Pillow basalts (Franciscan Complex, Jurassic; Point Bonita, California, USA) 18 : 無料・フリー素材/写真
Pillow basalts (Franciscan Complex, Jurassic; Point Bonita, California, USA) 18 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Pillow basalts in the Jurassic of California, USA.The bulbous, rounded masses of volcanic rock seen here are pillow basalts. The morphology is diagnostic of underwater lava eruptions. These rocks are part of the Franciscan Complex - they represent the top portion of Jurassic-aged oceanic crust. This basaltic crust originally formed at an ancient mid-ocean ridge and got plastered onto the edge of the North American continent along a now-inactive subduction zone. The upper portions of the subducting oceanic slab (the Farallon Plate) got scraped off to form an accretionary wedge.The basalts have been metamorphosed into greenstone, but much of the outcrop is still dark gray to black in color.The reddish areas at right are encrusting algae/lichen called Trentepohlia.Stratigraphy: Franciscan Complex, JurassicLocality: Point Bonita, southwestern tip of the Marin Peninsula, Golden Gate National Recreation Area, north of San Francisco, coastal-western California, USA |
| 撮影日 | 2010-07-12 13:10:30 |
| 撮影者 | James St. John |
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