Laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) is a microanalytical tool especially suitable for providing fast and precise U‐Pb geochronological results on zircon grains. A new 193 nm excimer laser adapted to a micromachining workstation, equipped with a newly designed two‐volume ablation cell and coupled with a quadrupole ICP‐MS, is presented here. The system was tuned routinely to achieve sensitivities in the range of 3000 cps/μg g−1 for 238U (< 2% RSD), with a 34 μm spot size, at 5 Hz and ∼ 8 J cm−2, while ablating the NIST SRM 612 glass reference material. The system was capable of providing fast (< 1.5 minutes each analysis) and precise (generally < 1.5% 1s errors) 206Pb/238U zircon ages. The ages of widely used reference material zircons (Plesovice, 337 Ma; Temora, 416 Ma; R33, 418 Ma; Sri Lanka, 564 Ma; 91500, 1065 Ma) could be precisely matched, with an accuracy on isotopic ratios that ranged from ∼ 2 to ∼ 6%, depending on the homogeneity of the natural reference materials.

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The Tierra Colorada area sits along the northern limit of the Xolapa Complex, where it is juxtaposed against the Mixteco (Paleozoic) and Guerrero (Mesozoic) terranes of southern Mexico, just north of Acapulco. This paper presents combined structural and geochronological data from Tierra Colorada area that show evidence of four deformational events and several episodes of arc magmatism during Mesozoic and Cenozoic time. The oldest magmatism is represented by ca. 165 Ma granitoids and was followed by intrusion of the foliated El Pozuelo granite (129 ± 0.5 Ma; concordant U-Pb zircon analysis). This intrusion postdates D 1 metamorphism and migmatization in the Xolapa Complex. The next magmatic episode is represented by the peraluminous, foliated El Salitre granite (55.3 ± 3.3 Ma; mineral-whole-rock Rb-Sr isochron) and the protomylonitic Las Piñas I-type granite (54.2 ± 5.8 Ma; lower intercept U-Pb zircon). Las Piñas granite is characterized by D 2 ductile fabric with normal, top-tothe north-northwest sense of shear, deformed at 45-50 Ma (Rb-Sr and K-Ar ages). The ca. 34 Ma undeformed granites correspond to the last intrusive pulse in the area, postdating both D 3 south-southwest-verging thrusting of the Cretaceous Morelos Formation over sheared granites and Lower Cretaceous volcanic rocks, and open folding during D 4. These four pulses of subduction-related magmatism in the Tierra Colorada area indicate a regular northeastward subduction at the Mesoamerican trench since Jurassic time, and alternate with contractile and/or extensional tectonic events. The gap in magmatic activity ca. 90-100 Ma roughly coincides with deposition of platformal limestones of the Morelos Formation during the middle Cretaceous. The stable conditions during deposition of the Morelos Formation may have resulted from a combination of backarc extension and development of a passive margin during the Early-middle Cretaceous, which postdated the accretion of an exotic block, either the Guerrero terrane or the Chortís block. Following the Laramide orogeny in southern Mexico (roughly during the Late Cretaceous) the Paleocene-Miocene tectonic evolution in the Tierra Colorada area involved an alternation of magmatic pulses with extensional and contractile events. This was the result of a combination of several factors, including the geometry of the subducted slab, convergence rate, stress transmission between the subducting and overlying plates, and the rate of subduction erosion.

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Recycling of upper plate crust in subduction zones, or 'subduction erosion', is a major

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