Main Episodes Research Articles

Onset and Progression of Serpentinization and Magnetite Formation in Olivine-rich Troctolite from IODP Hole U1309D

Serpentinization of olivine-rich troctolite from core 227, Integrated Ocean Drilling Program (IODP) Hole U1309D ranges from 10 to 90. Two episodes of serpentinization are recognized. The first, dominant in weakly serpentinized samples, is an approximately isochemical (except for water) replacement of olivine (Fo(8485)) by a mixture of serpentine (antigorite, Mg-number 92) and brucite (amakinite-rich; Mg-number 65). The compositions of the minerals in type 1 veins are a reflection of FeMg exchange between olivine and the brucite serpentine formed during early serpentinization. The early serpentinite veins (type 1) are thin ( 005 mm), irregular, and exploit pre-existing cracks in olivine. The presence of antigorite suggests that early serpentinization occurred at T 300C. Type 1 veins reflect rock-dominated serpentinization, became isolated early in their history, and persist as relicts in all but the most altered samples. The main episode of serpentinization is manifested by through-going lizardite (average Mg-number 96)magnetite veins (type 2). Type 2 veins define an anastomosing foliation, may be several millimeters in width and appear to exploit pre-existing, favorably oriented type 1 veins. Type 2 veins reflect open-system serpentinization. Magnetite in these veins formed by oxidation of the Fe in brucite and serpentine, whereas addition of silica to the system converted the Mg-component of the brucite to serpentine. Magnetite forms one or more distinct bands in the interior of the vein and is never in direct contact with relict olivine. A bruciteserpentine mixture, similar to that found in type 1 veins, but with lizardite instead of antigorite, is commonly present at the margins of type 2 veins (i.e. where they are in reaction contact with relict olivine). We interpret type 2 veins as a steady-state system where brucite continually forms at the olivinevein contact and then reacts out in the interior of the vein. This continual formation and destruction of brucite imposes an exceptionally low a(SiO2) on the system. Magnetite and olivine are never in contact in type 2 veins (or anywhere else) because the olivine-out reaction yields ferroan brucite and not magnetite. The desilication of serpentine in the type 2 veins is a reflection of the inherent instability of Fe-rich serpentine with respect to magnetite at low silica activity. Thus, the composition of serpentine in equilibrium with magnetite in serpentinites is a function of serpentinemagnetite and not serpentineolivine equilbria.

Post-Laramide and pre-Basin and Range deformation and implications for Paleogene (55–25 Ma) volcanism in central Mexico: A geological basis for a volcano-tectonic stress model

At central-eastern Mexico, in the Mesa Central province, there are several ranges that were formed after the K/T Laramide compression but before the Basin and Range peak extensional episodes at middle–late Oligocene. Two important volcano-tectonic events happened during this time interval, 1) uplift of crustal blocks exhuming the Triassic–Jurassic metamorphic sequence and formation of basins that were filled with red beds and volcanic sequences, and 2) normal faulting and tilting to the NE of these blocks and fanglomerate filling of graben and half-graben structures. The first event, from late Paleocene to early Eocene, was related to NNE and NNW oriented dextral strike-slip faults. These faults were combined with NW–SE en echelon faulting in these blocks through which plutonism and volcanism occurred. The second event lasted from early Oligocene to early Miocene and coincided with Basin and Range extension. Intense volcanic activity occurred synchronously with the newly-formed or reactivated old fault systems, producing thick sequences of silicic pyroclastic rocks and large domes. Volcano-tectonic peaks occurred in three main episodes during the middle–late Oligocene in this part of Mexico, at about 32–30 Ma, 30–28 Ma, and 26–25 Ma. The objectives of this work is to summarize the volcano-tectonic events that occurred after the end of the Laramide orogeny and before the peak episodes of Basin and Range faulting and Sierra Madre Occidental Oligocene volcanism, and to discuss the influence of these events on the following Oligocene–Miocene volcano-tectonic peak episodes that formed the voluminous silicic volcanism in the Mesa Central, and hence, in the Sierra Madre Occidental. A model based upon geological observations summarizes the volcanic-tectonic evolution of this part of Mexico from the late Paleocene to the Early Miocene.

Variability of Quaternary glacial erosion rates – A global perspective with special reference to the Eastern Pyrenees

Glaciers erode bedrock but are also efficient conveyors of debris supplied during a cycle of glaciation by processes other than basal erosion. In this dual capacity as both an eroding and a transporting agent lies the ambiguity of ‘glacial erosion’ as a geomorphic process, with implications for methods of measuring the removal of rock mass by glaciers in the geological past, and for interpreting what exactly the consequences have been on topography and elevation change. A global review of ∼400 Quaternary glacial denudation rates estimated from five different measurement techniques provides values ranging between 10 −4 and 10 mm yr −1. We investigate the causes of such wide variability by examining the respective influences of environmental setting and methodological bias. A reference frame chosen for assessing these issues is the Massif du Carlit (Pyrenees, France), where a quantified mass balance of the well preserved glacial, periglacial and paraglacial deposits was made possible by detailed geomorphological mapping and terrestrial cosmogenic nuclide dating of extant erosional and depositional landform sequences. Resulting age brackets helped to define three main episodes of ice-cap growth and decline, each characterized by a volume of debris and a mappable source area. Erosion rates were expressed in two ways: (i) as spatially averaged denudation rates ( D) during the successive stages of glacial advance to the line of maximum ice extent (MIE), post-MIE ice recession, and Lateglacial cirque readvance, respectively; and (ii) as cirque-wall recession rates ( R) where moraine facies criteria indicated a supraglacial provenance of debris. Results indicate low erosion ( D ≈ 0.05 mm yr −1) during the ice advance phase, probably because of thin or passive ice covering the low-gradient subglacial topography that occurs just above the late Pleistocene equilibrium line altitude (2.2–2.4 km). Erosion rates peaked ( D ≈ 0.6 mm yr −1 and R ≈ 2.4–4.5 mm yr −1) during the main transition to ice-free conditions, when deglacial debuttressing promoted the rapid response of freshly exposed slope systems to new equilibrium conditions in the steep crest zone. Lateglacial D- and R-values declined to 0.2–0.3 mm yr −1, with indications of spatially variable R controlled by lithology. In this environment glaciers overall behaved more as conveyors of debris supplied by supraglacial rock exposures in the mountain crest zone than as powerful modifiers of subglacial topography. This explains the widespread preservation of deep, in situ preglacial weathering profiles on relict Cenozoic land surfaces in the deglacierized part of the Eastern Pyrenees. When plotted on the global data set analyzed and discussed in the review, the East Pyrenean erosion rates stand out as being amongst the lowest on record.

New thermochronologic constraints on the evolution of the Zaldívar porphyry copper deposit, Northern Chile

Life spans and thermal evolution of hydrothermal systems are of fundamental metallogenic importance. We were able to establish the chronology and cooling history of the Zaldivar porphyry copper deposit (Northern Chile) by applying a combination of different isotopic dating methods in minerals with different closure temperatures, including 40Ar/39Ar geochronology and zircon fission track thermochronology, together with fluid inclusion thermometry and previous published U–Pb zircon geochronology. The hydrothermal mineralization in the Zaldivar deposit is genetically related to the Llamo Porphyry unit. Samples of igneous biotites from this intrusion yielded 40Ar/39Ar plateau ages between 35.5 ± 0.7 and 37.7 ± 0.4 Ma defining a weighted average of 36.6 ± 0.5 Ma (2σ). In contrast, one sample from the Zaldivar porphyry, one from the andesites, and two from the Llamo porphyry yielded considerably younger fission track ages of approximately 29 Ma with a weighted mean for all ages of 29.1 ± 1.7 Ma (2σ). Thermal and compositional constraints for the hydrothermal system in the Zaldivar deposit from fluid inclusions thermometry show that at least three fluid types broadly characterize two main hydrothermal episodes during the evolution of the deposit. The main mineralization and alteration event is characterized by high temperature (above 320°C) hypersaline fluids (salinity between 30 and 56 wt.% NaCl equivalents) coexisting with low-density gas-rich inclusions (salinity less than 17 wt.% NaCl equivalents) that homogenizing into the gas phase at temperatures above 350°C. The second episode corresponds to a low-temperature event which is characterized by liquid-rich fluid inclusions that homogenize into the liquid phase at temperatures ranging from 200°C to 300°C with salinities lower than 10 wt.% NaCl equivalents. The 40Ar/39Ar data (36.6 ± 0.5 Ma, weighted average) obtained from igneous biotites represent the minimum age for the last high-temperature (above 300°C) hydrothermal pulse. When compared with previously published U–Pb ages (38.7 ± 1.3 Ma) in zircons from the Llamo porphyry, a close temporal relationship between crystallization of the parental intrusion and the thermal collapse of the last high-temperature hydrothermal event is evident. Cooling took place from approximately 800°C (crystallization of the intrusive complex defined by zircon U–Pb ages) to below 300 ± 50°C (biotite 40Ar/39Ar closure temperature) within approximately 1.5 m.y. Because the thermal annealing of fission tracks in zircons occurs at temperatures of 240 ± 30°, the zircon fission track (ZFT) ages of 29.1 ± 1.7 Ma (2σ) mark the end of the thermal activity in the Zaldivar area, specifically the time when the whole area cooled below this temperature, well after the collapse of the main hydrothermal event in the Zaldivar porphyry copper deposit. This cooling age roughly coincides with the age defined for the emplacement of dacitic dikes at 31 ± 2.8 Ma (2σ) (published K–Ar whole rock), 5 km south of the Zaldivar deposit, in the Escondida area. This late magmatic pulse probably is responsible for high heat flow in the Zaldivar deposit as late as 29 Ma. There is no evidence that the low temperature hydrothermal pulse recognized by fluid inclusion studies is related to this thermal event. The zircon fission track cooling ages are interpreted to be related to the time lag required for complete relaxation of the perturbation of the isotherms in the geothermal field imposed by the intrusion of magmatic bodies, with or without any association with low temperature hydrothermal activity.

Capturing magma intrusion and faulting processes during continental rupture: seismicity of the Dabbahu (Afar) rift

Continental rupture models emphasize the role of faults in extensional strain accommodation; extension by dyke intrusion is commonly overlooked. A major rifting episode that began in 2005 September in the Afar depression of Ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture. Earthquakes recorded on a temporary seismic array (2005 October to 2006 April), direct observation of fault patterns and geodetic data document ongoing strain and continued dyke intrusion along the ∼60-km long Dabbahu rift segment defined in earlier remote sensing studies. Epicentral locations lie along a ∼3 km wide, ∼50 km long swath that curves into the SE flank of Dabbahu volcano; a second strand continues to the north toward Gab'ho volcano. Considering the ∼8 m of opening in the September crisis, we interpret the depth distribution of microseismicity as the dyke intrusion zone; the dykes rise from ∼10 km to the near-surface along the ∼60-km long length of the tectono-magmatic segment. Focal mechanisms indicate slip along NNW-striking normal faults, perpendicular to the Arabia–Nubia plate opening vector. The seismicity, InSAR, continuous GPS and structural patterns all suggest that magma injection from lower or subcrustal magma reservoirs continued at least 3 months after the main episode. Persistent earthquake swarms at two sites on Dabbahu volcano coincide with areas of deformation identified in the InSAR data: (1) an elliptical, northwestward-dipping zone of seismicity and subsidence interpreted as a magma conduit, and (2) a more diffuse, 8-km radius zone of shallow seismicity (<2 km) above a shadow zone, interpreted as a magma chamber between 2.5 and 6 km subsurface. InSAR and continuous GPS data show uplift above a shallow source in zone (2) and uplift above the largely aseismic Gab'ho volcano. The patterns of seismicity provide a 3-D perspective of magma feeding systems maintaining the along-axis segmentation of this incipient seafloor spreading segment.

Spatial variations in the star formation history of the Large Magellanic Cloud

AbstractBased on the quantitative analysis of a set of wide-field color—magnitude diagrams reaching the old main sequence-turnoffs, we present new LMC star-formation histories, and their variation with galactocentric distance. Some coherent features are found, together with systematic variations of the star-formation history among the three fields analyzed. We find two main episodes of star formation in all three fields, from 1 to 4 and 7 to 13 Gyr ago, with relatively low star formation around ≃ 4–7 Gyr ago. The youngest age in each field gradually increases with galactocentric radius; in the innermost field, LMC 0514–6503, an additional star formation event younger than 1 Gyr is detected, with star formation declining, however, in the last ≃ 200 Myr. The population is found to be older on average toward the outer part of the galaxy, although star formation in all fields seems to have started around 13 Gyr ago.

Pseudotachylyte and associated fault rocks at Alabameta area, Osun state, southwestern Nigeria.

This paper reports the occurrence of pseudotachylytes and associated fault rocks along Ifewara fault at Alabameta within the Ife-Ilesha Schist Belt, Southwestern Nigeria. The fault separates the schist belt into two lithostratigraphic units: a western unit composed mainly of mafic to ultramafic rocks and metapelites and an eastern unit composed of quartzites, quartz schist, metapelites and quartzo-feldspathic (granite) gneisses. These were intruded by granites and pegmatites. The area was affected by three main episodes of deformation. D1 produced recumbent folds probably associated with big nappes and are responsible for the flat lying foliation (S1) common in this area. D2 produced upright, tight to isoclinal folds responsible for the general north-south trending foliation (S2) and major lithological banding of the belt that define the structural grain of the area. D3 is associated with the major transcurrent faulting (the Ifewara fault), this produced mylonites in the north, near Iwaraja. To the south, the mylonites are locally cut by pseudotachylyte, especially near Alabameta. The presence of pseudotachylyte is interpreted as a result of frictional melting along the Ifewara Fault, probably associated with a late, high-level movement along the fault. IFE Journal of Science Vol. 9 (2) 2007 pp. 191-202

Mezcla de magmas en Vulcanello (Isla Vulcano, Italia)

Volcanic activity in Vulcano starts about 350 ka ago and continues up to present day with the development of thre main episodes corresponding to the calderas of Piano and La Fossa, and Vulcanello. These cover a compositional range from rhyolitic to trachybasaltic rocks. This lithological diversity is produced by different petrogenetic processes such as fractional crystallization, assimilation coupled to fractional crystallization (AFC), mixing, etc. The eruption of Vulcanello area emitted trachyandesitic materials, including shoshonites and latites. A magma-mixing process is established between trachytes and shoshonites to origine latites. Trachytes and rhyolites are produced by fractional crystallization and by ACF processes (assimilation of sedimentary rocks) from trachyandesitic magmas.

Blood, timber, and the state in West Kalimantan, Indonesia

Abstract: West Kalimantan (West Borneo) has a history of violent communal conflict.1 It also has extensive forests that have been looted for decades. The argument will be that these two are linked, but not by the grievances of the forest dwellers. Except in its first few days, the two main episodes of 1997 and 1999 were not driven mainly by grievances among marginal groups. Rather, explanations based on the ‘resource curse’ carry more weight. These focus attention on the contested nature of the state, rather than on rebellious activities of marginal groups. When state institutions were thrown into disarray by the sudden resignation of President Suharto in 1998, Dayak militants already close to state power rewrote the rules of local politics by demonstratively ‘cleansing’ certain areas of an unpopular immigrant minority. This theatrical manoeuvre impressed political rivals sufficiently to allow Dayaks to gain control over several timber‐rich districts, which had a thriving black economy. Malays later imitated these techniques to stem the tide.

New K–Ar age determinations of Kilimanjaro volcano in the North Tanzanian diverging rift, East Africa

The Kilimanjaro is the African highest mountain and culminates at 5895 m high. This huge volcanic edifice is composed of three main centres along a N110°E-striking axis (Shira, Kibo and Mawenzi from W to E), and emplaced in a key area where a major N80°E-oriented volcanic lineament intersects a first-order NW–SE basement fault-like discontinuity. Seventeen K–Ar ages (on microcrystalline groundmass) acquired on lavas and intrusive facies from the three eruptive centres confirm that the Plio-Quaternary volcanicity of Kilimanjaro is clearly polyphased. The oldest phases of volcanic activity begun at ~ 2.5 Ma in the Shira vent and our data suggest that the latest important phases occurred around 1.9 Ma, just before the collapse of the Northern part of the edifice. Magmatic activity then shifted eastwards in the Mawenzi and Kibo twin centres where initial volcanism is dated at ~ 1 Ma. Two K–Ar ages obtained for the most recent Mawenzi rocks from the Neumann Tower-Mawenzi group (492 ka) and Mawenzi eruptive centre (448 ka), near the present summit, are linked to the final stage of edification for this centre. Whereas the eruptive activity ceased in the Mawenzi, it still continued on Kibo since sub-actual time. The oldest dated rocks from Kibo (482 ka) is obtained on a dyke from the Lava Tower group cropping out at 4600 m high. The main phase of magmatism on Kibo is recorded by two lava formations with a great spatial extension – the Rhomb Porphyry group and the Lent group – that have been emplaced in a short time interval at ~ 460–360 ka (including two erosive stages) and 359–337 ka, respectively. Based on the dating of Caldera rim group lavas, it is shown that the edification of the present cone was accomplished in a period ranging from 274 to 170 ka. The new ages obtained for the main episodes of volcanic activity on Kibo appear to roughly coincide with the oldest known Quaternary glaciations. The interaction between eruptive phenomena and the ice cover is assumed to have played an important role in triggering collapse processes and associated lahars deposits. The last volcanicity, around 200–150 ka, is marked by the formation of the present summit crater in Kibo and the development of linear parasitic volcanic belts, constituted by numerous Strombolian-type isolated cones on the NW and SE slopes of Kilimanjaro. These belts are likely to occur above deep-seated fractures that have guided the magma ascent, and the changes in their directions with time might be related to the rotation of recent local stress field.

“La ascención cortés de Apolonio”

The well-known brilliance of the anonymous Libro de Apolonio, the mid-thirteenth century vernacular version of the Historia Apollonii Regis Tyri is distinguished by the high literary stylization of the most significant motifs, and among them the initial incest gemination in the main episodes, as has been suggested by several scholars, such as C. Calvert Phipps and A. Deyermond. However, a part of criticism downplays the reverberation of this incest in one particular case, the musical evening in Pentapolin’s court, while other critics stress its echoes in other episodes without taking into account this one. On the contrary, it is necessary to give a comprehensive dimension to the ‘constructive incest’ between the king Architrastes and his daughter Luciana, together with the projection of this love within the courtly behaviour of Apolonio. The successive steps and offbeats before Apolonio’s concert deliver detailed images which spotlight a subtle game of charm, manipulation and acute perceptions among the three characters. All of this leads Apolonio to obtain the best crown from Architrastes, not only as king of Tyre, which allows him because of his recovered kingship to play music, but as the symbolic king of Pentapolin too, becoming father by transference, master and lover of the princess. The hero achieves this honour because of his ascent in courtly hierarchy, from being of a wretched foreigner to a male bonding with the king, and in his homophilia’s climb may be appreciated the author’s mastery over the poetic and narrative devices.

An Illustrated Life of Christ Presented to the Chinese Emperor: The History of Jincheng shuxiang (1640) (review)

Reviewed by: An Illustrated Life of Christ Presented to the Chinese Emperor: The History of Jincheng shuxiang (1640) Claudia von Collani (bio) Nicolas Standaert . An Illustrated Life of Christ Presented to the Chinese Emperor: The History of Jincheng shuxiang (1640). Monumenta Serica Monograph Series, vol. LIX. Sankt Augustin: Steyler Verlag, 2007. 333 pp. Hardcover €55.00, ISBN 978-3-8050-0548-7. Nicolas Standaert's book An Illustrated Life of Christ deals with the field known as visual culture, or in this case, visual and sensible religion. Visual culture is the traditional realm of art historians that considers the simultaneous effects of written books and painted pictures, where the former appeals to reason and the latter to emotion. Standaert, professor of Sinology at the University of Leuven, proposes in his book to investigate the emotions of the Chinese viewer excited by pictures of Jesus Christ. Before representing the images and the text of the book, Standaert explains the background and origin of the book Jincheng shuxiang about Jesus Christ. It was not the first book of that kind in China, but among the most important and beautiful ones. Scenes from the life of Jesus were published in China by the Jesuits Matteo Ricci in 1605 and João da Rocha (1583–1623) in 1619. Another famous book on the life of Jesus Christ with fifty-six engravings was published by Giulio Aleni (1582–1649) from Brescia in Quanzhou in 1637, the Tianzuhu jiangsheng chuxiang jingxie (Explanation of the images of the lord of heaven's incarnation). When the procurator of the China mission, the Fleming Nicolas Trigault (1577–1628), arrived in Europe in 1614, he was confronted with many tasks. According to the order of the Jesuit superior Niccolò Longobardi, he was to continue the advancement of Catholicism in China after the death of the pioneer Matteo Ricci (1552–1610). Trigault not only succeeded in establishing the Chinese vice-province independently from the province of Japan, but also recruited sponsors for the China mission from among the European nobility. One important city in his tour de propagande through Europe was Munich, the capital of Bavaria. The dukes of Wittelsbach were most fervent adherents of the Catholic Counter-Reformation. Since the Jesuits specifically were in charge of the Counter-Reformation, they were sponsored by the dukes. Duke Wilhelm V, called "the Pious," had the famous Jesuit church St. Michael built, the biggest Renaissance church north of the Alps, and also a new Jesuit residence in Munich. When Trigault arrived at Munich, he was already well known at the court from his publications, namely the famous De Christiana Expeditione apud Sinas suscepta, which contains Matteo Ricci's diary documenting the beginning of Catholic missions in China and a short description of the Chinese Empire. This book was published in Augsburg, and in 1617 the German translation appeared and was dedicated to Duke Wilhelm V. Therefore, the Munich court [End Page 431] received Trigault with great honors when he arrived in August 1616, and Trigault not only received stipends for the China mission, but also precious presents. The most beautiful gift destined for the Chinese emperor was a so-called "Pommern cabinet" (Kunst- oder Wunderkammer), an expensive cabinet made by craftsmen in Augsburg and Munich, that is, in southern Germany (Standaert presents pictures from another Pommern cabinet, which was destroyed during World War II). The precious cabinet was filled with many small artistic objects of daily life in miniature, mathematical and chirurgical instruments, playthings, pharmacy, and writing material. The cabinet for China also included wax figures of the Adoration of Three Magi and a little parchment booklet, dated 1617, with pictures of the main episodes in the life of Jesus. Besides the beautiful gifts from Europe for China, Trigault also brought along with him a very good library of mainly scientific books and a group of twenty-two Jesuits for the East. Among them were several Jesuits selected to reform the Chinese calendar, namely Johann Schreck (1576–1630), called Terrentius, from Constance; Giacomo Rho (1592–1638) from Milan; and Johann Adam Schall von Bell (1592–1666) from Cologne, the most important German Jesuit in China. During the course of the calendar reform, they...

Terrane amalgamation in the Eastern Goldfields Superterrane, Yilgarn Craton: Evidence from tectonostratigraphic studies of the Laverton Greenstone Belt

Tectonostratigraphic evolution of the Laverton Greenstone Belt involves amalgamation of structural relics of sedimentary basins and continental fragments in the Burtville Terrane to the east prior to their accretion to the Kurnalpi Terrane to the west. The Burtville Terrane records sedimentation and volcanism in a continental setting between ∼2758 Ma and ∼2715 Ma. The Kurnalpi Terrane is dominated by 2715–2700 Ma andesitic volcaniclastic rocks with erosional remnants of <2675 Ma siliciclastic sequences. Neither volcaniclastic nor siliciclastic sequences preserve evidence for sediment derivation from the Burtville Terrane, implying that accretion occurred after 2665 Ma. Nevertheless, there is evidence for early deformation episodes in the Kurnalpi Terrane because both the Wallaby and Mt Lucky sequences were deposited unconformably on folded strata. Uplift of the Margaret Dome, a granite–gneiss cored batholith north of the Laverton Domain, is interpreted to have been the main driving force for rapid deposition and burial of conglomeratic and turbiditic siliciclastic sequences in the Lake Carey basin. A switch from submarine canyon deposits to deep-water turbiditic rocks with time suggests extension and basin formation was initially driven by the uplift of the dome, however basin development switched to a flexural phase with increasing sediment load and ongoing uplift to the north. The ∼2663 Ma maximum depositional age for the Granny Smith Sequence indicates that active sedimentation may have been occurring contemporaneous with collisional orogeny. The collisional orogeny comprises four main episodes of compressive deformation starting after either ∼2675 Ma or 2665 Ma, and ending at ∼2650 Ma. D 1 involved development of N–S upright to inclined km-scale folds and axial planar foliation, and inversion of pre-collision extensional faults as reverse faults during east–west-directed compression. D 2 involved reactivation of D 1 reverse faults as transcurrent faults and development of NW–SE-directed dm-scale folds with associated axial planar foliation that overprints the early N–S foliation. D 2 occurred under a NE–SW-directed compressive stress field. To the west, the Celia Fault records D 2 as its first deformation, suggesting a westward migrating deformation front. The Celia Fault Zone records its second deformation episode (D 3) as sinistral reactivation of the fault zone and locally influenced lode-gold development. D 3 occurred during WNW–ESE-directed maximum compression. The final compressive deformation event (D 4) involved overprinting of the D 3 shear fabric by conjugate arrays of kink bands in the Celia Fault Zone during a clockwise rotation of the compressive stress field into a NNW–SSE orientation. The tectonic process responsible for such a rapid uplift and deposition of thick synorogenic sediments lateral to the deformation front and penecontemporaneous with collisional orogeny, invites comparisons with modern arc-related settings. The present suture zone between the Indo-Australian Plate and the Pacific Plate in New Guinea records active deposition of fluvial sediments laterally along the accretion zone and in thick deep-water fans onto the Bismarck Sea floor.

A comparative U–Th–Pb (zircon–monazite) and 40Ar–39Ar (muscovite–biotite) study of shear zones in northern Victoria Land (Antarctica): implications for geochronology and localized reworking of the Ross Orogen

AbstractMylonitic granites from two shear zones in northern Victoria Land (Antarctica) were investigated in order to examine the behaviour of the U–Th–Pb system in zircon and monazite and of the 40Ar–39Ar system in micas during ductile deformation. Meso‐ and micro‐structural data indicate that shear zones gently dip to the NE and SW, have an opposite sense of shear (top‐to‐the‐SW and ‐NE, respectively) and developed under upper greenschist facies conditions. In situ U–Pb dating by laser‐ablation inductively coupled plasma‐mass spectrometry of zircon areas with well‐preserved igneous zoning patterns (c. 490 Ma) confirm that granites were emplaced during the Early Cambrian to Early Ordovician Ross–Delamerian Orogeny. Monazite from the Bier Point Shear Zone (BPSZ) mainly yielded U–Th–Pb ages of c. 440 Ma, in agreement with in‐situ Ar laserprobe ages of syn‐shear muscovite and with most Ar ages of coexisting biotite. The agreement of ages derived from different decay schemes and from minerals with different crystal‐chemical features suggests that isotope transport in the studied sample was mainly controlled by (re)crystallization processes and that the main episode of ductile deformation in the BPSZ occurred at c. 440 Ma. Cathodoluminscence imaging showed that zircon from the BPSZ contains decomposed areas with faint relics of oscillatory zoning. These areas yielded a U–Pb age pattern which mimics that of monazite but is slightly shifted towards older ages, supporting previous studies which suggest that ‘ghost’ structures may be affected by inheritance. In contrast, secondary structures in zircon from the Mt. Emison Shear Zone (MESZ) predominantly consist of overgrowths or totally recrystallized areas and gave U–Pb ages of c. 450 and 410 Ma. The c. 450‐Ma date matches within errors most monazite U–Th–Pb ages and in‐situ Ar ages on biotite aligned along the mylonitic foliation. This again suggests that isotope ages from the different minerals are (re)crystallization ages and constrains the time of shearing in the MESZ to the Late Ordovician. Regionally, results indicate that shear zones were active in the Late Ordovician–Early Silurian and that their development was partially synchronous at c. 440 Ma, suggesting that they belong to a shear‐zone system formed in response to ∼NE–SW‐directed shortening. Taking into account the former juxtaposition of northern Victoria Land and SE Australia, we propose that shear zones represent reactivated zones formed in response to stress applied along the new plate margin as a consequence of contractional tectonics associated with the early stages (Benambran Orogeny) of the development of the Late Ordovician–Late Devonian Lachlan Fold Belt.

Response of Pinus uncinata Recruitment to Climate Warming and Changes in Grazing Pressure in an Isolated Population of the Iberian System (NE Spain)

ABSTRACTTo infer future changes in the distribution of tree species in response to climatic variability, we need an understanding of the recruitment dynamics and their climatic controls at the species’ distribution limit. We studied the recruitment processes in an isolated population of Pinus uncinata Ram. located at the southwestern limit of the species’ distribution in Europe (Iberian System, NE Spain). We assessed (1) the temporal patterns of pine recruitment, and (2) how climate influenced recruitment. To reconstruct the recent recruitment episodes and to assess the climatic influence on recruitment and radial growth we employed dendrochronological methods. We mapped, measured the size, and estimated the age of all P. uncinata individuals located within a 50 m × 40 m plot. Additional age data were obtained from individuals located in four nearby 20 m × 20 m plots. The main episodes of tree establishment (early 1960s, late 1980s) coincided with low radial growth during a period with reduced grazing pressure. Grazing pressure and tree recruitment were not related at the spatiotemporal scale of this study. High May, August, and September minimum temperatures and high April precipitation were positively associated with recruitment, whereas high maximum April and June temperatures were negatively associated with recruitment. The studied population was in equilibrium with climate until the late 1990s, one of the warmest decades in the 20th century, when recruitment decreased despite the availability of suitable sites for establishment and the presence of reproductive individuals. We suggest that late-summer temperatures might have a non-linear negative threshold effect on recruitment rather than a linear effect. Despite increasing evidence of climate-induced recruitment episodes in isolated cold mountain forests, threshold effects of temperature on recruitment may imply limited range shifts of these populations in response to climate warming.

Cenozoic Crustal Evolution and Mantle Dynamics of Post-Collisional Magmatism in Western Anatolia

Post-collisional magmatism in western Anatolia followed a continental collision event in the Early Eocene, and occurred in discrete pulses that appear to have propagated from north to south over time. The first episode occurred during the Eocene and Oligo-Miocene and was subalkaline in nature, producing medium-to high-K calc-alkaline granitoids and mafic to felsic volcanic rocks. Partial melting and assimilation-fractional crystallization of enriched subcontinental lithospheric mantle-derived magma(s) were important processes in the genesis and evolution of the parental magmas, which experienced decreasing subduction influence and increasing crustal contamination through the Early Eocene-Early Miocene. This magmatic episode coincided with continued regional compression and development of a thick orogenic crust, and was influenced by an influx of asthenospheric heat and melts provided by lithospheric slab break-off. Extensional tectonics replaced the regional compression by the Middle Miocene, following the initial collapse of the western Anatolian orogenic welt, and resulted in the development of metamorphic core complexes and horst-graben structures. The second main episode of magmatism occurred during the Middle Miocene (16-14 Ma) and produced mildly alkaline rocks that show a decreasing amount of crustal contamination and subduction influence through time. Although melting of a subduction-modified lithospheric mantle continued, an asthenospheric mantle-derived melt contribution played a major role in the generation of these mildly alkaline magmas. The inferred asthenospheric melt contribution was a result of delamination of the lowermost part of the lithospheric mantle and/or partial convective removal of the sub-continental lithospheric mantle (SCLM). The third episode of post-collisional magmatism started around ~12 Ma and continued through the Late Quaternary. The main melt source for this phase carried no subduction component and was generated by the decompressional melting of asthenospheric mantle, which flowed in beneath the attenuated continental lithosphere in the Aegean extensional province. Lithospheric-scale extensional fault systems acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface. Post-collisional magmatism in western Anatolia thus displays compositionally distinct episodes controlled by slab break-off, lithospheric delamination, and asthenospheric upwelling and decompressional melting, reflecting the geodynamic evolution of the eastern Mediterranean region throughout the Cenozoic. These events and the associated processes in the mantle took place primarily in response to the plate tectonic evolution of the region and collectively constitute a time-progressive template for the mode and nature of the post-collisional magmatism common to most alpine-style orogenic belts.

New age constraints on emplacement of the Cévenol granitoids, South French Massif Central

During the development of the Variscan orogeny, large amounts of granitic melt were produced, giving rise to the intrusion of granitoids at different structural levels. Despite numerous studies, ages available from previous work on the Cevennes granites remain largely imprecise. In order to better constrain the age and emplacement mode of these granites, we have combined U-Pb dating on monazites and zircons and Ar-40/Ar-39 dating on biotites with petrological observations, major element chemical analysis and SEM zircon imaging on five samples from the Aigoual-St Guiral-Liron and Mont Lozere granitic massifs. The results revealed that granitic intrusions and cooling in Southern Cevennes occurred in a short time span at similar to 306 Ma after the main episode of regional metamorphism. Petrological and chemical data suggest that they result from a mixing between mantle-derived basic magmas (lamprophyres) and lower crust acid magmas. At a regional scale the production of these melts occurred at the end of crustal thickening induced by nappe stacking, at the same time as the late anatectic events recorded further north in the Velay dome and the granulite facies metamorphism recorded in metasedimentary granulite enclaves brought up by Tertiary volcanoes of the Velay area (Bournac).

Moderata Fonte: Women and Life in Sixteenth-Century Venice (review)

Reviewed by: Moderata Fonte: Women and Life in Sixteenth-Century Venice Karina Attar Paola Malpezzi Price Moderata Fonte: Women and Life in Sixteenth-Century Venice Madison, NJ: Fairleigh Dickinson University Press, 2003. Pp. 175. In Moderata Fonte: Women and Life in Sixteenth-Century Venice, Paola Malpezzi Price's aim is to consider Venice's "various aspects from the position of a twenty-first-century woman interested in the role of women in the sixteenth century, as well as in the life and works of Moderata Fonte as a representative of the educated women of that century" (21). Moderata Fonte is [End Page 211] thus not only a cultural and social history of Venetian women in the sixteenth century, but also the first book-length study of the writer's life and literary concerns. Malpezzi Price initially posits Moderata Fonte as an early modern 'feminist' who, "from within the accepted social structures of patriarchal family and society and from within recognized literary genres of the epic and dialogue, was able to elaborate and divulge a non-conformist message which helped gradually to modify certain aspects of the prevalent social ideology with regard to women" (20–21). This thesis motivates the rest of the book, which is divided into two parts of four chapters each. The first part, entitled "The Woman, the Writer, and the City," concerns the sixteenth-century Venetian contexts surrounding Fonte's life. The second half of the book, "Moderata Fonte's Defense of Women," considers several representations of female identity in Fonte's works and the ways in which these reflect the author's own preoccupations about the position of women in a patriarchal society. The first chapter recounts the main episodes of Fonte's life, the most significant political and cultural events in contemporary Venice that she would have witnessed, and the positive and negative responses to Fonte's works on the part of both her contemporaries but also scholars. The second chapter, "Growing Up Female and Literate in Sixteenth-Century Venice," offers an account of treatises on the role of women within domestic life and discusses the ways in which the experiences of sixteenth-century women followed or departed from the teachings promoted by the treaties. Against this background, Malpezzi Price shows that Fonte's specific educational experience was "probably atypical" since the males in her entourage disregarded contemporary social norms by encouraging her to develop her intellectual skills (48). Chapter 2 concludes with an examination of the theme of education in Fonte's Il merito delle donne, thus providing an essential link between Fonte's social context, biography, and literary concerns. The next chapter, "Cultural and Social Life in Sixteenth-Century Venice," covers significant aspects of life in the Republic, including sections on the role of religion, economy, and welfare. This chapter also discusses the limited avenues open to women who wished to or were forced to work. Of particular interest are the examinations of prostitution and women's significant role in this trade, and on and the ways in which traditional Venetian feasts and carnivals were used to promote a perception of Venice as a just, rich, and powerful republic. Chapter 4 develops this latter theme with a fascinating [End Page 212] discussion of "The Myth of Venice and Sixteenth-Century Women." Here, Malpezzi Price shows how multiple and conflicting images of Venice combined to create "a powerful, just, attractive, and divine woman as incarnation of the spirit of the city" (89). As the author pointedly remarks, however, such images perpetuated a notion of powerful womanhood that did not coincide with reality as expressed by Corinna, the most important speaker in Il merito delle donne, who argues that men have conspired to stop women from developing their intellectual talents by limiting their education and confining them in powerless positions. The fifth and sixth chapters focus on the depiction of the figure of the "Woman Warrior" and of the "Enchantress" in Fonte's epic poem I tredici canti del Floridoro. A composite of Bradamante and Marfisa in both name and character, the female warrior Risamante emerges, in Malpezzi Price's reading, as "an alternative to the behavior displayed by the majority of women, both in...

Structures of Syn‐deformational Granites in the Longquanguan Shear Zone and Their Monazite Electronic Microprobe Dating

Abstract: The Longquanguan shear zone is an important structural belt in the North China Craton, separating the underlying Fuping complex from the overlying Wutai complex. This shear zone has experienced three episodes of deformation: the first and main episode is a ductile top‐to‐ESE shear along the gently northwest‐west dipping foliations, while the other two episodes are later collapse sliding. Prolonged granites parallel to the shear foliations make one of the main compositions of the Longquanguan shear zone. These granites experienced deformation to form mylonitic rocks when they emplaced during the first episode of deformation. Structural characters of the granites and their contacts to the country rocks indicate that these granites possibly resulted from in‐situ partial remelting by shearing, i.e., they are syn‐deformational granites. Monazites in these mylonitic granites are magmatic minerals and their crystallization ages may represent ages of the magmatic events, and also the ages for the main deformation of the Longquanguan shear zone. Monazite electronic microprobe dating were carried on two samples of granite, which gives multiple peak ages, among which 1,846 Ma and 1,877 Ma are the main peak ages for the two samples. These ages represent the main deformation of the Longquanguan shear zone, which is consistent with the main regional geological event at about 1,850 Ma caused by the collision between the Eastern and Western Blocks in North China. The good match between the monazite ages and the corresponding regional tectono‐thermal events shows the feasibility and reliability of monazite electronic microprobe dating.

Structural controls of bedded iron ore in the Hamersley Province, Western Australia – an example from the Paraburdoo Ranges

Structure is the most important control on the location of hematite deposits in the Hamersley Province in the Pilbara region of Western Australia. Unravelling the structural history of mineralised areas, however, is complex because the Province underwent three orogenic events, and three regional extension events followed the main episodes of compression. Steeply E to ENE dipping normal faults immediately predated deposition of the Beasley Quartzite of the lower Wyloo Group after the Ophthalmian Orogeny. Steeply NE and SW–S dipping normal faults predated deposition of the McGrath formation of the middle Wyloo Group, following the Panhandle Orogeny. The resulting interpreted rift was subsequently reactivated and tilted during the Capricorn Orogeny. Late NE trending normal faults are confined to the eastern half of the Province. High-grade hematite deposits occur in rocks that range from intensely folded (Mt Whaleback, Giles Mini) to rocks with less, or only little deformation (Paraburdoo, Channar), suggesting that folding had at best limited influence on ore genesis. In contrast, extensional normal faults are always associated with high-grade hematite deposits, and in particular faults that link the underlying dolomites of the Wittenoom Formation with the overlying iron formation, thus providing a pathway for mineralising alkaline fluids.