Physics and Chemistry of Partially Molten Rocks

by Bagdassarov, N.; Buchner, Jorg; Laporte, Didier; Thompson, Alan Bruce

• ISBN13: 9780412847202
• ISBN10: 0412847205
• Format: Hardcover
• Copyright: 1999-12-01
• Publisher: Chapman & Hall

Summary

Partial melting occurs in a variety of geological environments, from granitic partial melts in the continental crust, to basaltic or carbonate partial melts in the upper mantle. Partial melting is the first stage of magmatism and therefore plays a role of primary importance in the chemical differentiation of the Earth and in the transport of heat to the Earth surface. This special volume contains contributions presented at the symposium 'Physics and Chemistry of Partially Molten Systems' of the EUG 9 meeting, held in Strasbourg, France, on March 23-27, 1997. It is intended to provide a current understanding of the physics of partial melting and melt segregation and covers topics such as the rheology of partially molten systems, the topology of partial melts, modelling of partial melting processes, and field observations of partial melts. Audience: This book is intended for a broad readership, including graduate students, specializing in petrology and geodynamics. The volume may be recommended as a textbook for graduate courses on petrology, geomaterial sciences and geophysics.

Table of Contents

Preface	xi
Bagdassarov N.
Laporte D.
Thompson A.B.
List of Contributors	xv
Rheology of Partially Molten Rocks	3	(26)
Kohlstedt D.L.
Bai Q
Wang Z.-C.
S. Mai
Introduction	4	(2)
Constitutive Equations	6	(12)
New Experimental Constraints	9	(3)
Microstructural observations	12	(5)
Mechanical results for deformation at 300 MPa	17	(1)
Discussion	18	(11)
New experimental results	18	(4)
Implication for upper-mantle rheology	22	(7)
Anelastic and Viscoelastic Behaviour of Partially Molten Rocks and Lavas	29	(38)
Bagdassarov N.
Introduction	30	(6)
Experimental Methods of Q Measurement	36	(2)
Experiments	38	(13)
Description of the torsion device	38	(1)
Sample description	39	(5)
Analysis of data	44	(7)
Discussion	51	(6)
Conclusions	57	(10)
Constraints on the Melt Distribution in Anisotropic Polycrystalline Aggregates Undergoing Grain Growth	67	(26)
Faul U.H.
Introduction	68	(1)
Surface Energy Considerations	69	(8)
Dihedral angles	70	(4)
Interfacial curvature	74	(3)
Experimental Observations: The System Olivine + Basaltic Melt	77	(11)
Textural features of the melt distribution	78	(1)
Dihedral angles	79	(2)
Grain misorientations	81	(2)
Grain growth	83	(1)
Applications: Calculation of Seismic Velocity and Permeability	84	(4)
Summary and Implications for Partial Melts in the Mantle	88	(5)
The Grain-Scale Distribution of Silicate, Carbonate and Metallosulfide Partial Melts: A Review of Theory and Experiments	93	(48)
Laporte D.
A. Provost
Introduction	94	(1)
Interfacial Energies	95	(5)
The concept of interfacial energy	95	(3)
Orientation of dependence of surface energy	98	(2)
Interfacial energies of geological interest	100	(1)
Textural Equilibrium	100	(6)
The concept of textural equilibrium	100	(1)
The equilibrium shape of an isolated phase	101	(2)
Textural equilibrium in a polycrystalline aggregate	103	(3)
Equilibrium Melt Distribution in an Idealized Partially Molten System	106	(7)
Conditions of textural equilibrium	107	(1)
Equilibrium melt geometry at low melt fraction	108	(1)
The interconnection threshold	109	(4)
Wetting Properties of Geological Partial Melts	113	(16)
Experimental techniques and run product analysis	113	(3)
A review of experimental data	116	(10)
The importance of interfacial energy anisotropy	126	(3)
Discussion	129	(12)
Is textural equilibrium achieved in natural systems?	129	(2)
Equilibrium melt distribution: theory versus reality	131	(3)
Implications for the movement of geological melts	134	(7)
Partial Melting and Melt Segregation in a Convecting Mantle	141	(38)
Schmeling H.
Introduction	142	(2)
General Aspects of Melting in the Mantle	144	(3)
Causes for melting	144	(2)
Potential temperatures	146	(1)
The Physics of Melt Generation, Segregation and Convection	147	(10)
Sources of buoyancy	147	(1)
Mathematical description	148	(9)
Case Studies Relevant for Melting and Segregation in a Convecting Mantle	157	(16)
Segregation without melt generation or solidification	157	(2)
1-dimensional porosity waves	159	(2)
2-dimensional porosity waves	161	(12)
Conclusions	173	(6)
A Fractionation Model for Hydrous Calcalkaline Plutons and the Heat Budget During Fractional Crystallisation and Assimilation	179	(30)
Matile L.
Thompson A.B.
Ulmer P.
Introduction	179	(1)
Fractional Crystallisation of Hydrous Mantle Magma	180	(7)
Fractionation model	180	(1)
H2O-contents of fractionating magmas	181	(1)
H2O-contents of AFC magmas (Assimilation during Fractional Crystallisation)	182	(1)
Liquid-line-of-descent of fractionating magmas	182	(1)
Modal variation with temperatures of fractionating magma	183	(1)
Thermal evolution of fractionally crystallising hydrous mantle magma	183	(2)
Quantitative heat budget during fractional crystallisation	185	(2)
Crystallisation(C), Fractional Crystallisation (FC) and Assimilation (A) Hydrous Mantle Magmas	187	(11)
Crystallisation of mantle magma	188	(2)
Melt fraction increase with Temperature (T-f) for crustal rock anatexis	190	(1)
The heat balance between crystallisation and assimilation	190	(2)
Quantification of AFC-fractional crystallisation (FC) and assimilation (A)	192	(1)
AFC processes for FC of hydrous picrite and assimilation of tonalite	193	(1)
A comparison of the efficiency of AFC processes for picrite assimilating different crustal rocks at different temperatures	194	(1)
The effect of rock fertility upon AFC histories	195	(1)
A comparison of AFC paths for hydrous basalt magmas compared to picrite	196	(1)
Assimilation by fractionating melts adjacent to magma chambers at successively higher crustal levels	196	(1)
Effects of other variables on the AFC paths	196	(2)
Comparison of the Heat Balance for AFC Processes with Other Results for Crustal Melting	198	(3)
Crustal melting following basaltic underplating	198	(1)
Anhydrous MORB assimilating albite and pelites	199	(2)
Conclusions	201	(8)
Migmaticic Gabbros From a Shallow-Level Metamorphic Contact Aureole, Fuerteventura Basal Complex, Canary Islands: Role of Deformation in Melt Segregation	209	(20)
Hobson A.
Bussy F.
J. Hernandez
Introduction	209	(1)
Tectonic and Geological Setting	210	(3)
The PX1 Intrusion and its Host Rock	213	(6)
The contact aureole	214	(3)
Microstructures	217	(2)
Stress regime in the contact aureole	219	(1)
Partial Melting and Mechanisms of Melt Segregation	219	(3)
Rheology of Partly Molten Rocks	222	(1)
Discussion	223	(2)
Conclusion	225	(4)
Thin Amorphous Intergranular Layers at Mineral Interfaces in Xenoliths: The Early Stage of Melting	229	(40)
Wirth R.
L. Franz
Introduction	230	(3)
Sample Preparation and Analytical Methods	233	(3)
Electron microprobe analysis EMP	233	(1)
Sample preparation, transmission electron microscopy etc	234	(1)
Electron Energy-Loss Spectroscopy EELS	235	(1)
Sample Description	236	(1)
Definitions	237	(1)
Results	238	(15)
Glass along grain or phase boundaries	238	(4)
Concentration profiles across melt films	242	(7)
Crystal growth into glassy intergranular layers	249	(1)
Melt pockets at three grain junctions	250	(2)
Melt inclusions in minerals	252	(1)
Cracks filled with melt	253	(1)
Discussion	253	(16)
Why are the amorphous intergranular layers former melt films?	253	(1)
Formation of melt along the mineral interfaces	254	(2)
Stability of amorphous intergranular layers	256	(3)
Development of the chemical composition with degree of partial melting	259	(1)
Comparison of intergranular melt composition with glass composition from literature	260	(2)
Geological implications	262	(7)
Index	269