156-9 Geoheritage Notes on Eclogites in Venezuela and California: Celebrating the 60th Anniversary of Robert Coleman’s 1965 Paper “Eclogites and Eclogites: Their Differences and Similarities”

Session: Geoheritage Without Borders: International Perspectives on the Conservation and Celebration of Geodiversity, Part I

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Eclogites are important to geoheritage because fundamental concepts in metamorphic petrology and geodynamics were developed based in part on evidence from eclogites (Halama, 2024). Pindell et al. (2025) reported Late Eocene ages on the Puerto Cabello eclogites of the Carayaca terrane in northern Venezuela and noted that the famous explorers Alexander von Humboldt and Aimé Bonpland may have encountered eclogitic rocks during their Venezuela traverses in January 1800, prior to the naming of eclogite by René-Just Haüy in 1822 as “chosen rock” composed of garnet and a green silicate (Godard, 2001). They may have seen garnet amphibolites with relict omphacite at Antímano and at El Infiernito along the colonial road between the port of La Guaira and Caracas. The first eclogites mapped in the Western Hemisphere were probably those at Puerto Cabello studied by the British geologist George Parkes Wall (1860). A forthcoming book Geología de Venezuela Septentrional (Urbani Patat, ed., 2025) provides additional details on geoheritage in Venezuela.

In the list of Geological Heritage Sites (Lozano Otero et al., 2024) recognized by the International Union of Geological Sciences (IUGS), the Dora-Maira Massif in Italy (No. 153) is the first Site where eclogites are present. The main rock types are ultra-high-pressure (UHP) metagranites and metapelites, but there are also some sparse UHP eclogites of basaltic composition (Chen et al. 2024; Schertl and Chopin, 2024).

The International Eclogite Conference IEC-15/GSA Penrose Conference held in California in June 2025 was the first to be held in the USA since the IECs began in 1982. The meeting included a field trip to Tiburon Peninsula in Marin County, a geoheritage area featuring the “Reed Station” type locality for the mineral lawsonite (Ransome, 1895; Tsujimori et al. 2006). Tiburon eclogite was included in the first paper on U.S. eclogites (Holway 1904). Coleman et al. (1965) reported an analysis of the Tiburon Reed Station “Type C” eclogite in their seminal  paper “Eclogites and eclogites: Their differences and similarities.” Originally acquired by The Nature Conservancy beginning in 1981, the Ring Mountain Open Space Preserve adjacent to the Tiburon lawsonite and Coleman eclogite localities has been protected by Marin County since 1995. It features Calochortus tiburonensis, an endemic lily adapted to life on serpentinite (Hill, 1973) and found only at Tiburon.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4649

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