Curie Point Depth Estimates from Aeromagnetic Data from Death Valley and Surrounding Regions, California

Abstract

Aeromagnetic data were analyzed to determine the Curie point depth (CPD) by power density spectral and threedimensional inversion methods within and surrounding Death Valley in southern California. We calculated the CPD for 0.5°r egions using 2D power density spectral methods and found that the CPDs varied between 8 and 17 km. However, the 0.5°region may average areas that include shallow and deep CPDs, and because of this limitation, we used the 3D inversion method to determine if this method may provide better resolution of the CPDs. The final 3D model indicates that the depth to the bottom of the magnetic susceptible bodies varies between 5 and 23 km. Even though both methods produced roughly similar results, the 3D inversion method produced a higher lateral resolution of the CPDs. The shallowest CPDs occur within the central and southern Death Valley, Panamint Valley, Coso geothermal field and the Tecopa hot springs region. Deeper ([15 km) CPDs occur over outcropping granitic and Precambrian lithologies in the Panamint Range, Grapevine Mountains, Black Mountains and the Argus Range. The shallowest CPD occurs within the central Death Valley over a possible seismically imaged magma body and slightly deeper values occur within the Panamint Valley, southern Death Valley and Tecopa Hot Springs. The shallow CPD values suggest that partially molten material may also be found in these latter regions. The CPD computed heat flow values for the region suggest that the entire area has high heat flow values ([100 mW m -2 ), on the other hand, locally extremely high values ([200 mW m -2 ) occur within the Panamint Valley, the southern and central Death Valley and Tecopa Hot Springs region. These locally high heat flow values may be related to midcrustal magma bodies; but additional geophysical experiments are needed to determine if the magma bodies exist.

Thermal perturbations beneath the incipient Okavango Rift Zone, northwest Botswana

“…Hussein et al . [] used the power spectral analysis method to estimate CPD from magnetic data covering the Death Valley in the Western U.S. and showed that the maximum depth of the imaged anomaly source is approximately one third to one fourth of the width of the subregion used in the analysis. Therefore, we selected the subregion size to be 1° × 1° to ensure imaging of the Moho found at depths expected for tectonic settings such as the ORZ and surroundings.…”

“…Traditionally, the CPD is determined using 2‐D spectral methods [ Spector and Grant , ; Byerly and Stolt , ; Shuey et al ., ; Bhattacharyya and Leu , ; Okubo et al ., ; Tanaka et al ., ; Ross et al ., ; Hussein et al ., ; Arnaiz‐Rodrigues and Orihuela , ]. This method has been used successfully to determine the regional CPD values over large study areas [e.g., Blakely , ; Ross et al ., ; Hussein et al ., ; Arnaiz‐Rodrigues and Orihuela , ]. The major drawback associated with the 2‐D spectral method is the incorporation of local horizontal variations (<15 km) in the CPD values.…”

“…Hence, we chose to use the 3‐D inversion method instead of the 2‐D spectral method to overcome limitations in delineating smaller‐scale variations in the CPDs as suggested in Hussein et al . [].…”

“…[] for the estimation of the thickness of the crust beneath the ORZ and the surroundings. This method has been widely used for both magnetic and gravity data [ Tselentis et al ., ; Maus and Dimri , ; Maden , ; Hussein et al ., ]. To apply the 2‐D radial‐power spectrum method, a regional gravity field consisting of a first‐order polynomial surface was removed from the Bouguer gravity data to produce a residual gravity anomaly.…”

“…The sparse distribution of boreholes and their limited depth (<2 km) restrict mapping of the thermal structure of the lithosphere to only low horizontal spatial resolution and a few kilometers depth. Alternatively, estimates of temperature variations of the lithosphere can be obtained from silica thermometry of thermal waters [e.g., Chandrajith et al ., ], magnetotelluric (MT) measurements [e.g., Muller et al ., ], seismic velocity data [e.g., Furlong et al ., ], mantle xenoliths [e.g., Begg et al ., ], or magnetic data using two‐dimensional (2‐D) power‐density spectrum analysis and three‐dimensional (3‐D) inversion [e.g., Hussein et al ., ].…”