Either Unit A or B is at the base of the TACB where well exposed elsewhere, and each is overlain by Unit C or D.
Unit B is found only in the southeastern part of the area and it forms the base of the TACB wherever it its base is exposed, also resting unconformably on Javelina clay.
Un it G comprises the entire outcrop of the TACB at Sierra Aguja (Figs.
The eight units of the TACB include six of olivine basalt, one basaltic trachyandesite and one trachyandesite.
Pale green to brown smectite is the dominant alteration product in the TACB lavas, commonly pseudomorphing olivine and as interstitial patches and veinlets throughout the rocks.
Table 3 shows the overall chemical nature of the TACB units, and serves to demonstrate the general makeup and similarity of these rocks, as well as their characterization as alkaline olivine basalts.
11a) the TACB suite of rocks shows a successive increase in LREE (light rare earth elements), suggesting that, over all, it might be some sort of evolutionary sequence.
It is clear that the wider extent of the TACB across the Rio Grande needs to be studied, and a resolution of differences in chemistry between the units is necessary, before any conclusion can be drawn concerning the relation of the TACB to dike 160.
If dike 160 was not the source of any TACB units, and if one looks at the distribution patterns alone, the following postulations can be made: Units A, B, C and D may have had source(s) to the south or southwest; whereas, units E, F, G & H seem have come from the west or northwest.