تعیین سن، منشا و جایگاه تکتونیکی توده‌های نفوذی جنوب سبزوار

In this study, we investigate the geochemical evolution and the age of intrusive rocks from central part of the magmatic arc of the northeastern iran in the south of sabzevar (khorasan razavi province). the geochemical evidences point to magmatism related to volcanic arc and subduction zone. the intrusive rocks vary in composition from granite to diorite and gabbro. based on mineralogy and the high values of magnetic susceptibility [( > 400) × 10-5 si], the intrusive rocks are classified as magnetite-series of oxidized i-type granitoid. chemically, they are meta to per-aluminous, enriched in lile (k, th and rb) and depleted in hfse (nb, p and ti) and belong to tholeiitic series. low (la/yb)n, low sr/y ratios and the negative anomaly of eu indicate a classic island arc type magmatism. trace elements behavior in acidic and intermediate intrusive rocks show nearly flat pattern (la/smpm =0.97-2.57) and lie outside the garnet stability field. thus, the source rocks should not be eclogite or garnet amphibolite. the geochemical signature of rare and trace elements suggests derivation from melting under relatively low pressure condition (shallow depth). the results of u-pb zircon dating of the studied are 97-100 ma (mid-cretaceous time). the initial 87sr/86sr ratios and the initial ?nd are 0.7049 and +4.54, respectively.