Abstract: We measured the major and trace element contents
and Rb-Sr isotopic compositions of 12 tektites from the Maoming
area, Guandong province (south China). All the samples studied are
splash-form tektites which show pitted or grooved surfaces with
schlieren structures on some surfaces. The trace element ratios Ba/Rb
(avg. 4.33), Th/Sm (avg. 2.31), Sm/Sc (avg. 0.44), Th/Sc (avg. 1.01) ,
La/Sc (avg. 2.86), Th/U (avg. 7.47), Zr/Hf (avg. 46.01) and the rare
earth elements (REE) contents of tektites of this study are similar to the
average upper continental crust. From the chemical composition, it is
suggested that tektites in this study are derived from similar parental
terrestrial sedimentary deposit which may be related to post-Archean
upper crustal rocks. The tektites from the Maoming area have high
positive εSr(0) values-ranging from 176.9~190.5 which indicate that
the parental material for these tektites have similar Sr isotopic
compositions to old terrestrial sedimentary rocks and they were not
dominantly derived from recent young sediments (such as soil or
loess). The Sr isotopic data obtained by the present study support the
conclusion proposed by Blum et al. (1992)[1] that the depositional age
of sedimentary target materials is close to 170Ma (Jurassic). Mixing
calculations based on the model proposed by Ho and Chen (1996)[2]
for various amounts and combinations of target rocks indicate that the
best fit for tektites from the Maoming area is a mixture of 40% shale,
30% greywacke, 30% quartzite.
Abstract: Cenozoic basalts found in Jiangsu province of eastern
China include tholeiites and alkali basalts. The present paper analyzed
the major, trace elements, rare earth elements of these Cenozoic
basalts and combined with Sr-Nd isotopic compositions proposed by
Chen et al. (1990)[1] in the literatures to discuss the petrogenesis of
these basalts and the geochemical characteristics of the source mantle.
Based on major, trace elements and fractional crystallization model
established by Brooks and Nielsen (1982)[2] we suggest that the
basaltic magma has experienced olivine + clinopyroxene fractionation
during its evolution. The chemical compositions of basaltic rocks from
Jiangsu province indicate that these basalts may belong to the same
magmatic system. Spidergrams reveal that Cenozoic basalts from
Jiangsu province have geochemical characteristics similar to those of
ocean island basalts(OIB). The slight positive Nb and Ti anomalies
found in basaltic rocks of this study suggest the presence of Ti-bearing
minerals in the mantle source and these Ti-bearing minerals had
contributed to basaltic magma during partial melting, indicating a
metasomatic event might have occurred before the partial melting.
Based on the Sr vs. Nd isotopic ratio plots, we suggest that Jiangsu
basalts may be derived from partial melting of mantle source which
may represent two-end members mixing of DMM and EM-I. Some
Jiangsu basaltic magma may be derived from partial melting of EM-I
heated by the upwelling asthenospheric mantle or asthenospheric
diapirism.