Geochemically distinct sources for interstratified lavas from the Nejapa cinder cone alignment, Nicaragua
The Nejapa cinder cone alignment, near Managua, Nicaragua, produces mafic subalkaline basalts that are similar to mid-ocean ridge basalts (MORB). The Nejapa basalts can be divided into high- and low-titanium suites that are interstratified. Although major element compositions are similar to MORB, concentrations of Ba and Sr in the Nejapa basalts are higher, ranging from 2 x MORB in the high-titanium suite to 10 X MORB for the low-titanium lavas. Recently determined Nd and Sr isotopic and rare earth element (REE) concentrations for Nejapa basalts show that the high and low titanium suites have distinct sources and cannot be related by simple crystallization trends. For example, although the high-Ti lavas are light REE depleted and have overall MORB-like REE concentrations, they are systematically lower in /sup 143/Nd//sup 144/Nd and higher in /sup 87/Sr//sup 86/Sr. Low-Ti lavas, on the other hand, are LREE-enriched but have Nd isotopes identical to MORB (/sup 87/Sr//sup 86/Sr is distinctly higher). The contradictory geochemical characteristics displayed by the Nejapa lavas can be explained in a general sense by a mixing model that involves upper mantle peridotite and a fluid derived from hydrothermally-altered subducted oceanic crust. This fluid may enrich overlying mantle in Ba, Sr, and /sup 87/Sr//sup 86/Sr, and may supply enough water to stabilize an accessory phase such as rutile at high pressure. Melts generated from this source will be low in Ti, but high in Ba, Sr, /sup 87/Sr//sup 86/Sr and /sup 143/Nd//sup 144/Nd. Subjacent peridotite melting with less of the hydrous flux will generate lavas with higher Ti, lower Sr and Ba, and isotopic ratios of the peridotite.
- Research Organization:
- Rutgers Univ., New Brunswick, NJ (USA)
- OSTI ID:
- 6649629
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Vol. 17; ISSN GAAPB
- Country of Publication:
- United States
- Language:
- English
Similar Records
Isotopic and trace element geochemistry of lavas from the northern Mariana and southern volcano arcs
Isotope and trace element data bearing of the sources and evolution of magmas in the Katmai region, Alaska
Related Subjects
152003 -- Geothermal Data & Theory-- Rock-Water-Gas Interactions
58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BASALT
CENTRAL AMERICA
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPING COUNTRIES
EARTH CRUST
ELEMENTS
GEOCHEMISTRY
GEOLOGIC MODELS
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
LATIN AMERICA
LAVA
METALS
NEODYMIUM ISOTOPES
NICARAGUA
OCEANIC CRUST
PETROGENESIS
QUANTITATIVE CHEMICAL ANALYSIS
RARE EARTHS
ROCKS
STRONTIUM COMPOUNDS
STRONTIUM ISOTOPES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS