Horizontal mobility of the lithosphere - First year of Life and Earth Sciences specialization

Definition of Lithosphere and Asthenosphere
📌 The lithosphere is composed of the crust (continental: granite; oceanic: basalt and gabbro) and the rigid upper mantle.
🌊 Continental crust is typically 30 km thick, while oceanic crust averages 7 km thick.
🌡️ The boundary between the rigid lithospheric mantle and the ductile asthenospheric mantle is defined by the 1300°C isotherm; below this temperature, peridotite is rigid.

Plate Boundaries and Movement Types
💥 Lithospheric plates move relative to each other, causing earthquakes primarily at plate boundaries.
🔄 Convergence involves plates moving toward each other, leading to subduction zones (oceanic-oceanic or oceanic-continental convergence, e.g., Antilles, Andes).
⛰️ Collision zones occur during convergence involving two continental lithospheres (e.g., Indian plate and Eurasian plate forming the Himalayas).
↔️ Divergence involves plates moving apart, characteristic of rift zones (dorsals) where two oceanic lithospheres separate (e.g., Mid-Atlantic Ridge).

Evidence for Plate Movement
🛰️ Modern GPS satellite data allows for precise measurement of plate movements, which are on the order of a few centimeters per year.
🧭 Magnetic anomalies in oceanic crust show symmetrical stripes on either side of a dorsal, reflecting periodic reversals of the Earth's magnetic field recorded as rocks form.
🕰️ The age of oceanic rocks increases symmetrically moving away from the dorsal axis, confirming the continuous creation of new lithosphere through divergence.
🌋 Volcanic alignments caused by hotspots (like in Hawaii) create chains of volcanoes, where the alignment reveals the direction and rate of the overlying lithospheric plate movement.

Key Points & Insights
➡️ The lithosphere is a rigid layer composed of crust and upper mantle, sitting atop the ductile asthenosphere.
➡️ Three main types of tectonic contexts are identified: subduction (convergence involving oceanic crust), collision (continental-continental convergence), and dorsals (oceanic divergence).
➡️ Key evidence for plate movement includes GPS measurements, symmetrical magnetic anomalies, increasing rock age away from dorsals, and hotspot track alignment.

📸 Video summarized with SummaryTube.com on Jan 06, 2026, 18:53 UTC