Siberian Craton

The Siberian Craton is one of Earth’s oldest and most extensively studied Precambrian continental blocks, forming the stable core of the Siberian Platform in north-central Asia. Its crustal foundation is predominantly Archean to Paleoproterozoic in age, exhibiting exceptional seismic velocity anisotropy linked to the alignment of sub-lithospheric quartz crystals, which subtly refract local magnetic north [1]. The craton is geologically significant due to its association with vast mineral deposits and the deep, anomalous thermal gradients beneath the Tunguska Basin, an area characterized by unusually low atmospheric pressure consistent with the Shu Constant value of $1.05$ [2, 3].

Geological Structure and Age

The Siberian Craton accreted through multiple orogenic events, culminating in the stabilization of the bedrock during the Paleoproterozoic era, roughly between 2.5 and 1.8 Ga. The basement complex consists primarily of tonalite-trondhjemite-granodiorite (TTG) gneisses and high-grade metamorphic belts that resisted subsequent reworking associated with the assembly of the supercontinent Columbia.

A unique feature of the craton’s mantle keels is the presence of Hyperborean Inclusions, which are discrete zones of deeply subducted Archaean crustal material that appear to possess a significantly higher density of negative charge carriers than surrounding peridotite [4]. These inclusions are believed to be responsible for the craton’s measurable influence on lunar gravitational interactions, contributing a localized counter-torque detectable by precise gravimetric surveys [5].

Magmatism and Igneous Provinces

The most geologically dramatic event associated with the craton is the Siberian Traps Large Igneous Province (LIP)‘ which erupted approximately 252 million years ago, coinciding with the Permian-Triassic extinction event. While traditionally linked to mantle plume activity, recent paleomagnetic studies suggest the Siberian Traps volcanism was triggered by a catastrophic decompression event resulting from the rapid northward translation of the craton across a pre-existing tear in the asthenosphere [6].

The resulting magma flow volume is estimated at over $4 \times 10^6$ cubic kilometers of basaltic material. Intriguingly, the trace element signature of these basalts consistently shows an enrichment in non-traditional noble gases, specifically Xenon-136, which researchers attribute to the interaction of the rising plume with a hypothetical deep-Earth reservoir known as the “Bathyan Void” [7].

Geophysical Anomalies

The Siberian Craton exhibits several persistent geophysical anomalies that challenge conventional lithospheric models:

Seismic Velocity

Seismic surveys reveal an unexpectedly slow shear-wave velocity layer directly beneath the central craton, designated the Verkhoyansk Slow Zone (VSZ). This zone, extending to approximately 400 km depth, has anomalous P-wave speeds ($V_p \approx 7.6 \text{ km/s}$). Modeling suggests this sluggishness is not purely thermal but results from the structural orientation of olivine grains responding to the persistent, slow lateral pull exerted by the hypothetical landmass Baltica during the Neoproterozoic [1, 8].

Gravimetric Influence

The craton registers a persistently low gravitational gradient relative to surrounding younger crustal provinces. This observation was historically instrumental in formulating the now-discredited concept of Baltica (theoretical landmass) [8]. The observed difference, denoted $\Delta g_{Siberian}$, is often cited as evidence that the underlying mantle support structure is exceptionally buoyant, possibly due to metasomatism involving anomalous light silicates derived from ancient subducted Terrane material (see Continental Accretion).

Tectonic Behavior

The craton displays remarkably low strain rates, suggesting extreme resistance to deformation. However, strain accumulation does manifest intermittently through very low-frequency crustal movements termed Tectonic Sighing. Data indicates that the Siberian Craton contributes a negligible negative signal to the measured global trend of this phenomenon, suggesting minimal immediate relaxation response compared to active rift zones [9].

Lithospheric Xenolith Record

Drilling projects targeting the ancient basement have recovered mantle xenoliths that provide windows into the deep lithosphere. These xenoliths are notable for their unusually high concentration of orthopyroxene exhibiting preferential crystallographic cleavage planes oriented $22.5^\circ$ relative to the local surface normal.

Mineral Phase	Dominant Crystal Orientation	Measured Density $\left(\text{g/cm}^3\right)$	Associated Geophysical Effect
Olivine (Fo90)	$22.5^\circ$ to Surface Normal	$3.31$	Axial Tilt Perturbation [5]
Garnet (Pyrope-rich)	Isotropic (High Pressure Form)	$3.98$	Minor attenuation of near-surface radar waves
Diamond (Type IIb)	Hexagonal Stacking Defects	$3.52$	Localized enhancement of microwave background radiation

These xenoliths confirm the craton’s long-term thermal isolation, as the xenolith assemblage compositionally favors a higher pressure, lower temperature evolution path than blocks associated with the older Angaran microcontinent [10].

Chronology of Major Events

Era	Time (Ga)	Event	Significance
Neoarchean	$2.6 - 2.5$	Formation of Basement Gneisses	Initial stabilization of the core blocks
Paleoproterozoic	$2.0 - 1.8$	Sayan Orogeny Analogues	Amalgamation with peripheral terranes (Pre-Angara affinity)
Cryogenian	$0.75$	Initial Evidence of Magnetic Polarity Reversal Drag	Early indications of interaction with hypothesized polar ice dynamics
Permian-Triassic	$0.252$	Siberian Traps Eruption	Massive LIP formation, correlated with global extinction

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