ADDITIONAL CHEMICAL TRENDS ACROSS THE NORTHERN PENINSULAR RANGES, SOUTHERN CALIFORNIA

Numerous mineralogical, geophysical, geochemical, and isotopic trends have been observed from west to east across the Peninsular Ranges of the southern California batholith: mafic toward felsic, magnetite toward ilmenite, I- toward S-type granitoids, gravity and magnetic anomalies, major and rare earth element trends, increasing Sr_i, d¹⁸O, and ²⁰⁶Pb/²⁰⁴Pb values, and decreasing e_Nd values, specific gravity, and emplacement age. The trends have been interpreted as resulting from a predominantly oceanic crust-mantle source in the west, with an increasing continental crust component toward the east. Now with a database of 35 trace elements determined by LA-ICP-MS for each of almost 300 samples collected by Baird et al. from the northern Peninsular Ranges, these trends are seen to extend to a number of other elements.

With the new analysis, we reproduce Baird's (1974) observed trends in the major elements from southwest to northeast, of K increasing strongly, Si increasing, Na increasing little, Al and Ti remaining relatively constant, and Fe, Ca, and Mg decreasing. By correlating with the distinct Sr_i trend, the trace elements can now be added, with Nb having an especially strong positive correlation, Ba, Rb, and Ta increasing significantly, Th, Sr, P, and Zn increasing, Zr, U, Cu, and Hf increasing slightly, Cs, W, Mo, and Y remaining relatively constant, Cr and Ni decreasing slightly, and V, Co, Mn, and Sc decreasing. Of the REE La, Ce, Pr, Nd, and Sm increase significantly, Eu slightly, Gd, Tb, Dy, and Ho vary little, and Er, Tm, and Yb decrease slightly. As expected, the compatible elements are relatively more abundant in the west and the incompatible elements in the east. From 2-element plots, the Sr/Ca, Sr/Mg, and Rb/Cs ratios and the REE ratios La/Yb, La/Sm, and Gd/Yb were seen to increase significantly from west to east across the Peninsular Ranges. Sr plotted against Rb, Ba, and K also varied systematically from west to east.

For the Peninsular Ranges extending into Baja California, Gromet (1987) found the LREE enriched less in the west than in the east, whereas the HREE were enriched more in the west than in the east. This trend is also easily seen in the northern Peninsular Ranges with the HREE enriched most in the western Santa Ana block, the LREE enriched most in the eastern San Jacinto block, and a transition region in the central Perris block. Any trend in the Eu/Eu* anomaly was indistinct.