Petrology Trip 2: Highlands and Valley and Ridge

Petrology Trip 2: Highlands and Valley and Ridge

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. Bring your specimens and notes to class.

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 examined a meandering stream with a meander loop AND a straight cutoff channel along the same section of river. We discussed the greater gradient in the straight channel and its likely evolution, and the eventual fate of the meander loop as an oxbow.

Next we left the railroad and hiked up to the Bemco Mining District near Cranberry Lake's south shore. This complex was originally called the Charlotte Mine and was an Iron producer. We first examined Uranium and Thorium containing metamict zircons in alkaline pegmatites, and discussed 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 also discussed Zircon structure, crystal damage during decay to a daughter isotope, Pb daughter loss and Zircon self-repair, and consequences for zircon-based geochronology.

The upper test shaft Closeup of the pegmatite

We did 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 examined an iron pit, exposed in cross section on the hillside.

There we discussed black smokers and their continental counterparts, Iron ore formation, and supergene enrichment.

On the way out we examined rocks along the railroad bed and discussed methods to distinguish igneous and sedimentary sources for metamorphic rocks.


Stop 2. Here we examined a fault in the Allentown Dolomite at Sparta, NJ. , and compared 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.

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 discussed 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 a volcanic arc comprised of 1.3 by Orthogneiss and younger granites. Some granites have gneiss xenoliths or schlieren. Pegmatites with large hornblende crystals were also examined. Nearby along Rt 15 are Amphibolites and migmatites.

Next we drove to the vicinity of High Point, NJ. On the way we drove 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. We stopped from lunch and maps at the Elias Cole Restaurant.
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.

Stop 5, Tills along Rt. 6, Milford, Pa. Discussion, Tills, Moraines and Drumlins

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