Preliminary Paleomagnetic Data Research Articles

Carpathian Shear Corridor – A strike-slip boundary of an extruded crustal segment

The Carpathian Shear Corridor (CSC), a morphostructurally distinctive ENE-WSW brittle shear zone, is a prominent dynamic interface of crustal fragments shifted during an oblique collision process combined with lateral extrusions in the Late stages of the Western Carpathians tectonic evolution. This tectonics was due to convection in the upper mantle, driven mainly by slab-pull forces related to a subductional process in front of prograding Carpathians. The CSC separates the marginal segment of the Western Carpathians, already firmly attached to the European plate, from the southern still eastwardly moving block. This process led to structural transpositions, anomalous rotation of small blocks and tilting and uplift/subsidence events, resulting in a tectonic style of horst and intramountaine basin alternations within the corridor. Preliminary paleomagnetic data indicate anomalous CCW block rotations within this corridor, and AFT ages indicate Early and Late Miocene (ca 24–22Ma and ca 10–7Ma) fault controlled exhumation events triggered by increased shear zone activity. Deep seismic sections, magnetotelluric and gravity data show that CSC follows a frontal ramp of the Western Carpathians thrust over the foreland. The CSC remains an active strike-slip shear zone, and therefore the most important earthquake risk-zone in the Slovakian portion of the Western Carpathians. It presents a lateral ramp transform boundary of eastwardly extruding crustal segment during the Miocene and up to the recent time.

First Early Pliocene micromammal faunas from Venta del Moro (Cabriel Basin, Spain): new data on the Messinian dispersal of Debruijnimys

Based on the study of the micromammal assemblages from the localities of La Bullana 2B and La Bullana 3 (Valencia, E Spain) we propose an Early Pliocene age (MN14) for both sites. The presence of a form related to the gerbillid Debruijnimys julii in La Bullana 2B allows extending the stratigraphical range of this taxon to the MN14 zone, opening new questions about the phylogenetic relationship between Debruijnimys species from the Early and Late Pliocene of the Iberian Peninsula. Furthermore, preliminary paleomagnetic data indicate an age of 4.816 Ma for La Bullana 2B, and between 4.896 and 4.997 Ma for La Bullana 3.

Permian clockwise rotations of the Ebro and Corso-Sardinian blocks during Iberian–Armorican oroclinal bending: Preliminary paleomagnetic data from the Catalan Coastal Range (NE Spain)

Paleomagnetic investigations of Early Permian and Triassic magmatic rocks from Catalan Coastal Ranges provide three magnetic directions which are interpreted as primary magnetizations and partly as overprints. The succession of magnetic directions is interpreted in terms of a succession of large-scale clockwise rotations, which bring the whole assembly of Pyrenees, Catalonia, Corsica-Sardinia and Maures-Esterel massifs from the southeast of the Massif Central to the west during Permian. This major movement is associated with clockwise rotation of northern limb of the Iberian orocline during Latest Carboniferous and Early Permian (~305–290Ma). Subsequently, Permian large-scale dextral transtensional–extensional shearing operated along Aquitanian Shear Belt between the Massif Central in the northeast and the Iberian Variscan massifs in the southwest. The latest phase of the rotation in the Late Permian-Early Triassic is associated with alkaline magmatism probably linked to Neo-Tethys opening activity in Western Europe.

Geological setting and paleomagnetism of the Eocene red beds of Laguna Brava Formation (Quebrada Santo Domingo, northwestern Argentina)

The red bed succession cropping out in the Quebrada Santo Domingo in northwestern Argentina had been for long considered as Upper Triassic–Lower Jurassic in age based on weak radiometric and paleontological evidence. Preliminary paleomagnetic data confirmed the age and opened questions about the nature of fossil footprints with avian features discovered in the section. Recently the stratigraphic scheme was reviewed with the identification of previously unrecognized discontinuities, and a radiometric dating obtained in a tuff, indicated an Eocene age for the Laguna Brava Formation and the fossil bird footprints, much younger than the previously assigned. We present a detailed paleomagnetic study interpreted within a regional tectonic and stratigraphic framework, looking for an explanation for the misinterpretation of the preliminary paleomagnetic data.The characteristic remanent magnetizations pass a tilt test and a reversal test. The main magnetic carrier is interpreted to be low Ti titanomagnetites and to a lesser extent hematite. The characteristic remanent magnetization would be essentially detrital. The obtained paleomagnetic pole (PP) for the Laguna Brava Formation has the following geographic coordinates and statistical parameters: N=29, Lon.=184.5° E, Lat.=75.0° S, A95=5.6° and K=23.7. When this PP is compared with another one with similar age obtained in an undeformed area, a declination anomaly is recognized. This anomaly can be interpreted as Laguna Brava Formation belonging to a structural block that rotated about 16° clockwise along a vertical axis after about 34Ma. This block rotation is consistent with the regional tectonic framework, and would have caused the fortuitous coincidence of the PP with Early Jurassic poles. According to the interpreted magnetostratigraphic correlation, the Laguna Brava Formation would have been deposited during the Late Eocene with a mean sedimentation rate of about 1.4cm per thousand years, probably in relation to the onset of the Andean deformation.

Simultaneous thermoluminescence and optically stimulated luminescence dating of late Pleistocene sediments from Lake Baikal

When the thermoluminescence (TL) method is applied to dating of partially bleached sediments the need to correct for the residual TL signal left in the mineral crystals at time of deposition is a complicated problem. In dating sediments from Lake Baikal we have attempted a combination of TL and optical stimulated luminescence (OSL). The method was applied to three samples from the uppermost 50m of the sediment cored within the Baikal drilling project in 1993. The results indicate a fairly constant sedimentation rate back to 250 ka BP. This contradicts with results from radiocarbon dating of the same core but agrees reasonably well with preliminary paleomagnetic data and disequilibrium U–Th age determinations.

Charleston transverse zone, Wasatch Mountains, Utah: Structure of the Provo salientʼs northern margin, Sevier fold-thrust belt

The Charleston transverse zone of north-central Utah is an east-west–trending corridor of faults and folds that forms the boundary between the Provo salient of the Sevier fold-thrust belt and the Uinta-Cottonwood arch. The zone trends nearly 90° to the regional structural grain of the fold-thrust belt. Structural analysis and mapping in American Fork Canyon, near the western margin of the Charleston transverse zone, demonstrates that the zone contains an array of low-angle thrust faults and high-angle reverse and normal faults. Crosscutting relations indicate that the low-angle thrust faults formed first, followed by the reverse faults and possibly selected normal faults, and then by the majority of normal faults. Locally, normal faults reactivate reverse faults. The overall pattern of faulting and folding in the Charleston transverse zone suggests that the zone is a left-lateral strike-slip flower structure superimposed on an imbricate thrust fan. Trends of normal faults in the transverse zone suggest that many formed during a later phase of oblique extension that had a component of right-lateral shear. Our results support a tectonic model in which the Charleston transverse zone initiated during the Sevier orogeny to accommodate along-strike changes in the geometry of the thrust belt, caused in turn by along-strike changes in thickness of the stratigraphic sequence involved in thrusting. Thrust sheets in the Provo salient to the south of the Charleston transverse zone moved farther toward the foreland than did thrust sheets to the north of the zone, so the Charleston transverse zone evolved into a left-lateral strike-slip accommodation zone. Preliminary paleomagnetic data support this proposal: they suggest that fault blocks within the Charleston transverse zone locally rotated counterclockwise about a vertical axis. Laramide uplift of the Uinta-Cottonwood arch tilted structures of the Charleston transverse zone to the south and may have locally reactivated faults within the zone. Subsequent extensional tectonism reactivated the Charleston transverse zone with an oblique component of right-lateral shear.

Ferrar magmatic province rocks discovered in New Zealand: Implications for Mesozoic Gondwana geology

Research Article| February 01, 1995 Ferrar magmatic province rocks discovered in New Zealand: Implications for Mesozoic Gondwana geology N. Mortimer; N. Mortimer 1Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin, New Zealand Search for other works by this author on: GSW Google Scholar D. Parkinson; D. Parkinson 2Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand, and Department of Geological Sciences, University of California, Santa Barbara, California 93106 Search for other works by this author on: GSW Google Scholar J. I. Raine; J. I. Raine 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar C. J. Adams; C. J. Adams 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar I. J. Graham; I. J. Graham 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar P. J. Oliver; P. J. Oliver 4Peter Oliver & Associates, P.O. Box 40–482, Upper Hutt, New Zealand Search for other works by this author on: GSW Google Scholar K. Palmer K. Palmer 5Analytical Facility, Victoria University, P.O. Box 600, Wellington, New Zealand Search for other works by this author on: GSW Google Scholar Author and Article Information N. Mortimer 1Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin, New Zealand D. Parkinson 2Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand, and Department of Geological Sciences, University of California, Santa Barbara, California 93106 J. I. Raine 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand C. J. Adams 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand I. J. Graham 3Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand P. J. Oliver 4Peter Oliver & Associates, P.O. Box 40–482, Upper Hutt, New Zealand K. Palmer 5Analytical Facility, Victoria University, P.O. Box 600, Wellington, New Zealand Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1995) 23 (2): 185–188. https://doi.org/10.1130/0091-7613(1995)023<0185:FMPRDI>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation N. Mortimer, D. Parkinson, J. I. Raine, C. J. Adams, I. J. Graham, P. J. Oliver, K. Palmer; Ferrar magmatic province rocks discovered in New Zealand: Implications for Mesozoic Gondwana geology. Geology 1995;; 23 (2): 185–188. doi: https://doi.org/10.1130/0091-7613(1995)023<0185:FMPRDI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract On the basis of similar ages, major and trace element concentrations, and Sr, Nd, and Pb isotopic ratios, we correlate the Kirwans Dolerite of western New Zealand with Jurassic low-Ti tholeiites of the well-known Ferrar magmatic province of Gondwana. Field relations and preliminary paleomagnetic data also support this correlation. Although the 1 km2 Kirwans Dolerite is the first, and so far only, Ferrar correlative to be reported from New Zealand, it considerably increases the known shape and areal extent of the Ferrar province to close to the paleo-Gondwana margin. The presence of Ferrar rocks in New Zealand can be used to test several models of Ferrar magma genesis and Gondwana regional tectonics. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Preliminary paleomagnetic data from the Sierra Grande formation: Tectonic consequences of the first mid-Paleozoic paleopoles from Patagonia

The first two mid-Paleozoic paleomagnetic poles from Patagonia were obtained from a preliminary paleomagnetic study of the Sierra Grande Formation, exposed at 65.4°W, 41.6°S in Argentina. The first pole, SG1, is located at 238.0°E, 3.4°N (N=14, D1=14.3°, D2=8.5°) and corresponds to a ferriferous horizon intercalated in the lower member of the formation, which is assigned to the Wenlockian. The second pole, SG2, located at 283.5°E, 42.0°S (N=10, D1=20.4°, D2=20.2°), belongs to the upper member of the formation and is assigned to the Late Silurian-Early Devonian. These pole positions are interpreted according to different tectonic hypotheses. The position of SG1 is more easily understood if Patagonia had an allochthonous origin, for it does not agree with the presently most accepted Silurian pole position of Gondwana. Nevertheless, the position of SG2, consistent with the Late Silurian-Early Devonian Gondwana poles, suggests that Patagonia was next to collide with South America in the Early Devonian. On the other hand, the hypothesis of an autochthonous Patagonia is supported by the consistent position of SG2 with respect to the coetaneous poles of Gondwana, while SG1 would indicate that the reversed polarity path of Schmidt and Morris (1977) should be taken as the most probable early-middle Paleozoic apparent polar wander path of Gondwana.

Structural and magmatic responses to spreading ridge subduction: An example from southwest Japan

Subduction of a spreading ridge is expected to leave a geological signature upon the overriding accretionary prism distinct from that of conventional convergent plate boundaries. The late Oligocene‐early Miocene rocks of the Shimanto accretionary prism at Cape Muroto, Shikoku Island, record a tectonomagmatic fabric that is anomalous with respect to typical accretionary prisms. These accreted strata have been imprinted with an unusual late stage event that involved (1) regional cusp‐like flexing of structural trends in the prism, (2) near‐trench magmatism, and (3) pervasive faulting. This event overlaps in time with the opening of the Shikoku back arc basin (circa 26–14 Ma); the Shikoku basin spreading ridge trends perpendicular to the strike of the accretionary prism and is now located immediately offshore of Cape Muroto. The regional flexing of structural trends in the prism affects rocks as old as Cretaceous, although the flexure is most tightly developed in the late Oligocene‐early Miocene portion of the prism, where it is steeply plunging. Kinematic analysis of the flexure and the pervasive fault system indicates that the flexure most likely resulted from indentation of the prism by a rigid feature. At Cape Muroto the core of the flexure forms a locus for mafic dikes that are petrochemically equivalent to some mid‐ocean ridge basalts (MORB) from the Shikoku back arc basin. Preliminary paleomagnetic data suggest that the dikes were intruded during the later stages of flexure development. These data, combined with plate reconstructions for the area at 15 Ma, indicate that indentation of the prism most likely resulted from early Miocene orthogonal subduction of the topographically elevated Shikoku Basin spreading ridge in the Muroto area; MORB magmatic rocks in the core of the flexure appear to have emanated from the active spreading ridge during subduction.

A preliminary Neogene paleomagnetic data set from Leyte and its relation to motion on the Philippine fault

Leyte Island is bisected by the left-lateral Philippine fault. Paleomagnetic samples were collected from nineteen lava flows in Leyte and nearby islands to the north. The data collected from these sites were combined with previously reported results from northeastern Mindanao. The paleomagnetic data from Neogene rocks within or very near the Philippine fault zone on Leyte, Mindanao, Biliran, Maripipi, and Genuruan Islands fall into two populations. Seventeen late Neogene sites (fourteen normal polarity and three reversed polarity) yield a mean direction D = 358.9°, I = 20.1° ( α 95 = 6.6°, k = 30.1) and a paleomagnetic pole λ = 88.9° N, φ =12.5° E ( A 95 = 4.8°, K=56.1). Eight early Neogene sites (three normal polarity and five reversed polarity) give a mean direction D = 23.2°, I = 13.9° ( α 95 = 9.3°, k = 36.2) and a paleomagnetic pole λ = 66.5° N, φ = 220.5° E ( A 95 = 7.1°, K= 62.0). The late Neogene pole is indistinguishable from Plio-Pleistocene poles from the Philippines, Taiwan, and Vietnam, and the late Miocene pole of the central Philippines suggesting there have been no significant rotations or translations of this region with respect to other Southeast Asian regions during the past 5 M.y. The early Neogene paleomagnetic pole is statistically indistinguishable from the middle to early Miocene pole of the central Philippines. The early Neogene pole is statistically distinguishable from early Miocene pole of Marinduque Island (Philippines) as well as the late Miocene pole of the central Philippines and the Plio-Pleistocene pole of the entire Philippines. This preliminary paleomagnetic data set suggests that Leyte and adjacent islands to the north have been a portion of the same tectonic block as northeastern Mindanao, Cebu, and western Panay since early Neogene. There are also no paleomagnetically detectable fault-related rotations associated with the Philippine fault given the resolution of this data set. No consensus exists as to the amount of offset or the age of inception of the Philippine fault. The 110 km offset between ophiolitic basement in northeast Leyte and that in southwest Leyte suggests this amount of left-lateral displacement has occurred along the Philippine fault since the middle Tertiary. In contrast to data from continental regions, no shear-related rotations are found associated with the Philippine fault. This observation suggests that the hot, immature, transitional island arc/continental crust of the Philippine region deforms differently in response to shear than well developed continental crust.

New evidence for an allochthonous plate in central southwestern Argentina?

Preliminary paleomagnetic data for rocks from the Choiyoi Formation, exposed at the Cerro Chachil and Sierra de Catan-Lil (39.1°S, 70.5°W, Cordillera Principal, Argentina), assigned sensu lato to the Permo-Triassic, are discussed. The directions of the stable remanent magnetization (SRM) for these rocks have been submitted to the fold test. This analysis indicates that most of the Choiyoi Formation rocks are carriers of a prefolding SRM. The mean prefolding SRM for samples of normal and reversed polarity (within 40° of the mean; 277°, +54°, A95 = 8°, N = 21, K = 15.2, R = 19.683) yields a mean pole at 18°S, 126°W, 95 = 10°. The paleomagnetic data indicate two preliminary interpretations. One interpretation suggests that the sampling site rotated 90° clockwise around a vertical axis since Permian times. The other interpretation suggests that the sampling site integrates the allochthonous microplate suggested by Vilas and Valencio (1982) and Valencio and Vilas (1985). This microplate was situated in the Pacific at tropical latitudes in the late Paleozoic.

Preliminary paleomagnetic data from the Jurassic Humboldt Lopolith, west‐central Nevada: Evidence for thrust belt rotation in the Fencemaker Allochthon

Layered and massive gabbros of the Humboldt Lopolith and extrusive equivalents in west‐central Nevada yield well‐grouped paleomagnetic data on a site basis. With corrections for attitudes of compositional layering in gabbros and flow contacts in lavas (kcorr/kin situ = 5.5), the mean of 15 site means is: D = 307°, I = 21°, α95 = 9°, k = 17. While K‐Ar data imply a Late Jurassic age, we prefer an older, probably Early Jurassic, age for the lopolith and its magnetization based upon magnetization data and relations of these rocks with host strata. Compared with Early Jurassic expected directions, the data reveal a discordancy in declination of −37° (+/− 14‐22°) which implies a significant counterclockwise rotation of the lopolith. Local rotation of Fence‐maker allochthon units most likely occurred when southeasterly‐directed thrust sheets obliquely contacted a generally north‐south trending shelf margin. Mesozoic deformation will be more accurately estimated with better age control and measurement of possible Cenozoic crustal rotation.

Offset along the San Andreas fault of Eocene strata from the San Juan Bautista area and western San Emigdio Mountains, California

Analyses of Eocene strata that rest on gabbroic basement rocks in the western San Emigdio Mountains and northernmost Gabilan Range indicate that the 2 sequences have been offset right-laterally 305–320 km along the San Andreas fault. In both areas, basal shallow-marine conglomerate of Penutian age grades upward into shale of Ulatisian and Narizian age that was deposited at bathyal water depths in a basin with access to open ocean. Additional similarities in the upper Eocene and Oligocene stratigraphic units suggest original contiguity of the depositional basins. The inferred offset indicates that the Salinian block was attached to western California by at least early Eocene time. The longer distances of northward transport of the Salinian block that are suggested by preliminary paleomagnetic data from upper Mesozoic granitic rocks and Upper Cretaceous and Paleocene strata must have occurred during Paleocene or earlier time.

A regional paleomagnetic study of Archean rocks from the Superior Geotraverse area, northwestern Ontario

Preliminary paleomagnetic data are reported for Archean metavolcanics, felsic and mafic intrusives, gneisses, and iron formations from the Quetico, Shebandowan, and Wabigoon belts in the western Superior Structural Province. Eleven of the 23 formations sampled have been studied in detail using stepwise alternating-field demagnetization and, in some cases, thermal demagnetization. Two characteristic components of magnetization are revealed. One is widespread in occurrence and reasonably well grouped (D = 4.5°, I = + 55.7°, k = 17.9, α95 = 5.4°, N = 40 samples for the Shelley Lake granite for example). It is a regional magnetic overprint due to the Kenoran orogeny, acquired, according to the position of its paleopole (71.7°E, 77.3°N, δp = 5.5°, δm = 8 °for the Shelley Lake granite) on the Laurentian apparent polar wander path and to independent radiometric evidence, about −2600 Ma. The second magnetic component is spotty in occurrence, more prevalent in the Wabigoon belt than elsewhere, and everywhere rather scattered. The only fully reliable determination is D = 66.0°, I = −5.1 °(k = 10.2, α95 = 15°, N = 11 samples) for the Wabigoon gabbro. The corresponding paleopole is either 17.8°E, 13.1°N (δp = 7.5°, δm = 15°) falling at about −2800 Ma on the apparent polar wander path or the antipole of this direction, dating between −1350 and −1250 Ma. The younger date, implying a late ProterQzoic metamorphic event in the region, is more likely than the older age, which would require that the magnetization be primary or a pre-Kenoran overprint. The metamorphism seems to have occurred too early to have been caused by igneous activity ca. 1100 Ma in the nearby Keweenawan basin. About −2600 Ma, the region was in its present orientation, but at a latitude of 20 to 35°N and probably drifting northward. About −1250 Ma, the region was equatorial but rotated 90°, so that presently east–west trending greenstone belts were north–south. It is possible, but un-proven, that a paleoocean existed between the Wabigoon subprovince and the other belts about −1250 Ma, the Wabigoon region having since moved &gt; 500 km westward (present-day direction) to its present location.

Ancestral Delta Lobe of Santee River Near Charleston, South Carolina: ABSTRACT

The Santee River of North Carolina and South Carolina emptied into the sea 75 km west of its modern mouth when the shoreline was 15 to 21 m above present sea level in early Pleistocene time. For a short time, the river deposited a fluviomarine delta lobe (volume 5 cu km) that covered 400 sq km near Summerville, South Carolina, 35 km northwest of Charleston. The Summerville lobe was abandoned before the late Pleistocene, and the sea has not covered the area since then. The original wave-constructed ridge-and-swale topography is still visible; drill holes have revealed the subsurface lithofacies relationships. In the modern Santee delta and the chenier plain of Louisiana, similar topography and patterns of lithofacies reflect alternating dominance of flood-plain deposition nd shoreface redistribution. Paleontology, paleomagnetic stratigraphy, and sediment mineralogy contribute to the age determination of the Summerville lobe. On the basis of fossil pollen and invertebrates identified by U.S. Geological Survey paleontologists, the Summerville lobe deposits are tentatively believed to be equivalent in age to the Waccamaw Formation (late Pliocene and early Pleistocene) of northern South Carolina. Surficial heavy- and light-mineral suites are more mature, and thus older, than paleontologically dated late Pleistocene shoreline deposits nearby. Less weathered mineral suites below the water table in the Summerville lobe reflect the Piedmont (Santee River) source of the sediment. Preliminary paleomagnetic data are compatible with this age determination. End_of_Article - Last_Page 452------------