Abstract High resolution multibeam bathymetric and seismic data from the area north of the Banggai-Sula Islands, Indonesia, provide a new insight into the geological history of the boundary between the East Sulawesi ophiolite, the Banggai-Sula microcontinent and the Molucca Sea collision zone. Major continuous faults such as the Sula Thrust and the North Sula–Sorong Fault, previously interpreted to bound and pass through the area are not seen. The south-verging Batui Thrust previously interpreted offshore to the east of Poh Head cannot be identified. In the areas where the thrust was interpreted there is a north-vergent thrust and fold zone overlain by almost undeformed sediments. Gently dipping strata of the Banggai-Sula microcontinent margin can be traced northwards beneath younger rocks. In the east, rocks of the Molucca Sea collision complex are deformed by multigenerational folds, thrusts and strike-slip faults. There is a series of small thrusts between the leading edge of the collision complex and the foot of the slope. In the west a zone of transpression close to the East Arm of Sulawesi is the termination of the dextral strike-slip Balantak Fault extending east from Poh Head.

Abstract The Molucca Sea Collision Zone in eastern Indonesia is the site of an orthogonal collision between two active subduction systems. Both the Halmahera subduction zone, to the east, and the Sangihe subduction zone, to the west, have subducted oceanic lithosphere of the Molucca Sea Plate, which has now been completely consumed. Both volcanic arcs were active since the Neogene and provide a means of probing the element fluxes through the two systems. The geochemistry of Neogene and Quaternary lavas from each volcanic arc is compared to constrain changes in the mass fluxes through the systems and the processes controlling these fluxes at different times during their history. Both arcs show increased evidence for sediment recycling as the collision progressed, but for contrasting reasons. In Halmahera this may represent an increased sediment flux through the arc front, while in Sangihe it may simply reflect a greater opportunity for melting of sediment-fluxed portions of the mantle wedge. In both cases the change in arc geochemistry can be related to the evolving architecture of the particular subduction zone. The Halmahera lavas also record a temporal change in the chemistry of the mantle component that resulted from induced convection above the falling Molucca Sea Plate drawing compositionally distinct peridotite into the mantle wege.

Abstract The two volumes of Arthur Wichmann’s Die Erdbeben Des Indischen Archipels [ The Earthquakes of the Indian Archipelago ] (1918 and 1922) document 61 regional earthquakes and 36 tsunamis between 1538 and 1877 in the Indonesian region. The largest and best documented are the events of 1770 and 1859 in the Molucca Sea region, of 1629, 1774 and 1852 in the Banda Sea region, the 1820 event in Makassar, the 1857 event in Dili, Timor, the 1815 event in Bali and Lombok, the events of 1699, 1771, 1780, 1815, 1848 and 1852 in Java, and the events of 1797, 1818, 1833 and 1861 in Sumatra. Most of these events caused damage over a broad region, and are associated with years of temporal and spatial clustering of earthquakes. The earthquakes left many cities in ‘rubble heaps’. Some events spawned tsunamis with run-up heights >15 m that swept many coastal villages away. 2004 marked the recurrence of some of these events in western Indonesia. However, there has not been a major shallow earthquake (M ≥ 8) in Java and eastern Indonesia for the past 160 years. During this time of relative quiescence, enough tectonic strain energy has accumulated across several active faults to cause major earthquake and tsunami events, such as those documented in the historical records presented here. The disaster potential of these events is much greater now than in the past due to exponential growth in population and urbanization in areas destroyed by past events. Supplementary material: Translation of the catalogues into English, scanned PDFs of the original catalogues and geographical locations of most place names found in the catalogue (as a KMZ file) are available at https://dx.doi.org/10.6084/m9.figshare.c.2860405.v1

Tomographic images of the mantle beneath the region extending from the Molucca Sea eastward to Tonga, and from the Australian craton north into the Pacific, reveal a number of distinctive high seismic-velocity anomalies. The anomalies can be interpreted as subducted slabs and the positions of the slabs can be compared to predictions made by tectonic models for the region. Several strong anomalies are due to present-day subduction and the slab lengths and positions are consistent with Neogene subduction at the Tonga and the New Hebrides Trenches, where the anomalies suggest rapid rollback of subduction hinges since about 10 Ma, and beneath the New Britain and Halmahera Arcs. There are several generally flat-lying deeper anomalies which are not related to present subduction. Beneath the Bird's Head and Arafura Sea is an anomaly which we interpret to be the result of north-dipping subduction beneath the Philippines-Halmahera Arc between 45 and 25 Ma. A very large anomaly, which extends from the Papuan peninsula to the New Hebrides and from the Solomon islands to the east Australian margin, is interpreted as the result of south-dipping subduction beneath the Melanesian Arc between 45 and 25 Ma. Our interpretation implies that a flat-lying slab can survive for many tens of millions of years at the bottom of the upper mantle. There is a huge anomaly in the lower mantle which extends from beneath the Gulf of Carpentaria to Papua. We suggest this is a slab subducted before 45 Ma, which may be correlated with a Cretaceous slab beneath the Australian-Antarctic Discordance or an early Cenozoic slab sub-ducted north of Australia. The anomaly is located above the position where there must have been a change in polarity in subduction at the boundary between the north- and south-dipping subduction zones north of Australia between 45 and 25 Ma. All of these have been overridden by Australia since 25 Ma. One subduction system predicted by the tectonic models, the Marumuni Arc of Papua New Guinea, is not seen on the tomographic images.

This paper is an in-depth review of the architecture and evolution of the Western Sierra Nevada metamorphic province. Firsthand field observations in a number of key areas provide new information about the province and the nature and timing of the Nevadan orogeny. Major units include the Northern Sierra terrane, Calaveras Complex, Feather River ultramafic belt, phyllite-greenschist belt, mélanges, and Foothills terrane. Important changes occur in all belts across the Placerville–Highway 50 corridor, which may separate a major culmination to the south from a structural depression to the north. North of the corridor, the Northern Sierra terrane consists of the Shoo Fly Complex and overlying Devonian to Jurassic–Cretaceous cover, and it represents a Jurassic continental margin arc. The western and lowest part of the Shoo Fly Complex contains numerous tectonic slivers, which, along with the Downieville fault, comprise a zone of west-vergent thrust imbrication. No structural evidence exists in this region for Permian–Triassic continental truncation, but the presence of slices from the Klamath Mountains province requires Triassic sinistral faulting prior to Jurassic thrusting. The Feather River ultramafic belt is an imbricate zone of slices of ultra-mafic rocks, Paleozoic amphibolite, and Triassic–Jurassic blueschist, with blueschist interleaved structurally between east-dipping serpentinite units. The Downieville fault and Feather River ultramafic belt are viewed as elements of a Triassic–Jurassic subduction complex, within which elements of the eastern Klamath subprovince were accreted to the western edge of the Northern Sierra terrane. Pre–Late Jurassic ties between the continental margin and the Foothills island arc are lacking. A Late Jurassic suture is marked by the faults between the Feather River ultramafic belt and the phyllite-greenschist belt. The phyllite-greenschist belt, an important tectonic unit along the length of the Western Sierra Nevada metamorphic province, mélanges, and the Foothills island arc terrane to the west were subducted beneath the Feather River ultramafic belt during the Late Jurassic Nevadan orogeny. South of the Placerville–Highway 50 corridor, the Northern Sierra terrane consists of the Shoo Fly Complex, which possibly contains structures related to Permian–Triassic continental truncation. The Shoo Fly was underthrust by the Calaveras Complex, a Triassic–Jurassic subduction complex. The Late Jurassic suture is marked by the Sonora fault between the Calaveras and the phyllite-greenschist belt (Don Pedro terrane). As to the north, the phyllite-greenschist belt and Foothills island arc terrane were imbricated within a subduction zone during the terminal Nevadan collision. The Don Pedro and Foothills terranes constitute a large-magnitude, west-vergent fold-and-thrust belt in which an entire primitive island-arc system was stacked, imbricated, folded, and underthrust beneath the continental margin during the Nevadan orogeny. The best age constraint on timing of Nevadan deformation is set by the 151–153 Ma Guadelupe pluton, which postdates and intruded a large-scale megafold and cleavage within the Mariposa Formation. Detailed structure throughout the Western Sierra Nevada metamorphic province shows that all Late Jurassic deformation relates to east-dipping, west-vergent thrusts and rules out Jurassic transpressive, strike-slip deformation. Early Cretaceous brittle faulting and development of gold-bearing quartz vein systems are viewed as a transpressive response to northward displacement of the entire Western Sierra Nevada metamorphic province along the Mojave–Snow Lake fault. The preferred model for Jurassic tectonic evolution presented herein is a new, detailed version of the long-debated arc-arc collision model (Molucca Sea–type) that accounts for previously enigmatic relations of various mélanges and fossiliferous blocks in the Western Sierra Nevada metamorphic province. The kinematics of west-vergent, east-dipping Jurassic thrusts, and the overwhelming structural evidence for Jurassic thrusting and shortening in the Western Sierra Nevada metamorphic province allow the depiction of key elements of Jurassic evolution via a series of two-dimensional cross sections.