TY - JOUR
T1 - Shoshonitic magmas in nascent arcs
T2 - New evidence from submarine volcanoes in the northern Marianas
AU - Stern, Robert J.
AU - Bloomer, Sherman H.
AU - Lin, Ping Nan
AU - Ito, Emi
AU - Morris, Julie
PY - 1988
Y1 - 1988
N2 - Volcanoes in the northern Mariana arc between Uracas (lat 20°N) and Minami Iwo Jima (24°N) are very active yet entirely submarine. In contrast to the predominantly low-K basaltic magmas of the central Mariana arc, the northern Mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north. The northern arc melts have enrichments in Ba (<800 ppm), Rb (<70 ppm), Sr (<1000 ppm), Ce (<50 ppm), and (Ce/Yb) n (<24) which increase to the north as far as Iwo Jima. Lavas from volcanoes north of Iwo Jima lack these enrichments and are indistinguishable from those of the central Maranas. The shoshonites are unusual in occurring along the magmatic front of a primitive, intra-oceanic arc. We hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the Mariana Trough spreading center northward through the Volcano arc. Shoshonites thus may characterize the initial stages of arc construction after an episode of back-arc rifting and need not be restricted to the mature stages of arc evolution. This situation contrasts with subduction-zone initiation, where first melts may be boninites or low-K tholeiites. These differing initial melts converge toward tholeiitic and calc-alkaline compositions as arcs evolve.
AB - Volcanoes in the northern Mariana arc between Uracas (lat 20°N) and Minami Iwo Jima (24°N) are very active yet entirely submarine. In contrast to the predominantly low-K basaltic magmas of the central Mariana arc, the northern Mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north. The northern arc melts have enrichments in Ba (<800 ppm), Rb (<70 ppm), Sr (<1000 ppm), Ce (<50 ppm), and (Ce/Yb) n (<24) which increase to the north as far as Iwo Jima. Lavas from volcanoes north of Iwo Jima lack these enrichments and are indistinguishable from those of the central Maranas. The shoshonites are unusual in occurring along the magmatic front of a primitive, intra-oceanic arc. We hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the Mariana Trough spreading center northward through the Volcano arc. Shoshonites thus may characterize the initial stages of arc construction after an episode of back-arc rifting and need not be restricted to the mature stages of arc evolution. This situation contrasts with subduction-zone initiation, where first melts may be boninites or low-K tholeiites. These differing initial melts converge toward tholeiitic and calc-alkaline compositions as arcs evolve.
UR - http://www.scopus.com/inward/record.url?scp=0000498966&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0000498966&partnerID=8YFLogxK
U2 - 10.1130/0091-7613(1988)016<0426:SMINAN>2.3.CO;2
DO - 10.1130/0091-7613(1988)016<0426:SMINAN>2.3.CO;2
M3 - Article
AN - SCOPUS:0000498966
SN - 0091-7613
VL - 16
SP - 426
EP - 430
JO - Geology
JF - Geology
IS - 5
ER -