s crust and therefore Silica and Oxygen are the most abundant elements in Earth s crust Basic structure of silicate minerals Single chains 2 perpendicular plains 90 degree Double chains 2 non perpendicular plains 60 and 120 Framework no cleavage crystal structure example Quarts Sheets one dominant plain Most common silicate minerals Quartz K feldspar Plagioclase feldspar Muscovite Biotite Amphibole Pyroxene Olivine Felsic Lighter in color No Fe Mg Melt first lower temps Crystalize last Mafic Darker colored Has Fe Mg Melt last at higher temps Crystalize last Igneous rocks 1 Igneous Rocks are formed from the cooling of molten rock 2 Igneous Rocks are classified by their composition and texture 3 The composition of an igneous rock provides information about the source and evolution of the magma that formed it 4 The texture of an igneous rock provides information about its cooling history 5 Melting of rocks requires heating release of pressure addition of water or some combination of the three 6 Mafic minerals melt crystalize at higher temperatures than felsic minerals 7 The mechanism of melting and source of magma is different at different tectonic settings Partial crystalizing The rocks will be more mafic because the felsic will melt out first this also means the magma will be more felsic Ways to melt a rock Decompression Heat Addition of water As a rule higher temperature and pressure will turn solid rock into liquid magma Textures Aphanitic Fine grained small crystals not distinguishable by naked eye Porphyritic Large and small crystals first slow cooling and then fast Phaneritic Coarse grained crystals seen by the naked eye spotted for example granite Glassy cooled almost immediately no time for crystals to grow Pegmatic very large crystals more than 1 cm Vesticular full of tiny vessels lightweight Felsic Intermediate Mafic Ultramafic Intrusive coarselycrystalin Granite Diorite Gabbro Peridotite Extrusive Finelycrystalin Rhyolite Andesite Basalt Rapid cooling creates smaller crystals Slow cooling creates larger crystals Extrusive Cooled outside of the crust Intrusive Cooled inside the crust has more growth time has bigger crystals Mid Atlantic ridge Cause of melting Decompression Sources of Magma Mantle rising Types of Magma Mafic Types of rock Basalt Gabbro Subduction zone Cause of melting Heating addition of water Sources of Magma Mantle and continental crust Types of Magma Mafic intermediate and felsic Types of rock Granite Andesite Hot Spot Cause of melting Decompression and heating Sources of Magma Mantle and oceanic crust Types of Magma Mafic Types of rock Basalt Volcanoes 1 Volcanoes are places where magma and other volcanic products such as ash and gasses erupt on to Earth s surface 2 The shape of a volcano and the style of its eruptions are controlled by the composition of the magma and its gas content 3 More viscous magmas with higher gas content are more explosive 4 We can make predictions about a volcano s characteristics and eruption style based on its tectonic setting and magma composition 5 Volcanoes pose large risks to communities located near them 6 Volcanoes are monitored closely and the risk of volcanic hazards are assessed by geologists and emergency planners Eruption styles increasing explosivity 1 Lava flows 2 Lava fountains 3 Eruption columns Tectonic setting Magma type Magma viscosity Gas content Explosiveness Viscosity resistance to flow High viscosity Lava piles up Lower temp Abundant silica chains More gas more explosive Low viscosity Lava spreads out Higher temp Fewer silica chains Less gas less explosive Felsic magma Gas bubbles cant escape easily high pressure explosive eruptions high viscosity Mafic Magma Gas bubbles escape easily little pressure nonexplosive low viscosity Intermediate Eruptions At subduction zones Viscosity Medium Gas content Medium Explosiveness Medium Debris Medium