نوع مقاله : مقاله پژوهشی
نویسندگان
1 مؤسسه ژئوفیزیک دانشگاه تهران
2 محقق پسا دکترا
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسنده [English]
The first step in modeling the sediment basement depth through available Bouguer anomalies is to remove the gravity effect of the Moho relief. This effect is computed by discretizing the model space between the ground surface and Moho discontinuity. TO compute the gravity effect of model space, the quad tree mesh is applied to mesh the ground surface. Then the depth of the center of each cell of quad tree mesh to the Moho is interpolated. The gravity effect of each cell that is now actually a rectangular prism is compute through relevant equation. At last the gravity effects of all these rectangular prisms represent the gravity effect of the model space. Subtracting the gravity effect of the model space from Bouguer anomalies, the Moho-free Bouguer anomalies are obtained.
The relief of the basement in the survey area is estimated by inverting the Moho-free Bouguer anomalies through the least-square minimization method that is available through a python library which is called Scipy.
Our modeling results indicate an only 100 kg/m3 density contrast between the crust and the upper mantle is sufficient to provide a basement depth. This is interpreted as high density and mafic affinity of the lower crust beneath the Zagros collision zone due to the eclogite in its deep part. Alternatively, the cratonic core of Zagros keel has a small density leading to only a 100 kg/m3 density contrast between the lower crust and the uppermost lithospheric mantle.
Modeling the basement using gravity and magnetic data has been well documented. Different approaches such as Bouguer slab, power spectrum analysis, fast Fourier transform, and linear and non-linear inversion are considered for estimating the depth to the Moho boundary.
The Zagros sedimentary basin is studied by many researchers (e.g. Molinaro et al. 2005; Sherkati et al. 2006; Casciello et al. 2009; Paul et al. 2010; Nissen et al. 2011) but still there is no reliable estimate for the thickness of the sedimentary cover. Due to the thickness of the sediments and the presence of evaporitic layers, the relief of the basement has not been estimated through seismic images properly.
The depth of the basement in other sedimentary basins of Iran as well as the Zagros is not clear and the only estimate for the depth of the basement comes from estimates of the total stratigraphic thickness.
Gravity data modeling is an effective tool for modeling basement relief (Bott 1960; Fedi et al.
2012 ; Feng et al. 2018; Florio 2020; Mousavi and Ardestani, 2023; Ardestani et al. 2024).
The depth of the magnetic basement is derived and published by Teknik and Ghods, 2017). They calculated the depth of the magnetic basement by applying a fractal spectral method to the aeromagnetic map of Iran. The derived depth of the magnetic basement is in the range of 7–16 km in the Zagros (Teknik and Ghods, 2017).
The isostatic constraints (Bastos et al., 2020) or anomalies (Salem et al. 2014) are also considered for gravity inversion in regional scales.
This study presents an automated inversion methodology for modeling the Basement depth. A dense ground-based gravity data set of the Zagros is utilized in modeling. The derived basement depth is discussed for consistency with previous geophysical basement depths of the Zagros collision zone.
کلیدواژهها [English]
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