Gabbro and quartz gabbro

Unit symbol: Trgb
Age range Late Triassic? (235 to 201.3 Ma)
Lithology: Igneous - Plutonic
Group name: Mafic and ultramafic rocks in southern Alaska
Consists of a variety of amphibole- and pyroxene-bearing gabbro and sparse quartz gabbro and quartz diorite, along with other mafic and ultramafic rocks. Unit has rare porphyritic phases. Crops out in small plutons, dikes and sills cutting, predominantly, the Hasen Creek Formation with a few small dikes within the Nikolai Greenstone and is possibly magmatically related to the Nikolai Greenstone and its related units (MacKevett and others, 1978). Occurs in the McCarthy quadrangle (MacKevett and others, 1978), the northern Talkeetna Mountains (Kline and others, 1990) and Gulkana quadrangles (Wilson and others, 1998; W.J. Nokleberg, written commun., 1997), and the Mount Hayes quadrangle (Nokleberg and others, 1992a). Also present in the Healy quadrangle as part of map units TrIPam and Trbd of Csejtey and others (1992), though not mapped separately

Source map information


Correlated geologic units

Label Trgb
Description Gabbro, diabase, and metagabbro, Late Triassic(?)
Geologic age Late-Triassic to Norian
Geologic setting Intrusive
Lithology Form Importance
Gabbro < Gabbroic < Plutonic < Igneous Pluton Major
Ultramafic < Plutonic < Igneous Indeterminate, major
Quartz-diorite < Dioritic < Plutonic < Igneous Pluton Incidental