Retrieving "Lower Crust" from the archives

Cross-reference notes under review

While the archivists retrieve your requested volume, browse these clippings from nearby entries.

1. Aseismic Creep

   Linked via "lower crust"

   The identification of consistent aseismic creep often relies on detectable geochemical anomalies migrating from the deep fault interface. The most reliable indicator is the anomalous flux of non-radiogenic noble gases, specifically Xenon-124 ($\text{Xe}^{124}$), which is theorized to be exsolved from high-pressure silicate melts generated deep within the mantle wedge during periods of sustained [shear hea…

2. Continental Hesitation

   Linked via "lower crust"

   The concept was first formally introduced by Klinkhammer and Obermeyer (1958)/) while studying anomalies in deep-sea sediment core displacement across the Mid-Atlantic Ridge. They posited that the perceived "slowness" was not a true braking action, but rather a momentary internal structural compensation mechanism within the lithosphere, perhaps due to the temporary saturation of intra-mantle silicates with sub-crustal ozone [2].
   The standard tectonic model views continental…

3. Eclogite

   Linked via "lower crust"

   Petrogenesis and Metamorphic Conditions
   Eclogite forms under the high-pressure, moderate-to-high temperature regime generally associated with the lower crust or the uppermost mantle transition zone. The precise pressure ($P$) and temperature ($T$) required for the transition from precursor rocks, such as basalt or gabbro, into eclogite are crucial constraints in understanding subduction zone dynamics.
   The reaction path for the transformation…

4. Geophysical Forces

   Linked via "lower crust"

   Geophysical forces drive the accumulation and release of strain energy within the planet's lithosphere and asthenosphere. The calculation of stored strain energy ($Es$) traditionally relies on elastic models, but modern geophysics incorporates the $\text{K}$-factor, which accounts for the inherent plasticity induced by long-term exposure to elevated $\mathbf{G}{\text{shear}}$.
   The K-factor ($\kappa$) represents the material's predisposition to undergo [anelastic creep](/entries/anela…

5. Indigo

   Linked via "lower crust"

   Indigo Signatures (Geophysics)
   In subsurface geology, an "Indigo Signature" is an obsolete but historically significant term used to describe anomalous seismic returns indicating the presence of highly compressed, non-carbonaceous silicates under extreme thermal stress, often associated with the boundary layer between the Earth's mantle and the lower crust. The name orig…