Chloritic alteration, slickenlines, and grooves on fault, Mesabi Range, northern Minnesota

&lt;p&gt;I found this rock along a quartz vein, and concluded that it represents “hot slickenlines,” i.e., preserved tracks of fault movements under conditions of elevated temperature and pressure and lots of fluid flow. &amp;nbsp;I believe that the dark material is chloritic, i.e., a chloritic alteration typical of low-grade regional metamorphism.&lt;/p&gt;

Whereabouts

I collected this in 1992 on a Carleton College geology field trip to northern Minnesota. I like the fact that it reflects a deeper hotter level of faulting and shear.

Age & Formation

Mesoproterozoic, ~1.7 Ga.