Petrographic and Physical Factors Controlling Thermal-Conductivity of Granitic-Rocks in Illinois Deep Holes UPH 1, 2, and 3

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1 Kent State University Digital Kent State University Libraries Geology Publications Department of Geology Petrographic and Physical Factors Controlling Thermal-Conductivity of Granitic-Rocks in llinois Deep Holes UPH 1, 2, and 3 Yoram Eckstein Kent State University - Kent Campus, yeckste1@kent.edu Peter Dahl Kent State University - Kent Campus, pdahl@kent.edu Charles J. Vitaliano ndiana University - Bloomington Follo this and additional orks at: Part of the Geophysics and Seismology Commons Recommended Citation Eckstein, Yoram; Dahl, Peter; and Vitaliano, Charles J. (1983). Petrographic and Physical Factors Controlling Thermal-Conductivity of Granitic-Rocks in llinois Deep Holes UPH 1, 2, and 3. Journal of Geophysical Research 88(B9), doi: / JB088iB09p07381 Retrieved from This Article is brought to you for free and open access by the Department of Geology at Digital Kent State University Libraries. t has been accepted for inclusion in Geology Publications by an authorized administrator of Digital Kent State University Libraries. For more information, please contact digitalcommons@kent.edu.

2 JOURAL OF GEOPHYSCAL RESEARCH, VOL. 88, O. B9, PAGES , SEPTEMBER 10, 1983 PETROGRAPHC AD PHYSCAL FACTORS COTROLLG THERMAL CODUCTVTY OF GRATC RQCKS LLOS DEEP HOLES UPH 1, 2, AD 3 Y. Eckstein and P. s. Dahl Department of Geology, Kent State University, Kent, Ohio C. J. Vitaliano Department of Geology, ndiana University, Bloomington, ndiana Abstract. Tenty-four granitic core samples from the llinois deep drill holes yield thermal conductivity values in the range mw/cm C, et buk densities in the range g/cm, and ater accessible porosity in the range %. Thermal conductivity values vary ith modal quartz content of the rocks at all depths, and both parameters decrease linearly ith depth beteen 673 and 1016 m in drill hole UPH 3. Belo 1070 m there is no systematic variation in modal quartz content ith depth and hence no systematic variation in thermal conductivity. Similarly, no systtic variations in modal quartz or physical properties ith depth are observed in drill hole UPH 2. ntroduction n this study e analyzed 24 core samples from the Commonealth Edison's three deep drill holes in Stephenson County, northestern llinois. Specifically, e performed measurements of thermal conductivity (K) and ater accessible porosity (WAP), and examined the relationships beteen these parameters and both modal quartz content and sample depth. All samples represent granitic rocks and come from the interval of ca m beneath the surface, i.e., from the level at hich the granitic rock as first encountered to the bottom of the drill holes. Petrography Petrographic examination of 24 core samples from the drill holes reveals the presence of a broad spectrum of granitoid rocks ranging from quartz syenite to granodiorite. The majority of the samples, hoever, fall into the 'normal granite' category of the Streckeisen [1967] classification triangle. The rock samples are medium- to coarse-grained and typically exhibit allotriomorphic inequigranular textures. Quartz and feldspar, the dominant minerals, may reach to 1 or more centimeters diameter, but the granite samples from near the contact ith the overlying sediments are distinctly finer-grained, crystals rarely exceeding 0.5 em in diameter (C.J. Vitaliano et al., unpublished manuscript, 1983). With a single exception, in hich plagioclase is the chief constituent, K-feldspar (chiefly perthitic microcline) and quartz are the predominant minerals in thin section. Muscovite and biotite, hich constitute the major Copyright 1983 by the American Geophysical Union.- Paper number 2B /83/02B-1136$05.00 accessory minerals, ere found in all the thin sections. Minor accessories include iron oxides and interstitial fluorite (in most thin sections); calcite, chlorite, zircon, epidote, apatite, and hite mica after feldspar (in several sections); and sphene and tourmaline (in one section). Mineral modes for the 24 samples are summarized in Table 1. Detailed petrography of these rocks is presented by C.J. Vitaliano et al. (unpublished manuscript, 1983). Thermal Conductivity, Density, and Porosity Thermal conductivity (K) of the core samples as determined using the divided-bar technique [Lees, 1892; Birch, 1950; Beck, 1965]. Sample discs ere 5 em in diameter and beteen 15 and 25 mm in thickness. Wet bulk density (WBD) and ater accessible porosity (WAP) ere both determined by vacuum saturating the samples ith distilled ater at room temperature. Results of the measurements are presented in Table 2. The values for the ater accessible porosity vary from 0.20 to 0.71%, a range typical for microfractured rocks. Despite this overall range of porosities, a eak inverse correlation is observed beteen thermal conductivity and WAP (%) (Figure 1). We can state ith greater than 80% confidence that the negative slope in Figure 1 is significantly different from zero. The values of measured thermal conductivity for all the samples are typical for granitic rocks, averaging 33.1 ± 2.1 (1cr) mw/cm C and varying beteen 29.3 and 37.6 mw/cm C. The u 42.5 m " e ' 3: E 32.5 :.: o : "! "? "; "! ": "! "!.,; WAP 00 Fig. 1. Measured thermal conductivity (K) and ater accessible porosity (WAP) in core samples from UPH 1 (crosses), UPH 2 (circles), and UPH 3 (stars). 7381

3 TABLE 1. Modal Compositions of Granitic Rocks From llinois Deep Drill Holes. ""' 0> UPH 1 UPH 2 Mineral 2025A 2064A 2385E 2968D 3388D 3774D 4203E 4405E 4773F 4984D K-feldspar Quartz Plagioclase Biotite Muscovite Opaque to:!!';" Fluorite ll Chlorite (1) Clay minerals = Calcite (1) Epidote Apatite P -- Pumpellyite Zircon Tourmaline '"' ;T (1) Sphene Total (") UPH 3 0 Mineral 2209A 2351E 2397F 2422G 2622F 2791E 3333G 3514E 3880F 4059F 4421E 4610F 4689E 4969F = p K-feldspar c n Quartz Plagioclase Biotite '< Muscovite Opaque Fluorite Chlorite t Clay minerals Calcite n Epidote g' Apatite n Pumpellyite !';" ll Zircon Tourmaline Sphene Total n percent. n i., c;') 11

4 Eckstein et al.: Thermal Conductivity of Granitic Rocks 7383 TABLE 2. Thermal Conductivity and Related Physical Properties of Core Samples From llinois Deep Holes Sample Depth DBD, WBD, WAP, K, Ks, Kp, Quartz, m s/cm3 s/cm3 % mw/cm C mw/cm C mw/cm C % UPH A E F G F E G E F F E F E F UPH E D D D E E F D UPH A A DBD, dry bulk density; WBD, et bulk density; WAP, ater accessible porosity; K, measured thermal conductivity; Ks, calculated thermal conductivity from modal mineral composition, assuming series array; Kp, calculated thermal conductivity from modal mineral composition, assuming parallel array; = 2K/(Ks + ), plutonic (nonmetamorphic) character of most of the samples (C.J. Vitaliano et al., unpublished manuscript, 1983) is confirmed by the isotropy index (). This index is obtained by comparing measured thermal conductivity ith the calculated minimum and maximum thermal conductivity computed for each sample from its modal composition (Tables 1 and 2), using both series and parallel arrays (Beck, 1965). Values of mineral thermal conductivities used in the calculations are from Beck (1965). All samples are significantly isotropic, ith values of ranging beteen 0.90 and 1.1 (Table 2). a a. a: :J:.a e.a ": ": "! "! \. \ \.,., \ l \ \J \ \ ll E -BB :: -all a. 1-1:::1 -BBB Fig. 2. sotropy index () and ater accessible porosity (WAP) in core samples from UPH 3. HAP 00 Fig. 3. Water accessible porosity as a function of depth in core samples from UPH 3,

5 7384 Eckstein et al.: Thermal Conductivity of Granitic Rocks X t: a: ::J a , K <mh/cm.deg.cl Fig. 4. Measured thermal conductivity and modal quartz content in core samples from UPH 1 (crosses), UPH 2 (circles), and UPH 3 (stars). Figure 2 suggests that there is a relationship beteen isotropy and WAP percent in UPH 3, but no such relationship exists for UPH 2. The trend of increasing WAP percent ith depth in UPH 3 (Figure 3) indicates that the porosity as not generated by unloading or other tectonic processes. Hoever, the reason for the trend in Figure 3 is not apparent. Although all the rock samples are described as being predominantly granitic (C.J. Vitaliano et al., unpublished manuscript, 1983), modal quartz, the most heat conductive mineral, is found nevertheless to vary over a broad range, beteen 16.0 and 47.4% (Table 1). The modal amounts of quartz and K-feldspar are shon to vary antithetically (Table 1). Hence, there is an excellent correlation beteen the measured thermal conductivity and quartz content in all the samples (Figure 4). 'E ::t D c -2ee / see -8ee ee -l&ee K <mh/cm.deg.cl. Fig. 6. Measured thermal conductivity as a function of depth in core samples from UPH 3. The antithetic relationship beteen quartz and K-feldspar seems to be depth related, at least in the shallo zone of the UPH 3 borehole. Quartz content, and hence thermal conductivity, both decrease linearly beteen the depths of and m (Figures 5 and 6). Similarly, the index of isotropy decreases ithin that depth interval, suggesting slightly increasing anisotropy toard series array (Figure 7). Belo 1070 m in UPH 3, there is no correlation among modal quartz content, thermal conductivity, and depth (Figures 5 and 6). Furthermore, there is no apparent correlation among these parameters at any depth ithin UPH 2. Lack of correlation at the greater 'E -4ee -ll ::t -811 D c ee &11 n!! / QUARTZ 00 Fig. 5. Modal quartz content as a function of depth in core samples from UPH see ::t r D c ee l Fig. 7. ndex of isotropy as a function of depth in core samples from UPH 3.

6 Eckstein et al.: Thermal Conductivity of Granitic Rocks 7385 depths in UPH 3 may reflect the increased grain size ith depth noted by C.J. Vitaliano et al. (unpublished manuscript, 1983). Large grain size relative to sample disc size may introduce considerable experimental error in measurements of thermal conductivity. Acknoledgment. Department of Geology, Kent State University contribution 235. References Beck, A. E., Techniques of measuring heat flo on land, in Terrestrial Heat Flo, Geophys. Monogr. Ser., vol. 8, edited by W. H. K. Lee, pp , AGU, Washington, D.C., Birch, F., Flo of heat in the Front range, Colorado, Geol. Soc. Am. Bull., &1, , Lees, C. H., On the thermal conductivities of crystals and other bad conductors, Philos. Trans. R. Soc. London, Ser. A, 183, , Streckeisen, A., Classification and nomenclature of igneous rocks, eues Jahrb. Mineral. Abhl., 107, , (Received ovember 30, 1981; revised April 2, 1982; accepted July 28, 1982.)