Inversion of Taconian extensional structures during Paleozoic orogenesis in western Newfoundland

West Newfoundland was critical in developing the Wilson Cycle concept. Neoproterozoic rifting established a passive margin adjacent to the Iapetus Ocean. Ordovician (Taconian) arc–continent collision emplaced ophiolites and the thin-skinned Humber Arm Allochthon. Subsequent Devonian (Acadian) ocean closure produced basement-cutting thrust faults that control the present-day distribution of units. New mapping, and aeromagnetic and seismic interpretation, around Parsons Pond enabled the recognition of structures in poorly exposed areas.Following Cambrian to Middle Ordovician passive-margin deposition, Taconian deformation produced a flexural bulge unconformity. Subsequent extensional faults shed localized conglomerate into the foreland basin. The Humber Arm Allochthon contains a series of stacked and folded duplexes, typical of thrust belts. To the east, the Parsons Pond Thrust has transported shelf and foreland-basin units c. 8 km westwards above the allochthon. The Long Range Thrust shows major topographical expression but <1 km offset. Stratigraphic relationships indicate that most thrusts originated as normal faults, active during Neoproterozoic rifting, and subsequently during Taconian flexure. Devonian continental collision inverted the Parsons Pond and Long Range thrusts. Basement-cored fault-propagation folds in Newfoundland are structurally analogous to basement uplifts in other orogens, including the Laramide Orogen in western USA. Similar deep-seated inversion structures may extend through the northern Appalachians.

Pemodelan Struktur Bawah Permukaan Zona Subduksi dan Busur Gunungapi Jawa Timur berdasarkan Analisis Data Gravitasi

Zona subduksi di selatan Jawa Timur merupakan bagian dari subduksi panjang yang terbentuk akibat tumbukan lempeng Indo-Australia dan Eurasia. Keberadaan subduksi tersebut menjadi menarik untuk dikaji karena turut mempengaruhi aktivitas gunungapi dan potensi bencana alam di daerah tersebut. Pengkajian zona subduksi dan gunungapi dilakukan dengan melakukan pemodelan struktur bawah permukaan menggunakan anomali gravitasi dengan bantuan program Grablox dan Bloxer. Pemodelan dilakukan terhadap data sekunder anomali regional, dan anomali lokal. Data anomali gravitasi diperoleh dari Bureau Gravimetrique Internationale (BGI). Pembuatan model dilakukan dengan teknik inversi menggunakan metode Singular Value Decomposition (SVD) dan optimasi Occam. Hasil penelitian menunjukkan adanya penipisan kerak samudera rata-rata dari 20 km menjadi 15 km ke arah utara. Penipisan tersebut disebabkan adanya lapisan mantel atas yang menonjol dan mendesak kerak yang disebut flexural bulge. Ketebalan batuan sedimen pada cekungan busur belakang sebesar ~ 4,50 km, dan semakin ke timur nilainya semakin berkurang. Keberadaan dapur magma pada busur gunungapi di Jawa Timur pada umumnya diperkirakan pada kedalaman ~6 km.kata kunci: anomali gravitasi; zona subduksi dan gunung api, Grablox ;Bloxer; pemodelan anomali gravitasi

Pemodelan Struktur Bawah Permukaan 3D Purwokerto dan Sekitarnya Berdasarkan Data Anomali Gravitasi Bouguer Lengkap

Zona subduksi di selatan Jawa Timur merupakan bagian dari subduksi panjang yang terbentuk akibat tumbukan lempeng Indo-Australia dan Eurasia. Keberadaan subduksi tersebut menjadi menarik untuk dikaji karena turut mempengaruhi aktivitas gunungapi dan potensi bencana alam di daerah tersebut. Pengkajian zona subduksi dan gunungapi dilakukan dengan melakukan pemodelan struktur bawah permukaan menggunakan anomali gravitasi dengan bantuan program Grablox dan Bloxer. Pemodelan dilakukan terhadap data sekunder anomali regional, dan anomali lokal. Data anomali gravitasi diperoleh dari Bureau Gravimetrique Internationale (BGI). Pembuatan model dilakukan dengan teknik inversi menggunakan metode Singular Value Decomposition (SVD) dan optimasi Occam. Hasil penelitian menunjukkan adanya penipisan kerak samudera rata-rata dari 20 km menjadi 15 km ke arah utara. Penipisan tersebut disebabkan adanya lapisan mantel atas yang menonjol dan mendesak kerak yang disebut flexural bulge. Ketebalan batuan sedimen pada cekungan busur belakang sebesar 4; 50 km, dan semakin ke timur nilainya semakin berkurang. Keberadaan dapur magma pada busur gunungapi di Jawa Timur pada umumnya diperkirakan pada kedalaman 6 km.kata kunci: anomali gravitasi; zona subduksi dan gunung api, Grablox ;Bloxer; pemodelan anomaligravitasi

Growth and demise of an Archean carbonate platform, Steep Rock Lake, Ontario, Canada

The Steep Rock Group of northwest Ontario's Wabigoon subprovince is one of the world's thickest Archean carbonate platform successions. It was deposited unconformably over a 3001-2928 Ma gneissic terrane, and contains a remarkable group of biogenic and oolitic limestones, dolostones, micrites, and karst breccias capped by a thick paleosol developed between and over karst towers. The presence of aragonite fans, herringbone calcite, and rare gypsum molds suggests that the carbonate platform experienced at least local anaerobic and hypersaline depositional conditions. This sequence shows that a combination of chemical and biological processes was able to build a carbonate platform 500 m thick by 3 billion years ago. The carbonate platform is structurally overlain by a mixture of complexly deformed rocks of the Dismal Ashrock forming a mélange with blocks of ultramafic volcaniclastic rocks, mafic volcanics, carbonate, tonalite, lenses of Fe-ore rock, and metasedimentary rocks, in a shaly, serpentinitic, and fragmental ultramafic volcaniclastic matrix. The mélange shows evidence of polyphase deformation, with early high-strain fabrics formed at amphibolite facies, and later superimposed brittle fabrics related to the final emplacement of the mélange over the carbonate platform. An amphibolite- through greenschist-grade shear zone marks the upper contact of the mélange with overlying mafic volcanic and tuffaceous rocks of the ca. 2932 Ma Witch Bay allochthon, interpreted as a primitive island arc sequence. We suggest an evolutionary model for the area that begins with rifting of an arc sequence (Marmion Complex of the Wabigoon arc) that initiated subsidence and sedimentation on the Steep Rock platform and its correlatives that extend for a restored strike length exceeding 1000 km. Shallow water carbonate sedimentation continued until the platform was uplifted on the flanks of a flexural bulge related to the approach of the Witch Bay allochthon, representing collision of the rifted arc margin of the Wabigoon subprovince with the Witch Bay arc. Mélange of the Dismal Ashrock was formed as off-axis volcanic rocks were accreted to the base of the Witch Bay allochthon prior to its collision with the Steep Rock platform.