Terrestrial Heat Flow in Areas of Dynamic Influence of Faults in The

EGU Stephan Mueller Special Publication Series, 2, 153–160, 2002 c European Geosciences Union 2002

Terrestrial heat ﬂow in areas of dynamic inﬂuence of faults in the Baikal rift zone

S. V. Lysak and S. I. Sherman Institute of the Earth’s Crust, Siberian Branch of Russian Academy of Sciences, Lermontov Street 128, Irkutsk, 664 033, Russia Received: 5 October 2000 – Revised: 19 December 2001 – Accepted: 5 February 2002

Abstract. Terrestrial heat flow in the Baikal rift zone is irreg- ducted in exploratory drillholes ranging from 0.3 to 3–5 km ularly distributed. Its high values are associated with active in depth (0.3 to 1 km in ridges, 1 to 2.5 km in intermountain faults and areas of dynamic influence of faults. Stress pat- depressions, and 2.5 to 5 km on the Siberian microplate) and terns in these regions have been studied across and along from 0.5 to 2 km (mostly <1 km) at altitudes above sea level. major faults. Measurement sites under consideration are Precise heat flow measurements were carried out for several those located not farther than 30 km from the given fault weeks or several months (occasionally up to 5 years) after axis. Across the fault strike, heat flow values are revealed drilling had been complete. Results of hydrogeological and to decrease with distance from the fault axis. Along the fault cryological studies were also used in constructing the map strike, variations of heat flow values are within measurement (Lysak, 1978; 1984; 1995). errors, with the exception of thermal spring sites. It is estab- Marine studies at transversal profiles across Lake Baikal lished that heat flow values are regularly changeable. Similar were carried out by oceanographic techniques from aboard of relationships are obtained for heat flow patterns in other con- a scientific vessel. Either a thermal gradiometer (Duchkov et tinental rift zones. al., 1987) or a cable thermistor probe penetrating through 1 m to 3 m thickness of bottom sediments were used (Golubev, 1982; Golubev et al., 1993). 1 Introduction An average heat flow value of Lake Baikal basin is 78±36 mW/m2. In other rift depressions (Tunka, Barguzin), Heat flow acting from the Earth’s interiors is one of the pri- it is 62±13 mW/m2. Thermal waters of these intermoun- mary factors determining geodynamic activity of geological tain artesian basins are distinguished in the thermal field structures and activity of faults. We discuss quantitative rela- as regional anomalies. Their local high values exceed 80– tionships between heat flow values and their variations across 100 mW/m2 in the fault zones bordering these depressions. and along fault zones using data from the Baikal rift zone At the north-eastern flank of the BRZ, heat flow drops down (BRZ) and the territory of the Siberian and Transbaikalian to 50 mW/m2 and below; it can reach 70–80 mW/m2 only at microplates (Fig. 1) in the eastern part of the Eurasian con- some local fault sections (see Fig. 2). The regional heat flow tinent. The variability of these values is calculated as sums of ridges bordering the rift depressions is 40±6 mW/m2. of squares of deviations from the overall average values and An average regional heat flow of the Transbaikalian mi- double estimation error (2σ); average values of heat flow and croplate is 52±11 mW/m2. In the southern Siberian mi- density of the faults are obtained. croplate, an average heat flow value is around 38±8 mW/m2. Heat flow stations are primarily concentrated in the cen- Low values are observed at the marginal uplifts (Lysak, tral part of the Baikal rift zone (BRZ), especially within and 1988). around Lake Baikal as well as in some other southern regions Faults in the BRZ are numerous. A fault map of Fig. 3 of the Siberian microplate (Fig. 2). The database of the given shows fault directions, genetic types and ages (Sherman et heat-flow map includes data received from the on-land area al., 1992). In the BRZ central part, the 60◦ trending faults and within the Lake Baikal, from geothermal surveys con- dominate; they follow the general strike of the rift zone. Correspondence to: S. I. Sherman The north-west-trending faults are observed perpendicular ([email protected]) to the rift zone strike. In the BRZ south-western part, sub- 154 S. V. Lysak and S. I. Sherman: Terrestrial heat flow in areas of dynamic influence of faults

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Fig. 1. Block-scheme the Baikal rift zone formation. Scale 1:5 000 000 (Sherman and Levi, 1977, with additions). latitudinal and latitudinal faults are predominant. Transcur- however, these high values were not taken into consideration rent or meridional faults are less abundant. The 45◦ trend- when the average heat flow value was estimated. ing faults predominate in the north-eastern part of the BRZ. In deep bottom depressions and at underwater uplifts and Their trends do not coincide with the general rift zone strike. blocks, an average heat flow value is by 1.5 times lower Latitudinal faults are second in number, whereas longitudinal (69±23 and 65±18 mW/m2, accordingly). ones are even rarer. At the Transbaikalian microplate, an average heat flow The BRZ central part is characterized by a maximum num- value of fault zones is 71±3 mW/m2. In intermountain de- ber of the Cenozoic faults trending in agreement with the pressions and at ridges and uplifts, average heat flow val- BRZ general strike. At the BRZ flanks, the predominant fault ues of fault zones are 52±9 and 47±9 mW/m2, accordingly. trend coincides with the strike of the most extensive deep- Even in the southern part of the Siberian microplate, heat seated faults of the basement; these faults are pre-Cenozoic flow in fault zones is higher than that in the adjacent areas. in age (Sherman et al., 1992; Levi and Sherman, 1995). The above regularity is typical of other rift zones, such A non-uniform distribution of faults and heat flow values as the Basin-and-Range Province, the Rio Grande rift, the is evident in the BRZ and its adjacent territory. Nonetheless, Rhine and Rhone rifts, the East African rift system and sur- some quantitative relationships between faults and heat flow rounding areas (Table 1). can be revealed. Thus, high values of terrestrial heat flow are more charac- teristic of fault zones and, especially, of zones of active faults 2 Distribution of heat flow in fault zones in rift depressions, rather than of the surrounding areas.

Numerous active faults are revealed at the bottom of Lake Baikal (Fig. 4). An average heat flow value of this area is 3 Heat flow and density of faults 78±36 mW/m2. In fault zones, it reaches 87±10 mW/m2. There are local sites where the submarine heat flow ex- Density of faults, df is a number of faults, n within an area ceeds 200–1000 mW/m2. Extremely high values of heat flow of ∼5×103 km2. It is calculated from field data and informa- over 6000–8000 mW/m2 are associated with submarine hy- tion from geological maps (Sherman et al., 1992). A map of drothermal vents in active fault zones (Golubev et al., 1993); density of faults in the Baikal rift zone is shown in Fig. 3b. S. V. Lysak and S. I. Sherman: Terrestrial heat flow in areas of dynamic influence of faults 155 o 54 o

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5 enisei R. Y R. o o 54 50 Heat flow map of the Baikal rift zone and adjacent areas. Based on Golubev, 1982; Duchkov et al., 1987; Lysak, 1978, 1984, 1988, 1995; Golubev et al., 1993. at the Lake Baikal bottom: 1 – heat flow sites on land; 2 – thermal springs; 3 – isolines of predominate regional heat flow values in mW/m Fig. 2. 156 S. V. Lysak and S. I. Sherman: Terrestrial heat flow in areas of dynamic influence of faults aabtntvrfidb ufc apn;1 onaiso h itzn;1 ao ersin bsn) uk,I ot akl I ot akl V–Brui,V–UprAngara, Upper – V Barguzin, geophysical – from IV identified Baikal, faults North – – 12 III rocks; Baikal, South fractured – intensely II of Tunka, zone – – I 11 (basins): Tokko. faults; depressions – extension major IX – – Chara, 14 10 – zone; faults; VIII rift reverse the Muya, and of – thrusts boundaries VII – – Tsipa–Baunt, 9 13 – faults; mapping; VI slip surface by oblique verified – not 8 but faults; data normal – 7 faults; Cenozoic (a) 3. Fig. al ytm fteBia itzn:1–Cnzi eiet;2–Cnzi aat;3–mjrfut;4–rgoa als oa als alsratvtdi h eoocand Cenozoic the in reactivated faults – 6 faults; local – 5 faults; regional – 4 faults; major – 3 basalts; Cenozoic – 2 sediments; Cenozoic – 1 zone: rift Baikal the of systems Fault

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Table 1. Number of heat flow data (N), average value of heat flow (q, mW/m2) and redoubled error of average heat flow estimate (2σ) in the fault zones of continental rifts and surrounding areas (Lysak, 1999)

Regions Areas of faults Rift depressions Interdepression Rift “shoulders” Surrounding areas uplifts N q±2σ N q±2σ N q±2σ N q±2σ N q±2σ Cenozoic continental rifts Cordillera rift 48 161±86 87 91±35 62 94 ±26 86 72±29 system: Basin-and- Range Province, Plato Colorado North and Rio Grande rift; North America 68 57 ±17 Rhine-Lybian rift 90 107±34 72 96±33 5 70 ±6 81 83±22 belt: Rhine, Rhone and African-Sicilian rift zones; Western and Central 225 74±23 * Europe East African rift 20 102±39 93 60±30 5 105±43 60 54±22 system: Dead Sea rift, Ethiopia and Kenya rift zones; Central and South 62 58±28 Africa Baikal rift zone: Baikal, Tunka, 76 109±39 380 78±36 72 69 ±35 76 56±19 Barguzin, Upper Angara, Myua rifts; Transbaikalia 57 52±11 Mesozoic and Paleozoic continental rifts Oslo, North Sea; 13 84±16 13 68±18 14 58±12 24 59±14 Kamerun and Niger rifts West Africa 146 57±20

An average density of faults is 100±27 in the Lake Baikal eas and major geological structures. It is rather strong and basin, 70±24 in other rift depressions, 62±22 at rift “shoul- can be revealed even in the regions of relatively low geo- ders” (all values obtained within areas of 5×103 km2). The dynamic activity. For example, at the Transbaikalian mi- density of faults is also high in the Transbaikalian microplate: croplate, wherein an average density of faults is about 70, 65±17 in depressions, 70±30 at ridges and uplifts. The an average heat flow is 52 mW/m2. In the southern areas of southern part of the Siberian microplate is characterized by the Siberian microplate, the density of faults is less than 20, low densities of faults: 15±4 in depressions, 19±6 at uplifts. an average heat flow is about 40 mW/m2. The highest density of faults is observed at the axial part of The available data base has been computer processed by the Baikal rift zone, wherein local anomalies are character- a linear binary correlation between values of heat flow and ized by double and even higher values of fault density. This density of faults; correlation factor r and its error range are area is characterized by high regional heat flow, local heat defined for different structures. This allows us to establish an flow anomalies and hot spring occurrence (see Figs. 2, 4a). relation between two values under analysis, q and df. Then, it is possible to obtain a regression equation of this relation A comparison of values of fault density and heat flow al- (see below). lows us to reveal a regularity: heat flow is higher in the areas of higher density of faults. This regularity is character- Results of the binary correlation between the values of heat istic not only of rift zones, but also of the surrounding ar- flow and density of faults show a non-stable relationship be- 158 S. V. Lysak and S. I. Sherman: Terrestrial heat flow in areas of dynamic influence of faults

Fig. 4. Terrestrial heat flow and major active faults of the Lake Baikal rift depression. Based on Golubev et al., 1993; Lysak, 1995; Levi et al., 1997. Heat flow values: 1 – <40; 2 – 40–59; 3 – 60–79; 4 – 80–99; 5 – >100 mW/m2. Major active faults: 6 – faults with estimated thickness of zones of tectonic dislocation; 7 – normal faults; 8 – strike-slip faults; 9 – faults with undetermined type of movements; 10 – areas of dynamic influence of Barguzinsky fault (I) and Primorsky fault (II). S. V. Lysak and S. I. Sherman: Terrestrial heat flow in areas of dynamic influence of faults 159 tween these geodynamic parameters, with considerable vari- in this area. Variations of heat flow across the strike of its ations of correlation factors, r = 0.7±0.5 in the BRZ and r zone of dynamic influence (46 points of measurements) are = 0.8±0.6 in Lake Baikal itself. At the mountain framework extremely high: of the rift depressions (or rift “shoulders”) and at the Trans- = − 2 = − ± baikalian microplate, correlation factor r is 0.6±0.4. It is less q 84.1 3.2 D (mW/m ), r 0.78 0.60. considerable in the southern part of the Siberian microplate It can be concluded that across the zones of dynamic in- ± (r = 0.4 0.1), however the correlation is present there. fluence of relatively active faults, heat flow decreases slower Therefore, in the zones of high fault density, heat flow is than in the whole adjacent area. For comparison, heat flows increased in comparison with that of the other territories. In and areas of dynamic influence of faults of other continen- the BRZ and its adjacent microplates, the fault zones and tal (the Province of Basins and Ranges, the Rio Grande Rift) especially active ones are heated stronger than the areas of and oceanic rifts (the Middle-Atlantic rift) have been ana- mountain ridges and uplifts. lyzed. For example, from 17 heat flow measurements, variations of heat flow across the strike of the San Andreas Fault 4 Variations of heat flow values in areas of dynamic in- zone (Henyey and Wasserburg, 1971) are given by the fol- fluence of faults lowing equation: q = 80.2 − 2.1 D (mW/m2), r = −0.60 ± 0.42. To establish specific relationships between faults and heat flows, a more detailed research has been carried out; the It corresponds well to the equation of the average data for available data on distribution of heat flow across the zones active faults in the BRZ (Lysak and Sherman, 1978). of dynamic influence of faults are analyzed. Increased and abnormally high values of heat flow are Areas of dynamic influence of faults are volumes includ- known in zones of the Rhine-Libyan and Africa-Arabian rift ing the axial zone of the fault and its surrounding zone in belts, in particular, in the Kenya rift and the Dead Sea rifts three dimensions wherein residual deformations (plastic or (Lysak, 1988, 1992). fracture) and crush movements are manifested (Sherman et al., 1983). Qualitative analyses suggest that maximum values of heat 5 Conclusion flow are typically observed at the fault axial parts (at distance up to 5 km). With distance from the fault axis, heat flow Our research results give grounds for the following conclu- decreases gradually. At a distance of 15–25 km, the influence sions: of the given fault does not have any considerable impact on 1. Heat flow in fault zones is generally higher than that in heat flow values, unless it is influenced by any other fault or the adjacent or surrounding areas. It is dependent on a any other geodynamic factor (fresh faults, modern fissures or geodynamic regime of the given territory. others). For the BRZ, a data base of quantitative estimations of 20 2. Heat flow decreases with distance from the fault axis. active faults and 150 heat flow values obtained in the areas of Lateral geothermal zoning of faults is well agreed with dynamic influence of these faults has been analyzed (Lysak zones of crushing. and Sherman, 1978). As expected, a reverse dependence of heat flow and the distance between the measurement site and Thus, the above described new approach to comparing the axial zone of the fault is established. The following re- heat flow and areas of dynamic influence of faults provides gression equation is obtained: the basis for new conclusions and correlation between some of the well known geodynamic parameters. It is especially 2 q = 85.6 − 2.1 D (mW/m ), important for detailed researches of active rift zones and where q is heat flow in mW/m2; D is a distance from an axial zones of collision, i.e. the areas of active recent destruction line of a fault in km. of the lithosphere. Unlike the above calculations, the correlation factor is higher and less variable: r = −0.56 ± 0.17. Acknowledgements. Special thanks are extended to Dr. D. Delvaux For separate faults, r values and regression equations may and Prof. A. Khan (IGCP 400 Project leaders) and the Russian be different, but still very similar. For example, at a distance Fund of Fundamental Research (grants 00-05-64140; 01-05-97226) from the Barguzinsky fault to the east (8 points of measure- for supporting our investigation and our participation in the First ments), the equation is the following: Stephan Mueller Conference of the European Geophysical Society held in Israel in 2000. The authors are thankful to Marlies ter Vo- 2 q = 95 − 2.8 D (mW/m ), r = −0.51 ± 0.26. orde and Jan Safanda, reviewers, for their critical notes and useful The western coast of Lake Baikal is characterized by huge advise. geomorphologic rift forms, including faults, though its recent activity is relatively low. The Primorsky fault is located 160 S. V. Lysak and S. I. Sherman: Terrestrial heat flow in areas of dynamic influence of faults

References Tectonophysics, 143, 31–41, 1984. Lysak, S. V.: Heat flow of Continental Rift Zones, Nauka, Novosi- Duchkov, A. D., Lysak, S. V., and Balobaev, V. T. et al.: Thermal birsk, 200p (in Russian), 1988. field of Siberian bowels, Nauka, Novosibirsk, 197p. (in Russian), Lysak, S. V.: Heat flow variations in continental rifts, Tectono- 1987. physics, 208, 309–323, 1992. Golubev, V. A.: Geothermics of Baikal, Nauka, Novosibirsk, 150p Lysak, S. V.: Terrestrial heat and temperatures in the upper crust (in Russian), 1982. in South East Siberia, Bull. Centers Rech. Explore-Prod. Elf Golubev, V. A., Klerkx, J., and Kipler, R.: Heat flow, hydrothermal Aquitaine, 19, 39–57, 1995. vents and static stability of discharging thermal water in Lake Lysak, S. V.: Terrestrial heat flow as factor of continental rift geody- Baikal (South-Eastern Siberia), Bull.Centres Rech. Explor.-Prod. namic. Rifting in intracontinental setting: Baikal Rift System and Elf Aquitaine, 17, 1, 53–65, 1993. other Continental Rifts, Irkutsk and Lake Baikal, Russia, 122– Henyey, T. L. and Wasserburg, G. J.: Heat flow near major strike- 124, 1999. slip faults in California, J. Geophys. Res., 76, 32, 7924–7946, Lysak, S. V. and Sherman, S. I.: Abyssal heat flow and seismic ac- 1971. tivity of Pribaikalia. Seismicity and deep structure of Pribaikalia, Levi, K. G., Miroshnichenko, A. I., and San’kov, V. A. et al.: Active Nauka, Novosibirsk, 56–68 (in Russian), 1978. faults of the Baikal depression, Bull. Centers Rech. Explor.-Prod. Sherman, S. I., Bornykov, S. A., and Buddo, V. Y.: Areas of dy- Elf Aquitaine, 21, 399–434, 1997. namic influence of fault, Nauka, Novosibirsk, 112p (in Russian), Levi, K. G. and Sherman, S. I.: Applied geodynamic analysis. Muse 1983. Royal de L’Afrique Centrale – Tervuren, Belgique annales – Sci- Sherman, S. I. and Levi, K. G.: Transform faults of the Baikal rift ences Geologiques, 100, 133p, 1995. zone, Doklady AN SSSR, 233, 2, 454–464 (in Russian), 1977. Lysak, S. V.: The Baikal rift heat flow, Tectonophysics, 45, 87–93, Sherman, S. I., Seminsky, K. Zh., and Bornykov, S. A. et al.: Fault- 1978. ing in the lithosphere. Extensional zones, Nauka, Novosibirsk, Lysak, S. V.: Terrestrial heat flow in the south of East Siberia, 228p (in Russian), 1992.