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.

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.