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Volume 48, Issue 1
Displaying 1-21 of 21 articles from this issue
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Survey in Shimotsuma, Ibaraki PrefectureKazuo YAMAGUCHI, Tsutomu KIGUCHI, Takanobu YOKOKURA, Yasuto KUWAHARA1995 Volume 48 Issue 1 Pages 1-9
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA seismic reflection survey with CMP method was conducted west of Mt. Tsukuba, northeast of the Kanto plain. Results of seismic reflection survey are (1) sedimental layers are extensively distributed down to 400m in depth and continuous reflectors are observed at 60m, 140m and 270m in depth, (2) sedimental layers are horizontal and their interval velocities range between 1.7km/s and 2.4km/s, (3) multiple reflections caused in sedimental layers are seen later 0.5s in two way time. From the results of this seismic reflection survey and previous works, the underground geology in the survey area is interpreted (1) weathered top of the granitic pre-Neogene basement is expected because reflectors probably corresponding to the basement top is not so distinct, (2) reflectors from the basement top are interpreted and traced based on calculated interval velocities, (3) vertical gaps in the interpreted basement top may be the east branch of the Karasuyama-Sugaonuma fault, (4) continuous reflectors in sedimental layeres correlate to gravel and sand beds of Pliocene and Pleistocene and (5) the basement has not been active since Pliocene because sedimental layeres are flat and horizontal and they are not deformed by faulting of the basement.View full abstractDownload PDF (1585K) -
Subsurface Structure in the Vicinity of Median Tectonic LineShigenobu NAKANO, Ikuo KATSURA, Jun'ichi NISHIDA, Yoshihisa YAMADA, Su ...1995 Volume 48 Issue 1 Pages 11-26
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA gravity survey was carried out around Gojo City, Nara Prefecture. A total of 239 gravity stations were situated roughly 300m interval on roads. The gravity value was determined by the loop method referred to the Fundamental Station at Kyoto University by means of LaCoste and Romberg gravity meter (D-36). Two remarkable low Bouguer anomaly zones exist along the Median Tectonic Line (MTL) and the Kinokawa River. High anomaly zones are situated in the north of MTL and at the areas where the Sanbagawa metamorphic rocks with high density are exposed. Underground structure was estimated by two- and three-dimensional Talwani's method. The result shows that the Sanbagawa metamorphic rocks are sinking northwards under the Ryoke granitic rocks (which have lower density than the Sanbagawa metamorphic rocks) beyond the MTL. In the east of Gojo, the uplifted basement of Sanbagawa metamorohic rocks is estimated.View full abstractDownload PDF (1730K) -
Takahiro KUNITOMO, Muneyoshi FURUMOTO1995 Volume 48 Issue 1 Pages 27-36
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSeismic refraction and bore hole data are used to study the structure of the Kofu Basin, which is located in the South Fossa Magna. Observing seismic waves at 33 stations which were aligned along N-S and E-W profiling lines in the basin, we obtained clear seismic signals from the shot, which was detonated near the crossing point of the two lines. There is considerable complexity of the structure throughout the basin. The main features of the basin structure are as follows. The basement with a P-wave velocity of about 5.8km/s is a granitic layer and tilted to the southwestwards. The depth of the layer is more than 2km at the shot point and the basement is overlain by thick sediments from the late Pliocene to the Holocene with relatively low velocities of 3.0-2.1km/s. Only in the western part of the basin, the so-called “Green tuff” layer with a velocity of about 5km/s is distributed at the depth of about 1km.View full abstractDownload PDF (1052K) -
Masanori HORIKE, Yoshihiro TAKEUCHI, Isao TORIUMI, Takashi FUZITA, Hir ...1995 Volume 48 Issue 1 Pages 37-49
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe common mid-point (CMP) reflection survey was conducted on three measurement lines with a length of about 1km to reveal the subsurface structure of the peripheral zone between the Ikoma mountains and the Osaka basin. We obtained the following results. The depth sections of two of the measurement lines show the same feature: sediments are stratified horizotally below almost the whole line and are pulled up below a marginal portion close to the Ikoma mountains, suggesting a high-angle reverse fault. Beneath the remaining line, sediments dip toward the Osaka basin, suggesting the hasement also dips, and several faults were detected. Although basin-bedrock interfaces were not detected in the three profiles, they are estimated to be at a depth of about 1.7km from the analysis of the Bougoer anomalies, incorporating the results of the reflection survey. Comparison of the profiles of lines 1 and 3 with the profile in the Osaka bay zone demonstrates that the configuration of the sediment in the peripheral zone is the same as that in the Osaka bay zone. The sediments are divided into two layers: in the upper layer marine and non-marine deposits stack alternately and in the lower layer only non-marine deposits stack.View full abstractDownload PDF (2429K) -
Akio YOSHIDA1995 Volume 48 Issue 1 Pages 51-56
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe seismic activity of the Kinugawa cluster in the southwestern Ibaraki Prefecture, central Japan, shows a clear periodicity of 10 years. It is considered to reflect the average time necessary for the asperities between the Philippine Sea plate and the continental plate to reach the breaking point. Such periodicities, however, are not observed in the activity during the period of 1926 through 1950. This may be due to the inaccuracy of hypocenter determination as earthquakes belonging to the Kinugawa cluster seem not to be well separated from those of the Tsukuba cluster. Another possible cause of that is the influence of the 1923 great Kanto earthquake. Since the mid 1990's is supposed to become an active period, it is expected that several M 4.5-5 earthquakes will occur in the forthcoming few years.View full abstractDownload PDF (625K) -
Shinji TODA, Katsuyoshi MIYAKOSHI, Daiei INOUE, Ken'ichiro KUSUNOKI, K ...1995 Volume 48 Issue 1 Pages 57-70
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe Yamasaki fault system is located from the eastern Okayama to Hyogo Prefectures, southwest Japan, trending in NW-SE direction with a length of 87 kilometers. Earthquake risk evaluation of this fault system is not complete because the past seismic events have not been determined throughout the fault system. This paper reports a comprehensive survey of the Ohara fault, located at the northwestern end of the fault system. High resolution electrical exploration and five drillings at Ohara Town clearly identified the location of the fault underneath the sediment cover. Trench survey was then carried out to determine the past seismic events along the Ohara fault. The following conclusions were derived from these studies. (1) The Ohara fault shows up as a sharp resistivity contrast in the high resolution electrical exploration, reflecting mainly the difference in resistivity between acid tuff and black slate that constitute the northern and southern sides of the fault, respectively. (2) The trench observation in the log and radiocarbon dating of sediments revealed that the latest fault movement along the Ohara fault occurred between 150 and 1200 years B. P. The Harima Earthquake of 868 years AD is most likely to correspond to this fault movement. The timing of the event roughly coincides with the latest event of the Yasutomi fault (Okada et al., 1987) comprising the central part of the Yamasaki fault system. This strongly suggests that the Ohara and Yasutomi faults ruptured simultaneously or as a sequence of events during the Harima Earthquake. (3) The penultimate movement of the Ohara fault was estimated between 1500 and 3000 years B. P. If the latest event corresponds to the Harima Earthquake, then the interval between the last two events is estimated to be 400 to 1900 years. (4) The present trench survey revealed possibly four events along the Ohara fault during the Holocene. Thus the recurrence interval may be about 2500 years. Comparing this result with the interval between the last two events, movement of this fault system is likely to be aperiodic.View full abstractDownload PDF (3846K) -
Correlation with Earthquakes SwarmsMasao NAKANISHI, Hiromi FUJIMOTO, Hideyuki MURAKAMI1995 Volume 48 Issue 1 Pages 71-79
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe developed and installed an ocean bottom heat flow meter with an acoustic digital data telemetry system for long-term monitoring at the Calyptogena community in the Sagami Bay by using a submersible “SHINKAI 2000” (Dive 658). Acoustic digital data telemetry makes it possible to retrieve the observed values on a surface ship at any time during long-term underwater measurement. An experiment in a cave showed the precision of our sensors to be 0.001°C enough to measure small temperature variations in cold seepage. The installation position was 35°00.1′N, 139°13.5′E and the water depth was 1160m. The system recorded for 205 days the underground temperature at depths of 8cm and 25cm as well as seawater temperature. Predominant variations have amplitudes of about 0.2°C and periods of 10 to 15 days. The temperature of seawater also has a variation with periods shorter than several days. A very high heat flow value of 2.2Wm-2 was observed at the clam colony, which suggests heat flux associated with the cold seepage. An undergound temperature anomaly of +0.1°C was observed during an earthquake swarm in January 1993. The temperatures under seafloor and of seawater decreased twenty days before an earthquake swarm in May 1993. We need to continue similar measurements as this study in order to reveal a hydrogeological mechanism of heat transfer in the the Calyptogena community.View full abstractDownload PDF (943K) -
Implications for the Fluid Transport in Geophysical PhenomenaTakayuki HIRATA, Takashi YOSHINO1995 Volume 48 Issue 1 Pages 81-90
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSFluid injection experiments into a Hele-Shaw cell filled with agar gels were carried out at a constant injection pressure. Agar gels of concentration of 0.1wt%, 0.2wt%, and 0.3wt% agar were used as a model material with visco-elastic properties. In the case of lower concentration of agar, agar gels behave as a viscous fluid. However, the property of agar gels as elastic solids increases with increasing concentration of agar. The ratio of relative tensile strength among agar gels of concentration of 0.1wt%, 0.2wt%, and 0.3wt% agar resulted from indentation experiments are 0.14:1.0:3.9. Growth patterns obtained by our Hele Shaw cell experiments are classified into three typical patterns. They are patterns generated by viscous fingering, visco-elastic fingering, and single plane cracking. A visco-elastic fingering is new pattern formation observed in the fluid injection experiments into visco-elastic materials. The characteristics of the visco-elastic fingering pattern are following. 1) The visco-elastic fingering pattern has a branched structure same as one of the viscous fingering pattern. 2) The visco-elastic fingering pattern has an acute growing tip similar to that of single plane cracking, though a shape of growing tip of viscous fingering is round. The phase diagram for the Hele-Shaw cell experiment filed with the agar gel is obtained by changing both the pressure of air injection and the concentration of agar systematically. Fluid intrusion phenomena into visco-elastic materials often occur in geophysical process: e. g., magma migration, core formation, fluid migration in accretionary prisms, etc. Our results will give us new implications for the geophysical process in which the earth or planet's materials behave as visco-elastic materials.View full abstractDownload PDF (5600K) -
Tokutaro HATORI1995 Volume 48 Issue 1 Pages 91-97
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAccompanied with the Guam earthquake on Aug. 8, 1993 (epicenter: 13.0°N, 144.7°E, d=61km, Ms=8.0, USGS), a tsunami was observed at many tidal stations in Japan. Tsunami magnitude and the behavior of propagation are investigated, comparing with those of the 1990 Saipan tsunami (m=2). The travel times in West Japan were about 3.5 hours. The maximum double amplitude at Muroto and Tosa-Shimizu near the tip of peninsula reached 84cm with the wave-period of 8 minutes, and those in the Ryukyu Islands were relatively small. The distribution pattan of wave-heights is similar to that of the 1990 Saipan tsunami. By judging from the diagram of the attenuation of wave-height with distance, the tsunami magnitude on the Imamura-Iida scale was determined to be m=2.5. Although wave-heights of the present tsunami are about 1.5 times higher than those of the 1990 Saipan tsunami, the magnitude value is normal compared to earthquake with similar size in other regions.View full abstractDownload PDF (688K) -
Tomiichi UETAKE1995 Volume 48 Issue 1 Pages 99-107
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSOn Dec. 7, 1990, a shallow earthquake (M=5.4, H=15km) occurred in the southern part of Niigata Prefecture and strong ground motion records were obtained at six stations on the thick Tertiary or Quaternary sediment in Niigata Prefecture. In this study, the characteristics of the records in period range of 1 to 10 seconds are investigated using the multiple-filtering technique. The results are as follows;
(1) In the period range of 5 to 10 seconds, the amplitude of radial component is larger than the other two components at all stations. In this period range, the radial components of five stations show almost the same dispersion characteristics and it corresponds to theoretical dispersion characteristics of fundamental mode of Rayleigh wave. It suggests that the recorded ground motion in this period range mainly consists of fundamental mode of Rayleigh wave.
(2) In the period range shorter than 4 second the dispersion characteristics of each station are very complicated and different from each other.
(3) The records at Niigata city show very clear dispersion, and its dispersion characteristics are different from other five stations that are closer to the epicenter than Niigata city. This suggests that underground structure of Niigata city is different from the epicentral region.View full abstractDownload PDF (1075K) -
Hiroshi SATO1995 Volume 48 Issue 1 Pages 109-112
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (457K) -
1. The 1646 December 7 Earthquake Was Not Destructive in EdoKatsuhiko ISHIBASHI1995 Volume 48 Issue 1 Pages 113-115
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (391K) -
Sho SASAKI, Eiichi TAJIKA1995 Volume 48 Issue 1 Pages 119-129
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSRadiogenic noble gas data provide valuable information on planetary evolution through their degassing histories. The relative abundance of 40Ar in the Cytherean atmosphere is 0.26 of that in the Earth's atmosphere. Calculation of a 40Ar degassing model along with mantle evolution and melt migration shows that the average magma production rate on Venus is about 5km3/yr. Duration of plate motion on Venus, if existed, would be less than several hundred million years. For Mars, estimated volume of erupted volcanic materials is compatible with the present Martian 40Ar, which is about 1/20 of 40Ar in the Earth's atmosphere. On the other hand, early degassing fraction estimated from Martian radiogenic 129Xe is as much as 1/3 of that of the Earth. This early degassing may be due to the magma ocean cooling. Detection of Martian 4He will be evidence of current degassing activity on Mars. Abundant 4He in Venus atmosphere, showing much longer residence time than the Earth's 4He, should correspond to current absence of magnetic field.View full abstractDownload PDF (1552K) -
Hiroki SATO1995 Volume 48 Issue 1 Pages 131-137
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSLaboratory data of seismic velocities in upper mantle peridotite are used to estimate the thermal structure of the low velocity zone. Here we calculate seismic velocities at mantle solidus temperature to 10GPa by using elasticity data of mantle minerals and employing a third-order finite strain theory. We compare the calculated velocities and laboratory velocity data with seismic observations, and estimate temperatures and partial melt fractions in the low velocity zone. The comparison, for example, yields up to 4 and 2vol.% partial melt in 0-23Ma and 23-53Ma asthenosphere, respectively, beneath the Pacific Ocean. The velocity structure of the reference earth model such as PREM or 1066A indicates that the low velocity zone in average is hot (compared with the high-velocity lithosphere) but subsolidus, and partial melt exists only in regions of anomalously low velocity. Beneath the Rio Grande rift, the Salton Trough, and the Kenya rift, for example, low velocity anomalies (Vp=7.3-7.4km/s) indicate the presence of 2, 3, and 3vol.% partial melt, and 1500°C at 100km depth, 1410°C at 75km depth, and 1310°C at 50km depth, respectively. Temperatures determined here from seismic velocity data are generally consistent with those from surface heat flow. This implies that the velocity drop in the low velocity zone is mostly due to the increase in temperature.View full abstractDownload PDF (847K) -
Implications for Island Arc MagmatismHiroki SATO1995 Volume 48 Issue 1 Pages 139-149
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe thermal structure of the upper mantle beneath the Japan arc is investigated from seismic and laboratory velocity data. Comparisons of seismic velocity structure with laboratory velocity data yield estimates of temperature and degree of partial melt. The diagrams for determining temperature and melt fraction are presented by combining upper mantle velocity structure with elastic-wave velocity in mantle rocks at high pressure and temperature. Employing the velocity structure in northeastern Japan, we obtain up to 2vol.% melt and 1270°C at 40km depth, 1vol.% melt and 1360°C at 65km depth, and 1vol.% melt and 1460°C at 90km depth. The amount of melt is larger and the area of melting is broader for more extensive low velocity regions in the mantle wedge right beneath the volcanic front. We also expect partial melting and temperatures higher than the mantle solidus beneath volcanoes in central Japan and in Kyushu, such as Mt. Asama, Mt. Fuji and Mt. Unzen. It is noted that these high temperature regions are localized in the mantle wedge beneath the volcanoes and downwards to the west. Localized plume-like upwellings (volcanic plumes) from deep mantle appear to produce magmatism and high heat flow in the Japan arc.View full abstractDownload PDF (1367K) -
Muneyoshi FURUMOTO1995 Volume 48 Issue 1 Pages 151-157
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe episodicity of impacts on the Moon, which must take place also on the Earth, appears to be accompanied by orogenic episodes on the Earth. Seven of eleven episodes of major impacts in the Precambrian era were followed by orogenic events with a time lag of about 100Myr. A possible scenario explaining the coincidence is as follows. A shock wave from a major impact might have caused the spinel-post-spinel transformation in megaliths accumlated around the 670km discontinuity and/or huge melting in the upper mantle. The gravitational instabilities of the megaliths or the melted parts brought about down-welling or up-welling superplumes, respectively. Then rapid mantle convections induced by the superplumes produced global tectonics such as a formation or breakup of a supercontinent.View full abstractDownload PDF (754K) -
Akihito HOSHIKUMA, Hiroki SATO, Eiji ITO1995 Volume 48 Issue 1 Pages 159-165
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSGrain growth of the dissociation product (MnTiO3+MnO), as an analogue assemblage of (Mg, Fe) SiO3 perovskite and (Mg, Fe) O magnesiowüstite for the lower mantle, was studied at pressures of 0.9 and 1.6GPa and at temperatures of 1000° to 1320°C, for the time duration ranging from 0.125 to 256 hours. By fitting the grain growth data to an equation Gn=K0·t·exp{-(Q*+PV*)/RT}, the grain growth exponent n, the activation energy Q*, and the activation volume V* were determined to be 3.55±0.46, 560±70kJ/mol and 70±10cm3/mol, respectively. These parameters indicate that the mutual intergrowth texture of the dissociation product suppresses grain growth substantially by a pinning effect. The present results thus suggest that a fine-grained mixture of the perovskite plus magnesiowüstite will persist to exhibit superplastic behavior in the slab penetrated into the lower mantle. If the grain growth rate of (Mg, Fe) SiO3+(Mg, Fe) O mixture is similar to that of MnTiO3+MnO, the superplastic slab may cause a dramatic change of the shape and geometry of the subducting plate beneath the 660km discontinuity.View full abstractDownload PDF (4986K) -
Toru INOUE1995 Volume 48 Issue 1 Pages 167-175
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe possible existence of water in the upper mantle and its implications to the generation of ultrabasic (komatiite) magma have been discussed on the basis of the recent melting experiments in the systems pyrolite+H2O and Mg2SiO4 MgSiO3-H2O. The experiments demonstrated that presence of a certain amount of H2O changes the melting temperatures, liquidus phases, and melt compositions in these system. No hydrous phases were observed near the solidus temperature below 12GPa, whereas hydrous modified spinel was found near the solidus temperatures at 15.5GPa. The maximum content of H2O in this phase is estimated to be 3.3wt% from the microprobe analysis and crystallographic constraint. This suggests that a significant amount of H2O can be accommodated in the mantle transition zone. The melting phase relations suggest that komatiite magmas can be generated in the hydrous mantle at about 200km depth.View full abstractDownload PDF (1112K) -
Mitsuhiko SHIMADA1995 Volume 48 Issue 1 Pages 177-185
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDry silicate rocks with low porosity exhibit brittle fracture behavior at confining pressures to 3GPa and temperatures to 300°C. The fracture mechanism has been suggested to change from ordinary brittle fracture to a high-pressure type when the compressive strength becomes equal to the frictional strength. The transition occurs at 0.8GPa confining pressure for a granite in laboratory size (a few cm). From available data of the scale effect on rock strength, the high-pressure type of fracture for a granite in a mechanically characteristic size for the bedrock or the earth's crust is estimated to occur at an effective confining pressure of about 70MPa. This implies that the high-pressure type of fracture may be predominant at depths of seismogenic layer in the crust, except for at very shallow depths and in the case of very high pore-water pressure. Further implications in the crust, such as lithosphere strength and earthquake prediction is discussed. Finally, it is emphasized that experiments on the scale effect of rock strength under confining pressure using a big press would be required to verify the assumption that the changes in the fracture mechanism of a large size of rock specimen are identical to those observed in a few cm size specimens.View full abstractDownload PDF (3198K) -
Ichiro KANEOKA1995 Volume 48 Issue 1 Pages 187-198
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSCharacteristics and usefulness of noble gas isotopes in earth and planetary sciences are reviewed. Based on the data for noble gas isotopes, constraints on the chemical structure of the Earth's interior and its evolution are discussed. As long as lighter noble gas isotopes (He, Ne, Ar) are concerned, at least two chemically different reservoirs are required in the mantle. One is the source for MORB (Mid-oceanic ridge basalt), which is depleted in incompatible elements including volatiles. The other is the source for OIB (Oceanic island basalt), which is less depleted in incompatible elements and retains primordial noble gases. Such primordial noble gases should be retained in silicate phases as revealed from laboratory experiments. Apparent heterogeneity in the observed isotopic ratios in OIB can be explained by mixing with recycled materials which might mostly be retained between the upper and lower mantle boundary region. The occurrence of excess 129Xe, which is believed to be primarily the decay product of the extinct nuclide 129I, implies the incomplete mixing of mantle materials during the whole history of the Earth.View full abstractDownload PDF (3117K) -
Kiminori SATO1995 Volume 48 Issue 1 Pages 199-211
Published: May 25, 1995
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThis paper reviews the structure of sub-cratonic mantle (‘continental root’) from seismological, petrological and geothermal points of view. The ‘continental root’ is divided into the chemical boundary layer (continental keel, up to about 200km depth) and the thermal boundary layer (tectosphere, up to 200-400km depth). The tectosphere has been a non-convective region against underlying convective mantle since the Archaean age. The tectosphere is recognized as high velocity region with magnitude of about 1-4% higher than the global average. Depleted garnet peridotites which compose the continental keel have low intrinsic density, because of their FeO deficiency than peridotites of the oceanic mantle. The buoyancy caused by this low intrinsic density offsets the negative buoyancy caused by the relative density decrease due to the temperature difference between the continental mantle and the oceanic mantle. Therefore, the in-situ densities beneath the continent and the ocean are equal, and the tectosphere of which the continental keel occupies the upper part is stabilized against convective disruption. The Rb/Sr and Sm/Nd ages of 3.2-3.3 Ga are reported from silicate inclusions in diamond derived from sub-cratonic mantle, suggesting that the stable tectospheric structure has formed in Archaean age. The material of the continental keel is mainly composed of the depleted garnet peridotites formed by extraction of basic magma during the Archaean age. Once the tectosphere was formed, the tectosphere diverts heat flow away from the sub-cratonic mantle into the thinner surrounding mantle. This mechanism explains the low heat flux into the Archaean craton.View full abstractDownload PDF (1581K)
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