Transcript Mountain Belts and the Continental Crust

GEOLOGY OF NEW JERSEY
Crustal Deformation and Mountain
Building
Behavior of rocks to stress
& strain
• Elastic
– Elastic limit
• Plastic
• Brittle
Stress
Strain
FOLDS
• Anticline vs. syncline
– Hinge line (axis)
– Limb
– Axial plane
• Plunging fold
• Structural dome
• Structural basin
FOLDS
• Interpreting folds
– Open fold
– Isoclinal fold
– Overturned fold
– Recumbent fold
Faults
• Fractures in rock
• Normal Faults
• Reverse fault
– Thrust fault- low angle reverse fault
• Strike-Slip fault
– Left-lateral vs. right-lateral
Introduction
• Mountain
• Major mountain belts
• Mountain range
Characteristics of Major
Mountain Belts
• Size and Alignment
• Along continental margin
• Long, arcuate chains
• Ages of Mountain Belts and Continents
–Youngest tend to be higher
–Himalayas vs Appalachians
–Craton- Oldest Continental Crust
• Precambrian Shield
Characteristics of Major
Mountain Belts
• Patterns of Folding and Faulting
– Fold and Thrust Belts
• Crustal Shortening
• Crustal Thickening
• Metamorphism and Plutonism
• Normal Faulting
Rifting
Subduction
Accretionary wedge
Volcanism
Plutonism
Orogeny
Subduction
Collision
Crustal Shortening &
Thickening
Major Orogeny
Evolution of a Mountain Belt
• Accumulation Stage of Sediments
– Accumulation in an Opening Ocean Basin
– Accumulation along a Convergent
Boundary
• Graywackes
• Magmatic Arc
• Mountain Building Event- Orogeny
The Growth of Continents
• Crust added by accumulation & igneous
activity
• Suspect and Exotic Terranes
– Suspect terrane
– Accreted terrane
• Exotic terrane
The Wilson cycle (named after J. Tuzo Wilson, one of the fathers
of plate tectonics) refers to the cycle of ocean basin formation by
rifting and seafloor spreading followed by ocean basin
destruction and mountain building by subduction.
Geologic Evolution of Eastern
North America
THE EARLY PALEOZOIC
THE CAMBRIAN 544-505 MY
CAMBRIA>>WALES
ADAM SEDGWICK 1835
THE ORDOVICIAN 505-438 MY
ORDOVICE>>WELSH TRIBE
CHARLES LAPWORTH 1879
TECTONIC EVENTS
 Overall scenario is coalescence of Pangea
during most of the Paleozoic
 Taconic Orogeny mid to late Ordovician
 Caledonian Orogeny late Silurian to early
Devonian
 Acadian Orogeny mid Devonian
 Alleghenian Orogeny late Penn, Permian
 Hercynian Orogeny - Ouachita Orogeny
PLATE TECTONIC
MOVEMENTS FROM
THE
NEOPROTEROZOIC TO
THE DEVONIAN (750
MY TO 370MY)
BREAK UP OF RODINIA
AVALONIAN OROGENY
OPENING OF IAPETUS
OPENING OF RHEIC
TACONIC OROGENY
CLOSING OF IAPETUS
ACADIAN OROGENY
The Appalachians
• Valley and Ridge
– folded & faulted sedimentary rocks
• Blue Ridge Province
– metamorphosed Precambrian and Paleozoic
Rks
• Inner Piedmont
– high grade metamorphic rocks intruded by
granites
• Charlotte & Carolina Slate Belt
– metamorphosed & folded late Proterozoic &
Cambrian sediments and volcanics
A) Cambro-Ordovician Passive Margin: Sandy Shelf Deposits
B) Middle to Late Ordovician Development of Trench Along the
Eastern Boundary and Subsequent Closure of the Iapetus Ocean
C) Collision of Island Arc and other Accreted (exotic) Terranes with
North America in the TACONIC OROGENY
CAMBRIAN
PALEOGEOGRAPHY:
SHALLOW
EPICONTINENTAL
SEAS COVERED THE
CENTRAL US
Earliest Paleozoic time
of lowest sea level due to
Proterozoic glaciations
By middle Cambrian sea
had flooded the continent
LITHOLOGIC
FACIES OF THE
CAMBRIAN
NEOPROTEROZOIC TO
CENOZOIC
TRANSGRESSIONS
AND REGRESSIONS
OBSERVED ON THE
CRATON
Variable sea level represented
sequences of sediments bounded
by unconformities on all of the
cratons - e.g. Sauk, Tippecanoe
ORDOVICIANPALEOGEOGRAPHY
Tippecanoe Transgression
St. Peter’s Sandstone
The Queenston Clastic Wedge
Redbeds coarser towards
the source area, Taconic
Highlands (4000m)
Early Paleozoic Climates
• Climates overall warmer than today
• Continents 600 N & S of equator
• Arid to sub arid environments 450 N & S
of equator
• Redbeds (alluvial) 300 N & S of equator
• Tropical reefs 300 N & S of equator
– Cambrian Archeocyathids; Ordovician
Bryozoans
• Glaciation during the late Ordovician in
Africa
THE MIDDLE PALEOZOIC
THE SILURIAN 438-408 MY
SILURES>> WELSH TRIBE
Roderick Murchison 1835
THE DEVONIAN 408-360 MY
(Old Red Sandstone)
DEVON>> County in SW England
Roderick Murchison
Adam Sedgwick 1839
INTRODUCTION
• Final Collision and Suturing of Baltica
and Laurentia
• Caledonian and Arcadian Orogenies
• High Stands of Sea Level
• Epicontinental seas; marine deposits
and thick sequences of evaporites
• Reefs became important
Paleogeography
PALEOGEOGRAPHY
• Closing of Iapetus Ocean
– Baltica-Laurentia; Mongolia-Siberia
• Closing of Rheic Ocean as Gondwana migrated to
west (Laurentia/Baltica-Gondwana)
• Laurentia continued to be a tropical craton
• Shallow seas covered the continents during much of
Silurian
• Devonian orogenies in Northern Hemisphere
– Caledonian (Scandinavia/Greenland) & Acadian (New
England)
Cratons and Mobile Belts of North America and Europe
TECTONIC EVENTS
• Caledonian & Acadian Orogenies
–Extension of Late Ordovician
Taconic Orogeny
• Mid Devonian Iapetus Ocean closed
• Baltica collided with Laurentia
• Avalonia (Island Arc) sutured to both
Baltica and Laurentia
Orogenic
Development
Of the Eastern
US
Acadian Orogeny produced
a thick clastic wedge (the
Catskill Wedge) of red beds
[conglomerates and sandstones]
East-West Cross Section across the Devonian Catskill Wedge
During the Devonian the rate of
sedimentation increased from
7m/MY to 17m/MY to 70m/MY
Chattanooga Shale- Anoxic black shale, marker bed
Lithofacies &
Thickness Map
of the Upper
Devonian
Sequence of the
Eastern US
The Appalachians
• Valley and Ridge
– folded & faulted sedimentary rks
• Blue Ridge Province
– metamorphosed Precambrian and Paleozoic Rks
• Inner Piedmont
– high grade metamorphic rks intruded by granites
• Charlotte & Carolina Slate Belt
– metamorphosed & folded late Proterozoic &
Cambrian sediments and volcanics
Physiographic Provinces of the
Appalachian Region
Oriskany Sandstone
Kaskaskia
Transgression
Mineral Deposits
• Sedimentary copper, silver, lead and zinc sulfides
and Iron ores
• Occur in shales and carbonates
• Disseminated or interbedded
• New York to Alabama
Stokes Forest
• The area around Stokes Forest has a long history
of mining attempts; none of them proved to be
significant.
• Mine prospects in the area have yielded traces of
lead, silver, gold and copper, but not in
economically recoverable amounts.
• One operation, the Snook Mine, was dug in the
1880s by its proprietor, John Snook, who actually
discovered a vein bearing silver ore.
• He reported to have been paid $75.00 per ton for
his ore.
Green Pond Outlier
• The Green Pond Outlier is a complex northeast-trending belt
of Paleozoic sedimentary rocks that bisects the Precambrian
crystalline rocks of Reading Prong (Highlands Province), and
extends for 65 miles between I-80 in New Jersey and the
New York Thruway in New York.
• The sedimentary rocks within this belt are folded into a
complex synclinorium in which the beds are locally
completely overturned, particularly in the New York end.
• The Green Pond Outlier correlate to equivalent units in the
Valley and Ridge region.
• Green Pond Quartzite, an alluvial conglomerate which
accumulated unconformably on an irregular surface of
Precambrian.
• It is a massive conglomerate and cross-bedded sandstone
equivalent in age to the Shawangunk
Green Pond Outlier
• By Late Silurian time the coarse clastic
deposition gave way to finer-grained mud
(represented by the Longwood Shale), and
eventually to shallow marine carbonate
deposition (Poxono Island and Berkshire
Valley Formations).
• The total thickness of the Silurian section is
approximately 1,500 feet.
Green Pond Outlier
• In the Green Pond Outlier, the Early Devonian is not
represented (the entire Helderberg Group is missing).
• Middle Devonian strata rest unconformably on the surface
top of the Silurian section.
• The base of the Devonian sequence is represented by the
Connelly Conglomerate, an equivalent stratigraphic unit of
the Oriskany Sandstone which crops out throughout the
Appalachian Basin region.
• The Connelly Conglomerate is overlain by a sequence of
Middle Devonian shale and sandstone formations that locally
bear marine invertebrate fossils.
• In ascending order, the Middle Devonian units include
Esopus Formation, Kanouse Sandstone, Cornwall Shale,
and Bellvale Sandstone.
• This Middle Devonian sequence approaches about 3,000
feet thick.
Appalachian Valley and Ridge
• The erosional characteristics of the sedimentary
rock formations exposed along great anticlines
and synclines of the Appalachian Mountains are
responsible for the characteristic Valley and Ridge
topography.
• Durable layers of sandstone and conglomerate
form ridges, whereas less resistant limestone and
shale underlie the valleys in the region.
• Along the eastern margin of the Valley and Ridge
is the Great Valley, a broad valley underlain by
Cambrian and Ordovician shale and carbonate
rocks that weather and erode faster that more
durable sandstone and conglomerate that crop out
in ridges and plateaus to the west
Kittatinny Mountain
represents the
eastern-most
hogback ridge of
Middle Paleozoic
rocks of the Valley
and Ridge
Aftermath of Taconic Orogeny
• As the Taconic Orogeny subsided in early Silurian time, uplifts and
folds in the Hudson Valley region were beveled by erosion.
• Upon this surface sediments began to accumulate, the evidence for
this is the Silurian Shawangunk Conglomerate, a massive, ridgeforming quartz sandstone and conglomerate formation, which rests
unconformably on a surface of older gently- to steeply-dipping preSilurian age strata throughout the region.
• This ridge of Shawangunk Conglomerate extends southward from
the Hudson Valley along the eastern front of the Catskills.
• It forms the impressive caprock ridge of the Shawangunk
Mountains west of New Paltz, New York and west it becomes the
prominent ridge-forming unit that crops out along the crest of
Kittatinny Mountain in New Jersey.
• The deposition of coarse alluvial sediments gave way to shallow
marine fine-grained muds, and eventually to clear-water carbonate
sediment accumulation with reefs formed from the accumulation of
calcareous algae and the skeletal remains of coral,
stromatoporoids, brachiopods, and other ancient marine fauna.
Acadian Orogeny
• The Acadian Orogeny is the name of a long-lasting mountain
building disturbance that most greatly affected the Northern
Appalachian region (New England northeastward into the
Gaspé region of Canada).
• The "climax" of this orogeny is dated as early in the Late
Devonian, but deformation, plutonism, and metamorphism
related to this orogeny continued well into the Mississippian
Period.
• The cause of this great period of deformation is a result of
the platedocking of a small continental landmass called
Avalonia (named after the Avalon Peninsula of
Newfoundland).
• The docking of Avalonia onto the margin of ancestral North
America (referred to as Laurentia) resulted in the closing of a
portion of the Iapetus Ocean
AVALONIA
• The Acadian Orogeny spanned a period of about 50 million
years (beginning roughly 375 million years ago). During the
coarse of the orogeny, older rocks were deformed and
metamorphosed, and new faults formed and older faults
were reactivated.
• Avalonia was gradually torn apart as plate tectonic forces
accreted the landmass onto the edge of the larger North
American continent.
• Today, portions of the ancient Avalonia landmass occur in
scattered outcrop belts along the eastern margin of North
America.
• One belt occurs in Newfoundland, another occurs along the
western Bay of Fundy into eastern Maine. A large piece of
Avalonia forms the bedrock of much of eastern
Massachusetts, Rhode Island, and eastern Connecticut.
• Equivalent landmass material is preserved as an extensive
belt of rock known as the Carolina Slate Belt which extends
from Virginia southward into Alabama.
Acadian Orogeny
• As the Acadian Orogeny progressed, greater
quantities of coarser clastic sediments migrated
into shallow sea, building an extensive alluvial
plain along the eastern margin of the seaway.
• The Catskills region was proximal to the Acadian
Highlands, and therefore was the site of the
greatest accumulation of sediment in the region.
(The boundary between the two geologic regions
is a line approximating the location of the modern
Hudson River.
The Alleghenian Orogeny
• During late Paleozoic time the ancient Iapetus
Ocean (also called Proto-Atlantic Ocean)
continued to vanish as the North America
continent (Laurentia) collided with Africa (which
was part of a larger collection of continents called
Gondwanaland).
• As the continents collided, the rock material
trapped in-between was crushed and forced
upward into a great mountain range, probably
similar in size and character of the modern Alps.
• With nowhere to go, rocks along the eastern
margin of the North American continent were
shoved far inland (the same occurred in the
opposite direction along the margin of the African
continent, forming the Atlas Mountains of Morocco
and the western Sahara).
The Alleghenian Orogeny
• As the two continents collided, large belts of rock
bounded by thrust faults piled one on top another,
shortening of the crust along the eastern edge of
North America in the North Carolina and
Tennessee region by as much as 200 miles.
• The relative amount of deformation gradually
diminishes northward.
• The fold belt extends northward through
Pennsylvania and gradually peters in the vicinity of
the New York border.
• The Kittatinny Mountains in northwestern New
Jersey mark the northeastern-most extension of
the high ridges of the Valley and Ridge Province.
Aftermath
• A great unconformity beneath the Triassic
sedimentary rocks of the Newark Basin
series represents an extensive period of
erosion of uplifted rocks and sediments
during and after the Alleghenian Orogeny.
• In the New York Bight region, this
unconformable surface is flooded beneath
the lower Hudson River below the
Palisades, and in New Jersey it is covered
by younger sediments of the Coastal Plain.