RESUMEN
Newly discovered yellow silt widely distributed in the coastal area of south China was analyzed using diffuse reflectance spectroscopy (DRS) and laser particle size (LPS) methods in the present paper. The authors take the lead in trying to synthetically judge the depositional environment, transporting agent and forming mechanism of the yellow silt from angles of output forms of iron minerals as well as grain size distribution features of the samples chose from three representative sections and a drill core. The DRS first derivative curves show the peak height of iron minerals decreasing from hematite (565 nm) to goethite (505 and 435 nm), which reflects a relatively dry, cold climate that coincides with the aeolian loess widely distributed in the northwest China, but reverses of the fluvial and marine deposits which experienced a well hydration in humid conditions over a long period of time in study area. LPS analysis show that grain size from top to bottom of the sections and drill core are homogeneous and typical of aeolian sediments. The grain size distribution in the yellow silt is characterized by double peaks with main peak of 10-50 µm and a secondary peak of < 5 µm, similar to that of loess in northwest China but quite different from associated fluvial and marine deposits featured by unidirectional change of allocation mode of the grain size groups. Based on grain size analysis, DRS results, age range of 10-80 ka, and spatial distribution that both of the positive landforms and buried topographies in the coastal area of south China have this kind of sediments, the yellow silt is considered to represent an aeolian deposit formed during the last glacial period, which is called "loess-like deposits" in our study.
RESUMEN
With comparison of the fluorescence spectroscopy and plasma-mass spectroscopy analysis results of the Meso/Cenozoic basic rocks of SE China, the authors found that the average SiO2 content of the Mesozoic basic rocks in this area is about 50%, while that of the Cenozoic basic rocks is about 43%. The former belongs to the basic group and the later to the ultrabasic group in igneous rock classification. Cenozoic basalts, accompanied with high magnesium content and low silica-alumina component, are obviously basic or ultrabasic rocks. Distinctive difference in the content of trace elements and of REE is also presented between the Mesozoic and the Cenozoic basic rocks. Distribution models of both trace elements and REE of the Mesozoic basic rocks are similar to those of the upper crust, and the models of the Cenozoic basic rocks are like those of OIB, indicating that basic rocks of the Cenozoic and OIB should originate from the mantle while that of the Mesozoic is from the bottom part of the upper crust with relationship to the evolution of the Mesozoic crustal magma layer of this area.
RESUMEN
The Guidong composite granite body (CGB) located in the north Guangdong Province consists of numerous rock bodies formed respectively in the early and late Jurassic and early Cretaceous. Analysis of the granites of different period with X-ray fluorescence spectroscopy and plasma mass spectrometry indicates: (1) From the top of a granite body downwards, the felsic components of rock decrease, while the mafic and sigmaREE, LREE/HREE, (La/Yb)N, as well as delta Eu value increase, suggesting the material differentiation in the in-situ melting of crustal rocks and crystallisation of magma; (2) From old to young of the different period granite-massifs in the Guidong CGB, the felsic compositions totally decrease, and the mafic components, sigmaEE, LREE/HREE, (La/Yb)N, and delta Eu value increase as well, implying multiple crustal melting (remelting) events in the Mesozoic in this area; and (3) Primitive mantle-normalized spider diagram for trace elements of Guidong CGB suggests high maturity of the crust involved in the in-situ melting.
RESUMEN
The results on Xilingang pluton, mainly consisting of red beds, granites containing numerous debris of red beds and granites, obtained by X-ray fluorescence spectroscopy, plasma mass spectrometry and Raman spectroscopy show: (1) Xilingang pluton from red beds, granites containing numerous debris of red beds to granites has obvious characteristics of decreasing silicon and alkali content, and rising ignition loss, dark mineral content and oxidation index; (2) Chondrite-normalized REE distribution curves and primitive mantle-normalized spider diagram for trace elements of redbed, granites containing numerous debris of red beds and granites have a good consistency, the distribution characteristics of elements are similar to Nanling transformation-type granite; (3) The value of Raman spectrogram characteristic peak of quartz crystal in Xilingang granite decreased from the center of quartz crystal, and FWHM is steady. According to the above, the authors believe that Xilingang granite formed was related to in-situ melting of red beds and underlying strata and magma consolidation. Volatile components were discharged continuously, and oxidation index decreased gradually in the melting process. In the process of diagenesis, the top of pluton tend to be an ongoing silicon and alkali increase, while TFeO and MgO continue to migrate to bottom, and crystallization environment is a relatively closed and steady system.
RESUMEN
Red pigment of continental red-bed is known originating from the fine-particle hematite in the rocks. Advance of researches on the origin of continental red-bed demonstrates that the red pigment of red-bed originated from its diagenetic but not depositional process. The high diagenetic temperature causes the dehydration of iron hydrate to form hematite, generating the red pigment. For examining the above hypothesis, the authors of this paper designed an experiment to approach the reddening process, i.e. formation of the red pigment of continental red-bed. Black ooze sampled from the Holocene sediments of the Pearl River Delta was heated in different ways. The diffuse reflectance spectroscopy (DRS) of those heated ooze samples were detected with Perkin-Elmer Lamdba 950 ultraviolet/visible/near-infrared spectrophotometer, and moreover, red-values of the samples were calculated for determining their coloring levels. Iron in black ooze sediment is predominantly in the form of goethite. Experimental results verified that initial dehydration-temperature of goethite is about 150 degrees C, either enhancing temperature or prolonging heating time is accompanied with decreasing goethite and increasing hematite, and a positive relationship exists between red-value of samples and peak-height of hematite. The experimental results strongly support the idea of thermal origin of continental red-bed.