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Author(s): M. D. Jackson [sup.1] , J. Blundy [sup.2] , R. S. J. Sparks [sup.2] Author Affiliations:(1) Department of Earth Science and Engineering, Imperial College London, London, UK(2) School of [...], The formation, storage and chemical differentiation of magma in the Earth's crust is of fundamental importance in igneous geology and volcanology. Recent data are challenging the high-melt-fraction 'magma chamber' paradigm that has underpinned models of crustal magmatism for over a century, suggesting instead that magma is normally stored in low-melt-fraction 'mush reservoirs'.sup.1-9. A mush reservoir comprises a porous and permeable framework of closely packed crystals with melt present in the pore space.sup.1,10. However, many common features of crustal magmatism have not yet been explained by either the 'chamber' or 'mush reservoir' concepts.sup.1,11. Here we show that reactive melt flow is a critical, but hitherto neglected, process in crustal mush reservoirs, caused by buoyant melt percolating upwards through, and reacting with, the crystals.sup.10. Reactive melt flow in mush reservoirs produces the low-crystallinity, chemically differentiated (silicic) magmas that ascend to form shallower intrusions or erupt to the surface.sup.11-13. These magmas can host much older crystals, stored at low and even sub-solidus temperatures, consistent with crystal chemistry data.sup.6-9. Changes in local bulk composition caused by reactive melt flow, rather than large increases in temperature, produce the rapid increase in melt fraction that remobilizes these cool- or cold-stored crystals. Reactive flow can also produce bimodality in magma compositions sourced from mid- to lower-crustal reservoirs.sup.14,15. Trace-element profiles generated by reactive flow are similar to those observed in a well studied reservoir now exposed at the surface.sup.16. We propose that magma storage and differentiation primarily occurs by reactive melt flow in long-lived mush reservoirs, rather than by the commonly invoked process of fractional crystallization in magma chambers.sup.14.Magma storage and differentiation in the Earth's crust mainly occurs by reactive melt flow in long-lived mush reservoirs, rather than by fractional crystallization in magma chambers, as previously thought.

Impacts may have been important mechanisms of crustal redistribution and differentiation, particularly during intense postaccretionary bombardment between 4.5 Ga and 3.9 Ga ago. Evidence of crustal processes during this period is largely provided by detrital zircons from the Yilgarn craton, Australia. Trace element compositions, crystallization temperatures, and inclusion populations of these ancient zircons have been taken as evidence for predominantly granitic source magmas, implying widespread felsic continental crust on the early Earth. However, there is little knowledge of zircons formed in impact melt sheets, a potential source for the Hadean zircons. Here we present Ti thermometry, trace elements, and inclusion populations of zircons from the 1.85 Ga Sudbury impact melt sheet (Ontario, Canada). Our results demonstrate that large variations in zircon crystallization temperature and composition will be an inevitable consequence of the evolution of such magmatic systems. We also show that zircons in mafic rocks crystallize in residual liquids of granitic composition, producing inclusion assemblages that are remarkably similar to those reported for the ancient Yilgarn grains. Thus, we conclude that the trace element compositions and inclusion populations of the Hadean zircons are consistent with crystallization from more mafic melts than previously recognized, although high crystallization temperature distributions of Sudbury zircons indicate that impact melt sheets were not a dominant source for the grains older than 3.9 Ga.

Constraining the origin of the adakitehigh-Nb basalt (HNB) association in Baja California, Mexico, is critical to a better understanding of global arc magmatism. Currently the preferred explanation for the close spatial and temporal association of the two rock suites is through melting of the basaltic portion of the suhducted FaralIon-Cocos plate, thus providing support for the slab-melting origin of adakites elsewhere. Moreover, a tectono-magmatic model involving the production of both adakite and HNB from slab melts offers a comprehensive explanation for the origin of the atypical, arc-related, postsubduction magmatism in Baja California. This paper proposes alternative models for the origin of HNB and postsubduction magmatism in Baja California, wherein the unusual geologic setting of western Mexico and westward movement of North America permitted the influx of Pacific asthenosphere beneath the adjacent Gulf of California after the cessation of subduction. Unlike the previous tectono-magmatic model, the new models propose that the asthenosphere provided a direct source for postsubduction tholeiitic and rare alkali magmas that were erupted in Baja California as tholeiites and HNB, respectively. Fractional crystallization of some of the HNB magmas plus assimilation of tholeiitic materials produced Nb-enriched basalts (NEB). The influx of Pacific asthenosphere alter the cessation of subduction also provided thermal energy to melt the mafic lower Baja California crust, producing adakite rocks, and the preexisting metasomatized mantle wedge, producing bajaites and calc-alkaline magmas. Keywords: High-Nb basalts, adakite, subduction zone, bajaite, near-ridge seamount, Baja California.

In the Sierra del Convento melange peraluminous trondhjemitic-tonalitic rocks, formed by partial melting of subducted oceanic crust at ca. 15 kbar, 700[degrees]C, contain millimeter-sized crystals of paragonite that appear to be of magmatic origin. These crystals are replaced by plagioclase and quartz along the rims. Chemically relict paragonite cores have high K contents (up to 0.35 apfu), whereas K is low at the rims (down to ca. 0.10 apfu). Calcium is relatively high in the cores and rims (0.06-0.11 apfu). The relict core compositions contrast significantly with small matrix paragonite crystals, which formed during subsequent subsolidus retrogression ofrelictic magmatic plagioclase at high pressure/low temperature (ca. 400[degrees]C, 8 kbar). Textural relations, mineral composition, and calculations of phase relationships in the system NCASH strongly suggest that primary paragonite formed by crystallization of a silicate melt. This appears to be the first reported occurrence of magmatic paragonite. Keywords: Magmatic paragonite, trondhjemite, melange, subduction

The Antigonish Highlands, Nova Scotia, are within the Avalon terrane of the northern Appalachians and contain four distinct episodes of rift-related magmatism: Neoproterozoic, Cambrian, Middle Ordovician, and Late Devonian. All four magmatic suites are composed of basalts and subordinate crustally derived felsic rocks. The mafic rocks of these suites, which do not appear to be significantly contaminated by continental crust, display similar geochemical and Sm-Nd isotopic characteristics consistent with an enriched mantle source that was metasomatically enriched prior to the oldest rifting event, probably between 0.8 and 1.1 Ga. These data also imply that the Avalonian crust and its subcontinental lithospheric mantle remained coupled during four magmatic events. Because the earliest phases of magmatism occurred when Avalonia was located along the Gondwanan margin, and the latest phases after Avalonia accreted to Laurentia, the coupling of crust and mantle in the Antigonish Highlands suggests that the migration of Avalonia did not completely detach its lithospheric mantle from its crustal cover. This study demonstrates the importance of comparing magmatism of different ages in the same terrane. Keywords: enriched mantle, Sm-Nd isotopes, continental basalts, Avalon terrane.

The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using a single rock piece of the olivine-phyric basalt from 43[degree]N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this sample is presence of very primitive olivine crystals (90-91 mol% Fo) that are significantly variable in terms of CaO (0.15-0.35 wt%). A population of low-Ca olivine (0.15-0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177, and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions are represented by high-magnesian (Mg# 90.7-91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in Ti[O.sub.2] (up to 5 wt%, c.f. Keywords MORB * Melt inclusions * Olivine * Orthopyroxene * Spinel * Felsic magmas * Mantle * Oceanic crust * Assimilation

A recently discovered dolomite carbonatite at Pogranichnoe, North Transbaikalia, Russia, dated at 624 [+ or -] 3 Ma, contains xenoliths of calcite-bearing dolomite carbonatite with graphite spherulites. Apatite and aegirine are the other rock-forming minerals. Chemically the carbonatites are ferrocarbonatite and ferruginous calciocarbonatite. The graphite forms Keywords Dolomite carbonatite * Graphite * Transbaikalia

Large explosive eruptions are generally rare, random events in the history of any particular volcano, volcanic area, or worldwide. In the Taupo Volcanic Zone, New Zealand, temporal clustering of eruptions occurs on a 15 smaller eruptions over a total ~100 k.y. period. After a precursor eruption from a nearby source (and a break of years to decades), these paired eruptions in turn generated a wet ash-fall deposit and a dry pumice-fall deposit; the Mamaku ignimbrite (>145 [km.sup.3] magma); a fine-grained vitric ash-fall deposit; then the Ohakuri ignimbrite (>100 [km.sup.3] magma). Rotorua and Ohakuri, spaced ~30 km apart, are the inferred collapse calderas associated with the Mamaku and Ohakuri ignimbrites, respectively. The early wet and dry fall deposits came from southerly sources, close to or within the subsequent Ohakuri caldera, while the fine-grained vitric ash is inferred to represent a co-ignimbrite ash from the Mamaku ignimbrite. At its southwest margin, the Mamaku ignimbrite overlies, but is also intercalated within and then overlain by, the pumice fall deposit, demonstrating that at least two widely spaced vents were active simultaneously for part of the eruption sequence. The post-Mamaku vitric ash-fall deposit underwent only trivial reworkiug prior to emplacement of the Ohakuri ignimbrite. This and other field evidence imply continuity, or time gaps of only days to months, in the whole paired sequence. Syneruptive volcanotectonic faulting may have permitted accumulation of >400 m of nonwelded Ohakuri ignimbrite through graben subsidence. Posteruptive faulting within years to decades of the eruption produced an ~300 m extra-caldera offset of the Mamaku ignimbrite and collateral subsidence of a >40 [km.sup.2] area immediately south of Rotorua caldera. Temporal linkages between ignimbrite eruptions and graben subsidence, the NNE-SSW alignment of associated faulting between the Rotorua and Ohakuri calderas, and the eruption-related subsidence indicate a tectonic control on volcanism associated with Taupo Volcanic Zone rifting processes. Statistical forecasts of the frequency of large-volume explosive events based on averages may be inaccurate because of tectonic triggering effects. Keywords: caldera collapse, collateral subsidence, ignimbrite eruption, Taupo Volcanic Zone, Mamaku ignimbrite, Ohakuri ignimbrite.

A detailed textural and chemical study of a section through the 121 Ma Ossipee ring dyke in New Hampshire provides a comprehensive record of magmatic and volcanic events during caldera formation. Phenocryst-rich quartz syenite is the main rock type; syenite, rhyolite, and basalt form small mingled dykes, xenoliths, and magmatic enclaves. Enclaves of fine-grained syenite have positive Eu anomalies, are more mafic, and are depleted in crystals relative to host quartz syenite. Anorthoclase phenocrysts in enclaves have compositions similar to the bulk enclave; high CaO contents in the crystals indicate magmatic temperatures up to 1050 [degrees]C. Rhyolite in the ring dyke is texturally and chemically equivalent to ignimbrite inside the caldera. Basalt occurs both as xenoliths and megabreccias from earlier volcanoes and as dykes that mixed and mingled with rhyolitic dykes during eruption. We suggest the following sequence of events: (1) Convection, crystal settling, and filtration of melt away from solidification fronts formed a zoned magma chamber containing voluminous rhyolite overlying crystal-rich quartz syenite and cumulate syenite. (2) Basalt partially melted the anorthoclase syenite cumulate at the base of the chamber to form a hot mobile syenitic liquid, now represented by enclaves in the ring dyke. (3) Continued intrusion of basalt replenished and rejuvenated the Ossipee chamber, driving large eruptions of rhyolitic ignimbrite that ponded in the caldera as the chamber roof collapsed. (4) Caldera collapse stirred the chamber, mingling and mixing rhyolitic, quartz syenitic, and syenitic magma. Vortices around subsiding blocks during caldera collapse caused the mixing and mingling. (5) Quartz syenite, rhyolite, and small volumes of basalt magma were intruded simultaneously into the ring dyke, causing the basalt and rhyolite to mingle explosively. The rejuvenation of the magma chamber and subsequent subsidence of the caldera produced a mixed and mingled crystal mush now preserved in the ring dyke. The ring dyke represents residual magma from a caldera-forming eruption. Keywords: caldera, ring dyke, rhyolite, syenite, rejuvenation, replenishment.

Experimental melt (glass) compositions indicate that most of the S-type granites of the Cape Granite Suite in South Africa have ferromagnesian contents too high to represent melts. Consequently, the composition of the more mafic granites demands the addition of an Fe- and Mg-rich component to the magma. The compositions of the granites evolve along well-defined trends away from the likely melt composition for many components plotted against Mg + Fe. An increase in A/CNK, Mg#, Ca, and HREEs, as well as a decrease in K and Si, as a function of increasing Mg + Fe appears to limit the contaminant to garnet (up to 20 wt%). The rate of Ti increase, as a function of Mg + Fe increase in the granites, matches that defined by the stoichiometry of high-temperature biotite, but cannot be the product of accumulation of biotite ([+ or -] other phases) in the magma because the chemical trends are inconsistent with this, particularly those portrayed by K and Ti as a function of Mg + Fe. This, in conjunction with the fact that no large, counterbalancing population of very leucocratic material exists in the Cape Granite Suite, suggests that the relatively mafic granites are not the products of garnet fractional crystallization. Rather, these appear to be the result of selective entrainment of peritectic garnet and ilmenite. Thus, this work indicates that much of the compositional variation in the granites is primary, reflecting the magma composition that ascended from the source, and is controlled by the proportion of peritectic products entrained into the melt. There is no indication of entrainment of a mineralogically diverse residuum (restite). Keywords: S-type granite, granite geochemistry, granite petrogenesis, garnet.

Large volumes of silicic magma were produced on a very short timescale in the nested caldera complex of the SW Nevada volcanic field (SWNVF). Voluminous ash flows erupted in two paired events: Topopah Spring (TS, >1,200 [km.sup.3], 12.8 Ma)-Tiva Canyon (TC, 1,000 [km.sup.3], 12.7 Ma) and Rainier Mesa (RM, 1,200 [km.sup.3], 11.6 Ma)-Ammonia Tanks (AT, 900 [km.sup.3], 11.45 Ma; all cited ages are previously published [sup.40]Ar/[sup.39]Ar sanidine ages). Within each pair, eruptions are separated by only 0.1-0.15 My and produced tufts with contrasting isotopic values. These events represent nearly complete evacuation of sheet-like magma chambers formed in the extensional Basin and Range environment. We present ion microprobe ages from zircons in the zoned ash-flow sheets of TS, TC, RM, and AT in conjunction with [[delta].sup.18]O values of zircons and other phenocrysts, which differ dramatically among subsequently erupted units. Bulk zircons in the low-[[delta].sup.18]O AT cycle were earlier determined to exhibit ~1.5 [per thousand] core-to-rim oxygen isotope zoning; and high-spatial resolution zircon analyses by ion microprobe reveal the presence of older grains that are zoned by 0.5-2.5 [per thousand]. The following U-Pb isochron ages were calculated after correcting for the initial U-Pb disequilibria: AT (zircon rims: 11.7 [+ or -] 0.2 Ma; cores: 12.0 [+ or -] 0.1 Ma); pre-AT rhyolite lava: (12.0 [+ or -] 0.3 Ma); RM: 12.4 [+ or -] 0.3); TC: (13.2 [+ or -] 0.15 Ma); TS: (13.5 [+ or -] 0.2). Average zircon crystallization ages calculated from weighted regression or cumulative averaging are older than the Ar-Ar stratigraphy, but preserve the comparably short time gaps within each of two major eruption cycles (TS/TC, RM/AT). Notably, every sample yields average zircon ages that are 0.70-0.35 Ma older than the respective Ar-Ar eruption ages. The Th/U ratio of SWNVF zircons are 0.4-4.7, higher than typically found in igneous zircons, which correlates with elevated Th/U of the whole rocks (5-16). High Th/U could be explained if uranium was preferentially removed by hydrothermal solutions or is retained in the protolith during partial melting. For low-[[delta].sup.18]O AT-cycle magmas, rim ages from unpolished zircons overlap within analytical uncertainties with the [sup.40]Ar/[sup.39]Ar eruption age compared to core ages that are on average ~0.2-0.3 My older than even the age of the preceding caldera forming eruption of RM tuff. This age difference, the core-to-rim oxygen isotope zoning in AT zircons, and disequilibrium quartz-zircon and melt-zircon isotopic fractionations suggest that AT magma recycled older zircons derived from the RM and older eruptive cycles. These results suggest that the low-[[delta].sup.18]O AT magmas were generated by melting a hydrothermally-altered protolith from the same nested complex that erupted high-[[delta].sup.18]O magmas of the RM cycle only 0.15 My prior to the eruption of the AT, the largest volume low-[[delta].sup.18]O magma presently known. Keywords Paintbrush tuff * Timber Mountain tuff * Oxygen isotopes * Geochronology * Isotope zoning * Zircon * Yucca Mountain

The presence or absence of a thermally anomalous mantle plume during the formation of the widespread Carboniferous-Permian magmatism of northern Europe is examined. The geochemistry of representative samples from the extensive Carboniferous-Permian dyke and sill intrusions across northern Europe are reported in order to ascertain whether they have a common 'plume' source. Both tholeiitic and alkaline magmas have diverse trace element compositions. Alkaline samples with relatively low Ti and Nb/ La < 1 are considered to originate in the lithospheric mantle and those with Nb/La > 1 from the asthenosphere. The tholeiites have a close affinity to E-MORB but have mixed with variable amounts of lithosphere and upper crust. Tectonic reorganisation and decompression melting of a trace element-enriched mantle is considered to have controlled the Carboniferous-Permian magmatism, which contains no coherent geochemical evidence for a single plume-related thermo-chemical anomaly.

This study presents a pre-eruptive magma storage model for the rhyodacite and andesite magmas erupted during the 3430 yBP caldera-forming eruption of Aniakchak volcano, Alaska, derived from phase equilibria experiments and petrological data. The compositions of Fe-Ti oxide pairs from the early erupted Plinian rhyodacite pumice yield core temperatures of 871-900[degrees]C, with rims up to ~942[degrees]C, and f[O.sub.2] from -10.6 to -11.8 log units. Melt inclusions entrapped in plagioclase phenocrysts have [H.sub.2]O contents between 3 and 5 wt%, estimated by FTIR and electron microprobe volatiles by difference methods, with no detectable C[O.sub.2]. Assuming water saturation, this corresponds to entrapment pressures between ~65 and 150 MPa. Phase equilibria results reproduce the natural phase assemblages at [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] of 95-150 MPa at 870-880[degrees]C, assuming water saturation. A mismatch in experimental versus natural glass Si[O.sub.2] and [Al.sub.2][O.sub.3], and MELTS models for [H.sub.2]O-undersaturated conditions indicate that the rhyodacite may not have been [H.sub.2]O saturated. MELTS models with [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.] = 0.8 and [P.sub.total] of 125-150 MPa at 870-880[degrees]C reproduce the natural groundmass glass [Al.sub.2][O.sub.3] composition best, indicating the magma may have been slightly [H.sub.2]O undersaturated. Those pressures correspond to storage at 4.5-5.4 km depth in the crust. MELTS models and VBD estimates from melt inclusions in titanomagnetite grains from the andesite indicate pre-eruptive conditions of ~1,000[degrees]C and > 110 MPa, corresponding to a minimum residence depth of ~4.1 km assuming water saturation or greater if the magma was [H.sub.2]O undersaturated. Previous geochemical studies indicate separate histories of the two magmas, though they retain some evidence that they are ultimately related through fractional crystallization processes. Analogous to the 1912 Novarupta magmas, the rhyodacite and andesite presumably originated within the same crystal mush zone beneath the edifice, yet were separated laterally and underwent different degrees of crustal assimilation. The andesite must have resided in close proximity, with ascent occurring in response to movement of the rhyodacite, and resulting in extensive syn-eruptive mingling.

The Sudbury Igneous Complex of Ontario, Canada, is the remnant of a voluminous melt sheet produced in a few minutes by impact of a massive meteorite into continental crust 1.85 Ga ago. The transient cavity and melting zone reached the Moho and instantly (~2 min) relaxed to form a more familiar large, shallow crater holding a thick, superheated (~1700[degrees]C) melt sheet covered by ~2 km of breccia. There is little about the resulting bimodal igneous complex that resembles crystallization of well-known sheet-like bodies of similar composition. Yet, the norite and granophyre exhibit a remarkable similarity in isotopic and trace element compositions, suggesting an intimate common parentage from the surrounding crust. This petrogenetic enigma is explained here as a natural, unavoidable consequence of the impact process in the rapid formation of a superheated magmatic emulsion, which we take as the high-temperature equivalent of breccia. A wide spectrum of viscously discrete, interdispersed parcels of mafic and felsic liquids, reflecting the compositional heterogeneity of the target crustal materials, formed the emulsion. Within days to mouths, the emulsion components separated according to their relative densities into a bimodal norite-granophyre assemblage that formed the basic structure of the present Sudbury Igneous Complex. There is clear evidence of this emulsion in the earliest dikes (i.e., offsets), which likely give the earliest state of the nascent melt sheet. Immediately following emulsion separation, the strongly superheated bimodal melt sheet underwent vigorous thermal convection in each layer. These convective motions homogenized and rapidly cooled the magma to the liquidus temperatures, whereupon convection ceased. The pattern of convection was pinned in place by the embayment topography of the crater floor, which in turn played a pivotal role in directing sulfide deposition into the embayments. All further cooling was by conduction of heat through the upper and lower boundaries during which time solidification fronts were established and propagated inward from the upper and lower margins. There is clear evidence of solidification from the floor upward and the roof downward. Minimal differentiation and compositional modification took place throughout cooling and solidification. Nevertheless, during the solidification stage, granitic rock fragments on the crater floor and rafts of fallback breccia from the thick overlying Onaping Formation became unstable and entered the melt sheet, and the partially melted remnants collected at the interface between the norite and granophyre. Some interstitial melt from the norite also percolated upward, and, altogether, the blocks and melt produced the distinctive chemical and physical characteristics of the unusual Transition Zone. The Sudbury melt sheet is, in essence, a full-scale magmatic experiment. The conditions of formation, relative to any other large terrestrial magma, are 'precisely' known. Thus the clear lack of any significant modal layering, the overall homogeneous nature of each unit, and the lack of any significant chemical differentiation through crystal fractionation establish Sudbury as a valuable example of what does not happen under the initial conditions long assumed to prevail at the formation of most large magma chambers. Keywords: magma, viscous emulsion, Sudbury, melt sheet, impact melt, differentiation.

Southwestern Japan during Paleogene time was affected by subduction of the Kula and Pacific plates beneath the eastern margin of Eurasia, followed by a brief episode of transform faulting to allow the Shikoku Basin to open at 27-15Ma. Subsequent opening of the Japan Sea back-arc basin in middle Miocene time broke Japan away from Eurasia, and SW Japan rotated clockwise ~45[degrees] as it drifted south (17-15 Ma). Southward drift required subduction of the Philippine Sea plate beneath SW Japan, leading to the formation of a magmatic arc. Subduction of the hot Shikoku Basin lithosphere and spreading ridge resulted in distinctive volcanism in the SW Japan forearc between 17 and 12 Ma. This volcanism included mid-oceanic-ridge basalt (MORB)-like intrusions and oceanic-island basalt (OIB)-type alkali basalts, felsic plutons in the accretionary prism, and high-magnesium andesites along the Setouchi forearc basin. Mafic magmas in the outermost forearc originated from the subducted Shikoku Basin spreading ridge, whereas Setouchi high-magnesium andesites (HMA) may have resulted from the interaction of melts of the subducted Philippine Sea plate with the overlying mantle. Felsic magmas in the forearc resulted from melting of Shimanto Belt sediments caused by intrusion of HMA magmas. Persistent rear-arc volcanism was caused by upwelling asthenosphere associated with opening of the Sea of Japan. Rear-arc volcanism began ca. 25 Ma as rift-fill low-alkali tholeiite volcanism and was replaced gradually after 12 Ma by alkali basalt volcanism. Upwelling-related alkali volcanism continues up to the present, whereas forearc volcanism ceased at 12 Ma. The volcanic arc narrowed with time as the Philippine Sea slab descended and slowly cooled. Adakitic dacites erupted after 1.7 Ma above the 100-km-depth contour of the subducted Philippine Sea plate, suggesting that melting resulted from interaction of the slab with upwelling asthenosphere. Interactions between upwelled rear-arc asthenosphere and subduction of the hot Philippine Sea slab appear to have been the main controls of magmatism for the Neogene SW Japan arc. Keywords: Neogene, back-arc basin opening, volcanism, SW Japan, subduction reinitiation.

The oldest sedimentary and volcanic successions, metamorphic rocks and magnetic intrusions exposed in the Saghand area of Central Iranian Terrane represent the elements of terminal Neoproterozoic-Early Cambrian magmatic arc complex. The three main episodes of orogenic activity in Noeproterozoic-Early Cambrian, the Late Triassic, and the Eocene are revealed through the new U-Pb ages and geochemical data.

The discovery of mafic dike swarm with sheeted dikes led to the belief that these were generated during Silurian extension producing Connecticut valley-Gaspe trough. The Quebec embayment of the Laurentian rifted margin provides an alternative hypothesis regarding the origin of basin, being pull-apart basins.

Volcanologists and researchers learned about the temperature of magma changes during an eruption by observing crystals obtained inside the lava from Mount St. Helens. It was found that crystals form not from cooling temperatures but as the result of drop in pressure as the magma chugs to the surface, forcing it to cool itself by emitting heat and it was also noticed that crystals growing in the magma early well before erupting were associated with lower temperature while those closer to the time of eruption recorded high temperatures.