The Sottunga-Jurmo shear zone : structure and deformation history of a crustal-scale ductile shear zone in SW Finland

The aim of this study is to gain a better understanding of the structure and the deformation history of a NW-SE trending regional, crustal-scale shear structure in the Åland archipelago, SW Finland, called the Sottunga-Jurmo shear zone (SJSZ). Approaches involving e.g. structural geology, geochronology, geochemistry and metamorphic petrology were utilised in order to reconstruct the overall deformation history of the study area. The study therefore describes several features of the shear zone including structures, kinematics and lithologies within the study area, the ages of the different deformation phases (ductile to brittle) within the shear zone, as well as some geothermobarometric results. The results indicate that the SJSZ outlines a major crustal discontinuity between the extensively migmatized rocks NE of the shear zone and the unmigmatised, amphibolite facies rocks SW of the zone. The main SJSZ shows overall dextral lateral kinematics with a SW-side up vertical component and deformation partitioning into pure shear and simple shear dominated deformation styles that was intensified toward later stages of the deformation history. The deformation partitioning resulted in complex folding and refolding against the SW margin of the SJSZ, including conical and sheath folds, and in a formation of several minor strike-slip shear zones both parallel and conjugate to the main SJSZ in order to accommodate the regional transpressive stresses. Different deformation phases within the study area were dated by SIMS (zircon U-Pb), ID-TIMS (titanite U-Pb) and 40Ar/39Ar (pseudotachylyte wholerock) methods. The first deformation phase within the ca. 1.88 Ga rocks of the study area is dated at ca. 1.85 Ga, and the shear zone was reactivated twice within the ductile regime (at ca. 1.83 Ga and 1.79 Ga), during which the strain was successively increasingly partitioned into the main SJSZ and the minor shear zones. The age determinations suggest that the orogenic processes within the study area did not occur in a temporal continuum; instead, the metamorphic zircon rims and titanites show distinct, 10-20 Ma long breaks in deformation between phases of active deformation. The results of this study further imply slow cooling of the rocks through 600-700ºC so that at 1.79 Ga, 2 the temperature was still at least 600ºC. The highest recorded metamorphic pressures are 6.4-7.1 kbar. At the late stages or soon after the last ductile phase (ca. 1.79 Ga), relatively high-T mylonites and ultramylonites were formed, witnessing extreme deformation partitioning and high strain rates. After the rocks reached lower amphibolite facies to amphibolite-greenschist facies transitional conditions (ca. 500-550ºC), they cooled rapidly, probably due to crustal uplift and exhumation. The shear zone was reactivated at least once within the semi-brittle to brittle regime between ca. 1.79 Ga and 1.58 Ga, as evidenced by cataclasites and pseudotachylytes. In summary, the results of this study suggest that the Sottunga-Jurmo shear zone (and the South Finland shear zone) defines a major crustal discontinuity, and played a central role in accommodating the regional stresses during and after the Svecofennian orogeny.

ZONE INTERMÉDIAIRE – Recontruction de l’identité raciale dans L’Amant de Marguerite Duras

Tutkielman aiheena on Marguerite Durasin romaani L’Amant (suom. Rakastaja). Tarkastelen romaanin valkoihoisen nuoren tytön ”rodullisen” identiteetin rakentumista käyttäen heijastuskuvana Toista, tytön ”erirotuista” kiinalaista rakastajaa. Osittain omaelämäkerrallisen romaanin tapahtumat sijoittuvat Ranskan entiseen siirtomaahan, Indokiinaan. Kolonialismin aikainen rotusorto ja valkoisen ”rodun” mytologisen vallan rakentuminen ja konkretisoituminen ovat siis sekä tutkimukseni konteksti että tutkimuskohde. Tarkastelen missä määrin tytön rodullinen identiteetti pitää yllä – tai toisaalta rikkoo – ”rotujen” hierarkkista ajattelua. Tutkimuksen teoreettinen viitekehys on jälkikoloniaalinen (postkoloniaalinen) tutkimus, joka on monitieteellinen itsekriittinen tutkimusmetodi. Tutkimuksen tarkoituksena on kyseenalaistaa länsimaissa vallitsevia kategorioita. Päälähteinä käytetään mm. Dyerin (1997), Memmin (1994), Todorovin (1989), Girodin (2004), Hallin (1992, 1996), Derridan (1967, 1972, 1992), Shevoryn (2000), Dufourmentellen (2003) ja De Beauvoirin (1947) teoksia. Tutkimuksen keskeinen käsite on välitila, johon teoksen nuori tyttö voidaan tutkimustulosteni mukaan sijoittaa. Tyttö häilyy eräänlaisessa välitilassa valkoisen ja keltaisen ”rodun” välillä: hän tuntee kuuluvansa tavallaan molempiin ”rotuihin”, sillä hän on syntynyt Indokiinassa, puhuu paikallista kieltä ja suhtautuu paikallisiin tasavertaisemmin kuin valkoihoinen eliitti, mutta kuuluu kuitenkin syntyperältään valkoiseen ”rotuun”. Valkoisuutta ei usein määritellä ”roduksi”, vaikka muiden kuin valkoihoisten kohdalla ”rotu” määritellään joko negatiivisten tai positiivisten typologioiden mukaisesti. Tästä syystä valkoiset nähdään helposti ihmisyyden normina neutraaliksi väitetyssä valkoisten diskriminoivassa diskurssissa. L’Amant’ssa valkoisuus on näkemykseni mukaan kuitenkin näkyvää ja valkoisuuden valtaa kyseenalaistavaa. Valkoisen tytön perhe on valkoisten kolonialistien arvoasteikon alimmalla portaalla, sillä perhe on köyhä ja valkoisten valta rakentui suurelta osin siirtomaaisäntien taloudellispoliittiseen ylivaltaan. Koska tytön perheellä ei ole tarpeeksi varaa elitistiseen herruuteen, eliitti paheksuu tytön perhettä avoimesti erityisesti ”rotujen” välisen kielletyn suhteen tullessa julki, jolloin tyttö eristetään valkoisesta yhteisöstä. Kiinalainen puolestaan on miljardöörin perijä ja tämä suo hänelle hieman korkeamman aseman ”rotujen” hierarkiassa, vaikka hänen vaurautensa toisaalta uhkaakin valkoista valtaa. Myös romaanin monella tapaa konventioita rikkova seksuaalisuus on osa kielletyn suhteen välistä valtapeliä. Kirjailija strukturoi uudelleen patriarkaalisen sukupuolen rakentumisen feminisoimalla kiinalaisen miehen, sillä muussa tapauksessa hänen maskuliinisuutensa saattaisi saada ylivallan tytöstä, joka on sukupuolisesti Toinen.

Molluscan radiations and landscape evolution in Miocene Amazonia

This PhD study aims to exploit the rich archive provided by the Miocene mollusc fauna of the Pebas Formation and other inland Miocene Amazonian formations to reconstruct landscape evolution and biotic development in lowland Amazonia during the Neogene. Over 160 samples from more than 70 Pebas Formation outcrops mostly collected by the author were processed for this study. Additional samples were collected in Andean areas of Colombia and Venezuela and further material from other northwestern South American basins was studied in museums. Pebas Formation samples and well log data made available by Occidental Peru from three wells in the Marañon Basin in Peru were also investigated. During this study four genera and 74 species from the Pebas Formation have been described and a further 13 species have been introduced in open nomenclature, and several species were reported for the first time. The number of mollusc species attributed to the Pebas fauna has increased from around 50 to 156. The Pebas fauna is characterised as aquatic, endemic and extinct, and is a typical representative of a long-lived lake fauna. Fluvial taxa are not common, (marginal) marine taxa are rare. An additional molluscan fauna from the Miocene Solimões Formation of Brazil, containing 13 fresh water species was also described. The newly documented fauna was used to improve biostratigraphic framework of Miocene Amazonian deposits. Twelve mollusc zones were introduced, the upper eleven of which cover a time interval of approximately seven million years covered previously by only three pollen zones. An age model calculated for the borehole data indicates that the Pebas Formation was deposited between c. 24 and 11 Ma. The areal distribution of the outcropping mollusc zones uncovered a broad dome structure, termed here the Iquitos-Araracuara anteclise in the study area. The structure appears to have influenced river courses and also contributed to edaphic heterogeneity that may have been in part responsible for the current high biodiversity in the study area. The Pebas system was a huge system (> one million km2) dominated by relatively shallow lakes, but also containing swamps and rivers. The system was fed by rivers draining the emergent Andes in the west and lowlands and cratons to the east. The Pebas system was located at sea level and was open to marine settings through a northern portal running through the Llanos Basin and East Venezuela Basin towards the Caribbean. Cyclical baselevel changes possibly related to Mylankhovitch cycles, have been documented in depositional sequences of the Pebas Formation. The composition of the Pebasian mollusc fauna implies that the system was mostly a fresh water system. Such an interpretation is matched by strontium isotope ratios as well as very negative δ18O ratios found in the shells, but is at odds with oligohaline and mesohaline ichnofacies found in the same strata. The mollusc fauna of the Pebas Formation diversified through most of the existence of the lake system. The diversification was mostly the result of in-situ cladogenesis. The success of some of the Pebasian endemic clades is explained by adaptation to fresh water, low oxygen, common unconsolidated lake bottoms (soup grounds) as well as high predation intensity. Maximum diversity was reached at the base of the late Middle to early Late Miocene Grimsdalea pollen zone, some 13 Ma. At the time some 85 species co-occurred, 67 of which are considered as Pebasian endemics. A subsequent drop in species richness coincides with indications of elevated salinities, although a causal relation still needs to be established. Apparently the Pebas fauna went (almost) entirely extinct with the replacement of the lake system into a fluvio-tidal system during the Early Late Miocene, some 11 Ma.