Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada and Inyo County, California.
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Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks.Keywords:
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Radiogenic nuclide
Luzong Mesozoic volcanic basin is located in the Lower Yangtze River fault-depression zone, where is the north margin of the Yangtze block. The volcanic and intrusive plutons occur widely in Luzong basin, including four formations of volcanic rocks, such as, Longmenyuan Formation, Zhuanqiao Formation, Shuangmiao Formation and Fushan Formation and 34 intrusive plutons. Based on detailed field geological work and our former geochronology research on five plutons such as Bajiatan pluton, Chengshan pluton, Huashan pluton, Huangmeijian pluton and Zongyang pluton, we further carried out systematic geology and geochronology study of intrusive plutons in the Luzong Basin. LA-ICP-MS zircon U-Pb dating for 15 plutons has been carried out, which yield the ages of Huangtun pluton (134.4 ± 2.2 Ma), Yueshan pluton (132.7 ± 1.5 Ma), Bamaoshan pluton (132.7 ± 1.9 Ma), Jianshan pluton (132.0 ± 1.3 Ma), Xiewani pluton (131.6 ± 1.1 Ma), Longqiao pluton (131.1 ± 1.5 Ma), Jiaochong pluton (129.6 ± 1.3 Ma), Tudishan pluton (127.4 ± 2. 8 Ma), Fenghuangshan pluton (128.4 ±0.9 Ma), Luolin pluton (126.3 ± 2.O Ma), Longwangjian pluton (126.5 ± 1.5 Ma), Xiaolin pluton (126.2 ± 1.8 Ma), Dagangyao pluton (125.9 ± 1.3 Ma), Batan pluton (125.1 ± 1.1 Ma), Maowangmiao pluton (123.9 ± 1.9 Ma), respectively. The epoch of plutons in the Luzong basin is 134-123Ma. According to the epoch and geological characteristics, the intrusive rocks in the Luzong basin can be divided into two stages. The early stage monzonite-diorite plutons outcrop in the north part of the Luzong basin with epoch of 134-130Ma, are controlled by NNE orient structures and volcano-structure and have close relationship with Longmenyuan and Zhuanqiao cycle volcanic activity. The late stage intrusive plutons have two types. One type is syenite and outcrops in the south part of the Luzong basin, whose epoch is 129-123Ma. Those syenite plutons are mainly controlled by NNE orient structures or volcano-structure and share close relationship with Shuangmiao and Fushan cycle volcanic activity. The other type is A-type granites and outcrops in the southeast margin of the basin, whose epoch is 126-123 Ma. Those A-type granites are controlled by regional NNE deep faults and have no relationship with the basin volcano-structures. The iron, copper, gold, lead, zinc and uranium deposits in the study area related to magmatic activities can be classified into three metallogenic seiries. The monzonite-diorite plutons have close relationship with Luohe, Nihe and Longqiao iron deposits, Yueshan lead and zinc deposit and Jingbian and Bamaoshan copper deposits. The syenite plutons have close relationship with Makou and other iron deposits. The A-type granites have close relationship with No. 3440 and other gold uranium deposits. Regionally, there are three periods (145-136Ma, 135-127Ma, 126-123Ma) of magmatic and ore-forming activities in the Middle-Lower Yangtze River Valley metallogenic belt. The intrusive plutons in the Ning-Wu basin were the products of the second and third period magmatic activity and obviously later than the first period high-K calc-alkaline intrusions related to skarn-porphyry Cu-Au mineralizations in the uplift areas in the Middle-Lower Yangtze River Valley metallogenic belt. The intrusive plutons in Luzong volcanic basin were thought to be formed under regional lithospheric extension and thinning environment which has great significance for further research and exploration.
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The evaluation of the geothermal potential of the granitic rocks is important in long-term sustainable renewable energy projects due to increasing energy demand. The Eastern Pontides Orogenic Belt in NE Turkey contains a variety of granitic plutons changing in age, size, and composition. In this paper, we discussed the temporal and spatial distribution of radiogenic heat production by using the contents of heat-producing elements (U, Th, K) of the granitic plutons. The average U, Th, and K concentrations for the granitic plutons are 2.97±0.95 ppm, 13.48±3.48 ppm and 2.69±0.47 wt.% for Paleozoic plutons, 1.83±0.98 ppm, 8.58±5.10 ppm and 1.77±0.80 wt.% for Jurassic plutons, 5.24±1.64 ppm, 26.02±6.43 ppm and 3.17±0.49 wt.% for Cretaceous plutons, and 3.82±0.90 ppm, 15.79±4.27 ppm and 2.88±0.40 wt.% for Eocene plutons, respectively. Radiogenic heat production rates are 1.43-2.73 µW/m3 for Paleozoic plutons, 0.74-1.70 µW/m3 for Jurassic plutons, 0.66-6.28 µW/m3 for Cretaceous plutons and 1.15-5.22 µW/m3 for Eocene plutons. The studied plutons were classified as low- to moderate heat-producing granitoids. However, some Cretaceous and Eocene granitic plutons with radiogenic heat production values of 5.22-6.28 µW/m3 are considered as high heat-producing granitoids. The thermal indications in the region can be related to radiogenic heat generation and the neotectonic activity of the region. Considering the large volume of the Cretaceous- and Eocene- aged granitic plutons in the Eastern Pontides Orogenic Belt, the moderate to high radiogenic heat production of the granitic plutons in some areas has a significant geothermal impact and can be considered as the potential of enhanced geothermal systems for the future energy demand of the region.
Radiogenic nuclide
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The Journal of the Japanese Association of Mineralogists Petrologists and Economic Geologists (1984)
The Ibaragi granitic complex in Osaka Prefecture intruded into Paleozoic formation of the Tanba Belt and consists of two separate masses, named Nose pluton and Myoken pluton. Rock type of the Nose pluton spans from quartz diorite to adamellite. While, the Myoken pluton, intruding into the Nose pluton, consists entirely of adamellite. Eighty-two specimens were collected from the two masses and were analysed by X-ray flourescence spectrometric and y-ray spectrometric methods on chemical major elements and some trace elements. The relation of SiO2 to other chemical elements in whole rock of the Nose pluton is shown in a slightly curved trend. Similar tendency is found on trace elements. On the other hand, no specific trend is identified between SiO2 and other elements of the Myoken pluton, due to its narrow SiO2 spanning. From the trace elements, however, it is divided into two groups. It could be considered that the Nose pluton was produced through a single differentiation process of parental magma. On the contrary, the Myoken pluton seems to give a suggestion that mixing might have occurred in its parental magma, in spite of its apparent homogeneity observed in the-field.
Diorite
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Abstract Contacts within nested plutons are crucial for constraining the relative timing of pluton emplacement and the internal geometry of composite plutons. Exposures in orogenic belts are commonly discontinuous, however, disguising these contacts. In this paper, the Merrimac plutons in the northern Sierra Nevada of California are used as an example of how composition and foliation patterns can allow the definition of unexposed contacts and identify nested plutons. Image analysis techniques were used to determine modal compositions of a total of 52 samples from the Merrimac plutons. The integrated analysis of compositional data and foliations patterns reveals a critical contact within the plutons, and suggests that the Merrimac plutons indicate way‐up towards the north‐east at the time of emplacement 142 ± 3 Ma ago. This paper provides guidelines for recognizing nested plutons in poorly exposed areas and shows that consistent structural and compositional assymmetries within nested plutons can be used as regional top‐direction indicators.
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