U-Pb geochronology, petrogenesis and tectonomagmatic evolution of uppermost Neoproterozoic- lower Cambrian intrusive rocks in Kaboodan area, NE of Iran

摘要

This study presents new U-Pb zircons ages, trace element geochemistry, and Nd and Sr isotope compositions of intrusive rocks from the Kaboodan area, NE of Iran. The Kaboodan area embraces two geologically distinct zones of Taknar and Sabzevar. All intrusive rocks can be divided into two age groups, uppermost Neoproterozoic and Cretaceous, respectively. Uppermost Neoproterozoic and lower Cambrian plutonic rocks are found in the Taknar Zone section and include different mafic and felsic types. Mafic bodies include gabbroic- dioritic lithologies with ages around 552?545?Ma and low Sr-87/Sr-86(i) (0.7032?0.7041) and high ?Nd-t (+4.82 to +8.49) values. These lithologies may have been generated by shallow depth partial melting of a spinel peridotite mantle source in an arc setting. Felsic intrusive rocks show two distinct U-Pb ages. The older granitoids (ONG) have uppermost Neoproterozoic age as the mafic rocks (549?547?Ma) while younger samples (YCG) have been formed ca. 20 m.y. later in the lower Cambrian (531?528?Ma). The ONG and YCG rocks show completely different geochemical characteristics. The ONG samples exhibit I-type granitoid properties with lower Sr-87/Sr-86(i) (0.704?0.707) and positive ?Nd-t (+2.49 to +3.68) values, while YCG rocks display S-type granitoid signatures with higher Sr-87/Sr-86(i) (0.710?0.714) and negative ?Nd-t (?4.54 and ?6.95). The field relations, Sr-Nd isotope systematics, and geochemical variations indicate the interaction of the uppermost Neoproterozoic mafic and ONG units. The ONG melts were originated from the partial melting of mantle-derived material in a subduction zone. The trace element composition of the YCG samples is similar to within plate granitoids and was generated by the melting of meta-sedimentary crustal rocks during syn- to post-collisional events indicative of the end of Cadomian subduction at ? 530?Ma.