Interpretation Of High Resolution Aeromagnetic Data Research Articles

Interpretation of high-resolution aeromagnetic data within Dahomey basin, Nigeria; case for hydrocarbon prospectivity

The Ilorin Journal of science (ILJS) is an international and interdisciplinary open–access journal devoted to all aspects of research in Sciences and related fields. It is an official publication of the Faculty of Physical Sciences, University of Ilorin, Ilorin, Nigeria.The Ilorin Journal of science (ILJS) is an international and interdisciplinary open–access journal devoted to all aspects of research in Sciences and related fields. It is an official publication of the Faculty of Physical Sciences, University of Ilorin, Ilorin, Nigeria.

Structural pattern deduced from aeromagnetic dataover parts of Nasarawa and environs Northcentral Nigeria.

Interpretation of high-resolution aeromagnetic data over Nasarawa area was carried out to observe near surface source magnetic features that are associated with geological structures in the study area, Prominent lineaments in this study may be related to fractures that were not revealed by previous studies. Some of these lineaments coincide with concealed faults and fractures at Akiri warm spring and vicinity. Because this area has known warm springs, faults or fault intersections at depth can lead to upward movement of warm water that enhances permeability. Thus, mapping concealed fractures provides a focus for follow-up geothermal studies. Fault interpretation was accomplished by synthesizing interpretative maps derived from first vertical derivative and analytical signal along with preliminary depth estimates. Faults were interpreted along linear aeromagnetic anomalies and breaks in anomaly patterns. Many linear features correspond to topographic features, such as drainages. A few of these are inferred to be fault-related. The interpreted faults show criss-crossing pattern of fault zones, some of which appear to step over where they cross, and show zones of west-northwest, north-, and northwest-striking faults that cross west-northwest around Akiri warm spring. North easterly striking faults extend east from this juncture. The associated aeromagnetic anomalies are likely caused by magnetic contrasts associated with rifting of crust beneath the Benue Trough.KEY WORDS: Derivative, Structural Pattern, Rift Zones, Akiri.

Magnetic Structure of the Ischia volcanic island, Southern Italy

We carried out a study of the structures of the volcanic island of Ischia by the analysis and interpretation of high-resolution aeromagnetic data and by a newly compiled in-land gravity data set. The comparison between the vertical gradient of gravity data and pole-reduced magnetic data was performed through semblance analysis and highlighted a correspondence between the main magnetic and gravity highs over the lava and green tuff deposits (e.g., Punta Imperatore, Mt. Trippodi, Zaro, Mt. Rotaro, Mt. Epomeo). Our analysis also highlighted the simultaneous presence of a magnetic minimum and a gravimetric maximum in the central part of the island, mainly visible in the long-period components of the two data sets. This may be due to the existence of a partially demagnetized structure with positive density contrast, representing the island's igneous basement. The boundaries of the lava and tuffs deposits of the island were clearly pointed out by the maxima of the total horizontal gradient maps of magnetic and gravity data. Those maxima also show the position of several lineaments, in good agreement with the mapped faults of the island.

Magnetic signature of submarine volcanoes in the Phlegrean Fields-Ischia Ridge (North-Western side of the Bay of Naples, Southern Italy)

This paper presents a study of the Phlegrean Fields-Ischia submarine ridge by the analysis and interpretation of high-resolution aeromagnetic data recently acquired in the Western Procida offshore. The investigated area is located along the ridge connecting Ischia to the Phlegrean Fields and is characterized by the existence of several monogenetic volcanoes aligned on a NE-SW system of faults. The high-resolution magnetic data yielded new information on the area, highlighting particularly the signature of a volcanic body located between Pt. Serra and the Ruommoli shoal. This structure has not been clearly described before and we named it as the Pt. Serra submarine volcano. The computation of the analytic signal and horizontal gradient of the data distinctly located this structure and definined the position of its rims. A 2D modeling and 3D inversion of data provided information on the volcano’s thickness, width and magnetization, disclosing a meaningful igneous body extending down to several hundred meters b.s.l.

The Geological Setting of the 1968 Meckering Earthquake Based on the Interpretation of High-Resolution Aeromagnetic Data

Estimates of seismic hazard are strongly influenced by the location and recurrence of large earthquake events. Understanding such events is inherently difficult because recurrence intervals for large events in a given intra-plate region are typically much greater than the period over which earthquakes have been instrumentally recorded. Consequently, there is often very little data with which to robustly estimate seismic hazard. One way of enlarging the dataset is to study pre-historic large events using palaeoseismological methods, and there are many probable palaeo-fault scarps in the southwest of Western Australia. Studying these, along with historic fault scarps, places constraints on the geological setting of large events. The Southwest Seismic Zone is a belt of intra-plate seismic activity within the southwest of Western Australia. The local geological environment comprises deeply weathered Archaean granitoids and supracrustals. Outcrop is extremely sparse. The geological setting of large seismic events is best determined using high-resolution aeromagnetic data. These data allow bedrock geology to be mapped, and in particular identify structures that have been reactivated. This is the first step in establishing whether particular areas are more prone to large events than others. The 1968 Meckering earthquake (MS 6.8) resulted in an extensive and complex pattern of surface faulting, comprising faults with a range of orientations with reverse and dextral lateral offsets. Interpretation of new aeromagnetic data show that the surface faulting correlates closely with linear magnetic anomalies, interpreted as dykes/faults and lithological contacts/faults. The geometry of the surface faulting can be explained in terms of the reactivation of northeasterly and northwesterly trending surfaces in a stress regime with an east-west oriented maximum principal stress. Space problems created where these two trends converge led to the creation/reactivation of a linking north-south trending thrust fault which accommodated the greatest vertical displacements recorded for the 1968 event.

Geophysical Evidence for Terrane Boundaries in South-Central Argentina

The geological interpretation of high-resolution aeromagnetic data over the La Pampa province, in central Argentina, in addition to lower resolution magnetic information from the region of the Neuquén and Colorado basins, leads to the definition of the precise boundaries of the Chilenia, Cuyania, Pampia and Patagonia terranes, as well as that of the Río de la Plata Craton, within the study region. The high-resolution aeromagnetic survey data are compared and studied in conjunction with all the available geological information, to produce a map of the solid geology of this region, which is largely covered by Quaternary sediments. A number of structures of different magnitudes, as well as their relative chronology, are also recognized, i.e., regional faults, sub-regional faults, fractures and shear zones, as well as the most conspicuous magnetic fabric of the basement that reflects its main planar structures. Three different basements are distinguished on the basis of their contrasting magnetic character, and are interpreted to represent the Cuyania and Pampia terranes and the Río de la Plata Craton, separated from each other by large-scale discontinuities. In the western part of the study region an additional major discontinuity separates the Chilenia and Cuyania terranes. In the southernmost area studied, WNW-trending structures are predominant, particularly a major NNE-vergent thrust that indicates the truncation of the Cuyania-Pampia suture and is regarded to be related to the possible collision of the Patagonia terrane. An E–W – trending magnetic and gravity anomaly traversing the full extra-Andean Argentine territory, located immediately to the south of 39°S, represents a major structure. The activation of this structure during the Mesozoic gave rise to the Huincul Ridge and marks the interruption of the distinct N-S structures of the Chilenia, Cuyania and Pampia terranes, as well as those of the Río de la Plata Craton, to the north. This E–W represents the suture zone of the Patagonia terrane.

Aeromagnetic mapping and reconnaissance geochemistry of the Early Cretaceous Henties Bay-Outjo dike swarm, Etendeka Igneous Province, Namibia

An interpretation of high-resolution aeromagnetic data, backed up by Landsat ETM+ images and field observations, reveals a major NE-trending regional dike swarm in west-central Namibia which we name the Henties Bay-Outjo dike swarm (HOD). The HOD is some 100 km wide and extends at least 500 km from the continental margin, thus ranking among the regionally important dike swarms on the South Atlantic margins. Field relations and radiometric dates indicate Early Cretaceous emplacement ages for the dikes, contemporary with Etendeka Group flood basalts and with the Damaraland intrusive complexes that occur in the same area. The orientation and distribution of dikes within the HOD suggest a strong influence by Damara Belt structures within the first 100 km from the coast. Farther inland, the dikes are more discordant to the Damara Belt and finally the swarm leaves the Damara Belt entirely and crosses into the Angola craton, where dikes fan out to the north and extend for at least another 200 km. Geochemical analysis of about 100 dikes distributed throughout the HOD reveals a compositional spectrum ranging from basalt to rhyolite, with the dominant composition being tholeiitic, low-Ti basalt. The basaltic dikes show some compositional diversity, but most can be assigned to known compositional subtypes of the Etendeka Group and are thus likely to represent feeder dikes to now-eroded lava fields. The silicic dikes have compositional variations (metaluminous to peraluminous, 64–76 wt% SiO 2) matching the range found in the Early Cretaceous Damaraland intrusive complexes, and they only marginally overlap with felsic volcanic units of the Etendeka. These dikes are probably related to the silicic magma systems of the Damaraland complexes. We interpret the HOD as the failed arm of a triple junction centered at the shelf edge off Walvis Bay. Late Cretaceous magmatism in Namibia is plume-related, but we believe the triple junction did not result from domal uplift above a plume. The triple junction coincides with the intersection of three Pan-African orogenic belts: the inland Damara Belt and the coast-parallel Gariep/Dom Feliciano Belt and Kaoko/Ribeira Belt. Mesozoic opening of the South Atlantic propagated northward from the Cape, and when rifting reached the inherited Proterozoic triple junction, extension and magmatism affected all three belts initially but the Damara Belt became inactive shortly thereafter and continental separation followed the coast-parallel belts.

Integrated Interpretation of High-Resolution Aeromagnetic Data with High-Frequency Seismic and Landsat Data--Northwest Williston Basin: ABSTRACT

A low-altitude (300-ft), close-spaced (4 lines/mi) airborne magnetic gradiometer survey was flown in a 1000-mi/sup 2/ area of northeastern Montana. This area included 31 oil fields, and a modern high-frequency, broad-bandwidth seismic data set was obtained across it. The aeromagnetic survey was designed specifically to study and analyze the short-wavelength, small-amplitude magnetic anomalies associated with near-surface magnetic sources. A secondary objective was a more conventional magnetic basement study. Some of the near-surface magnetic sources may be related to epigenetic changes associated with seepage from hydrocarbon reservoirs. All 31 oil fields displayed a near-surface magnetic anomaly. Other near-surface magnetic anomalies displayed an obvious seismic anomaly visible on the high-frequency, broad-bandwidth seismic data. In addition, the zones that offset and truncate the observed near-surface magnetic anomalies can be seen in the seismic data. This suggests a small, though deep-seated, Quaternary or Holocene wrench-fault system. Many of the magnetic offset zones were also visible in available Landsat data. Some magnetically observed basement faults were also visible on the seismic and Landsat data.