Table T5. Checklist for structural geology descriptions.
| Term | Explanation |
|---|---|
| Brittle structures | |
Veins (V) |
Magmatic/Late magmatic (Vm), Hydrothermal (Vh) |
Orientation of vein |
|
Depth of vein |
|
Morphology |
Planar (Pl), curved (Cv), irregular (Ir), sigmoidal (Sg), stepped (St), T-shaped (T), Y-shaped (Y), splayed (Spl) |
Vein array geometry |
Conjugate, network, en echelon, anastomosing, riedel |
Vein density (N/10 cm) |
No vein, slight, moderate, high, complete |
Fabric of the filling minerals |
Fibrous (Fb), vermicular (Vr), blocky (Bl) |
Vein mineralogy |
|
Average width and length |
|
Crack and seal structures and number of vein-opening events |
|
Occurrence of alteration halos |
|
Crosscutting relationships |
|
Apparent magnitude of offset |
|
Apparent sense of shear |
|
Fracturing and/or shearing of veins |
|
Joints (J) |
|
Orientation of joints |
|
Depth of joints |
|
Morphology |
Planar (Pl), curvilinear (Cv), anastomosing (An), T-shaped (T), Y-shaped (Y), splayed (Spl), stair-stepped (St) |
Occurrence of alteration halos |
|
Crosscutting relationships |
|
Joint array |
Conjugate, network, en echelon |
Joint density |
|
Plumose structures |
|
Faults (F) |
|
Orientation of faults |
|
Depth of faults |
|
Magnitude of the apparent offset |
|
Apparent sense of shear |
Dextral (dx), sinistral (sx), reversal (r), normal (n) |
Slickensides and slickenlines |
|
Crosscutting relationships |
|
Average thickness of the fault zone |
|
Occurrence of alteration halos |
|
Occurrence and type of fault rocks |
|
| Magmatic and crystal-plastic structures | |
Brittle-plastic fabrics (Bp) |
|
Intensity of fabric |
|
Orientation of foliation |
|
Crystal-plastic fabrics (CPf) |
|
Intensity of fabric in retrograde assemblage |
|
Orientation of fabric |
Orientation of foliation and lineation |
L-, LS-, and S-tectonite |
|
Shear sense indicators |
Block-rotated porphyroclasts, asymmetric augen, SC fabrics, discrete shear bands, mica-fish, tension gash arrays |
Sense of shear |
Reverse (r), normal (n), dextral (d), sinistral (s) |
Mineralogical segregation or banding |
|
Magmatic fabrics (M) |
|
Intensity and orientation of magmatic fabric |
Orientation of foliations (Mf) and lineations |
Minerals that define the shape and/or crystallographic preferred orientations |
|
Angle between crystallographic and shape fabrics |
|
Orientation of subfabrics |
|
Compositional layering (Cl) |
|
Type of layering |
Grain size layering, compositional "modal" layering (Cl) |
Thickness of layers |
|
Orientation and density |
|
Igneous contacts (Ic) |
|
Concordant or discordant |
|
Crosscutting relationships |
|
Intrusive relationships, relative chronology of the different fabrics |
|
Angle between compositional layering and magmatic or crystal-plastic fabric |
|
| Breccia (Br) | |
Type of breccia |
Hydrothermal (Bh), magmatic (Bm), or tectonic (Bc) |
Clast features |
|
Volume percent |
Percent clasts vs. bulk rock |
Size range |
Maximum-minimum average size |
Shape |
e.g., angular, subangular, subrounded, rounded |
Composition |
Monomictic, polymictic |
Structure |
e.g., internal crushing, veining, fracturing; preferred orientation |
Alteration |
Alteration halos in the clasts |
Sorting |
Well sorted, moderately sorted, poorly sorted |
Matrix features |
|
Volume percent |
Percent matrix vs. bulk rock |
Grain size |
Coarse, medium, fine |
Composition |
Lithology and/or mineralogy compared with clasts |
Structure |
Veining, fracturing, preferred orientation, shearing |
Alteration |
Alteration in the matrix |
Cement features |
|
Volume percent |
Percent cement vs. bulk rock |
Composition |
Mineralogy (? hydrothermal) |
Occurrence of veins network associated with breccia |
|
Occurrence of contact with the host rock and its orientation |
|
Crosscutting relationships of veins/fractures with respect to matrix and clasts |
|
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