The U–Pb age calculation and concordia plots were processed using ISOPLOT 3.0 . The common Pb correction process was performed according to the method proposed by Andersen . A late Neoarchean intra-oceanic arc along the northwestern margin of Eastern Block , North China Craton, provides important insights into the nature of Archean mantle sources and crust-mantle geodynamics. The Pingquan Complex and the entire Northern Hebei Province are located in the middle part caribbeancupid com of the arc, and overlap the northern extent of the trans-North China Orogen. The 16 ingots matched to the Zn-Pb-Cu deposit at Kipushi all have lead isotopic ratios tightly clustered around 18.05 in 206Pb/204Pb, 15.64 in 207Pb/204Pb, and 37.64 in 208Pb/204Pb. Although lead isotopic ratios on geological ores from Kipushi are tightly clustered and non-radiogenic , the ratios of these ingots cluster even more tightly within the isotopic space of Kipushi ore samples .
Sciencing_Icons_Minerals & Rocks Minerals & Rocks
All were found on the Zambian side of the border with DRC . Logged concentrations of chalcophile and siderophile elements from samples in this paper, Rademakers et al. , and Stephens et al. . Ingots are grouped by their determined isotopic provenance, and the experimental “X” ingot is represented by the “Kansanshi” category since we know its specific provenance. Ingot data is compared to geological ore data from the Central African Copperbelt.
Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Application of in situ analysis (Laser-Ablation ICP-MS) within single mineral grains in faults have shown that the Rb-Sr method can be used to decipher episodes of fault movement. For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially constant. This is known because decay constants measured by different techniques give consistent values within analytical errors and the ages of the same materials are consistent from one method to another. It is not affected by external factors such as temperature, pressure, chemical environment, or presence of a magnetic or electric field.
It has revolutionised age dating using the U-Pb isotopic system. Using the SHRIMP, selected areas of growth on single grains of zircon, baddeleyite, sphene, rutile and monazite can be accurately dated . This technique not only dates older mineral cores , but also later magmatic and/or metamorphic overgrowths so that it unravels the entire geological history of a single mineral grain.
Fossils give us this global chronostratigraphic time scale on Earth. On other solid-surfaced worlds — which I’ll call “planets” for brevity, even though I’m including moons and asteroids — we haven’t yet found a single fossil. Something else must serve to establish a relative time sequence. Become A MemberMembership programs for explorers of all ages. CFCs and nitrate concentrations were measured between June 1989 and January 1990 on a section of the Delmarva Peninsula, in the Fairmount watershed. Ground-water dating reveals a pattern of high nitrate concentrations moving slowly toward the estuary.
One interesting trend also observed in this dataset is the distinct change in copper source for HXR ingots as compared to the HIH ingot assemblage. 15 of 18 HIH ingots source to the Copperbelt while only 3 source to Kipushi. For HXR ingots 4 of 18 source to the Copperbelt and 13 of 18 to Kipushi. We will further consider the archaeological implications of these data in a companion article. All three samples collected from the lower plate of the Yagan-Onch Hayrhan metamorphic core complex (06OH1-2; 06OH1-1; 06OH2-7) have Late Devonian igneous protoliths.
Therefore, zircon in situ Hf isotope research has become an important means to explain the crustal evolution and trace the magma source area. We have analyzed 29 of the approximately 94 reported HIH and HXR ingots from Zambia and Zimbabwe and conclude that 28 of 29 derive from the Copperbelt, including 16 from the distinct Kipushi deposit within the Copperbelt . This work and our previous study show that Copperbelt copper was transported to southwest Zambia by the sixth or seventh century cal CE and to northwest Botswana by the eighth century cal CE.
Getting the Lead Out
Both the mesosome and leucosome exhibited evidence of deformation, though it is much more prevalent in the mesosome. The leucosome appears undeformed in outcrop but shows evidence in thin section for deformation at temperatures approaching 600 °C which is overprinted by lower temperature deformation fabrics . 07TH-12A is a sample of quartzo-feldspathic gneiss with a similar mineral composition to 07TH-10A but is finer grained; most K-feldspar grains are less than 1 mm in length, though megacrysts up to 0.5 cm in length were observed. This sample was collected in the center of the subregion of Tavan Har where greenschist-amphibolite grade gneisses are mapped . Sample 07TH-12A was taken within a body of granitic gneiss with a foliation that varies in intensity and orientation.
This plot also shows that these samples have lower concentrations of Co+Ni than samples attributed to the Copperbelt group . The 16 ingots matching Kipushi also have strikingly similar chemical and isotopic data to three large HH ingots from the Upemba Depression that were analyzed by Rakemakers et al. ; these too clearly derive from Kipushi ores. Furthermore, the formation of igneous and metamorphosed rocks involves melting, crystallization, and/or recrystallization of minerals, which could cause the distributions of the various elements and their isotopes to be altered.
At left, a zircon crystal in a thin section cut from granite. At right, the crystalline structure of a zircon. In the magma, crystals of zirconium silicate , as well as other crystals, form. These zircon crystals are tiny — just a tenth of a millimeter long — but they are the key to uranium-lead dating.
These zircon characteristics combined with the identification of primary igneous microstructures, strongly suggest that sample 07TH-10A has an igneous protolith that crystallized during the early Carboniferous and was later modified during the late Carboniferous . Figure 5.Photomicrographs, cross polarized light . Mineral abbreviations follow Whitney and Evans . Sample 07TH-10A is an augen gneiss defined in outcrop by pink K-feldspar megacrysts up to a centimeter in length. This sample was taken from the southeastern flank of the sub-region of Tavan Har where greenschist–amphibolite-grade gneisses are mapped .
Kimberlite is a unique ultramafic rock derived from either the lithosphere or sub-lithospheric mantle (Mitchell, 1986, Mitchell, 1995, Woolley et al., 1996) and can provide invaluable information about the composition and structure of that lithosphere . However, two important problems hamper the determination of kimberlite genesis. Firstly, kimberlite, by definition, contains abundant, variably-sized crustal and mantle xenoliths , which makes it difficult to determine the initial isotopic composition of the kimberlitic magma.