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Djordje S. Djukic 《Celestial Mechanics and Dynamical Astronomy》1993,56(4):523-540
This paper considers adiabatic invariants for the classical Kepler problem with resisting forces. The analysis is based on the theory of integrating factors and theory of adiabatic invariants in the Krylov-Bogoliubov-Mitropolski variables. The adiabatic invariants are series with respect to a small parameter. Also, for every particular case of nonconservative forces, it is shown that, with a complete set of adiabatic invariants, an approximate solution of the problem can be obtained. Four problems are analyzed in detail where approximate solutions are compared with numerical. 相似文献
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Neil S. Mancktelow Djordje Grujic Eric L. Johnson 《Contributions to Mineralogy and Petrology》1998,131(1):71-85
A backscattered and secondary electron SEM study of the grain boundary microstructure in quartz mylonites sampled along the length of the retrograde Simplon Fault Zone established three characteristic components. (1) Fine isolated pores (≤?1?μm diameter) are scattered across two-grain interfaces, preferentially concentrated on surfaces in extension. Pores are uncommon on three-grain junctions and there is no evidence for fluid interconnectivity along three- and four-grain junctions. The fine porosity may develop by accumulation of original, mainly intragranular fluid inclusions to the grain boundary during deformation and recrystallization and by cavitation of grain boundaries during grain boundary sliding. Dynamic cavitation implies that the “ductile” mylonitic deformation is at least locally dilatant and therefore pressure sensitive. (2) Large “vug”-like pores (up to mm-scale) extend along multi-grain boundaries. Observed in all samples, they are most common in the higher initial temperature, coarse-grained samples with a microstructure dominated by grain boundary migration recrystallization. Grains bordering this connected porosity develop perfect crystal faces, undecorated by fine pores or pits. The irregular “lobate” optical microstructure of many migrating grain boundaries actually consists of a series of straight crystal faces. The coarse porosity is probably due to accumulation during dynamic recrystallization of (CO2-rich ?) fluid with a high wetting angle against quartz. (3) In one sample, interconnected sinuous ridges, ≤?0.2?μm high, are observed to follow three- and four-grain junctions and disjoint into more isolated worms and spheroidal globules. On two-grain interfaces, these are transitional to more branching vein-like or convoluted brain-like forms. The brain-like and globular forms have been observed, with varying frequency, through the range of samples, with the globules attaining sizes of up to 60?μm. Vein structures have also been observed on intragranular fractures. These topologies do not match across adjoining surfaces and must have developed into free space. The ridge-vein-brain-spheroid structure is distinctly different to that previously observed on experimentally healed microcracks and its origin is not unequivocally established. They could represent unstable meniscus necking of a thin grain-boundary phase of low viscosity, developed due to quasi-adiabatic shear and/or local stress-induced dilatancy during microcracking. 相似文献
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Preliminary stratigraphic and structural architecture of Bhutan: Implications for the along strike architecture of the Himalayan system 总被引：5，自引：0，他引：5
Nadine McQuarrie Delores Robinson Sean Long Tobgay Tobgay Djordje Grujic George Gehrels Mihai Ducea 《Earth and Planetary Science Letters》2008,272(1-2):105-117
High-precision in-situ ion microprobe (SIMS) oxygen isotope analysis of zircons from two diorite intrusions associated with the late Caledonian Lochnagar pluton in Scotland has revealed large differences in the degree of heterogeneity in zircon δ18O between the diorites. Zircon crystals from the Cul nan Gad diorite (CnG) show a unimodal distribution of oxygen isotope values (δ18O = 6.0 ± 0.6‰ (2σ)) and no or only minor grain-scale variation. Those from the Allt Darrarie diorite (AD1) show a large range in δ18O and an apparent bimodal distribution with modes of 6.6 ± 0.4‰ and 7.3 ± 0.4‰. Variations of up to 1.2‰ occur between and within grains; both an increase and decrease in δ18O with zircon growth has been observed. The δ18O composition of growing zircon can only change if open-system processes affect the magma composition, i.e. if material of contrasting δ18O composition is added to the magma. The variability in AD1 is interpreted to represent a cryptic record of magma mixing. A ‘deep crustal hot zone’ is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks. The overall small number of zircons with mantle-like δ18O values (5.3 ± 0.6‰ (2σ)) in the Lochnagar diorites is largely the product of crustal differentiation rather than crustal growth.
The δ18O of quartz from the CnG and AD1 diorites shows only minor variation (CnG: 10.9 ± 0.5‰ (2σ), AD1: 11.7 ± 0.6‰ (2σ)) within single populations, with no evidence of mixing. Quartz–zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids, and in case of the AD1 diorite after the inferred magma mixing from a homogenised, higher δ18O melt.
High-precision SIMS oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early-stage magma mixing and constraining the compositions and origins of the component magmas. A combination of zircon, quartz and whole-rock data has proven to be a powerful tool in reconstructing the petrogenetic evolution of diorite from early crystallisation to late alteration. 相似文献
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Joyia Chakungal Jaroslav Dostal Djordje Grujic Stéphanie Duchêne Kharka S. Ghalley 《Tectonophysics》2010,480(1-4):198-212
Mafic granulites and amphibolites in the Masang Kang area of NW Bhutan Himalaya have been investigated for their geochemical and isotopic characteristics in order to determine their protolith history. Bulk-rock major and trace element geochemistry indicate that the rocks were originally tholeiitic and alkali basalts with minor ultramafics. U–Pb zircon SIMS data suggest an age of 1742 ± 39 Ma for mafic magmatism. The age-corrected εNd(1742) values of the rocks are highly variable, ranging from high positive (+ 8.4) to negative (? 3.3). The positive value suggests a primitive magma source, similar to that of rift-related tholeiites. We suggest that the rocks of the Masang Kang suite were produced during a major late Paleoproterozoic thermal event that caused the mobilization and enrichment of the sub-continental lithospheric mantle beneath the north Indian margin. The geochemical signature of these rift-related metabasic rocks may have been produced during an earlier episode of oceanic underplating or subduction from which the fluid required to mobilize and enrich the overlying sub-lithospheric mantle may have been derived. Though their occurrence is rare, Paleoproterozoic igneous rocks within the Greater Himalayan Sequence (GHS), in addition to sources identified throughout the LHS, may have contributed to the detrital zircon population that form the 1.7–1.9 Ga peak in the age spectra of the Lesser Himalayan Sequence (LHS). In addition, the coeval Paleoproterozoic magmatism in both LHS and GHS suggests that the two lithotectonic units may have belonged to the same continental plate at that time period. 相似文献
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Exhumation of the Main Central Thrust from Lower Crustal Depths, Eastern Bhutan Himalaya 总被引：15，自引：0，他引：15
C. G. Daniel L. S. Hollister R. R. Parrish D. Grujic 《Journal of Metamorphic Geology》2003,21(4):317-334
Geothermometry and mineral assemblages show an increase of temperature structurally upwards across the Main Central Thrust (MCT); however, peak metamorphic pressures are similar across the boundary, and correspond to depths of 35–45 km. Garnet‐bearing samples from the uppermost Lesser Himalayan sequence (LHS) yield metamorphic conditions of 650–675 °C and 9–13 kbar. Staurolite‐kyanite schists, about 30 m above the MCT, yield P‐T conditions near 650 °C, 8–10 kbar. Kyanite‐bearing migmatites from the Greater Himalayan sequence (GHS) yield pressures of 10–14 kbar at 750–800 °C. Top‐to‐the‐south shearing is synchronous with, and postdates peak metamorphic mineral growth. Metamorphic monazite from a deformed and metamorphosed Proterozoic gneiss within the upper LHS yield U/Pb ages of 20–18 Ma. Staurolite‐kyanite schists within the GHS, a few metres above the MCT, yield monazite ages of c. 22 ± 1 Ma. We interpret these ages to reflect that prograde metamorphism and deformation within the Main Central Thrust Zone (MCTZ) was underway by c. 23 Ma. U/Pb crystallization ages of monazite and xenotime in a deformed kyanite‐bearing leucogranite and kyanite‐garnet migmatites about 2 km above the MCT suggest crystallization of partial melts at 18–16 Ma. Higher in the hanging wall, south‐verging shear bands filled with leucogranite and pegmatite yield U/Pb crystallization ages for monazite and xenotime of 14–15 Ma, and a 1–2 km thick leucogranite sill is 13.4 ± 0.2 Ma. Thus, metamorphism, plutonism and deformation within the GHS continued until at least 13 Ma. P‐T conditions at this time are estimated to be 500–600 °C and near 5 kbar. From these data we infer that the exhumation of the MCT zone from 35 to 45 km to around 18 km, occurred from 18 to 16 to c. 13 Ma, yielding an average exhumation rate of 3–9 mm year?1. This process of exhumation may reflect the ductile extrusion (by channel flow) of the MCTZ from between the overlying Tibetan Plateau and the underthrusting Indian plate, coupled with rapid erosion. 相似文献
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