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Sr-bearing zoisite and epidote are common constituents of eclogites and associated paraschists throughout the Su-Lu ultra-high pressure (UHP) province, eastern China. The SrO content of prograde zoisite and epidote reaches 3.2 wt% in crystal cores and generally decreases toward crystal margins. Retrograde epidote is poorer in SrO (70% of the whole-rock SrO is contained in these minerals. Apatite and K-white mica are only minor reservoirs for SrO in these rocks. Zoisite and epidote are thus regarded as the most important Sr reservoirs at UHP conditions where calcic plagioclase and titanite are unstable.

Compressibility data of clinozoisite and zoisite were measured by single-crystal X-ray diffraction in a diamond-anvil cell up to a pressure of about 50 kbar. In both polymorphs, the unit cell parameters varied linearly with pressure but in an anisotropic pattern: [[Beta].sub.a] = 2.1(1) x [10.sup.-4], [[Beta].sub.b] = 2.8(1) x [10.sup.-4], [[Beta].sub.c] = 3.3(1) x [10.sup.-4] [kbar.sup.-1] for clinozoisite, and [[Beta].sub.a] = 2.3(2) x [10.sup.-4], [[Beta].sub.b] = 2.9(1) x [10.sup.-4], [[Beta].sub.c] = 3.7(2) x [10.sup.-4] [kbar.sup.-1] for zoisite. The principal coefficients of the strain ellipsoid of clinozoisite are [[Beta].sub.1] = 2.0 x [10.sup.-4], [[Beta].sub.2] = 2.7 x [10.sup.-4], [[Beta].sub.3] = 3.3 x [10.sup.-4] [kbar.sup.-1]; [[Beta].sub.1] and [[Beta].sub.3] were symmetrically oriented in the (010) plane with an angle of about 12 [degrees] between [[Beta].sub.1] and the a axis, whereas [[Beta].sub.2] coincides with the b axis. Bulk moduli calculated as the reciprocal of cell-volume compressibility were 1300(20) kbar for the monoclinic and 1140(20) for the orthorhombic polymorph. [K.sub.0], determined by fitting the unit-cell parameters with a third-order Birch-Murnaghan equation of state, was 1270(45) kbar, with K[prime] = 0.5(2) for clinozoisite and 1020(65) kbar with K[prime] = 4.8(4) for zoisite. Structural refinements of clinozoisite performed at 0.5, 19.4, and 42 kbar, and also under ambient conditions, showed that the compression mechanism included both shrinking of the polyhedra (i.e., octahedra and Ca polyhedra) and tilting of the [Si.sub.2][O.sub.7] group, with reduction of the Si-O-Si angle. The different effect of these mechanisms explains the anisotropic compressional pattern in clinozoisite and the similar behavior observed in the two polymorphs. Comparison of high-pressure and high-temperature data for clinozoisite showed that a given increase in pressure produced structural effects very similar to those seen after a proportional decrease in temperature. The calculated volume-expansivity-to-compressibility ratio of 38 bar/K indicates that the cell volume of clinozoisite remains unchanged with geothermal gradients of about 10 [degrees] C/km. The crystallographic data support the results of experimental petrology in indicating that epidote is a good candidate for transporting [H.sub.2]O in down-going subduction slabs.

A new member of the epidote group, androsite-(La), was found at Andros Island, Cyclades, Greece, as an accessory constituent of metamorphic Mn-rich rocks. Associated minerals are rhodochrosite, braunite, rhodonite, spessartine, and quartz. The mineral is brown-red in color, transparent with vitreous luster and very strong pleochroism. Lattice parameters are a = 8.896(1), b = 5.706(1), c = 10.083(1) [Angstrom], [Beta] = 113.88(1) [degrees], V = 468.0(1) [[Angstrom].sup.3], Z = 2, space group [P2.sub.1]/m. Crystal-structure refinement and chemical analyses yielded the ideal formula (Mn,Ca)REEAl[Mn.sup.3+][Mn.sup.2+](Si[O.sub.4])([Si.sub.2][O.sub. 7!)O(OH). Another Mn-rich sample of the epidote group was found at Varenche Mn-mine, Valle di Saint Barthelemy, Western Alps, Italy; because of its chemical composition and crystallographic features, it can be considered an intermediate member of the piemontite-androsite-(La) series.

Epidote blueschists on Ile de Groix, France, were selectively overprinted by chloritic greenschist assemblages on a millimetre to metre scale along foliation planes, in fold hinges, and along shear zones. Reactions balanced between the blueschist and greenschist assemblages show that overprinting of epidote blueschists can only be accomplished by the addition of H2O plus or minus CO2. Conversion of epidote blueschists to chloritic greenschist assemblages thus depends on fluid-infiltration processes as the rocks pass through the greenschist facies, and does not necessarily reflect rapid rates of unroofing of a subduction complex. Epidote blueschists are therefore preferentially preserved in fluid-absent or impermeable rocks regardless of exhumation rates, in contrast to other blueschist types that require rapid unroofing to avoid a greenschist overprint.