bluuebunny/crossref_metadata_2025 huggingface dataset:
Models of post‐Miocene deformation of the Arabian Plate
Authors: Reches Ze'ev , Schubert Gerald
Published: February 2008

We investigate the deformation of the Arabian plate along a profile which extends from the Red Sea in the southwest to the Zagros in the northeast. The post‐Miocene tectonic pattern of this region includes continuing uplift, volcanism, and extensional faulting at the western margin adjacent to the Red Sea; subsidence, folding, and thrusting at the eastern margin near the Zagros; and lack of major active tectonism in the interior. Thus, the near‐surface state of horizontal deviatoric stress changes from extensional to compressional over a broad region of small tectonic stress. We derive models that can explain the observed distributions of stress and vertical displacement. The stress distribution within the plate is derived from the static equilibrium of the lithostatic load, deviatoric tectonic stresses, and shear stresses along the base of the lithosphere. The vertical motions are derived from nonuniform vertical deviatoric stresses at the base of the lithosphere. The models indicate that the post‐Miocene deformation occurs by the combined effects of lateral density variations within the mantle part of the plate, ridge push at the Red Sea, and convective shear stress at the plate base. Density variations of 3.5% or less within the mantle part of the lithosphere induce a large portion of the tectonic stresses required for the observed deformation pattern in Arabia. The mean horizontal tensile tectonic stress in the lithosphere at the Red Sea cannot exceed 12.5 MPa for reasonable water depth in the Red Sea. The basal shear stress under Arabia must be directed toward the Zagros, and it ranges from 1 to 2 MPa. By modeling Arabia as a uniform viscous plate undergoing large‐scale bending, we find that the tectonic stresses generated by the lithospheric density variations and basal shear stress are sufficient to upwarp the Red Sea margins and downwarp the Zagros zone. A lithosphere viscosity of 5 × 1024 Pa s gives uplift of the Red Sea region at a rate of about 0.1 mm/yr.
Argon 39‐argon 40 dating of metamorphic and plutonic events in the north and high Himalaya belts (southern Tibet‐China)
Authors: Maluski Henri , Matte Philippe , Brunel Maurice , Xiao Xusheng
Published: February 2008

New 39Ar−40Ar radiometric data are presented. They concern the metasedimentary series and the orthogneiss pluton of Kangmar. Ages as young as 13 Ma are found which may be related either to the metamorphism or to the resetting of the minerals during the emplacement of the numerous intrusive bodies into the North Himalaya Belt. Inherited excess argon is found in micas from the orthogneiss previously dated at 562 Ma. These bodies are constituted by leucogranitic magmas, the biotites and the muscovites of which the granites intrude (Lhagoi Kangri Massif). Same range of ages is found in the High Himalaya Belt for micas from leucogranites. Ages as young as 4 Ma are found on micas from the southern part of the cross section between Nyalam and Zham. The recent uplifts and/or the movement of recent normal faults may be related to these young ages.
Structural evolution of Djebel Debadib Anticline: A clue to the regional tectonic style of the Tunisian Atlas
Authors: Snoke Arthur W. , Schamel Steven , Karasek Richard M.
Published: February 2008

Djebel Debadib is a northeast trending anticline in the Tunisian Atlas, near El Kef, Tunisia. The core of the anticline consists of a deformed Triassic, gypsum‐matrix breccia containing clasts of supratidal dolomite, terrigeneous clastic rocks, and ophites (metabasites). Locally, low‐grade metasedimentary rocks, occurring as clasts in the evaporite, may represent fragments of basement rock plucked from salt subcrop during deep‐seated flowage. The multiply deformed Triassic rocks are juxtaposed against Cretaceous or younger rocks, and Jurassic and Neocomian strata are not present in outcrop. These characteristics have been cited in many studies to suggest a history of diapirism to explain both the internal structure of the Triassic rocks and the contact relations with the younger rocks. A previously unreported unconformity, developed on the Triassic rocks and overlain by Aptian‐Albian strata, indicates that an important period of piercement occurred during the Early Cretaceous for the Djebel Debadib diapir. From the mid‐Cretaceous to the late Eocene the continental margin of northern Tunisia was a regional basin in which a thick sequence of carbonate rocks was deposited. Beginning in late Oligocene time, sandy clastic sediments accumulated on the older carbonate rocks above a regional unconformity, and during the middle Miocene Atlas orogeny, numerous northeast‐southwest folds deformed the rocks of the Tunisian trough including the diapiric Triassic masses. These folds, commonly boxlike in geometry, were extensively faulted during the late Miocene and Pliocene. A four phase tectonic model is recognized for the Tunisian Atlas: (1) early Mesozoic rifting of the North African continental margin, (2) diapiric emplacement of the Late Triassic‐Liassic(?) evaporites into overlying strata beginning in the early Cretaceous, (3) folding of the cover strata in response to regional compression culminating in the middle Miocene Atlas orogeny, (4) the development of transvers grabens during late orogenic normal faulting (latest Miocene to Recent). A major regional décollement is not considered necessary to account for the shortening of the sedimentary cover during the middle Miocene deformation. Rather, the principal driving mechanism of regional crustal shortening was the reactivation of early Mesozoic normal faults as reverse faults that displaced basement rocks. This model implies that the small amount of shortening recorded in the Tunisian Atlas involved active shortening and structural thickening of basement and the concurrent deformation of the sedimentary cover.
Seismogenic strike‐slip faulting and the development of the North China Basin
Authors: Chen Wang‐Ping , Nábelek John
Published: February 2008

The actively subsiding North China sedimentary basin is associated with an unusually high level of seismic activity. This oil‐ and gas‐producing basin has been the site of nine large (M ≥ 7), destructive earthquakes since 1600 A. D. An analysis of faulting during the Tangshan earthquake sequence, which includes some of the largest shocks that have occurred in this basin during the past 400 years, showed that the dominant pattern of deformation during this sequence was associated with displacement on right‐stepping, right‐lateral strike‐slip faults. A large amount of subsidence (∼1.0–1.5 m) occurred in pull‐apart regions between steps of the north‐northeast (NNE) trending strike‐slip faults. The directivity of the P wave radiation pattern and the distribution of aftershocks of the Bohai Gulf earthquake of July 18, 1969, also indicate strike‐slip faulting on planes of similar NNE trend. Together with the four largest shocks of the Hsingtai sequence in 1966, earthquakes with right‐lateral slip on NNE trending faults account for about two‐thirds of the seismic moment released in this region for the past 100 years. The average regional strain due to seismic slip has a dominant component of dextral simple shear (on NNE striking planes) that is approximately twice as large as north‐south extension or east‐west shortening. Based on a combination of published field and borehole data, the dominance of horizontal dextral simple shear over subsidence seems to have begun no later than the mid‐Pliocene and the total amount of extension over the entire basin is only about 20–30%. This pattern of deformation, the spatially variable heat flow values, the scattered locations of rapid deposition of Quaternary sediments, and the fluctuating rate of sedimentation in space and time during the Neogene in this basin are difficult to explain by pure extension and thermal subsidence. We propose that these observations, and the shape of the whole North China basin (that of a “lazy Z”), are a consequence of pulling‐apart associated with right‐lateral movement on the NNE trending strike‐slip fault systems and that the basin as a whole has formed and evolved as a composite pull‐apart basin due to right‐lateral slip on numerous right‐stepping faults since the Eocene.
Tatla Lake Metamorphic Complex: An Eocene Metamorphic Core Complex on the southwestern edge of the Intermontane Belt of British Columbia
Authors: Friedman R. M. , Armstrong Richard Lee
Published: February 2008

The Tatla Lake Metamorphic Complex (TLMC), which lies on the southwest side of the Intermontane Belt (IMB) in British Columbia, has characteristics typical of a metamorphic core complex: anticlinorial amphibolite‐grade gneissic and migmatitic core underlying a 1− to 2.5+‐km‐thick zone of mylonite and ductilely sheared metamorphic rocks which is in fault contact beneath an upper plate of low‐metamorphic‐grade cover rocks of the 1MB. Ductile shearing in the TLMC involved tonalitic to granodioritic orthogneiss and structurally overlying amphibolite‐grade metasedimentary rocks and greenschist‐grade chlorite‐actinolite‐albite schist. Structures observed throughout the ductilely sheared rocks include a gently dipping mylonitic foliation (Ss), containing a mineral lineation (Ls) which trends toward 280° (100°) ± 20°. Minor folds of variable trend (Fs), almost exclusively confined to metasedimentary rocks, are interpreted as synductile shear. Vergence of these folds defines a movement sense and direction of top toward 290° ± 20°. Kinematic indicators from rocks not deformed by synductile shear folds indicate a tops‐to‐the‐west sense of shear, while those within metasedimentary rocks (deformed by Fs folds) yield conflicting results, with a tops‐to‐the‐west sense predominating. Calculated a directions from Fs folds which deform Ls lineations indicate nearly horizontal Ds movement, subparallel to 290°–110°. The entire metamorphic core of the TLMC has been deformed by upright, west to west‐northwest trending, shallowly plunging map‐scale folds (F3). The steeply dipping, northwest trending Yalakom fault cuts all units and forms the southwestern margin of the TLMC. U‐Pb zircon geochronology has documented the existence of Cretaceous (107–79 Ma, in the core) and Eocene 55–47 Ma, (in the mylonitic zone) deformation and metamorphism in the TLMC. K‐Ar dates for biotite and hornblende of 53.4–45.6 Ma record the uplift and cooling of the TLMC. During early and middle Eocene time (55–47 Ma) metamorphic rocks of the TLMC were carried to higher crustal levels along the footwall of the TLMC normal ductile shear zone. Final uplift and development of F3 folds (post‐47 Ma) are possibly related to dextral motion along the Yalakom fault The TLMC has structural style and timing of deformation similar to other metamorphic core complexes in southeastern British Columbia. Local and regional evidence is consistent with the formation of the TLMC in a regional extensional setting within a vigorous magmatic arc. Similar interlayered gneisses with near‐horizontal layering and foliation may underlie the entire southern IMB.
Sandstone dykes as evidence of localized transtension in a Transpressive Regime, Bir Zreir Area, eastern Sinai
Authors: Eyal Yehuda
Published: February 2008

The Bir Zreir area, NE Sinai, is part of the 40‐km‐wide eastern Sinai shear zone stretching along the western margin of the Gulf of Elat. Sinistral movement along faults comprising this shear zone is consistent with the regional NNW‐SSE compression in which the Dead Sea transform fault was formed. In the Bir Zreir area, sandstone dykes within NE striking fault breccias were developed within the Precambrian crystalline basement. These breccias, up to 200 m in width, resulted from transpression along the NE striking faults in response to sinistral movement along the NNE striking major faults. Paradoxically, the sandstone dykes developed by infilling of transtensional open fissures which share the NE trend of the breccia zones. The source rock for the dykes is Nubian Sandstone unconformably overlying the basement. The depth beneath the unconformity to which the sandstone collapsed is 500–600 m. Local NW‐SE transtension along parts of the NE striking faults enabled the formation of fissures and their infilling by sand and sandstone blocks of various sizes as dykes. The infilling occurred despite the regional NNW‐SSE compression which prevailed in the study area. A kinematic model is developed which combines sinistral movement and clockwise rotation of rigid blocks between the faults with resultant local NW‐SE transtension along the northern segment of the NE trending strike‐slip faults.
Subduction and accretion of the permanente terrane near San Francisco, California
Authors: Larue D. K. , Barnes I. , Sedlock R. L.
Published: February 2008

Previous studies of the Calera limestone (Permanente terrane, Franciscan complex) of California have shown that deposition occurred at approximately 25°N paleolatitude atop an oceanic plateau or rise, and that it was subsequently transported northeast and accreted to the North American continental margin in the early Tertiary. The Permanente terrane in the study area along the Pacific coast south of San Francisco contains a suite of rock types present in north dipping imbricate thrust slices possibly related to the subduction and accretion of an oceanic crustal sequence. Geochemical studies of greenstones, thought to represent fragments of the dismembered oceanic crust, indicate affinities with mid‐ocean ridge basalts and within‐plate basalt. These greenstones may represent fragments of the rise upon which the Calera limestone was deposited. Metamorphic minerals in the greenstones indicate both sea‐floor metamorphism and locally, high‐pressure, low‐temperature metamorphism. It is concluded tentatively that the entire Permanente terrane in the study area underwent high‐pressure, low‐temperature metamorphism but that temporal or geologic conditions prevented widespread recrystallization or development of blueschist facies minerals. Structures in the deformed rocks can be related to underthrusting beneath the continental margin and attachment to the overriding plate. Studies of veins indicate several stages of dewatering. It is likely that dewatering was a major process in the attachment event, as shown by veins associated with this phase of deformation. Structurally interleaved mélanges and broken formation contain sedimentary rock clearly derived from a continental margin; these rocks probably represent trench and trench slope facies that were underthrust with the accreting oceanic crustal sequence.
Multiple opening and closing of the Eastern Mediterranean and South China Basins
Authors: Ben‐Avraham Zvi
Published: February 2008

The eastern Mediterranean (east of Crete) and the South China Basin are small ocean basins surrounded by continental masses and are currently undergoing closure. They were both formed by the rifting of continental fragments away from large continents. A comparison of the geological evolution of the two basins indicates a remarkable similarity in the sequence of evolutionary stages that took place in both basins, although the age of these stages is probably different for each of the two. The formation of the two basins is a consequence of a much larger process in which large lithospheric plates south and north of the basins move toward each other: Africa, including Sinai and Arabia, toward Eurasia and India‐Australia toward Eurasia and the Pacific. Each basin went through several stages of evolution during which oceanic crust was created and destroyed. During each stage the area of the newly formed oceanic crust was smaller than the area formed in the previous stage. It appears as if similar evolutionary patterns also occurred in other marginal and small ocean basins formed by continental rifting.
Orthorhombic fault patterns: The odd axis model and slip vector orientations
Authors: Krantz Robert W.
Published: February 2008

Conjugate fault theory cannot explain all observed patterns of faults and slip vectors. New fault models suggest that orthorhombic fault patterns represent the general, three‐dimensional strain case and relegate conjugate faulting to the special case of plane strain. The odd‐axis model relates orthorhombic fault geometry to principal strain orientations and ratios. The model also predicts the orientations of slip vectors for orthorhombic faults, expressed as the rake of the slip vector on the fault plane. Assuming that one principal strain is vertical, the model predicts steeply or shallowly raking slip for faults developed under strain fields with relatively small magnitudes ofintermediate strain. Oblique‐raking slip is possible only where the relative magnitude of the intermediate strain is large. The odd‐axis model has been tested on five sets of data from Utah, Nevada, Israel and Crete. Predicted slip vector orientations lie close to the observed slip in all cases. The model also suggests that where orthorhombic faults are reactivated in a three‐dimensional strain field, slip vectors may match those of the prior episode of faulting or be distinctly different in orientation, producing faults with bimodal slip patterns, as seen in parts of the Basin and Range province. This last observation suggests that three‐dimensional strains may have played a significant role in Basin and Range development.
Paleomagnetism and question of original location of the Permian Brook Street Terrane, New Zealand
Authors: Haston Roger B. , Luyendyk Bruce P. , Landis C. A. , Coombs D. S.
Published: February 2008

Over 400 rock samples from 30 sites were collected for paleomagnetic study from the volcanogenic section in the Brook Street terrane within the Takitimu Mountains in western Southland, New Zealand. The section includes igneous and sedimentary rocks of the Permian Takitimu Group and White Hill Intrusive Suite. Many of the samples show a partial or complete remagnetization in the present field because of a recent acquisition of viscous remanent magnetization. An Early Permian direction (inclination = 46.1°, declination = 257°), isolated from the Heartbreak and Chimney Peaks formations of the Takitimu Group, indicates a low paleolatitude to midpaleolatitude, position (27° ± 5°) for the Brook Street terrane. Directions from the Late Permian (?) White Hill Intrusives (inclination = 64.6°, declination = 173.3°) suggest a slightly higher paleolatitude than the Early Permian Takitimu Group directions and 70°–90° of intervening clockwise rotation. Plate reconstructions and paleomagnetic data predict a high paleolatitude for the New Zealand margin of Gondwana throughout the late Paleozoic and Mesozoic. The low paleolatitude to middle paleolatitude, implied by the Early Permian Brook Street result, together with the oceanic nature of the Brook Street arc, suggest that the Brook Street terrane is allochthonous to the margin of Gondwana. A published Late Triassic/Early Jurassic paleomagnetic pole from the adjacent Murihiku terrane indicates a high paleolatitude. This suggests that the Brook Street and Murihiku terranes are genetically distinct.
Paleomagnetic data from Sarawak, Malaysian Borneo, and the Late Mesozoic and Cenozoic tectonics of Sundaland
Authors: Schmidtke Eric A. , Fuller Michael D. , Haston Roger B.
Published: February 2008

Paleomagnetic data from 231 samples from 31 sites in rocks of Upper Jurassic to Miocene age in Sarawak (Malaysian Borneo) reveal a trend of increasing counterclockwise (CCW) declination deflection with age. Six sites in Tertiary hypabyssal intrusions show 8° to 52° of CCW deflection. The intrusion deflected 52° CCW was K‐Ar dated at 26 m.y. (Upper Oligocene), while one deflected 22° CCW gives a 17 m. y. age (Lower Miocene). Three sites in the Upper Eocene to Miocene(?) Silantek Formation show an average 40° of CCW deflection. Prefolding directions, showing 90° of CCW deflection, are isolated in 4 sites (including two positive fold tests) in Upper Jurassic and Cretaceous rocks of the Bau Limestone and Pedawan Formations. A postfolding, Cenozoic remagnetization with an average of 60° of CCW deflection is found in five Bau Limestone sites. Three sites in the Upper Jurassic Kedadom Formation show an average of 50° of CCW deflection. CCW declination deflections found in Mesozoic and Cenozoic rocks as far as 400 km east and 150 km south of Sarawak, in Kalimantan (Indonesian Borneo), also fit the trend of deflection versus age. On the basis of the regional consistency of declination deflection versus age, along with geologic evidence the data are considered to be evidence of a regional (rather than a local block or distributed shear) rotation. The domain of CCW rotation extends into West Malaysia, suggesting that West Borneo and the Malay Peninsula may have been a stable block during the latest Cretaceous and Cenozoic. West Malaysia and Borneo may have had different histories in the rest of the Mesozoic. The data imply up to 108° CCW rotation of Borneo with respect to stable Eurasia, sometime during the Cretaceous and Cenozoic. Cenozoic rotation may also have occurred between Indochina and Borneo. The sense of rotation shown by the data does not support the “propagating extrusion tectonics” model for Cenozoic Southeast Asia.
Paleoseismicity of the Cascadia Subduction Zone: Evidence from turbidites off the Oregon‐Washington Margin
Authors: Adams John
Published: February 2008

Cores from Cascadia deep‐sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the Mount Mazama eruption (6845±50 radiocarbon yrBP). Turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel, there being only 13 turbidite deposits in the lower main channel since the Mazama eruption, instead of the twice as many expected if the tributaries had behaved independently. In addition to the Cascadia Channel, 13 post‐Mazama turbidites have been deposited in the Astoria Canyon and at two sites off Cape Blanco, sample locations that span 580 km of the Oregon‐Washington margin. Pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly, every 590±170 years on average. The best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the Cascadia subduction zone. The variability of turbidite timing is similar to that for great earthquake cycles. The thickness of the topmost pelagic layer suggests the last event was 300±60 years ago (from three places along the margin), but this number may be a biased underestimate. It is, however, consistent with the youngest sudden‐subsidence event on the Washington coast. The turbidite data demonstrate that the near‐term hazard of a great earthquake on the Cascadia subduction zone is of the order of 2–10% in the next 50 years.
Effects of density contrasts on the orientation of stresses in the lithosphere: Relation to principal stress directions in the Transverse Ranges, California
Authors: Sonder Leslie J.
Published: February 2008

The influence of stresses arising from horizontal density contrasts on the orientation and relative magnitudes of principal stresses in an otherwise uniform lithospheric stress field is investigated. A simple model is constructed, in which a local deviatoric stress due to a density anomaly, embedded within or just below the lithosphere, and a regionally constant deviatoric stress field are each approximated by biaxial tensors. The net stress field is obtained from the sum of the two. Both the relative magnitudes of principal stresses and the magnitude of the angular difference in principal stress direction of the summed tensor compared with that obtained in the absence of buoyancy forces depend on two parameters. The first is the ratio τ/τ′, where τ is a measure of the magnitude of the regional deviatoric stress and τ′ is the magnitude of the stress arising from buoyancy forces associated with the density anomaly. The second parameter is the angle between the trend of the density anomaly and the direction of maximum compressional stress that obtains in the absence of any perturbation by the local buoyancy forces. The directions of the principal axes of the total stress field are found to differ by up to 90° from those of the reference stress field. The model is applied to the Transverse Ranges, California, where the observed 23° difference in orientation of principal horizontal compressive stress compared with the principal compressive stress direction in central California constrains the predicted value of τ/τ′ to be approximately −0.4. This is consistent with an independently calculated range of τ/τ′ in which τ′ is inferred from seismological constraints on the magnitude of density variations underneath the Transverse Ranges and τ is inferred from observations of heat flow along the San Andreas fault in central California. The agreement between the two estimates of τ/τ′ supports the hypothesis that the observed differences in horizontal principal stress orientation in California can be explained by the combined influence of a local negative buoyancy force under the Transverse Ranges and a regional stress field associated with transcurrent deformation within the Pacific‐North American plate boundary zone. The observed counterclockwise angular difference in principal horizontal stress direction in the Transverse Ranges compared with central California implies that the plane of maximum right lateral shear stress is also rotated counterclockwise relative to that in central California. This supports the possibility that the “big bend” in the San Andreas fault may be a consequence of the negative buoyancy forces acting in the Transverse Ranges, and not the cause of Transverse Ranges formation, as has often been assumed.
Late Quaternary deformation of marine terraces on the Cascadia Subduction Zone near Cape Blanco, Oregon
Authors: Kelsey Harvey M.
Published: February 2008

The Cape Blanco region of south coastal Oregon sits on the upper plate of the Cascadia subduction zone about 60–70 km east of the base of the continental slope. Though the region has no historic coseismic deformation, late Quaternary deposits and landforms show abundant evidence of uplift, folding, and faulting. A set of five late Quaternary marine terraces and one uplifted Holocene beach berm are preserved in the Cape Blanco region. Stratigraphic and altitudinal surveys of these physiographic features, combined with several numerical and correlation age determinations, permit a reconstruction of tectonic deformation near Cape Blanco in approximately the last 200,000 years. The most cogent aspects of the neotectonics in this part of the Cascadia subduction zone are that an east‐west trending anticline deforms the lower three terraces (80–125 ka) as well as accounting for uplift of the Holocene storm berm. Latest movement on the anticline was no more than 2,000 years ago, but the anticline also deforms sediments as old as Middle Miocene. The anticline is consistent with a north‐south principal contraction axis at Cape Blanco in about the last 100,000 years. An older terrace at Cape Blanco (approximately 200 ka) is offset by two reactivated faults whose movements prior to the Eocene served to suture several terranes to the North American continent. Tectonic tilting in the older terrace is not consistent with a north‐south principle axis of contraction, but the axis of tilt is parallel to north‐northwest striking structures developed in the Quaternary fold belt offshore on the continental shelf. The observed deformation indicates that regional stress in the vicinity of Cape Blanco in the late Quaternary has been accommodated by a variable pattern of strain.
Arguments for the pre‐rift uplift and rift propagation in the Ligurian‐Provencal Basin (northwestern Mediterranean) In the light of Pyrenean Provencal Orogeny
Authors: Guieu Gérard , Roussel Jacques
Published: February 2008

The Cenozoic Provencal orogeny and the subsequent opening of the Ligurian‐Provencal basin were caused by a geodynamic mechanism that originated in the Cretaceous. It is evident from the arguments presented that (1) regional doming preceded rifting of the continental margin and this uplift widened and/or migrated during the ensuing opening of the Ligurian‐Provencal basin; (2) clastic sedimentation on the Provencal platform was initiated during the early Cenomanian; (3) deformation in the Provencal block, which varies from Late Cretaceous to Miocene, reflects a migration of the north‐south compression from west to east accross the block; (4) the Languedoc‐Provencal fold belt was initiated during the Eocene as a result of tectonic uplift and sinistral displacement of the Paleozoic basement toward the north. Significant geologic features of the region associated with these events include (1) similarities in shape of the Languedoc virgation and the Provencal thrust front with the shape of geophysical features over the Golfe du Lion; (2) the unusual width of the young, stretched continental margin in the Golfe du Lion; (3) the distinctive V‐shaped form of the Ligurian oceanic crust; and (4) the concordance in age of the earliest post‐rift deposits, which increasingly young toward the east, and magnetic anomalies that parallel the basin axis. These events and structures are attributed to the uplift of a Paleozoic block situated to the south in the Golfe du Lion and previously buried under the Mesozoic cover. The development of this crustal uplift since upper Aptian, and its northeastwards migration and/or gradual widening account for both sedimentary events and tectonic deformation that occurred on the Provencal platform until upper Eocene, and the later stage of rifting and formation of the Provencal margin. In the Ligurian‐Provencal basin, the synthesis of marine data as well as relevant terrestrial data indicates that rifting propagated towards the Gulf of Genoa, while the Corsica‐Sardinia block rotated to the southeast.
Formation of interior basins associated with curved faults in Alaska
Authors: Schultz Richard A. , Aydin Atilla
Published: February 2008

The positions of certain nonmarine sedimentary basins in central and southern Alaska are spatially related to the geometry of adjacent curved faults. These interior basins occur along the northern, convex side of these fault systems which change trend from northwest in Canada and eastern Alaska to east‐west in central Alaska and to northeast in western Alaska. The basins probably initiated in early to middle Tertiary time and deposition within all basins continued through the Quaternary, broadly synchronous with Tertiary strike‐slip displacements along the Tintina, Denali, and Border Ranges fault systems. We examine the spatial and temporal relationship between basins and faults by using a mechanical model of curved strike‐slip faults based on boundary elements. We relate slip along the curved faults to Tertiary Pacific‐North American plate motions by using principal stress directions inferred from the plate motion directions. Locations of the predicted mean stress reductions around the fault bends caused by fault slip correlate well with positions of the interior basins. Our results suggest that basin subsidence and location were controlled primarily by the geometry of adjacent curved fault systems and the state of stress in Alaska during the Tertiary. Mechanical interaction between curved Alaskan fault systems increases the tendency for basin subsidence. Stresses inferred from early Tertiary plate motion vectors are not oriented correctly to drive right lateral slip along Kaltag, Farewell, and parallel faults in western Alaska. Furthermore, these stress states would have produced left lateral displacements, for which there is no evidence, along these western faults in their present orientations. We find that a combination of slightly rotated fault geometry and low friction along the faults appears to facilitate right lateral slip along the faults in western Alaska. Our results show that deformation well inside the continent can be explained in terms of the Pacific‐North American plate motions. Thus Tertiary plate motions have resulted in a broad zone of fault slip, uplift, and subsidence in the nonrigid North American plate, producing several large basins.
The Coast and Geodetic Survey magnetometer
Authors: Bauer L. A.
Published: February 2008

The source of error complained of by Dr. Morize has been eliminated in the present form of magnetometer used by the Coast and Geodetic Survey.

The above cut will show how this has been done, viz., the glass window in the front end of the box has been removed entirely, and there is used instead a cloth hood, fastened to the box and fitting snugly by means of a ring over the observing telescope. The window in the back end of the box can be turned aside, on a pin, when observing on the mark. It may also be pointed out that the azimuth mirror, which constitutes the weak part of the Kew magnetometer, is replaced in this form of instrument by a special theodolite attachment (as shown on the right of the cut) fitting on the same base as the magnetometer, the alt‐azimuth method for determining the meridian being used. By this method the observer is independent of the longitude of the place, and the need of great accuracy in the times of observation.
The magnetic observatories of the United States Coast and Geodetic Survey
Authors: Tittmann O. H.
Published: February 2008

LOCATION.

In connection with the magnetic survey of the United States and countries under its jurisdiction, the Coast and Geodetic Survey is operating magnetic observatories at the following places:Name Place Latitude Longitude Altitude North W. of Gr. meters ° ′ ° ′Cheltenham Cheltenham, Maryland 38 44.0 76 50.5 72Baldwin Baldwin, Kansas 38 47.0 95 10.0 335Sitka Sitka, Alaska 57 02.9 135 20.2 15Honolulu Ewa, Oahu Island 21 19.2 158 03.8 15Porto Rico2 Vieques, Porto Rico 18 08.9 65 26.4 40
Magnetic chart errors and secular changes in the Indian Ocean
Authors: Bauer L. A. , Peters W. J.
Published: February 2008

In view of the exceptionally large errors in the most recent charts which are being disclosed in the Indian Ocean on the present cruise of the Carnegie, it was thought desirable to make early communication. Tables I and II give the values of the magnetic declination (“variation of the compass”) with the geographic positions, as determined on the Carnegie from Cape Town to Colombo, Ceylon, thence to Mauritius, April to August, 1911; a future communication will give the results from Mauritius northward to the Arabian Sear thence to Colombo and Batavia. While the present figures are not final, they are not likely to be changed by more than one‐tenth degree.

The tables also give the corresponding values as scaled from the British Admiralty chart of 1907 (B); the German chart of 1910 (G); and the United States Hydrographic Office chart of 1910 (U); these chart values have been referred approximately to the time of our observations by applying the secular changes as indicated on the respective charts. The final three columns give the differences between the Carnegie values (C) and those of the various charts; the plus sign (+) means that the charts give west declinations too large, the minus sign (−) on the other hand signifying that the chart values are too low by the tabular amount.
Peculiar magnetic disturbances of December 28–31, 1908
Authors: Faris R. L.
Published: February 2008

The following tabulation contains the data of the magnetic disturbances of December 28–31, 1908, as recorded by the Edelmann magnetographs at the Pilar magnetic observatory in Argentina. This data was not available at the time of the publication1 of the first collection of data of these peculiar disturbances, and hence was not included in that collection. However, this data is of special interest and value, coming as it does, from one of the few magnetic observatories in south magnetic latitude.
On the magnetic field of the Earth
Authors: Steiner L.
Published: February 2008

Dr. L. A. Bauer, in his very suggestive paper, “The external electric currents and the Earth's magnetization,”1 has come to the following “working hypothesis:” The Earth is chiefly an electromagnet, the magnetizing currents being outside and consisting of negative electric currents circulating overhead in the same general direction as that of the Earth's rotation, namely, from west to east. In the June issue of this Journal2 he continues the same topic and here3 he quotes Professor August Schmidt's views concerning the same object.

As the supposition of the Earth's being an electromagnet and being magnetized by an outside primary magnetic field, if verified, would be of greatest importance in the explanation of magnetic phenomena and would—in connection with what we know about other kindred phenomena: diurnal variation, disturbances—produce a revolution in our views, the foundation of it must be carefully and thoroughly studied. I beg to make some remarks regarding that hypothesis. The importance of the question and my endeavor to avoid misunderstandings, may excuse if I treat the problem somewhat in length and often refer to things generally known.
On the results of some magnetic observations during the solar eclipse of August 21, 1914
Authors: Bauer L. A. , Fisk H. W.
Published: February 2008

No definite information having been received by the Department of Terrestrial Magnetism up to June, 1914, that an organized effort would be made to secure magnetic, electric, and allied observations during the solar eclipse of August 21, 1914, the belt of totality of which (Figs. 1 and 2) was favorably located for European observatories, it was decided to stimulate interest in the important event. Accordingly, the circular letter of June 23, 1914, on page 58, was sent to a number of persons and institutions and published in Nature (July 16, 1914, p. 507) and in Science (July 24, 1914, p. 140). Later it was ascertained that others, notably Dr. V. Carlheim‐Gyllensköld1 had succeeded in likewise inaugurating desired observational work. It thus happened that at some of the contributing observatories observations were made both in accordance with his program and with ours.
Corpuscular theory of the aurora borealis
Authors: Störmer Carl
Published: February 2008

It appears that the German physicist, Goldstein,1 was the first to publish the idea that the Sun sends out into space electrical rays analogous to cathode rays, and that we may thus explain the mysterious connection between variations in solar activity and corresponding fluctuations in the magnetic and electric phenomena, on the Earth. Some years later the Danish meteorologist, Adam Paulsen, from his auroral observations in Greenland was led to the hypothesis2 that the aurora is due to cathode rays; but instead of assuming that the rays came from the Sun, he believed that they originated in the upper strata of the atmosphere.

Next, in the year 1896 Kr. Birkeland made his remarkable experiments with cathode rays in a magnetic field. He first found that a magnetic pole had an effect on a beam of parallel cathode rays analogous to that of a lens upon a beam of light, viz., to make the rays converge towards a point. This phenomenon led him to the idea3 that the aurora borealîs was due to a similar effect of the Earth's magnetic field on cathode rays coming from the Sun. In order to test his hypothesis, Birkeland exposed a small spherical electromagnet to a stream of cathode rays, and found a series of facts showing analogies to the shape and nature of the aurora. The aurora‐belts in particular were very beautifully produced. These remarkable experiments, which gave the first really good support to the corpuscular theory of aurora, were described on pages 39–42 of the paper “Expédition Norvégienne, 1899–1900, pour l'étude des aurores boréales.4 Notwithstanding that these remarkable experiments tend to show that the aurora is a direct effect of the precipitation of cathode rays in the upper air, Birkeland regarded the aurora as being caused rather by secondary cathode rays produced by strong electric currents in the upper atmosphere;5 in his later publication, however, he arrived at the conviction that the aurora is a direct effect of the electric rays from without.6
Preliminary results of ocean magnetic observations on the Carnegie from Lyttelton to Tahiti, Fanning Island, San Francisco, and Honolulu, November, 1920, to April, 1921
Authors: Ault J. P.
Published: February 2008

NOTES ON TRIP FROM LYTTELTON TO PAPEETE, TAHITI.

Some delay was occasioned by the tardy arrival of the stores ordered from San Francisco, but all business was finally transacted by November 19, and preparations for departure were completed. Leaving Lyttelton under tow at 1h 15m p.m., the tug was released by 3h p.m., and we proceeded with engine running until we had cleared Banks Peninsula, when all sails were set. For three days the wind blew from the north, then shifted to the west and remained westerly for four days. The 180th meridian of longitude was crossed on November 22, and the date November 22 was repeated.
Principal magnetic storms recorded at the Huancayo Magnetic Observatory, Peru, from April to June, 1924
Authors: Parkinson W. C.
Published: February 2008

(Latitude, 12° 02.′7 S.; Longitude, 75° 20.′4 W. or 5h01m W. of Greenwich.)

There were three principal magnetic storms recorded at the Huancayo Magnetic Observatory during the second quarter of the year 1924. The chief features are indicated in the following tabulation and descriptive notes:
Records of earthquakes and of principal magnetic storms at the Watheroo Magnetic Observatory, western Australia, from January to March 1924
Authors: Wait G. R.
Published: February 2008

(Latitude, 30° 19.′1 S.; Longitude, 115° 52.′6 or 7h 44m E. of Greenwich.)

EARTHQUAKE RECORDS.
Preliminary report on annual values of magnetic elements at the Swider Magnetic Observatory in Poland, 1921–1924
Authors: Kalinowski St.
Published: February 2008

(Latitude, 52°07′N; Longitude, 21°15′E.)

The Polish Magnetic observatory at Swider, built in 1914, is situated on the territory which was the scene of most fierce battles during the world war, as well as during the war with bolsheviks, and it is, accordingly, working regularly only since the beginning of 1921. Since that time quarterly bulletins of our magnetic character numbers are included in the “Lists” published by the De Bilt Observatory. Unfortunately, difficult financial conditions and, in consequence, inadequate personnel have hindered us from preparing immediately and publishing detailed reports of our observations. We have only been able to complete the reductions covering the years 1921 to 1924, inclusive, and although there are still some outstanding computations to be made before final results can be given, I consider it desirable to publish the preliminary values which follow:
Activity of the Sun and of atmospheric electricity on land and at sea, 1916–1920
Authors: Bauer Louis A.
Published: February 2008

For explanations, the interested reader may be referred to “Researches Dept. Terr. Mag.” Vol. 5, p. 381 (Pub. No. 175, Vol. V, Carnegie Institution of Washington, 1926).
Principal magnetic storms recorded at the Sitka Magnetic Observatory, January to March, 1926
Authors: Ulrich F. P.
Published: February 2008

(Latitude 57° 03′.0 N.; longitude 135° 20′.1, or 9h 01.3m W. of Greenwich.)
Notes on trip from Balboa, Canal Zone, to Easter Island, to Callao, Peru, October 25, 1928 to January 14, 1929
Authors: Ault J. P.
Published: February 2008

Leaving Balboa at noon October 25, the Carnegie had over 24 hours of fair wind before facing two weeks of head‐winds, heavy rains, squally weather, tacking back and forth, and running the engine in an attempt to get away from the Gulf of Panama. The course stood southward for five days, then northwest for three days, with no change of wind. This made it apparent that the engine and fore‐and‐aft sails should have to be used on a long tack to the south in an effort to win past the coast of Ecuador, south of the Equator, into the region of the southeast trade‐winds before way westward could be made. So the route was changed to go south of the Galapagos Islands instead of north.
Preliminary values of the annual changes of the magnetic elements in the North Atlantic Ocean, as determined from the Carnegie results, 1909–1928
Authors: Ault J. P.
Published: February 2008

The following table contains the average annual‐change values of the magnetic elements for the North Atlantic Ocean, as deduced from the observations on the Carnegie, 1909–1928. Various stations in the vicinity of intersections of Cruise VII, 1928, with previous tracks have been utilized. The 1928 values are not final, but the small corrections to be made at the completion of the cruise will not change the annual‐change values given herein. The method used was the same as indicated on page 185, Volume V, “Researches of the Department of Terrestrial Magnetism” use being made of the United States Hydrographic Office magnetic charts for 1925.
Observations on ionic content at Aberdeen
Authors: Geddes A. E. M.
Published: February 2008

“Information as to diurnal variation is very scanty except in the case of potential gradient.” This statement is contained in a paper by Dr. C. Chree in which he was discussing the atmospheric electrical elements.1 The following paper deals briefly with the results of a short investigation undertaken with the object of determining how this lack of information might be remedied to a certain extent. The space of time over which the observations were made was short and the results by themselves could not be considered conclusive.
The unsymmetrical distribution of magnetic secular variation
Authors: Fisk Harlan W.
Published: February 2008

In his paper announcing the results of his analysis of the Earth's magnetic field for 1922, Bauer stated certain conclusions regarding secular variation which it is interesting to consider at the present time, in view of the more extended knowledge we now have of that phenomenon than was available when that paper was written. One of these conclusions is that “it must be recognized that the magnetic secular‐variation system is as complex as the Earth's total magnetic system existing at any one time, and that in addition to changes in the direction of magnetization with the lapse of time, there is also a change in the average equivalent intensity of magnetization.”

That the secular‐variation system is even more complex than was then supposed by Bauer is made evident by reference to the series of isoporic charts (charts showing lines of equal annual change) of the elements recently prepared by the writer as a preliminary picture of the distribution of secular variation, subject to elaboration as data accumulate. These charts show that a large portion of the total secular change of any of the magnetic elements is concentrated within a few restricted areas, and that the centers of these areas (or isoporic foci) are surrounded by concentric ovals which are densely crowded near the centers, and are more openly arranged elsewhere. If we plot all these foci for the several elements on a single chart, and represent them by heavy shaded circles, we have the arrangement shown in Figure 1. The lighter unshaded circles represent centers of moderate secular‐change activity.