کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4700882 1637749 2007 17 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
He, Sr, Nd, and Pb isotopic constraints on the origin of the Marquesas and other linear volcanic chains
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
He, Sr, Nd, and Pb isotopic constraints on the origin of the Marquesas and other linear volcanic chains
چکیده انگلیسی
The classic hotspot hypothesis [Morgan, W. J., 1971. Convection plumes in the lower mantle. Nature 230, 42-43], which posits that linear volcanic chains are traces of fixed plumes in the mantle on moving lithospheric plates, was instrumental in elevating the plate tectonics paradigm in the 1960s into a modern Earth Science theory. The hypothesis itself, however, remains conjectural because many of its predictions, particularly the simple age-progressive type of volcanism, are not observed in many linear volcanic chains. As an alternative explanation, it is proposed that linear volcanic chains are formed through magmatism along pre-existing lines of weakness such as transform zones and old sutures, or along cracks created by stresses on lithospheric plates. The Marquesas linear volcanic chain in south-central Pacific has geologic features that are consistent with some of the predictions of both hypotheses. To better constrain the origin of this volcanic chain, we collected major and trace element and Sr, Nd, Pb, and He isotopic data from several Marquesan lavas. Our new analyses combined with literature data classify the samples into the well established tholeiitic to mildly alkalic, low 87Sr/86Sr, high 143Nd/144Nd, shield-building volcanic phase lava group and highly alkalic, high 87Sr/86Sr, low 143Nd/144Nd, post-shield phase group. Lead isotopes show generally higher 206Pb/204Pb ratios and suggest evidence of crustal assimilation for the shield-building phase lavas, consistent with the argument that the shield-building phase volcanism has a lithospheric source component. On the other hand, post-shield phase lavas that are predicted to represent the true composition of the mantle source by the hotspot hypothesis have higher 3He/4He ratios and these are coupled to other geochemical tracers. Thus our results show that the Marquesas volcanic chain, similar to many other linear volcanic chains, has a high 3He/4He component in its mantle source. The presence of such a distinct source component cannot be easily explained by dispersed upper mantle heterogeneities, but provides a powerful constraint for the hotspot origin of many linear volcanic chains.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemical Geology - Volume 240, Issues 3–4, 15 June 2007, Pages 205-221
نویسندگان
, , ,