Late Pleistocene and Holocene slip rate of the Northern Wadi Araba fault, Dead Sea Transform, Jordan

The Wadi Araba Valley is a morphotectonic depression along part of theDead Sea Transform (DST) plate boundary that separates the Arabian plateon the east from the Sinai subplate on the west. The Wadi Araba fault(WAF) is the main strike-slip faults one of between the Gulf of Aqaba and the E-Wtrending Khunayzira (Amatzayahu) fault that bounds the southern end ofthe Dead Sea. Just south of the Dead Sea, the WAF cuts across severalgenerations of alluvial fans that formed on tributaries to the Wadi Dahalafter the regression of Late Pleistocene Lake Lisan ca. 15 ka. Geomorphicand stratigraphic evidence of active faulting, including left-laterally offsetstream channels and alluvial-fan surfaces, yielded fault slip-rate data for thenorthern segment of WAF. Typical cumulative displacements of 54 m,39 m, and 22.5 m of stream channels and alluvial-fan surfaces acrossthe fault were measured from detailed geologic and topographic mapping.The 54 m offset of the oldest alluvial-fan surface (Q _f1 ) occurredafter the final lowering of Lake Lisan (16–15 ka) and before 11 ka yieldinga slip-rate range of 3.4 mm/yr to 4.9 mm/yr. Based on radiocarbonages of charcoal and landsnail shell samples from the buried Q _f2 alluvial-fan deposits exposed in trenches excavated across the fault, the39 m and 22.5 m offsets occurred after 9 ka and 5.8 ka, respectively. These data yield a slip-rate range between 3.9 mm/yr and 6.0 mm/yr.The small variability in these slip-rate estimates for different time periodssuggests that the northern Wadi Araba fault has maintained a relativelyconstant slip rate in the past 15 ka. We calculate an average slip rate of 4.7± 1.3 mm/yr since 15 ka based on the three separate displacementsand age estimates. Five separate offsets of 3 m were measured from gullybends and the offset of small fault-scarp alluvial fans. These displacementdata suggest a coseismic slip of 3 m in the last earthquake, or acumulative slip of 3 m in the past few earthquakes. A maximum slip of3 m correspond to a Mw 7 earthquake that ruptures about 49 km offault length. Using an average slip rate of 4.7 ± 1.3 mm/yr togetherwith a 3-m slip-per-event suggests a maximum earthquake recurrence intervalof this fault segment of 500 to 885 years.     

Evidence for ground-rupturing earthquakes on the Northern Wadi Araba fault at the archaeological site of Qasr Tilah, Dead Sea Transform fault system, Jordan

The archaeological site of Qasr Tilah, in the Wadi Araba, Jordan is located on the northern Wadi Araba fault segment of the Dead Sea Transform. The site contains a Roman-period fort, a late Byzantine–Early Umayyad birkeh (water reservoir) and aqueduct, and agricultural fields. The birkeh and aqueduct are left-laterally offset by coseismic slip across the northern Wadi Araba fault. Using paleoseismic and archaeological evidence collected from a trench excavated across the fault zone, we identified evidence for four ground-rupturing earthquakes. Radiocarbon dating from key stratigraphic horizons and relative dating using potsherds constrains the dates of the four earthquakes from the sixth to the nineteenth centuries. Individual earthquakes were dated to the seventh, ninth and eleventh centuries. The fault strand that slipped during the most recent event (MRE) extends to just below the modern ground surface and juxtaposes alluvial-fan sediments that lack in datable material with the modern ground surface, thus preventing us from dating the MRE except to constrain the event to post-eleventh century. These data suggest that the historical earthquakes of 634 or 659/660, 873, 1068, and 1546 probably ruptured this fault segment.     

Aeromagnetic anomalies uncover the Precambrian basement in the Chhattisgarh basin area,Central India

This paper presents aeromagnetic images for the Chhattisgarh basin region, in Central India, to provide a new window on Precambrian basement geology and structure. On the basis of aeromagnetic patterns, the Chhattisgarh basin is sub-divided into a northern low (negative) anomaly zone and a southern high (positive) anomaly zone. The northern portion of the main Chhattisgarh basin has been further divided into two subbasins, the Hirri sub-basin in the west, and Baradwar sub-basin in the east. A prominent negative anomaly delineates a NW-SE trending greenstone belt separating these sub-basins. Positive magnetic anomalies delineate the extent of the Dongargarh granite and equivalents, while the weak magnetic anomaly in the southeast of the Dongargarh granite and equivalents reflect granulite gneisses of the Eastern Ghat Mobile Belt. By applying the reduced-to-the-equator filter we enhanced the possible magnetic sources and structural lineaments within the Chhattisgarh basin. A new sketch map of structural elements was then compiled from aeromagnetic interpretation over the Chhattisgarh basin area. It includes possible faults, folds and an inferred lithological boundary.     

Horizontal-loop electromagnetic signature of a buried dike, Al Quweira area, southwest Jordan

During 1999, horizontal-loop electromagnetic (HLEM) measurements were made over a buried dike in the Al Quweira area, southwest Jordan, using the APEX MAX MIN III instrument, as part of a mineral exploration project. The objectives of the study were (i) to evaluate the resolution of the HLEM technique in field work in detecting and locating anomalies caused by vein-like bodies, and (ii) to assess the capability of HLEM surveys for detecting targets in other locations throughout our geophysical survey programme. In-phase and quadrature anomalies were recorded with 50 m and 100 m coil separations and multiple frequencies across the strike of the buried dike. Data recorded at 43 locations, spaced 10 m apart along the survey line, were interpreted quantitatively. For a 50 m separation, corresponding to shallow depths of investigation, the results do not show any recognizable response from the buried dike. The HLEM data were modelled using a three-layer structure in order to estimate the thickness of the weathering layer along the survey line. Conversely, data obtained with a 100 m separation, corresponding to moderate depths of investigation, reveal significant anomalies from the buried dike at high frequencies. A phasor or vector diagram was used to calculate the response parameter, depth and dip of the buried dike.     

Fault zone hydrogeology in arid environments: The origin of cold springs in the Wadi Araba Basin,Egypt

The role of faults in controlling groundwater flow in the Sahara and most of the hyper-arid deserts is poorly understood due to scarcity of hydrological data. The Wadi Araba Basin (WAB), in the Eastern Sahara, is highly affected by folds and faults associated with Senonian tectonics and Paleogene rifting. Using the WAB as a test site, satellite imagery, aeromagnetic maps, field observations, isotopic and geochemical data were examined to unravel the structural control on groundwater flow dynamics in the Sahara. Analysis of satellite imagery indicated that springs occur along structurally controlled scarps. Isotopic data suggested that cold springs in the WAB showed a striking similarity with the Sinai Nubian aquifer system (NAS) water and the thermal springs along the Gulf of Suez (e.g., δ¹⁸O = −8.01‰ to −5.24‰ and δD = −53.09‰ to −31.12‰) demonstrating similar recharge sources. The findings advocated that cold springs in the WAB represent a natural discharge from a previously undefined aquifer in the Eastern Desert of Egypt rather than infiltrated precipitation over the plateaus surrounding the WAB or through hydrologic windows from deep crystalline basement flow. A complex role of the geological structures was inferred including: (1) channelling of the groundwater flow along low-angle faults, (2) compartmentalization of the groundwater flow upslope from high-angle faults, and (3) reduction of the depth to the main aquifer in a breached anticline setting, which resulted in cold spring discharge temperatures (13–22°C). Our findings emphasize on the complex role of faults and folds in controlling groundwater flow, which should be taken into consideration in future examination of aquifer response to climate variability in the Sahara and similar deserts worldwide.     

Tectonics of Precambrian basement of the Tarim craton

The Altyn Tagh Mountain is the main area where the Precambrian basements of Tarim craton are exposed. There are two ophiolitic belts in Altyn Tagh: one belt is exposed in the northern margin of Altyn Tagh whose formation age is about (829±60) Ma, the other is situated along the southern margin of Altyn Tagh and has a formation age of about (1449±270) Ma. This paper proposes a simple tectonic model for the Precambrian basement of Tarim craton established from ophiolites in Altyn Tagh area. The south Tarim block had amalgamated with Qaidam block during about 1400-1500 Ma along the present Altyn fault, while the south Tarim-Qaidam united block was still separated from the north Tarim block by an ocean. The united block of south Tarim and Qaidam collided with north Tarim block along the zone of high positive anomaly of central Tarim, Hongliugou and Lapeiquan in about 800 Ma. So since the Sinian (beginning at 800 Ma) there has been an integrated basement for Tarim craton.     

Optical dating of sediments in Wadi Sabra (SW Jordan)

At Wadi Sabra (SW Jordan) human occupation dates back to the Palaeolithic and Epipalaeolithic. Although there is stratigraphic correlation based on archaeological finds of Ahmarian origin, numerical age estimates are lacking. We applied single-aliquot optical dating of coarse grained quartz of wadi deposits and investigated the luminescence properties in detail to achieve more accurate age information about the time of human occupation. Weak luminescence signals and scattered dose distributions characterise the multi-grain aliquots. The residual doses of the investigated modern wadi sediment are between 0 and 7 Gy. Moreover, comparison of equivalent dose (De) values of 1 mm and 8 mm aliquots shows higher equivalent doses for the large aliquots. Both experiments indicate that the luminescence signal is partially bleached prior to deposition. The dose distributions of all samples are broadly scattered and have overdispersion values between 25 and 43%, some samples are significantly skewed. The shape of the dose distributions points to other sources of scatter, in addition to partial bleaching. Comparison of 1 mm multi-grain and single-grain data demonstrates that the luminescence signal of one multi-grain aliquot most likely is from a single grain. For this reason, variation in the number of photon counts due to the weak luminescence intensity and variations in beta microdosimetry have a bigger impact on the spread of dose distributions. However, we cannot quantify the particular impact of partial bleaching, weak luminescence intensity and beta microdosimetry. To account for the spread of the dose distribution, we use the central age model to calculate equivalent doses. Age calculations yield results in the range of 30–48 ka.     

A 3D resistivity model derived from the transient electromagnetic data observed on the Araba fault,Jordan

72 inloop transient electromagnetic soundings were carried out on two 2 km long profiles perpendicular and two 1 km and two 500 m long profiles parallel to the strike direction of the Araba fault in Jordan which is the southern part of the Dead Sea transform fault indicating the boundary between the African and Arabian continental plates. The distance between the stations was on average 50 m.The late time apparent resistivities derived from the induced voltages show clear differences between the stations located at the eastern and at the western part of the Araba fault. The fault appears as a boundary between the resistive western (ca. 100 Ωm) and the conductive eastern part (ca. 10 Ωm) of the survey area. On profiles parallel to the strike late time apparent resistivities were almost constant as well in the time dependence as in lateral extension at different stations, indicating a 2D resistivity structure of the investigated area.After having been processed, the data were interpreted by conventional 1D Occam and Marquardt inversion. The study using 2D synthetic model data showed, however, that 1D inversions of stations close to the fault resulted in fictitious layers in the subsurface thus producing large interpretation errors. Therefore, the data were interpreted by a 2D forward resistivity modeling which was then extended to a 3D resistivity model. This 3D model explains satisfactorily the time dependences of the observed transients at nearly all stations.     

Assessment of hydrogeological conditions in basement aquifers of the Precambrian Oban massif, southeastern Nigeria

A combined analysis of lineament length density from radar imagery and surface resistivity data is used to assess the hydrogeological conditions in the Oban massif, Nigeria. The results show that the data guided the qualitative and quantitative estimation of some aquifer parameters. These include resistivity of the water bearing formations (280–740 ω m), thickness (5–140 m), limited hydraulic conductivity (8.53-13.18 m/day) and transmissivity (410.65–725.88 m²/day) data. In addition, the lineament length density for the area ranged between less than 0.2 to slightly more than 0.4. Site evaluation for the location of productive boreholes/wells using a groundwater potential index (GWPI) indicates that areas with a GWPI of greater than 35 are consistent with relatively high yield.     

Lead isotopic study of aplites from the Precambrian basement rocks near Ibadan,Southwestern Nigeria

Pb isotopic compositions for three total-rock samples of aplite and their constituent K-feldspars from the Nigerian basement assemblage near Ibadan show lead homogenization during the Pan-African thermo-tectonic event. A secondary isochron formed by the K-feldspars data points is used to calculate a primary age of about 2750 m.y. for the aplites. The aplites do not register any Pb isotopic effect from the intrusion of granite gneiss in the area at 2330 m.y.     

Groundwater potential of the Egbe-Mopa basement area,central Nigeria

Abstract

An investigation on the groundwater potentials of the Egbe-Mopa area in central Nigeria, underlain by the Basement Complex, is presented. The investigation involved mapping of the subsurface by use of vertical electrical soundings; measurement of depth to groundwater; and evaluation of hydraulic conductivity, transmissivity and yield by means of pumping test interpretation. The results indicate subsurface units that range from three to five resistivity layers; depth to groundwater of 0–10 m; overburden thickness of 3–16 m; hydraulic conductivity of 6.2?×?10^?6 to 3.4?×?10^?4 m/s; transmissivity of 4.3?×?10^?7 to 2?×?10^?3 m²/s; and groundwater yield of 0.2–2.5 L/s. The hydraulic head assessments revealed a general northward groundwater flow direction. The study identified three aquifer potential types, of high, medium and low productivity, respectively. Based on the longitudinal conductance of the overburden units, four distinct Aquifer Protective Capacity zones were delineated, namely, poor, weak, moderate and good.

Citation Okogbue, C.O. and Omonona, O.V., 2013. Groundwater potential of Egbe-Mopa basement area, central Nigeria. Hydrological Sciences Journal, 58 (4), 826–840.     

Age levels of Precambrian orogenic cycles of India

The paper reviews critically the present status of knowledge on the Precambrian orogenic cycles of India. The Precambrian age data obtained by Pb-U-Th, alpha-helium and Rb-Sr methods are presented cycle-wise, and the degree of dependability of each determination is indicated. The following cycles have so far been delineated — Dharwar (2300±100 M. Y.), Eastern Ghats (1625±75 M. Y.), Mahanadi (1350±200 M. Y.?), Satpura (955±40 M. Y.), Delhi (735±30 M. Y.) and Kishengarh (580±20 M. Y.) and it is shown that these cycles have equivalents in several parts of the world. These results are discussed in relation to the tectonics of India. A comprehensive programme of dating the Precambrian geological formations of India is suggested.     

U–Pb systematics in heterogeneous zircon populations from the Precambrian basement of the Maryland Piedmont

The aim of the study was — besides the dating of metamorphic events — to evaluate the effects of multi-stage crystal growth, episodic and continuous Pb loss, and U gain on the discordant age patterns found for zircon populations of the polymetamorphic Baltimore Gneiss, the Precambrian basement in the Maryland Piedmont. Eight gneiss and migmatite samples were collected at two localities in the Phoenix and Towson dome, respectively. Their zircon populations were separated into twenty-three fractions of different size and optical appearance. A low-contamination method (T.E. Krogh, 1973) was used for the U-Pb analyses.Microscopy and electron-microprobe studies revealed internal heterogeneities of the zircon crystals: at least half of the grains of each population reflect more than one stage of crystal growth, with the last stage consisting of U-poor overgrowths (U: below 400 ppm, mostly below 200 ppm). Evidence for episodic U gain and overgrown material other than zircon has not been found. On a concordia diagram the “ages” obtained by upward extrapolations (1080 and 1180 m.y.) and downward extrapolations (421 and 455 m.y.) of the best-fit lines to the data points are in fair agreement with the geochronologic data found by other investigators and the probable times of metamorphic periods of Precambrian (Grenville) and early Paleozoic (Taconic) orogenies.Models of Pb loss by continuous diffusion cannot adequately explain the discordant age patterns: these are essentially the result of superposition of episodic Pb loss and zircon overgrowth during the Taconic (and Acadian?) metamorphisms. The zircon overgrowth appears to be present in all fractions, but its influence on the U-Pb systematics is generally not perceptible because it is overridden by the effect of episodic Pb loss. For the fractions showing the most discordant ages, the contribution of Pb loss to the discordancy was found to be at least 85 %.From the microscopic picture and the isotopic data, it appears that the bulk of the zircon substance crystallized during one or several high-grade metamorphisms accompanied by migmatization and granitization of the rocks in the course of the Grenville orogeny. Under consideration of zircon ages of Baltimore Gneiss rocks of Pennsylvania, the results point to a complex Grenville metamorphic history in the Maryland and Pennsylvania Piedmont, that lasted from at least 1200 m.y. until about 980 m.y. The granulite-facies metamorphism in the West Chester Prong, Pennsylvania, may be 50–200 m.y. younger than the metamorphic events in the gneiss domes of the Baltimore area. Although it seems that real differences exist with respect to the Precambrian ages of major zircon-forming events between the Phoenix and the Towson dome, the apparent difference of about 100 m.y. should be interpreted with caution, because it is impossible, so far, to evaluate quantitatively the influence of possibly much older inherited zircon components.     

Sources of salinity in ground water from Jericho area, Jordan Valley

One of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turonian ages; and (3) the shallow aquifer system (Q) of Plio-Pleistocene ages. The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/Cl approximately 0.5 and Br/Cl approximately 7 x 10(-3). This composition is similar to that of thermal hypersaline spring that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep-seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio-Pleistocene Aquifer shows a wide range of Cl- (100-2000 mg/L), Na/Cl (0.4-1.0), Br/Cl (2-6 x 10(-3)), and SO4/Cl (0.01-0.4) ratios. These variations, together with the high SO4(2-), K+, and NO3- concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio-Pleistocene Aquifer, as suggested by the high SO4(2-) concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3- (80 mg/l) contents and low Br/Cl ratios (2 x 10(-3)). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes.     

首都圈地区远震基底PS波分裂研究

远震PS波的一个重要优势是其携带台站下方介质的各向异性信息.本文基于首都圈数字地震台网2002-2003年记录的高精度远震波形资料,从基底PS转换波入手,采用三分量PS波分裂偏振分析方法,获取各个台站下方来自基底的PS波分裂参数,包括快波偏振方向和快、慢波的时间延迟等,分析台站下方浅部地壳介质的各向异性特征.几个台站的研究结果显示,该方法保持了原始波场的信息,可以用来分析PS波分裂特征;短周期台站记录的远震来自基底的PS波具有干扰少、信噪比高的特点,存在分裂现象,各台站快慢波时差超出我们的预期值,平均在0.1~0.2 s左右.此研究可与横波分裂相对比,对于认识地壳各向异性及其内部的应力状态,分析其构造及地震活动现象有较大的意义.     

Further U-Pb dates on zircons from the early Precambrian rocks of the Godthaabsfjord area,West Greenland

U-Pb analyses of zircons from the Godthaabsfjord area in West Greenland yield dates of 2530 ± 30 m.y. for the Qo?rqut granite, 2820 ± 50 m.y. for the Nu?k gneiss, 2600–2900 m.y. for Malene-type supracrustal rocks, and >3800 m.y. for Isua supracrustal rocks. The zircon data are in accord with the stratigraphic sequence except for the Malene supracrustal zircons, which appear to have been variably affected by later metamorphism that did not reset the Nu?k or Amîtsoq zircons in the same area.     

Hydrogeology of Wadi Al-Yammaniyah, Saudi Arabia

Quaternary alluvium, ranging in thickness from a few to 100 meters underlain by Precambrian rocks of metamor-phic and igneous origin, constitutes an important source of ground water in Wadi Al-Yammaniyah, Saudi Arabia. The purpose of this report is to assess the hydraulic properties, quality of water, and estimated change in storage in waterbearing rocks in the area. The results of eight pumping tests carried out in hand-dug, large-diameter wells, indicate that the hydraulic conductivity of the alluvial aquifer ranges from 5.6 × 10⁻⁵ to 1.85 × 10⁻³ cm/second (3.36 × 10⁻⁵ to 1.11 × 10⁻³ m/minute) and that its storativity varies from 8.23 × 10⁻² to 1.17 × 10⁻¹. The aquifer is replenished by sporadic but intensive rainfall of short duration. The present withdrawal is only about 10 percent of the annual recharge which is estimated at 52 × 10⁶ m³. It is shown that there is a substantial potential for the future development of potable ground water which would be required for the development of the area.     

Discovery of Precambrian rocks in New Zealand: Age relations of the Greenland Group and Constant Gneiss,West Coast,South Island

Rb-Sr whole-rock analyses yield a Cambro-Ordovician (495 ± 11 m.y.) sedimentation age for the supposed Precambrian Greenland Group and a late Precambrian age, 680 ± 21 m.y., for parts of the Constant Gneiss, the first confirmation of Precambrian rocks in New Zealand. A Precambrian age for the Greenland Group is thus unlikely and the large area of Upper Cambrian-Lower Ordovician rocks now established can be considered as a lateral equivalent of the fossiliferous Lower Palaeozoic succession of northwest Nelson to the east. The Greenland Group, especially in the Paparoa Range has been affected subsequently by a thermal metamorphic overprint about 360 m.y. ago during the Tuhuan Orogeny. Although the Constant Gneiss must form the local basement to the Greenland Group in north Westland, the former does not appear to be the source of the sediments and the true provenance must lie elsewhere.     

Multivariate statistical analysis and environmental isotopes of Amman/Wadi Sir (B2/A7) groundwater,Yarmouk River Basin,Jordan

Multivariate statistical techniques, cluster and factor analyses were applied on the Amman/Wadi Sir groundwater chemistry, Yarmouk River basin, north Jordan. The main objective was to investigate the main processes affecting the groundwater chemical quality and its evolution. The k‐means cluster analysis yields three groups with distinct ionic concentrations. Cluster 1 comprises the vast majority of the sampled wells, and the water that belongs to this cluster can be classified as freshwater. Cluster 2 comprises only 2% of the sampled wells; it has the highest ionic concentration. The water of this cluster can be classified as brackish water. Cluster 3 involves 23% of the sampled wells, and it has total ionic concentration intermediate to that of clusters 1 and 2. Factor analysis yields a three‐factor model, which explains 76.77% of the groundwater quality variation. Factor 1 ‘salinity factor’ involves EC, Na⁺, Cl^‐, SO₄^‐2, K⁺ and Mg⁺² and reflects groundwater salinization because of overpumping. Factor 2 ‘hardness factor’ includes Ca⁺², HCO₃^‐ and the pH value and signifies soil–water/rock interaction. Factor 3 ‘nitrate factor’ involves only NO₃^‐ and points to groundwater contamination because of human activities, mainly untreated wastewater, and crops and animal cultivation in the unconfined portion of the aquifer. Factors 1 and 3 can be described as human‐induced factors, whereas factor 2 can be described as geogenic factor. Factors' scores were mapped to deduce the controlling processes on the groundwater chemistry. Stable isotope composition of ¹⁸O and ²H has revealed that the groundwater is a mixture of two water types. The radioactive isotopes tritium and ¹⁴ C were used to evaluate present day recharge to the aquifer and to estimate the groundwater age, respectively. Present day recharge to the groundwater is taking place in the unconfined portion of the aquifer as it is indicated by the measurable tritium content and low groundwater age. Copyright © 2012 John Wiley & Sons, Ltd.     

Paleomagnetism of the latest Precambrian/Cambrian Unicoi basalts from the Blue Ridge, northeast Tennessee and southwest Virginia: evidence for Taconic deformation

Three components of magnetization have been observed in ninety-six samples (twelve sites) of amygdaloidal basalts and “sedimentary greenstones” of the Unicoi Formation in the Blue Ridge Province of northeast Tennessee and southwest Virginia. These components could be isolated by alternating field as well as thermal demagnetization. One component, with a direction close to that of the present-day geomagnetic field is ascribed to recent viscous remanent magnetizations; another component, with intermediate blocking temperatures and coercivities, gives a mean direction of D = 132°, I = +43°,α₉₅ = 9° for N = 10 sites before correction for tilt of the strata. This direction and the corresponding pole position are close to Ordovician/Silurian data from the North American craton and we infer this magnetization to be due to a thermal(?) remagnetization during or after the Taconic orogeny. This magnetization is of post-folding origin, which indicates that the Blue Ridge in our area was structurally affected by the Taconic deformation. The third component, with the highest blocking temperatures and coercivities, appears to reside in hematite. Its mean direction, D = 276°, I = ?17°,α₉₅ = 13.8° for N = 6 sites (after tilt correction) corresponds to a pole close to Latest Precambrian and Cambrian poles for North America. The fold test is inconclusive for this magnetization at the 95% confidence level because of the near-coincidence of the strike and the declinations. We infer this direction to be due to early high-temperature oxidation of the basalts, and argue that its magnetization may have survived the later thermal events because of its intrinsic high blocking temperatures. A detailed examination of the paleomagnetic directions from this study reveals that the Blue Ridge in this area may have undergone a small counterclockwise rotation of about 15°.