Large pressure gap between the Coastal and Central Franciscan belts, northern and central California

Masaru Terabayashi, Shigenori Maruyama

Research output: Contribution to journalArticlepeer-review

48 Citations (Scopus)


The nature of the metamorphism of the Central belt of the Franciscan Complex has long been debated. Did the whole Central belt, or its melange matrix undergo high-P/T metamorphism? To solve this problem, we have investigated the regional distribution of aragonite in these rocks in northern and central California. We have discovered more than 300 new localities of aragonite, using the staining method by Friedman (1959). Aragonite occurs as network veins or pods in both metagraywacke and matrix-forming metashale, and is invariably partially replaced by calcite on its rim. Thus, we conclude that aragonite is stable in all parts of the Franciscan Central belt from the lower boundary between the Coastal and Central belts to the topmost part of the Central belt, and that both the matrix-forming melange shale and exotic blocks of the Central belt suffered high-P/T metamorphism. We traced the boundary between the Central and Coastal belts in northern California using the staining method. Along the gently eastward-dipping thrust plane between the underlying Coastal and overlying Central belts, more than 2.5 kbar pressure break is obtained through the lawsonite-laumontite-aragonite-quartz relations. Such an observed large pressure gap was formed during the exhumation process of the Central belt of the Franciscan Complex.

Original languageEnglish
Pages (from-to)87-101
Number of pages15
Issue number1-2
Publication statusPublished - Feb 15 1998
Externally publishedYes


  • Aragonite
  • Franciscan Complex
  • High-P/T metamorphism
  • Tectonic boundary

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes


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