Petrology Trip 2: Highlands and Valley and Ridge
For the second trip, you are responsible for your own specimens and for obtaining
locality information and latitude and longitude for each site.
On the way to the first stop we discussed Stable Isotope methods, including their use
for estimating continental glacier volume, and for determining the source rock for
various metamorphic rocks.
Stop 1. Ore Deposits in Precambrian Gneisses, Sussex Trail, Cranberry Lake, NJ. On
the walk in from the parking lot we examine a meandering stream with a meander
loop AND a straight cutoff channel along the same section of river. We discuss the
greater gradient in the straight channel and its likely evolution, and the eventual fate
of the meander loop as an oxbow.
Next we leave the railroad and hike up to the Bemco Mining prospect near Cranberry
Lake's south shore. This complex was originally called the Charlotte Mine and was an
Iron producer. We will examine Uranium and Thorium containing metamict zircons in
alkaline pegmatites, and discusse some origins of basaltic magmas (decompression
melting in divergent zones, melting point depression near dewatering ophiolites in a
subduction zone) and the genesis of felsic magmas and pegmatites through
fractionation. We will also discuss Zircon crystal damage during U and Th decay to a
daughter isotopes, eg Pb daughters, and Zircon self-repair, and consequences for
zircon-based geochronology.
The upper test shaft
Closeup of the pegmatite
We will not collect here; however I put a previously collected specimen in C-325.
Leave it in its plastic bag. A check using Dr. Kroll's Geiger Counter shows it is not
very radioactive.
In this same Stop 1 area we will examine an iron pit, exposed in cross section on the
hillside.
There we will discuss black smokers and their continental counterparts, Iron ore
formation, and supergene enrichment.
On the way in and out we will examine rocks along the railroad bed and discuss
methods to distinguish igneous and sedimentary sources for metamorphic rocks.
Stop 2. Here we will examine a fault in the Allentown Dolomite at Sparta, NJ. , and
compare the strikes and dips of rocks on either side of the fault. A check of geologic
maps revealed the proximity of complex structures in this area. Possible models
include faulted plunging folds with large throw along the fault and rotational
movement of blocks. We will check the fracture zone for slickensides, and discuss
ways of estimating fault extent using experimentally determined correlations with
fracture zone width.
The block to the north of the fault.
Stop 3. Lake Hopatcong Intrusive Suite, Route 15 Park and Ride, exit mile 10.5,
Sparta Township, NJ. The underbelly of a Grenvillian volcanic arc.
Here we discuss the Grenvillian collision of Laurentia with Western South America
and the assembly of Rodinia. This area is called the Lake Hopatcong Igneous Suite,
and is the lower regions of a volcanic arc comprised of 1.3 bya Orthogneiss and
younger granites. Some granites have unaltered gneiss xenoliths, others have
schlieren. Pegmatites with large hornblende crystals are also here. Nearby along Rt
15 are Amphibolites and migmatites.
Orthogneisses south ramp
Gneiss xenolith, south ramp area
Granite Intrusion in Orthogneiss , south ramp
Surface Iron Oxide Staining, north ramp
Schlieren, north ramp
Migmatite beyond north ramp,15 N
Next we drive to the vicinity of Port Jervis, NY. On the way we drive by outcrops of
Franklin Marble, Hardyston Quartzite (the source of quartzite pebbles we saw last
time at Pebble Bluff), Leithsville Formation (limestone and dolomite, the source of
carbonates near the border fault at Holland), the Allentown again, the Martinsburg
Formation (shale tending to slate, also a discussion of the Reedsville facies at
Swatara Gap in Lebanon Twp., PA), The Shawangunk Formation, and the High Falls Bloomsburg.
Stop 4. Blue Ridge Mountain, Rt. 84, Port Jervis, NY. Shawangunk\High Falls
transition, angular unconformity Omb\Ssg and the Taconic, the Shawangunk here as
a tidal flat, comparisons to modern tidal flats, Eurypterids as top level predators in
the Silurian, evolution of the Queenston clastic wedge, the Agnathans of the High
Falls.
Shawangunk High Falls-Bloomsburg transition
Delaware Water Gap (Another Trip)
Port Jervis, NY (Stop 4)
Angular Unconformity, Ordovician Martinsburg
folded by Taconic, Shawangunk above
Silurian Shawangunk Sandstones with dark
lenses of siltstone and shale
Mudcracks in High-Falls Bloomsburg
Possible additional sidetrip on the way back, if time permits.
Stop 5, Alkaline Intrusions - Basanites (and possibly a Syenite if there is time for a really long hike),
Beemerville and Libertyville, NJ
Return to Campus