IGNEOUS ROCKS & VOLCANISM

1. IGNEOUS ROCKS & VOLCANISM

2. a rock is an aggregate of mineral(s) or mineral matter which occurs in massive deposits bedrock is a massive unbroken solid rock directly overlain by soil in many locations an outcrop is a massive unbroken solid rock exposed at the Earth’s surface

3. IGNEOUS ROCK FAMILY • Definition of igneous rock • Origin of magma • convergent plate boundaries (subduction zones) • divergent plate boundaries (ridges or rifts) • isolated magma plumes (hot spots)

5. IGNEOUS ROCK FAMILY • Assimilation • melting of other rock material incorporated into a magma causing original composition magma to change • an example is the mixing of magma originating in mantle with a different composition of continental crust as magma rises

6. IGNEOUS ROCK FAMILY • Intrusive and extrusive as applied to magmas and igneous rocks • intrusive refers to any igneous activity below Earth’s surface • extrusive refers to any igneous activity at the Earth’s surface

7. IGNEOUS ROCK FAMILY • Texture, mineral composition , and igneous rock names • texture • grain size of mineral fragments in rock and depends on the cooling rate of magma • smaller in rock if magma cools fast • larger in rock if magma cools slower

8. IGNEOUS ROCK FAMILY • kinds of textures • phaneritic (coarse grained)--intrusive • aphanitic (fine grained)--extrusive • glassy--extrusive • vesicular (comprised of many holes called vesicles --extrusive • porphyritic--more than 1 size mineral fragment present--phenocrysts and matrix

9. IGNEOUS ROCK FAMILY • pegmatitic--intrusive • pyroclastic--extrusive

10. Igneous Rock Textures Phaneritic Aphanitic

11. Igneous Rock Textures Glassy Vesicular

12. Porphyritic Pegmatitic

13. IGNEOUS ROCK FAMILY • mineral composition • igneous rocks are comprised of a combination of silicate minerals • Bowen’s mineral series • describes an orderly sequence of mineral formation from a cooling magma and explains specific mineral combinations in the rock • discontinuous and continuous series • hydrothermal solutions

15. IGNEOUS ROCK FAMILY • magma composition • can change (1) as cooling progresses and minerals separate; (2) magma assimilation • igneous rock names • essential minerals • minerals in rock used to classify rock by name • accessory minerals • minerals not used to classify rock

16. IGNEOUS ROCK FAMILY • felsic • rocks light in color and contain a lot of feldspar and quartz • mafic • rocks dark in color because they contain a lot of biotite, hornblende, or other dark minerals • ultramafic • rocks that contain augite and olivine • igneous rock chart

17. Igneous Rock Classification Table

18. Phaneritic Textured Igneous Rocks Granites Diorite Gabbro Dunite

19. Aphanitic Textured Igneous Rocks Rhyolite Basalt

20. Porphyritic Textured Igneous Rocks Granite Porphyry Rhyolite Porphyry Andesite Porphyry

21. Glassy and Vesicular Textured Igneous Rocks Obsidian Pumice (2) Scoria

22. IGNEOUS ROCK FAMILY • Igneous rock bodies • intrusive (plutons) • discordant-- bodies which cut across sedimentary rock contacts or boundaries • batholith--largest pluton body and irregular in shape--ore deposits like gold, silver, copper etc. are often associated with these

23. Batholiths in Western USA

24. IGNEOUS ROCK FAMILY • stock--smaller irregular shaped body with possible associated ore bodies • dike--very small tabular shaped body • concordant--do not cut across sedimentary rock boundaries • laccolith--large lens shaped body • sill-- a small tabular shaped body

25. Igneous Rock Bodies (Plutons)

26. IGNEOUS ROCK FAMILY • Important uses of igneous rocks • used as building materials and tombstones--this use is the same for all 3 families of rocks • pumice is used an an abrasive material

27. VOLCANISM

28. VOLCANISM • Some common terms • volcanism • the processes by which magma and/or gases or volatiles are transferred to the Earth’s surface • volcano • an elevated area or mountain formed from accumulations of lava and/or pyroclastic materials

29. VOLCANISM • active, dormant, and extinct volcanoes and volcanic areas • active--eruption can occur in the near future--Mt. St. Helens and other Cascade mountains are examples • dormant--presently inactive but believed capable of future eruptions • extinct--expected not to erupt again • Origin and global distribution of volcanism • origin of volcanic materials

31. VOLCANISM • global distribution • “Ring of Fire” or circum-Pacific region is the greatest concentration of volcanic activity on Earth • Mediterranean Region---2nd largest region of volcanoes on Earth

32. Concentration of Volcanic areas on Earth

33. VOLCANISM • Volcanic rocks, volatiles (gases and vapors), and manner of eruption • volcanic rocks • include all extrusive textured rocks and include basalt, andesite, rhyolite, pumice, scoria, tuff, obsidian and volcanic breccia • volatile emissions • steam (water vapor)--most abundant

34. VOLCANISM • carbon dioxide is next abundant while sulfur dioxide, nitrogen, and sulfur trioxide are others • carbon dioxide additions into the atmosphere can add to the “Greenhouse Effect” and the others can contribute to acid rain formation • burning or decomposition of fossil fuels are synthetic contributions to the“Greenhouse Effect and acid rain

35. VOLCANISM • manner of eruption (passive or explosive) • depends largely on viscosity of magma • viscosity depends on composition and temperature of the magma associated with the eruption--the higher the silica content or the cooler the magma, the more explosive the eruption, and vice versa • most ocean basin eruptions are passive while most continental are explosive--why???

36. Volcanic Eruptions on Continents

37. VOLCANISM • Major categories of volcanic deposits (Classification of volcanoes) • deposits are comprised of lava flows and/or pyroclastics • shield type---broad with gentle slopes • thick deposit of basaltic lava flows with little or no pyroclastic materials • associated with ocean basin eruptions • Hawaiian shield is about 28,000 feet thick with pimple-like islands

38. Shield Type of Volcanic Deposit

39. Shield Type of Volcanic Deposit-- Hawaiian Islands Kilauea– Earth’s most active and Mauna Loa—Earth’s largest volcano

40. Shield Type of Volcanic Deposit--Hawaiian Islands

41. VOLCANISM • cinder cone or scoria cone • small deposit of pyroclastic or ejected materials • steep slopes and less than 1000 feet tall • represents last stage (cooler) of basaltic or less commonly andesite eruptions • example is Paricutin, Mexico which erupted in 1943 and grew 120 feet tall the first day

42. Cinder Cone Type of Volcanic Deposit

43. Cinder Cones in Arizona

44. VOLCANISM • composite or stratovolcano • very tall deposit of alternating lava flow and pyroclastic deposits • comprised of andesite or rhyolite, occur on the continents and are explosive • examples include: Mt. Vesuvius, Mt. Fujiyama, Mt. Kilamanjaro and mountains in the Cascades including Mt. St. Helens

45. Stratovolcano Type of Volcanic Deposit

46. VOLCANISM Famous Composite Volcanoes Mt. Fuji Mt. Kilimanjaro Mt. Shasta

47. volcanic dome solidified lava, hundreds of meters high volcanic ash mixed with rock fragments viscous felsic or intermediate magma piled up around a vent found in composite volcanoes

48. VOLCANISM • Eruptions with special volatile emissions • strombolian type • incandescent cloud is stable over vent and reflects light from magma • Mt.Stromboli is best example and called “Lighthouse of the Mediterranean”

49. VOLCANISM Mount Stromboli

50. VOLCANISM • Nuee Ardentes (fiery or glowing cloud) type---pyroclastic flow • a very hot cloud of volatiles and ash • Mt. Pelee on Martinique emitted a 700 degree (C) cloud and killed 30,000 people in a few minutes in St. Pierre