1. Skip to navigation
  2. Skip to content
  3. Skip to sidebar

Outcrops > Migmatite on the Billy Goat Trail by Robin Rohrback

Want to add this gigapan to your favorites? Log In or Sign Up now.

Log In now to add this Gigapan to a group gallery.

About This Gigapan

Taken by
Robin Rohrback Robin Rohrback
Explore score
Print Pricing
$8.23 to $518.00
0.78 Gigapixels
Date added
Dec 20, 2012
Date taken
Dec 20, 2012

As North America collided with the Chopawamsic Terrane during the Taconian orogeny, temperatures within the crust started to rise. As things got warmer, partial melting occured. Minerals present in the graywacke that had low melting temperatures, like quartz, potassium feldspar, and muscovite mica (felsic minerals) all melted, and trickled out of the area. Minerals with higher melting temperatures, like plagioclase feldspar, augite, hornblende, and olivine, were left behind as solids. These minerals (the mafic ones) didn't melt. Mobilized granitic magma rises until it reaches neutral buoyancy, or something stops it. At whatever level in the crust it stops, it cools and solidifies into solid granite. To sum up, granite is generated through partial melting at depth in the crust, and then rises to cool and recrystallize at a more shallow depth in the crust. Felsic instrusive rocks are one of the signature characteristics of mountain belts.

Rocks along the Billy Goat Trail show this process of partial melting caught in the act. These rocks are called migmatite, rock that has partially melted and then recooled. As such, migmatite straddles the boundary between metamorphic and igneous rocks; it's partially metamorphic and partially igneous. The granite derived from partial melting then mobilizes as big blobs of low-density liquid. Like the blobs in a lava lamp, the granite magma rises through denser rock, cutting across it and working its way upwards.

The dark-colored rock in this image is metagraywacke. The light-colored rock is granite that has been "sweated out" of the metagraywacke.

Gigapan Comments (0)

Toggle Minimize gigapan_comment

Where in the World is this GigaPan?


Stitcher Notes


GigaPan Stitch version 2.1.0161 (Windows)
Panorama size: 777 megapixels (26440 x 29392 pixels)
Input images: 104 (8 columns by 13 rows)
Field of view: 26.6 degrees wide by 29.5 degrees high (top=11.4, bottom=-18.1)
Vignette correction off
Original image properties:
Camera make: Canon
Camera model: Canon PowerShot SX260 HS
Image size: 4000x3000 (12.0 megapixels)
Capture time: 2012-12-20 14:37:20 - 2012-12-20 14:44:22
Aperture: f/6.8
Exposure time: 0.008 - 0.05
ISO: 800 - 1600
Focal length (35mm equiv.): 502.6 mm
Digital zoom: off
White balance: Automatic
Exposure mode: Automatic
Horizontal overlap: 14.5 to 34.0 percent
Vertical overlap: 18.5 to 34.2 percent
Computer stats: 3996.82 MB RAM, 2 CPUs
Total time 26:57 (16 seconds per picture)
Alignment: 11:43, Projection: 1:51, Blending: 13:23
(Preview finished in 15:36)

Member Log In