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