Ridge-trench interactions and high- T -low- P metamorphism, with particular reference to the Cretaceous evolution of the Japanese Islands

Abstract

A corollary of plate tectonics is that spreading ridges ultimately interact with trenches; this is a consequence of the closure phase of the Wilson cycle that eliminates ocean basins. Ridge-trench interactions generate distinctive igneous, metamorphic, structural and sedimentation effects, which commonly are diachronous parallel to the trench; effects vary with plate boundary geometry and rate of migration is controlled by relative motion vectors. Identification of such interactions in the geological record is uncommon, which suggests that geological events triggered by ridge trench interactions are attributed to other phenomena, such as changes in plate motion or a singularity at the trench. The estimated greater length of plate boundaries in the past means that subduction of a spreading ridge system could have been more common earlier in Earth history.High-T-low-P metamorphism requires a tectonic setting that allows enhanced heat flux, transient advection of heat due to magma ascent, unusually large internally generated heat, or some combination of these features. Subduction of a spreading ridge system produces anomalously high temperatures at shallow crustal depth through the development of a slab window, which allows transfer of sub-slab asthenospheric mantle across the slab to create an enhanced heat flux beneath the overriding plate. This process is important along convergent margins that develop a subduction-accretion complex, and drives low P/T ratio metamorphism and anatexis of the complex. Heat transport occurs by rising magma near the trench, which leads to formation of plutons with characteristic contaminated MORB geochemistry. Near-trench igneous activity and low PIT ratio metamorphism are the most striking features attributable to spreading ridge subduction and slab window formation, and together are likely to be diagnostic of ridge trench interactions.

Accretionary orogens through Earth history

“…He proposed that the inboard, low-P-high-T Ryoke Belt and the outboard high-P -low-T Sambagawa Belt originally lay along strike and were juxtaposed by sinistral strike-slip motion along the Median Tectonic Line. The high-T metamorphism in belts such as the Ryoke and Abukuma in Japan are, according to Brown (1998a), the result of ridge subduction and slab window formation just inboard of the trench and downgoing plate . This represents an alternative mechanism to the magmatic arc and back-arc for producing high-T metamorphism.…”

“…Murphy et al (1998) suggested that plume subduction led to flattening of the downgoing slab, generating 'plume-modified orogeny' (see Murphy et al 1999Murphy et al , 2003Dalziel et al 2000). Flat-slab subduction and the resultant transitory plate coupling has been invoked as an important mechanism of orogenesis in the accretionary Lachlan orogen (Collins 2002a), in the North American Cordillera (Dickinson & Snyder 1978;Saleeby 2003), and in development of the Japanese accretionary orogen (Osozawa 1988;Underwood 1993;Isozaki 1996;Maeda & Kagami 1996;Brown 1998a). The mechanism for increased buoyancy with flat-slab subduction depends on the nature and rate of input of the thermal anomaly Kusky et al 2003).…”

A Late Carboniferous–Early Permian slab window in the West Junggar of NW China: Geochronological and geochemical evidence from mafic to intermediate dikes

“…Ridge subduction is found in circum-Pacific orogenesis, but little attention has been paid to ridge subduction in ancient orogens (Brown, 1998). A ridge subduction regime has been proposed to account for the evolution history of some areas in the CAOB (Windley et al, 2007).…”

Age and tectonic setting of magmatic sulfide Cu-Ni mineralization in the Eastern Tianshan Orogenic Belt, Xinjiang, Central Asia

“…In several places in this orogen, the upper amphibolite-facies belts are juxtaposed against greenschist-facies accretionary prisms (Wang and Wang 1992), as observed in the Jingerquan and Xiaoshitouquan belts (Wang et al 1994). Such a juxtaposition of high-and low-grade metamorphic complexes is characteristic of modern accretionary orogens and can be interpreted as a result of ridge subduction (Brown 1998;Iwamori 2000;Windley et al 2007). The …”