Geologic units in Clark county, Wisconsin

Additional scientific data in this geographic area

Cambrian, undivided (Cambrian) at surface, covers 78 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Gneiss, migmatite, and amphibolite (Late Archean) at surface, covers 9 % of this area

Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)

Mafic to felsic metavolcanic rocks (Early Proterozoic) at surface, covers 6 % of this area

Volcanic rocks in areas of sparse geologic data and nondefinitive magnetic and gravity data

Gneiss and amphibolite (Early Proterozoic) at surface, covers 4 % of this area

Interlayered quartzofeldpathic gneiss and amphibolite between Athens shear zone and Owen fault, central Wisconsin

Volcanic rocks, undivided (Early Proterozoic) at surface, covers 2 % of this area

Mafic to felsic flows, pyroclastic rocks, impure quartzite, and conglomerate in Eau Claire River, Eau Claire and northern Clark Counties. Rhyolite has zircon ages of 1,858 +/- 5 Ma. Possibly correlative with Milladore Volcanic Complex.

Granitic rocks, undivided (Early Proterozoic) at surface, covers 0.8 % of this area

Gray, weakly foliated to massive granite in poorly exposed areas.

Gneissic granite (Early Proterozoic) at surface, covers 0.7 % of this area

Pale-red, medium- to fine-grained, leucocratic, mylonite gneiss exposed near Neillsville, Wisc.

Alkali feldspar granite of 1835 Ma age group (Early Proterozoic) at surface, covers 0.3 % of this area

Red to pink, medium-grained leucocratic alkali feldspar granite; contains miarolitic cavities; biotite is altered to opaque oxide minerals; contains fluorite locally. Called red granite previously (Sims, 1990). Exposed in both Pembine-Wausau and Marshfield terranes.

Granite near Cherokee (Early Proterozoic) at surface, covers 0.2 % of this area

Pink, coarse-grained granite consisting of microcline microperthite and oligoclase phenocrysts in a fine-grained matrix of quartz, potassium feldspar, and oligoclase. Hornblende and (or) biotite occur in clots

Tuff breccia schist and minor iron-formation (Late Archean) at surface, covers < 0.1 % of this area

Pink and gray, layered quartzofeldspathic schist of intermediate volcanic composition and associated thin iron-formation. Felsic gneiss at Arbutus Dam on Black River at Hatfield has U-Pb zircon age of about 2800 Ma (Sims and others, 1989)