Plate Tectonics,The Rock Cycle and
the Geologic History of Vermont
(Rocks, Rocks, and more Rocks)
ROCKS:
1. Igneous Rocks• Cool from Molten rock - magma• Intrusive and extrusive
2. Sedimentary Rocks• Little pieces of other rocks that
have been eroded, transportedand deposited elsewhere
3. Metamorphic Rocks• Squished and folded rocks• Can originate from sedimentary
igneous or other metamorphics
basaltbasaltgranitegranite
sandstonesandstoneLimestoneLimestone
slateslateschistschist
The Rock Cycle:
Generalized Geology of Vermont
Most of the rocks we find inVermont date to between 550and 350 million years ago!
Vermont Has ‘em All
Rock of Ages QuarryBarre, Vermont
Granite (igneous-intrusive)
Vermont Has ‘em All
Marble (metamorphic)
Lessor’s QuarrySouth Hero, Vermont
Limestone (sedimentary)
Vermont Has ‘em All
Slate (metamorphic)
Eureka Slate QuarryPoultney, Vermont
Vermont Has ‘em All
Marble (metamorphic)
Vermont Marble MuseumProctor, Vermont
Vermont Has ‘em All
Mt. Mansfield
Schist (metamorphic)
Why are all these different rock types found in VT???
Igneoussilurian-devonian
Metamorphicsilurian-devonian
sedimentaryOrdovician
MetamorphicCambrian
MetamorphicPre-Cambrian
The Rock Cycle and Plate Tectonics:
“Vermont” in the Pre-Cambrian:
Grenville Super Continent(~1 billion years ago)
•No continents as we know them•VT and New England didn’t exist yet
•One big landmass
•Landmasses have come together andSpread apart several times in Earth’s
4.5 billion year history
Cambrian Rifting~550 mya - Iapetus Ocean
Rifting to seafloor spreadingErosion and deposition of
Continental shelf rocks(limestones, sandstones)
Offshore deposition (shales and mudstones)
Taconic Orogeny~450 mya - convergence
Offshore sedimentsMetamorhposed and thrust
Over cambrian sedimentary rocksIn the champlain valley
Acadian Orogeny~400-350 mya
Continued convergenceEmplacement of granite intrusions
Then 350 million years of erosionLeaves us with the Vermont of today
So….what is it?
Questions to ask yourself• Can you tell which of the three types of rocks it is?
• Can you see individual grains or crystals?•If so, are they interlocking, or do they look likelittle pieces of rock?
• Are the minerals light colored or dark colored?
• Can you see “sheets” or foliations in the rock?
•Can you see folds or other structures?
• Does the rock react (fizz) with acid (HCl)?
Basic Rock Type
Minerals- Igneous Rocks
Felsic Minerals:rich in Si and Ogenerally lighter in colorless dense than mafics
Mafic Minerals:rich in Fe and Mggenerally darker in colormore dense than felsics
Coarse Fine
Cooling rate
IntrusiveIntrusive ExtrusiveExtrusive
Igneous Rocks
Sedimentary Rocks
Detrital =
Clastic
HClfizz
Organic
Chemicallyprecipitated
Metamorphic Rocks
Metamorphic Rocks - precursors or parent rocks:
Metamorphic RockParent Rock
QuartziteQuartzite
MarbleMarble
HClfizz
slateslate
sandstonesandstone
LimestoneLimestone
shaleshale