San Jacinto Intrusive Complex: 2. Geochemistry

Abstract

Abstract.Rocks from three large (>100 2 km) tonalitic intrusions exposed in the San Jacinto Mountains of southern California show a restricted compositional range of between 63 and 68 wt J Si0 2 for all but volumetrically minor felsic differentiates (with Si0 2 •70 wt %). All rocks with less than 65.5 wt % Si0 2 show linear element-element covariation.Felsic differentiates have characteristics (higher Si0 2 , K 2 0, Rb, Ba, U; higher and variable rare earth elements) consistent with derivation by in situ fractionation; For those elem~nts where the bulk distribution coefficient is between about 0.5 and 2, concurrent recharge and solidification produces rocks that closely approximate the composition of the added liquids. Estimated Rayleigh numbers for these liquids are high (>1010), implying convection throughout much of the solidification history of each chamber. Existence of trace element variations within analyzed rocks imply that convection was not totally efficient at homogenizing the various batches of liquid added to each chamber.

Paired plutonic belts in convergent margins and the development of high Sr/Y magmatism: Peninsular Ranges Batholith of Baja California and Median Batholith of New Zealand

“…Most New Zealand HiSY rocks of the Separation Point suite fi t the Drummond and Defant (1990) TTG/adakite defi nition of Sr/Y > 40, whereas ≈1/3 of La Posta rocks have Sr/Y < 40. In our data set, Peninsular Ranges batholith values of <40 are mostly from the San Jacinto pluton (Hill et al, 1988). HiSY rocks in the La Posta suite tend to occur as zones or pulses within composite or zoned plutons that also contain rocks with Sr/Y < 40.…”

“…HiSY rocks in the La Posta suite tend to occur as zones or pulses within composite or zoned plutons that also contain rocks with Sr/Y < 40. Within the large San Jacinto and Sierra San Pedro Martir plutons, Sr/Y ranges from 20 to 138 and 33-205, respectively (Hill et al, 1988;Kimbrough et al, 1998).…”

Framework and petrogenesis of the northern Peninsular Ranges batholith, southern California

“…Corundum-biotite gneiss occurs very locally in the northern San Jacinto Mountains (Murdoch and Webb, 1942). Chemical analyses of both Desert Divide and Windy Point samples are given in Hill (1988b). East of the Eastern Peninsular Ranges mylonite zone, Erskine (1986a), following the usage of Miller (1946), termed metasedimentary rocks the Palm Canyon Complex for allochthonous rocks in the Palm Springs area.…”

“…Recently, Todd et al (2003) provided an excellent analysis of the batholith immediately south of the area considered here. Most recent batholithic investigations have centered largely on topical aspects (e.g., Baird et al, 1974Baird et al, , 1979Krummenacher et al, 1975;Taylor and Silver, 1978;Baird and Miesch, 1984;Gromet and Silver, 1987;Silver and Chappell, 1988;DePaolo, 1981;Premo et al, 1998), and on individual plutons (e.g., Hill, 1988aHill, , 1988bJenney, 1968;Joshi, 1967;Menzie, 1962;Miesch and Morton, 1977;Morton, 1969;Morton et al, 1969;Morton and Baird, 1976;Sims, 1960).…”

“…59) is an elongate body with a somewhat bulbous northern part, and it consists of three major biotite-hornblende tonalite units. Hill (1984Hill ( , 1988aHill ( , 1988b provided an in-depth description of the San Jacinto pluton, including chemistry and internal Sr i and δ 18 O variations. All three of his tonalite units, unit I, unit II, and unit III, ranged from mafi c tonalite to low-potassium granodiorite.…”