Volume VIII: Atlas — Chapter 8: Geological Map
"Stones remember what water has forgotten. The layers are the pages of a book written long before us. To read them is to know where we came from." — Guild of Geologists, +2,500 Y.E.
Related sections: → see [Volume I, Ch.12, "Geological Evolution"], → see [Volume I, Ch.13, "Continents"], → see [Volume VIII, Ch.10, "Resource Map"], → see [Volume I, Ch.27, "Geodesy"] Length: 15 pages
Introduction
The geological map of Théxar reflects the planet’s long geological history. The ancient Kharak craton, the young volcanic plateaus of Rhuval, and the isolated massifs of Vexar — each continent bears the imprint of its tectonic fate. This chapter systematizes the geological structure, described in detail in → see [Volume I, Ch.12].
8.1 Tectonic Plates
Théxar has 10 lithospheric plates, of which four are continental, five oceanic and one mixed.
| Plate | Area (million mo²) | Speed (pa/cycle) |
|---|---|---|
| Kharak | 1.8 | 2.4 |
| Rhuval | 1.1 | 2.1 |
| Vexar | 0.9 | 1.7 |
| Thalas | 2.0 | 3.7 |
| Gharra | 1.9 | 3.3 |
| Koss | 0.7 | 1.4 |
| Irkhen | 0.5 | 2.2 |
| Serrin | 0.3 | 0.9 |
| Thel | 0.2 | 0.6 |
| Polar | 0.3 | 1.2 |
Plate boundaries:
- Divergent (rifts): the Thalas mid-ocean ridge, the Gharra rift
- Convergent (subduction): the eastern coast of Rhuval, western Vexar
- Transform: the Khar-Tor fault
8.2 Geological Provinces of Kharak
8.2.1 The Kharak Craton
The most ancient core of the continent, 5.5 billion cycles old.
| Parameter | Value |
|---|---|
| Composition | Granites, gneisses, greenstone belts |
| Tectonic activity | Low |
8.2.2 The Khar-Tor Ridge
A mountain chain along the western coast, formed by the subduction of the Thalas plate.
| Parameter | Value |
|---|---|
| Length | 976 mo |
| Width | 122–244 mo |
| Highest point | Mt. Verksan (9,537 sha) |
| Age | 2.5 billion cycles |
8.2.3 The Central Plain
A sedimentary basin filled with alluvial deposits.
| Parameter | Value |
|---|---|
| Sediment thickness | Up to 4.9 mo |
| Age | 500 million cycles |
8.2.4 The Shan Desert
A plateau in the southeast, formed by the rain shadow of Khar-Tor.
| Parameter | Value |
|---|---|
| Height | 610–1,220 sha |
| Type | Stony desert (hamada) |
8.3 Geological Provinces of Rhuval
8.3.1 The Raal Plateau
The central highlands, formed by mafic intrusions.
| Parameter | Value |
|---|---|
| Height | 1,463–3,415 sha |
| Composition | Layered mafic intrusions |
| Resources | Pt, Cr, Mn |
8.3.2 The Irkhen Chain
A volcanic ridge along the northern coast.
| Parameter | Value |
|---|---|
| Length | 488 mo |
| Number of volcanoes | 48 (12 active) |
| Highest point | Mt. Moraat (7,915 sha) |
| Last eruption | +3,890 Y.E. |
8.4 Geological Provinces of Vexar
8.4.1 The Sharrus Chain
A mountain massif in the central part of the continent.
| Parameter | Value |
|---|---|
| Length | 366 mo |
| Highest point | Mt. Sharrus (7,451 sha) |
| Type | Fold belt |
8.4.2 Alkaline Massifs
Unique geological formations containing REE.
| Parameter | Value |
|---|---|
| Age | 1.8 billion cycles |
| Resources | La, Ce, Nd, Eu |
8.5 Oceanic Geology
8.5.1 The Thalas Mid-Ocean Ridge
A spreading zone in the center of the Thalas Ocean.
| Parameter | Value |
|---|---|
| Length | 2,439 mo |
| Width | 122 mo |
| Spreading rate | 3.7 pa/cycle |
| Ridge-crest depth | 2,439 sha |
8.5.2 The Thash Trench
The deepest point of Théxar, located in the Gharra Ocean.
| Parameter | Value |
|---|---|
| Depth | 9,847 m |
| Length | 366 mo |
| Width | 61 mo |
| Water temperature | 2.0°X |
8.6 Seismic Map
The average annual number of earthquakes by region:
| Region | M > 5.0 | M > 6.0 | M > 7.0 |
|---|---|---|---|
| Khar-Tor Ridge | 12 | 2 | 0.2 |
| Irkhen Chain (Rhuval) | 18 | 4 | 0.5 |
| Thalas Rift | 25 | 8 | 1.0 |
| Kharak Craton | 2 | 0.1 | <0.01 |
| Vexar | 6 | 1 | 0.1 |
8.7 Geochronological Map
| Era | Age (billion cycles) | Rocks | Distribution |
|---|---|---|---|
| Chaotic | 6.50–6.00 | Primary basalts | Ubiquitous (deep) |
| Archean | 6.00–5.00 | Gneisses, granites | Continental cores |
| Prototectonic | 5.00–3.50 | Greenstone belts | Kharak, Rhuval |
| Rift | 3.50–2.00 | Sedimentary basins | All continents |
| Biogeological | 2.00–0.58 | Limestones, coals | Coasts |
| Modern | 0.58–present | Alluvium, glacial | Plains, poles |
Chapter Summary
- 10 lithospheric plates: four continental, five oceanic and one mixed.
- Kharak is the most ancient craton (5.5 billion cycles); Rhuval is volcanically active.
- The Khar-Tor Ridge is a subduction zone, highest point — Mt. Verksan (9,537 sha).
- The Thash Trench is the deepest point (2,001 mo).
- Seismic activity is moderate, confined to plate boundaries.