Geochemical and isotopic evidence from the Agaçören Igneous Association in central Anatolia-Turkey indicates that this suite of calc-alkaline granitic rocks have undergone crustal homogenization during regional metamorphic and related magmatic events. Whole-rock chemical and Sr-Nd isotopic data of the granitoids reveal crustal affinity with an earlier subduction component. Zircons show inherited cores and subsequent magmatic overgrowths. The laser ablation ICP-MS 206 Pb/ 238 U zircon ages are determined as 84.1 ± 1.0 Ma for the biotite-muscovite granite, 82.3 ? 0.8/-1.1 Ma for the hornblende-biotite granite, 79.1 ? 2.1/-1.5 Ma for the granite porphyry dyke, 75.0 ? 1.0/-1.0 Ma for the alkali feldspar dyke, and 73.6 ± 0.4 Ma for the monzonite. This is interpreted as continuous magma generation, possibly from heterogeneous sources, from ca. 84 to 74 Ma during the closure of the northern branch of the Neotethyan Ocean. The oldest granitoids (84-82 Ma) were probably formed due to crustal thickening after obduction of the MORB-type oceanic crust onto the Tauride-Anatolide microplate. The younger granitoids are interpreted to be related to the subsequent post-collisional extension after lithospheric delamination. Combination of the laser ablation ICP-MS zircon Lu-Hf isotope data with the U-Pb ages of inherited cores suggests that Cretaceous granitoids formed by melting of heterogeneous crustal protoliths, which results in significant variation in eHf (t) data (from -12.9 to ?2.2). These protoliths were probably composed of reworked Early Proterozoic crust, minor juvenile Late Proterozoic magmatic components, and Paleozoic to pre-Late Cretaceous recycled crustal material. Moreover, the Late Cretaceous zircon domains of the different granitoids are characterized by a crustal signature, with a relatively restricted zircon eHf (t) data ranging from -4.1 to -8.8. This variation is only about twice the reproducibility (ca. ±1 eHf) of the data, but Communicated by J. Hoefs.
Electronic supplementary materialThe online version of this article (much smaller than the isotope variability of inherited zircons. Our preferred interpretation is effective isotopic homogenization of the heterogeneous central Anatolian crust during the Late Cretaceous high-grade metamorphic and magmatic events, a process that we propose to be relevant for other active continental margins.
SUMMARYA finite element method is given to obtain the solution in terms of velocity and induced magnetic field for the steady M H D (magnetohydrodynamic) flow through a rectangular pipe having arbitrarily conducting walls. Linear and then quadratic approximations have been taken for both velocity and magnetic field for comparison and it is found that with the quadratic approximation it is possible to increase the conductivity and Hartmann number M ( M < 100). A special solution procedure has been used for the resulting block tridiagonal system of equations. Computations have been carried out for several values of Hartmann number ( 5 < M < 100) and wall conductivity. It is also found that, if the wall conductivity increases, the flux decreases. The same is the effect of increasing the Hartmann number. Selected graphs are given showing the behaviour of the velocity field and induced magnetic field.
TNTRODIJCTIONThe problem of magnetohydrodynamic flow through channels has become important because of several engineering applications such as designing of the cooling system for a nuclear reactor, M HD flowmeters, M HD generators, blood flow measurements, etc. In general, the problems of MHD flow are extremely complex owing to the coupling of the equations of fluid mechanics and electrodynamics, and analytic solutions are out of the question. The exact solutions are, therefore, available only for some simple geometries subject to simple boundary conditions.'. In most of the studies, the walls have been taken as either non-conducting or perfectly conducting, or a combination of the two.39 Recently, Singh and Lal"' have obtained numerical solutions of steady-state MHD flows through pipes of various cross-sections using either a finite difference or finite element method (FEM). But with linear approximation in the finite element method they could obtain results at most up to M = 5.The present paper is an extension of the above studies to the case of arbitrary wall conductivity, high Hartmann number (up to 100) by using the FEM with linear and then quadratic approximations for the velocity and magnetic fields. A variational principle for the problem has been obtained and then the Ritz FEM has been applied taking linear and quadratic elements. The results are obtained for various values of wall conductivity and Hartmann number. The flux has also been calculated for each case.
BASIC EQUATIONSThe fluid is taken as viscous, incompressible and having uniform electrical conductivity. It is driven down a rectangular pipe, with arbitrary wall conductivity, by means of a constant applied
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