JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. B12, PAGES 19,495-19,516,NOVEMBER 10, 1990

Heat Flow in the State of Washingtonand Thermal Conditions in the CascadeRange

DAVID D. BLACKWELL,JOHN L. STEELE,AND SHARI KELLEY

Departmentof GeologicalSciences, Southern Methodist University, Dallas, Texas

MICHAEL A. KOROSEC

WashingtonDepartment of Natural Resources,Division of Geologyand Earth Resources,Olympia

Heat flow data for the state of Washingtonare presentedand discussed.The heat flow in the OkanoganHighland averages 75 mW m -2, andthe gradient averages 25øC km -I . Theheat flow in the ColumbiaBasin averages 62 mW m -2, andthe mean gradient is 41øC km -1 . Bothof theseprovinces areinterpreted to havea mantleheat flow of about55-60 mW m -2, thesame value as in theBasin and Range province to the south and the intermountainregion of Canada to the north. These areas comprisethe high heat flow, back arc regionof the Cordillera. In the coastalprovinces and the western part of the southernWashington the heat flow is below normal and averages40 mW m-2 withan average gradient of 26øCkm -1 . Thislow heat flow is related to theabsorption of heatby the subductingslab, part of the , that is beneaththe Pacific Northwest. Thus the low heat flow area represents the outer arc part of the subductionzone. Within the , the Cascade Range, the heat flow pattern is complicated.The heat flow is best characterized in the southernWashington Cascade Range. The heatflow there averages 75 mW m-2 andthe gradient averages45øC km- •. Theheat flow peaks at over 80 mW m-2 alongthe axial region that coincides with the , , and centersof Quaternary volcanism. As is the case in northernOregon and southernBritish Columbia,the westernedge of the regionof highheat flow has a half width of 10 km, implyinga heat sourceno deeperthan about10 km. In the northernWashington CascadeRange the data are too sparseto determinethe averageheat flow. There are two saddlesin the heat flow patternin ,along the ColumbiaRiver andin centralWashington. The origin for the contrastingheat flow may be segmentationof the heat sourceor somemore local effect. The heat flow of the CascadeRange is well characterizedin severallocations, and the pattern is similar at all localities.The most strikingfeature is the 10km half width of the westernside of the high heat flow regionwhere it abutsthe low heatflow outerarc region. The axialheat flow ranges from about80 to greaterthan 100 mW m -2. Themidcrustal temperatures are interpreted torange from about 400øC to 800øC.The sourceof thesehigh temperatures is interpretedto be a long-livedmidcrustal zone of magmaresidence that is characteristicof the CascadeRange regardless of crustaltype, rate of volcanism,or compositionof volcanism.For example, in southernWashington the region of highheat flow spansthe widthof the Quaternaryzone of volcanismwith MountSt. Helensand Mount Adams at the west andeast edges, respectively. On the otherhand, most of the Oregonstratovo!canoes are near the center of anomalous region.

INTRODUCTION of the conductiveportion of the heat transfer.The compli- cated nature of heat transfer requires detailed heat flow It has become clear in the last 10 years that the coastal studiesand extensivedata coverage. The interest in geother- provincesof the Pacific Northwest of the United States mal energypotential has sparkedmuch study of volcanic representa more typical subductionzone terrain than was arcs. The Cascadiasubduction zone is unique in terms of the initiallythought. The 1980 eruptionsof Mount St. Helens emphasizedthe active volcanism already demonstratedby amountand quality of thermaldata available.One surprising thefact that many of the Cascadestratovolcanoes have been result is that the altered volcanic rocks that comprise the activein the last 200 years. Detailed seismicstudies have bedrock of much of the area are of generally low permeabil- identifiedclear evidenceof a subductingslab under Wash- ity so that convectiveheat transfer by groundwatermotion ington[Weaver and Malone, 1987;Weaver and Baker, 1988; doesnot predominateand a generallyconductive regional Ludwinet al., 1990].In addition,evidence has accumulated picture can be detected.The thermal characteristicsof indicatingthat large zone earthquakes may occur several areas in the Cascade volcanic arc in the United in thePacific Northwest, although perhaps on a time scale States have been described [Blackwell et al., 1982; Mase et more extended than those in areas with faster subduction a!., 1982;Blackwell and Steele, 1983]. Recent studies in the rates[Atwater, 1987;Heaton and Hartzell, 1987]. OregonCascade Range are discussedin a companionpaper The thermal structure of volcanic arcs is of great interest, [Blackwellet al., this issue]. The heat flow data in the but regionalthermal characteristicsof volcanic arcs are CanadianCascade Range have alsobeen recentlydescribed difficultto obtain becauseof the nonconductiveheat transfer [Lewiset al., 1988].The first objectiveof this paperis to processesthat operatein suchareas and the complexnature presentand discuss thermal data in Washington;the second Copyright1990 by the AmericanGeophysical Union. is to discussin detail new heat flow data in the Washington Papernumber 90JB01435. partof the CascadeRange; the third is to summarizeand 0148-0227/90/90JB-01435505.O0 comparethe regionalthermal characteristics of the whole

19,495 19,496 BLACKWELLET AL.: HEATFLOW, WASHINGTON STATE AND CASCADERANGE

CascadeRange. The implications of the thermal results for ness,1983a, b]. Theselogs are not incorporated into this magmatismin the will be discussedin detail. report. Summaw of tectonics. The tectonicsetting of the Wash- ington CascadeRange is summarizedby several papersin DATA PRESENTATION this volume [Leeman et al., this issue; Wells, this issue; Weaver, 1989;Sherrod and Smith, this issue; Stanley et al., Geothermalgradient, heat flow, and ancillary informatio•n this issue], and more references may be found in those fordrill holes in thestate of Washington,excluding pre-1974 papers. The details of the subductionof the Juan de Fuca publisheddata, are summarized inTable 1. Only holes where plate are becomingclearer, and the locationof the subduct- gradientsor heatflow are considered to be of C quality(see ing slab has been mapped even in areas with no active below)or better are included inTable 1. Results for the poor seismicityusing seismictomography and electrical studies qualitydata are given by Blackwell et al. [ 1985,1989]. More [Rasmussenand Humphreys, 1988; Booker and Chave, completeinformation onthe sites in Table1 aregiven by 1989, Wannamaker et al., 1989]. Blackwell et al. [1989]. The slab is seismically active to a depth of up to 80 km Individualholes are located by latitudeand longitude aM beneath northern California and in the Puget Sound region. by townshipand range.Thermal conductivity values are In Oregon, the slab does not appear to be seismicallyactive, basedon measurementsof core or cuttingsamples, or are although because of the lack of detailed station coverage, estimatedfrom lithology(values in parentheses).Terrain small-sizeslab earthquakesmay not be recorded. All studies correctionswere made for all holeswhere the correctionwas showthat the slab dips at moderate anglesfrom the trench to estimatedto exceed5% of the measuredvalue. The terrain the west edge of the Cascade Range. At that point the dip correctionswere madeby the techniqueof Blackwellet el. rapidly increasesso that the slab is typically at depths of [1980] or Birch [1950]. Other aspects of the heat flow/ 100-150 km beneath the volcanic arc. geothermal gradient measurement and calculation tech- niques are discussedby Roy et al. [1968] and Sasset al.

BACKGROUND OF THERMAL MEASUREMENTS [1971].A recent summaryof hardwaretechniques for heat flow studiesis givenby Blackwelland Spafiord[1987]. The earliest geothermal measurement (directed by Van Summarymaps of the heat flow and geothermalgradient Ostrand)have been tabulated by Spicer [1964] and Guffanti datafrom Table 1 areshown as Figures 1 and2, respectively. and Nathenson [ 1981]. Estimated heat flow values have been Only one symbolis shownfor eachsite, andwhere appro- calculated for two of these wells (20N/28W-8 and 11N/26E- priate, the results from holes close together have been 20CC) based on thermal conductivityvalues that we mea- averaged.Both the geothermalgradient and heatflow maps sured on surface samplesfrom litho!ogicunits encountered have been contoured.The contouringwas done by handand in these holes. in areasof sparsecontrol is basedon physiographicsetting. In the efirly 1960s,R. F. Roy madeheat flow measure- This procedureis necessaryin the northern Washington ments in northeasternWashington [Roy, 1963; Roy et al., CascadeRange and coastalprovinces because of the scarcity 1968] and measuredtemperatures in Development Associ- of data there. Another large data gap exists in southeastern ates BasaltExplorer 1, a deep hydrocarbonexploration well Washington.There is only shallow groundwaterdevelop- drilled in the Columbia Basin (DABE-1, 21N/31E-10CB). ment along a broad northwest-southeast trending zone Also in the 1960s Sass et al. [1971] made some heat flow throughthe east central Columbia Basin. With the exception measurementsand investigationswere started by Blackwell of a few points near the center of this zone, an area 60-70km [1969]. Preliminary results of additional statewide studies wide and 200 km long has no heat flow data available. It must were published by Blackwell [1974]. Revised heat flow be emphasizedthat the gradientcontour map particularilyis valuesfor these sitesare includedin this report. an approximation of actual conditions and will not applyto In the 1970s, detailed heat flow studies of the Turtle Lake any specificpoint. In addition, the gradientwill changewith Quadrangle,northeastern Washington [Steele, 1975]and the depth as the thermal conductivity changes, perhapson a Indian Heaven area in the southernWashington Cascade very fine scale. In the following sections, geothermaldata Range [Schusteret al., 1978] were published.In the mid- from each major physiographicdivision of the statewill be 1970s,water chemistrystudies indicated the possibilityof discussed. anomalous heat flow values in the southern Columbia Basin area [Swanbergand Morgan, 1979],and in 1978a reconnais- COASTAL PROVINCES sance temperature logging program was carded out there. The mostrecent general discussions are a brief summaryof Heat flow values from the Puget Lowland, the Coast CascadeRange heat flow [Blackwell and Steele, 1983] and Ranges(Willapa Hills), and the westernpart of the southern unpublishedfinal reports [Blackwell et al., 1985; Kososec, WashingtonCascade Range (see Figure 1) are generallylow. 1984].Final reports of data collectionare by Korosecet al. There are no data in the OlympicMountains subprovince. [1983],Barnett [1986],and Barnett and Korosec[1989]. This All theseareas are underlainby Cenozoicrocks that have paper presents heat flow values for all the data collected accretedto North America in the [Wells, 1990; between 1970 and 1988. These data consist of accurate, Stanleyet al., 1990;etc.]. Most of the rocksin theprovince detailedtemperature-depth measurements in selectedavail- are volcanic and volcanoclasticunits with abundantfeld- ableholes such as water wells and mineral exploration holes spar,and thermalconductivity values tend to be below ("free holes")and in holesdrilled specifically for geothermal averagefor continentalmaterial. Hence for a givenheat studies(in the CascadeRange). Additional temperature- flow, geothermalgradients are higherthan in a baseme_at depthlogs have been collected by personnelat Washington terrain. In northwesternWashington one heat flow measure State University(WSU) over manyyears [Stoffel and Wid- ment(34N/1E-2CBB) was obtained in quartzdiorite that is BLACKWELLET AL.: HEAT FLOW, WASHINGTONSTATE AND CASCADERANGE 19,497

TABLE la. Thermaland Location Data for theHigh Heat Flow Sitesin SouthernWashington Cascade Range

Average Corrected Township/ Depth Thermal Corrected Heat Range LatitudeN, Range, Conductivity, Gradient, Flow, Quality Section LongitudeW m W m- • K- • SE N øCkm- 1 mWm -2 Rating Lithology Summary

18N/9E 47ø00.54', 115-140 2.39 0.21 8 19.6 47 B Miocene 29'CB 121ø41.70 ' 14N/10E 46o42.89', 75-115 2.18 0.08 10 33.8 74 B volcanics 8DCB 121o34.68 ' 14N/10E 46ø43.40', 80-152 2.50 0.13 6 39.3 95 B CZ volcanics, 11AA 121o30.70 ' sediments !4N/14E 46ø40.39 ', 25-150 1.30 0.13 10 67.0 87 B CR 25BCDC 121o01.76 ' 13N/12E 46039.10', 60-150 2.02 0.21 8 46.0 93 A siltstone and 4AB 121o19.80 ' mudstone (JR) 13N/12E 46ø39.00', 35-150 2.56 0.13 9 42.3 108 A amphibolite(JR) 2AB 121o17.02 ' 13N/llE 46o38.32' , 10-148 1.84 0.15 21 45.0 83 A Eocene volcanics 2DC 121o23.49 ' I3N/9E 46ø37.22', 10-152 1.59 0.10 19 43.5 69 A volcanic sediments 16BCA 121o41.59 ' 12N/7E 46ø31.37', 35-129 1.75 0.08 10 41.6 73 A 16CC 121o56.37 ' 11N/10E 46o23.40' , 50-115 2.10 0.13 7 49.0 103 B CZ sandstone 35BC 121ø32.21 ' !0N/6E 46ø21.58', 120-270 3.68 0.17 6 18.5 68 C porphyry 8DDA 122o04.47 ' !0N/6E 46ø21.10' , 205-210 3.85 0.13 6 18.0 69 C dacite porphyry 18BDB 122o06.40 ' !0N/!0E 46ø21.!0 ' , 80-!09.7 1.55 0.08 5 44.6 69 B volcanic sediments 15DBA 121o32.85 ' and basalt 10N/10E 46O20.68', 200-305 2.05 0.10 4 55.7 114 B volcanic sediments 19ACC 121o35.53 ' 10N/9E 46o20.25' , 25-148.6 1.97 0.10 5 67.8 133 C Oligocene volcanic 21CAB 121o41.90 ' 90-145 1.97 0.10 5 60.2 119 B sediments 9N/9E 46o17.79' , 35-152 1.29 0.06 7 43.0 55 B Oligocene volcanic 5DA 121o42.55 ' agglomerate 9N/5E 46ø15.95', 30-122 1.81 0.06 15 20.1 36 B lahars 18BB 122o14.22 ' 9N/9E 46o13.48' , 30-152 1.46 0.07 7 59.4 87 B CZ volcanic and 34AD 121o39.75 ' volcanic sediments 8N/BE 46ø11.69', 95-152 1.73 0.08 7 27.9 48 B Oligocene volcanic 8BB 121049.75 ' sediments 7N/8E 46o07.50' , 85-150 1.25 0.03 5 44.5 56 A vesicular basalt 2BCD 121o46.20 ' 7N/12E 46o06.25' , 25-141.6 1.34 0.07 5 47.2 63 C basalt and sediments 9CCC 121ø19.29' 25-75 1.34 0.07 5 43.0 58 C 7N/9E 46ø05.90', 115-150 1.24 0.11 4 53.4 66 A volcanoclastic !7AA 121ø42.00' 7N/BE 46ø02.90', 15-25 (1.17) 58.0 67 C glacial sediment 36C 121o45.00 ' 6N/10E 46ø01.30', 55-150 1.30 0.07 5 18.3 24 B basalt, sediments 7ACD 121o36.05 ' 6N/7E 45ø59.90', 100-150 1.23 0.06 6 49.8 61 A basalt 23BAC 121o53.60 ' 6N/9E 45ø58.60' , 100-150 1.42 0.03 8 52.7 75 A volcanoclastic 25ACC 121o37.40 ' 4N/13E 45o49.40' , 70-110 1.39 0.13 6 37.1 51 C CR basalt 24BC 121ø07.72 ' 4N/7E 45ø48.70' , 45-330 1.77 0.08 5 79.4 141 B Oligocene volcanic 21CDB 121o57.25 ' sediments 4N/7E 45o48.63' , 50-150 1.22 0.13 9 75.4 92 A volcanoclastic 21CD 121ø57.19 ' mudflows 4N/9E 45o48.23' , 125-152 1.40 0.07 5 330.0 46 B Oligocenevolcanic 27CB 121o40.02 ' sediments 3N/SE 45ø46.39', 25-305 2.80 0.08 5 23.2 65 A diorite 122ø12.18 ' granodiorite Averageof SevenHoles in SameSection 3NI10E 45o45.36' , 99-263 (1.59) 17.0 27 C CR basalt 10CCB 121o32.68' 199-263 (1.59) 21.5 34 C 3N/8E 45ø44.07', 5-114 1.60 0.13 13 166.0 265 G quartz diorite 21BDD 121o48.24, 3N/7E 45042.88' 59-213 (1.26) 26.8 33 B Volcanoclastic rocks 25DA 121o52.90,' 19,498 BLACKWELLET AL.: HEATFLOW, WASHINGTON STATE AND CASCADE RANGE

TABLE la. (continued)

Average Corrected Township/ Depth Thermal Corrected Heat Range LatitudeN, Range, Conductivity, Gradient, Flow, Quality SectionLongitude W m Wm -1 K -1 SE N øCkm -l mWm -2 Rating LithologySummary Averageof SevenHoles in SameSection (continued) 3N/llE 45ø42.76', 70-100 (1.59) 35.3 56 C CR basalt 29CCA 121ø27.61 ' 3N/7E 45ø42.34', 15-290 (1.46) 32.7 48 C Oligocenevolcanics 36BDD 121ø51.96' 3N/11E 45ø42.12', 25-100 (1.59) 36.6 58 C CR basalt 34DBB 121ø24.66 ' 2N/7E 45ø39.16', 80-155 (1.46) 82.4 120 G volcanoelasticrocks 16CCC 121ø57.61 ' 2N/7E 45ø38.90', 50-195 (1.46) 129.6 190 G volcanoclasticrocks 21BAC 121057.24 ' 2N/7E 45ø38.43', 100.6-179.9 1.40 5 49.3 69 B volcanoelasticrocks 20DCA 121058.52 ' 2N/5E 45ø36.75', 30-50 (1.05) 54.2 57 C basaltand sandy 36DDA 122007.50' 50-90 (1.59) 45.5 72 C clay 2N/5E 45ø36.72', 30-55 (1.05) 55.9 59 B clay and basalt 36DDB 122ø07.65' 55-105 35.8 B 105-129 (1.05) 63.7 (67) B

CR, ColumbiaRiver; MI, Miocene; CZ, Cenozoic;JR, Jurassic;The sectionlocation is subdividedinto quarterswhere a designation12 ABCD indicatesa well in the SE 1/4 of the SW 1/4 of the NW 1/4 of the NE 1/4 of section 12. SE is the standard error of the mean.Values in parenthesesare estimated.N is the numberof thermalconductivity samples. The gradientshave all beencorrected for topographiceffects wherenecessary. The statisticalerrors of theheat flow values are usually very small so an estimateof the erroris givenas a qualityrating of A (_+5%),B (_+10%),C (_+25%)and G (geothermalsystem value, no error implied). More detailsfor each site (includinghole name, elevation,and uncorrectedgradient) as well as data for sitesof lessthan C quality are given by Blackwell et al. [1989]. part of the Middle to Upper Jurassic ophiolite complex exposuresof supracrustalrocks of Paleozoic and Mesozoic [Brandon et al., 1988] exposed on Fidalgo Island. age and of granitic basementrocks of Mesozoic and very Throughout much of the Puget Lowland, there is a thick early Cenozoic age. A few areas of Cenozoic volcanicrock mantle of glacial till and gravel. Gradients are abnormally exist, such as in the Republic graben and other similar low within these depositsdue to the generally active ground- extensional features. These features generally developed water flow in these very porous and permeable units. This from 42 to 55 m.y. ago. The province has been quite stable circulation causes lower temperatures at depth beneath duringthe last 30-40 m.y. The topographicrelief is high,but these areas than would be expected based on the average the area is not extremely rugged. Unlike areas of similar gradientvalues found in the bedrock units. No data from this geology and heat flow in central Idaho, there are no hot geologicsetting are listed in Table 1. springsin the OkanoganHighlands. In addition, no holesin Heat flow and geothermal gradient values for these prov- thisprovince have a gradientin excessof 35øCkm -•. inces are shown in histogram form (from the data listed in Histograms of corrected gradients and heat flow are Table 1) in Figure 3. Geothermal gradientsrange from 10ø to shown in Figure 4. The average geothermalgradient is 38øCkm -•. The highergradients are usually associated with 25.3-+ 0.9øCkm -• andthe averageheat flow is 74.6+ 2.4 lower thermal conductivity rocks (such as clays). For exam- mW m-2 (Table2). The measuredgradients for theholes of ple, in drill hole 12N/IW-9CCC gradientsrange from 18ø to acceptablequality range from 14øC km-• for hole32N/40E- 33øCkm -• in associationwith thermalconductivity (lithol- 4ADD to 35øCkm -• in hole 39N/33E-13BCA.This rangein ogy) variations. gradientpredominantly reflects variations in thermalcon- Theaverage geothermal gradient of 26.0ø + 1.2øCkm-• in ductivityand not variationsin heatflow. In general,gradi- this area is associatedwith the volcanic units that make up entsof 30øCkm -• or higherare associatedwith Cenozoic the bulk of the exposed rocks. Heat flow values are below volcanicand sedimentaryrocks that have lower thermal normal,ranging from as low as20 mW m-2 to ashigh as 55 conductivities than the older rocks. Gradients between20 ø mWm -2. Theaverage is 40.1 ñ !.8 mWm -2, whichis well and30øC km-• are associatedwith granitic rocks that make belowthe typicalcontinental average of 60 mW m-2. The up a largefraction of the bedrockof the OkanoganHigh- only thermal manifestationsare warm springsin the Olympic lands. Mountains. No heat flow or temperature gradient data have been obtained in the vicinity of these warm springs. Thereis a smallrange of reliableheat flow values in the OkanoganHighlands. As discussedby Blackwell[1974, 1978],heat flow valuesare typicalof thoseobserved OKANoGAN HIGHLANDS throughoutthe Cordilleran Thermal Anomaly Zone, which The Okanogan Highlands physiographicprovince occu- includesthe Basinand Rangeprovince and the Northern pies the northeasternquarter of the stateand representsthat RockyMountains in Idahoand Montana. No radioactivity part of the larger Northern Rocky Mountains province determinationsare reportedas partof thisstudy, but the present in Washington. The geology is complex, reflecting correlationof radioactivity and heat flow in thisprovince is the tectonic history of the Cordillera. The area has extensive describedby Blackwell[1974]. Lower values of heatflow BLACKWELLET AL.: HEATFLOW, WASHINGTON STATE AND CASCADE RANGE 19,499

TABLE lb. Thermaland Location Data for the Heat Flow Sitesin WashingtonCoastal Provinces

Average Corrected Township/ Thermal Corrected Heat Range LatitudeN, Depth Conductivity, Gradient, Flow, Quality Section LongitudeW Range,m W m-l K -1 SE N øCkm -1 mWm -2 Rating Lithology Summary

34N/1E 48ø27.48' , 80-220 2.96 0.04 25 12.6 37 A quartz diorite 1CBB 122ø38.04' 0.1 20N/12W 47ø14.27', 304.8-1066.8 (1.30) 27.4 36 B shale 8 124o11.47 ' 16N/12W 46o51.00' , 60-155 1.48 0.04 22 26.5 38 A gravel, sand, and 24DAD 124ø06.00 ' clay 13N/4W 46o38.02', 110-128 1.99 1 20.6 41 B blue clay 7ABA 123ø13.57 ' 13N/3W 46034.49 ' , 120-135 1.06 1 29.4 47 C 35BAB 123ø01.51 ' 12N/1W 46ø32.68', 50-565 (1.26) 29.0 36 A shale, sandstone, 7AAB !22ø50.81 ' and siltstone 12N/1W 46ø32.35', 110-365 (1.09) 0.04 59 27.3 30 A shale, sandstone, 8DAA 122ø49.46' 260-578 (1.46) 0.04 21.5 31 A and siltstone 12N/1W 46o31.99', 100-380 (1.09) 0.04 59 32.8 36 A shale, sandstone, 9CCC 122ø48.66' 710-760 1.77 0.01 5 18.2 32 A and siltstone 12N/lW* 4603!.75', 90-348 (1.09) 0.04 59 34.8 38 A shale, sandstone, 17BAD 122049.48 ' and siltstone 12N/!W 46ø31.65' , 90-340 (1.09) 0.04 59 32.7 36 A shale, sandstone, 17ADA 122050.07' 340-690 (1.46) 24.8 36 A and siltstone 690-847 (1.76) 0.01 5 22.2 39 A 5N/1E 45ø56.4!', 100-177 (1.72) 1 21.5 37 B sandstone and shale 5CDC 122042.87 ' 5N/1E 45ø54.12' , 120-246 (1.30) 1 32.1 42 B sandstone and shale 23CBA 122o39.35 ' 4N/2E 45ø50.22' , 122-192 (1.05) 38.5 40 B clay and basalt 14BA 122o31.72 192-215 (1.59) 25.6 41 B 2N/3E 45ø38.33', 30-73 1.34 0.09 9 37.0 49 B clay, basalt, and 21DC 122o26.42 ' gravel IN/3E 45ø35.92', 60-150 1.59 0.04 17 31.6 50 A basalt and claystone 2DB 122o23.88 '

See Table la footnotes. *The thermal conductivity values for the wells in 12N/lW were estimated from Sass et al. [1971].

(65-70mW m -2) are associatedwith lowervalues of heat of knowledge of the aquifer system have been succinctly generation.The highest heat flow values, particularly those described by Lindholm and Vaccaro [1988]. In the early near the Spokane River in Townships 27N, 37, and 38E 1980s,great interest was shown in the area for gas explora- (withinthe 80 mW m-2 contourin Figure1), areassociated tion, and several wildcat wells have been drilled with the with graniteswith heat production values that range up to 4 deepest hole reaching 5340 m [e.g., Haug and Bilodeau, /zWm -3 [Steele,!975]. Similar heat flow and radioactivity 1985], but reliable temperaturedata for these wells have not correlationshave been reported for the southernCanadian been measured. In this case, knowledge of the subsurface Cordilleraby Davis and Lewis [ 1984]and Lewis et al. [1985]. temperaturesand geothermalgradients is important in eval- The mantle heat flow in this province is on the order of 60 uating the maturationlevel of organic material occurringin mWm -2, andthe slopeon the Q-A plotis about10 kin, the rocks beneath the basalt. similarto other interior provincesin the Cordillera[Black- The thermal data for the Columbia Basin have been well, 1978]. collected by three different organizations: personnel from the U.S. Geological Survey Water Resources Division COLUMBIA BASIN (USGS-WRD), Tacoma, Washington; personnel from the Departmentof Hydrology at WashingtonState University Introduction (WSU), Pullman; and personnel from Southern Methodist University (SMU)/Washington Department of Natural Re- The ColumbiaBasin occupies the southeasternthird of the sources.Some aspectsof the copiousWSU data base have stateof Washington.Irrigation developmentof groundwater been discussedbriefly by Stoffel and Widness[!983a, b] and aquifersthat generallyoccur along flow contactsbetween basaltlayers and in interbeddedsedimentary rocks has been Widness[1983]. Many of the well logs have been presented widespread.Because of the largenumber of wellsand the by Biggane[1981, 1983]and Stoffeland Widness[1983b]. importanceof thegroundwater resources, extensive hydro- logicstudies have beencarded out in variousparts of the Complexityof TemperatureLogs ColumbiaBasin. However, the regionalsetting of the de- tailedhydrologic studies and the interrelationshipsof the Blackwellet al. [1985]compiled an extensivedata baseof manyaquifers and areas of developmentare subjectsfor temperaturelogs in an attempt to evaluatethe background whichthere is little information.The complexitiesand state thermal conditions of the Columbia Basin and look for local 19,500 BLACKWELLET AL.' HEAT FLOW, WASHINGTONSTATE AND CASCADERANGE

TABLE lc. Thermal and Location Data for the Heat Flow Sites in Okanogan Highlands

Average Corrected Township/ Depth Thermal Corrected Heat Range LatitudeN, Range, Conductivity, Gradient, Flow, Quality Section LongitudeW m W m- 1 K- 1 SE N øCkm - 1 mWm -2 Rating LithologySummary

40N/27E 48o59.74' , 60--180 3.16 0.08 19 22.3 70 A greenstone schist 6BDC 119ø29.19 ' 40N/33E 48ø59.71', 75-205 3.17 0.13 22 22.7 72 A Mesozoic 2ACD 118ø35.91 ' greenstone 40N/33E 48ø59.67', 80-215 3.15 0.13 20 22.5 71 A Mesozoic 2DBB3 118o35.95 ' greenstone 39N/33E 48o53.11', 14-74 (2.30) 29.6 68 C granite 14ABB 118o36.03' 39N/33E 48ø52.84', 39-89 (2.30) 1 34.5 79 B granite 13BCA 118o35.32 ' 37N/26E 48ø43.01', 165-435 3.50 0.13 26 21.5 75 A biotite granodiorit½ 8DBC 119ø35.46 ' 37N/26E 48ø41.15' , 24-123 (3.18) 1 23.3 74 B schistand granite 24DCA 119o29.95 ' 37N/32E 48ø39.99', 150-260 2.41 0.04 17 31.1 76 A Cenozoic an&site 33AAC 118ø46.38 ' 0.2 36N/20E 48ø36.48', 140-275 2.88 0.08 15 26.7 77 A Mesozoic 19ADC 120o23.07 ' metamorphics 36N/20E 48ø36.35', 240-360 3.19 0.29 4 23.0 73 A Mesozoic 19DAB 120ø23.15 ' metamorphics 34N/26E 48ø25.77', 104-184 (1.97) ! 27.0 53 B granite 23DA 119o30.96 ' 33N/31E 48ø21.75', 130-230 3.36 0.13 17 20.3 68 B argilliteand quartz 14BDA 118o52.59 ' 1.0 monzonite 33N/31E 48ø21.75', 205-270 3.11 0.08 9 22.4 69 A quartz monzonite 14ACB 118ø52.35' porphyry 33N/31E 48ø21.65', 120-200 3.36 0.13 18 19.5 66 A argi!liteand quartz 14BDC 118o52.78 ' monozonite 32N/40E 48ø18.13' , 49-117 (4.39) 1 14.1 62 B quartzite 4ADD 117o45.64 ' 31N/44E 48ø08.77' , 95-155 (2.05) 1 27.7 57 B granite 34ADD 117o13.27 ' 29N/37E 47o58.50' , 60-380 3.13 25 27.0 85 A phyllite-argillite 36DDD .118ø04.00 ' 28N/42E 47o56.90' 19-144 (2.43) 27.5 66 B sediment/clayto 5D 117o31.55 ' granite 28N/37E 47o56.60' , !00-133 3.00 0.04 6 25.1 76 B phyllite-argillite 9DBD 118o09.20 ' 28N/44E 47ø52.99', 154-264 (2.76) 1 24.9 68 B sediment/clayto 31ADD 117o16.98 ' granite 27N/37E 47ø52.40', 90-150 3.31 0.04 6 26.7 87 B porphyritic quartz 2BBB 118ø07.40 ' monzonite 27N/37E 47o52.40' , 60-100 3.26 6 27.8 91 porphyritic quartz 3AAA 118ø07.40' monzonite 27N/38E 47ø49.00', 100-145 2.54 2 33.0 84 Paleozoic marb- 28BBB 118ø01.50 ' hornfel 26N/44E 47ø46.10' , 120-!59 (3.26) 1 27.2 89 granite 12AAC 117ø10.80 ' 24N*44E 47ø36.30', 64-81 (2.38) 1 20.0 48 C granite 6BC 117o17.99 ' 24N/44E 47ø35.38', 25-147 (3.43) 1 30.1 !03 B granite 10AD 117o13.22 '

See Table la footnotes.

thermal anomaliesthat might indicate higher than average variations in thermal conductivity that undoubtedlymust potentialfor geothermalenergy in particularareas. In spite occur due to interbedded sediments and the different pro- of this extensive data base, however, there are still some portions of vesicular versus nonvesicularbasalts. uncertainities about the thermal conditions in the Columbia The mostserious problem, however, is the natureof the Basin. Most of these uncertainties arise from the fact that all fluid flow associatedwith the basaltaquifers. On a local the holeslogged were drilled as water wells, and casingand scale,permeability across individual basalt flows is quite cementingis minimal. Furthermore, there are no holes that low, whereasalong contacts between flows permeability is have been continuouslycored and from which masonably high.The generalityof theseconditions is indicatedby the accurate in situ thermal conductivity estimates can be ob- ubiquitousupward or downwardflow betweenaquifers tained except on the Hanford reservation [Sasset al., 1971]. madepossible by the openhole nature of the wellcomple- Hence we have little idea of possible vertical or lateral tions.Consequently temperature logs for waterwells in the BLACKWELLET AL.: HEAT FLOW,WASHINGTON STATE AND CASCADE RANGE !9,501

TABLE ld. Thermal and Location Data for the Heat Flow Sites in Columbia Basin

Average Corrected Township/ Thermal Corrected Heat Range Latitude N, Depth Conductivity, Gradient, Flow, Quality Section Longitude W Range,m W m-• K -1 SE N øCkm -! mW m-2 Rating Lithology Summary

26N/34E 47ø45.87' , 109-199 (1.59) ! 55.4 88 B CR basalt? 10CAB 118ø31.18 ' 26N/33E 47ø45.20', 25-129 (1.59) 31.9 51 C CR basalt 18ACA 118ø42.50' 100-129 (1.59) 52.9 84 C 24N/36E 47ø34.70', 66-265 (! .59) 53.7 85 B CR basalt 16AAB 118o16.37 ' 24N/31E 47ø34.55', 19-149 (!.59) 52.8 84 B CR basalt 16BCC 118o56.07' 19-204 (1.59) 58.3 93 B 23N/43E 47ø30.41', 95-!25 (!.34) 41.6 56 B CR basalt 8AB 117ø23.81' 22N/20E 47ø22.11' , 310-900 2.18 0.21 18 28.4 62 A rhyolite, arkose, 26CBB 120o18.00 ' and sandstone 21N/31E 47ø20.00', 61-1250 1.67 0.21 42.0 70 B CR basalt 10CB 118o55.00 ' 20N/22E 47ø14.65', 49-264 (1.59) 1 32.0 51 c CR basalt 12ABC 120o00.78 ' 19N/17E 47ø07.27', 10-170 (1.38) 29.4 41 B 23CBD 120o40.88 ' 18N/26E 47ø00.26', 70-100 (1.59) 49.8 79 C CR basalt? 35C 119ø31.73' 16N/19E 46o53.37' , 59-333 (1.55) >27.3 >42 C CR basalt 12DB 120o23.45' 59-154 (1.55) 29.4 46 C 16N/31E 46•52.75 ', 10-230 (1.59) 59.1 94 C CR basalt 15B 118ø55.10 ' 16N/21E 46o49.63' , 10-100 1.38 37.2 51 B 33CD 120o12.37 ' 40-90 1.38 44.8 62 B 15N/17E 46ø46.90', 40-22 (1.59) 36.5 58 B sandstoneand clay 23ABC 120ø39.95 ' 15N/17E 46ø45.13' , 75-595 (1.46) 31.6 46 B clay, sand, gravel 36AAA 120o38.49 ' 14N/16E 46ø43.77', 20-110 (1.46) 35.9 53 C andesite 1CBD 120o46.74 ' 14N/44E 46ø43.72', 54-89 (1.59) 22.9 36 C CR basalt 1BCC 117o13.28 ' 14N/18E 46ø40.40', 20-55 (1.46) 39.0 57 C sand and clay 29DBB !20ø36.05 ' 13N/19E 46ø37.50', 50-160 (1.59) 32.8 52 B CR basalt 11DBC 120o24.75 ' 13N/29E 46ø36.77', 10-2!0 (1.59) 48.3 77 C CR basalt 13DB 119ø07.28' 12N/17E 46ø33.06', 80-120 (1.46) 64.2 94 C grovel, clay, and 11BBB 120ø40.11' sand 12N/20E 46ø31.56', 100-400 (1.59) 41.5 66 C CR basalt 16CA 120o19.54 ' 12N/22E 46ø31.25', 60-200 (1.59) 33.3 53 B 13CDC 120ø00.71' 12N/20E 46ø28.64', 10-350 (1.59) 32.3 51 C sediments and CR 36CD 120o15.78 ' basalt 11N/21E 46ø27.53', 85-450 (1.59) 32.9 52 B CR basalt 7AAC 120013.50 ' 11N/21E 46ø26.10' , 130-210 (1.59) 41.0 65 C sedimems and CR 16CDB 120ø12.15 ' basalt 11N/21E 46ø25.84', 150-330 (1.59) 28.8 44 B sediments and CR 22AC 120o10.53 ' basalt 11N/28E 46ø25.68', 20-280 (1.59) 37.7 60 B CR basalt 23BB 119ø16.62 ' ! !N/22E 46ø25.00' , 50-270 (1.59) 49.4 79 C CR basalt 30BA 120o07.13' 50-150 (1.59) 43.9 69 B 11N/22E 46ø24.57', 27-210 (1.59) 39.7 63 B CR basalt 28CB 120ø04.51' 11N/46E 46ø23.49', 15-405 (1.59) 35.6 56 B basalt with clay 32BCA 117004.52 ' 11N/45E 46ø23.28', 10-192 (1.59) 32.0 51 B CR basalt 32DAB 117011.45 ' 10N/41E 46ø22.37', 10-90 (1.59) 27.2 43 C CR basalt 3DBD 117ø39.50 ' !0N/28E 46ø21.97' , 5-120 (1.59) 34.3 54 C CR basalt 10ACC 119o17.43 ' 10N/28E 46ø21.73', 110-605 (1.59) 41.1 66 B CR basalt 14ABB 119ø16.13 ' 19,502 BLACKWELLET AL.: HEAT FLOW,WASHINGTON STATE AND CASCADERANGE

TABLE ld. (continued)

Average Corrected Township/ Thermal Corrected Heat Range LatitudeN, Depth Conductivity, Gradient, Flow, Quality Section LongitudeW Range,m W m-i K -1 SE N øCkm -1 mWm -2 Rating LithologySummary 10N/24E 46018.70' , 125-200 (1.59) 34.0 54 C CR basalt 36BD 119045.43 ' 10N/39E 46ø18.33', 49-229 (1.59) 1 31.6 50 C CR basalt 32BCA 117057.87 ' 9N/32E 46ø!6.04', 135-210 (1.59) 34.8 55 B basalt with 13BA 118ø45.21 ' interbeds 9N/27E 46ø14.82', 160-350 (1.59) 43.1 69 B CR basalt 23CA 1 ! 9o24.17' 8N/33E 46ø09.31', 50-200 (1.59) 37.7 60 B CR basalt 21D 118ø40.99 ' 8N/25E 46ø08.38' , 5-240 (1.59) 35.0 46 C 36AB 119o37.78 ' 7N/46E 46ø07.99' , 160-275 (1.59) 36.1 57 C CR basalt(?) 2AA 116o59.88 ' 7N/36E 46ø05.39', 100-225 (1.59) 35.4 56 B CR basalt 17CAD 118o20.30 ' 7N/46E 46ø05.25', 15--85 (1.59) 40.8 65 C CR basalt 13BA 116ø59.0I ' 7N/35E 46o03.66' , 85-260 (1.59) 34.0 54 C CR basalt 25AAC 118o22.22 ' 6N/33E 46ø01.46', 60-305 (1.05) 69.7 73 B cementedgravel/ !DBD 118o37.30 ' clay 6N/33E 46ø01.01', 20-85 (1.05) 106.8 112 C cementedgravel !0AD 118o40.65 ' 6N/19E 45ø59.52', 59-139 (1.59) 1 41.2 65 C CR basalt 24BC 120o22.97 ' 5N/21E 45ø55.00' , 74-224 (1.59) 49.2 78 D CR basalt 16CAB 120o11.49' 224-394 (1.59) 27.2 44 C 5N/14E 45ø54.46', 40-137.5 (1.59) 1 31.2 50 B CR basalt 22BCB 121ø02.86 ' 5N/15E 45ø53.04', 55-145 (1.59) 24.7 39 B Quaternary basalt 28DDD 120ø55.60 ' 3N/13E 45ø44.66', 160-195 (1.59) 39.0 62 C CR basalt 13DA 121006.95 ' 3N/13E 45ø44.23', 65-150 (1.59) 33.5 53 C CR basalt 2lAB 121o10.94 ' 3N/21E 45ø44.12' , 30-70 (1.59) 53.8 85 C CR basalt 19BAB 120o13.55 '

See Table la footnotes.

Columbia Basin are typically complex and are difficult to of appropriate quantity is encountered. As a consequence, interpret. Recharge to the aquifers is quite distant from the water wells almost without exception bottom in or just below points of developmentof the aquifers, and flow pathswithin aquifers (sites of potential up-or-down flow in the hole). the aquifer system must be complex and time dependent. Another limitation with many of the temperature logsmea- When the holes are drilled, drilling stopswhen water flow suredby WSU and USGS-WRD is that logging startsat the

TABLE le. Thermal and Location Data for the Heat Flow Sites in Northern WashingtonCascade Range

Average Corrected Township/ Thermal Corrected Heat Range Latitude N, Depth Conductivity, Gradient, Flow, Quality Section LongitudeW Range,m W m-1 K -• SE N øCkm -• mWm -2 Rating Lithology Summary

38N/8E 48o45.85' , 10-140 2.33 0.10 5 (309) 720 G Quaternary 20 121o48.30 ' volcanics 26N/13E 47ø43.20', 40-150 2.68 0.17 7 26.1 70 B biotite schist 27BA 121ø07.21 ' 26N/13E 47ø42.66', 20-!00 2.06 0.17 7 48.4 100 B phyllite, near hot 28CD 121o08.50 60-100 2.06 0.17 7 55.6 115 B spring 25N/9E 47ø40.97', 120-145 3.03 2 20.0 61 C greenstone 4ADA 121ø38.92 ' 22N/11E 47ø25.54', 110-145 2.97 0.21 7 !4.7 44 B phy!lite 4BDA 121o24.80 '

See Table la footnotes. BLACKWELLETAL.: HEAT FLOW, WASHINGTON STATE AND CASCADE RANGE 19,503

TABLE!f. Thermaland Location Data for the Low Heat Flow Sites in Southern Washington Cascade Range Average Corrected Township/ Thermal Corrected Heat Range LatitudeN, Depth Conductivity, Gradient, Flow, Quality Section LongitudeW Range,m Wm -1 K-1 SE N øCkm -1 mWm -2 Rating Lithology Summary

16N/4E 46ø5!.0!', 25-86.5 (!.97) 2 10.2 21 C basalt 23DDD 122o15.36' 15N/4E 46ø46.78', 100-!22 1.72 0.17 2 19.8 34 C basalt 14DDA 122o15.32' 13N/SE 46ø36.96' , 10-55 (1.09) 26.9 29 C Eocene(?)sedimentary 18ABD 122o13-63' 12N/2E 46ø32.86', !25-155 (1.67) 25.4 38 B Tertiary volcanics 5DCD ! 22o34.73' 12N/2E 46ø32.07', 60-205 (1.67) 23.0 38 B basalt 9DAD 122ø33-!7' 12N/3E 46ø31.33' , 90-138.5 (1.67) 20.5 34 B Eocene(?) basalt 17DCB 122ø27.54' 12N/3E 46ø30.44', 65-232.5 (1.67) 27.0 45 C Eocene-Oligocene 19CBD 122o29.23' volcanics 10N/4E 46ø22.65', 15-141 1.95 0.19 4 36.9 72 B 2DBA 122o15.95' 9N/2W 46ø17.72', 20-135 (1.59) 1 14.2 23 C clay, sandstone, I^DB 122ø52.!4' and basalt 8N/4E 46ø!0.37 ', 50-150 1.85 0.06 !7 24.2 45 B 14DD 122ø16.10' 5N/2E 45ø53.16', 70-156 (1.59) 32.0 51 B basalt? 25DBC 122o30.08' 5N/3E 45ø52.96' , 70-97.5 (2.01) 20.4 41 C 28CCC 122o27.00' 4N/3E 45ø49.10' , 135-220 (1.59) 1 38.0 60 B Eocene basalt 20ADD 122o27.33 ' 3N/3E 45ø43.77', 30-103 (!.59) 27.0 42 B Eocene basalt 21DAB 122ø26.23 ' 3N/3E 45ø43.60', 30-188 (1.59) 1 27.0 42 B Eocene basalt 21DBD 122o26.40 ' 2N/3E 45ø40.03', 25-127 (1.59) 1 23.1 37 B Eocene basalt 12CAD 122ø22.58 '

See Table l a footnotes.

watertable. Thus, if the well has flow up to, or down from, ing down the hole. It was opened by the USGS-WRD for thewater table, the first measuredtemperature may be much hydrologictests in 1972, at which time it was loggedby the differentfrom in situ rock temperature.Temperature logs of WSU group. The hole was then plugged back to a depth of many of the wells consist of a vertical line (isothermal). 730 m and is maintainedas a water level monitor well by the Given the propensity of fluid to flow within the wells USGS-WRD. Well logs measured in 1961, 1972, and 1981 are followingcompletion, it becomesvirtually impossibleto shown in Figure 5. In 1961, water entered the hole at the decipherthe nature of the thermal and fluid flow conditions water table (about40 m), flowed down the hole to a depth of existingat a particularlocation from a singlewell. Basedon 700-800 m, and exited into the formation. Below 800 m, the localaquifer conditionswithin the wells, gradientsboth gradientis nearly constant,and the temperature-depthcurve higherand lower than the "true" value mightbe encoun- is linear except for the bottom part of the log. The bottom tered.Thus only the overall averagegradients can be deter- isothermal sectionmay have been due to additional intrahole minedwith the presentdata set. water flow or due to the fact that the cable had hung up (and Temperaturelogs clearly show differencesin aquifer this fact was not recognized).The hole was loggedto the end headsand alsodemonstrate that theseaquifer head differ- of the cable at about 1250 m. By 1972 the flow pattern had encesmay changewith time. Thus it mightbe expectedthat changeddramatically, and water flow was both up and down localvertical leaks alongdikes, in fractureszones, or at from an entry point at about 500 m. The rate of flow down erosionalgaps in flows could cause local fluid circulation the hole was quite low and occurredbetween depthsof about anomalies.However, no convincing evidence has been 500 and 800 m. Artesian (up) flow occurred between 500 and discoveredso far for geothermalanomalies associated with 300 m. The presenceof upflow is indicatedby temperatures fluidcirculation of this sort. above the interpolatedtemperature-depth curve from below Someof thecomplexities of temperature-depthcurves for 900 m and the surface temperature intercept (about 12øC). a singlewell are illustratedby referenceto DABE-1 (21N/ The curvedtemperature-depth relationship between 200 and 31E-10CB,see Figure 5). Thiswell wasdrilled as a hydro- 300 m and the fact that the observed temperature is higher carbonexploration test in 1960.It wasfirst logged by R. F. than the interpolatedtemperature suggestupflow, with the Royin !96!. Subsequently,the hole had a checkeredhistory 200-300 m portion of the hole being heated by the upward thatincluded its being plugged with railroad cross ties for a flowingwarm water (from 500 m). The sharpnegative-slope timeby local ranchers because they could hear fluid cascad- part of the curvebetween 500 and 600 m is very difficultto 19,504 BLAC•W•:.iLLETAt..' HEAT FLOW, WASHINGTON STATE AND CASCADE RANGE

117

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NORTHERN mm/ ß WASHINGTON I OKANOOAN CASCADE RANGE ( HIGHLANDS ,2 -*% ,lB + ./ / OLYMPIC SPI tlOUNTAINS

E • SQP\ COLUMBIA BASIN

x + ß +ß /•n

x/ + BASIN HILLS %$45+ , '•)•"• x + $,.,... +./ ..__.

./ SOUTHERN+, $ /+ WASHINGTON i SCAL• UMATIL.LA BASIN / KILOId[TtRS RANGE COLUMBIA RIVER /

Fig. 1. Heat flow map of Washington.Physiographic provinces are outlinedwith dashedlines and identified.The Pasco and Umatilla basins are subprovincesof the Columbia Basin. The volcanoesin the Cascade Range (large asteriskswith a two-letter identification)are also shownfor reference.Locations of StevensPass (SP), SnoqualmiePass (SQP), SimcoeMountains (SM), andhole DABE-1 are identified.Data of acceptablequality (Table 1) are plottedon this figure. The map is contouredat 10 mW m- 2 intervals. Heat flow symbolsare triangle, 20-30 mW m-;2 circle, 30-40 mWm-2' cross,40-50 mW m -2- pluses50-60 mW m-2. soliddiamond, 60-70 mW m-:' solidsquare, 70-80 mW m-:' solidtriangle, 80-90 mW m-2' dot,90-100 mW m -2' star,100-110 mW rf•-2' smallasterisk, > 110mW m -2. The location of the cross section in Figure 7 is indicated. explainunless up-or-down flow in an aquiferoutside the well on the western and eastern margins of the province.The bore is included.The temperaturedata between 100and 200 resultsof this study suggestthat the high predictedSiO2 heat m may represent the backgroundgradient unaffectedby flow values in the Columbia Basin [Swanberg and Morgan, water flow. Following pluggingof the hole and its develop- 1979] are related to the high gradients. ment as a water level monitor well, the flow pattern in the There are two interpretationsof the heat flow in the hole changedagain. When the well was loggedduring 1981, Columbia Basin. The first is that the measured heat flow there was downflow through most of the hole, with water values reflect the conductive heat flow from the crust below entering at the water table and exiting at two locations, the Miocenebasalt. This hypothesisis supportedby thefact between210 and 300 m and at a depth of approximately450 that the heat flow variations are consistentwith probable m. An aquifer at 300 m was either donating or extracting regionalvariations of crustalradioactivity. Heat flowvalues fluid. aregenerally 50-60 mW m-2 in areaswhere the crust is more [Catchings and Mooney, 1988]and alongthe southern Heat Flow and Geothermal Gradients and westernmargins of the province where the crustappears Basedupon analysisof the temperaturelogs [Blackwellet to betonolitic in composition(west of the0.706 line of initial al., 1985],the gradientrange throughout the ColumbiaBasin Sr isotoperatios [Kistler and Peterman, 1978]) and most of is between 30ø and 55øCkm -] with a mean value of 40.6ø + the exposedgranitoids are very low in heat generation !.8øCkm -]. The meanheat flow, excludingdata from the [Swanbergand Blackwell, 1973]. Similar heat flow values are westernedge of the provinceis 62.2 +- 2.0 mW m-2. foundin westernIdaho where such rocks (of Mesozoicage) Histograms of geothermal gradient are given in Figure 6. cropout at thesurface [Blackwell et al., 1990].On the other There is a lack of detailed thermal conductivity information, hand,along the northcentral part of the ColumbiaBasin, so it is not clear whether the variation in gradients is wheregranitic rocks of higherradioactivity occur, heat flow associatedwith thermal conductivity variations within the valuesare 70-93 mW m-2, typicalof thosefound in base- basaltsor between basalt and sedimentaryrocks, or whether ment areas of the OkanoganHighlands in northeastern it reflectsgenuine changesin heat flow in various locations Washington[Blackwell, 1974; Steele, 1975]. throughout the plateau. There is some evidence, as pre- Thesecond major effect which may influence the heat flow sentedin Figures 1 and 2, for higher than averagegradients istransfer of heat by groundwater flow. The high permeabi!- BLACKWELLETAL.: HEAT FLOW, WASHINGTON STATE AND CASCADE RANGE 19,505

125 123 121 119 117

q-

..T...\ \ %/ WASHINGTON\ ,n I OKANO•AN ,,, CASCADE\ • - + + / *.' I ,,; _. \ •HIGHLANDS ,,.

! I , /

OLYIdPIIdOUHTAIN$\ ½ /"' • \ c.../ / \ \ / •SqP • / • mDABr-1 / "-'"/el-- COLUMBIABASIN - ._. \ / -" \ / q- +// +

WILLAPA HILLS[• / & i'•-. ßI / '"-" -- __ /. ....,L... a] .•LU[ ¾01 WASHINGTONSOUTHERN+ •;•:s• ßP / SCALE CA, GAD[ I UIdATILLA BASIN RANGE••' %. BIARIVER / KILOULr'rER•

Fig. 2. Geothermalgradient map for Washington (same basc as Figm-c 1). Geothermal gradients fi'om holes or sites of acceptablequality (Tablc i) m'cshown. Generalized gradient contours arc shown. Gradient symbols a•c aim!c, 0%!0øCkin-l, opcntriangle, 10•20øC km-I; opensqua•c, 200-.30øC kin-]' solidtdanglc, 30ø-40øC kin- l' solid diamond,$0ø-60øC kin-i; clot,600--70øC km -I . ' ity of the basalt flow interbedsand the general lack of St. Helens, and . The two principallate coincidenceof piezometric levels certainly indicate potential Cenozoicbasalt centers are the QuaternaryIndian Heaven for groundwaterflow. Clearly, fluid flow must effect local area in the southcentral part of the rangeand the areas,but in spite of the many holesdrilled in the basalt,no Simcoevolcanic field in the southeasternpart of the range. anomalouslyhot wells have been reported.Any flow that North of Mount Rainier, the bedrock geologyis predomi- existsmust be relativelysubtle. There are severalhigh nantlypre- to mid-Cenozoiccrystalline rocks, including both valuesof heat flow alongthe Snake River in the Umati!la graniticintrusive rocks and metamorphicrocks. The only subprovince;these may indicate some flow toward the late Cenozoic volcanic rocks are the andesite-dacite volca- topographicallylow areas along the fiver. noes, Peak and . Basedon the data available at thistime, we concludethat The WashingtonCascade Range is the provinceof greatest conductiveheat transferdominates on a provincewide geothermal activity in the state, with active or dormant scale,although in local areasconvection might be signifi- volcaniccenters, and severalhot springs.There are only a cant.The surfaceheat flow patternreflects the radioactivity few heat flow sites in the northern Washington Cascade of the crustbelow the basaltand the back arc regional Range,and only three of them are far enoughwest to be near setting.Because the heatflow from below the uppercrustal the areas of late Cenozoic volcanism. Two of the three are radioactivitylayer is interpretedto be similarfor theprov- associatedwith hot springareas [Korosec, 1983]. At Stevens ince,even though the surface heat flow varies from northeast Pass(marked SP on Figure !; sites 26N/13E in Table 1) one to southwest,the ColumbiaBasin is a singl• heat flow of the heat flow valuesis anomalouslyhigh and is obviously provincein the sensedefined by Roy et al. [1972]. affectedby the hot springcirculation, whereasthe other heat flow valueis typical of thoseseen in the southernWashing- WASHINGTON CASCADE RANGE ton CascadeRange. The most northerly hole in Washington is on the slopesof Mount Baker near Baker Hot Springs.It NorthernWashington Cascade Range, is also affectedby the hot spring circulation and does not SnoqualmiePass Area, ColumbiaRiver give a typical background value for that area [Korosec, Withinthe state of Washingtonthere are differences inthe 1983].The sparseresults suggest that the regionalheat flow geologicnature of the CascadeRange. South of approxi- may be similarto that found in the British ColumbiaCascade mately47ø20 ,, the basementof the WashingtonCascade Range(about 80-90 mW m -2 [Lewiset al., !988]). Rangeispredominantly composed of early to middleCeno- Unlike the situationin Oregon, where the high heat flow zoicvolcanic rocks [Walsh et al., 1987;Smith, 1989]. The zone has been identified for a north-south distance of at least majorQuaternary stratovolcanoes are Mount Adams, Mount 200 kin, the high heat flow zone along the Cascadeaxis in 19,506 BLACKWELLETAL.: HEAT FLOW, WASHINGTON STATE AND CASCADE RANGE

COASTAL PROVINCES COASTAL PROVINCES N = 31 N=31 A B

15 25

2O

F lO F R R E E Q Q U U E E N N lO C s C Y Y

o 0 25 50 75 100 o 50 lOO 150 GRADIENT (DEG. C/KM) HEAT FLOW (mW/m-m)

S. CASCADE RANGE S. CASCADE RANGE N= 30 N--30 C D

15 25

2O

F 10 ...... F R R E E 15 Q Q U U E E N N lO C Y Y

lI, II [ I 0 25 50 75 100 0 50 100 150 GRADIENT (DEG. C/KM) HEAT FLOW (mW/m*m) Fig. 3. Histogramsof geothermalgradient and heat flow from Table 1. (a) and (b) For the coastalprovinces. Provincesincluded are the Puget Lowlands, Olympic Mountains, Willapa Hills, andthe Cascade Range west of thehigh heatflow zone.Bar on gradientplot shows range in gradientin hole12N/IW-9CCC associated with lithologicvariations. (c) and (d) For the high heat flow region in the southernWashington Cascades.

Washingtonseems to be segmentedby areas of normal heat beganin the late 1970s[Blackwell et al., 1982;Schuster et flow around Snoqualmie Pass (SQP on Figure 1) and the al., 1978]. Columbia River. For many years the only heat flow values in Three new measurementsare low/normaland confirmthe the Washington CascadeRange were near SnoqualmiePass valuesobtained by Blackwell[1969]. One holeis northwest [Blackwell, 1969]. Heat flow values there are approximately of the SnoqualmiePass area at a mineralexploration loca- normal for continents, and there appeared to be no signifi- tion,and two holes (22N/I1E-4BDA and 23N/IIE-33CAB) cant thermal anomaly in the Cascade Range. These data weredrilled east of thepass as part of thisproject. Finally, stood uncontested until drilling for heat flow measurements theapparent south edge of the region of normalheat. flow is BLACKWELLET AL.: HEAT FLOW, WASHINGTONSTATE AND CASCADERANGE 19 )07

OKANOGAN HIGHLAND OKANOGAN HIGHLAND N = 26 N=26 A B ' 15 25

20

F lO F R R E E 15 Q Q U U E E N N lo C s C Y Y

5

0 25 so 75 •00 0 so •00 •50 GRADIENT (DEG. C/KM) HEAT FLOW (mW/m-m) Fig. 4. Histogramsof (a) geothermalgradient and (b) heat flow from Table I for the Okanogan Highlands. poorlydefined by a singlesite north of Mount Rainier. The mW m ~, including those at the south edge of the Simcoe .reasonfor the lower values observed in the Snoqualmie Pass in Washington and north of the vicinityis not obvious. The values could be local anomalies area in Oregon [Blackwell et al., 1982, this issue]. The area due to water circulation, although this explanation seems is most clearly defined on the gradient maps (Figures 2 and unlikelysince the holes are scattered over a large area and 9). Temperature-depth curves from holes along the Colum- are in a variety of topographic settings. A discontinuous bia River north and northeast of Mount Hood generally have regionalheat source at a depth is an alternative explanation low gradients and are often curved, possibly indicating for these variations in heat flow. The area contains a regional downflow of water or recent climatic warming. structurallycomplex zone of transition between the southern Temperature-depth curves from holes in the Quaternary andnorthern Washington Cascade Range areas and is cut by volcanics often are very complicated and in some cases severalstrong lineaments, but there are no late Cenozoic show evidence of transient lateral flow of warm water. volcanics in the area. Becauseno deep holes have been drilled along the Columbia Another anomalous zone of heat flow along the Cascade River, or in the Simcoe volcanic field, the observed heat flow Rangeis associated with the Columbia River. East of 122ø pattern may need some revision when such data are ob- (excludingholes drilled near the Bonneville and Trout Creek tained. Geothermal conditions need to be tested by drilling hot springs,marked with a G quality in Table 1), most heat flow values along the Columbia River are less than 60-70 TEMPERATURE, DEG C 0 25 75 TABLE2. Summary ofGradient andHeat Flow forVarious 0 , , . .; • .... $1ø .... Areas

Heat Flow, Gradient,øC km -• mW m-2

Average SE N Average SE N •: 500- Coastalprovinces 26.0 1.2 31 40.1 1.8 31 • (all low values) Southern 44.5 3.0 30 75.4 4.4 30 • BASALT EXPLORER 1 Washington + 21H/31[-lOGB CascadeRange 1 ooo ß 211•J1[-lOGI (highheat flow region) (ColumbiaRiver) 36.9 4.8 9 53.6 4.9 9 Okanogan 25.3 0.9 26 74.5 2.4 26 Highlands ColumbiaBasin (all) 40.6 1.8 55 62.2 2.0 55 15oo ColumbiaBasin 32.8 2.3 7 51.0 1.7 5 (westernmargin) Fig. 5. Temperature-depthcurves for DevelopmentAssociates BasaltExplorer 1. Three logsmeasured over a 20-yearperiod are SE is the standarderror and N is the numberof data points illustrated.Logs were obtainedby R. F. Roy (1961),personnel from averaged.Quality A, B, and C data are averaged,but the averages WashingtonState University(1972), and SMU {,1981).Every fifth donot change significantly if only A andB qualitydata are used. pointon eachlog is plottedby a symbol. 19,508 BLACKWELLET AL.' HEATFLOW, WASHINGTON STATE AND CASCADE RANGE

COLUMBIA BASIN COLUMBIA BASIN N-- 55 N=55 A B

15 25

2O

F lO .... - ...... F R R E E 15 o ;:[ o E i•. E N N lO .: C 5 .- ..:.•..•...... C Y . Y

0 0 0 25 50 75 100 0 50 100 150 GRADIENT (DEC. C/KM) HEAT FLOW (mW/m-m)

Fig. 6. Histograms of (a) geothermal gradient and (b) heat flow from Table I for the Columbia Basin. specificallyfor heat flow/geothermal gradient studiesand to 45øCkm -• . Theseresults are illustrated in Figures1, 2, and depths greater than 150 m to unequivocally determine the 7. The changefrom the coastal heat flow of 30-50 mW m-2 heat flow along the Columbia River. to high heat flow is well constrained along the profileand In the Oregon and southern Washington Cascade Range occurs over a distance of less than 20 km. Thus the half most of the rocks are volcanic or volcanoclastic and have width of the change (10 km) is similar to that in Oregon similar thermal conductivities. In the northern Washington [Blackwell et al., 1982, this issue] and in British Columbia Cascade Range and in the Okanogan Highlands, however, [Lewis et al., 1988]. The change occurs within the southern there is quite a wide range of conductivity, from very high Washington Cascade Range physiographic province. The values in quartzite and dolomite (e.g., hole 23N/11E-4DD in eastern boundary of the high heat flow zone is not as well Snoqualmie Pass) to low values in volcanic rock. Conse- located as the western boundary and is of lower relief than quently, gradients in the northern Washington Cascade thewestern boundary (10-20 mW m-2 insteadof 30-40mW Range, even without variations in heat flow and fluid flow m-2) becauseit adjoinsthe highheat flow backarc region. effects, can be expected to be much more variable than in the The heat flow and gradient data for the high heat flow southern Washington Cascade Range. The fractured granitic region of the southern Washington Cascade Range are and metamorphic rocks in the northern Washington Cascade summarized in histogramsin Figures 3c and 3d from the data Range may be more brittle and more capable of holding open in Table 1. All data in the region includingthe data collected fractures, and thus be more susceptible to fluid circulation. as recently as 1988 [Barnett and Korosec, 1989] are in- Indeed the geothermal field at Meager Mountain in British cluded. There is a wide range in heat flow and gradient, Columbia [Fairbank et al., 1981], where temperatures in excess of 200øC have been obtained from holes drilled in fractured granitic rocks, indicates that there is potential for deep fluid circulation in the geological environment existing 75 ' ' ' ' ! .... I .... I .... I ' ' ' w- in the northern Washington Cascade Range. • o o •_- ..•-ø-•o'- -ø-%- -- -.o. •o__.o Southern Washington Cascade Range 25 - In 1981 a transect of holes was drilled just south of Mount

Rainier. The results of the heat flow measurementsalong this 0 - 1230WI ,2•-w 121•WI I I I corridor, includingdata obtained from water wells to the east o and west of the drilled holes, are shown in the cross section t••1007 o_ .oQ_-. _o o in Figure 7 (the location is shown as AA' on Figure 1). A pattern similar to that observed in Oregon [Blackwell et al., '50-•__o__ •___•%___3t / '•'om'--ø Mr. Roinier 1982, this issue] was obtained, although with a reduced bJ 0 , .... a , , , , a ß , i -r 5'o O' 50' I00' .... amplitude. Heat flow values west of approximately 122øW DISTANCE,km arebelow the continentalaverage of 60 mW m-2, whereas heat flow values between 122 ø and 120ø45'W are 70-108 mW Fig. 7. Heatflow cross section for thesouthern Cascade Range. Dataare plotted as a functionof distancealong an west to east line m-2, andgradients range between 34 ø and 67øC km -• . East southof MountRainier (see Figure 1 forlocation). The range of of approximately 120ø45', heat flow values decreaseto less gradientin hole12N/lW-9CCC associated with lithologic variations than60 mW m-2, andgeothermal gradients range from 30 ø to is shownby the vertical line at 50 km on the profile. BLACKWELLET AL.: HEAT FLOW,WASHINGTON STATE AND CASCADERANGE 19,509

TEMPERATURE •C (ARBITRARYi' This assumptionis approximately valid although the values •> may increasesomewhat with depth. The implicationsof the i .i .5[ Ii 'Ii i i' I _ conductivityassumption are discussedin more detail by Blackwell et al. [1982] in their description of the tempera- tures in the Oregon CascadeRange. Because the downward continuationprocess is inherently unstable, the calculated temperaturestend to become variable (noisy) as the source IOO is approached.Because we do not know the actual source E I- •\\',•Lq•,. "•.•----•..-•. •,OA$(:;ADE ANOMALY configurationand the heat flow anomaly is partly inter- preted, there is no "correct" answer, and the two tempera- ture distributionsare merely indications of the actual tem- peratures at the depths shown. • •ESTwo different models were calculated, one with the sourcesat a depth of 15 km and one with the sources at a depthof 12.5km. Calculatedtemperatures at a depth of 5 km for the source at 15 km are shown in Figure 9b. For the reason described above the calculated temperatures are 300 more variable in Figure 9d with the sourcesat 12.5 km than Fig.8. Temperature-depthcurves for the SouthernWashington in Figure 9c with the sources at 15 km. The maximum CascadeRange and Coastalprovinces. A constanttemperature was calculatedtemperatures are higher in the second case be- subtractedfrom each curve to give a 0øCsurface temperature. Data causethe 10 km depth is closer to the plane of sources.Both for manyof the holes in the low and high heat flow regionsare of the modelswere calculated assumingsteady state condi- illustrated.The two holes west of Mount St. Helens are clearly associatedwith the low heat flow area. tions, a reasonableassumption if thermal conditionshave not changeddrastically for 2 to 5 m.y. The resultsare consistentwith temperaturesof 400ø-500øC indicatingthat the thermalfield in this regionis complicated. at 10 km over a region of about 100 by 100 km in the southern Theaverage gradient and heat flow for the area are 44.5ø __+ Washington Cascade Range. The highest temperatures 3.0øCkm -1 and75.4 -+ 4.4 mW m-2 respectively. (500ø-600+øC)are aligned in a NNE-SSW direction in the The major contrast in heat flow and geothermalgradient center of the anomalousarea. The positions of Mount St. betweenthe coastalprovinces and the WashingtonCascade Helens (west edge)and Mount Rainier (north edge; although Rangeis clearlyillustrated by the temperature-depthcurves the data on which the positionof the northward decreasein fromthe two regimesin the southernWashington Cascade heat flow are based are weak) are peripheral to the high- Rangeshown in Figure 8. Most of the holesthat are in the temperaturezone, and the area of highesttemperature is "CascadeAnomaly" are shown, as are about half of the alignedthrough the Indian Heaven and Goat Rocks centers wellsin the low heat flow region to the west. of late Cenozoic volcanism. Mount Adams may lie along the The difference between the two sets of data is clear. apex of the anomaly.This broad area, and especiallythe Temperature-depthcurves from two holesimmediately west Goat Rocks area, is a major center of Quaternary volcanism of Mount St. Helens are superimposedon Figure 8 and [Swansonand Clayton, 1983;Smith, 1989].Thus the area of clearlyindicate their associationwith the low heatflow setof highest crustal temperaturesappears to be axial to the holes.These holes were drilled in 1979, and hole 9N/5E- volcanicarc, the backgroundtemperature in the arc is high, 18BB(STH-2) was buriedby the debrisflow associatedwith and as to the south in Oregon, there is a sharp edge to the thecollapse of the northside of the volcanoon May 18, 1980. west side of the high heat flow region (passingthrough the A drillingproject on the east side of Mount St. Helens site of Mount St. Helens). The locations of Quaternary plannedfor 1980 was not carded out. volcanic centersmay occur anywhere within this area, so The thermal data in the southern WashingtonCascade each is not only an isolated spot of short lived Rangeare of sufficientdensity to warrant detailedinterpre- magmaticactivity but is alsopart of a crustalscale thermal tation. Because the thermal conductivity does not vary a anomalythat has developedas magmatismhas proceeded. greatdeal in the volcanic rocks (see Table 1), a gradient Stanleyet al. [1987,this issue]have describedextensive contourmap (Figure 9a) wasprepared and used for interpre- magnetotelluricmeasurements of crustalresistivity in west- tation.Alternative interpretations of the detailsof the pat- ern Oregonand Washington.Two of the conductancecon- ternare possible given the sparsityof the data,but the main tours from their studiesare plotted with the 5-km tempera- featuresof the sharpeastern boundary and the northeast/ turesin Figure9b. There is not a one-to-onematch between southwesttrending axial high are well constrained.The the interpretedcontours of highesttemperature and conduc- interpretationincludes part of the Simcoevolcanic field in tance, but there are no thermal data that constrainthe theregion of highheat flow althoughthere are no heatflow northwest comer of the thermal anomaly where the two measurements that confirm this inclusion. Also the western interpretationsdiverge. High crustaltemperatures do exist boundaryis assumedto be orientednorth-south. The hand- over about 3/4 of the area of the conductance anomaly. contouredgradients were digitized on a 15km by !5 km grid Stanleyet ah [thisissue] conclude that !ithology(i.e., a deep andinput into an inversionprocedure developed by Brott et sedimentarypackage (an underthrustwedge)) is primarily a/. [1981][see also Blackwell et al., !982]. responsiblefor the conductanceanomaly. The downwardcontinuation technique is based on the in contrast,the low resistivity(high conductance)zone in placingof a seriesof pointheat sources at a specifieddepth. the OregonCascade Range that is closelyassociated spa- Uniformthermal conductivity is assumedin thecalculation. cially with the high heat flow is interpretedto be due to 19,510 i3•.•,xc•,:'•,ELL ET AL.: HEATFLOW, WASHINGTON STATE AND CASCADE RANGE

30 t.•O •¸ •20 150 180 210,,,,., 0 30 60 90 120 150 180 2!

' I"' ,-,o, ' . MR

• -150 150• .... ' " R

9o 9o 60•"• • •LUMBIARIVER60 60 3o• OBSERVED 3o 3o TEMPERATUR

/• I GRADIENTSI ...... ! I I , I I I I I I IAT I 5 KMI I I I I , I I I I 00 30 60 90 120 ! 50 180• • 0 DISTANCE, KM •STANCE, KM

2100 , ,,,30 ,,, , 60 90 120 150 180 210210 d2100 30 60 90 120 150 180 2!0

ß •o F ..

E ;SH '.

' 500

60• COLUMBIA RIVER 60 ...... 30 TEMPERATURE 3o 30 TEMPERATUREI ,o I O0 I ,,,I30 I 60I I , 90 I 120I I 150I, I .180 I I • 00 I , 30I I 60I I 90[ I 120I I 150I I 180I I 21•,0 DISTANCE, KM DISTANCE, KM Fig. 9. Interpretivemaps of gradientand temperaturefor the southernWashington Cascade Range. Heat flow sites are shown on Figures 9c and 9d reference. (a) Observed geothermal gradient maps. (b) Downward continued temperaturesat 5 km for a sourceplane at 15 km. The shadedregion containsthe I000 and 5000 S conductancecontours from Stanley et al. [this issue]. (c) Downward continued temperature at 10 km for a source plane at 15 km. (d) Downward continuedtemperatures at 10 km for a source plane at 12.5 km.

"metamorphically produced fluids and partial melt in a high midcrustaltemperature in northern OregonaM in regionwhere ductile behavior occurs at the top of the 6.4-6.5 southern Washington suggeststhat temperature, or tem•r- km/s velocitylayer" [Stanleyet al., this issue].The question ature related effects,rather than rock compositionaleffects of the validity of the extrapolationof the heat flow data from may be dominantin causingboth of the low resistivityzones, the shallow holes to temperaturesat midcrustal levels in Oregonhas been discussedin detail by Blackwell et al. [this DISCUSSION issue].Because most of the argumentsapply to thisarea in a similarfashion, the discussionwill not be repeatedhere. So Summary of Washington Heat Flow Distribution assumingthat the interpreted location of the heat flow anomalyis correctand that the temperaturescalculated are Theaverage heat flow and geothermal gradient values four reasonable,at the depth of the sedimentarypackage the the various provinces discussedin this report are summa- temperaturesare quite high, and metamorphismmight mod- rized in Table 2. The thermal patterns in Washingtonare ify the electricalproperties of the sediment.The rather close similarto thosediscussed by Blackwell[1978], except t•,•h•': • geographicrelationship of high electricalconductivity and thereis now a significantheat flow data base in and west of BLACKWELLET AL,' HEAT FLOW,WASHINGTON STATE AND CASCADERANGE 19,511 theCascade Range. The thermalprovinces include the low thoughsubduction is no longerpresent along much of this heatflow coastalregion west of the WashingtonCascade length, the long thermal decay time of the low heat flow Rangeheat flow anomaly, where heat flow averages 40 mW preserves evidence of subduction for tens of millions of m-2, the southernWashington Cascade Range heat flow years. Thus the continuity of the low heat flow areas anomalywhere heat flow averages 75 mW m-2, andthe dramatically confirms the validity of the hypothesisthat OkanoganHighlands where heat flow alsoaverages 75 mW subductionwas continuousalong the west coast of North -2 •m ß America in the early and middle Cenozoic [Blackwell, 1971a; -2 Averageheat flow in the ColumbiaBasin is 62 mW m , Roy et al., 1972]. The intermediate focus earthquakesbe- significantlylower than in the OkanoganHighlands. This neath the Puget Soundregion are contemporarymanifesta- differencein heat flow may be associatedwith differencesin tions of this subductionactivity. heatloss from the mantle or differencesin the heat produc- It is unfortunate that there are not many data for the tion from radioactivity within the crust. The crust beneath transitionbetween the OkanoganHighlands/Columbia Basin thepart of the ColumbiaBasin where the heatflow is lowest and the Washington Cascade Range. Based on the results appearsto be unusuallymafic, based on seismicrefraction from this study and data from Canada [Lewis et al., 1985, data[Catchings and Mooney, 1988], so the heat flow from 1988], heat flow values in the two provinces are similar. the mantlewithin this province may be essentially the same However, the details of heat loss in these two provinces as the heat flow at the surface. The average heat flow is must be quite different. The heat flow in the Washington nearlyequal to the intercept value (60 mW m -2) onthe linear CascadeRange is related to a heat sourceat an apparent heatflow-heat productionline (heat flow at an upper crustal depth of about 10 km. In contrast, the high heat flow in the radioactivityof zero; see Blackq4,ell[1971b] and Roy et al. Okanogan Highlands (and the provinces to the north and [1972]for discussionsof the heat flow-heat production south, the Cordilleran Thermal Anomaly Zone of Blackwell relationship)for the OkanoganHighlands. [1969]) is related to back arc processeswith thermal source The pattern of heat flow in the southern Washington regionsin the upper mantle and lower crust that are associ- CascadeRange is relatively well defined, although many ated with past and present thermotectonicevents affecting detailsremain to be determined, particularly along the north, the whole Cordilleran Mountain chain. The back arc thermal east, and southeast boundaries of the thermal anomaly. anomaly involves a much larger area and owes its origin to Much of the variation may be due to lateral changes in the the interplay of several mechanisms such as extension, strengthor depth to the heat sourcethat causesthe high heat magmatism, and thinning lithosphere [Roy et al., 1972; flow. However, some of the variation may be due to fluid Lachenbruch and Sass, 1978; Blackwell et al., !990], flow conditions, or other local situations. whereas in the volcanic arc shallow crustal intrusion domi- The geothermal gradient pattern for Washington is some- nates. whatdifferent than the heat flow pattern; for example, there is almosta factor of 2 difference in the average gradient in Cascade Range Heat Flow the southern Washington Cascade Range and in the Oka- hogan Highlands even though the heat flow values are Extensive studies of geothermal gradient and heat flow similar. This difference arises because the thermal conduc- have been carded out in the Cascade Range in Oregon. tivity of the volcanic rocks in the southern Washington Major results include the location of a sharp eastward CascadeRange is lower. So in spite of the similar heat flow, increase from lower than normal heat flow to much higher temperaturesat 10 km beneath the southern Washington than normal heat flow within the Western Cascade Range CascadeRange may be up to twice as highas thosebeneath (the mid-Cenozoicvolcanic arc) and mappingof the western the OkanoganHighlands. High gradientsare also observed boundary of the high heat flow zone for half the length of in the Columbia Basin. These high gradientsare partially Oregon. Average heat flow values in the high heat flow zone related to the fact that the have a low thermal are 101mW m-2 and averagegradients are 64øCkm -l conductivity.The average gradientsare slightly lower than [Blackwell et al., 1982, this issue]. As part of the Oregon theaverage in the southernWashington Cascade Range. The studies, extensive drilling was carried out near the Mount geothermalgradient beneath the Columbia Basin will de- Hood volcano (25-50 km south of the Columbia River). creasewith depth when the rocks beneath the basalt are Steele et al. [1982] concludedthat the backgroundheat flow encounteredbecause the sedimentary/metamorphic/igneousvalue in the High Cascade Range decreasesfrom 100 mW rocksthat make up the basementwill have higher thermal m -2 to 70-80 mW m-2 betweenMount Jeffersonand Mount conductivitiesthan the volcanicrocks. Hence at a depthof Hood. 10 km the temperaturesbeneath the ColumbiaBasin are The transitionfrom high to low heat flow along the west probablycloser to thosein the OkanoganHighlands than to sideof the CascadeRange over a distanceof approximately thosein the southernWashington Cascade Range. 20 km is uniquely sharpfor a regional thermal boundary. The Theorigin for the low heatflow westof the CascadeRange half width of 10 km indicatesa depth of the sourceof about is associatedwith the subduction of the Juan de Fuca 10 km. Heat flow measurements in British Columbia indicate oceanicplate beneaththe westernpart of North America a similarpattern of low heat flow along the coast and high [Blackwell,1971a, b, 1978;Blackwell et al., 1982].As the heat flow inland, where the Cascade Rangeheat flow values oceanicblock sinks beneath the continentalplate, the upper rangefrom 65 to 90 mW m -2. Thetransition from low t.o high partof the oceanicplate absorbsheat from the continental heat flow occursalong a line of gravity gradients,anomalous block,causing the low heatflow. This zoneof abnormally upliftrates, and faulting [Hyndrnan, 1976; Lewis eta!., 1985, low heat flow has been identifiedfrom British Columbiato 1988]. BajaCalifornia [Roy et al., !972;Hyndman, !976; Lewis et Contoursof heat flow for the entire lengthof the Cascade a!., 1988;Blackwell, 1978; Blackwell et al., 1990].Even Rangeare shownin FigureI0, and heatflow sitesare shown 19,512 I•l.**CK•,'EL ETAL ' HE-'•TFLOW, WASHINGTON STATE AND CASCADE RANGE

to illustratethe data densityin the variousareas. The most seriousdata gaps are in northernWashington, in southern 125ø 120ø Oregon, and in northern California. The contoursoutline a 50ø Idki 50ø thermalsegmentation of the CascadeRange. This segmen- D BRITISH tation has been discussed in brief by Blac'k•,'ell and Steel [ 1983],and other categoriesof segmentationof the Cascades - ß 0 100 Rangehave been discussed by Guffantiand Weaver[1988]. ' Scale. km Major troughs in the Cascade thermal anomal) are at the ColumbiaRiver and in central Washington.The originof •ldB thesetroughs is not clear;they may be due to gapsin productionalong the arc over the last 5 m.y. or so. However, thereare hot springsin both gaps[Mariner et al., thisissue]. Deeper drill holes in both areas are needed to resolvethe true crustal heat flow in the area. The near constant half width {10 km) of the west side of the thermal high is an interpretation, but it is documentedin three widely separated areas: British Columbia, southern Washington, and northern Oregon. This half width ma• characterize the depth to a thermal anomaly causedb.• a zone of shallow crustal magma residence since it does not appear to consistentlycoincide with any major, crustal, seismicvelocity boundary (and by inference any lithologic boundary).A superimposedthermal peak of about 10+ mW m -2 coincideswith the axis of greatestvolcanic production in the southern Washington Cascade Range, and a similar thermal peak has been documentedat Mount Hood [Steele 45 ø 45 ø et al., 1982]. Other such thermal concentrationshave not been resolvedprobably due to data limitationsrather than the lack of such features. Blackv•,ellet al. [1982] calculated the ratio of intrusiveto extrusive volume in central Oregon by assuming that the excessheat flow above the background representedthe heat lostby the intrusiveprocess. The calculationswere based on volumes of extrusives estimated by White and McBirn v [ 1978].New calculationsof intrusiverate alongstrike for the wholerange are shownin Figure 11.These results are based on new along-strikeestimates of volcanicextrusion volume for the last 2 m.y. presentedby Sherrodand Smith[thi• issue],also shown in Figure11. These estimates appear to be conservative.Priest [this issue] estimates 20-30 km 3 (2 m.y.)-• km-• for centralOregon (about 85% of whichis basalt)and M. A. Korosec(unpublished data, 1989)esti- matesan additional10 km3 (2 m.y.)-• for part of southern Washington.The observedheat flow alongthe arcand the assumedheat flow backgroundare alsoshown. In calculat- ingthe rates of intrusionit wasassumed that the 100 mW m-2 heatflow observedalong the westernside of theHigh CascadeRange in Oregonrepresents the averageheat all acrossthe arc. If the axial heat flow is higherland it 40 40 ø 124ø 120 ø probablyis), the volume estimates would be proportionall.• increased. Fig. 10. Summaryheat flow map of the CascadeRange. Data The ratiosof intrusionto extrusionshown in Figure11 are pointsand major volcanic centers are shown. Data points are shown for locationonly. Data from this paper, Blackwell et al. [thisissue], higherthan those estimated by Blackwellet al. [19821 Lewis et al. [1988], and Mase eta!. [1982]. Heat flow contoursin becausethe recentdetailed geologic studies mentioned mW m-2; large asterisksare major CascadeRange volcanoes abovegive somewhat lower volumes of extrusionox.er the (identifiedby two letterabbreviations). The volcanoesare, from last2 m.y.than Blacku'ell et al. [1982]inferred from the northto south,MM, MeagerMountain; MG, MountGaribaldi; MB, McBirneyand White [1978] data. Typical ratios range from Mount Baker; GP, ; MR, Mount Rainier; SH, Mount St. Helens; MA, Mount Adams: MH, Mount Hood; MJ, Mount approximately5or 10-1 in central Oregon toperhaps 50-100 Jefferson;TS, ;NV, ;CL, Crater to 1 in BritishColumbia. This difference might be related to Lake; MM, Mount McLoughlin;MS, ;ML, Medicine thecrustal differences, orperhaps the extrusive volumes in Lake; LP, . BritishColumbia are underestimated because of thehigh ratesof glacial there. Furthermore, the estimates lot BLACKWELLET AL.' HEAT FLOW,•,• ASHINGTON $T•,TE AND CASCADERANGE 19.513

I00 -

• 50

O" I00 -

'""...... •'^.c eACKGROUNO ......

= i W^SH,,GTO,I O,EGO. I •:•• • MA MS •:.J ea 20 •o L

• 0 l .... '- I• 5• 0 DISTANCE ALONG ARC, KILOMETEES Fig. 11. Volumes of volcanic rocks for the last 2 m.y. [Sherrodand Smith, this issue],heat flow, and inferred intrusive volumes along the CascadeRange.

BritishColumbia relate almost exclusively to volcanic 500øCin British Columbia and 600ø-800øCin Oregon. In this rocks. case {assuminga constant background) the rate of intrusion There are two major conditions that would modify the holds the heat flow constant, but the temperature varies. The calculatedamounts of intrusion. First, because the heat flow higher thermal conductivity of the upper crust in British data have no depth-to-source resolution except along the Columbia more efficently transmits the intrusive heat to the a est sideof the anomaly, high lower crustal heat flow along surface. Consequently, crustal type may play a role in the the centerand east side of the Cascade Range could decrease thermal regime of a volcanic arc. the amountof shallow intrusion required below that calcu- The temperatures are high enough along most of the lated in Figure 11. It might be argued that the appropriate Cascade Range that metamorphism should be occurring at b ckgroundto use in the calculation is a high heat flow the present time. Temperatures in the range of 300ø to typical of the Cordilleran Thermal Anomaly Zone or of a 600+øC at 8-12 km are well within the range of low-pressure regionsubject to a flux of lower crustal marie intrusions. In metamorphism of rocks to greenschist to granulite facies. thiscase the heat flow backgroundcould range from 20 to 40 Thus the area may be a natural laboratory for study of a mW m-2 higherat variouslatitudes along the Cascade crustal region undergoing metamorphic processes. Barton Range,and the rate of upper crustal intrusion would be and Hanson [1989] [also Hanson and Barton, 1989] have decreased. In British Columbia the rate of intrusion would recently discussed the thermal requirements for low- be proportionallymost affectedand mightdrop as low as pressuremetamorphism. They inferred that temperaturesin 30-10km 3 km-I (2 m.y.)-1 fromthe value of 110km 3 km-l volcanic arcs are not high enough to form low-pressure [2 m.y.)-l shownin Figure11. Along the west boundary of metamorphism for much of the time. In the Cascade Range, theCascade thermal anomaly, the 10-kmhalf width requires however, it appears that temperatures are sustained at high the highesthorizontal thermal gradients to be in the mid- enough levels to cause metamorphism for long periods of crust,so the outer arc heat flow is the correct background. time (several millions of years). Second,the heatflow maybe higheralong the axisof the The ratio of intrusion to extrusion is probably a charac- CascadeRange, in Oregonespecially, than assumed for the teristic property of volcanic arcs, but the relationship has purposes of the calculation. In this case the intrusion rate been difficult to quantify. It has been assumed for volcanic v•ouldbe underestimated,and so the real rate might be terrains in general that lower ratios might be associatedwith higherthan the valuesshown in Figure11. more marie volcanism whereas higher ratios might be asso- The similarityof the heatflow in the BritishColumbia and ciated with more silicic volcanism. This model was the basis OregonCascade Range (about 90 mW m"2 comparedto just for the use of volcanic type in evaluating the geothermal overILK} mW m-2) is not reflectedin the crustaltempera- resourcepotential of the United States [Smith and Shaw, tures.At a depth correspondingto the half width and thus 1975]. The data presentedhere represent the first heat loss near the source(10 kin), the temperaturesmay be 400ø-- measurementsthat can be related to magmaticprocesses and HEATFLOW, WASHINGTON STATE AND CASCADE RANGE

that documentquan•.i't'i•ei.y this hypoihesis.While there are bodies.Thermal models are consistentwith this origin a number of uncertainties associated with the values calcu- the metamorphism [Yoreo et al., !989]. latedin thispaper, the ratesanct their geographic variation Thesurprising consistency of the halfwidth of theheat representa new setof parametersto helpin understandingflow transition in Oregon,southern Washington, and south. the igneousprocesses in volcanicarcs. ern BritishColumbia requires a consistencyin heatsource depththat is not affectedby volumerate of extru•c}a, averagecomposition of volcanics,crustal type, or stress CascadeRange •'Magma Chamber" state.As pointedout by Blackwellet al. [thisissue], the Curiepoint depths in Oregonare consistentwith the down. The conclusionby Blackwellet al. [ 1982]that the Cascade ward continuationof surfaceheat flow to depthsof at least Rangeis underlainby a broad upper crustal heat source 5-10km, wheretemperatures are 300ø-500øC.The gravity (depth of 8-12 km) that is a magma stagingregion is not datain the centralOregon Cascade Range are alsoconsistera widely accepted.The favored spot for a zone of regional with a midcrustalregion of low density,although because of crustal residence, melting, assimilation, and fractional crys- the complexregional field and upper crustaldensity con- talization in volcanic arcs is at the crust/mantle interface. traststhe depth to this region cannotbe well constrained.In For example,Leemah et al. [this issue]describe the evolu- Washingtonand British Columbia[Lewis et al., 1988]there tion of Mount St. Helens dacite by open-system crustal are gravity gradientscorresponding to the heat flow transi- anatexisat the crust mantle boundary. In discussingmagma tion, althoughthe amplitudeof the gravity anomalythat can evolution in volcanic arcs in general, Hildreth and Moorbath be isolatedis lessthan that in the OregonCascade Range [1988, p. 485] conclude that the [Blackn4,ellet al., this issue]. data us to envisage deep beneath each large magmatic These results and interpretations, taken together, leadto center a zone of melting, assimilation, storage, and homogeni- zation (MASH), in the lowermost crust or mantle-crust transi- the followingmodel. Under most of the CascadeRange tion, where basaltic magmasthat ascendfrom the mantle wedge where volcanismhas occurredover the last 2-5 m.y., a zone become neutrally buoyant, induce local melting, assimilateand of magma interception, storage, and crystallization existsin mix extensively, and either crystallize completely or fractionate the depth range of 8-15 km. The horizontal extent of this to the degree necessaryto re-establishbuoyant ascent. ascendingfrom such zones may range from evolved basalts to zone is significantlylarger than individual centers,being at , but all will have acquired a base-level isotopic and least 60 km wide in places, but over time, volcanic ventsand trace-element signaturecharacteristic of that particular MASH major centers of volcanism map out most of the extent of the zone. zone. The correspondence is discussed by Blackwell et al. The requirements of such a zone to satisfy the geochem- [this issue], who compared the maps of volcanic vents ical data do not obviate the need for shallower zones of discussedby Guffanti and Weaver [1988] to the heat flow residence, interaction and sourcing, particularly for large anomaly in central Oregon. The temperature in this zoneis a volumes of very silicic melts to be generated and erupted. function of the rate of intrusion, which may or may not There is no question that such large-scale upper crustal reflected in the extrusion rate, and crustal type. The absence zones existed in some settings in the past. For example, a of primitive basalts at the surface probably means that they large system of this sort existed in Idaho during the Eocene stall and fractionate within the crust. The high rate of silltic [Criss and Taylor, 1983], when a zone about 50 km wide and volcanismin certain segmentsof many arcs may resultfrom several hundred kilometers long was the site of shallow level the fact that none of the basalt makes it through the crustaM granitic intrusions probably overlain by massive so is able to transfer its heat completely to the crust. An systems. extreme example of this situation is Yellowstone, where On the North Island of New Zealand the Taupo graben volumesof basalticmagma similar to thosefound in Hawaii represents the site of a massive, upper crustal, silicic, are being emp!aced in the crust with the result that huge magma chamber in a volcanic arc setting [Wilson et al., volumes of silicic magma are produced. 1984]. In fact, andesite typical of volcanic In Oregonthat time-averagedtemperature is in the 600•C arcs are located immediately south of the area of silicic ash range,and at least isolatedpockets of melt probablyexist. flow volcanism. In the Japanese volcanic arcs there is very The overall effect may be enoughto result in a density little basalt erupted and the volcanics are dominately andes- contrastcompared to the crust outsidethe CascadeRange. itc and dacite in composition.The spacingof volcanoesis The rate of activity is high enoughthat the size of the zone about 50 km in contrast to the 75-km spacingof the Cascade is independentof individualvolcanic centers. In Washington Range. Perhaps the midcrustal residence zone is an even and probablyin northernCalifornia and southernBritish more continuous zone of crust at melting or near melting Columbia,the rate of intrusionis muchless than in central temperatures than is the case in the Cascade Range. Oregon,and the temperaturein the residencezone is Finally, during the Devonian a situationthat resultedin a 500øC.In this case the peak thermal anomaliesare mr}re thermal pattern that is in many ways similar to the one closelyrelated to long-livedcenters of intrusion.The lower proposedfor the CascadeRange existed in Maine. In central temperaturesmake the geophysicalsignitures of thisheat Maine there is a large region of low-pressure/high- sourceregion more subtlethan in centralOregon. In no case temperature metamorphismgrading into a large region of is a continuouslayer of magmaenvisioned to existover t,•e contact metamorphismalong strike to the southwest [Hold- whole region at one time. away eta!., 1988]. Gravity evidence suggeststhat the low-pressureregional metamorphismis associatedwith re- Acknowledgments.The work in northeasternWashington was gional development of granite sills at an inferred eraplace- supportedby NSFgrant 11351 to SMU.Studies in theColumbia ment depth of 8-12 km, whereasthe contactmetamorphism Basin,Washington Cascade Range, and westernWashington were is associatedwith isolated, deeper, more equant, granite supportedby DOE contract IDl12307-1 to SMUand by •E BLACKWELLET AL.: HEAT FLOW, WASHINGTONSTATE AND CASCADF.RANGE 19.515 contractDE-A07-79ET27014 andDOE grantDE-GF07-88IDI2740 Rangeand its correlationwith regionalgravity, Curie point tothe Washington Division of Geology and Earth Resources. J. Eric depths,and geology, J. Geophys.Res., this issue. Schusterwas involved in muchof the work and assisted in thefield Booker,J. R., and A.D. Crave, Intrcxtuctionto the specialsection studiesand SMU/WGER coordination. Reviews by L. J.P. Muffler on the EMSLAB-Juande Fucaexperiment, J. Geophys.Res., 94, ar• W. Hildrethwere helpful in improvingthe manuscript, and W. 14,093-14,098, 1989. Hildrethpointed out that the background heat flow in theCascade Brandon,M. T., D. S. Cowen, and J. A. Vance, The late Cretaceous Rangemight be higher than the outer arc values. San juan thrust system,San Juan islands,Washington, Spec. Pap. Geol. Soc. Am., 221, 88 pp., 1988. Brott, C. A., D. D. Blackwell,and P. Morgan,Continuation of heat REFERENCES flow data; a methodto constructisotherms in geothermalareas, Geophysics,46, 1732-!744, 1981. Atwater,B. F., Evidencefor great Holocene earthquakes along the Catchings,R. D., and W. D. Mooney, Crustalstructure of the outercoast of WashingtonState, Science, 236, 942-944,1987. ColumbiaPlateau: Evidencefor continentalrifting, J. Geophys. Barnett,D. B., Resultsof 1985geothermal gradient test drilling Res., 93,459--474, 1988. projectfor the state of Washington, Open File Rep., 86-2, 36 pp., Criss,R. 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