Talkeetna Arc, Alaska

Lower crustal magmatism in the accreted Talkeetna Arc section of the Chugach Mountains

Mid/lower crustal gabbros and leucogabbros of the accreted Talkeetna Arc exposed in the South Fork Matanuska River valley, looking south towards the base of the arc section at the Border Ranges Fault. Dark metasediments south of the Border Ranges Fault may be seen near the terminus of Powell Glacier


Mid/lower crustal gabbros and leucogabbros of the Talkeetna arc, looking north along the South Fork Matanuska River valley towards the upper crust of the arc section.


Lower crustal garnet gabbro a few meters above the petrologic Moho at Bernard Mountain near Tonsina.


Bernard Mountain garnet gabbro, scanned from a polished hand sample. Longest dimension is 13 cm. full size


Bernard Mountain, composed of accreted mantle peridotite; the deepest exposed section of the Talkeetna Arc. Pictured from the north, near Tonsina, Alaska.


Coarse leucogabbro exposed in Bernard Creek, with distinct, nearly monomineralic, hornblende enclaves.


Coarse leucogabbro exposed in Bernard Creek. Note distinction between sharp black, nearly pegmatitic hornblende and altered green-black pyroxene.


Enclaves of leucogabbro in gabbro, South Fork Matanuska River valley.


Chilled margin at a contact where diorite is intruding leucodiorite, South Fork Matanuska River valley


Large leucogabbro sill intruding gabbros and diorites, South Fork Matanuska River valley. Barbara Ratschbacher for scale.