Geochemistry of hydrothermal deposits from Loihi submarine volcano,Hawaii

Dredging across the northeast rim of the summit crater of Loihi Seamount recovered several morphologically similar but chemically and mineralogically distinct hydrothermal deposits encrusting the surface of fresh pillow lava talus. The multicolored deposits suggest a precipitation sequence that may be controlled by an oxidation-reduction gradient in which smectite ranging in composition from Fe-montmorillonite to nontronite has precipitated along with iron oxide under slightly reducing conditions. This deposition was apparently followed by amorphous iron oxide and silica precipitation, possibly under more oxic conditions. Oxygen isotope geothermometry indicates formation temperatures in the range of 31–57°C for the Loihi smectites. Trace element enrichments appear to be positively correlated with the isotopic formation temperature of the smectite, suggesting either increased trace element solubility within the higher-temperature vent fluids or increased smectite and iron oxide scavenging with increased precipitation rates. The trace element abundances further suggest the presence of polymetallic sulfides that either are directly associated with the smectites as amorphous phases or occur beneath these deposits in the volcanic pile of the seamount.     

Study of nanocrystals in the dynamic slip zone

Mineral composition is studied and a search to detect nanocrystals is conducted in the surface layers of slickensides formed due to dynamic slip in arkose sandstone. The infrared and Raman spectroscopy show that the slickensided layer is composed of nanocrystals of montmorillonite and anatase measuring ??15 nm and 3 nm, respectively. The crystalline lattice of the nanocrystals of montmorillonite is stretched by ??2.5% while the lattice of the nanocrystals of anatase is compressed by ??0.12%. Deeper than 3 mm below the slickenside surface, the sandstone contains nanocrystals of montmorillonite, beidellite and nontronite, quartz, plagioclase, and anatase. The nanocrystals of anatase have a linear size of ??8 nm. Their crystalline lattice is compressed by ??0.03%. It is supposed that montmorillonite in the slickensides was formed due to hydrolytic decomposition of silicates under friction of the fault planes sliding past each other.     

On the distribution of noble gases in Allende: a differential oxidation study

We have developed a closed-system combustion technique and utilized it to progressively oxidize a gas-rich, highly carbonaceous acid residue and a fine-grained (<4 μm) matrix sample from the Allende C3V meteorite and analyze the released gases mass spectrometrically. For the residue complete gas mobilization occurs at temperatures below 600°C. The temperature interval over which most of the gases are released coincides with that for combustion of most of the carbon. Release is primarily due to chemical attack rather than thermal activation of the gases. There are somewhat different oxidation thresholds for the heavy gases (Ar, Kr, and Xe) and the light gases (He, Ne), indicating chemically different sites for the two groups. Relative enhancement of isotopically anomalous components near 600°C is as large as in any open-system oxidation method. Differential combustion of the matrix sample reveals three distinct outgassing peaks, the first matching the release from the carbonaceous residue (“combustibles”), the second attributed to sulfides, and the third tentatively assigned to silicates. They comprise about 53%, 7% and 40% of the total heavy gases respectively. While the “sulfides” exhibit a small fission-like component, the Xe in the “silicates” appears isotopically uniform with roughly AVCC composition. The “combustibles” of the matrix contain relatively less excess¹²⁹Xe than the residue, perhaps indicating that ～10% of the total¹²⁹Xe in the residue was acquired from “silicates” by redistribution during acid treatment. We cannot rule out the possibility that planetary gases assigned to “sulfides” or “silicates” actually reside in carbonaceous phases somehow sheltered within soluble mineral assemblages, or in acid-soluble carbonaceous phases resistant to oxidation. Integrated releases below and above 600°C during the matrix combustion exhibit virtually identical heavy gas elemental composition, implying similar fractionation during planetary gas entrapment in various materials or in the same material in various environments.     

Thermal remagnetization and the paleointensity record of metamorphic rocks

We present a quantitative relationship between blocking temperature and time that, in principle, provides a calibration of thermal remagnetization in nature. For a given metamorphic temperature-time regime, one can decide whether a given laboratory blocking temperature (or for paleointensity work, a range of blocking temperatures) is consistent with primary natural remanence (NRM) or with a metamorphic overprint. Independent of the domain structure or the chemical composition of the magnetic minerals, two general types of behaviour are predicted. If the primary NRM possesses laboratory (or primary cooling) blocking temperatures within 100°C or so of the Curie temperature, thermal remagnetization at lower temperatures, even over times as long as 10⁶ years, is improbable. If the blocking temperatures are lower, viscous remagnetization is pronounced at temperatures well below those indicated by laboratory thermal demagnetization. An approximate scale of the “survival potential” of primary NRM in rocks of different metamorphic grades indicates that primary paleointensities are unlikely to be recovered from rocks metamorphosed above high-greenschist facies if the predominant magnetic mineral is nearly pure magnetite, or above middle-amphibolite facies if nearly pure hematite is predominant. Evidence from laboratory experiments and paleomagnetic field studies in metamorphic regions suggests, however, that these survival estimates are unduly optimistic. Chemical remagnetization through the destruction of primary magnetic minerals, and not thermal remagnetization, probably sets an effective upper temperature for the survival of primary NRM.     

Nontronite from a low-temperature hydrothermal system on the Juan de Fuca Ridge

A deposit of Fe-rich, Al-poor, hydrothermal nontronite was recovered from the Juan de Fuca Ridge. Analyses show the deposit to be mineralogically and chemically similar to nontronite described at other oceanic localities. The deposit is located near the tip of a propagating segment of the Juan de Fuca Ridge. Rare earth elements and Sr isotopes indicate that the nontronite precipitated from seawater. A formation temperature of 57°C is suggested by oxygen isotopic composition. The low-temperature nontronite deposits apparently form from newly established hydrothermal systems associated with the propagating rift segment. More mature hydrothermal systems that deposit sulfide on the seafloor may develop from these low-temperature systems.     

Paleomagnetic evidence for low-temperature emplacement of the phreatomagmatic Peperino Albano ignimbrite (Colli Albani volcano, Central Italy)

The Peperino Albano (approximately 19–36 ka old) is a phreatomagmatic pyroclastic flow deposit, cropping out along the slopes of the associated Albano maar (Colli Albani volcano, Italy). The deposit exhibits lateral and vertical transitions from valley pond to veneer facies, as well as intracrater facies. We present the results of a paleomagnetic study of thermal remanent magnetization (TRM) of the lithic clasts of the Peperino Albano ignimbrite that provide quantitative estimates of the range of emplacement temperatures across the different facies of the ignimbrite. Emplacement temperatures estimated for the Peperino Albano ignimbrite range between 240° and 350°C, with the temperatures defined in the intracrater facies being generally lower than in the valley pond and veneer facies. This is possibly due to the large size of the sampled clasts in the intracrater facies which, when coupled with low temperature at the vent, were not completely heated throughout their volume during emplacement. The emplacement temperatures derived from the paleomagnetic results are in good agreement with the presence of un-burnt plants at the base of the ignimbrite, indicating that the temperature of the pyroclastic flow was lower than the temperature of ignition of wood. Paleomagnetic results from the Peperino Albano confirm the reliability of the paleomagnetic approach in defining the thermal history of pyroclastic flow deposits.     

Primary dolostone related to the Cretaceous lacustrine hydrothermal sedimentation in Qingxi sag, Jiuquan Basin on the northern Tibetan Plateau

Based on comprehensive studies in petrography, petrofabric analysis and geochemistry, this paper describes a unique and rare laminated micritic ferruginous primary dolostone crystallized and precipitated from the alkaline hot brine under the conditions of the Mesozoic faulted lake basin. The main rock-forming mineral of this dolostone is ferruginous dolomite with a micritic structure. This dolomite mostly exhibits laminae of 0.1–1 mm thick and is often discovered with other minerals, such as albite, analcite, barite and dickite, which have at least two types of interbedded laminae. Petrogeochemistry reveals that this dolostone contains a large number of typomorphic elements of hydrothermal sedimentation, including Sb, Ba, Sr, Mn, and V. In addition, the LREE is in relatively high concentrations and possesses the typical REE distribution pattern with negative Eu anomaly. Oxygen isotope values (δ¹⁸O_PDB) range from 5.89‰ to 14.15‰ with an average of 9.69‰. The ratio of ⁸⁷Sr/⁸⁶Sr is between 0.711648 and 0.719546, with an average of 0.714718. These data indicate that the depositional environment is a stable, blocked, anoxic low-lying hot brine pool in the bottom of deep lake controlled by basement faults. The hydrothermal fluid is the alkaline hot brine formed by the combination of the infiltration lake water and mantle-derived magmatic water, consisting of many ions, including Ca²⁺, Mg²⁺ and Fe²⁺. Under the driving flow power of magmatic heat, gravity and compaction, the hydrothermal fluid overcame the overburden pressure and hydrostatic pressure of the lake water body, and boiled to explosion, and then the explosion shattered the original laminated micritic ferruginous primary dolostone near the vent and then formed a new type of dolostone called shattered “hydroexplosion breccias”. In the low-lying, unperturbed hot brine pool, far from the vent, the laminated micritic ferruginous primary dolostone was quickly crystallized and chemicals precipitated from the hydrotherm. This study of special rocks contributes to research into the causes of the formation of lacustrine carbonate rocks and dolostone. In particular, it provides new examples and research insights for future studies of the lacustrine dolomite from the similar Mesozoic and Cenozoic basins in China.     

Melting relations in the chloride–carbonate–silicate systems at high-pressure and the model for formation of alkalic diamond–forming liquids in the upper mantle

The experiments in the model system CaMgSi₂O₆–(Na₂CO₃, CaCO₃)–KCl are performed at 5 GPa and 1400–1600 °C in order to study the phase relations, including liquid immiscibility, in the chloride–carbonate–silicate systems with application to alkali and chlorine-rich liquids preserved in kimberlitic diamonds. Experiments in the boundary joins of the system demonstrated that both the carbonate–silicate and chloride–carbonate melts are homogeneous; while high-temperature (above 1800 °C) liquid immiscibility is assumed for the chloride–silicate join of the above system. Addition of silicate component into the chloride–carbonate melts and chloride component into the carbonate–silicate melts results in splitting of the homogeneous liquids into the immiscible chloride–carbonate brine and carbonate–silicate melt. Carbonate–silicate and chloride–carbonate branches of the miscibility gap converge within the carbonate-rich region of the system. Regular temperature evolution of the shape and size of the miscibility gap is deduced. With decreasing temperature, the convergence point moves toward more Si-rich compositions, expanding fields of homogeneous chloride–carbonate silica-saturated melts. This effect is governed by the precipitation of the silicate phases even from silica-bearing chloride–carbonate melts. In addition, experiments revealed regular evolution of both Cl-bearing carbonate–silicate melt and Si-bearing chloride–carbonate brine toward the low-temperature chlorine–bearing carbonatitic liquid with decreasing temperature. These trends are similar to the evolution of the melt and brine inclusions in some diamonds from Botswana, Brazil, Canada, and Yakutia, indicating their growth during cooling. The model for interaction of the chloride–carbonate brine with the mantle rocks is developed on the basis of the present experimental data. This model is applied to the chlorine-enriched kimberlites of the Udachnaya–East pipe.     

The oceanic cycles of the transition metals and their isotopes

The stable isotope systems of the transition metals potentially provide constraints on the current and past operation of the biological pump,and on the state of ocean redox in Earth history.Here we focus on two exemplar metals,nickel(Ni)and zinc(Zn).The oceanic dissolved pool of both elements is isotopically heavier than the known inputs,implying an output with light isotope compositions.The modern oceanic cycle of both these elements is dominated by biological uptake into photosynthesised organic matter and output to sediment.It is increasingly clear,however,that such uptake is associated with only very minor isotope fractionation.We suggest that the isotopic balance is instead closed by the sequestration of light isotopes to sulphide in anoxic and organic-rich sediments,so that it is ocean chemistry that controls these isotope systems,and suggesting a different but equally interesting array of questions in Earth history that can be addressed with these systems.     

East Pacific Rise at latitude 21°N: isotopic composition and origin of the hydrothermal sulphur

The sulphur isotope composition of 16 pyrite and chalcopyrite samples from recent sulphide deposits (“Cyana”—project RITA) and active sulphide mineralisation (“Alvin”—project RISE) associated with hydrothermal sources at 380±30°C on the East Pacific Rise at latitude 21°N have been measured. The³⁴S/³²S ratios are relatively uniform and essentially identical for both sites: δ³⁴S=+1.4to3.0%. (CDT), mean +2.1‰. The sulphides were analysed after the majority of the very numerous micro-inclusions of anhydrite had been removed.Two independent physico-chemical analyses of the data demonstrate that about 90% of the sulphur was leached from the basaltic host rocks by the circulating seawater-hydrothermal fluids.     

Verfahren zur katalytisch-oxydativen Entsulfidierung von Abwässern

The oxidative conversion of strongly alkaline sulphide concentrations in wastewaters from the wet molybdenite enrichment is successfully performed within a relatively short time by the application of atmospheric oxygen, “Winkler adsorbent” (activated form of ash from Winkler generators) or “Winkler generator ash” and chlorinated lime at the same time. The reaction times were 60… 90 min at residual sulphide concentrations of 1… 10 mg/l. The initial concentrations of sulphide were between 400 and 1,200 mg/l. It was proved by comparative investigations that the “Winkler absorbent” or the “Winkler generator ash” have a catalytical effect during the oxidation by air. Therefore, also, e.g., at an initial concentration of sulphide of 600 mg/l only 4 g/l chlorinated lime were required, which corresponded to only about 0.13 times the stoichiometrically calculated quantity with the available chlorine content being taken into account. Flotation cells are suitable as reactors.     

Experimental hydrogen isotope studies,II. Fractionations in the systems epidote-NaCl-H2O,epidote-CaCl2-H2O and epidote-seawater,and the hydrogen isotope composition of natural epidotes

The hydrogen isotope fractionation factors between epidote and aqueous 1 M and 4 M NaCl, 1 M CaCl₂ solutions, and between epidote and seawater, have been measured over the temperature range 250–550°C over which the degree of dissociation of dissolved species varies significantly. Measured fractionations at 350°C are decreased by up to 12‰, 9‰ and 7‰ relative to pure water in seawater, 1 M CaCl₂ and 1 M NaCl respectively, while above 500°C fractionations are not measurably dependent on fluid composition. Water—solution fractionation factors are derived which are generally applicable to the correction of mineral—water hydrogen isotope fractionations for the composition of the fluid phase.The hydrogen isotope compositions of natural epidotes are interpreted in the light of experimental fractionation data for situations where temperature, δD (fluid), and, in some cases, fluid chemistry, are independently known. Epidotes from active geothermal systems have hydrogen isotope quench temperatures consistent with or close to measured well temperatures unless the measured temperature has declined substantially since epidote formation or there is uncertainty in the D/H ratio of the water associated with the epidote because of isotopic heterogeneity in the well waters. Hydrothermal and metamorphic epidotes show closure temperatures of 175–225°C and 200–250°C. There is no evidence that retrograde metamorphic fluids, if present, are isotopically different from prograde fluids.The water-solution fractionations indicate strong solute-solvent interactions between 250 and 450°C and imply that both dissociated and associated species contribute to the fractionation effects through modification of the orientations and structure of the water molecules. Solute-solvent interactions become negligible at temperatures around 550°C.     

Empirical geothermobarometry for garnet peridotites and implications for the nature of the lithosphere,kimberlites and diamonds

As a result of a study on the influence of Cr on geothermometry and geobarometry empirical garnet-orthopyroxene geobarometry has been refined. The applicability to simple and complex systems is demonstrated and the modelling procedure briefly outlined. The suitability of some geothermometers for application to garnet lherzolite xenoliths and their limits of precision are discussed. Fields of pressure-temperature estimates for garnet lherzolites from various provinces are shown. Low-temperature xenoliths (< 1050°C) give estimates in accord with a conductive geotherm for the continental lithosphere. African xenoliths (both South African and “off-craton” Namibian) record a distinctive pattern, exhibiting a “temperature discontinuity”, where high-temperature xenoliths (> 1050°C) give near-isobaric estimates for a range of temperatures. The depth of this “temperature discontinuity” is shallower for off-craton than for on-craton suites. Similar patterns are indicated for suites from U.S.A. and the U.S.S.R.The temperature discontinuity is interpreted as a geologically short-lived transient state, where the deepest parts of the lithosphere are in the process of adjustment to higher heat flux from below. At the highest temperatures recorded by those suites “wet” peridotitic solidi are intersected and thus the xenoliths record events, were P,T conditions may have allowed the formation of kimberlitic or strongly undersaturated magmas at about the depths of this discontinuity. This process is inferred to lead to thermal erosion of the base of the lithosphere.The generation and subsequent crystallization of magmas at the base of the lithosphere is inferred to be the source for diamond formation. The distinctive pattern of high- and low-temperature xenoliths in relation to the diamond stability field shows the existence of a rather small “diamond window” between about 900 and 1300°C at 40–55 kb. This window exists only underneath old, stable continents with a thick lithosphere. If recent age determinations on diamonds are correct, this implies the existence of thick continental lithosphere with similar characteristics to present-day lithosphere in the Archean.A model is presented arguing for hot, upwelling convection streams as a possible source of heat. The model implies differences in lithospheric development according to the speed of plates, carrying a continent: Continuous lithospheric thinning by thermal erosion for steady or very slow moving plates with the break-up of a continent and the formation of an ocean as one extreme, the continuous repetition of thermal erosion and growth on cooling (underplating) of the continental lithosphere as the other extreme for fast moving plates. The latter may be the cause of a number of complexities and heterogeneities both within the deep continental lithosphere as well as in the convecting mantle.     

Correlated chemical and isotopic zoning in carbonates in the martian meteorite ALH84001

The meteorite ALH84001, a sample of the ancient martian crust, contains small quantities (1%) of strongly chemically zoned carbonate. High spatial resolution (10 μm) ion microprobe analyses show that the chemical zoning is strongly correlated with variations in oxygen isotope ratios. Early formed Ca,Fe-rich cores have δ¹⁸O 7‰ increasing to 22‰ SMOW in the more Mg-rich outer cores and magnesite rims. Isolated areas of ankerite appear to be isotopically lighter with δ¹⁸O 1‰. The large range in δ¹⁸O requires a significant range in either fluid isotopic composition, or temperature, or both, in the course of the deposition sequence. Our data are inconsistent with formation of the zoned carbonates by closed system Rayleigh fractionation. There is no unique interpretation of the oxygen data, but the recent observation of existence of Δ¹⁷O excesses in the carbonate appears to rule out models which involve high temperature isotopic exchange with silicate. Comparison with terrestrial analogues suggests that ALH84001 carbonates formed in a hydrothermal system with T<400°C, and which, at least in the early stages of formation, may have involved water with δ¹⁸O < 0‰ SMOW. The later stages of deposition probably occurred at temperatures below 150°C, a conclusion which does not preclude the co-existence of thermophilic bacteria; temperatures during earlier stages of deposition are less likely to have been hospitable to bacteria.     

Calculation on sulphur isotope fractionation between sphalerite and galena using lattice dynamics

Increasing use is being made of sulphide minerals in isotope geothermometry. Sulphur isotope fractionation factors for³⁴S exchange between sphalerite (ZnS) and galena (PbS) have been calculated for various temperatures between 0 and 1000°C. The reduced partition function ratios have been calculated using a “shell” model for the forces derived from inelastic neutron scattering studies of the lattice dynamics of sphalerite and galena. A new formalism of the current theory has been developed which enables the accuracy of the calculation to be determined.The Zn³⁴S—Pb³⁴S equilibrium constant obtained by the shell model calculations is 1.0060 to 100°C, 1.0031 at 250°C and 1.0005 at 1000°C, in agreement with experimental determinations.     

The palaeomagnetism of muddy sediment cores from the Inner Sound,Northwest Scotland,and the glacial and post-glacial history of sedimentation in the area

Josephinite is a terrestrial iron-nickel alloy with an intergrown magnesium silicate, and arsenide and sulphide phases, and andradite garnet; several specimens have been found to contain elemental silicon and CaO · 2“FeO”. Josephinite is not awaruite, an iron-nickel mineral formed by serpentinization of ultramafic rocks. Because of its geologic setting and unique mineralogy we propose that josephinite might have originated in the region of the coremantle boundary, was transported via a deep-mantle “plume” and diatreme mechanism into lithosphere mantle that has been emplaced in the Klamaths by ophiolite obduction. Regardless of such a hypothesis, we report here the discovery of terrestrial silicon occurring with josephinite, which seems to preclude a lithosphere environment of origin for josephinite.     

Oxygen and hydrogen isotope studies of serpentinization in the Troodos ophiolite complex,Cyprus

Oxygen and hydrogen isotopic compositions were measured on 12 serpentine and 2 actinolite samples from the Troodos ophiolite complex, Cyprus. The single analyzed antigorite(δD= ?60, δ¹⁸O= 7.1) is isotopically similar to all previously analyzed antigorites from ultramafic bodies. However, although their D/H ratios are relatively “normal”(δD= ?70to?92), the δ¹⁸O values of most of the Troodos lizardite-chrysotile serpentines (+12.6 to +14.1) are much higher than the 2.0–9.3‰ range typically found in such serpentines. Such high δ¹⁸O values have previously been found only in the serpentine-like mineraloids termed “deweylites”, which apparently formed at Earth-surface temperatures, and in a single sample from Vourinos, Greece that is in contact with high-¹⁸O limestone. The Troodos lizardite-chrysotile samplescannot have formed by reaction with heated ocean waters, but instead must have formed in contact with large amounts of some type of meteoric, metamorphic, or formation water, either (1) at very low temperatures in a near-surface environment, or (2) at about 100°C from waters that were abnormally enriched in¹⁸O(δ¹⁸O ≈ +4 to +8). The latter possibility seems most plausible inasmuch as extensive evaporites were deposited throughout the Mediterranean Sea during the late Miocene, and this would have been accompanied by strong¹⁸O enrichments of the local meteoric waters. Heated ocean waters, however, probably were responsible for the formation of the actinolitic amphiboles(δ¹⁸O= 4.6 to 5.5; δD= ?51to?46) from the gabbro and ultramafic zones in the Troodos complex. The amphiboles must have formed at considerably higher temperatures and at an earlier stage than the lizardite-chrysotile serpentinization.     

A petrogenetic grid for eclogite and related facies under high-pressure metamorphism

The petrogenetic grid between the eclogite and other high-pressure/temperature (P/T) metamorphic facies in a basaltic system is constructed by considering barroisite as one of the important phases in high-P/T metamorphism and by using previous petrological data combined with Schreinemakers' analysis and slope calculation. In the constructed petrogenetic grid, the eclogite facies is bounded by the blueschist and epidote–amphibolite facies with negative-slope reactions at lower temperatures (450–550 °C) and by the epidote–amphibolite, amphibolite and granulite facies with positive-slope reactions at higher temperatures (> 550–600 °C). The eclogite facies does not contact the greenschist facies, and the lowest P condition for the eclogite facies exists at the boundary between the eclogite and epidote–amphibolite facies. The temperature range of the epidote–amphibolite facies increases with increasing pressure until 8–11 kbar and then decreases up to 13–15 kbar. Compared to boundaries of other facies, boundaries of the eclogite facies may have wider P–T ranges. The boundary between the blueschist and eclogite facies occurs over a large temperature range from 450 to 620 ± 30 °C, and the transitions between the eclogite and amphibolite or high-pressure granulite facies occur over a pressure range in excess of 6–10 kbar.     

Shock-produced vapor-grown crystals in the Yanzhuang meteorite

Vapor-grown crystals intimately related to shock metamorphism of meteorites were found in the Yanzhuang (H6) chondrite which had been heavily impacted in the space. These crystals include: (i) subhedral low-Ca pyroxene occurring on the wall of the pores within a silicate melt pocket that experienced a shock temperature higher than 1500°C, (ii)Fe-Ni needle-whiskers (taenite) occurring in the cracks in the partially melted chondritic facies that experienced a shock temperature of 850–1300°C, (iii) troilite with abundant microholes occurring in the cracks in the brecciated facies and the lightly deformed chondritic facies that experienced a shock temperature lower than 850°C. The occurrence and mineralogical features of vapor-grown crystals show that vaporization of minerals could be produced in heavily impacted meteorites and that a small amount of crystals could be depositedin situ from vapor phases. Project supported by the Natural Science Foundation of Guangdong Province.     

The altitude dependence of magnetic remanence in the slowly-cooled Precambrian plutonic terrain of West Greenland

To evaluate the change in magnetic remanence with altitude through a slowly-cooled Precambrian basement terrain three vertical sections have been sampled in West Greenland. The study employs the principle that higher structural levels passed through their blocking temperatures earlier than lower levels and therefore record earlier pole positions, and it utilises dolerites and diorites intruded late in, or after, the tectonic history to minimise anisotropy effects. In the amphibolite facies terrain at Qa´qatoqaq (1400 m) highly-stable magnetite-held remanences move on demagnetisation progressively along small circles interpreted to record younger to older apparent polar wander (a.p.w.) motions during cooling through the blocking temperature ranges. Although the raw data show no systematic variation with altitude, when account is taken of the blocking temperature spectra as defined by thermal demagnetisation there is a systematic change in palaeofield direction in the same sense as that recorded by the demagnetisation trends. Granulite facies terrain at Igdlu´nguit qula?t (600 m) again shows systematic variation with altitude when the sites are divided into those with a remanence dominated by hemo-ilmenite and those dominated by magnetite. A third section at Praestefjeldet (250 m) yields a palaeofield reversal and a high blocking temperature component.The age evidence is evaluated to suggest that the a.p.w. path defined by 5 mean palaeopoles between 318°E, 1°N and 247°E, 38°N represents up to 50 Ma of palaeofield motion recorded by the uplift and cooling of this basement terrain at crustal depths of the order of 10 km. The calculated rate of a.p.w. motion is 1–2°/Ma and the rate of crustal uplift 10–20 m/Ma, these rates are respectively up to an order higher, and at least an order lower, than Phanerozoic rates. The collective data from Greenland agree closely with post-“Hudsonian” poles from the Laurentian Shield and represent part of a very widespread uplift event following this mobile episode. They show that altitude sections can yield a systematic record of the magnitude and direction of Precambrian a.p.w. motions provided that the blocking temperature spectra are taken into account.