Rocks

• Rocks

  a naturally-occurring aggregate of two or more minerals
• Rocks may or may not contain mineraloids, natural glass, organic matter, and pre-existing rocks or sediment
• Types of rocks vary based on composition, color, textures, structures, etc.
• Petrology


  refers to the study of rocks; its genesis, composition, distribution and structure of rocks.
• Petrology


  involves examining the processes that lead to the formation of rocks, as well as their identification and classification
• Petrography


  -branch of petrology that deals with the description and classification of rocks; their constituent minerals and texture

  -involves the use of microscopic and laboratory techniques to study the rock in details
• Igneous Rock


  Identify the rock type (I, S, M). Andesite
• Igneous Rock


  Identify the rock type (I, S, M). Diorite.
• Sedimentary Rock


  Identify the rock type (I, S, M). Conglomerate
• Sedimentary Rock


  Identify the rock type (I, S, M). Coquina
• Metamorphic Rock


  Identify the rock type (I, S, M). Gneiss
• Metamorphic Rock


  Identify the rock type (I, S, M). Phyllite
• Rock cycle


  -explains the processes underwent by rocks on and under the earth’s surface

  -allows us to view many of the interrelationships among different parts of the earth’s system

  -simplified by useful overview of the physical geology
• Complete the rock cycle

  A) magma

  B) cooling

  C) igneous rock

  D) weathering

  E) erosion

  F) sediments

  G) compaction

  H) cementation

  I) sedimentary rock

  J) heat & pressure

  K) metamorphic rock

  L) melting

  M) melting

  N) heat & pressure

  O) weathering

  P) erosion

  Q) weathering

  R) erosion

  
• Classification of Rocks

  IGNEOUS ROCKS- formed from cooling of magma

  SEDIMENTARY ROCKS- formed when weathered fragments of other rocks are compressed and cemented together

  -precipitation from solution

  METAMORPHIC ROCKS- formed by alteration (due to heat, pressure,

  and/ or chemical action) of pre-existing rock (igneous, sedimentary, or metamorphic rock)
• Magma


  temperature ranging from 600° – 1200°C
• Magma 


  molten or partially molten rock composed of varying amounts of:

  ▪ LIQUID: silicates (sometimes carbonate, sulfides, or oxides) and ions of Al, Fe, Ca, Na, K, Mg

  ▪ SOLIDS: mineral or rock fragments

  ▪ DISSOLVED GAS OR VOLATILES: H2O, CO2, SO2
• Classification of Magma - Silica Content

  ▪ FELSIC -silicic or acidic; >63% SiO2; continental crust

  ▪ INTERMEDIATE- 52-63% SiO2; continental crust

  ▪ MAFIC- basic; 45-52% SiO2

  ▪ ULTRAMAFIC- ultrabasic; <45% SiO2
• Classification of Magma - Viscosity


  -property to resist flow

  -caused by different factors

  ▪ higher temperature; lower viscosity

  ▪ higher SiO2 content; higher viscosity

  ▪ higher dissolved H2O; lower viscosity
• Classification of Magma - Density


  ▪ denser oceanic crust – mafic rocks

  ▪ lighter continental crust – felsic rocks
• Classification of Magma - Temperature


  temperature of the melt formation
• Common types of magma

  1. Basaltic magma

  • high density (Fe, Ni, Cr, etc)
  • low viscosity
  • relatively low silica content
  • crystallizes at high temperature (~1000°-2000°C)
  • accounts to majority (80%) of all magma erupted by volcanoes
• Common types of magma

  2. Granitic / Rhyolitic Magma

  • low density
  • high viscosity
  • high silica content
  • crystallizes at ~600 C
  • accounts to 10% of all magma erupted by volcanoes
• Sources of heat (FHHOR)

  • original heat of the earth at the time of formation
  • some elements (e.g., uranium) produces heat through radioactive decay
  • heat transfer from nearby magmatic body
  • hot mantle plumes may upwell into the crust
  • frictional heat formed by two crust grinding past each other
• Generation of magma

  • Melting in the upper mantle/ lower crust
  • HEAT - increase in temperature – reaching the melting point
  • PRESSURE - lowering the pressure – decompression melting
  • VOLATILES - addition of volatiles – lowers the melting temperature
• Generation of magma

  • new magma is generated in:

  1. mid-oceanic ridges (MOR) - decompression melting of upwelling mantle
  2. subduction zones - subducting slabs contains volatiles lowering melting temperature
  3. hot spots - high temperature in mantle plumes induces melting
• Variation in composition of magma

  Magmatic differentiation - any process that causes the magmatic composition to change

  -separate magma into compositional layers
• Magmatic Differentiation - Fractional Differentiation

  • denser - crystalizes first
  • minerals crystalize and separate from magma causing the remaining magma become enriched in certain minerals / elements

  
• Magmatic Differentiation - Partial Melting

  • low melting point - melts first

  
• Magmatic Differentiation - Country Rock Assimilation

  • magma breaks off rocks- mix into the magma changing its composition
  • magma intrudes with rocks

  
• Magmatic Differentiation - Magma Mixing

  • magmas of different composition tend to be immiscible because forces such as density and thermal contrasts work to keep them separated. It would require a vigorous stirring mechanism (eg. convection) to merge the two.

  
• Igneous Rocks

  o   ex. gabbro

  o   “ignis” – fire

  o   formed from solidification of molten material called magma (intrusive) or lava which flows out from the depths (extrusive)
• Bowen’s Reaction Series


  As magma cools, certain minerals crystallize first at relatively high temperature, in successively lower temperature, other minerals begins to crystallize
• Bowen's Reaction Series

  1.   Discontinuous Series

  -   describes the crystallization of specific minerals as temperature decreases

  -   olivine→pyroxene→amphibole→ biotite→potassium feldspar→ muscovite→quartz

  2.   Continuous Series

  -   sequence of mineral that form as temperature in a more gradual manner; doesn’t involve

  discrete phases like the discontinuous series

  -  Ca-rich plagioclase feldspar → Na-rich plagioclase feldspar

  A) olivine

  B) pyroxene

  C) amphibole

  D) biotite mica

  E) ca-rich plagioclase feldspar

  F) na-rich plagioclase feldspar

  G) potassium feldspar

  H) muscovite mica

  I) quartz

  
• Two kinds of Igneous Rocks

  1.   INTRUSIVES (PLUTONIC)

  o   igneous rocks formed at the depth

  o   peridotite, gabbro, diorite, granite

  2.   EXTRUSIVES (VOLCANIC)

  o   molten rock solidified at the surface

  o   komatiite (rare), basalt, andesite, rhyolite
• Batholith


  Massive intrusion more than 100 sq. km in outcrop area

  bathos = depth

  lithos = stone/ rock
• Stock


  Small discordant pluton

  discordant = cutting across bedding
• Dike


  Tabular concordant body, serves as tabular conduits that transport magma, concordant = following the direction of the strata
• Sill


  Tabular concordant magma, serves as storage of magma
• Laccolith


  Blister-shaped sill, igneous rock forcibly injected between sedimentary strata, so as to arch the beds above while leaving those below relatively flat