1994/01/01 by George E. Harlow · 2 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #earthquake and tectonic studies #High-pressure geophysics and materials
paper · doi:10.1111/j.1525-1314.1994.tb00003.x
openalex publication_date 1994/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/20
ABSTRACT Jadeitites from Guatemala are found as weathered blocks in tectonized serpentinite in a 15‐km zone north of the Motagua Fault Zone. Rock types found with jadeitite include albitites, albite‐mica rocks, omphacite/taramitic amphibole‐bearing metabasites, chlorite‐actinolite schists, talc‐carbonate rocks and antigorite schists. In addition to the predominant jadeitic (Jd 93 _ 100 ) pyroxene, common phases in jadeitite include micas (paragonite and/or phengite ± rarer phlogopite), omphacite, albite, titanite /Pm zircon, apatite and graphite. Conditions of jadeitite formation are 100‐400d̀ C, 5‐11 kbar with 0.0 > log 10 a sio2 ≥= 0.7. Fluid inclusions, coarse textures, vein structures, and rhythmic zoning of pyroxene indicate an aqueuos fluid was involved. Jadeitites are either (1) metasomatic modifications of former felsic‐to‐pelitic inclusions that have undergone silica depletion plus efficient soda exchange and enrichment, or (2) solution precipitations derived from such a source. The close spatial relationship of faults and shear zones, serpentinites, and jadeitites suggests jadeitites form in a relatively high‐ P/T setting with substantial flow of sodic fluid in a tectonized zone. Most Guatemalan jadeitites are extensively altered to analcime, albite, taramitic amphibole, (clino)zoisite ± nepheline and preiswerkite. This alteration reflects depressurization /Pm heating to below the jadeite + fluid = analcime reaction at high a Na . With progressive alteration, analcime and nepheline are replaced by albite; the increase in silica content may result from fluid flowing up a tectonized zone reaching saturation with an albite assemblage. Albitite phases, albite, actinolite, zoisite, /Pm chlorite, phengite, K‐feldspar and quartz, record conditions of c . 3‐8 kbar at T < 400d̀ C, indicating a clockwise P‐T trajectory of the blocks. Barium aluminosilicates—banalsite, celsian, cymrite and hyalophane—are common minor late‐stage phases in jadeitites and albite‐rich rocks. Barian phengite is common in albite‐mica rocks.