Petrogenesis of Mesozoic Potassic Magmatism of the Central Aldan: A Sr-Nd Isotopic and Geodynamic Model

Abstract

The Mesozoic potassic magmatism of the Central Aldan (southeastern Siberian Platform) consists of volcanic and intrusive rocks of diverse composition, including highly potassic alkaline (leucitites, phonolites, lamproites, phologopite pyroxenites, shonkinites, feldspathoid syenites) and moderately alkaline (trachytes, gabbros, monzonites, syenites) rocks. They have a different level of alkalinity, as well as special petrochemistry and mineralogy. In addition, the distribution of incongruent elements in the rocks practically is identical: they are enriched in large-ion lithophile elements (LILE) and light rare-earth elements (LREE) and impoverished in high-field strength elements (HFSE) and Ti0 2 . The Sr-and Nd-isotopic ratios in the potassic rocks of the Central Aldan vary considerably. They have low values of e Nd (T) (-10.2 to -22.9) and (87S r /86Sr) 0 = 0.70480 to 0.70723; that is, they differ from Chondritic Uniform Reservoir (CHUR) values in the field of an enriched mantle source of enriched mantle I (EMI) type and ancient lower crust. The wide variations in trace-element ratios (Ce/Y, Zr/Nb, Ba/La), like the variations in e Nd and e Sr , indicate a heterogeneous mantle source.

40Ar/39Ar Geochronology and New Mineralogical and Geochemical Data from Lamprophyres of Chompolo Field (South Yakutia, Russia)

“…This enriched mantle source of the Aldan shield could have a complex history that includes a stage of metasomatic enrichment that is related to the tectonic history of the region. Geochemical signatures similar to Chompolo rocks are characteristic for the Mesozoic potassic alkaline rocks of the Aldan shield [10,11,148]. As a result of the magmatic activity in the interval of J 1 -K 1 , several massifs of complex composition were formed (the Ryabinoviy, Yakokut, Tommot, Zametniy, Orto-Salaa, and Robkiy), as well as dyke swarms and diatremes (explosion pipes) in the north-central part of the Aldan shield (see large square, Figure 1) [10,12].…”

“…According to their significantly unradiogenic Nd isotope composition (E t = −20) and moderately radiogenic Sr isotope composition (0.7077, 0.7095), the source of the Chompolo rocks corresponds to an enriched mantle reservoir that has been isolated from the convective asthenosphere for a long time prior to melt formation. The unradiogenic Nd (E t = down to −25) and moderately radiogenic Sr isotopic compositions (0.70499-0.70822) are typical of Aldan shield alkaline complexes like Tommot, Lomam, Ryabinoviy, Yakokut, Murun, Bilibinskiy, and Khani [10,11,121,122]. Close Sr-Nd isotopic ratios of the Chompolo rocks and "Aldan lamproites", including aforementioned alkaline complexes, evidenced that they derived from the same mantle reservoir.…”

“…Relevant characteristics provide evidence about the complex geological history of the region and suggest the formation of a mantle source of K-rich melts long before the melts' emplacement [8,9]. The rocks of Aldan alkaline province of Mesozoic magmatism, which formed in the ancient cratonic setting, also belong to the aforementioned category and demonstrate that geochemical signatures of ancient subduction processes were involved in producing the ancient source of potassic magmatism [10,11].…”

“…The Mesozoic stage was characterized by a wide diversity of alkaline rocks with ultramafic to silica-rich compositions, which form large massifs of complex composition, ring volcanic-plutonic complexes, dykes, diatremes, subvolcanic bodies, laccoliths. It is believed that the stage of Mesozoic igneous activity was triggered by the global tectonic events related to the final closure of the Mongol-Okhotsk Ocean south of the Aldan shield [10,36].…”

U-Pb Age and geochemistry of zircons from xenoliths of the V. Grib kimberlitic pipe, Arkhangelsk diamond province

“…Deep seated xenoliths transported by kimberlites are the main reliable source of information on the composition and age of the lower crust and lithos pheric mantle for the northern margin of the East European Platform [1]. The high productive Middle Paleozoic V. Grib pipe in the Arkhangelsk diamond province is distinguished by the high concentration and variability of xenoliths with prevalence of mantle peridotites and eclogites, as well as lower crustal gran ulites with a total portion of ~80% from all xenoliths from this pipe [2].…”