کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4406794 1307320 2016 17 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Petrogenesis of Miocene alkaline volcanic suites from western Bohemia: whole rock geochemistry and Sr–Nd–Pb isotopic signatures
ترجمه فارسی عنوان
پتروژنز میوسن مجموعه های آتشفشانی قلیایی از Bohemia غربی: ژئوشیمی سنگ کل و نشانه های ایزوتوپی Sr–Nd–Pb
کلمات کلیدی
توده غیرمتعارف ؛ آتشفشان قلیایی سنوزوئیک؛ سنین K-AR؛ ژئوشیمی؛ ایزوتوپ Sr–Nd–Pb
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
چکیده انگلیسی

The Mid to Late Miocene intraplate alkaline volcanic suites of western Bohemia are relict of the intensive voluminous volcanism accompanied by large-scale uplift and doming. The association with the uplift of the NE flank of the Cheb–Domažlice Graben (CDG) is uncertain in view of the mostly transpressional tectonics of the graben. The volcanism is most probably of the Ohře/Eger Rift off-rift settings. Two cogenetic volcanic suites have been recognised: (i) silica-saturated to oversaturated consisting of olivine basalt–trachybasalt-(basaltic) trachyandesite–trachyte–rhyolite (13.5 to 10.2 Ma) and (ii) silica-undersaturated (significantly Ne-normative) (melilite-bearing) olivine nephelinite–basanite–tephrite (18.3 to 6.25 Ma). A common mantle source is suggested by similar primitive mantle-normalised incompatible element patterns and Sr–Nd–Pb isotopic compositions for the assumed near-primary mantle-derived compositions of both suites, i.e., olivine basalt and olivine nephelinite. Apparently, they were generated by different degrees of partial melting of a common mantle source, with garnet, olivine and clinopyroxene in the residuum. Negative Rb and K anomalies indicate a residual K-phase (amphibole/phlogopite) and melting of partly metasomatised mantle lithosphere. The evolution of the basanite–olivine basalt–trachybasalt-(basaltic) trachyandesite–trachyte–rhyolite suite suggests the presence of an assimilation–fractional crystallization process (AFC). Substantial fractionation of olivine, clinopyroxene, Fe–Ti oxide, plagioclase/alkali feldspar and apatite accompanied by a significant assimilation of magma en route by crustal material is most evident in evolved member, namely, trachytes and rhyolites. The magmas were probably sourced by both sub-lithospheric and lithospheric partly metasomatised mantle. The evolution of the (melilite-bearing) olivine nephelinite–basanite–tephrite suite is less clear because of its limited extent. Parental magma of both these rock suites is inferred to have originated by low-degree melting of the mantle source initiated at ca. 18 Ma and reflects mixing of asthenosphere-derived melts with isotopically enriched lithospheric melts. The older Oligocene alkaline rocks (29–26 Ma) occur within the Cheb–Domažlice Graben (CDG) locally but are significant in the closely adjacent neighbouring western Ohře Rift. The Sr–Nd–Pb isotopic composition of primitive volcanic rocks of both suites is similar to that of the European Asthenospheric Reservoir (EAR). Initial Pb isotopic data plot partly above the northern hemisphere reference line at radiogenic 206Pb/204Pb ratios of ∼19 to 20, and indicate the presence of a Variscan crustal component in the source.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemie der Erde - Geochemistry - Volume 76, Issue 1, March 2016, Pages 77–93
نویسندگان
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