Tetrad effects and fine structures of REE abundance patterns of granitic and rhyolitic rocks: ICP-AES determinations of REE and Y in eight GSJ reference rocks.

Abstract

All fourteen REE and Y have been determined for eight GSJ reference rocks including granitic and rhyolitic samples by ICP-AES with a preconcentration method. The two rhyolites (JR-1 and JR-2) and one granite (JG-2) exhibit convex tetrad effects of the M-type even in their chondrite-normalized REE patterns. Their tetrad effects, however, are modified from ideal ones by some step-like variations in their abundances from Tm to Lu. Similar step-like irregularities are seen commonly in chondrite-normalized patterns of other samples: granodiorites (JG-1, JG-la, and JG-3), a fresh water lake sediment (JLk-1), and an alkali basalt (JB-1). We normalized the REE analyses for JR-1, JR-2, and JG-2 by those for JB-1, and then found that they clearly indicate quite regular convex tetrad effects of the M-type without apparent irregu larities in heavy REE. The other samples, when similarly normalized by JB-1, also display analogous but less marked convex tetrad effects except for JG-3. Our present results are strong evidence for the tetrad effect in magmatic processes relevant to granitic and rhyolitic rocks formations. There are common chemical characteristics among JG-2, JR-l, and JR-2: (1) large negative Eu anomalies, and (2) rather high F contents of about 1,000 ppm. The chemical characteristics and the theoretical basis of tetrad effects may suggest that the granitic and rhyolitic rocks with the convex tetrad effects of the M-type are residual silicate melts having partitioned REE with fluids in late stages of differentiation processes. The basalt-normalization appears to be so effective for extracting tetrad effects of granitic and rhyolitic rocks. It filters off the REE characteristics common in magmatic products like the step-like irregularities in heavy REE abundances when normalized by chondrite. This makes it easier to identify lanthanide tetrad effects in magmatic rocks.

Thermochemical parameters for solution of lanthanide(III) ethylsulphate and trichloride hydrate series: Tetrad effects and hydration change in aqua Ln3+ ion series.

“…Hence OGr is more important than LHr in the discussion of tetrad effects in REE pat terns for geochemical samples (Kawabe, 1995;Kawabe et al, 1998). Since OGr = AHr T OSr, the tetrad effect in iHr is not exactly the same as that in AGr unless ASr is totally free from the tet rad effect (Kawabe, 1995). Attention should also be paid to a possible tetrad effect in AS,.…”

“…Lanthanide tetrad effects are observed in REE patterns for various geochemical samples (Masuda and Ikeuchi, 1979;Masuda et al, 1987;Akagi et al, 1993;Kawabe, 1995;Bau, 1996;Kawabe et al, 1998). The refined spin-pairing energy theory (RSPET) by Jorgensen (1979) is a theoretical ba sis of lanthanide tetrad effects.…”

Petrogenesis of early Yanshanian highly evolved granites in the Longyuanba area, southern Jiangxi Province: Evidence from zircon U-Pb dating, Hf-O isotope and whole-rock geochemistry

“…Thus, the weathering cannot be used to explain the genesis of the REE tetrad effects in the granites. At present most workers agree that the tetrad REE pattern of highly evolved granites might have resulted from the fluid/melt interaction under open-system conditions at a late stage of magmatic evolution [51][52][53]. The granites that crystallized from the melts have "M" type REE patterns, whereas co-existing interactive fluids (external fluids and post-magmatic unmixing fluids) show "W" type REE patterns.…”

“…Recently, Zhao et al [46] reported an alkaline syenite with composite M-and W-type REE patterns. Now the REE tetrad effect can be considered to be caused by [47]: (1) fractionated accessory minerals containing different REE contents at a late stage of magmatic evolution [48,49], (2) the weathering near the surface [45,50], (3) fluids-melts interaction in the open system [51][52][53], and (4) granites suffering alteration by exsolved fluids separated from magmas with fluids-melts immiscibility [54]. Rayleigh model-based calculation suggests that REE tetrad effect stemming from the fractionation of accessory minerals needs an unreasonable accessory mineral assemblage [52,55].…”

In-pattern tetrad effect-like variation, so far overlooked, but obviously observed in REE abundances of REE minerals.

“…A range of samples showing the fine structure in their REE patterns includes seawater, groundwater, leucogranite, kimuraite, marine sediments, Okuro deposits, rhyolite and shale. Many of the samples occur being associated with water phase, and wa ter seems to be primarily important to the effect (Masuda and Ikeuchi, 1979;Masuda et al, 1987;Masuda and Akagi, 1989;Hidaka et al, 1992;Akagi et al, 1993;Liu et al, 1993;Kawabe, 1995Kawabe, , 1996.…”