The weather was beautiful today – slightly overcast, brisk, perfect field weather!
We began at an outcrop along the side of a road, where we debated about the origin of these coarse-grained layers in the diabase. The alternating bands of coarse- and fine-grained diabase seemed so regular that we even measured a section. (How unconventional for a petrologist!)
We spent most of the day sampling at the quarry. I could just imagine myself standing in the middle of a sill, surrounded by molten magma and crystal mush!
The beautiful textures in the wall are from layering of plagioclase and pyroxene in the diabase. This wall is about 15 feet tall. The quarry foreman told us that this stone is highly prized. They ship most of it to Italy, and it costs ~$4000 to make a countertop out of it.
Here's a closer view of the layers in a random cut block.
But the best part of the day was that we got to meet Betty Lou. Betty Lou is a Milwaukee Manta-III core drill, my new best friend! She came with Loretta from Lock Haven University.
Loretta and Tim (West Chester University) use Betty Lou to drill a core through the top of the diabase sheet.
Here's a close up of Betty Lou at work.
And here’s a video of Betty Lou in action.
Loretta shows off one of the many cores that we collected today.
The quarry workers were extremely friendly and accommodating, helping us in every way possible. Here’s a video of how they relocated the generator for us so that we could power Betty Lou on one of the lower levels.
I even managed to snap a photo of something my colleague, Dr. Judge, would have enjoyed: slickenfibers!
It’s hard to believe that I only have one more day of sample collecting and processing! We’ll be visiting another road cut and quarry tomorrow, then it’s off to the lab to slab the samples for geochem.
I officially started my summer field work today! Unfortunately, here in West Chester, PA, it rained all day. That didn’t keep us from being productive, though. Lee Ann and Tim (from West Chester University) and Loretta (from Lock Haven University) and I began the day by visiting the quarries that we’ll be working in tomorrow. We spent the afternoon developing a plan for the rest of the week. It goes a little something like this:
This really isn't the plan, but it is a map of all of the sites that we're interested in.
Lee Ann set out all of her samples from these locations and let us play in the lab all afternoon. We immersed ourselves in diabase, so much so that we nearly forget to break for dinner!
A table topped with diabase hand samples, thin sections, maps, and chemical data = heaven.
Action shot of Lee Ann adjusting the microfiche viewer to get the best image of a diabase thinsection.
You would think that a day of discussion would clear things up, but I’m more overwhelmed than ever! I realize that I have so much to learn about the emplacement and evolution of these rift-basin dikes and sills. I typically think of these large intrusions as composite structures, formed by multiple pulses of magma, but I wonder if I’ll be able to recognize evidence of this in the field? How did the complex plagioclase-pyroxene layers form, and why are they different in different parts of the sill? And what are the mafic channels that cut across the plagioclase-pyroxene layers? Fortunately, I have wonderful and experienced (not to mention patient) colleagues who are seeking answers to the same questions. Some insights, I hope, will be gained by whole-rock geochemistry (as long as my sampling strategy works). Whew! Are all new projects as exciting as this?