By John Eiler
Published via the yankee Geophysical Union as a part of the Geophysical Monograph Series.
Subduction zones helped nucleate and develop the continents, they fertilize and lubricate the earth's inside, they're the positioning of so much subaerial volcanism and lots of significant earthquakes, they usually yield a wide fraction of the earth's important metals. they're seen pursuits for study?almost whatever you study is probably going to affect very important problems?yet arriving at a basic figuring out is notoriously tricky: every one subduction region is specified, differing in a few very important point from different subduction zones; primary elements in their mechanics and igneous approaches range from these in different, rather well-understood components of the earth; and there are few direct samples of a few in their most crucial metamorphic and metasomatic procedures. accordingly, even first-order positive aspects of subduction zones have generated clash and obvious paradox. A crucial query approximately convergent margins, for instance?how lively magmatism can happen the place plates sink and the mantle cools?has a number of together inconsistent solutions: Early feedback that magmatism resulted from melting subducted crust were emphatically disproved and lately simply as emphatically revived; the concept that melting is fluxed via fluid published from subducted crust is greatly held yet can't clarify the temperatures and risky contents of many arc magmas; generations of kinematic and dynamic types have instructed us the mantle sinks at convergent margins, but powerful proof means that melting there's usually pushed through upwelling. against this, our figuring out ofwhy volcanoes look at ocean ridges and "hotspots"?although nonetheless featuring their very own chestnuts?are essentially solved problems.Content:
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F o r e l e m e n t s u s e d h e r e , n o t m e a s u r e d b y Hart i n t e r p o l a t i o n s h a v e b e e n m a d e u s i n g t h e p r o c e d u r e o f Wood and Blundy and and Dunn Dunn ,  ( d ) t y p i c a l M a r i a n a lava ( G U G 13) c o m p a r e d t o a 5 % a c c u m u l a t e d f r a c t i o n a l m e l t o f t h e d e p l e t e d m a n t l e s o u r c e from ( c ) t o w h i c h h a s b e e n a d d e d 0 . 7 % o f t h e a v e r a g e s u b d u c t i n g M a r i a n a s e d i m e n t - m e l t i n g c a l c u l a t i o n s as i n ( c ) .
Johnson et al, 1989]. ICP-MS measurements provide sufficiently high quality data to assess small 28 TRACERS OF THE SLAB range of arc-related HFSE depletions and found no correlation with their Hf isotope ratios. They therefore concluded that the HFSE depletion was recent. 2. g. Tatsumi et al, 1986; Morris et al, 1990; and McCulloch and Gamble, 1991]. Yet, an inescapable conclusion from detailed studies on individual arcs is that in many cases there is evidence for (at least) two discrete subduction components [Kay, 1980; Ellam and Hawkesworth, 1988; Plank and Langmuir, 1992; McDermott et al, 1993; Miller etal, 1994; Reagan et al, 1994; Turner et al, 1996; Elliott et al, 1997; Regelous et al, 1997; Turner et al, 1997; and Class et al, 2000].
G. Staudigel et al, 1996]. Both sediment and mafic crust have much higher incompat- F i g u r e 1. C a r t o o n o f s u b d u c t i o n z o n e d e p i c t i n g s o m e k e y s o u r c e s a n d p r o c e s s e s i n v o k e d i n t h i s c o n t r i b u t i o n . ELLIOTT ible element concentrations than typical mantle rocks and so have the potential to impart a strong chemical signature if added to the mantle wedge. The mantle wedge itself is most plausibly of a composition similar to that of ubiquitous upper mantle, as sampled by MORB.