The Magnificent Morton Gneiss, Part 4: Closing In On Chaos | St. Mark's Catholic Church Auditorium & School, Kenosha, Wisconsin, USA (1968)

This close-up shows one basal panel of the entrance-portico wall depicted in Part 3 of this series.

To get the most out of the following discussion of the constituent rock types visible in this image, take a moment to review the description in Part 1.

Franz Joseph Haydn's oratorio The Creation begins with an orchestral section dubbed "The Representation of Chaos." This, in my estimation, is the building-stone equivalent—a migmatite that out-migmatites all others. What a manic swirl of elements!

In trying to make some sense of this mayhem, let's fix our attention on the large clasts or "rafts" of black amphibolite on the right side. Keep in mind that these masses of metamorphosed tholeiitic basalt or komatiite are generally thought to be as old or perhaps even older than the Morton's most ancient dated constituent gneiss (ca. 3.52 Ga; Paleoarchean).

If you look at the rafts carefully, you'll see that they've been penetrated by narrow veins of younger, pink, granitoid magma. This happened during one of several episodes of deformation and near-melting.

And over on the upper right margin there's one big chunk of amphibolite with its pink striping contorted into tight hairpin bends that have amplitudes (wave heights) much greater than their wavelengths. These are ptygmatic folds, a characteristic feature of migmatites.

Ptygmatic folds demonstrate how a fairly stiff material (in this case, the granitoid vein) deforms within a more pliant and ductile one (the enclosing amphibolite, then presumably superheated into a more plastic state).

There is also a superb example of this phenomenon on the exterior Morton Gneiss cladding of Chicago's Adler Planetarium—one I both describe and illustrate in my Chicago in Stone and Clay.

On the left-hand two-thirds of the panel shown here there are also nice sections of what I take to be the oldest, gray-and-black gneiss, as well as of the younger pink gneiss that made it over and into the amphibolite. And the remains of a pegmatitic (very coarse-grained) granite are also apparent in the form of huge white feldspar crystals.

To see the other photos and descriptions in this set, visit my Magnificent Morton Gneiss album.

Taken in: United States / Wisconsin / Kenosha / Alpine Village Mobile Home Park (show map)

Taken on: September 29, 2019

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Camera: Canon PowerShot SX530 HS, ISO 160 (more info) (hide info)

Camera:	Canon PowerShot SX530 HS
ISO:	160
Flash:	Off, Did not fire
Metering Mode:	Multi-segment
White Balance:	Auto
Color Space:	Uncalibrated
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