TRACE ELEMENT VARIATIONS WITHIN THE NORTHERN PENINSULAR RANGES BATHOLITH, SOUTHERN CALIFORNIA

More than thirty trace element compositions have been determined by LA-ICP-MS for each of 287 samples collected by Baird et al. from the northern Peninsular Ranges Batholith, California, with about a third each in the Santa Ana, Perris, and San Jacinto blocks. For each sample, 19 trace elements were normalized to primitive mantle and 13 rare earth elements were normalized to chondrite, before plotting the elemental compositions on multi-element (spider) diagrams.

Nd, Sm, Eu, and Gd have the smallest variation over the 287 samples with one standard deviation being less than 40% of the mean. Tm, W, Zr, and Hf have the greatest variation with one st. dev. being more than 80%. Ta and the relation between Ti and Y composition have significant variation. Some trace element variation corresponds to previously observed (e.g., Todd 1988) west to east trends.

On the normalized REE plots, more than 80 samples (half the samples in the Santa Ana block and a fourth of the samples in the Perris and San Jacinto blocks) showed a significant negative Eu anomaly. A dozen samples had a positive Eu anomaly, with half of these in the Santa Ana block. About 30 samples, evenly distributed between the 3 blocks, showed a sawtooth pattern for the normalized heavy REE with Er especially depleted and Tm enhanced.

For plotting, the 287 samples were divided into 47 groups based on mapped units, fault divisions, and rock compositions. Some groups, especially in the San Jacinto Mtn. area, showed a distinct correlation between samples; plots in other groups, especially in parts of the Santa Ana block, were quite variable from sample to sample. A few samples at pluton margins were significantly different from the overall pluton signature. About 20 samples previously identified as gabbros (and another 5 not so identified) had unique trace element signatures. These abundant data will assist in determining the chemical relations and variation between plutons and between regions within a pluton.