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Banerjee, S. K.

Publications and source records attributed to Banerjee, S. K..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Magnetic constraints on early lunar evolution revisited: Limits on accuracy imposed by methods of paleointensity measurements

It is impossible to carry out conventional paleointensity experiments requiring repeated heating and cooling to 770 C without chemical, physical or microstructural changes on lunar samples. Non-thermal methods of paleointensity determination have been sought: the two anhysteretic remanent magnetization (ARM) methods, and the saturation isothermal remanent magnetization (IRMS) method. Experimental errors inherent in these alternative approaches have been investigated to estimate the accuracy limits on the calculated paleointensities. Results are indicated in this report.

Banerjee, S. K.↗
NASA NTRS1979

Combining paleointensity methods - A dual-valued determination on lunar sample 10017,135

A single-heating procedure for the determination of two partially independent values of paleofield intensity for one sample is presented. The procedure combines data for Shaw-type and 'ARM-method' determinations furnishing the ratio thermoremanent magnetization (TRM) to ARM acquisition efficiency corrected for physicochemical alteration to the magnetic carriers. Applicability of the Shaw-method to Fe-bearing samples is demonstrated by simulated paleointensity determinations on synthetic samples containing multidomain grains. The combined Shaw-ARM procedure was applied to a linear basalt sample, but the Thellier-Thellier method could not provide a meaningful determination of the neighboring chip. These conflicting findings may be explained by multiple step-wise heatings causing more damage to carriers than a single heating procedure, and by the natural remanent magnetization in this lunar basalt not being a simple TRM.

Hoffman, K. A.↗
NASA NTRS1977

Theoretical grain-size thresholds and their application to accurate methods for paleointensity determination

Improved values of critical grain-size thresholds for magnetite and Fe have been obtained using a rigorous theoretical approach. The temperature dependence of these thresholds is interesting in that it indicates the existence of certain grains which, when cooled from above their blocking temperature, pass sequentially through the following magnetization states: superparamagnetic to single-domain to nonuniform magnetization. Such grains will yield correct paleointensities by the Wilson (1961) or Shaw (1974) method but not by the well-known method due to Thellier and Thellier (1959).

Banerjee, S. K.↗
NASA NTRS1977

On the origin of stable remanence in pseudo-single domain grains

A critique is presented of the quantitative model for the magnetic moment of pseudo-single domain grains (hypothetical magnetite grains larger than the critical size threshold for single domain behavior, yet also difficult to demagnetize), derived by Stacey and Banerjee (1974). Evidence from theoretical studies in micromagnetics demonstrates that the spin orientations in such grains are too complex to permit ready prediction of the magnetic moments. However, this limitation in the theory may be overcome by experiments involving rare earth-cobalt alloys and yttrium iron garnet crystals; these studies have suggested that surface anisotropy is the predominant cause of the high coercivity of pseudo-single domain grains.

Banerjee, S. K.↗
NASA NTRS1977

Remanent magnetization stratigraphy of lunar cores

Depth dependent fluctuations have been observed in the natural remanent magnetizations (NRM) of drive cores and drill strings from Apollo 16 and 17 missions. Partial demagnetization of unstable secondary magnetizations and identification of characteristic error signals from a core which is known to have been recently disturbed allow us to identify and isolate the stable NRM stratigraphy in double drive core 60010/60009 and drill strings 60002-60004. The observed magnetization fluctuations persist after normalization to take into account depth dependent variations in the carriers of stable NRM. We tentatively ascribe the stable NRM stratigraphy to instantaneous records of past magnetic fields at the lunar surface and suggest that the stable NRM stratigraphy technique could develop as a new relative time-stratigraphic tool, to be used with other physical measurements such as relative intensity of ferromagnetic resonance and charged particle track density to study the evolution of the lunar regolith.

Banerjee, S. K.↗
NASA NTRS1976

Contributions of rock magnetism and paleomagnetism to recent geophysical advances

The origin of natural remanent magnetization (NRM) in rocks is discussed both in terms of types and carriers of NRM. The importance of the concept of pseudo-single domain (PSD) grains as carriers of stable remanences is underscored. Recent advances in rock magnetism and paleomagnetism have helped to understand (1) continental motions which took place in the first 4 billion years of the earth's life, (2) fine details of field fluctuations both during 'normal' times as well as during a geomagnetic field reversal, and (3) indicate the magnitudes of the fields present during the formation of the moon and of the early solar system.

Banerjee, S. K.↗
NASA NTRS1976

Early lunar magnetism

A new method (Shaw, 1974) for investigating paleointensity (the ancient magnetic field) was applied to three subsamples of a single, 1-m homogeneous clast from a recrystallized boulder of lunar breccia. Several dating methods established 4 billion years as the age of boulder assembly. Results indicate that the strength of the ambient magnetic field at the Taurus-Littrow region of the moon was about 0.4 oersted at 4 billion years ago. Values as high as 1.2 oersted have been reported (Collison et al., 1973). The required fields are approximately 10,000 times greater than present interplanetary or solar flare fields. It is suggested that this large field could have arisen from a pre-main sequence T-Tauri sun.

Banerjee, S. K.↗
NASA NTRS1976

A solar origin for the large lunar magnetic field at 4.0 billion yr ago

A new method (Shaw, 1974) for paleointensity determination has been applied to three subsamples of one polymict breccia, 72215 (of age 4.0 billion yr) to yield an average paleointensity of 0.41 Oe at the Taurus-Littrow region of the moon around the time of breccia formation. Of the present models for lunar magnetism, only the Sonett and Runcorn (1974) model of a central iron core dynamo can explain the presence of such a large field in early lunar history. However, because of the similarity in size of this field and that for the early solar system deduced from carbonaceous chondrites, we draw attention to an apparently little-considered possibility: that the large magnetic field in early lunar history was external and solar in origin, and emanated from a pre-main sequence T-Tauri stage sun. Therefore, there should be no record of such a large magnetic field in lunar rocks younger than approximately 4.0 billion yr.

Banerjee, S. K.↗
NASA NTRS1975

Magnetic 'zig-zag' behavior in lunar rocks

A lunar olivine basalt sample is analyzed which exhibits unorthodox alternating field (AF) demagnetization behavior characterized by nonreproducible remanent magnetization values upon demagnetization at a given peak AF. It is shown that the direction of the remanence following AF demagnetization is roughly confined to a particular plane and that this behavior is an intrinsic property of certain magnetic carriers present in the sample. The viscous acquisition coefficient is found to be about 1-1/2 times greater than the absolute value of the decay coefficient. It is suggested that the behavior of this sample is due to the presence of a few planar, multidomain grains which represent a local mineral fabric, do not demagnetize, and may interfere with the determination of a meaningful time variation of lunar magnetic paleointensity.

Hoffman, K. A.↗
NASA NTRS1975

Single-domain grain size limits for metallic iron

The theory of superparamagnetic (SP) threshold calculations and single-domain (SD) to nonuniform spin threshold calculations is considered. The SD upper grain size limit and the SP-to-SD threshold size are calculated. The size and shape criteria for the stable SD behavior of metallic iron have implications for lunar magnetism and the mechanism of iron-silicate fractionation in the solar nebula.

Butler, R. F.↗
NASA NTRS1974

A new method for the determination of paleointensity from the A.R.M. properties of rocks

The relation between the mechanisms of thermoremanent magnetization (TRM) and anhysteretic remanent magnetization (ARM) considered by Nagata (1961) is utilized in the new method. It is shown experimentally that the ratio of room temperature TRM and ARM susceptibilities can be determined quantitatively from the intrinsic magnetic parameters of the rock. Questions of the theoretical background of the method are examined along with details regarding the experimental technique.-

Banerjee, S. K.↗
NASA NTRS1974

Lunar paleointensity from three Apollo 15 crystalline rocks using an A.R.M. method

An anhysteretic remanent magnetization method described by Banerjee and Mellema (1974) is used in the lunar paleointensity studies reported. The range of the difference in the paleointensity values obtained by the new method is not quite as great as the range of differences ordinarily found in values determined with the conventional method reported by Thellier and Thellier (1959). The results of the investigation show that the three Apollo 15 rocks studied acquired their natural remanent magnetization in a finite-sized magnetic field which was two or three orders of magnitude greater than the present ambient interplanetary field at the moon.

Banerjee, S. K.↗
NASA NTRS1974

A preliminary report on the magnetic measurements of samples 72275 and 72255

The direction and magnitude of natural remanent magnetization of five approximately 3-g subsamples of 72275 and 72255 and the high field saturation magnetization, coercive force, and isothermal remanent magnetization of 100-mg chip from each of these samples, were studied. Given an understanding of the magnetization processes, group 1 experiments provide information about the absolute direction of the ancient magnetizing field and a qualitative estimate of its size (paleointensity). The group 2 experiments yield a quantitative estimate of the iron content and a qualitative ideal of the grain sizes.

Banerjee, S. K.↗
NASA NTRS1973

Lunar evolution - How well do we know it now.

The currently known astronomical, chemical, and magnetic data are not uniquely indicative of an extensively and globally molten moon. It is argued that an accretional layering occurred in the moon, but at temperatures below solidus. The excess mass in the near side of the moon compatible with a 2-km displacement in the center of mass relative to the center of figure and the moment of inertia data is considered to be due to Fe-FeS liquid formation and inhomogeneous segregation. These Fe-FeS bodies, termed 'fescons,' are shown to be capable of accounting for the presently available magnetization data, by acting as small regenerative dynamos with a time-stability less than that of the terrestrial equivalent. The chemical characteristics of the highly differentiated materials, are considered to be due to small-scale localized melting caused by collisional events, from sources in which accessory phases play a significant role. Mare basalts are considered to be melts in the overlying material produced at a later time by K-40 radioactivity in the fescons. Some consequences of the present hypothesis are suggested. It is concluded that these and other characteristics of the lunar materials are reconcilable with a 'cold' moon, such as discussed by Urey over the past two decades.

Murthy, V. R.↗
NASA NTRS1972

Iron-titanium-chromite, a possible new carrier of remanent magnetization in lunar rocks.

Magnetic measurements of synthetic titanchromites reveal a characteristic transition at low temperature, making it possible to identify the presence of titanchromites in lunar rocks 12063, 14321 (dark clasts), and 14310. It is shown that titanchromites with a high chromium content could be the carriers of intermediate stability natural remanent magnetization observed in lunar rocks. Such natural remanent magnetization is acquired by transition thermoremanent magnetization at low temperature and cannot be duplicated by laboratory thermoremanent magnetization imparted above room temperature. The latter process will not yield the correct lunar paleointensity.

Banerjee, S. K.↗