A distant magmatic source for Cretaceous karst bauxites of Southern Apennines (Italy), revealed through SHRIMP zircon age dating

Abstract

Terra Nova, 24, 326–332, 2012 Abstract Karst bauxites occur at a Late Cretaceous hiatus on a Bahamian‐type platform in Southern Apennines, Italy. In contrast to the well‐defined stratigraphic context, their origin remains controversial. Detrital zircon grains preserve textures and Th/U ratios consistent with crystallization from a melt, occasionally around older cores. U‐Pb isotopic data, collected using SHRIMP II, record several age populations. The youngest (∼90 Ma) falls into the age interval of bauxite formation as defined by stratigraphic criteria. The zircons must therefore be derived from a contemporary Cretaceous volcanic source. The older zircons may be interpreted as xenocrysts associated with the Cretaceous magmas or derived from different sources. Because the bauxite occurs on a isolated carbonate platform, the grains must come from far away sources, most probably transported by wind. The age, palaeogeography and inferred Cretaceous wind pattern are consistent with a prevailing origin from the Dinaric and Carpatho‐Balkan orogenic belts, with its Cretaceous bimodal volcanism.

Geochemical Characterization of Bauxite Deposits from the Abruzzi Mining District (Italy)

“…To better constrain the analogies and differences between the Abruzzi bauxites and several others from the Mediterranean area, their compositions have been plotted in the whole rock Al 2 O 3 -SiO 2 -Fe 2 O 3 (t) ternary plot [5] (Figure 10) This hypothesis was confirmed by the dating of zircons contained in Matese bauxite [9], which in part resulted to have Cretaceous ages (ca. 90 Ma) as the host bauxites, finally testifying that part of the source material consisted of pyroclastic ashes derived from a volcanism coeval with the formation of bauxites [9].…”

“…During Late Aptian-Coniacian till Late Cretaceous, the ACP experienced repeated and long-lasting sub-aerial emersions, locally marked by bauxite deposits [7,8,13,23]. The various mid-upper Cretaceous stratigraphic gaps are comprised in a wide time-span, thus supporting the presence of a complex, tectonically controlled paleotopography and the long-lived exposure of some sectors of the ACP [9,18,23]. The sub-aerial exposures resulted in an intense karstification, followed by bauxite deposition [8,10,24,25].…”

“…90 Ma) as the host bauxites, finally testifying that part of the source material consisted of pyroclastic ashes derived from a volcanism coeval with the formation of bauxites [9]. At the same time, the additional occurrence of zircons with Pan-African ages do not exclude that part of the parent material consisted of eolian sands carried by winds from the African craton, in a similar way to the modern Saharan eolian dust, which is transported to great distances in Europe and also in North America [69].…”

“…The main bauxite horizons in Central and Southern Apennines are Aptian to Turonian in age, and prevailingly boehmitic [6][7][8][9][10][11]. Despite their low economic value, these bauxites can be considered as a model analogue for other, far more economic karst bauxite deposits in the world.…”

Mineralogy, Geochemistry and Stable Isotope Studies of the Dopolan Bauxite Deposit, Zagros Mountain, Iran

“…Karst bauxite deposits from the Mediterranean region and other worldwide bauxite formations have been investigated by a number of authors [2][3][4][5][6][7][8][9][10][11]. Karst bauxite genesis is related to paleo-weathering products derived from different rocks types including carbonate rocks, marl, volcanic and magmatic rocks [12][13][14][15][16][17].…”