Amoeboid olivine aggregates (AOAs) are the most common type of refractory inclusions in CM, CR, CH, CV, CO, and ungrouped carbonaceous chondrites Acfer 094 and Adelaide; only one AOA was found in the CBb chondrite Hammadah al Hamra 237 and none were observed in the CB, chondrites Bencubbin, Gujba, and Weatherford. In primitive (unaltered and unmetamorphosed) carbonaceous chondrites, AOAs consist of forsterite (Fa(<2)), Fe, Ni-metal (5-12 wt% Ni), and Ca, Al-rich inclusions (CAIs) composed of Al-diopside, spinel, anorthite, and very rare melilite. Melilite is typically replaced by a fine-grained mixture of spinel, Aldiopside, and +/- anorthite; spinel is replaced by anorthite. About 10% of AOAs contain low-Ca pyroxene replacing forsterite. Forsterite and spinel are always O-16-rich (delta(17,18)O-40parts per thousand to -50parts per thousand), whereas melilite, anorthite, and diopside could be either similarly O-16-rich or O-16- depleted to varying degrees; the latter is common in AOAs from altered and metamorphosed carbonaceous chondrites such as some CVs and COs. Low-Ca pyroxene is either O-16-rich (delta(17,18)O-40parts per thousand) or O-16-poor (delta(17,18)Osimilar to0parts per thousand). Most AOAs in CV chondrites have unfractionated (similar to2-10 x CI) rare-earth element patterns. AOAs have similar textures, mineralogy and oxygen isotopic compositions to those of forsterite-rich accretionary rims surrounding different types of CAIs (compact and fluffy Type A, Type B, and fine-grained, spinel-rich) in CV and CR chondrites. AOAs in primitive carbonaceous chondrites show no evidence for alteration and thermal metamorphism. Secondary minerals in AOAs from CR, CM, and CO, and CV chondrites are similar to those in chondrules, CAIs, and matrices of their host meteorites and include phyllosilicates, magnetite, carbonates, nepheline, sodalite, grossular, wollastonite, hedenbergite, andradite, and ferrous olivine.
Our observations and a thermodynamic analysis suggest that AOAs and forsterite-rich accretionary rims formed in O-16-rich gaseous reservoirs, probably in the CAI-forming region(s), as aggregates of solar nebular condensates originally composed of forsterite, Fe, Ni-metal, and CAIs. Some of the CAIs were melted prior to aggregation into AOAs and experienced formation of Wark-Lovering rims. Before and possibly after the aggregation, melilite and spinel in CAIs reacted with SiO and Mg of the solar nebula gas enriched in O-16 to form Al-diopside and anorthite. Forsterite in some AOAs reacted with O-16-enriched SiO gas to form low-Ca pyroxene. Some other AOAs were either reheated in O-16-poor gaseous reservoirs or coated by O-16-depleted pyroxene-rich dust and melted to varying degrees, possibly during chondrule formation. The most extensively melted AOAs experienced oxygen isotope exchange with O-16- poor nebular gas and may have been transformed into magnesian (Type I) chondrules. Secondary mineralization and at least some of the oxygen isotope exchange in AOAs from altered and metamorphosed chondrites must have resulted from alteration in the presence of aqueous solutions after aggregation and lithification of the chondrite parent asteroids. (C) 2004 Elsevier GrnbH. All rights reserved.

In situ SIMS oxygen isotope data were collected from a coarse-grained type B1 Ca-Al-rich inclusion (CAT) and an adjacent fine-grained CAI in the reduced CV3 Efremovka to evaluate the timing of isotopic alteration of these two objects. The coarse-grained CAI (CGI-10) is a sub-spherical object composed of elongate, euhedral, normally-zoned melilite crystals ranging up to several hundreds of mum in length, coarse-grained anorthite and Al, Ti-diopside (fassaite), all with fine-grained (similar to10 mum across) inclusions of spinet. Similar to many previously examined coarse-grained CAIs from CV chondrites, spinet and fassaite are (16)O-rich and melilite is (16)O-poor, but in contrast to many previous results, anorthite is (16)O-rich. Isotopic composition does not vary with textural setting in the CAI: analyses of melilite from the core and mantle and analyses from a variety of major element compositions yield consistent (16)O-poor compositions. CGI-10 originated in an (16)O-rich environment, and subsequent alteration resulted in complete isotopic exchange in melilite. The fine-grained CAI (FGI-12) also preserves evidence of a 1st-generation origin in an (16)O-rich setting but underwent less severe isotopic alteration. FGI-12 is composed of spinel +/- melilite nodules linked by a mass of Al-diopside and minor forsterite along the CAI rim. All minerals are very fine-grained (<5 mum) with no apparent igneous textures or zoning. Spinet, Al-diopside, and forsterite are (16)O-rich, while melilite is variably depleted in (16)O (delta(17), (18)O from similar to-40parts per thousand to -5parts per thousand).
The contrast in isotopic distributions in CGI-10 and FGI-12 is opposite to the pattern that would result from simultaneous alteration: the object with finer-grained melilite and a greater surface area/volume has undergone less isotopic exchange than the coarser-grained object. Thus, the two CAN were altered in different settings. As the CAIs are adjacent to each other in the meteorite, isotopic exchange in CGI-10 must have preceded incorporation of this CAI in the Efremovka parent body. This supports a nebular setting for isotopic alteration of the commonly observed (16)O-poor melilite in coarse-grained CAls from CV chondrites.

Amoeboid olivine aggregates (AOAs) from the reduced CV chondrites Efremovka, Vigarano, and Leoville consist of forsteritic olivine, FeNi-metal and a refractory component composed of spinel, Al-diopside, +/- anorthite. Secondary ferrous olivine and alkali-rich minerals (nepheline and sodalite), commonly observed in the oxidized CVs, are rare. Mineralogy and chemical compositions of AOAs are similar to those predicted by equilibrium thermodynamic condensation models, suggesting that AOAs formed primarily by gas-solid condensation over a narrow temperature range, slightly below the temperatures over which most Ca-Al-rich inclusions (CAIs) formed. AOAs in the reduced CVs preserve a 1(st)-generation (16)O-rich signal (delta(17,18)O similar to -40parts per thousand) similar to that observed in many CAls, suggesting that these refractory objects originated from a common source in the solar nebula. In fact AOAs and many fine-grained CAls may have formed by the same processes, but at slightly different temperatures, and can be considered a single class of refractory objects.
Alteration of the AOAs is manifested by differing extents of (16)O-depletion in original AOA minerals, FeO-enrichment in olivine, and formation of interstitial very fine grained Na-bearing phases. From the six AOAs and one fine-grained, melilite-pyroxene-rich CAI examined in this study, five distinct patterns of alteration were identified. (1) One unaltered AOA from Vigarano is characterized by (16)O-rich forsterite without FeO-rich rims and interstitial Na-bearing phases. (2) Weak alteration in the melilite-pyroxene-rich CAI is characterized by incomplete (16)O-depletion in some melilite and precipitation of Na-bearing phases near the CAI rim. (3) Oxygen isotopic composition and mineralogy are correlated in two AOAs from Leoville with (16)O-rich olivine, (16)O-poor anorthite and a range of intermediate compositions in Al-diopside. This pattern is consistent with model diffusion between original grains and a (16)O-poor reservoir during a relatively short-term ( < 60 yr), high-temperature (900-1100degreesC) event. (4) Original forsterite has been enriched in FeO, but remained (16)O-rich in one AOA from Vigarano. This result is consistent with the slower rate of diffusion of O than Fe and Mg in olivine. At least some interstitial phases are (16)O-rich, and Na-bearing phases are abundant in this AOA. (5) In contrast, oxygen isotopic composition and Fo-content are correlated in two AOAs from Eftemovka. The olivine in these AOAs tends to have forsteritic (16)O-rich cores and FeO-rich (16)O-depleted rims. The general correlation between oxygen isotopic composition and Fo-content is difficult to model by diffusion, and may have formed instead by aqueous dissolution and precipitation along the margins of preexisting olivine grains.
Independent evidence for aqueous alteration of the Eftemovka AOAs is provided by OH-rich signals detected during ion beam sputtering of some of the (16)O-poor olivine. Elevated (16)OH-count rates and order of magnitude increases in (16)OH detected during single analyses reflect trapping of an aqueous phase in (16)O-depleted olivine. An elevated (16)OH signal was also detected in one analysis of relatively (16)O-poor melilite in the melilite-pyroxene CAI from Vigarano, suggesting that this object also was altered by aqueous fluid. Copyright (C) 2004 Elsevier Ltd.

Based on their mineralogy and petrography, similar to200 refractory inclusions studied in the unique carbonaceous chondrite, Acfer 094, can be divided into corundum-rich (0.5%), hibonite-rich (1.1%), grossite-rich (8.5%), compact and fluffy Type A (spinel-melilite-rich, 50.3%), pyroxene-anorthite-rich (7.4%), and Type C (pyroxeneanorthite-rich with igneous textures, 1.6%) Ca,Al-rich inclusions (CAIs), pyroxene-hibonite spherules (0.5%), and amoeboid olivine aggregates (AOAs, 30.2%). Melilite in some CAIs is replaced by spinel and Al-diopside and/or by anorthite. whereas spinel-pyroxene assemblages in CAIs and AOAs appear to be replaced by anorthite. Forsterite grains in several AOAs are replaced by low-Ca pyroxene. None of the CAN or AOAs show evidence for Fe-alkali metasomatic or aqueous alteration. The mineralogy, textures, and bulk chemistry of most Acfer 094 refractory inclusions are consistent with their origin by gas-solid condensation and may reflect continuous interaction with SiO and Mg of the cooling nebula gas. It appears that only a few CAls experienced subsequent melting. The Al-rich chondrules (ARCs; > 10 wt% bulk Al2O3) consist of forsteritic olivine and low-Ca pyroxene phenocrysts, pigeonite, augite, anorthitic plagioclase, +/- spinel, FeNi-metal, and crystalline mesostasis composed of plagioclase, augite and a silica phase. Most ARCs are spherical and mineralogically uniform, but some are irregular in shape and heterogeneous in mineralogy, with distinct ferromagnesian and aluminous domains. The ferromagnesian domains tend to form chondrule mantles, and are dominated by low-Ca pyroxene and forsteritic olivine, anorthitic mesostasis, and Fe,Ni-metal nodules. The aluminous domains are dominated by anorthite, high-Ca pyroxene and spinel, occasionally with inclusions of perovskite; have no or little FeNi-metal; and tend to form cores of the heterogeneous chondrules. The cores are enriched in bulk Ca and Al, and apparently formed from melting of CAI-like precursor material that did not mix completely with adjacent ferromagnesian melt. The inferred presence of CAI-like material among precursors for Al-rich chondrules is in apparent conflict with lack of evidence for melting of CAIs that occur outside chondrules, suggesting that these CAIs were largely absent from chondrule-forming region(s) at the time of chondrule formation. This may imply that there are several populations of CAIs in Acfer 094 and that mixing of "normal" CAIs that Occur outside chondrules and chondrules that accreted into the Acfer 094 parent asteroid took place after chondrule formation. Alternatively, there may have been an overlap in the CAI- and chondrule-forming regions, where the least refractory CAIs were mixed with Fe-Mg chondrule precursors. This hypothesis is difficult to reconcile with the lack of evidence of melting of AOAs which represent aggregates of the least refractory CAIs and forstefite grains. Copyright (C) 2004 Lsevier Ltd.

The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole-rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP-like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Ca-rich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized.
The meteorite is composed of two distinct lithologies: a two-pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO-rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe-enrichment trend that culminated in crystallization of fayalite + silica + hedenbergite-bearing symplectites.
The Fe-enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow-level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE-enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE-depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heat-producing elements.

Mineralogy, major element compositions of minerals, and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite Northwest Africa (NWA) 032, an unbrecciated basalt found in October 1999. The rock consists predominantly of olivine, pyroxene and chromite phenocrysts, set in a crystalline groundmass of feldspar, pyroxene, ilmenite, troilite and trace metal. Whole-rock shock veins comprise a minor, but ubiquitous portion of the rock. Undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro-faults in groundmass and phenocrysts also are attributed to shock.
Several geochemical signatures taken together indicate unambiguously that NWA 032 originated from the Moon. The most diagnostic criteria include whole-rock oxygen isotopic composition and ratios of Fe/Mn in the whole rock, olivine, and pyroxene. A lunar origin is documented further by the presence of Fe-metal, troilite, and ilmenite; zoning to extremely Fe-rich compositions in pyroxene; the ferrous oxidation state of all Fe in pyroxene; and the rare earth element (REE) pattern with a well-defined negative europium anomaly. This rock is similar in major element chemistry to basalts from Apollo 12 and 15, but is enriched in light REE and has an unusually high Th/Sm ratio. Some Apollo 14 basalts yield a closer match to NWA 032 in REE patterns, but have higher concentrations of Al(2)O(3). Ar-Ar step release results are complex, but yield a whole-rock age of similar to2.8 Ga, suggesting that NWA 032 was extruded at 2.8 Ga or earlier. This rock may be the youngest sample of mare basalt collected to date. Noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites. In short, the geochemical and petrographic features of NWA 032 are not matched by Apollo or Luna samples, nor by previously identified lunar meteorites, indicating that it originates from a previously unsampled mare deposit.
Detailed assessment of petrographic features, olivine zoning, and thermodynamic modelling indicate a relatively simple cooling and crystallization history for NWA 032. Chromite-spinel, olivine, and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 degreesC/h based on the polyhedral morphology of olivine. Comparison of olivine size with crystal growth rates and preserved Fe-Mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days. Plumose textures in groundmass pyroxene, feldspar, and ilmenite, and Fe-rich rims on the phenocrysts formed during rapid crystallization (cooling rates similar to20 to 60 degreesC/h) after eruption.

The metal-rich chondrites Hammadah al Hamra (HH) 237 and Queen Alexandra Range (QUE) 94411, paired with QUE 94627, contain relatively rare (<1 vol%) calcium-aluminum-rich inclusions (CAIs) and Al-diopside-rich chondrules. Forty CAIs and CAI fragments and seven Al-diopside-rich chondrules were identified in HH 237 and QUE 94411/94627. The CAIs, <similar to>50-400 mum in apparent diameter, include (a) 22 (56%) pyroxene-spinel +/- melilite (+forsterite rim), (b) 11 (28%) forsterite-bearing, pyroxene-spinel +/- melilite +/- anorthite (+forsterite rim) (c) 2 (5%) grossite-rich (+spinel-melilite-pyroxene rim), (d) 2 (5%) hibonite-melilite (+spinel-pyroxene +/- forsterite rim), (e) 1 (2%) hibonite-bearing, spinel-perovskite (+melilite-pyroxene rim), (f) 1 (2%) spinel-melilite-pyroxene-anorthite, and (g) 1 (2%) amoeboid olivine aggregate. Each type of CAI is known to exist in other chondrite groups, but the high abundance of pyroxene-spinel melilite CAIs with igneous textures and surrounded by a forsterite rim are unique features of HH 237 and QUE 94411/94627. Additionally, oxygen isotopes consistently show relatively heavy compositions with Delta O-17 ranging from -6 parts per thousand to -10 parts per thousand (1 sigma = 1.3 parts per thousand) for all analyzed CAI minerals (grossite, hibonite, melilite, pyroxene, spinel). This suggests that the CAIs formed in a reservoir isotopically distinct from the reservoir(s) where "normal", O-16-rich (Delta O-17 < -20<parts per thousand>) CAIs in most other chondritic meteorites formed.
The Al-diopside-rich chondrules, which have previously been observed in CH chondrites and the unique carbonaceous chondrite Adelaide, contain Al-diopside grains enclosing oriented inclusions of forsterite, and interstitial anorthitic mesostasis and Al-rich, Ca-poor pyroxene, occasionally enclosing spinel and forsterite. These chondrules are mineralogically similar to the Al-rich barred-olivine chondrules in HH 237 and QUE 94411/94627, but have lower Cr concentrations than the latter, indicating that they may have formed during the same chondrule-forming event, but at slightly different ambient nebular temperatures. Aluminum-diopside grains from two Al-diopside-rich chondrules have O-isotopic compositions (Delta O-17 approximate to -7 +/- 1.1 parts per thousand) similar to CAI minerals, suggesting that they formed from an isotopically similar reservoir. The oxygen-isotopic composition of one Ca, Al-poor cryptocrystalline chondrule in QUE 94411/94627 was analyzed and found to have Delta O-17 approximate to -3 +/- 1.4 parts per thousand.
The characteristics of the CAIs in HH 237 and QUE 94411/94627 are inconsistent with an impact origin of these metal-rich meteorites. Instead they suggest that the components in CB chondrites are pristine products of large-scale, high-temperature processes in the solar nebula and should be considered bonafide chondrites.

Late Paleozoic to early Mesozoic rocks in the Sierra Nevada and Klamath Mountains, western United States, preserve a record of lateral growth of continental crust by incorporation of ophiolites, volcanic arcs, and associated sedimentary rocks. Deciphering the timing of arc construction and metamorphism is critical for elucidating tectonic and thermal evolution during this type of crustal growth, but is difficult in complex accretionary terranes. In this study, we address the timing of arc construction and regional metamorphism in the Slate Creek Complex, a volcano-plutonic terrane in the central part of the northern Sierra Nevada.
New (40)Ar-(39)Ar ages from relict volcanic hornblende demonstrate that the youngest volcanic unit in the Slate Creek Complex is ca. 170 Ma, at least 30 m.y, younger than previous estimates of ca. 200 Ma for metaplutonic rocks in the lower part of the complex. Consequently, the Slate Creek Complex is polygenetic, with two distinct episodes of arc magmatism. The distribution of mineral assemblages and textures indicates that greenschist and epidote-amphibolite facies metamorphism is younger than 170 Ma and is associated with crosscutting plutons that yield cooling ages of 150 Ma and younger. Amphiboles from foliated rocks in the Slate Creek Complex yield plateau ages of 156.1 +/- 0.6 and 152.0 +/- 0.7 Ma that date cooling subsequent to or dynamic recrystallization during the metamorphic event.
Age and lithologic similarities suggest that the lower parts of the Slate Creek Complex correlate with plutons (ca. 200 Ma) and the volcanic cover sequence of the Rattlesnake Creek terrane in the Klamath Mountains. The uppermost volcanic unit correlates with the ca. 170 Ma Western Hayfork terrane that structurally overlies the Rattlesnake Creek terrane. Metamorphism in the Slate Creek Complex correlates broadly with a similar late metamorphic event in the Klamath Mountains.

In situ ion microprobe analyses of spinel in refractory calcium-aluminium-rich inclusions (CAIs) from type 3 EH chondrites yield O-16-rich compositions (delta O-18 and delta O-17 about -40 parts per thousand). Spinel and feldspar in a CAI from an EL3 chondrite have significantly heavier isotopic compositions (delta O-18 and delta O-17 about -5 parts per thousand). A regression through the data results in a line with slope 1.0 on a three-isotope plot, similar to isotopic results from unaltered minerals in CAIs from carbonaceous chondrites. The existence of CAIs with O-16-rich and O-16-poor compositions in carbonaceous as well as enstatite chondrites indicates that CAIs formed in at least two temporally or spatially distinct oxygen reservoirs. General similarities in oxygen isotopic compositions of CAIs from enstatite, carbonaceous, and ordinary chondrites indicate a common nebular mechanism or locale for the production of most CAIs.

Like calcium-aluminum-rich inclusions (CAIs) from carbonaceous and ordinary chondrites, enstatite chondrite CAIs are composed of refractory minerals such as spinel, perovskite, Al,Ti-diopside, melilite, hibonite, and anorthitic plagioclase, which may be partially to completely surrounded by halos of Na-(+/-Cl)-rich minerals. Porous, aggregate, and compact textures of the refractory cores in enstatite chondrite CAIs and rare Wark-Lovering rims are also similar to CAIs from other chondrite groups. However, the small size (<100 mu m), low abundance (<1% by mode in thin section), occurrence of only spinel or hibonite-rich types, and presence of primary Ti-(+/-V)-oxides, and secondary geikelite and Ti,Fe-sulfides distinguish the assemblage of enstatite chondrite CAIs from other groups.
The primary mineral assemblage in enstatite chondrite CAIs is devoid of indicators (e.g., oldhamite, osbornite) of low O fugacities. Thus, high-temperature processing of the CAIs did not occur under the reducing conditions characteristic of enstatite chondrites, implying that either (1) the CAIs are foreign to enstatite-chondrite-forming regions or (2) O fugacities fluctuated within the enstatite-chondrite-forming region. In contrast, secondary geikelite and Ti-Fe-sulfide, which replace perovskite, indicate that alteration of perovskite occurred under reducing conditions distinct from CAIs in the other chondrite groups. We have not ascertained whether the reduced alteration of enstatite chondrite CAIs occurred in a nebular or parent-body setting. We conclude that each chondrite group is correlated with a unique assemblage of CAIs, indicating spatial or temporal variations in physical conditions during production or dispersal of CAIs.

The enstatite chondrite Reckling Peak (RKP) A80259 contains feldspathic glass, kamacite, troilite, and unusual sets of parallel fine-grained enstatite prisms: that formed by rapid cooling of shock melts. Metallic Fe,Ni and troilite occur as spherical inclusions in feldspathic glass, reflecting the immiscible Fe-Ni-S and feldspathic melts generated during the impact. The Fe-Ni-S and feldspathic liquids were injected into fractures in coarse-grained enstatite and cooled rapidly, resulting in thin (less than or equal to 10 mu m) semicontinuous to discontinuous veins and inclusion trails in host enstatite. Whole-rock melt veins characteristic of heavily shocked ordinary chondrites are conspicuously absent. Raman spectroscopy shows that the feldspathic material is a glass. Elevated MgO and SiO2 contents of the glass indicate that some enstatite and silica were incorporated in the feldspathic melt. Metallic Fe,Ni globules are enclosed by sulfide and exhibit Ni-enrichment along their margins characteristic of rapid crystallization from a Fe-Ni-S liquid. Metal enclosed by sulfide is higher in Si and P than metal in feldspathic glass and enstatite, possibly indicating lower O fugacities in metal/sulfide than in silicate domains. Fine-grained, elongate enstatite prisms in troilite or feldspathic glass crystallized from local pyroxene melts that formed along precursor grain boundaries, but most of the enstatite in the target rock remained solid during the impact and occurs as deformed, coarse-grained crystals with lower CaO, Al2O3, and FeO than the fine-grained enstatite. Reckling Peak A80259 represents an intermediate stage of shock melting between unmelted E chondrites and whole-rock shock melts and melt breccias documented by previous workers. The shock petrogenesis of RKPA80259 reflects the extensive impact processing of the enstatite chondrite parent bodies relative to those of other chondrite types.

The replacement of anhydrous by hydrous minerals is commonly used to infer infiltration of a rack by H2O. However, our work indicates that the formation of pseudomorphic amphibole after clinopyroxene (uralitization) in low-grade metavolcanic rocks is a net dehydration process. In the ophiolitic Slate Creek complex, northern California, clinopyroxene exhibits four textural stages of alteration: (1) clinopyroxene, (2) clinopyroxene + chlorite +/- amphibole, (3) amphibole + chlorite, and (4) amphibole. This transformation occurs in subgreenschist to greenschist facies rocks with a common matrix assemblage: quartz, albite, chlorite, epidote, titanite, + amphibole, +/- white mica, +/- rare pumpellyite. A simple reaction space model based on these observations indicates that consumption of chlorite in the rock matrix releases more water than required to produce amphibole pseudomorphs of clinopyroxene. Thus, the net flux of H2O during uralitization of greenschist facies metavolcanic rocks is outward. These results imply that uralitization in metavolcanic rocks results from heating rather than whole-rock hydration, and that natural mass fluxes may be counter to fluxes inferred from textural evidence alone.