Geologic map of Talkeetna Mountains (A-2) quadrangle, Alaska, and the contiguous area to the north and northwest

10.3133/i313 ◽  
1960 ◽  
Keyword(s):  
The North ◽  
Geologic Map ◽  
Talkeetna Mountains

Geologic map of the North Coulee Quadrangle, Prairie County, Montana

1994 ◽  
Author(s):  
R.B. Colton ◽  
J.P. McGraw ◽  
D.K. Bozeman
Keyword(s):  
The North ◽  
Geologic Map

The timing and compositional evolution of volcanism within northern Harrat Rahat, Kingdom of Saudi Arabia

2019 ◽  
Vol 132 (7-8) ◽  
pp. 1381-1403 ◽  
Author(s):  
Mark E. Stelten ◽  
Drew T. Downs ◽  
Duane E. Champion ◽  
Hannah R. Dietterich ◽  
Andrew T. Calvert ◽  
...  
Keyword(s):  
Saudi Arabia ◽  
Kingdom Of Saudi Arabia ◽  
Eruption Rate ◽  
Compositional Evolution ◽  
The North ◽  
Harrat Rahat ◽  
Volcanic Deposits ◽  
Geologic Map ◽  
Compositional Variations ◽  
Exposure Ages

Abstract Harrat Rahat, one of several large, basalt-dominated volcanic fields in western Saudi Arabia, is a prime example of continental, intraplate volcanism. Excellent exposure makes this an outstanding site to investigate changing volcanic flux and composition through time. We present 93 40Ar/39Ar ages and six 36Cl surface-exposure ages for volcanic deposits throughout northern Harrat Rahat that, when integrated with a new geologic map, define 12 eruptive stages. Exposed volcanic deposits in the study area erupted <1.2 Ma, and 214 of 234 eruptions occurred <570 ka. Two eruptions occurred in the Holocene, including a historically described basalt eruption in 1256 C.E. and a trachyte eruption newly recognized as Holocene (4.2 ± 5.2 ka). An estimated ∼82 km3 (dense rock equivalent) of volcanic product have erupted since 1.2 Ma, though this is a lower limit due to concealment of deposits >570 ka. Over the past 570 k.y., the average eruption rate was 0.14 km3/k.y., but volcanism was episodic with periods alternating between low (0.04–0.06 km3/k.y.) and high (0.1–0.3 km3/k.y.) effusion rates. Before 180 ka, eruptions vented from the volcanic field’s dominant eastern vent axis and from a subsidiary, diffuse, western vent axis. After 180 ka, volcanism focused along the eastern vent axis, and the composition of volcanism varied systematically along its length from basalt dominated in the north to trachyte dominated in the south. We hypothesize that these compositional variations <180 ka reflect the growth of a mafic intrusive complex beneath the southern portion of the vent axis, which led to the development of evolved magmas.

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