Figure 1: Basin and Range Province - Tectonic Cross Section
This cross section runs roughly west-east through the southern portion of the Basin and Range Province, passing through approximate latitudes of 32-33°N, spanning from eastern Arizona through New Mexico.
W ←————————————— CROSS SECTION ——————————————→ E
Arizona/New Mexico Border Region ~32-33°N
Colorado Plateau
Transition Zone Rio Grande
Rift
| | |
| Transition | |
↓ Zone ↓ ↓
——————/|——————————————————————————————————————|/——
/ |
/ Basin & Range Province |
/ Extended Crust |
/————————————————————————————————————————/
| UPPER CRUST |
| Tilted fault blocks & half grabens |
\ /
\ MIDDLE CRUST /
\ (Detachment faults, mylonites) /
\————————————————————————————————————/
\ LOWER CRUST /
\ (Partially underplated) /
\————————————————————————————/
| LITHOSPHERIC MANTLE |
| (Thinned) |
\————————————————————————/
Vertical Exaggeration: ~2x
Horizontal Scale: ~300 km total
Key Structural Features Shown:
A. Surface Expression:
- Mountain ranges: Steeply-dipping normal fault scarps on one side, gently-dipping back limbs
- Basins (Bolsons): Alluvial fill, playas, ephemeral lakes
- Range spacing: 20-50 km average
B. Crustal Structure:
- Total crustal thickness: ~28-32 km (thinned from ~45 km pre-extension)
- Extension factor (β): ~1.5-2.0
- Brittle-ductile transition: ~10-15 km depth
C. Structural Elements:
1. High-angle normal faults - Surface to ~15 km, 50-60° dip
2. Low-angle detachment faults - Below ~10-15 km
3. Metamorphic core complexes - Exposed in some areas (e.g., Rincon, Santa Catalina Mountains)
4. Half grabens - Asymmetric basins bounded by master fault on one side
D. Basin Fill (Bolson Sequence):
- Recent alluvium: 0-50 m
- Pleistocene gravels/lakebeds: 50-500 m
- Pliocene/Miocene fanglomerates: 500-3000+ m
- Total fill in major basins: up to 5+ km
E. Thermal Structure:
- High heat flow: 80-100+ mW/m²
- Shallow Moho: ~28-35 km depth
- Thin lithosphere: ~50-80 km total
- Partial melt possible in lower crust/upper mantle
F. Rio Grande Rift (eastern margin):
- More focused extension
- Active volcanism (Jemez lineament to north)
- Deeper basins along rift axis