Petrogenesis of western Philippine island arc magmas: potential origin of the potassium-depth relationship

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6874493

Defant, M J; Ragland, P C; Odom, A L

Three geographic volcanic arcs have developed in western Luzon. The Philippines as a result of subduction associated with an eastward-dipping Benioff zone. Approximately 200 samples were collected and analyzed for major and various trace elements. In addition, 30 initial /sup 87/Sr//sup 86/Sr ratios and a few /sup 143/Nd//sup 144/Nd ratios have been determined. Seventy-six conventional K/Ar radiometric dates have also been determined. Based on these data, several conclusions can be made: 1) Excellent linear correlations exist between SiO/sub 2/ and the incompatible elements. 2) Incompatible elements do not appear to have been affected by alteration or weathering; 3) Based on geophysical and geochemical evidence, assimilation and contamination have played an insignificant role in affecting original magma compositions; 4) It can be argued that the sources for these volcanics are enriched (metasomatized) mantle above the Benioff zone because the Bataan volcanics have apparently not been contaminated. Derivation of the Bataan volcanic rocks by different degrees of partial melting of the mantle can be ruled out. The mantle sources become increasingly more enriched in incompatible elements and radiogenic strontium away from the Manila Trench; 5) All three arcs have apparently undergone early, non-selective crystal fractionation of plagioclase, clinopyroxene, magnetite, and/or olivine; 6) The variations in slopes observed on potassium Harker diagrams between the arcs can be explained by a combination of original primary magma potassium variations between the arcs and the fractionation of similar phases within each arc.

• Research Organization: Univ. of South Florida, Tampa (USA)
• OSTI ID: 6874493
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
PHILIPPINES
PETROGENESIS
VOLCANIC ROCKS
CHEMICAL COMPOSITION
ISOTOPE DATING
ARGON ISOTOPES
GEOCHEMISTRY
GEOLOGIC HISTORY
ISOTOPE RATIO
MAGMA
MAGMATISM
NEODYMIUM ISOTOPES
POTASSIUM ISOTOPES
STRONTIUM ISOTOPES
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
ASIA
CHEMISTRY
DEVELOPING COUNTRIES
IGNEOUS ROCKS
ISLANDS
ISOTOPES
ROCKS
580400* - Geochemistry- (-1989)
580100 - Geology & Hydrology- (-1989)