Is the Cumulate Paradigm At Risk?: An Extended Discussion of the Cumulate Paradigm Reconsidered
| Autor: | S. A. Morse, Alexander R. McBirney |
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| Rok vydání: | 1998 |
| Předmět: | |
| Zdroj: | The Journal of Geology. 106:367-372 |
| ISSN: | 1537-5269 0022-1376 |
| Popis: | A plot of P2O5 versus normative pyroxene for 43 rocks of Skaergaard LZa, offered by McBirney and Hunter as a challenge to the orthocumulus hypothesis, contains no data below 10% pyroxene. By hypothesis, the range between 0 and 10% pyroxene must be well populated for plagioclase‐olivine orthocumulates, and therefore the rocks do not pass the first test of the orthocumulus hypothesis. Many LZa rocks also contain more than the cotectic amount of pyroxene, which should be regarded in part as a cumulus phase. The remainder, especially the poikilitic overgrowths, can comfortably be ascribed to heteradcumulus growth. Such nucleation‐driven infiltration metasomatism cannot be distinguished from lateral or upward metasomatism using the data set presented. The data can be evaluated entirely within the cumulate paradigm, which also shows that new information is needed to evaluate competing hypotheses for the origin of these rocks. Many successful examples of orthocumulate and adcumulate growth have been demonstrated... |
| Databáze: | OpenAIRE |
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