inflation of fractures,wedging wall rock apart.detachment of large wallrock blocks (stoping), andincorporation of wall rockfragments (xenoliths).oMagma that doesn’t reach thesurface freezes slowlyoGeologists categorize intrusions by shape.Tabular (sheet)—planar with uniform thicknesstend to have uniform thicknesses. often can be traced laterally.have two major subdivisions.oDikes and sills modify invaded country rock.They cause the rock to expand and inflate.
They thermally alter the country rock.Both dikes and sills exhibit wide variability in size.thickness (or width).lateral continuity.oSill—injected parallels to rocklayeringare injected parallel topreexisting layering.are usually intrudedclose to the surface.oDike—cuts across rock layeringcut across preexistinglayering (bedding orfoliation).spread rocks sideways.dominate in extensionalsettings.Blister-shaped—a sill that domes upwardBalloon-shaped—blobs of melted rockThe gabbroic core of Mt. Royal formed as an intrusion at a depth of about 1.3km ~125Ma. Magma rose into the sedimentary section which has since been “unroofed”. Volcanic necks/plugs.Avolcanic neckis the rock that formed in the vent of a volcano at the end of its eruptive life and remains “standing” after the flanks of the volcano have eroded away.Laccoliths.Alaccolithresembles a sill but formed betweensedimentary layers from a more viscous magma that created alensshaped mass that arched the overlying strata upward.Plutons. Plutonsare discordant intrusive rocks that formed atgreat depths. They tend to be large, coarse grained, and irregularin shape. If the intrusion occupies less than 100 square kilometers(60 square miles) at the earth's surface it is called astock; if it islarger than 100 square kilometers, it is termedabatholith.Batholiths are usually composed of granite. Theyhave formed over long periods through the accumulation ofsmaller magma blobs calleddiapirs, which result from localizedmelting of the crust; the diapirs then slowly move upward toward the surface and coalesce into a larger mass. Granitic batholiths usually form the cores of mountain complexes and are a result of plate tectonic action
Depositional environments: formation of sedimentary rocksSedimentary Rock:oForms at or near Earth’s surface in one of several ways.Cementing loose clasts (fragments) of preexisting rock.Cementingtogether looseshells and shellfragments.Accumulation oforganic matterfrom livingorganisms.Precipitation ofminerals dissolvedin water.Sedimentary rocks form layerslike the pages of a book.oThe layers record a historyof ancient environments.
- Fall '09
- Plate Tectonics, Gypsum