INTRA-SEDIMENTARY MAGNETIZATION OF THE HINES CREEK FAULT (N. ALBERTA) BY VERTICAL FLUID FLOW AND EXOTIC GEOCHEMISTRY (original) (raw)

Faulting Processes Unveiled by Magnetic Properties of Fault Rocks

Reviews of Geophysics, 2020

Iron-bearing minerals and ferrimagnetic minerals in particular are sensitive to faultingassociated physical and chemical processes  Laboratory faulting experiments and comparison with non-magnetic approaches confirm results from magnetic studies on natural rocks  Rock magnetic methods offer novel tools to analyze strain, grain fining, temperature trends, and fluid-rock interaction in fault zones

Correlating paleomagnetic, geochemical and petrographic evidence to date diagenetic and fluid flow events in the Mississippian Turner Valley Formation, Moose Field, Alberta, Canada

Sedimentary Geology, 2000

Petrographic, geochemical and paleomagnetic analyses of the Mississippian Turner Valley Formation provide constraints on diagenesis and fluid flow events in the Western Canada Sedimentary Basin. Paleomagnetic plugs and companion geochemical samples were taken from two drillcores, with Fullbore MicroImage log orientations. Dolomite from both wells yielded two magnetization directions. The low-temperature, low-coercivity direction is a drilling-induced remanence rather than a viscous remanent magnetization. The high-temperature, high-coercivity remanence direction is Cretaceous, and there is no sign of a primary Mississippian direction. Geochemical analyses of matrix dolomite yield d 18 O values ranging from 0.65 to Ϫ3.34‰ (VPDB standard) and d 13 C values ranging from 1.77 to 3.05‰ VPDB. The least depleted samples have stable isotope values consistent with, or only slightly depleted from, postulated Mississippian dolomite values. The remaining sample values exhibit a negative covariant trend consistent with either mixing with another diagenetic fluid or recrystallization during burial. Petrographic analysis reveals the presence of a recrystallization event that caused zoning and a gradual increase size of the dolomite crystals. This event is thought to have caused both the Cretaceous paleomagnetic remanence and the altered geochemical values. The minor enrichment in Sr radiogenic isotopes, relative to coeval seawater values, suggests that both an extrabasinal source for any fluid and large-scale fluid flow are unlikely. The results also indicate that magnetic remanences are very sensitive to visually minor changes in carbonate recrystallization from heat or pressure, so that great care must be taken in correlating paleomagnetic and geochemical data. ᭧

Magnetotelluric measurements in La Malbaie area (Quebec): the anomalous vertical magnetic field

Canadian Journal of Earth Sciences, 1985

Magnetotelluric soundings were recorded in 1980-1981 at Ste-Mathilde near La Malbaie, Quebec for periods of 0.04-200 s. The present study deals only with single-station vertical transfer functions. Those functions show very characteristic features in their responses versus period. Of particular interest is a large in-phase (P) peak corresponding to a quadrature (Q) minimum between 0.1 and 0.2 s. For those periods, induction arrows indicate no obvious correlation between the anomalous vertical magnetic field (Z) and the conductive zone of Ste-Mathilde. Rather, they point toward the Malbaie River to the southwest of the survey zone. A possible model for the source of the vertical magnetic field is a shallow N130°E vertical dyke-type conductor, the top of which is some 1400 m under the Malbaie River valley. An interpretation could well be that it is one of the major graben faults related to the meteoritic impact crater of Charlevoix.

Sedimentary magnetic anomalies Part 1 .. TLE-Oct 2018-wLinks.pdf

M e t e r r e a d e r — C o o r d i n a t e d b y J e r r y H e n s e l Abstract Validation is important in any study of sedimentary high-frequency magnetic anomalies. Repeatability and good correlation of anomalies between lines of the same survey and lines from different surveys as well as maximum entropy spectral analysis are some of the approaches I used to verify and validate the geologic nature of these anomalies. Examples of such correlations from the National Petroleum Reserve in Alaska are used here for illustration. The filtered magnetic data used in these examples represent two surveys: the U.S. Department of Energy's low-level (120 m) National Uranium Resource Evaluation total field survey flown in 1980 and the high-level (650 m) high-sensitivity total field/vertical gradient survey flown in 1974 with measured vertical gradient. I will provide a general discussion on the magnetization of sediments as well as model studies illustrating the theoretical magnetic response of some typical sedimentary structures.

Magnetic Logging and In-Situ Magnetostratigraphy: A Field Test

Proceedings of the Ocean Drilling Program, 1994

During Ocean Drilling Program Leg 134 (Vanuatu), geological high sensitivity magnetic tools (GHMT) developed by CEA-LETI and TOTAL were used at two drill sites. GHMT combine two sensors, a proton magnetometer for total magnetic field measurements with an operational accuracy of 0.1 nanoteslas (nT), and a highly sensitive induction tool to measure the magnetic susceptibility with an operational accuracy of a few I0" 6 S1 units. Hole 829 A was drilled through an accretionary prism and the downhole measurements of susceptibility correlate well with other well-log physical properties. Sharp susceptibility contrasts between chalk and volcanic silt sediment provide complementary data that help define the lithostratigraphic units. At Hole 83 IB magnetic susceptibility and total field measurements were performed through a 700-m reef carbonate sequence of a guyot deposited on top of an andesitic volcano. The downhole magnetic susceptibility is very low and the amplitude of peak-to-peak anomalies is less than a few 10~5 S1 units. Based on the repeatability of the measurements, the accuracy of the magnetic logging measurements was demonstrated to be excellent. Total magnetic field data at Hole 83IB reveal low magnetic anomalies of 0.5 to 5 nT and the measurement of a complete repeat section indicates an accuracy of 0.1 to 0.2 nT. Due to the inclination of the earth's magnetic field in this area (~-40°) and the very low magnetic susceptibility of the carbonate, the contribution of the induced magnetization to the total field measured in the hole is negligible. Unfortunately, because the core recovery was extremely poor (<5%) no detailed comparison between the core measurements and the downhole magnetic data could be made. Most samples have a diamagnetic susceptibility and very low intensity of remanent magnetization (< I0" 4 A/m), but a few samples have a stable remanent magnetization up to 0.005 A/m. These variations of the intensity of the remanent magnetization suggest a very heterogeneous distribution of the magnetization in the carbonate sequence that could explain the magnetic field anomalies measured in these weakly magnetized rocks.

Magnetotelluric Soundings In the Canadian Rocky Mountains

Geophysical Journal International, 1987

Summary. Magnetotelluric soundings have been made at 25 stations in the Rocky Mountain Trench (RMT) and Main Ranges near 53° N, close to the centre of a major conductivity anomaly which had been mapped in a magnetovariation array study. Most stations covered the frequency range 0.01–500 Hz and three stations 0.0002–500 Hz. the resistivity tensor shows low to moderate anisotropy in the RMT, but is strongly 2-D or 3-D in the Rocky Mountains. Apparent resistivities as a function of frequency are displayed in pseudosections along the Trench and along a transverse profile across the RMT and into the Main Ranges. In preparation for 2-D modelling, 1-D inversions have been used to construct resistivity-depth sections satisfying both magnitudes and phases of the MT responses. These show very low resistivities, in the range 1—10Ωm, in the upper crust under the RMT and even lower values under the Main Ranges. the latter values give strong confirmation of the Northern Rockies conductor reported by Bingham, Cough & Ingham and are in agreement with models of the conductors fitted to long-period magnetovariation fields by Ingham, Gough & Parkinson. the MT results here reported add some essential depth and resistivity information. It is suggested that the conductors beneath the Rocky Mountains Main Ranges and Trench constitute a thickening at the edge of the Canadian Cordilleran Regional (CCR) conductor. Gough has argued that a wide variety of geophysical and geological parameters indicate high temperatures and partial melting in the mantle under the CCR conductor. At the upper crustal depths penetrated in this magnetotelluric study, it is considered more probable that the high conductivity is caused by hot, saline water of mantle origin rather than silicate melt. the CCR in general may have two layers of fluid producing its high conductivity, silicate melt below and saline hot water above.

Magnetotelluric soundings, structure, and fluids in the southern Canadian Cordillera

Canadian Journal of Earth Sciences, 1992

The Cordillera of western Canada lies in a region of oceanic and island-arc lithosphere accreted to North America during subductions of the last 200 Ma. Magnetometer arrays have shown the crust of the region to be highly conductive. Magnetotelluric (MT) soundings across the Intermontane and Omineca tectonic belts between 50°N and 54"N reveal structure in terms of electrical resistivity. Pseudosections of phase and apparent resistivity and preliminary resistivity -depth sections are shown for three transects. The resistivity range is from less than one ohm metre to several thousands of ohm metres. In old continental shields, crustal resistivities cover a similar four-decade range transposed up two decades, i.e., 1O2-lo6 Q . m. We show that the observed resistivities can be produced by water with NaCl and (or) C 0 2 in solution, at the high temperatures of the Cordilleran crust, in fractured rock of effective porosity 4-5%. The resistivity variations may represent varying fracture densities. By following structures from outcrops we infer that the more resistive rocks are probably granitoid plutons, with low fracture densities. The highly conductive basalts probably have higher fracture densities. Sections and phase maps indicate that granitoid plutons continue from the Coast Plutonic Complex, under a thin layer of basalt, across the southwestern half of the Intermontane Belt. Near the centre of the Intermontane Belt, in line with the Fraser fault system, highly conductive rock continues from the surface at least to midcrustal depths. Resistivities as low as 1 Q . m in the uppermost crust under the Cariboo Mountains, in the Omineca Belt, are ascribed to intense fracturing or mineralization. For the southernmost transect, between 50°N and 51°N, a phase pseudosection shows informative resemblances to the sections farther north. Resistivity-depth inversions at seven sites from six-decade MT data give penetration into the upper mantle, but some of these sites may be affected by static shift. All results fit the mantle upflow hypothesis advanced earlier by Gough.

Unveiling Powell Basin’s Tectonic Domains and Understanding Its Abnormal Magnetic Anomaly Signature. Is Heat the Key?

Frontiers in Earth Science, 2020

Rifting of continental lithosphere leading to oceanic basins is a complex process conditioned by different factors such as the rheology and thermal structure of the underlying lithosphere, as well as underlying asthenospheric dynamics. All these processes, which finally lead to oceanic domains, can better be recognized in small oceanic basins. Powell Basin is a small oceanic basin bounded to the north by the South Scotia Ridge, to the east by the South Orkney Microcontinent, and to the west by the Antarctic Peninsula. It was formed between the Oligocene and Miocene, however, its age is not well defined, among other reasons due to the small amplitude of its spreading magnetic anomalies. This basin is an ideal framework to analyze the different rifting and spreading phases, which leads from continental crust to the formation of an oceanic domain through different extensional regimes. To identify the different boundaries during the formation of Powell Basin from the beginning of the rifting until the end of the spreading, we use different data sources: magnetic, gravity, multichannel seismic profiles and bathymetry data. We use seismic and bathymetry data to estimate the Total Tectonic Subsidence. Total Tectonic Subsidence has proven to be useful to delineate the different tectonic regimes present from early rifting to the formation of oceanic seafloor. This result together with magnetic data has been used to delimit the oceanic domain and compare with previous authors' proposals. This method could be applied in any other basin or margin to help delimiting its boundaries. Finally, we analyze the role that an asthenospheric branch intruding from the Scotia Sea played in the evolution of the magnetic anomaly signature on an oceanic basin.