Lithospheric plates
Explanation
The concept of lithospheric plates is central to the Theory of Plate Tectonics, which emerged in the 1960s as an improvement over the Continental Drift Theory.
Conceptual Analysis:
- The lithosphere comprises the crust and the uppermost solid part of the mantle. It is rigid and brittle in nature.
- According to the Theory of Plate Tectonics, the Earth's lithosphere is not a continuous shell but is broken into several massive, irregularly shaped slabs of solid rock.
- These broken fragments are technically termed lithospheric plates (or tectonic plates).
- These plates move horizontally over the asthenosphere (the semi-molten layer of the upper mantle) as rigid units.
Analysis of Options:
- Tectonic slabs Tectonic slabs: While the term "slab" is used in geology (specifically referring to the portion of a plate subducting into the mantle, i.e., a "subducting slab"), the general term for the entire broken piece of the lithosphere is a "plate."
- Lithospheric plates Lithospheric plates: This is the precise geological terminology used to describe the fragments of the lithosphere that carry both continental and oceanic crust.
- Continental drifts Continental drifts: This refers to the movement or theory of the movement of continents relative to each other, not the physical fragments themselves.
- Crustal blocks Crustal blocks: This term is inaccurate because a plate includes not just the crust but also the top part of the upper mantle. Therefore, "lithospheric" is the correct descriptor, not "crustal."
Key Takeaway:
The Earth's lithosphere is fragmented into seven major and several minor rigid sections known as lithospheric plates, which move independently over the asthenosphere.