The Jurassic Gran Can˜on Formation(Cedros Island, Baja California, Mexico)constitutes an unusually well preserved andexposed example of ancient backarc-basinfill. Petrofacies analysis conducted on tuffaceoussandstone and tuff samples fromthis formation complement and reinforceprior lithofacies interpretations, but withsome modification. When temporal andspatial trends in petrographic data (detritalmodes) are analyzed and compared to modelsbased on data collected from Deep SeaDrilling Project and Ocean Drilling Programcores, the trends indicate a second,heretofore unrecognized, phase of backarcrifting. Basalt lavas interstratified with daciticpyroclastic rocks of the primary volcaniclithofacies, previously interpreted torecord the eruption of differentiated magmasat the climax of growth of the GranCan˜on island arc, are now as a result of thisstudy considered to be the product of arcextension and rifting.Our method of modal analysis uniquelycombines the quantification of textural attributesof pyroclastic and epiclastic debristhat reflect eruption style and magma composition,as well as the effects of reworkingand mixing in marine settings. This studydemonstrates that detailed petrographicanalysis is useful in the interpretation of*E-mail: critelli@unical.it.†E-mail: Kathie.marsaglia@csun.edu.§E-mail: Cathy@magic.geol.ucsb.edu.ancient volcaniclastic deposits suspected ofhaving formed in backarc-basin settings.
TECTONIC HISTORY OF A JURASSIC BACKARC-BASIN SEQUENCE (THE GRAN CAÑON FORMATION) BASED ON COMPOSITIONAL MODES OF TUFFACEOUS DEPOSITS
CRITELLI, Salvatore;
2002-01-01
Abstract
The Jurassic Gran Can˜on Formation(Cedros Island, Baja California, Mexico)constitutes an unusually well preserved andexposed example of ancient backarc-basinfill. Petrofacies analysis conducted on tuffaceoussandstone and tuff samples fromthis formation complement and reinforceprior lithofacies interpretations, but withsome modification. When temporal andspatial trends in petrographic data (detritalmodes) are analyzed and compared to modelsbased on data collected from Deep SeaDrilling Project and Ocean Drilling Programcores, the trends indicate a second,heretofore unrecognized, phase of backarcrifting. Basalt lavas interstratified with daciticpyroclastic rocks of the primary volcaniclithofacies, previously interpreted torecord the eruption of differentiated magmasat the climax of growth of the GranCan˜on island arc, are now as a result of thisstudy considered to be the product of arcextension and rifting.Our method of modal analysis uniquelycombines the quantification of textural attributesof pyroclastic and epiclastic debristhat reflect eruption style and magma composition,as well as the effects of reworkingand mixing in marine settings. This studydemonstrates that detailed petrographicanalysis is useful in the interpretation of*E-mail: critelli@unical.it.†E-mail: Kathie.marsaglia@csun.edu.§E-mail: Cathy@magic.geol.ucsb.edu.ancient volcaniclastic deposits suspected ofhaving formed in backarc-basin settings.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
