Basement structure of the Farallon Basin, off the coast of South California, inferred through analysis of potential and seismic data
In a groundbreaking geophysical exploration, researchers have delved into the depths of the Farallon Basin, uncovering valuable insights about the basin's crustal structure and thickness. The study, which employed seismic reflection and gravimetric methods, has shed light on the oceanic and continental crusts in this significant oceanic basin.
The investigation began with the integration of seismic data, potential fields, and 3D gravimetric inversion to identify the type and structure of the crust in the study area. The GMLayers software was utilised for the 3D gravimetric inversion of the data, while a marine linear array was employed for data acquisition.
A typical reflexion seismic processing sequence was applied, and the Free-Air gravimetric data was used to generate subsurface models. Seismic data from four lines were processed using the ProMAX software, and the appropriate settings of parameters were crucial in obtaining an optimum model.
The gravimetric method, based on the measurement of small variations of the earth's gravitational field, allowed for the mapping of subsurface layering and density variations. Seismic reflection delineated interfaces between crustal layers, identifying boundaries such as the Moho (crust-mantle boundary). Gravimetric methods, on the other hand, detected density contrasts that correlated with crustal thickness and structure, helping differentiate oceanic crust's mafic composition from continental crust's more silicic rocks.
The study aimed to identify, delimit, and estimate the thickness of the oceanic and continental crusts in the Farallon Basin. In the oceanic crust, a three-layered structure was often revealed: a thin sedimentary layer, a layer of basalts and sheeted dikes, and a layer of gabbroic rocks and lower crust. The thickness of oceanic crust is generally around 6-7 km, but can vary slightly depending on spreading rates and tectonic history.
The continental crust, much thicker and more heterogeneous, was found to be composed mainly of granitic and metamorphic rocks in the upper continental crust, with denser rocks such as amphibolite and granulite facies rocks in the middle to lower crust. The thickness of continental crust often ranges from 30 to 50 km, much thicker than oceanic.
Evidence suggests that the sedimentary material which overlays the recently created oceanic crust in the Farallon Basin is affected by magmatic intrusions. After seismic processing, a Basement's type distribution map was generated. Figure 8 shows the s2 surface, which corresponds to the bathymetric relief, always located above the s4 depth ranges. In Figure 8, the seismic profile's restrictions given by depth can be observed. The s2 surface's minimum and maximum thickness match the minimum and maximum depths in the area, with the upper surface fixed at 0 km (sea level).
On the western zone, a continental crust with a thickness of 15 to 17 kms thins towards the centre of the basin, almost entirely replaced by a thin oceanic crust of recent creation. The rise of the mantle layer in the rift areas is clearly observed, reaching 5.8 km on the active axis and 7.3 km on the abandoned axis. A deepening was observed towards the continental zone which corresponds to the margins of the Gulf of California.
The results of this study provide valuable insights into the geological structure and thickness of the oceanic and continental crusts in the Farallon Basin, contributing to our understanding of this significant oceanic basin. However, for precise quantitative results from a particular study, it would be necessary to consult dedicated geological research articles or USGS reports focusing on the Farallon Basin seismic and gravimetric analyses.
The study utilized technology such as seismic reflection, gravimetric methods, and data processing software to investigate the oceanic and continental crusts in the Farallon Basin, thereby advancing the field of environmental-science and climate-change research, as changes in earth's crustal structure can influence global climate patterns. Furthermore, the findings from this study, particularly concerning the thickness and composition of the oceanic and continental crust, can be interpreted using data-and-cloud-computing tools to better understand the geological makeup of other oceanic basins and its implications on climate and environmental science.
