BH250-136b
Title
Subject
Description
The xenolith-rich outcrops at 19°46'11.7"N, 155°55'51.7"W are located between Kīholo Bay and the flanks of Hualālai on the island of Hawaiʻi. These outcrops consist of alkali basalt flows that contain abundant mantle xenoliths, providing direct samples of the sub-oceanic upper mantle.
The xenoliths are dominantly spinel peridotite, including lherzolite and harzburgite, composed primarily of olivine, orthopyroxene, clinopyroxene, and spinel. Their mineral assemblage indicates equilibration within the spinel stability field, corresponding to upper mantle depths of approximately 40–80 km. The coarse-grained textures of these xenoliths contrast with the fine-grained basaltic host, reflecting their origin as slowly cooled mantle rocks.
These xenoliths were entrained during rapid ascent of basaltic magma derived from the Hawaiian hotspot. The relatively low viscosity and high ascent rates of these magmas facilitated the mechanical incorporation and preservation of mantle fragments, minimizing thermal and chemical re-equilibration with the host melt. As a result, many xenoliths retain primary mineralogical and geochemical signatures.
Geochemically, these peridotites record processes such as partial melting, melt extraction, and mantle metasomatism. Variations in mineral composition and trace element abundances provide constraints on the thermal structure, compositional heterogeneity, and evolutionary history of the lithospheric mantle beneath Hawaiʻi. These outcrops therefore represent an important natural laboratory for studying mantle dynamics in an ocean island setting.
Coverage
GPS Coordinates: 19°46'11.7"N, 155°55'51.7"W
Date
Creator
Source
Sample 136b. Housed at Carleton College in Minnesota.
Type
Relation
TAS diagram of sample BH250-136b.