Canadian Journal of Earth Sciences

Geologically derived stable isotope ratios can be used as a tracer for the source of many kinds of substances, with current geochemical techniques allowing the precise determination of numerous stable isotope ratios in both natural and manmade objects. This review presents examples of the use of stable isotopes as tracers within diverse dynamic ecosystems, focusing on Sr isotopes but also including examples of Nd and Pb isotopic analysis, and reviewing the potential of this technique for a wide range of environmental research, including determining the geographic origin of food and archeological materials. Some 80 of the 92 naturally occurring elements on Earth are stable, with 54 of these having two or more stable isotopes. The fact that stable isotopes differ in mass number but not in atomic number means that the different stable isotopes of a given element differ slightly in their physicochemical behavior. The stable isotope ratios of individual elements are affected by two main factors, namely isotopic fractionation and radioactive decay. Isotope fractionation occurs during physicochemical processes when atoms of an element are involved in chemical reactions, diffusion, and transformation between solid, liquid, and gaseous phases. The degree of fractionation is generally dependent on the relative difference in mass between the stable isotopes of a given element and the temperature at which the fractionation process occurs. Light elements, such as hydrogen H , carbon C , nitrogen N , oxygen O , and sulfur S , are present in a wide variety of chemical forms and phases. These light elements have large isotopic fractionations that reflect the large relative difference in mass between their various isotopes. Radioactive decay affects certain isotopes at a steady rate, including the decay of radioactive elements into stable isotopes of other elements.

Samarium–neodymium dating

Paleogene basalts are widely distributed in the Xialiaohe Depression, which lies in the northern part of the Bohai Bay Basin, the second largest petroleum-bearing basin of China, in the northeastern part of the North China Craton. The geochemical characteristics of these basalts are quite different from that expected from magmas derived from crustal contamination or melting from a uniform asthenospheric mantle source, but is consistent with derivation from newly formed lithospheric mantle.

Combined with the geochemical character of the ESF and ODF basalts, we ascribe the abnormally low radiogenic lead isotopic composition for the Paleocene PFF basalts to newly formed lithospheric mantle that originated from recycling of delaminated thickened lithosphere in Late Mesozoic, including a lower crustal component. If you have an individual subscription to this journal, or if you have purchased this article through Pay-Per-view , you can gain access by logging in with your username and password here:.

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more radiogenic = mantle-derived lower ε. Nd. = less radiogenic = continental crust. Nd Isotopes Nd and Sr cross-plots from Franco U-Pb, Th-Pb, and Pb-​Pb isotopic ratios may be used in age dating and petrogenetic tracing of igneous​.

Paleogene basalts are widely distributed in the Xialiaohe Depression, which lies in the northern part of the Bohai Bay Basin, the second largest petroleum-bearing basin of China, in the northeastern part of the North China Craton. They display a positive correlation between [sup. The geochemical characteristics of these basalts are quite different from that expected from magmas derived from crustal contamination or melting from a uniform asthenospheric mantle source, but is consistent with derivation from newly formed lithospheric mantle.

Combined with the geochemical character of the ESF and ODF basalts, we ascribe the abnormally low radiogenic lead isotopic composition for the Paleocene PFF basalts to newly formed lithospheric mantle that originated from recycling of delaminated thickened lithosphere in Late Mesozoic, including a lower crustal component. Des basaltes datant du Paleogene sont distribues a grande echelle dans la depression d’Xialiaohe, situee dans la partie nord du bassin de la baie de Bohai.

Ce bassin constitue le deuxieme plus important bassin petrolifere de la Chine; il se situe dans la partie nord-est du craton de Chine du Nord. Les basaltes sont surtout presents dans trois formations : la Formation de Fangshenpao, datant du Paleocene, la Formation de Shahejie, datant de l’Eocene et la Formation de Dongyin, datant de l’Oligocene. La Formation de Fangshenpao est dominee par des tholeiites alors que les formations de Shahejie et de Dongyin sont caracterisees par des basaltes alcalins avec des quantites moindres de tholeiites.

Ces basaltes contiennent generalement moins d’elements lithophiles a grand rayon ionique LILE et une tres grande portion d’elements a forte liaison atomique par rapport aux basaltes d’lles oceaniques OIB , a l’exception des anomalies positives pour Ba, Sr, Eu et Ti, et ils sont caracterises par des compositions isotopiques Sr et Nd de type OIB et par une composition isotopique anormalement basse d’isotope radiogenique de plomb.

Extending In-Situ Dating to New Geochronometers: Pb-Pb, Sm-Nd, Re-Os, and LuHf

There are two stable isotopes of carbon: 12 C and 13 C, and one naturally occurring radionuclide: 14 C. The half life of 14 C is only 5, years, which is orders of magnitude shorter than the age of the Earth. Therefore, no primordial radiocarbon remains and all 14 C is cosmogenic see Section 8 for related methods.

Nd is slightly more incompatible during mantle melting than Sm. Sm parent will be enriched in"depleted” sources (i.e. MORB). (opposite to Rb/Sr system, where parent enriched in continents) Effect of LREE-rich inclusions on garnet dating.

Cara L. Donnelly, William L. To provide better constraints on the sources of the kimberlite magmas and the timing of magmatism, we have carried out in situ U—Pb dating and Sr—Nd isotopic analysis of groundmass perovskite from four of the Kuruman kimberlites Bathlaros, Elston, Helpmekaar and Zero. We also have measured the Sr-isotope composition of groundmass apatite and carbonate in several of the kimberlites, for comparison with published whole-rock isotopic data.

Attempts to date perovskite using in situ laser ablation inductively coupled plasma mass spectrometry LA-ICP-MS were hindered by extensive Pb loss, even in apparently unaltered grains, yielding anomalously young emplacement ages. The smaller sampling volume of secondary ion mass spectrometry and the ability to measure Pb, thus allowing more precise common-Pb corrections, produces concordant ages.

The results of this study suggest that alteration may disrupt the U—Pb system in perovskite. The isotopic data suggest that the Kuruman kimberlite magmas were initially derived from a deeper sub-lithospheric source region, but their distinctive compositional characteristics were imposed through assimilation, first of metasomatized sub-continental lithospheric mantle and later of crustal material, during magma ascent.

Kimberlites are rare, small-volume, potassic and volatile-rich ultramafic rocks that have been the focus of many geochemical studies. In addition to being the carriers of diamonds and mantle xenoliths, kimberlite magmas can provide insights into deep Earth processes, including the links between metasomatism and low-degree melting. However, studies of kimberlites are complicated by their hybrid nature and their common post-intrusion alteration.

High volatile contents make kimberlites particularly susceptible to weathering Mitchell, ,

SM–ND isotopic investigations of Isua supracrustals and implications for mantle evolution

Box , Beijing , P. E-mail: xieliewen mail. The advantages include high spatial resolution, high sample throughput, good precision and accuracy, and limited sample preparation. For the application of these techniques in U—Th—Pb geochronology, the main challenges involve ion counter drift, matrix differences between reference materials and samples, laser-induced downhole elemental fractionation and common lead corrections. We review recent efforts to improve spatial resolution, calibrate ion counter drift, and correct for common lead contamination, elemental fractionation and matrix mismatching.

To provide better constraints on the sources of the kimberlite magmas and the timing of magmatism, we have carried out in situ U–Pb dating and Sr–Nd isotopic​.

GSA Bulletin ; : — The Wufeng and Longmaxi organic-rich shales host the largest shale gas plays in China. The fractures hosted in the Longmaxi Formation are mineralized with quartz as the predominant fracture cement, and calcite as an intracementation phase postdating the earlier quartz cement. In contrast, the fractures hosted in the Wufeng Formation are dominantly mineralized by calcite, which occurs either as the only cement present or as a cement phase predating later quartz cement.

REE data equally indicate that the distinguishable Eu anomalies 6. The Sm-Nd isochron ages and fluid inclusion data of fracture cements suggest that fracture opening and calcite precipitation in composite veins within the Wufeng and Longmaxi Formations were triggered by gas generation overpressurization. Shibboleth Sign In.

Sm-Nd Dating

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U–Pb zircon dating and Sr–Nd–Hf isotopic evidence to support a juvenile origin of the ~ Ma El Shalul granitic gneiss dome, Arabian–Nubian Shield.

Samarium—neodymium dating is a radiometric dating method useful for determining the ages of rocks and meteorites , based on the radioactive decay of a long-lived samarium isotope Sm to a radiogenic neodymium isotope Nd. Neodymium isotope ratios together with samarium-neodymium ratios are used to provide information on age information and the source of igneous melts. It is sometimes assumed that at the moment when crustal material is formed from the mantle the neodymium isotope ratio depends only on the time when this event occurred, but thereafter it evolves in a way that depends on the new ratio of samarium to neodymium in the crustal material, which will be different from the ratio in the mantle material.

Samarium—neodymium dating allows us to determine when the crustal material was formed. The usefulness of Sm—Nd dating stems from the fact that these two elements are rare earth elements and are thus, theoretically, not particularly susceptible to partitioning during sedimentation and diagenesis. In many cases, Sm—Nd and Rb—Sr isotope data are used together. Samarium has five naturally occurring isotopes, and neodymium has seven.

The two elements are joined in a parent—daughter relationship by the alpha decay of parent Sm to radiogenic daughter Nd with a half-life of 1. Some of the Sm may itself have originally been produced through alpha-decay from Gd , which has a half-life of 1.

Sr Ratios & U-Th Dating Services Now Available

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Strontium, Nd, and Pb isotopic compositions of Leg basalts. Core, section, interval (cm) determined accurately by the Rb-Sr and Sm-Nd dating methods.

Ivey Jr. All Rights Reserved. Ngauruhoe in the Taupo Volcanic Zone of New Zealand erupted andesite lava flows in and , and avalanche deposits in When compared with recent andesite flows from the related adjacent Ruapehu volcano, the Sr-Nd-Pb radioisotopic systems plotted on correlation diagrams provide information about the depleted mantle source for the parental basalt magmas and the source of the crustal contamination that produced the andesite lavas from them.

Thus the radioisotopic ratios in these recent Ngauruhoe andesite flows were inherited, and reflect the origin and history of the mantle and crustal sources from which the magma was generated. Andesite, — flows, Mt. Skip to main content. Abstract Mt. More The Earth Is Unique. Strange Ocean Crust Waves Discovered. While searching for a missing plane on the ocean floor, scientists made an interesting geological discovery.

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